Embed Size (px)
Citation preview
Andreas Rosengren
TRITA-NA-E04039
Digital Geometrical Verification of Productand Equipment Changes in Manufacturing
NADA
Numerisk analys och datalogi Department of Numerical AnalysisKTH and Computer Science100 44 Stockholm Royal Institute of Technology
SE-100 44 Stockholm, Sweden
Andreas Rosengren
TRITA-NA-E04039
Master’s Thesis in Computer Science (20 credits)at the School of Computer Science and Engineering,
Royal Institute of Technology year 2004Supervisor at Nada was Kai-Mikael Jää-Aro
Examiner was Lars Kjelldahl
Digital Geometrical Verification of Productand Equipment Changes in Manufacturing
AbstractThis thesis is the documentation of a Master’s project at Scania studying equip-ment simulation. A demonstrator system for simulation/visualisation of manu-facturing equipment has been developed within this project. The demonstratorsystem is the result of studying the needs and requirements of equipment simula-tion at Scania. Based on a series of user studies and experience from equipmentchange projects, this system has been developed in a user centered process, wheredesired basic functionality has been implemented to test the benefits of equipmentsimulation/visualisation to Scania.
Graphical 3D simulation /visualisation can provide a more detailed view of theimplications of a change project and can be a valuable tool in discussions on layoutof machine groups and robot cells. By providing means of exploring a layout pro-posal by immersive studies, inspecting machines from a first person view, manyimportant issues can be detected in an early stage of a project. The demonstratorsystem has been aimed to facilitate the cooperation between production engineersand operators in the early discussions on plant layout planning.
This project has taken the views of three main fields in the study: Productionengineering, Computer Graphics and Human-Computer Interaction.
Digital geometriverifikation av förändringar i produkter ochtillverkningsutrustning
Examensarbete
SammanfattningDenna rapport dokumenterar ett examensarbete i datorgrafik vid Scania i Södertäl-je. Syftet med examensarbetet har varit att kartlägga Scanias behov och nytta avutrustningssimulering. En produkt av projektet är ett demonstratorsystem för simu-lering/visualisering baserat på standardteknik. Demonstratorsystemet har tagitsfram efter att en förstudie kartlagt användarkategorier, behov och förutsättningar.
En rådande tanke är att man med hjälp av VR-teknik kan skapa en bättreförståelse för hur utformningen av en ny utrustning påverkar olika intressenter.Demonstratorsystemets kärna är att vara ett stöd för samarbetet mellan produk-tionstekniker och operatörer i inledningsskedet av layoutdesignen. Tanken är ävenatt tekniken ska vara behjälplig som såväl besluts- som diskussionsunderlag.
Utgångspunkten för arbetet har varit en korsning av tre huvudsakliga veten-skapsdiscipliner: produktionsteknik, datorgrafik och människa - datorinteraktion.
Preface
This thesis is the result of 20 weeks of painstaking efforts in trying to cast somelight upon the wonderful world of equipment simulation and its place in the worldof virtual manufacturing. This thesis is officially about computer graphics, albeitstill rather well tied to this field, it is to a great extent centered around productionengineering and human-computer interaction.
I would like to express my grateful thanks to all the people at Scania whose pa-tience and help has been an invaluable source of information and support duringmy work in this master´s project.
Contents
1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.1 Questions and activities . . . . . . . . . . . . . . . . . . . . . 21.3 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 Preliminary study and user categorization . . . . . . . . . . 31.3.2 The Demonstrator . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Method 52.1 Interviews with project veterans . . . . . . . . . . . . . . . . . . . . 52.2 Participation in an ongoing project . . . . . . . . . . . . . . . . . . . 52.3 Task analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.4 The Contextual Inquiry method . . . . . . . . . . . . . . . . . . . . . 62.5 User modelling according to USTM/CUSTOM . . . . . . . . . . . . 72.6 Implementation of a demonstrator system . . . . . . . . . . . . . . . 8
2.6.1 VRML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.7 Evaluation of Demonstrator . . . . . . . . . . . . . . . . . . . . . . . 9
2.7.1 Heuristic Evaluation . . . . . . . . . . . . . . . . . . . . . . . 9
3 Theoretical frame of reference 113.1 Virtual Manufacturing and simulation . . . . . . . . . . . . . . . . . 11
3.1.1 Simulation in general . . . . . . . . . . . . . . . . . . . . . . . 133.2 Simulation in production engineering . . . . . . . . . . . . . . . . . 15
3.2.1 Flow simulation . . . . . . . . . . . . . . . . . . . . . . . . . . 153.2.2 Process simulation . . . . . . . . . . . . . . . . . . . . . . . . 153.2.3 Equipment simulation . . . . . . . . . . . . . . . . . . . . . . 163.2.4 Integrating tools for VM . . . . . . . . . . . . . . . . . . . . . 173.2.5 Verification of models using physical equipment . . . . . . . 19
3.3 Computer Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3.1 The graphics pipeline . . . . . . . . . . . . . . . . . . . . . . 193.3.2 Model data representation . . . . . . . . . . . . . . . . . . . . 213.3.3 Model density, Level of Detail and Polygon reduction . . . . 24
3.4 Virtual Reality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4.1 HCI in virtual environments . . . . . . . . . . . . . . . . . . 293.5 The VRML language . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.5.1 What is VRML? . . . . . . . . . . . . . . . . . . . . . . . . . . 373.5.2 The background of VRML . . . . . . . . . . . . . . . . . . . . 373.5.3 The structure of VRML . . . . . . . . . . . . . . . . . . . . . . 383.5.4 The VRML browser . . . . . . . . . . . . . . . . . . . . . . . . 393.5.5 External communication . . . . . . . . . . . . . . . . . . . . . 39
4 Scania at the present 424.1 Scania AB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.1.1 Business areas . . . . . . . . . . . . . . . . . . . . . . . . . . . 424.1.2 Mission statement . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2 Scania product structure . . . . . . . . . . . . . . . . . . . . . . . . . 434.3 The product development process . . . . . . . . . . . . . . . . . . . 434.4 Scania Production System – SPS . . . . . . . . . . . . . . . . . . . . . 45
4.4.1 Production engineering . . . . . . . . . . . . . . . . . . . . . 454.5 The process of equipment change . . . . . . . . . . . . . . . . . . . . 46
4.5.1 Production Equipment Investment Process (PEIP) . . . . . . 46
5 Practical frame of reference 495.1 Pre-study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.1.1 Paper based 2D layout drawings . . . . . . . . . . . . . . . . 495.1.2 Aspects of the layout discussed . . . . . . . . . . . . . . . . . 535.1.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.2 CAD systems at Scania . . . . . . . . . . . . . . . . . . . . . . . . . . 585.2.1 Plant layout design . . . . . . . . . . . . . . . . . . . . . . . . 585.2.2 Compatibility with product development systems . . . . . . 595.2.3 Design and styling . . . . . . . . . . . . . . . . . . . . . . . . 60
5.3 Equipment simulation at Scania . . . . . . . . . . . . . . . . . . . . . 605.3.1 Part handling and machine loading cells . . . . . . . . . . . 605.3.2 Robot intensive applications . . . . . . . . . . . . . . . . . . 61
5.4 Laser scanning methods for data acquisition and verification . . . . 61
6 Results I — Requirements 646.1 The benefits of equipment simulation . . . . . . . . . . . . . . . . . 646.2 Properties of drawings needed for decision support . . . . . . . . . 666.3 Specification of needs and requirements . . . . . . . . . . . . . . . . 67
7 Results II — The Demonstrator 707.1 Goal of the demonstrator system . . . . . . . . . . . . . . . . . . . . 707.2 System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.2.1 Java-VRML-EAI . . . . . . . . . . . . . . . . . . . . . . . . . . 717.2.2 Workshop model assembly . . . . . . . . . . . . . . . . . . . 717.2.3 Viewing and manipulating . . . . . . . . . . . . . . . . . . . 74
7.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.4 Requirements on IT-infrastructure . . . . . . . . . . . . . . . . . . . 76
8 Results III — Evaluation and comparison 788.1 User feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
8.1.1 Choice of test subjects . . . . . . . . . . . . . . . . . . . . . . 788.1.2 The test situation . . . . . . . . . . . . . . . . . . . . . . . . . 788.1.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
8.2 Heuristic evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
9 Discussion 819.1 Equipment simulation at Scania . . . . . . . . . . . . . . . . . . . . . 819.2 The demonstrator system . . . . . . . . . . . . . . . . . . . . . . . . 839.3 The project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
10 Conclusion and recommendations 8510.1 General reflections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8510.2 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8610.3 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
11 The Aftermath 8811.1 The heritage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
11.1.1 Further work . . . . . . . . . . . . . . . . . . . . . . . . . . . 8811.1.2 Internal communication . . . . . . . . . . . . . . . . . . . . . 8911.1.3 Alternative technology . . . . . . . . . . . . . . . . . . . . . . 89
References 90
A Glossary 93A.1 Notions and Concepts used in this report . . . . . . . . . . . . . . . 93
B Example output file 94
C Interview answers 97
List of Figures
3.1 The theoretical orientation of this thesis . . . . . . . . . . . . . . . . 113.2 Model-driven development . . . . . . . . . . . . . . . . . . . . . . . 133.3 Screen dump of a flow simulation in Extend . . . . . . . . . . . . . . 163.4 Simulation of cylinder head casting . . . . . . . . . . . . . . . . . . . 173.5 Simulation of sheet metal forming . . . . . . . . . . . . . . . . . . . 183.6 Robot simulation in Robot Studio . . . . . . . . . . . . . . . . . . . . 183.7 Diagram of the graphics pipeline . . . . . . . . . . . . . . . . . . . . 203.8 Example of different data representations . . . . . . . . . . . . . . . 223.9 Example in VRML . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.10 Model of a rabbit at different levels of detail . . . . . . . . . . . . . . 253.11 Robot model in three stages of polygon reduction . . . . . . . . . . 263.12 Vertex clustering in 2D . . . . . . . . . . . . . . . . . . . . . . . . . . 273.13 Progressive mesh in different LOD . . . . . . . . . . . . . . . . . . . 283.14 Impossible geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.15 SpaceMouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.16 BUILD-IT: plant layout planning system [6] . . . . . . . . . . . . . . 343.17 Avatars for user representation . . . . . . . . . . . . . . . . . . . . . 363.18 The VRML browser model . . . . . . . . . . . . . . . . . . . . . . . . 40
4.1 Scania´s PD process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444.2 SPS house . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464.3 Scania´s PEIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.1 Paper based 2D layout . . . . . . . . . . . . . . . . . . . . . . . . . . 505.2 Organisational overview . . . . . . . . . . . . . . . . . . . . . . . . . 505.3 Paper layout with handmade notes . . . . . . . . . . . . . . . . . . . 535.4 Proposals on bulletin board . . . . . . . . . . . . . . . . . . . . . . . 535.5 Cluttered inner ceiling of a workshop . . . . . . . . . . . . . . . . . 565.6 Screen dump of Catia v5 . . . . . . . . . . . . . . . . . . . . . . . . . 595.7 Cab assembly in Catia v5 . . . . . . . . . . . . . . . . . . . . . . . . . 625.8 Spot-welding simulation . . . . . . . . . . . . . . . . . . . . . . . . . 635.9 Laser scanner on tripod . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.1 Simulation types in relation to Scania´s PEIP . . . . . . . . . . . . . 65
7.1 Architectural overview of the demonstrator system . . . . . . . . . 727.2 Screen dump of WorkShopAssembler . . . . . . . . . . . . . . . . . 737.3 Screen dump of resulting VRML scene in IE . . . . . . . . . . . . . . 75
How to read this Thesis
Education. . . has produced a vast population able to read but unable todistinguish what is worth reading.G. M. Trevelyan (1876 – 1962), English Social History (1942)
Chapter 1: Introduction
This chapter introduces the subject and presents a short background. Objectivesand goals of the projects are given along with limitations to subject and methods.
Chapter 2: Method
Research methods used in the work during this project are presented and moti-vated in this chapter. Methods used come mainly from the HCI field and havebeen used to define the role of a simulation/presentation system in the process ofproduction equipment change.
Chapter 3: Theoretical frame of reference
An overview of simulation and “Virtual Manufacturing” in general is followed upwith a more detailed description of the specific circumstances around which thisproject has been centered. This chapter also introduces related research from thefields of Computer Graphics, Virtual Reality and HCI.
Chapter 4: Scania at the present
This chapter gives an introduction to the world of Scania. It establishes the role ofthis project from the aspects of the Scania organization.
Chapter 5: Practical frame of reference
This chapter describes the practical work being done in this Master’s project. A de-scription of the pre-study and its focus. A more detailed view of how the theoriesrelate to current work at Scania is also included here.
Chapter 6: Results I — Requirements
This section focuses on the results from the preliminary study of how a projectof equipment change is carried out today and what requirements of a system forequipment simulation to support this process has been found.
Chapter 7: Results II — The Demonstrator
The demonstrator system developed in this master’s project is one of the mainresults of the work and is therefor dealt with in this separate chapter. This chapterincludes a detailed description of the system along with a proposed methodologyfor assembling the scenes.
Chapter 8: Results III — Evaluation of demonstrator system
This chapter presents the results from user tests on the demonstrator system. Theresults are based on both the user tests and a heuristic evaluation.
Chapter 9: Discussion
This chapter discusses the results of this Master’s projects and passes some per-sonal reflections upon the subjects of equipment simulation and the specific nichechosen for the demonstrator
Chapter 10: Conclusions and recommendations
This chapter summarises the findings in this master’s project and points to a list ofappropriate activities for future work.
Chapter 11: The Aftermath
This chapter gives a few suggestions on what to do with the demonstrator systemand the experience gained from development of this system. There are questionsabout the choice of technology that are presented and discussed in this chapter.
Chapter 1
Introduction
1.1 Background
The use of simulation, in particular Discrete Event simulation, at Scania has of latesteadily increased. Due to the success of a few simulation studies the benefits ofsimulation has now been realised and the interest in using simulation for decisionsupport is increasing.
The main objective and desired effect of simulation is to reduce the time usedin the planning stage and thereby the costs in early stages of an equipment changeproject. Other benefits include improved decision support, which helps making cor-rect technology choices, as well as reduced stop time.
Simulation activities in manufacturing can be divided into three main cate-gories, or layers:
1. Flow simulations, where the simulation aims to aid production engineers inoptimizing work flow within the production process. The above mentionedDiscrete Event simulation belongs to this category.
2. The second layer deals with simulation of production equipment and facilities.This includes machine tools, handling equipment and infrastructural equip-ment such as building elements.
3. Process simulation concerns more fundamental aspects of production. An im-portant part in this layer is modelling of material properties and process pa-rameters.
(See chapter 3 for a more detailed description of simulation.)The digital verification of product and equipment changes belongs to the sec-
ond layer and is an area in which the use of VR technology can assist productionengineering projects to assess the compatibility of new or changed equipment withsurrounding equipment, facilities and personnel.
Even though CAD drawings in 3D are being used today, the full advantageof VR technology has not yet been realised or deliberately examined in the dailywork process of production engineering at Scania.
1
Some of the most important and difficult problems of changes to equipment in pro-duction systems are related to workshop layout and the traditional way of present-ing suggestions of improvement in 2D drawings comprises difficulties in revealingimportant implications of proposed layouts.
1.2 Objectives
The objectives of this Master´s project are to:
• survey the needs and benefits of graphical 3D simulations and visualisationsof machine groups in the process of product and/or equipment changes.
• develop a demonstrator of such a system, based on standard software tech-nologies.
• evaluate this demonstrator to determine the potential value and benefits ofequipment simulation to Scania.
1.2.1 Questions and activities
From the main objectives the following questions have been derived, to help aim-ing the activities towards the objectives.
1. How can Scania´s requirements and needs be described?
2. Which are the user categories for an equipment simulation system and howcan their roles be defined?
3. What are the requirements on information infrastructure to enable system-ised handling of models of different origin?
4. Is there software or other technologies available today?
5. What are the project values and possible outputs from a simulation/visual-isation system?
6. How can Scania proceed with the work in the field of equipment simulation?
To be able to answer the questions above, a number of activities have been identi-fied. These activities include:
• Perform interviews within Scania in order to define the problem, distinguishuser categories and various requirements within the organization.
• Perform interviews and studies concerning the related information infrastructurewithin Scania.
2
• Develop a 3D simulation model (using the recommended software) of one ormore machine cells that are part of the ongoing workshop planning projectat the transmission workshop (building 075)
• Compare simulation result to actual result
• Perform interviews to capture the experienced benefits in the project organi-zation, as well as among the decision makers linked to the project. Describea preferred general methodology
1.3 Limitations
Equipment simulation can play different roles depending on the actual equipmentto be simulated. The scope of simulation in this project is the type of equipmentthat is common in the machining workshops at Scania, where machine cells usu-ally consist of a smaller number of machines, grouped tightly together and servedby a robot. The main aspect of simulation/visualization this project is concernedwith is geometric simulation to determine the most efficient placement of machinecell components, as well as presenting proposals of machine layouts as a base fordiscussions and decision support. More robot intensive applications will be givena brief description in section 5.3 on equipment simulation and off-line program-ming at Scania´s CAB factory in Oskarshamn.
In chapter 3 a more thorough description of different types of simulation willbe given and the objectives of these will be described in detail.
1.3.1 Preliminary study and user categorization
The focus of the preliminary survey of the present situation is how paper based2D drawings are being used today and to determine their role and value. In thisstudy I have defined and categorized different user groups based on their role inthe process and relation to the drawings.
Among the defined user groups, this project has focused on production en-gineers/project leaders, which is the group of users mostly effected by the thesystem. They are the creators of some models and responsible for the layout ofmachines.
Decision makers and other more peripheral stakeholders will be dealt with inshorter terms.
1.3.2 The Demonstrator
Developing a full scale system for simulation of equipment is complex and timeconsuming and the demonstrator system is therefore implemented to demonstratesome functions of this kind of system.
In order to do this without implementing a full working system, some of theproblems have been dealt with outside the system. These problems include:
3
• Import/ExportThe demonstrator system works only with VRML models, which means thatmodels have to be exported to VRML from the CAD systems.
• Polygon densityDifferent polygon reduction techniques are required to reduce the complex-ity of models exported from CAD systems, which often have a very high levelof detail. The models imported to the demonstrator have been prepared us-ing some shareware software for polygon reduction.
• Robot kinematicsIn the implemented robot models it is possible to move each axle separately.A desirable feature of a robot would be inverse kinematics enabling linearmovements similar to the robot´s real patterns of movement.
• Model assemblyImporting models of different origin comprises a number of issues. There iscurrently no particularly smart way of determining coordinate systems andreference points of an imported arbitrary model. The demonstrator assumessome preparation of the models to ensure proper placement on the workshopfloor. In the layout planning CAD system, reference points may vary fromusing a building based origin to a local machine group based origin.
The Demonstrator is implemented using standard software technology. VRML isthe choice of file format for model files due to its open nature. The Demonstratorsystem includes a methodology for creating workshop assemblies of files exportedfrom CAD systems. A Java application has been developed to assist the user inthis assembly. The application contains functions for adding interactivity to theexported models.
4
Chapter 2
Method
The first phase of the this project has focused mainly on determining the natureof the problem at hand and based on this information assess the requirements ofa graphical 3D visualisation tool. In this work I have used methods from the HCIfield.
2.1 Interviews with project veterans
At the department where this master´s project has been organised, most of thestaff are older and highly experienced project managers whose main function is tosupport production engineers all over the world of Scania. These persons has beenused as references in most questions regarding the work of an equipment changeproject. Informal interviews and conversations over time has made it possible toextract an enormous amount of information from this source.
2.2 Participation in an ongoing project
At an early stage of this Master´s project I have been following a project of equip-ment change and workshop layout planning in one of Scania´s workshops. Theproject group has been used for informal field studies and structured interviews,as well as for testing and evaluation of the resulting demonstrator system.
In order to get some second opinions on the subject, interviews with peopleworking in similar situations outside the project has been carried out.
2.3 Task analysis
Intertwined in the different activities in the early stages of this project task analysishas been used to assess information on how the system will provide support fortasks involved in using the system. In a task analysis questions like:
• Who, what, where, when, how often?
5
• Relationship between users and data?
• What other tools do the users have?
• What happens when things go wrong?
are considered.
2.4 The Contextual Inquiry method
In the pre-study methods have been chosen from the HCI and Participatory Designfields to study how the paper based 2D workshop layouts are being used as a basefor discussions in a equipment change project today. The users all have differentbackgrounds and experience from working with layout drawings. The differentuser categories also use the drawings in various different physical context duringa project and therefore Contextual Inquiry is a method well suited to obtain a betterunderstanding of the problem at hand while providing answers to the questionsasked in the task analysis.
Contextual Inquiry is a method for performing structured interviews in anearly stage of the software design process. This method is based around threemain concepts used to encapsulate the influence of context in which the productor system is used. These basic concepts are described at the Usor Website [4] as:
• Context – The context in which the system is used may influence the designand by observing and performing the interviews in the right context, theinterviewer will gain a better understanding of this.
• Partnership – It is important to acknowledge the user as an expert on his or herpersonal work situation. The interview is supposed to be open and informalin order to gain insights in the users opinions, experience, motivation andcontext.
• Focus – It is important that the interviewer keeps track of his or her focusduring the interviews. The focus is a combination of our assumptions, be-liefs and concerns of a particular situation. All notions are filtered throughthis focus and the goal of the inquiry hereby depends on the focus. The in-terviewer has to be able to shift or expand the focus during the process.
This method is often used to gather information about a potential problem and toinvestigate whether or not there is a problem to be solved. A lot of the informationfrom a Contextual Inquiry is subjective and will answer questions like how peoplefeel about their job, how the information flows through the organisation etc.
In the initial phase of this method identification of users and clear definition ofuser groups has to be performed and for this an adaptation of the socio-technicaluser modelling method USTM/CUSTOM, described in section 2.5, was chosen.The motivation for this choice of method is that it facilitates a clear distinction of
6
different user groups and provides information needed for user modelling in thedesign process.
2.5 User modelling according to USTM/CUSTOM
A socio-technical model is a tool for user requirements modelling described by Dixet al. [5] It is important to realise that technology is not developed in isolation butas part of a wider organisational environment or context. Socio-technical modelsconsider social and technical issues side by side in order to include information onhow the system is to be used. I have chosen to use a method from this field calledUSTM/CUSTOM. I have used this method both as a tool for identifying the usersin the initial phase of the Contextual Inquiry and for modelling the user needs indesigning the prototype.
USTM is an abbreviation of User Skills and Task Match and the appendix CUS-TOM refers to a variant of this method specially adapted to smaller organisations.This method identifies stakeholders of the system at different levels of interactionas:
• Primary – The first hand users of the system
• Secondary – People that do not use the system but are dependent on the out-put from the system or provide its input.
• Tertiary – People that do not fall under the two previous categories, but thatare affected by the success or failure of the system.
• Facilitating – People involved in design, development and maintenance of thesystem.
As a framework this method seeks answers to the following questions:
• What does a stakeholder have to achieve and how do we measure success?
• What are the stakeholder´s sources of job satisfaction? What are the sourcesof dissatisfaction and stress?
• What knowledge and skills does the stakeholder have?
• What are the stakeholder´s attitudes towards work and the proposed tech-nology?
• Are there any work group attributes that will affect the acceptability of thesystem to the stakeholders?
• What are the characteristics of the stakeholder´s task in terms of frequency,fragmentation and choice of actions?
7
• Does the stakeholder have to consider any particular issues relating respon-sibility, security or privacy?
• What are the physical conditions under which the stakeholder is working?
2.6 Implementation of a demonstrator system
One of the more tangible results of this Master´s project is the development andimplementation of a limited Demonstrator. This system will demonstrate the basicfunctionality of a simulation/visualisation system using common public technolo-gies.
2.6.1 VRML
The requirement of using common and freely available technologies has madeVRML (Virtual Reality Modelling Language) a very good choice of technology.Reasons for this include:
• VRML is well spread.
• Most CAD-systems have built-in functionality for export of models in VRML.
• VRML files may be viewed in a standard Internet browser using a free plug-in.
• VRML-files are text based and hence easy to manipulate, both by hand andby some dedicated parsing program.
• It is rather easy to add functionality for interactions in VRML which enablesreal-time manipulation.
Dynamic VRML content
In conjunction to VRML there are a number of technologies developed to facil-itate dynamic content and external communication to the VRML scene. For thedemonstrator the choice has fallen on External Authoring Interface (EAI), which isa technology that enables a Java-applet to interact with a VRML scene in a browseron the same HTML page using the browser´s javascript interface. (See section 3.5on page 37 for a more detailed description of VRML and EAI)
The WorkshopAssembler is a Java application developed to facilitate the as-sembly of models to a complete scene. This application has been implemented inJava and the reason for this is that it is fairly simple and fast for creating graphicaluser interfaces.
8
2.7 Evaluation of Demonstrator
Evaluation of system design is often wrongfully thought of as an activity in theend of the system development process. Evaluation is ideally an ongoing processthat moves along the whole project providing useful feedback to motivate mod-ifications in the design. Used this way evaluation can be a useful instrument inpreventing interactional flaws at an early stage when it is still fairly easy to adjust.The main goals of the evaluation are to [5]:
• assess the extent of the systems functionality
• assess the effect of the interface on the user
• assess the effect of the user on the interface
• identify specific problems with the system
By ongoing evaluations the systems functionality may be adjusted to better meetthe predetermined requirements. The systems functionality is often well defined inthe beginning of a development project, but continuous evaluations may provideincentives for new ideas or changes in the implementation of certain functions.The effect of the interface on the user can be assessed by measuring how easy thesystem is to learn, its usability and the user´s attitude towards using it.
The main goal of evaluation can be formulated as the desire to identify specificdesign problems that may be aspects of the design which, when observed in theirintended context, cause unexpected results or confusion amongst users. The Eval-uation applies to both the functionality and the usability of the system´s design.
2.7.1 Heuristic Evaluation
Heuristic evaluation is a theoretical approach to evaluation from a set of generalrules of thumb. Based on these rules, a list of potential usability problems can beestablished and evaluated. Heuristic evaluation is an expert evaluation methodwhich means that an expert on interaction design analyses the user interface basedon the heuristics at hand in order to find possible interaction problems.
The heuristics have been developed by Jacob Nielsen and Rolf Molish. The listof heuristics is [5]:
1. Visibility of system status – The system should keep users informed aboutwhat is going on and give appropriate feedback within reasonable time.
2. Match between system and the real world – The system should be welladapted to the language of the users everyday life. Using the same termsand concepts for specific objects and properties in the field of use.
3. User control and freedom – The user must have the option to undo mistakesand cancel actions.
9
4. Consistency and standards – Systems should not break well known conven-tions for actions, names and situations.
5. Error prevention – A design that prevents errors from occurring is betterthan providing good error messages.
6. Recognition rather than recall – Objects, actions and options should be clear-ly visible. It is much better to understand by looking at a situation whichoptions are available than having to remember specific tasks and actions.
7. Flexibility and efficiency of use – Shortcuts to frequent actions are goodways of facilitating for experienced users.
8. Aesthetic and minimalist design – Dialogs should not include informationirrelevant or rarely needed.
9. Help users recognise, diagnose and recover from errors – Error messagesshould be explained in plain text and not in code, explain the problem andsuggest a solution.
10. Help and documentation – The system should provide help and documen-tation that is easily accessed, searchable and focused on the user´s tasks.
10
Chapter 3
Theoretical frame of reference
The related research studied in this Master´s project comes from the fields of Pro-duction Engineering (PE), Virtual Reality (VR) and Computer Graphics (CG). Allof these fields are important in determining the specific needs of a visualizationsystem for plant layout planning but have completely different points of origin.Figure 3.1 maps the theoretical framework for this thesis as the union of the threedifferent research fields. The field of HCI is referenced in a somewhat wider mean-ing since it also applies to the separate fields respectively.
Figure 3.1. The theoretical orientation of this thesis
3.1 Virtual Manufacturing and simulation
This section describes the terms Virtual Manufacturing and Simulation and disting-uishes the immediate differences between the terms. The simulation/visualisationdemonstrator system developed in this Master´s project has a place right in the
11
middle of all these technologies and should therefore be seen from the three fieldsrespectively.
Virtual manufacturing (VM) is a term used to define all levels of simulationsintegrated into one synthetic manufacturing environment, or context. Such a sys-tem is based upon several models rather than just a single model as often is thecase in traditional manufacturing simulation. Johansson & Rosén [9] define threemain types of VM based on the purpose of use:
1. Design Centered Virtual ManufacturingUsed to evaluate a product in terms of produceability.
2. Production Centered Virtual ManufacturingUsed to evaluate properties of a production system such as efficiency. Exam-ples of this type are flow simulations and process simulations.
3. Control Centered Virtual ManufacturingOff-line programming of complex machining or robot intensive productionsystems are examples of this type of simulation. Output from the simulationsis used to generate programs for controlling the production equipment.
The system of simulation/visualisation developed in this project sorts under Pro-duction Centered VM rather than Control Centered VM even though more con-ventional equipment simulation systems clearly fall under Control Centered VM.Properties of the production system we are interested in are usage of physical spaceand machine placements implications on the work place of operators and materialflow. In systems for Control Centered Virtual Manufacturing this information isoften gained as extra bonus material, these systems are often very complex andnot likely to be available for conducting studies of this kind alone. To some extentthe system will be of some benefit in design centered VM as well, because a prod-uct designer will be able to use it to evaluate physical limitations of a modelledproduction system.
Figure 3.2 describes another important part of Virtual Manufacturing; model-driven development of production systems. The red line describes the progressof development starting from a digital model of the product. From this modelrequirements on machining can be derived, which in turn set requirements on ma-chines. This thinking propagates upwards towards factory design aspects such asbuildings, logistics and media. The process then turns back downwards throughthe different levels in the Control systems development phase where data obtainedin earlier simulations on models can be recycled to form the base for programs inthe control systems. In a model-driven development process the models evolvein a natural order which will facilitate the reuse of models, rather than creation ofseveral models at different levels. A model that has evolved from a lower level canbe simplified or otherwise adapted for use at another, higher, level simulation.
12
In this figure (3.2) the different simulation types can be mapped accordingto the level at which they serve. Process Simulation applies to process and ma-chine/station levels, Equipment Simulation to the line/cell level and finally FlowSimulation to the upper factory level.
Figure 3.2. Viewpoints of Manufacturing systems development (Sven Hjelm, Scania)
3.1.1 Simulation in general
The term “simulation” is described in Merriam-Webster Online Dictionary [16] as:
SimulationEtymology: Middle English simulacion, from Middle French, from Latinsimulation-, simulatio, from simulare Date: 14th century 1 : the act orprocess of simulating 2 : a sham object : COUNTERFEIT 3 a : the im-itative representation of the functioning of one system or process bymeans of the functioning of another <a computer simulation of an in-dustrial process> b : examination of a problem often not subject to di-rect experimentation by means of a simulating device
In this project a somewhat more condensed and for the purpose, better adaptedinterpretation of the term has been chosen. It is introduced by Bruno Bernard [2]:
Simulation is the process of executing a model of a system in order tounderstand and/or evaluate the behavior of this system.
The process of simulation in this sense comprises three basic steps [2]:
13
• Modelling – Creation of the model that is to represent the system. This step,in turn, includes:
– Delimiting a well defined production situation
– Formulating goals of the simulation
– Identification of possible problems
– Decisions on structure, extent and level of detail.
• Elaboration – Manipulation of parameters controlling the model and the be-havior of the system.
• Evaluation – Gaining understanding or drawing conclusions from the notedbehavior. Recommendation and documentation are also important parts ofthis step.
The simulation model is an abstract representation of the system to be modelled. Itcan contain structural, logical or mathematical relationships between comprisingcomponents to be interpreted by the computer based simulation software. It is alsopossible to think of physical models as simulation models, but since this project ex-clusively deals with computer based simulation, this type will not be consideredin this thesis. In computer based simulations distinctions are made between Con-tinuous and Discrete simulation based on the influence of time in the model.
Some general benefits from simulation include the abilities to [19]:
• test new ideas in a risk free environment.
• predict behaviors of a system.
• gain greater understanding of complex systems.
• reduce time consumption.
• no disruption of ongoing operations.
Along with these benefits there are a number of limitations and difficulties of sim-ulation which include:
• difficulties in determining the right level of detail in modelling.
• designing a model is a complex task that requires training, experience alongwith correct and reliable input.
• difficulties in finding the correct objectives and goals.
• conclusions are based on abstract simplifications of a real situation.
• difficulties in interpreting and analyzing the results.
14
3.2 Simulation in production engineering
Simulation at different levels has of late increased in importance at Scania. Processsimulation has been used for some time to retrieve cutting data for machines andfor doing stress calculations on products. Discrete Event Simulations, or flow sim-ulation has become a successful method for analyzing material flow in the presentproduction facilities and in planning of new production facilities.
3.2.1 Flow simulation
Flow simulation supports the initial planning of a production system and is a toolfor optimising internal logistics, which is another term for material flow through-out the facilities. This flow concerns the parts as well as tools, scrap and othermaterial. As highlighted by Randell [20], typically there are three types of simula-tion studies:
• An explorative study of an existing system. This type of study usually in-volves finding possible improvements to a system. A simulation model ismade and changes are quickly implemented if improvements are found.
• A study of an existing system. This study is similar to the one above butwith the difference of using the model to validate proposed improvements,not finding them.
• Designing and validating a new system. Simulation is used in the designprocess to validate the performance of the system.
At Scania a software named Extend (see fig 3.3) is being used for flow simulations.In this system the model is built up by components linked together and controlledby conditions such as cycle-time and buffer-sizes.
This type of simulations are getting more common at Scania since a few pi-lot cases have shown its potential to assist production engineers in dimensioningnew production process facilities. Flow simulation often reveals bottle-necks in aproduction chain or problems in internal logistics otherwise not seen.
3.2.2 Process simulation
Process simulation is an area that is harder to define in simple terms, mostly be-cause of the wide meaning of the term process. At Scania Process Simulation isdefined as simulation of value-adding processes, i.e. manufacturing processes thatchange the material properties and/or the physical shape or performance of dis-crete parts.
Figures 3.4 and 3.5 show examples of process simulation at Scania. Data ob-tained in these simulations are used in tool design to compensate for obstructingprocess phenomena. Sheet metal forming is a complex process where it is impor-tant to maintain control of how the sheet metal wrinkles when it is formed in thepressing machines.
15
Figure 3.3. This figure shows an example consisting of a part generator that putsnew objects into the flow. The next component is an attribute setter, which attachesattributes to the objects. On the side there is a random number generator that is con-nected to the attribute setter, introducing stochastic elements according to a predefinedprobability function or statistical distribution. The next component in this example isa flexible FIFO (First In First Out) buffer, in which parts or objects queue up waiting toenter the processing part of the flow. The lower loop of the flow handles resources thatare attached to the objects in the batch block just before the processes and unbatchedjust after. The last two components are a sink collecting the finished objects and aplotter displaying, in this case, the size of the buffer over time.
3.2.3 Equipment simulation
Equipment simulation or geometrical simulation is presently often tightly relatedto robot cells and off-line programming. This relation is natural since it has provenvery cost efficient to generate robot programs directly from geometrical data ac-quired through this type of simulation.
Simulating functions and material flow in a virtual manufacturing system ofmachines and handling equipment early in the design process, with the opportu-nity to manipulate design parameters has proven to provide new and better meansfor both design and decision by flow simulation. Concrete questions about reach-ability, accessability and cycle time, on the other hand, can be addressed by equip-
16
Figure 3.4. An example of process simulation, where the casting process of Scania´scylinder heads is being simulated. Colors indicate the temperature of the molten steelin the mould. (Scania)
ment simulation. Information and insights gained from equipment simulation canthen be used as feed-back to both part and tool design. The ability to move freelywithin the virtual machine cell can provide information on work ergonomics andmaintainability of a machine cell. These are questions more difficult to quantifyand therefore harder to evaluate.
Figure 3.6 shows a robot cell for welding simulated in ABB´s Robot Studio.In this project equipment simulation is referred to as equipment simulation/visualisa-tion. This is mainly because the degree of simulation in this particular case is some-what less important than the visualisation. Equipment simulation as it is usedtoday will be given a more detailed description in section 5.3
3.2.4 Integrating tools for VM
A major challenge in realising the idea of virtual manufacturing is to make useof standard interfaces between applications from different brands supporting dif-
17
Figure 3.5. Simulation of sheet metal forming. Colors indicate the level of strain in thematerial (Scania)
Figure 3.6. Simulation of welding robot in RobotStudio (www.abb.com)
ferent aspects of virtual manufacturing. Today, developers of tools for VM havea propensity to use internal data formats that make the use of a mix of programsawkward and in many cases inefficient. Today there are two major suppliers ofthese tools; Delfoi and Tecnomatix. Both these companies uses a similar structurefor organising products, resources and processes. Another common ambition ofthese companies is the propensity to over-integrate the comprising parts of the vir-
18
tual manufacturing system, in order to deliver a super system featuring all possibleservices within the boundaries of virtual manufacturing. It would be desirable tobe able to choose different parts from different suppliers, to avoid becoming de-pendant on one supplier´s solution alone.
3.2.5 Verification of models using physical equipment
Recent research in Virtual Manufacturing has addressed the problem of verifica-tion of digitally modelled equipment and workcells. Berlin and Bergqvist [1] de-scribe a method of 3D laser scanning to verify digitally modelled equipment andadjust geometries of these from the physical equipment after installation. If the vi-sion of virtual manufacturing shall be realised, one important requirement is thatthe digital models are accurate enough for performing simulations in prototyp-ing new products or other changes. Berlin and Bergqvist claim this technique willclose the loop between the real and the virtual world. This method is described inmore detail in section 5.4.
3.3 Computer Graphics
From the computer graphics point of view there are a number of issues that needto be considered and this section will point at these and discuss their implicationsfor equipment simulation. These issues include:
• Data representation in CAD-formats
• File Format Conversions
• Model resolution
• Level of Detail
• Polygon reduction and compression
This section starts off with a brief introduction to the graphics pipeline, whichdescribes the system of 3D graphics rendering.
3.3.1 The graphics pipeline
The graphics pipeline describes the consecutive process of transformations in diff-erent three-dimensional spaces. Object representations are transformed form spaceto space, from local coordinate space to the display space on the computer screen.
It is important to be familiar with the graphics pipeline and the different trans-formations when working with 3D computer graphics programming, but most im-plications of the graphics pipeline in this projects are dealt with behind the scenesby the VRML scene graph system. However, a general understanding of opera-tions in the graphics pipeline is helpful in determining properties of the models tobe used.
19
Figure 3.7. Diagram of the graphics pipeline
Interesting transformations between the different coordinate systems in thegraphics pipeline are [23]:
• Modelling transformationIn this step the model is transformed from its local coordinate system intothe world coordinate system. This transformation can include translations,rotations and scaling of individual objects.
• Viewing transformationThe second step includes definition of the view frustum, which is the volumecontaining objects that are to be projected to the screen view. In this stepobjects that do not coincide with this volume are eliminated.
• Projection transformationIn this next step further eliminations are made in respect to parts of objects torender. Backface culling means eliminating surfaces that face away from theviewing direction and hence can not be seen. This is made by calculating thedot product of the surface normal and the line-of-sight vector and eliminatesurfaces where this dot product < 0. Clipping of polygons intersecting theborders of the frustum is also performed in this step. Objects hidden behindother objects are also removed or clipped by comparisons of distance to theview point.
• Viewport transformationThe last transformation determines the projection of the view volume ontothe view plane.
20
3.3.2 Model data representation
There are a number of different ways to represent data for 3D models, all withdifferent objectives and advantages. The motivation for this diversity is [23]:
• Ease of rendering
• Ease of shape editing
• Suitability for animation
• Dependence on the attributes of the raw data
The way chosen to represent model data can often be traced back to how the modelwas created. There are no rules of thumb to rely on in choosing data representationfor a model.
Examples of model data representations include [23]:
• Polygon meshObjects are approximated by a number of planar polygonal surfaces. Theaccuracy or resolution can be chosen more or less arbitrarily for any shape.
• Constructive Solid Geometry (CSG)Models comprise combinations of primitive shapes.
• Bi-cubic parameter patchSurfaces are represented by patches of mathematically defined surfaces.
• Spatial subdivision techniquesThis technique means partitioning the object space into elementary cubes,also known as voxels. The voxels contains information whether or not theycontain a part of the object or not. A voxel can be looked upon as a three-dimensional pixel.
• Implicit representationObjects can be defined by implicit functions. For example a sphere is definedby the function: x2 + y2 + z2 = r2 In computer graphics this way of repre-senting data is limited by the fact that only a limited number of objects canbe represented in this way. It is also a rather inconvenient representation asfar as rendering is concerned.
These different ways of representing data can be divided into three groups:
• Wire frame modellingA polygon mesh is a typical wire frame model. It is very simple to handlebut contains none or poor information to calculate contours and volume.
• Surface modellingSurface models are basically a wire frame where surfaces are approximated
21
or interpolated between points. A surface is divided into patches. A patch,in turn, can be modelled as a bicubic spline or a Bézier surface, interpolatedusing points in the mesh. A general Bicubic patch is defined by [15]:
p(u, v) = {x(u, v), y(u, v), z(u, v)} (3.1)
p(u, v) =m∑
i=0
n∑
j=0
kijuivj (3.2)
and the Bézier patch by:
p(u, v) =3∑
i=0
3∑
j=0
Bi,m(u)Bj,n(v)pi,j u, v ∈ [0, 1] (3.3)
• Solid modellingSolid models are defined by volumes rather than by points, lines and sur-faces. CSG, mentioned above, is a representation of this kind where modelscomprise combinations of primitive shapes. By performing boolean oper-ators on positioned primitives new, more advanced, geometries can be ob-tained. A directed graph is used as data structure to store the model [15].
Figure 3.8. Sphere modelled with polygon mesh, as solid geometry and with NURBS
The most common model data representation is the polygon mesh [23]. The twomain reasons for this is that creating models is straightforward and effective algo-rithms for producing shaded versions of this representation exist. It is often thecase in other representations that the models are transformed to a polygon mesh
22
representation just before rendering. This combination of representations is also apractical way of meeting requirements of both model accuracy and render speedin 3D CAD systems.
In digitizing an existing, physical, model or environment a laser scanner maybe used, this method produces a large set of points in R3, which may be triangu-lated into a polygon mesh representation.
Data representation in VRML
The way models are represented in VRML depends on how they were created. Acommon way of creating models is to build objects by combining basic primitivesolids like, boxes, cylinders, spheres and cones into a larger compound model.
In VRML polygon mesh representation is supported by the node IndexedFace-Set{}, which is a node containing two arrays; one array of points and another withindices to the points in the first array to define edges in the polygons.
Figure 3.9. VRML figure of the example above
IndexedFaceSet {coord Coordinate {
point [ 1 0 -1, # point 0-1 0 -1, # point 1-1 0 1, # point 2
1 0 1, # point 30 2 0 ] # point 4
}
23
coordIndex [ 0 4 3 -1 # face A, right1 4 0 -1 # face B, back2 4 1 -1 # face C, left3 4 2 -1 # face D, front0 3 2 1 ] # face E, bottom
}
This way of storing the polygon mesh is common in other systems for graphical 3Drendering. The left model in Figure 3.9 shows the resulting figure of the exampleabove. The right model shows the same geometry as a wireframe model withcorners accentuated.
3.3.3 Model density, Level of Detail and Polygon reduction
CAD systems used to create models of products as well as machines and toolsoften work with parametric surfaces such as splines and NURBS. This representa-tion of models is space efficient and makes good looking models, however whenexporting models to VRML a polygon mesh is created consisting of points andedges defining polygons in 3D. This is the most common representational form ofobjects in 3D [23].
Model density
The transformation into a polygon mesh representation often means losing accu-racy in comparison with the representation of parametric surfaces and this is clearwhen working with models with smooth and curved surfaces or high levels of de-tail. The model export functions in the CAD systems often compensate for thisloss by increasing point density on the models where these smooth surfaces andcomplex shapes occur and the result is hence huge files which are awkward to pro-cess in real-time. In terms of real-time rendering this representation often meansthat the graphic pipeline has to process thousands of polygons that project onto afew pixels on the screen and as the projected polygon size decreases, the polygonoverheads soon become significant with loss of performance as a result.
The resulting density in polygons from the CAD-system depends on the algo-rithms used for this export.
Level of detail
In the kind of simulation/visualisation described in this project, the requirementsin model accuracy is lower while process speed is more important since visualimpression is an important objective.
The problem with polygon overhead can be addressed in different ways, butan often chosen way is by introducing a number of different representations for thesame objects, all with a different number of polygons. If the object to be rendered
24
only projects onto a small number of pixels a less detailed model will be chosenand as the object gets closer, a more detailed model is chosen for rendering. Theobvious downside to this solution is that it is more space consuming, thanks to alarger number of models having to be stored.
Figure 3.10 shows an example of a model represented by four individual mod-els with a decreasing number of polygons from left to right.
Figure 3.10. Model of a rabbit at different levels of detail (LOD)
In creating these models of different resolution a process of polygon reductionis applied to the original model.
Polygon reduction
Figure 3.11 shows a 3D model of a Kuka robot manipulator drawn with three dif-ferent numbers of polygons. The model to the left is the original model consistingof 22999 triangles. This model is the VRML result of an export from a CAD sys-tem. The model in the middle has been reduced by 80% to consist of merely 4599triangles. As the figure shows there is no major decrease in the visual impression,hence there are many points in the original model that do not actually contributeto the visual quality of the model. The rightmost model has been reduced to 688triangles and is starting to look heavily distorted.The last and most reduced model clearly illustrates an interesting property of mostpolygon reduction algorithms, namely a propensity to distort and lose symmetricproperties of the model. This phenomenon comes from the process of edge col-lapsing, which is often used in polygon reduction.
The basic idea of a simplification algorithm is to reduce the number of verticesand edges in a mesh model, while at the same time, avoid reducing the quality ofthe model´s visual impression. There are a number of different approaches to thisoptimization problem. Some examples of simplification algorithms/strategies are[12]:
• Triangle mesh decimation
• Vertex clustering
25
Figure 3.11. Robot model in three stages of polygon reduction
• Multiresolution analysis of arbitrary meshes
• Voxel-based object simplification
• Simplification envelopes
• Appearence-preserving simplification
• Quadric error metric
• Image-driven simplification
• Progressive meshes
• Hierarchical dynamic simplification
In determining which method for model simplification to choose, Luebke [13] in-troduces three questions to assist in specifying the needs and requirements for aparticular situation:
• Why do we need to simplify the polygonal objects?
– Elimination of redundant geometry
– Reduction of model size
– Improvement of runtime performance
• What are the models like?
– Complex organic forms
– Mechanical objects
– High-complexity
26
– Large assemblies of many small objects
• What matters the most?
– Geometrical accuracy
– Visual fidelity
– Preprocess time
– Drastic simplification
– Completely automatic
– Simple to implement
Based on these questions a recommendation of simplification method can be given.In the case of the application discussed in this thesis, where the main objective ofsimplification is to improve run-time performance of complex models of mechani-cal components, the recommendation is to use vertex clustering or progressive meshesand these algorithms will therefore be the only ones described in this thesis. Themain difference between algorithms for mesh simplification lies in the strategyused to categorize vertices for removal.
Vertex clustering
(Adapted from Garland [7]) A simple form vertex clustering algorithm spatiallypartitions the set of vertices into a new set of clusters. In these clusters, a newvertex is calculated, based on criteria such as edge length, to represent the includedvertices. This method of simplification is fast and easy to implement efficiently,but has a propensity to make poor quality approximations. Vertices belonging toseparate parts of an object or to separate objects, but located close to each othermay in this case be clustered into the same new vertex and hence merge the twoparts (See fig. 3.12).
Figure 3.12. Clustering in two dimensions (before and after) [7]
27
Progressive meshes
(Adapted from Hoppe [8]) The other suggested simplification method; progressivemesh, is basically a model data representation which includes simplification data.The idea is to store a reduced model with additional information on how to getback to the original model. In a progressive mesh form, an arbitrary mesh M isstored as a much coarser mesh M0 together with a sequence of n detail records onhow to incrementally refine M0 exactly back into the original mesh M = Mn. Thesequence of detail records contains a series of vertex splits, which is the reversetransformation of edge collapsing often used in mesh simplification. The ways ofdetermining the appropriate edge collapse strategy may vary depending on theapplication at hand. Hoppe [8] approaches this problem by casting it as minimisa-tion of an energy function:
E(M) = Edist(M) + Erep(M) + Espring(M),
where the goal is to find a mesh M = (K, V ), where K is a representation of themesh connectivity and V the set of vertices, that approximates a set X of pointsxi ∈ R3 and has a small number of vertices.
The algorithm evaluates all edges that can be collapsed according to this en-ergy function and sorts them into a priority queue. The energy function is thenminimised in a greedy fashion by performing an edge collapse on the first edgein the prioritised queue. Nearby edges are then reevaluated and sorted into thequeue. This procedure is repeated down to a pre-determined level, where the re-maining edges comprise the base mesh M0. The edge collapses performed aresaved in reverse order to comprise the hierarchy of vertex splits.
Figure 3.13. Progressive mesh in different LOD[7]
This representation makes access to different levels of detail (LOD) very efficient.
3.4 Virtual Reality
The term Virtual Reality is and has been surrounded with some sense of sciencefiction, mostly due to the complexity of systems supporting all features of VR,
28
including stereoscopic view, audio surround system, movement tracking, hapticinput devices and the possibility to collaborate and interact with other users withinthe virtual environment. The rapid development in traditional 3D graphics hasnow started to blur the borders of VR and introduced some of the features fromthe original ideas into regular desktop computers, albeit with some limits.
Originally the term VR referred to immersive VR, which means that the userenters or immerses into the virtual environment by means of using stereoscopicviews, three dimensional input devices and other tools.
In Virtual Reality some of the main areas of interest are:
• Navigation in 3D spaceThe way we move around in a virtual space is not always obvious, there aredifficulties to consider in navigating an environment. Landmarks and otherdetails used to navigate in the real world, might be absent in the abstractvirtual world.
• Interaction with the environmentHow can we define logical and understandable ways of interacting with theenvironment? Is the experience of the VE close enough to “the real world”?What technical means for interaction does the system provide?
• Visualization and presentationHow do we present the virtual environment to the user? 2D/3D? Screen/3D-goggles/Cave/Power wall (See section 3.4.1)?
• Collaboration with other usersShould the virtual environment support collaboration between different users?What kind of special tools or functionality are required for this?
3.4.1 HCI in virtual environments
In the field of Human-Computer Interaction (HCI) there are a number of heuristicshas been developed to define requirements on the user interface of a system. Manyof these ideas apply to Virtual Environments, but there are also new aspects toconsider when introducing a third dimension.
Affordance and metaphors
Donald Norman [18] introduced the term “perceived affordance” in the fields ofHCI and usability. The term affordance originates from the perceptual psychol-ogist J.J.Gibson in the 70´s and refers to actionable properties in the relationshipbetween the world and an actor. In software design, Norman´s adaptation to per-ceived affordance refers to properties of an object that afford some certain actions,i.e a button affords clicking, in that we immediately know from the look of a buttonthat it can be clicked. In a wider sense, placement, caption and context may evengive us some perception of what actions the clicking on the button will achieve.
29
The difference between the original term and Norman´s adaptation to design,lie in the distinction of real versus perceived affordance.
Affordance should be seen as a property of the conceptual model of a system.Norman [18] explains the conceptual model as the model formed by the user fromaffordances, constraints and mappings of a system or a tool. From these perceptionsthe user forms a conceptual model of the system, simulating its function and fromthis understands its intended use and function. “A good conceptual model allowsus to predict the effects of our actions.” [18]
In traditional HCI the use of design metaphors is a common way to supportaffordance of a user interface. In virtual environments it is more difficult to findsuitable metaphors. For instance, in most modern operating systems today, thedesktop metaphor is used to support affordance of the provided services of thesystem. A folder affords placing and organising of files within them, the trash canaffords erasing of files etcetera. The more or less obvious choice of metaphor in aVE is the real-world metaphor. This choice is not without complications since thelevel of detail in the modelled VE lacks many of the natural affordances found inthe real world.
3D versus 2D interaction
Hilary McLellan points to five important elements of interaction in virtual envi-ronments compared to traditional 2D space. Four of these that apply to this projectare [14]:
• Dimensionality3D versus 2D planar viewing. 3D viewing potentially offers a more realisticview of the geography of an environment than a 2D contour map.
• MotionDynamic versus static display. A dynamic display appears more real than aseries of static images of the same material.
• InteractionClosed-loop versus open-loop interaction. A more realistic closed-loop modeis one in which the user has control over what aspects of the world areviewed or visited. This makes the user an active navigator as well as anobserver.
• Frame of referenceInside-out (ego referenced) versus Outside-in (world referenced) frame ofreference. Inside-out frame of reference means that the environment is viewedfrom a first person perspective compared to the “God’s eye” view in a 2Drepresentation.
In a virtual environment it is not always realism that is the primary goal, but ratherthe abstraction from reality in itself that will provide a useful filter of detail in order
30
to accentuate a specific phenomenon. Users might expect to find elements in theenvironment that are not included in the model due to the different assessments ofimportance between user groups.
Dynamic displays also lack the advantage of easy comparisons. Static displayscan be put alongside each other for a quick comparison.
Another point more closely related to creation of models is the issue of geo-metrical accuracy. Displayed in 2D, a projection of a 3D model is presented in onesingle plane. In abstracting 3D models into 2D impossible geometry can pass unde-tected. Fig 3.14 shows an example of an impossible geometry by Oscar Reuterswärdthat illustrates this phenomenon, albeit in an extreme figure.
Figure 3.14. Example of impossible geometry (Oscar Reuterswärd)
Navigation in 3D space
The abstraction of reality and the filtering of details may also have a negative im-pact on finding the way in a virtual environment. Visual cues for way-finding inreal environment are often subtle things that may be absent in the clean modelof the virtual environment. Support for navigation may include pre-defined viewpoints, which can be accessed from a menu function. Another solution to thisproblem can be to use some sub-system for navigation that gives an overview ofthe world and supports teleportation.
In a study of navigation, wayfinding and place experience within a virtual city,Murray et al [17] point at a number of interesting insights in how people interact
31
with the environment in the virtual city. In this study a small number of respon-dents were asked to locate a certain adress in a virtual city. The city was computergenerated and contained buildings, streets and other features found in a real city.The respondents were observed and video filmed during the session and the re-searchers noted behavior and comments during the experiments. The user testsshowed that respondents often, in the VE, adopt a behavior from the real world.For instance, when walking around, some favoured walking on the pavementsrather than just strolling in the middle of the streets. In terms of wayfinding, re-spondents thought the sparse details in the environment did not provide enoughaffordances for the task. Other important findings included problems in determin-ing if a certain place had been previously visited as well as problems in ascertainrotational angles when rotating. Proposed solutions to these problems in the vir-tual city includes the introduction of a static sun as a universal reference point toestablish a virtual, yet natural sense of direction.
The test environment also featured the ability to fly over the city in order toget a better overview. It turned out this feature seemed unnatural and thereforestrange to the respondents and they prefered staying “on the ground” most of thetime. The respondents also provided insights in the importance of the computa-tional performance of the system. Smooth and realistic movement was found to beimportant to provide the sense of presence in the VE.
The virtual city contained a number of landmarks to facilitate navigation. Theselandmarks were of two main categories, ordinary anticipated landmarks such asfountains and gazebos and other more unexpected like Stonehenge, a dinosaur andEaster Island statues. The latter category of landmarks was often actively notedand commented by the respondents, which indicates their usefulness in designinglandmarking strategies for a VE.
Conclusions of this study points to pros and cons of the real-world metaphorused in the virtual city. Murrey et al [17] claim that “the crude adoptation of real-world metaphors in the design of VE may mean that their practical and subjectivesignificance are lost as materiality is reimposed by new practices”. At the sametime, the real-world metaphor provides affordances to facilitate for people to usetheir real-world understandings and behaviors in performing tasks in the VE.
Interaction with objects in a Virtual Environment
There are some fundamental problems associated with interaction with a virtualenvironment. In 2D space, one has the ability to click on an object and hence selectthis object for manipulations. This is a central function in most PC systems today,however in 3D space this is not without complications. An ordinary mouse onlysupports two degrees of freedom (position in X and Y) and it seems to be sufficientwithout considering rotational degrees of freedom. In 3D space it is often requiredto be able to have some level of control over most degrees of freedom [10]. In manysystems for virtual environments this is solved by implementing different modesof movement controlled by a regular mouse. A mode for walking will for instance
32
make the avatar move about the XY-plane (depending on world orientation). Byswitching the input device into another mode for rotation, access to rotational de-grees of freedom will be achieved. This is often done by using a virtual sphere.Other modes may be flying, where the avatar moves about a plane defined by theline of sight and actual roll.
CAD systems and 3D modelling tools often use multiple windows to separatethe views into pairs of orthogonal projections of the same object.
At product development departments at Scania, most Catia CAD workstationsare equipped with a three dimensional space mouse. This 3D input device consistsof a “hockey-puck”-like handle that can be pushed and rotated in 6 degrees offreedom (See fig. 3.15).
Figure 3.15. SpaceMouse 3D input device (www.logicad3d.com)
Visualisation and presentation
The way the virtual environment is presented to the user also implies some spe-cial considerations. Often systems use stereoscopic views to enhance the sense ofdepth. This sense of depth can otherwise be obtained by motion parallax frommoving around in the virtual environment.
More advanced systems may use a Power wall or a Cave where the virtual envi-ronment is projected on three or more walls and lets the user enter the VE wearingspecial purpose glasses for stereoscopic viewing.
An interesting project related to the subject of this project is described in areport: “BUILD-IT: Intuitive plant layout mediated by natural interaction” [6].BUILD-IT is an experimental tool based on computer vision technology that usessmall bricks as a tactile interactional medium for planning the layout of a work-shop (See fig. 3.16). The system is comprised of a table where a 2-dimensionallayout is projected. The users sit around the table moving bricks representing ob-jects around on the projected layout. A computer vision system tracks the bricksand presents a 3-dimensional view of the workshop on a separate screen.
The main ambition of the project has been to find a way to support naturalbehavior in the interaction with a computer system. From theories on task analysisand action regulation, six design principles were established to form the foundation
33
on which the BUILD-IT application was built. The proposed design principles arethe following:
• Assure that mistakes only imply low risk so that epistemic1 behavior is beingstimulated.
• Allow users to choose between epistemic and pragmatic actions
• Support complete regulation of pragmatic as well as epistemic behavior.
• Allow users to take on planning functions in a direct and intuitive way.
• Clearly indicate which objects and tools are useful for task solving accom-plishment.
• Clearly show the result of the user action.
Figure 3.16. BUILD-IT: plant layout planning system [6]
The resulting system BUILD-IT is centered round the ideas of a tactile interface andcoinciding action and perception space, where the user manipulates object in thereal world and the result is visible in the virtual world. Many of these ideas comefrom the field of Augmented Reality (AR), where the idea is to augment propertiesor appearance of physical objects with computer generated features.
Collaboration in VE
Some systems may incorporate means of collaboration between different usersworking within the environment simultaneously. In this case the system needsto support forms of awareness2. These aspects are covered in the research fieldof CSCW (Computer Supported Collaborative/Cooperative Work), where specific
1epistemic – knowledge-based, pragmatic – practice-based2Awareness – term used in the HCI field, which refers to the ability of a system to provide infor-
mation on other users´ activities in order to provide a work context for your own activities
34
features to support and facilitate cooperative work is the main focus. Systems thatallow for simultaneous work by more than one user, are often referred to as group-ware and can be categorized by the users´ relations in terms of time and space [5].
The system presented above; BUILD-IT, is a good example of a collaborativesystem where a number of users work with the system at the same time in thesame room. Another system may allow for simultaneous work but separated inspace, which means two, or more, users sitting at separate computers collaborat-ing within the same virtual environment. This is an appealing feature for a systemof simulation/visualisation of workshop layouts where a guided tour would bepossible to undertake inviting participants located at different places. One aspectof the proposed system in this project is that of decision support and this is a taskthat may be well suited for this synchronous remote interaction with a shared ap-plication. A term often used in discussing systems of this kind is WYSIWIS [5], anabbreviation of What You See Is What I See and relates to the importance of sharingthe same information. In a shared virtual environment, where each participant isallowed to walk free, it is important to know where the other co-workers are andwhat they are looking at. This is of course tightly coupled with the term awarenessdiscussed earlier.
Related research on these issues includes a report on formal VR-meetings byLenman et al [11] addressing the question of how the use of avatars3 may assist instrengthening the sense of awareness. The avatar, in its simplest, works as a centerof attention. The location, orientation and body posture of an avatar may also pro-vide bystanders information on the other users´ actions and attentions. Predefinedgestures and facial expressions are other common ways of using avatars to expressemotions and activity. Fundamental features or abilities of the avatars are [11]:
• mark presence of a person
• show location of the person in the VE
• should present personal identity for recognition
• be adaptable
• be truthful, in the sense that their appearance should not imply abilities theydo not possess
• should provide information on activities
• indicate attention of the user (direction of view etc.)
• indicate what objects the user is manipulating or interacting with
• implement gestures and facial expressions
There are no particular reasons for making avatars realistic, they can be quite ab-stract without losing purpose [11]. The design of avatars can be categorised intothree main types: Antropomorphic, Figure like and Abstract. (See fig. 3.17)
3avatar – embodiment, incarnation in human form
35
Figure 3.17. Different types of avatars [11]
The purpose of using avatars does not really favor any of the categories beforeanother, aspects of higher importance are [11]:
• Recognition and identification
• User acceptance
• Anonymity
• Poses and body movement
• Movement in the environment
Another issue with avatars is the control of its movement and expressions. It isimportant that the work of controlling the avatar does not take the focus of themain task. Research in this field has suggested a variety of techniques to auto-mate avatar movement and ideas span from simple keyboard control to advancedbiometric devices and voice recognition-driven lip synchronisation.
36
3.5 The VRML language
3.5.1 What is VRML?
In the Annotated VRML97 reference manual [3] found at web3d.org the first chap-ter begins with the following paragraph:
VRML, sometimes pronounced vermal, is an acronym for the VirtualReality Modeling Language. Technically speaking, VRML is neithervirtual reality nor a modeling language. Virtual reality typically im-plies an immersive 3D experience (such as a head-mounted display)and 3D input devices (such as digital gloves). VRML neither requiresnor precludes immersion. Furthermore, a true modeling language wouldcontain much richer geometric modeling primitives and mechanisms.VRML provides a bare minimum of geometric modeling features andcontains numerous features far beyond the scope of a modeling lan-guage.
VRML can most easily be seen as a 3D interchange format that supports commonfeatures such as hierarchical transformations, light sources, geometry, animations,visual effects, material properies and texture mapping. VRML has been designedto be an analog to the commonly used HTML, in that it is a multi-platform lan-guage for publishing web content in a relatively simple and straight-forward way.
3.5.2 The background of VRML
VRML was first initiated by Rikk Carey and Paul Strauss at Silicon Graphics in1989. The project´s objectives were to design and build an infrastructure for inter-active 3D graphics applications [3]. The first outcome of this project was the IrisInventor 3D toolkit released in 1992 and was a toolkit in C++ that defined manyof the semantics found in VRML. In 1994 a revised version of this toolkit was re-leased under the name Open Inventor, based on Silicon Graphics´ OpenGL techno-logy. At this time an early prototype of a 3D web browser, called Labyrinth, wasbuilt. At this time a mailing list, www-vrml, was created with calls for proposalsfor a formal specification for 3D on the WWW. The connection to the work on OpenInventor was early realised and it came to form a base for this work after addingsome and removing some features of the Inventor file format. The specificationof VRML 1.0 was published in October 1994 at the Second International Confer-ence on the World Wide Web. At SIGGRAPH 96 in New Orleans, a first version ofthe specification for VRML 2.0 was released, introducing new key features such asanimation, interaction and behavior in the VRML language. In 1996, at the Inter-national Standards Organization´s (ISO) JTC1/SC24 committee meeting in Kyoto,the specification was accepted and published as Committee Draft(CD) 14772. Thetext was submitted in 1997 under the name VRML97, following the ISO namingconvention.
37
Up until 1999 Cosmo Viewer was the “preferred” VRML browser. It was originallydeveloped by SGI, who later created the separate company Cosmo Software to focuson developments in VRML. Cosmos Software was later bought by another com-pany called Platinum, that had the intentions of making the browser open sourceand handing it over to the web3D consortium. In 1999 Platinum was bought byComputer Associates and the negotiations with the web3D Consortium dragged anddied. Most of the work within the VRML community had so far been done by vol-unteers, who at this point were discouraged to carry on their work. Other browserswas developed during this time, but without the common efforts of a driving com-munity, VRML started to drift off into different less compatible versions. 4
VRML today
Lately the development efforts has started to increase again in the developmentof the next generation of VRML – X3D. X3D is an XML implementation of VRML.This work has just begun and so far there are only a few beta versions of browserssupporting the new format. However, the future is once again starting to lookconsiderably brighter.
X3D includes nodes supporting more complex representations of geometry,like the NurbsSurface node.
3.5.3 The structure of VRML
A VRML file consist of the following main parts:
• HeaderThe header of the file tells the VRML parser that the file is an actual VRML fileof a certain version, along with the file´s encoding type. It has the followingformat:
#VRML V2.0 utf8 [optional comment] <line terminator>
• Scene graphThe scene graph contains nodes which describe objects and their properties.It contains hierarchically grouped geometry to provide an audio-visual rep-resentation of objects, as well as nodes that participate in the event generationand routing mechanism. [3]
• PrototypesA Prototype is a node type created by the user by providing extensions to thestandard set of nodes. A prototype can be seen as the struct data type inANSI C, or as a macro.
4This part is an adaptation of information from email correspondence with Anders Jepsen of theweb3D Consortium
38
• Event routesSome VRML nodes generate events in response to environmental changesor user interaction. Event routes provide the creator of a scene means ofcatching these events and route them into other nodes that respond to theseevents.
• Script nodesScript nodes are nodes used to catch and process events from other nodes.By using Scripts, more advanced functions can be achieved, rather than justthe sheer passing of messages that is done by the event routing.
3.5.4 The VRML browser
The VRML files created are interpreted and presented by the browser. The browsercan be either a stand-alone application or a plug-in for an ordinary web browsersuch as Internet Explorer. The browser presents the geometry of the VRML scenegraph along with means of interacting, navigating and exploring the virtual world.
Figure 3.18 shows the conceptual model of the VRML browser. The main com-ponents of the browser are the Parser, the Scene graph and the Presentation modules.The Parser reads the VRML file and constructs the hierarchical structure of trans-formations and geometry nodes comprising the scene graph from this information.
The presentation module renders the scene graphically and audibly back to theuser.
3.5.5 External communication
As an extension to VRML, there are some ways of having the VRML scene commu-nicating with an outside source. External Authoring Interface (EAI) is one way ofachieving this functionality. EAI is designed to allow an external program (a Javaapplet) to access nodes in a VRML scene using the existing VRML event model.
The External Authoring Interface allows 4 types of access into the VRML scene[22]:
1. Accessing the functionality of the Browser Script Interface.
2. Sending events to eventIns of nodes inside the scene.
3. Reading the last value sent from eventOuts of nodes inside the scene.
4. Getting notified when events are sent from eventOuts of nodes inside thescene.
The External Authoring Interface is patterned after the Script Authoring Interface(the interface used by scripts inside a Script node). The first 3 access types aboveare conceptually identical to this interface. For type 1 access, a Browser object isavailable to an applet to give access to the Browser Script Interface. For type 2 and
39
Figure 3.18. The conceptual model of the VRML browser[3]
3 access, a pointer to a node can be obtained at which point events can be sent toits eventIns and the value of its eventOuts can be read.
The 4th access type is conceptually different since creating a ROUTE is notpossible between the VRML scene and the applet. The applet must create a methodto be called when the eventOut occurs. The method is registered with an eventOutof a given node. When the eventOut generates an event this registered method iscalled.
Nodes in VRML are named using the DEF construct and can then be accessedby an applet. Once a pointer is obtained the eventIns and eventOuts of that nodecan be accessed.
A Java applet communicates with a VRML world by first obtaining an instanceof the Browser class. This class is the Java encapsulation of the VRML world. Itcontains the entire Browser Script Interface as well as the getNode() method, whichreturns a Node with given a DEF name string.
40
EAI and X3D
Like so many other VRML related technologies, the future support for EAI in thecoming X3D standard is currently under consideration for implementation. In theX3D standard, an API called SAI (Scene Access Interface) is under development.SAI is designed to make scripting consistent across programming languages, both“inside” (e.g. Script node) and “outside” (e.g. Document Object Model DOM,External Authoring Interface EAI) the X3D/VRML browser.
So, even though the current support for EAI in X3D is somewhat unclear, therewill be support in X3D for communication with external systems.
41
Chapter 4
Scania at the present
Reality is merely an illusion, albeit a very persistent one.Albert Einstein (1879 – 1955)
4.1 Scania AB
The purpose of this section is to give a brief overview of the company, the productsand other areas of interest, in which Scania acts.
4.1.1 Business areas
The business areas of Scania can be divided into the following three main cate-gories:
• Heavy Trucks
• Buses and Coaches
• Industrial and Marine Engines
The first category, Heavy Trucks, represents the core business and on this marketScania is the fourth largest actor in the world and the third in Europe. Scania hasdeliberately focused on heavy trucks, which means trucks with a gross vehicleweight of more than 16 tons.
Today Scania is the world´s fourth largest manufacturer of buses and coaches formore than 30 passengers. The product range includes chassis for buses and touristcoaches, as well as fully assembled buses for public transport systems. About twothirds of sales consist of public transport vehicles.
The Industrial & Marine Engines business area is a specialised operation in whichScania has a strong international position. It supplies Scania engines in custom-ised versions for such applications as boats, electrical generators, earth-movingmachines and harvesters
42
4.1.2 Mission statement
At Scania´s home page on the Internet, www.scania.com, the following is given asa mission statement [21]:
Scania´s mission is to supply its customers with high-quality vehiclesand services related to the transport of goods and passengers by road.By focusing on customer needs, high-quality products and services aswell as respect for the individual, Scania shall create value added forthe customer and grow with sustained profitability. Scania thereby alsogenerates shareholder value.
Scania´s industrial operations specialise in developing and manufac-turing vehicles, which shall lead the market in terms of performance,life-cycle cost, quality and environmental characteristics.
Scania´s commercial operations, which include the sales and serviceorganisation, shall supply customers with vehicles and after-sales sup-port, thereby providing maximum operating time at minimum costover the service life of their vehicles.
Scania´s operations are based on a worldwide network of more than 1,500 au-thorised Scania workshops in some 80 countries, as well as a service parts distri-bution system.
4.2 Scania product structure
Scania´s products are built on a unique module system, in which all producedtrucks, buses or industrial engines are produced uniquely from a specification ofrequirements. This specification generates a component variant string, which in turngenerates a list of the comprising components to be produced and assembled.
The component variant string can be viewed as analog to a DNA-string in bio-logy, based on the customer´s requirements. The modular thinking helps reducethe number of parts while enabling a wide program of products. The theoreticalnumber of different truck configurations is today as high as 1027.
4.3 The product development process
The product development process (fig. 4.1) at Scania is divided into three mainareas (internal Scania document):
• Pre-development – Yellow arrowIn this phase the aim is to develop possible products and knowledge for fu-ture projects. Incentives for pre-development include:
– Reduce the risk in future projects through testing of new ideas beforeimplementation.
43
Figure 4.1. The PD process at Scania (Scania)
– Development of new ideas and innovations.– Create a portfolio of new concepts and innovations.– Increase planning precision in development projects.– Reduce Time-To-Market (TTM)
• Concentrated introduction – Green arrowIn this phase the work is performed in project form and is marketed towardscustomers. This work includes adapting new or improved products for man-ufacturing, backwards compability as well as market introduction (MI).
• Product follow-up – Red arrowProduct follow-up maintains and updates the current product range. Thetypes of assignments include:
– Field Quality (FQ)– Product change requests– Cost reduction– Design adjustments– Specification adjustments
The PD process includes common methods for product development to facilitatefor cross-functional and parallel work principles and to assess experiences fromprojects.
44
4.4 Scania Production System – SPS
As a global industrial manufacturer of complex mechanical products, Scania hasdeveloped a standardised system of production to ensure that the same philoso-phies, principles and priorities apply throughout the world. This system goes bythe name SPS. It is based on Toyota Production System (TPS) and has been adaptedand developed further at the company´s own workshops and is now a natural partof every employee´s working life.
The Scania Production System is based on the following four main principles:
• Standardised working method – the normal situationA well defined normal situation will make it easier to detect deviations at alllevels and facilitate the use of standardised working methods and routines.
• “Right from me”A strong focus on early detection of deviations in quality and ways of pre-venting them from reoccurring. The basic idea is “doing things right the firsttime”.
• Consumption-controlled productionA production flow based on the actual sales, where buffers may be minimisedand hence a more efficient production process will be achieved. In servicefunctions this principle has been adapted and renamed Demand-driven Out-put.
• Continous improvementsContinous improvements mean discovering and eliminating waste, then ap-plying the resulting liberated resources to more productive tasks.
All departments at Scania adjust their daily operations to comply with SPS and avisualisation of the interpretation is the Scania House (see figure 4.2). It is importantto see all new systems, tools and routines in the context of SPS.
4.4.1 Production engineering
Production engineering is a function within the manufacturing units concernedwith rationalising the production process at different levels. Capacity calculationis one important task that often triggers equipment changes. During projects ofequipment change, the production engineer is, in most cases, the project leader.Optimisation of material flow and work methods are other important tasks of theproduction engineer.
Clients of the production engineer´s services are production and workshopmanagers.
Process planning is another function within production engineering concernedwith development of process methods, tool design and work instructions. Theprocess planner is also responsible for produceability analysis in the product de-velopment process.
45
Figure 4.2. The "Scania house" (SPS)
To establish an interpretation of SPS for production engineering, guidelines forbuilding production facilities has been developed. In these guidelines all aspectsof SPS are presented in the form of a description of an ideal production line. Theintended use for the guidelines are as a source of inspiration and checklist.
4.5 The process of equipment change
The work of investing in new equipment or change in present equipment at Scaniacomprises two parallel processes. PEIP, which is a description of the productionequipment investment process and CE-marking, which is the process of ensuringthe equipments compliance to laws and regulations on safety.
4.5.1 Production Equipment Investment Process (PEIP)
Scania has developed a standardized routine for how to perform and control in-vestment projects called PEIP. This routine describes the process from initiation tocompletion and provides the project manager with a checklist to ensure that allsteps are considered.
The main phases of the PEIP are:
• InitiationThe project might be triggered by a number of different reasons including:
46
Figure 4.3. Scania´s PEIP
– Wear on present equipment– Rationalisation of the process– Capacity requirements– Increased demands on Quality– New products– Environmental issues
• Preliminary studyThis phase includes making a rough proposal of:
– Alternative layouts– Manufacturing methods– Risk analysis– Requirements specification– Budget tender– Profitability calculation– Block layouts
as well as initiation of CE-marking.
• Feasibility studySuitable suppliers are identified and selected. The installation project areinitiated and an operational organisation is put together. A detailed require-ment specification is formulated on the basis of function and application.
• DevelopmentWhen the order to the supplier has been placed, another project group is puttogether where the supplier appoints a project leader. This project group willverify the purchased technology and the detailed drawings of the equipmentas well as make a more detailed project plan. This phase runs up until testruns and inspections at the supplier.
47
• ImplementationThe implementation phase includes physical installation of equipment andtraining of the operational organisation. An official take-over also takes placein this phase and includes in turn:
– Acceptance test or function test
– CE-marking, preliminary safety inspection
– Operator training
– Operational user documentation
• Project completionIn this phase Scania´s personnel fully take over the operation of the equip-ment and the warranty period starts.
• EvaluationAfter completion an important step is to evaluate the project to see if all pre-requisites were met and that the selected solution was the correct one. Budgetfollow-ups are also performed and documented.
When a project has been initiated, the production engineer will start working withlayout ideas on a block level to determine the material flow of the process. Afterthis the available physical space is taken into consideration and a more detailedlayout proposal is made in a CAD system using models of similar machines. Inthis rough proposal an appreciation of cost and required resources are included.This proposal is often used as support for decision on the future of the project.
CE-marking is a process, of which the purpose is to ensure the equipment´scompliance with European safety regulations. This process is parallel to the PEIPand is initiated in the pre-study phase of the PEIP.
Throughout the whole process the layout is used extensively for a vast varietyof different purposes. Apart from being a tool, or a map showing where all theequipment will be placed, it is used for discussions with decision makers, safetyengineers and other peripheral stakeholders.
To ensure a standardised way of specifying requirements on new equipment,Scania has developed a publication called "Scania TFP – Technical Directives forProduction Equipment". The intention and purpose of this publication is to stateScania´s basic requirements on all equipment and functions as a complement tothe specification of requirements of purchased equipment.
48
Chapter 5
Practical frame of reference
This chapter describes the work being done in the pre-study phase preceding thedevelopment of the demonstrator. The focus and the results of the pre-study arealso discussed.
A description of the layout planning routines and systems used at Scania today.This system is the primary source of data for the simulation/visualisation demon-strator and the connection between the two systems will be discussed here alongwith other sources of models.
Equipment simulation as it is used in conjunction with off-line programmingin robot-intensive applications at Scania will be given a brief description.
An alternate method of laser scanning for model data acquisition has of latestarted to appear and its relation to equipment simulation and virtual manufactur-ing will be mentioned at the end of this chapter.
5.1 Pre-study
In the pre-study the focus has been on how the paper based layout drawings in 2Dare used today as a base for discussions and presentation. These drawings consistsof a large paper sheet showing the placement of machines in the workshop fromabove and they often function as a center point around which discussions in theproject take place. From studying how these drawings are being used to addressmost issues related to a project of equipment change, ideas on how to improve thework and requirements of a 3D system have been derived.
5.1.1 Paper based 2D layout drawings
Participation in the project has provided an opportunity to observe and explorethe roles and relations of the different stakeholders in the project and this informa-tion has formed the base for categorising these according to the USTM/CUSTOMmethod described in chapter 2.
49
Figure 5.1. Paper based 2D layout
Organisation
Figure 5.2. Organisational overview
Primary stakeholder – direct users of the system
The primary stakeholders of an ongoing equipment change project and hence theproposed system are:
• Production engineersThe paper based 2D layout drawings are prepared and maintained by the
50
production engineer. It is his/her ideas that form the first proposals for thelayout in the form of a block layout. The production engineer ideally worksclose to the workshop floor and has a close relation to the operators andthereby a fairly good understanding of the daily operations in the productionprocess.
• OperatorsOperators work close to the production engineer in the design. Operatorshave experience in machining and the daily work. They base their criticismof the layout proposals on the information provided by the drawings andexperience from working in the production process. Their concern is oftenthe implications to the physical work place.
• Process planners and tool designersThe process planners and tool designers will become primary users of theproposed system but have a somewhat peripheral role in the use of 2D paperdrawings. The drawings in 2D do normally not provide information that hasany influence on tool design. The interesting information in tool design aregeometrical issues such as whether a workpiece clamping fixture will fit in-side a machine or not. Can the clamping fixtures and tools be easily changed?Will a robot with a certain gripper be able to reach into a machine and loada workpiece into the clamping fixture? The 2D drawings of today does notprovide satisfying answers to questions of this kind, so this information isusually obtained by inspection of physical equipment, prior experience fromsimilar equipment or by separate machine specific documentation.
Secondary stakeholders – providers of input and/or dependants of output
• Decision makers at higher levelsAs a base for discussions on what ideas to pursue in a change project the 2Dpaper layout drawings provide important means of explaining and sellingideas. Normally the production engineer brings the drawings to the work-shop manager for discussions on the suggested layout.
• Safety engineeringWhen the new layout of the workshop has been determined, the drawing isused in discussions with safety engineers to measure safety distances, place-ment of safety equipment such as emergency stops and protective walls.
• External and internal contractorsIn the installation phase the 2D layout works as a map where contractorssee where to place machines and external facilities. The 2D layouts are usedextensively in this phase and will most probably continue to do so.
51
Tertiary stakeholders – People that do not fall under the two previous categories,but that are affected by the success or failure of the system
• SuppliersWhen machines or other types of equipment are being ordered from sup-pliers, a layout drawing is often sent to describe placement and immediatesurroundings. The supplier may also provide the production engineer withmodels and drawings of the machine to import into the layout CAD system.
Facilitating stakeholders – People involved in design, development and mainte-nance of the system
This stakeholder category has not been focused at during this project. Systemmaintenance is an important area but the idea of the demonstrator system is tominimise its dependance on Scania´s information infrastructure and be a tool usedlocally at the production engineer´s personal desktop computer.
According to this categorization interviews with people representing the differ-ent stakeholder categories were performed using the Contextual Inquiry method(see chapter 2). Examples of interview questions and answers can be found in ap-pendix C. The interviews have lead to interesting results that have been importantin surveying the requirements on a computer based 3D system. Looking deeperinto the context in which the 2D drawings are used, important subtle aspects arerevealed. The 2D drawing works essentially as a map defining the terrain in whichthe project takes place. The production engineer often keeps it hanging on thewall in his/her office making it very accessible. Participants from all stakeholdercategories agree on the advantage of the portability and the simplicity of the pa-per based 2D drawings. They are easy to bring to meetings and to gather aroundduring discussions. Notes are often written directly on the drawing and are hencedirectly associated with a specific element or location (see fig. 5.3).
The operators are organised in improvement groups and in the dialog betweenthe production engineer and the operators the 2D drawings have an importantrole. The drawings are often in the early stages of a project used as a jigsaw puz-zle, where the machines are cut out and moved around physically and placedwith magnets on the bulletin board. This way of “low fidelity” prototyping hasproven very effective in many projects of equipment change. When a couple ofmore concrete suggestions have surfaced from these initial discussions, the pro-duction engineer takes the ideas and implements them into the proposed layoutin the CAD system. The different suggestions are then printed out and posted atbulletin boards on the workshop floor (See figure 5.4).In the installation phase of a project the paper based 2D drawing has a centralrole. All personnel, including external contractors, use the drawing extensively toplan their work and to assess where to place machines and equipment. Normally,during this phase, a bulletin board is placed in a central location for easy access,showing the drawing along with other important documentation.
52
Figure 5.3. Paper layout with handmade notes
Figure 5.4. Proposals on bulletin board
5.1.2 Aspects of the layout discussed
In the contextual inquiry interviews were performed with the different stakehold-ers having a focus adjusted to this persons relation to the drawings. Many of the
53
aspects of the different stakeholders coincide, but there are some important dif-ferences. Operators are more concerned about workplace ergonomics, productionengineers about production flow while decision makers have a larger focus on theover-all operations including economic aspects related to the project. Economic as-pects can be questions like personnel savings and interoperability with surround-ing processes and departments.
Primary stakeholders
Production engineers often start to plan the layout based on available space anddesired material flow. Simple layout proposals are made by using models of ex-isting machines similar to the types of machines to be used. In this stage detailsare left out and the static top view of the paper-based 2D layouts is often sufficientfor presenting the ideas. When a more detailed layout is being done, questionsabout cycle-times of machines and handling equipment plays an important role.In order to do an adequate cycle-time analysis of a robot cell, robot simulationsystems like IGRIP and RobCAD have to be used. These systems simulate the con-trol systems and servos of robots which makes it possible to predict movementin detail. Another issue concerning robot movements is singularities in the robotwork area. Mathematically speaking, singularities occur when the matrix describ-ing translations and rotations of the robot coordinate system is not invertible. Inmore practical terms, it means positions where two two or more axes line up andthe orientation of the robot joints can not be uniquely defined. The singular area isthe area (it is actually a volume) surrounding the singular point. Placement of therobot can minimize the effect of singularities and simulation can help productionengineers detect problems of this kind. A simple simulation or 3D view can alsoprovide information sufficient to avoid singular areas in the critical work areas.The absence of these complex simulation systems often lead the production en-gineer to make qualified guesses of robot performance based on experience fromexisting robot installations. In the layout CAD system used at Scania it is possibleto import robot models with some kinematics added to test for reachability.
Operators in the improvement groups support the production engineer through-out the process, they have the most experience in the matters concerning machin-ing, daily maintenance and quality control work. Access to control panels anddisplays, maintenance places, manual part handling and compliance with SPS areexamples of questions discussed in the improvement groups.
Secondary stakeholders
Decision makers often have a background in production engineering and are usedto working with the 2D drawings. The simplicity of the drawings is one of themost appreciated properties expressed. In meetings where layouts are discussedthe production manager is more concerned with overview rather than details and
54
the 2D drawings contain most of the information needed for this. Production man-agers interviewed expressed some resistance towards working with a computer-based system, since it is likely to introduce elements of technical disturbances tomeetings.
General issues
A major problem often encountered in the process of making the plant layout hasto do with the reliability of previous drawings. When a new layout is made, exist-ing drawings of the building are used as a base for this. These drawings includeinformation on floor surfaces as well as placement of pillars and other obstacles.Errors in these drawings are very common, it is not rare to find deviations fromreality up to several meters in measurement. Buildings seldom consist of right an-gles and plane surfaces and as the size of the building increases, the errors mightget sufficiently large to become a problem in the layout planning process. Alter-ations to the buildings are also something that is rarely implemented into thesedrawings.
In the installation phase, media (compressed air, coolant liquids etc.) and venti-lation are often completed in an ad hoc manner, which makes it difficult to updatethe drawings afterwards. The result is that the inner ceilings of many workshopbuildings are cluttered with tubes, pipes and power supply lines (See fig. 5.5), allundocumented in current drawings.
The problem of obtaining accurate drawings of buildings and media can beaddressed by new methods of laser scanning. This method is presented briefly insection 5.4.
Most of these aspects are rather well covered by the 2D drawings and can bedealt with in the project work. In this project the main question is how we canutilize a 3D visualisation system to facilitate discussions on these questions. Indetermining the prerequisites of a 3D visualisation system to complement the 2Ddrawings the following questions need to be answered:
• Where lies the main difference in addressing these issues in 2D compared to 3D?
• How can a 3D system complement the 2D drawings as a tool for discussion on fac-tory layout?
• What is a reasonable level of simulation in this system?
To answer these questions a comparison between the presentation forms is needed.The comparison can be made by addressing elements of interaction in virtual en-vironments presented by McLellan [14] (see section 3.4.1).
Dimensionality — 2D versus 3D viewing
It was stated earlier that 3D viewing potentially offers a more realistic view ofthe geography of an environment. This statement holds, in this case for studying
55
Figure 5.5. Cluttered inner ceiling of a workshop
workplace ergonomics aspects of the layout. By providing the possibility of animmersive walk-through of the machine cell, problems with operator´s reachabil-ity can be detected at an early stage. It is easier to gain a better understanding ofthe work area in which the operators will work. Potential safety issues related toclearance heights and three dimensional motions of comprising components canbe detected early thanks to the first person view. Maintainability is also an aspectthat is likely to be better understood from a 3D view, since the walk-trough willpresent maintenance points at its correct level above the floor. In terms of compli-ance with safety regulations the 2D drawing might actually provide a better basefor decisions than the 3D environment. In this case the 3D environment will be ofmore assistance in verification of the implications of the safety regulations.
The idea of making notes directly in the layout, connected to specific locationsalso involves some conflict of dimensionality. Text is ideally two-dimensional andcan easily be placed on the 2D drawing, in 3D on the other hand, it may not alwaysbe self evident how to place a note without losing the connection to the specificlocation.
Motion — Static versus Dynamic display
In discussions on the layout it is often important that the people involved sharethe same view of a matter at hand. The possibility of unlimited transitions and
56
Property 2D support 3D supportOverview Map metaphor ViewpointsInstallation instruction Map with printed measures Poor supportMedia declaration Drawing of connections Poor supportEasy access Physical artefact Standard PC and softwareDiscussion focus Gather around CSCW functionalityNotes and protocol Notes on drawing Virtual notesWorkplace ergonomics Experienced PE Immersive studiesProcess flow Birds eye view Walk throughMaintainability Abstract locations Actual space explorationSafety Measurements on drawing Immersive studiesUpdating after change Back to CAD On-line editingMeta data Separate documentation Stored in model (ideally)Version handling Scrapping old drawings Maintaining the model
Table 5.1. Aspects of drawings discussed
orientations may be a source of confusion since it can be hard to return to the sameview between two different occasions. In comparing two different proposals at thesame time a static view will make it considerably easier to focus on the differences.This problem may be solved with some implementation of viewpoints, where acamera position and orientation are saved.
Frame of Reference — Inside-out versus Outside-in
The difference between experiencing an environment in first person rather thanfrom a God´s eye view is that in the first person case the view is an instant personalview of the environment and can be hard to recreate or come back to. In somesenses this can be seen as a source of confusion, where peoples´ opinions are basedon different views of the same thing and therefore harder to compare. The God´seye view, on the other hand, with its flat static image, may hide important aspectsaffecting workers on a more personal level.
5.1.3 Summary
A conclusion to be drawn from the comparisons above is that generally the 3Denvironment will support verification of softer gut-feelings rather than measurabledata questions.
Table 5.1 lists aspects of the layouts addressed in discussions related to plantlayout. The second and third columns of the table relate the properties to pre-sentation format. This comparison between 2D and 3D provides some clues ondesirable functionality of a 3D system, based on aspects related to 2D. Propertiesnot very well supported by 3D visualisation relate to the installation phase of aproject, where the drawing is used as an instructional document.
57
5.2 CAD systems at Scania
There are a number of different CAD systems currently in use at Scania and thissection will give a brief introduction to these. There is currently a huge projectrunning on migrating to the new Catia v5 CAD system at Scania. This system willreplace many of the running systems, starting with tool design and productionpreparation. With this new system at hand a series of new opportunities has arisento provide a new range of services earlier not found in the CAD system.
5.2.1 Plant layout design
Plant layout design is primarily a task carried out by production engineers andsince 2000 the main software system for this has been AutoCAD FactoryCAD.
FactoryCAD
FactoryCAD is an enhancement of Autodesk´s AutoCAD that includes function-ality for designing factory workshop layouts in 3D. One of the key reasons forchoosing FactoryCAD as a replacement for the older layout CAD system, is thatmost of the external suppliers of machines and other equipment use AutoCADas a standard tool for design and the choice of FactoryCAD makes integration ofmodels from suppliers easier when little or no conversions is necessary.
Standard components
In LayCad at Scania, a library of standard components is available. These standardcomponents include conveyors, robots and furniture. The models in the libraryhave a set of parameters which can be adjusted to fit the layout. A conveyor can,for instance, be set to a certain height, width, length as well as number of legs.The robots in the library include simple kinematics, which enables moving jointsto check for reachability.
External model suppliers
Models and drawings of machines are ideally delivered together with other for-mats of documentation when a machine is being purchased. Today there are noparticular standards developed specifying digital models, but Scania has lately re-alised the need for it and work in this area has started. Often machine suppliersdo not deliver drawings in 3D and the production engineers have to extrude 2Ddrawings to 3D. Due to this, the existing models of machines are very differentwith respect to level of detail and accuracy, very much depending on the produc-tion engineer´s knowledge and experience in CAD.
58
5.2.2 Compatibility with product development systems
Compatibility with product development systems are important features of anequipment simulation system. Models of products need to be easily transferredbetween the systems.
Today, models of products are stored in a system that has built in functionalityfor file conversions in import and export of models. Today, this system is used foraccess to products for use in layouts and tool design. A problem in this export,is that the product models most often are very complex, which means some man-ual work has to be performed in order to adapt the models for layout purposes.This issue was discussed with personnel at the maintenance department for CADsystems and apparently model complexity reduction can be incorporated in theimport and export functions of the current system.
In product development Catia is used in most design processes. Other systemsare used for styling and calculation of material properties.
Figure 5.6. Screen dump of Catia (www.ibm.com)
59
5.2.3 Design and styling
The design department uses Alias Wavefront to model surfaces of the truck. Raytracing techniques are used for rendering of reflections to study properties of sheetmetal surfaces. The design department at Scania also keeps a Power wall, that isused in discussions and decision making about different design proposals.
The Power wall at Scania consists of a wall, upon which the computer displayis projected. The display presents a stereoscopic view of the models. During thisproject some models of machine layouts have been tested on the Power wall. Thesoftware used for presenting models in stereoscopic views has some support forimport of VRML files, though poor support for non-trivial nodes, such as sensorsand scripts. The Power wall is set up in a room with seats arranged facing thedisplay. These facilities are very well suited for presentations and discussions ofworkshop layout proposals.
5.3 Equipment simulation at Scania
RobCAD, RobotStudio and IGRIP are three systems for simulation and off-lineprogramming of robot systems. These systems cover many of the aspects of equip-ment simulation/visualisation addressed by the demonstrator system developedin this project. These systems are very complex and perform simulations of therobot systems not only on a geometrical or kinematic level, but also by simulat-ing the servo control system of the robots making it possible to predict movementspeeds and cycle times. This ability to predict the cycle time of a certain robot cellis very important and a service frequently asked for. The downside to this is thatcreating models accurate enough to provide relevant results is time consuming anddifficult.
In 2001, an internal study at Scania made a comparison of the three main sys-tems of robot simulation for the purpose of off-line programming. IGRIP and Rob-CAD was found to be technically equal in performance. RobCAD was the mainchoice of off-line programming system due to good support functions in Swedenand the fact that most subcontractors and equipment suppliers use it. At the timeof the study, ABB´s Robot Studio was fairly new and hence not fairly compared.Robot Studio is part of a larger software package from ABB including an off-lineprogramming editor, robot control system configuration tools and a virtual con-troller. By emulating the complete robot controller all system parameters are ac-counted for in both simulation and programming, which makes it possible to domost configurations off-line at an early stage in the installation process. The down-side to this system is that it only supports robot systems from ABB.
5.3.1 Part handling and machine loading cells
In the type of robot applications focused on in this project, where robots are pri-marily use for handling and loading of machines, the level of simulation motivated
60
in the planning stage is not focused on cycle time calculations, but rather geometricproperties of the application. The ability to assess whether or not a certain robot´swork area is sufficient for the application, is a common question needed to be an-swered. Will a layout of a work cell´s comprising parts or machines present anyspecific geometrical implications to the robot?
5.3.2 Robot intensive applications
There are, at Scania, some rather extreme robot intensive applications where sim-ulation of the more complex nature is clearly motivated. In Scania´s cab factoriesthere are applications where up to 14 robots work together to assemble the cabs.In these applications synchronisation of the robots is crucial and cycle time is oneof the key issues when planning a cell. The cells are mainly delivered as a turn-keysolution from an external supplier who, in most cases, has modelled and simu-lated the equipment. As a part of the vision of the Digital Plant, these applicationshave a central role in defining the value of simulation. At Scania´s CAB Factoryin Oskarshamn, the use of RobCAD and the models delivered with the real equip-ment by the external supplier, have been used to test the equipment with new andchanged products and tools.
In Oskarshamn, a complete model of the new cab assembly welding line wasmade and used for programming and simulation before the physical equipmentwas built. Figure 5.7 shows the digital version of the new assembly line as pre-sented in CATIA v5.
In this virtual assembly line it is possible to test new robot equipment for reach-ability. Figure 5.8 shows a close-up of a spot-welding robot simulated in IGRIP.
5.4 Laser scanning methods for data acquisition and ver-ification
During this project the opportunity to look into a method of laser scanning formodel data aquisition and verification appeared and since it is related to the sub-ject, a brief description of this method will be given.
Laser scanning has two main functions; to scan new undocumented objects into3D models and to verify geometry of physical work cells “as built”.
The first step of the method is to plan the scan. The laser scans a surround-ing sphere and the number of scans necessary to cover the work area has to beassessed. When the number of scans needed along with the locations for these hasbeen determined, reference points are marked in the areas. These marks are laterused to stitch the scans together to one model.
The laser scanner is placed on top of a tripod at the different locations (seefigure 5.4). The laser head rotates in two directions scanning a sphere around it,making approximately 200 000 measurements per second. A typical scan takesabout 160 seconds, resulting in over 30 million measured points per location.
61
Figure 5.7. Cab assembly/welding simulation in the Oskarshamn factory (Scania)
At each measured point, the intensity value of that location is stored. The resultis presented as a 2D grey-scale image, where each pixel contains an xyz-coordinate.Dedicated software is then used for manipulating the collected data. Measure-ments can, for instance, be done quite straight-forward in the gray-scale image. Itis also possible to export parts of the scanned area to CAD systems for verificationof layouts.
Once a complete scan of a workshop has been done, complementary scans canbe made covering only smaller parts to verify changes. The reuse of referencemarks will make this update procedure possible.
Though the potential of this method of surveying workshops is obvious, sometesting needs to be done to assess the actual benefits to Scania.
62
Figure 5.8. Close-up of spot-welding robot simulation in the Oskarshamn factory (Sca-nia)
Figure 5.9. Laser scanner on tripod (www.iqvolution.com)
63
Chapter 6
Results I — Requirements
This chapter addresses the results corresponding to the first objective of this project,where a survey of the needs and benefits of graphical 3D simulation/visualisationat Scania has been done.
6.1 The benefits of equipment simulation
Equipment Simulation (ES) is a large area where almost all aspects of equipmentcan be simulated. Figure 6.1 shows the scope of ES in relation to Scania´s Pro-duction Equipment Investment Process (PEIP) (see section 4.5.1). The role of ES invirtual manufacturing should be seen as a parallel process to PEIP, where the simu-lation model evolves as more details are added. In the beginning of the investmentprocess generic models of machines and equipment are used to visualise ideas andthe lack of accuracy in models makes it inconvenient to simulate for cycle time andoff-line programming purposes. However, 3D visualisation of layout proposals isa very beneficial task that can be performed even at a low level of accurate details.
Collaboration with improvement groups
The pre-study showed that collaboration between the production engineers andmachine operators in the improvement groups is an important part of the devel-opment process and the CAD systems used today have little or poor support forthis specific collaboration. The way this collaboration is done today varies betweendifferent departments and is highly dependent on the characteristics of personalrelations. The level of participation by operators is an important issue. Operatorsoften have experience of similar machines and operations and are a useful resourcein the development of new plant layouts and during the interviews production en-gineers pointed to problems with communicating and reasoning about proposalswith operators. Although operators are involved in the project organisation it is
64
Figure 6.1. Simulation types in relation to Scania´s PEIP
often difficult to maintain a continuous discussion. Operators work shift whichmeans different operators attend project meetings at different times.
In the series of interviews performed in the pre-study phase of this project,decision makers expressed some concern over the amount of extra work and ed-ucation needed for realising the idea of using simulation as a standard tool forproduction engineers in their daily work. This concern may be seen as an expres-sion of past experiences, where simulation has failed to deliver anticipated results.As mentioned in section 3.1.1, simulation does not come without difficulties andpitfalls. Common reasons for failed simulations at Scania include lack of under-standing on the behalf of persons modelling and performing the simulation, poorinput to simulations and the amount of time taken to reach sufficiently accurateresults. The last few years have seen an increase in the use of simulation andthanks to some good examples of successful simulations, the resistance towards ithas started to decline. The development of new and improved tools for simulationalong with routines for modelling well known processes are important factors offuture increase in the use of simulation at Scania.
The demonstrator system provides simple, yet powerful, tools for exploringand manipulating layout proposals and is designed to mimic and to further de-velop the low fidelity manipulation with paper models described earlier in section5.1.1. These features are likely to strengthen the design process and ensure a bettercompliance with Scania´s SPS.
Model-driven development
Model-driven development as described in section 3.1 implies reuse of evolvingmodels throughout the development process and enables different kinds of sim-
65
ulation depending on the maturity of the models. When more accurate modelsof machines is added, reachability studies may be performed and this simulationcan help determining machine placement as well as decisions on robot types tobe used. In one of the projects followed this became a real problem when it wasdiscovered after installation that a robot was out of reach of a conveyor and therobot had to be modified to fit the layout. The main reason for this mistake wasthat the 2D layout presenting a circle describing the robot´s work area did not takethe gripper angle into account. A simple simulation would have helped to preventthis problem from occurring.
In the final phases of an investment project, the model is hopefully accurateenough to make off-line programming a feasible task. This kind of more advancedES has been used in Scania´s more robot intensive applications, where the com-plexity of the equipment is a strong enough incentive to motivate the extra workneeded to prepare and to perform complex simulations. In simpler robot cells, theamount of extra work needed to perform simulation of cycle time and off-line pro-gramming is significant compared to just creating a layout and hence more difficultto motivate. The latest development in CAD systems, however, has started to re-duce the amount of extra work by implementing simulation functionality directlyinto layout CAD systems using either simulation plug-in modules or simulationfunctionality in existing standard components.
6.2 Properties of drawings needed for decision support
In the pre-study, the role of the 2D drawings has pointed at a number of proper-ties supporting discussions and decision support innate in the 2D drawings. Inorder to assess which of these properties that can be handled by a 3D simula-tion/visualisation system, some limitations on requirements has to be made. Itis not the ambition to replace the 2D drawings by a 3D version of the same infor-mation, rather to complement these drawings with a tool for exploring proposedplant layouts semi-immersively on a desktop PC. As a complement to existingCAD systems it is important that the system is simple and fast, trying to minimisethe amount of extra work needed to create the models.
Points where 3D visualisation adds benefits include:
• Reachability of handling equipmentThanks to the ability to move axes of robots in a work cell model, it is possibleto test the robot for reachability. This is an important feature for determiningwhat model/size of robot to use and to catch incompatibility with robot toolsand grippers.
• Singular point detection in robotsExperience from robot installations and programming shows the importanceof the robot´s placement in order to minimise the risk of singular areas coin-ciding with critical work areas.
66
• Access to maintenance placesImmersive studies provide a better view of maintenance places and makeit possible to take these aspects into account at an early stage. Ergonomicaspects, in particular, are interesting to study and evaluate. Maintenanceplaces are locations of service points such as lubrication and hydraulic oilrefill, filters and inspection places to be accessed on a daily or weekly basisby operators and maintenance personnel.
• Safety inspectionsThe first person view can provide additional information in safety discus-sions and potential safety issues may be detected.
• Workplace ergonomics analysisIn the improvement groups of operators, an immersive system will providea more realistic view of the workplace. Placement and implications of main-tenance places, workbenches, tools, quality control places and other facilitiescan be evaluated early.
6.3 Specification of needs and requirements
From the structured interviews and observations made when attending discus-sions, the role of the system and some basic requirements have been identifiedfor the specific use cases. The foundation of a factory layout comes from discus-sions between production engineers and operators in the early stages of the layoutdesign process and today there are no simple tools available to support this collab-oration.
Specific requirements tied to activities include:
• Creation of layout visualisationsThe system must support simple means of importing models from externalsources. This step might be done partly outside the system by a well de-scribed routine, using third-party utility programs for file conversions andreduction of complexity. The ability to extract information on manipulationmade to the layout in the discussions is necessary in order to take this backto the CAD system and reflect the changes in the master CAD drawing. Mostproduction engineers spend a considerable time creating 3D models of ma-chines. Machine suppliers often deliver documentation in 2D CAD format,which makes it necessary to extrude 3D volumes from these models. This isa painstaking and time consuming task that could be avoided provided thata standard for 3D models that are to be delivered by the machine suppliercan be developed. This standard should regulate the level of detail neededfor layout design, according to the specific type of machine it concerns. Forinstance, a higher level of detail may be needed at more crucial locations onthe model, such as interfaces for tools and fixtures as well as access points forexternal loading equipment such as robots or conveyors.
67
• Collaboration with the improvement groupThe proposed system will be a facilitating tool for collaboration in develop-ment of layout proposals between production engineers and operators in theimprovement groups. The layout proposals shall be available on terminalson the workshop floor for easy access. The system should support simplemanipulation of layout proposals and provide intuitive means of exploringthe changes in the virtual environment. The operators must be able to storeproposals of improvements for future discussions with other operators andthe production engineer. An important feature of the models still lacking, isthe highlighting of maintenance places at machines. These are often crucialin the every day work by the operators. To realise this there needs to be someform of standardisation of coloring on the models in the CAD system.
• Decision supportThe interviews with the decision makers showed that the main interest atthis level is the proposed machine layout as a part of the flow in the entirefactory. If the system is to be a facilitating tool for decision support and dis-cussions with decision makers, it needs to be easy to use and efficiently pro-vide information on internal flow, serviceability and inter-operability withsurrounding machines and equipment. The plant manager interviewed ex-pressed concerns about the amount of extra work needed for creating thevisualisation as well as the increased dependency on computers at meetings.
• Support for input from external sourcesIf the system is available outside Scania´s internal communication infrastruc-ture, it may assist external stakeholders with a better understanding of acomponent´s context.
• Safety discussionsA correct layout with sufficient level of detail may provide the ability to workwith safety issues earlier in the process, where the immersive nature of the 3Dpresentation can provide new aspects and viewpoints. The ability to movemoveable objects in the 3D environment may also facilitate the safety discus-sions.
The above requirements concern the specific tasks and situations where the systemmay be of assistance in the production development process. In the pre-study,a number of aspects and properties of the paper based layout were discovered.Properties of the 2D paper based layouts that are subtle but very important toconsider when designing a computer-based system include:
• Note-takingThe pre-study showed the paper-based layout´s central place in the discus-sions, where notes was often written directly onto the drawing and are stronglyconnected to the static view of the drawings. Implementing this functionalitywould imply some difficult issues on storage and access from other systems.
68
• Simplicity and mobilityOne of the strong advantages of the paper-based drawings has to do withtheir simple nature; they are very easy to bring along to meetings, to gatheraround and to copy and distribute to project members. They do not need arunning computer to be displayed and are often placed on bulletin boardsfor continuous display.
69
Chapter 7
Results II — The Demonstrator
Computers make it easier to do a lot of things, but most of the thingsthey make it easier to do don’t need to be done. Andy Rooney (1919 – )
A demonstrator system has been developed to incorporate some of the needs andrequirements found in the pre-study. The system comprises a methodology forexporting equipment models from CAD-systems, reduction of model complexity,a Java application for import and assembly of models into a complete scene andfinally a presentation part in a VRML enabled web browser. This chapter describesthe demonstrator in a walk-through of the system as well as the proposed method-ology.
7.1 Goal of the demonstrator system
The goal of the demonstrator system development has been to implement func-tionality found important in the pre-study. The main focus has been to develop asystem to support the collaboration of production engineers and operators in theimprovement groups. A particular point of interest has been the way operators usethe paper layout drawings to cut out machines, physically playing around withthese on a bulletin board to come up with suggestions for layouts. The productionengineer presents a rough proposal that the operators may play around with andmanipulate to come up with solutions fitting their needs. Key issues for a systemof this kind are simplicity and ease of use, along with technical requirements suchas feedback to the original CAD-system.
7.2 System overview
The demonstrator is built upon the idea of using standard technology to assemblemodels from Scania´s different CAD-systems and to present the proposed layout ina virtual environment. An important requirement is to keep the system relatively
70
open and not too complex, which means that many of the different steps in build-ing the scene includes manual file manipulation. Making the system less complexand open in nature will reduce the amount of system administration needed tokeep it fully functional. One trade-off of this approach is that it comes with a spec-ified methodology, or checklist of activities needed to perform its tasks.
Figure 7.1 shows a diagram over the demonstrator system with the main func-tions grouped as blocks. At the bottom are the different CAD-systems from whichmachine models are exported as VRML models to the local file system. The com-plexity of these models is reduced, if necessary, using third party polygon reduc-tion software.
In the center of the diagram is the WorkshopAssembler application, which isused to collect the different models into one single VRML file. The applicationalso provides means of adding manipulation means to the models. Robots aregood examples of pre-prepared models that can be imported to the scene. Thesemodels have added kinematics which makes it possible to move their axes in thescene. The WorkshopAssembler application produces three files; a compilationof comprising machines and handling equipment, an external file containing theworkshop´s floor boundaries with optional ceiling and a file containing a list ofadded components.
7.2.1 Java-VRML-EAI
In the proposed demonstrator system feedback from the user´s interactions andadjustments is fed back to a log file (the top part of figure 7.1). The EAI interfaceprovides means of extracting information and status of a certain node in the scenegraph. This stage is still one of the bottle-necks for the demonstrator system dueto the fact that the models are not actually created within the system, but ratherassembled from VRML exports from other CAD sources. As a way of at leasttrying to get this information back to the initial creator of the workshop layout thesystem will give back information on status changes and transitions in the form ofa log file containing information about status changes.
In order to get references to the nodes in the scene graph, the WorkshopAssem-bler application along with the VRML scene produces a list file containing thenames of the nodes assembled. This way the Java applet controlling the scenemay reference the correct nodes and retrieve information on transformations onthese after a session is closed.
7.2.2 Workshop model assembly
The WorkshopAssembler application (see fig. 7.2) is the core of the demonstratorsystem. It is designed to facilitate the assembly of machines and let the user addinteractional functionality to the objects and place them on a workshop floor.
The WorkshopAssembler does not interpret the VRML files, but rather handlesurl:s referencing files exported from CAD systems.
71
Figure 7.1. Architectural overview of the demonstrator system
In adding components to a scene, the application parses the VRML file containingthe model and calculates the bounding box of the component. These boundingboxes are presented on the overview to the right, to present a simple and abstracttop view of the layout. In order to center the view of the imported models, thebounding box of the complete assembly is calculated every time a new model isadded and the group of machines is translated in the overview. Current version ofthe application does not support any manipulations of the layout in the overview,though some means of dragging components in the top view would be an impor-tant enhancement.
If an added component has been chosen to be moveable in the scene, the com-ponent is encapsulated in a PlaneSensor node and a script node along with an eventroute is added to the VRML file. Appendix B contains the printout of a VRMLfile created in WorksopAssembler with added sensor and script nodes along withevent routing.
72
Figure 7.2. Screen dump of WorkShopAssembler
Java implementation
The WorkshopAssembler application is implemented in Java. The main reason forthis is Java´s simple support for creating graphical user interfaces. The system isbuilt on the following three classes:
• MainFrame.javaThis is the main class of the application that extends JFrame. The class con-tains the graphical user interface and some special data types to hold refer-ences to machines and robots in the scene. Creation of the main scene outputfile is done by this class.
• Maskineri.javaThis class is the object equivalent to a robot or a machine. When a machineis added to the scene it is instantiated as an object of this class. The classcontains the name given to the object, a URL that points to the VRML filecontaining the model and the geometrical boundaries of the object. When in-stantiated a method, calcbounds parses the VRML file, finding the bound-ing rectangle in x and y.
• Display.javaThis class is an extension of the Java Swing component JPanel. The class
73
holds three vectors containing boundaries of machines, robots and workshopfloor areas. The class draws the preview in 2D of the imported objects andhandles the creation of workshop floor and ceiling. The boundary vectoralso includes the bounding box and translation of the full assembly in orderto center the preview on the drawing surface.
Coordinate system issues
There are some differences in coordinate systems to consider when assemblingCAD models into a VRML scene. In the computer graphics community, the con-ventional orientation of the world coordinate system places the z-axis parallel tothe line of sight and a view plane in x and y. In the CAD world, on the otherhand, the z-axis ideally points upwards while the x and y axes define the groundplane. In VRML the length unit is meters while the layout CAD system uses mil-limeters. In the layout CAD system machines are referenced to an Origin for thespecific building to which they belong. In manipulating the assembled scene, it isconvenient to work in a local coordinate system. Especially when imported stan-dard components, like robots, are added. All of these differences mean modelshave to be rotated, scaled and translated before they are added to the VRML mainscene. While rotation and scaling is fixed, they are easy to implement into theWorkshopAssembler application. The translation on the other hand, is a bit morecomplicated. It has to be calculated and updated as new machines are added.These calculations are implemented in the WorkshopAssembler today, but workonly with models exported from LayCAD provided they do not contain any inter-nal translations.
7.2.3 Viewing and manipulating
When models have been imported, robots added and the workshop floor defined,the user hits the save button. A VRML file is now created and opened in IExplorerusing the Cortona VRML plug-in from Parallel Graphics (See fig. 7.3).
Navigation in the virtual workshop is done using the built-in modes in theCortona plug-in. Three navigation modes are available:
• WalkLinear movements tied to the ground plane (x, z).
• FlyLinear movements tied to the plane defined by the line of sight and x
• StudyRotational movements around x and y axes.
74
Figure 7.3. Screen dump of a finished workshop assembly in IExplorer/CortonaVRML player
7.3 Methodology
In using the demonstrator system there is a certain procedure, or methodologythat has to be followed. Since the demonstrator is built mainly on standard tech-nology, there is a fair amount of manual work that has to be performed. Some ofthese manual steps have been integrated in the WorkshopAssembler application,but others still need to be addressed externally. The Methodology consists of thefollowing main steps:
• Export from LayCadThis step includes choosing level of grouping of the comprising components.
75
A machine may in this step be bundled with another components if theirinternal geometrical relations are to be fixed in the layout.
• Polygon reductionThe VRML export function in LayCad tessellates the models to a level of de-tail often unnecessarily complex. It is therefore often advised to reduce thecomplexity of the model to a level better suited for the purpose of visualisa-tion. Polygon reduction is done by opening the VRML file in an external pro-gram called Vizup Optimizer, which is a shareware program well suited forthis purpose. This program shows the original model on the screen. ChooseReduce -> Start from the menu. The program will now reduce the model asmuch as possible. With the button on the scale in the upper part of the win-dow, an appropriate level can be chosen. Save the model and this step of theprocedure is done.
• Assembling components and adding interactivityThis step is the most complicated step and has therefore been implementedas the stand-alone Java application WorkshopAssembler (See fig. 7.2). The ap-plication allows the user to point to files containing the reduced models onthe local file system and add them to the final assembly. To add a machine tothe scene, give it a name in the name field and press the "Browse" button toopen a file browser to point to the VRML file. To make the model movable inthe scene, mark the checkbox by the name field, then press "Add to list". Therectangular boundaries of the chosen machine will now be calculated andpresented on the workshop overview pane to the left.
Robots are pre-prepared models with some interactivity added. They areadded from a library within the application. The user chooses make andmodel from the dropdown-lists and press "Add to list". In this case the bound-ing box of the robots work area will be presented in the overview to the left.
In the workshop overview it is possible to define workshop floor boundariesby drawing rectangular fields onto the screen. To make more complex shapesof floor surfaces, combinations of rectangles can be used. When the button“Generate floor” is pushed, a VRML file containing the floor will be gen-erated and placed in the current project folder. It is also possible to add aceiling to the workshop by checking the box and provide a height in the textfield. The ceiling is presented in the generated scene as a semi-transparentsurface above the floor.
7.4 Requirements on IT-infrastructure
The demonstrator system in its intended use does not add any substantial require-ments to the IT-infrastructure of Scania. The system is based on exporting modelsfrom CAD systems for immediate use. There will be no need to store the exported
76
and simplified models for more than shorter periods of use. This storage is sug-gested to be at the ordinary PC network file system for easy access.
The VRML plug-in supports hardware acceleration via DirectX and OpenGL,which is supported by most graphic cards today.
77
Chapter 8
Results III — Evaluation andcomparison
This chapter presents the evaluation of the demonstrator system according to theprerequisites found in the pre-study.
8.1 User feedback
The demonstrator system has been tested on four users from two of the stake-holder categories´. Production engineers, production planners and operators fromScania´s diesel engine and transmission workshops.
8.1.1 Choice of test subjects
During the development of the demonstrator system, a large project of equipmentchange has been running at the Diesel engine workshop. Models and layout pro-posals from this project have been used as a test platform and therefore the produc-tion engineers and process planner from this department were chosen for testing.To get a second opinion one production engineer from the transmission workshopwas chosen to complement the tests and to assess the influence of the first cate-gory´s familiarity with the equipment.
8.1.2 The test situation
The user tests have mainly been focused on the WorkshopAssembler applicationand the produced VRML scenes. The test was, due to some shortage of time, morean informal discussion on, and demonstration of the system.
During the test, each step has been demonstrated and discussed in reverse or-der of the normal procedure. First, a complete scene showing a proposed layoutof a machine group of a pilot project in the diesel engine workshop was presented.
78
The respondents were given the opportunity to navigate the scene, while differ-ent aspects were discussed. The reason for starting with a finished scene was tointroduce the virtual environment and create a sense of curiosity.
8.1.3 Results
Since the user test was performed as a demonstration/discussion, it is difficult toreach any concrete conclusions. However, the tests gave some interesting feedback.
In seeing and navigating a finished scene the feedback from most respondentswas a bit mixed; they were impressed by the possibilities of navigating the virtualenvironment, while at the same time sceptic, thinking it must have taken hours toprepare it. This response was anticipated and intentional. The scepticism was agood ice breaker that triggered a lot of questions on how to create a scene. TheVRML plug-in has a built-in set of tools presented in toolbars to the left and atthe bottom of the screen. The toolbars are used to change navigation modes andzooming in and out in the scene. The sparse options in the toolbars were somewhatconfusing to the test users providing very few clues on available options. Movingmoveable machines in the scene is done using the PlaneSensor node in VRML andan important downside to the sensor is that it is in itself invisible. When movingthe mouse pointer over a plane sensor, the cursor changes to show the presence ofthe sensor. Just the plane view of a group of machines does not provide any af-fordances. To get around this problem some kind of prototype interaction widgetscould be used to provide the appropriate affordances.
The Workshop Assembler was demonstrated using a set of VRML models pre-pared in advance. The steps needed to assemble a scene similar to the one demon-strated in the browser, is very simple and the test users were all positively sur-prised by how easy it actually was.
The concern about the amount of extra work needed to create the visualisationwas eased by trying the WorkshopAssembler application and the production en-gineers and the process planner all expressed some hope that this might be a goodway of supporting the collaboration with operators, which often is a difficult andtime consuming process.
8.2 Heuristic evaluation
The heuristic evaluation of the demonstrator system has been done mostly in or-der to find weaknesses, or points for improvement. The system is, as its nameimplies, only a demonstrator system containing basic functionality. Nevertheless,the heuristic evaluation is a powerful tool for finding potential usability flaws earlyin a development process and therefore a good idea. In carrying out this evalua-tion, ideas on how to comply with the heuristics has been of greater importancethan how the different functions have been implemented today. The evaluationrefers directly to Jacob Nielsen´s heuristics described earlier in section 2.7.1.
79
Results
1. Visibility of system statusThe preview pane on the right side in the main window has been imple-mented to provide information on how the assembled models are placed onthe workshop floor. It shows the bounding boxes of the added equipmentas rectangular fields. In order to more clearly separate the different mod-els, some labels would be helpful. Whether or not a floor surface has beendefined is also important information that needs to be visualised. In work-ing with groups of machines covering a larger space, it will be necessary toimplement some means of zooming and panning, and preferably a largerdisplay. In navigating the virtual environment, it is important to visualisewhether or not a certain machine is moveable.
2. Match between system and real worldIn the WorkshopAssembler application, there are no immediate contradic-tions to this point. In navigating the environment this issue is more inter-esting. The system itself does not consider the model´s resemblance to realmachines,
3. User control and freedomIn the WorkshopAssembler´s controls it is easy to add and remove objectsfrom the lists.
4. Consistency and standardsThere are no violations of conventions for actions, names and situations.Standard file dialogs and buttons have been used throughout.
5. Error preventionFile type filters should be used in the file open/save dialogs to prevent usersfrom importing incorrect files, even though an error message will appear if itis done.
6. Recognition rather than recallThe ability to recognize the equipment in the environment has very much todo with the level of detail chosen for the models.
7. Help and documentationA standard help function should be implemented into the system explainingspecific functions and tasks.
80
Chapter 9
Discussion
I would never die for my beliefs because I might be wrong.Bertrand Russell (1872 – 1970)
This chapter discusses the results of this Master´s projects and makes some per-sonal reflections upon the subject of equipment simulation.
9.1 Equipment simulation at Scania
In most projects of equipment change at Scania, questions concerning equipmentplacement arise. It is often difficult to decide on what robot models to choose toefficiently make use of available floor space. The questions like if a robot will beable to reach the machines in a work cell can be difficult to answer without a goodoverview of the cell. In time-critical systems there is clearly a need to know if acertain robot will be able to meet the requirements on cycle-time, which is veryhard to approximate without simulation.
Today most CAD application work with 3D models and workshop layouts aremade at least in parts in 3D. The CAD tools used for this purpose have some builtin functions to analyze robot work areas which can be used to assess requirementson robots. In this sense equipment simulation is already used today at Scania.
An important prerequisite of equipment simulation is the availability of 3Dmodels of sufficient level of detail. Today this is a problem. Suppliers of machinesand equipment often have problems delivering these models in 3D and the pro-duction engineers therefore have extrude 3D geometry from 2D drawings whichis a painstaking and time consuming process. Due to this, the availability of 3Dmodels in the layout CAD system varies much between different departments.
Another important problem that arises when working with factory layouts in3D is the size of the models. A factory layout may consist of a number of machinesranging from a handful up to several hundreds. Even though each of the machinemodels is reduced in respect to complexity, the size of an entire factory layout willbe very large. The CAD system used for factory layout design is not very well
81
suited for handling models of these large sizes and the performance of the systemis often suffering from this making the work frustrating and tedious.
In the pre-study the collaboration between production engineers and operatorshas been of particular interest. The CAD systems are often too complicated to usein making rough proposals and quick changes and the demonstrator system wastherefore developed to address these needs as a complement.
Most of the benefits of 3D visualisation comes from the immersive study andin this respect graphical performance is often more important than geometricalaccuracy. Some CAD systems have implemented light-format visualisation func-tionality for presentational purposes, with no means of manipulation.
Today´s CAD system for layout creation
The idea of virtual manufacturing and model-driven development is highly de-pendant on accurate models of machines and equipment but the CAD system usedfor layout design at Scania has some problems related to this. AutoCAD with theFactory CAD module that is used today, uses light weight, parameterized modelsof generic equipment, which can be accessed through libraries built in to the sys-tem. This way models are kept rather simple, in geometrical terms, and they arevery easy to manipulate. In the phase of an investment project where no machinesyet exists, this is a very efficient way of making layout proposals. When machineshas been decided and ordered however, the generic models used for layout designbecomes inaccurate and in many cases misguiding. It has been described earlierin this report that machine suppliers today often have problems with deliveringmodels of machines in 3D. These problems comes from both insufficient CAD dataand an uncertainty of choosing right level of detail in models. Machine supplierare also cautious about revealing too much information that comes with a higherlevel of detail.
There has been some attempts in describing a template model to describe alevel of detail well suited for layout purposes at Scania but in this case only pre-requisites for layout creation has been considered. In order to make better use ofmachine models, the ability to mount virtual models of tools and other equipmentwould be desirable.
CAD integration of simulation tools
During this project I have been given the opportunity to follow a project at Sca-nia, aimed to assess the benefits of some of the external modules in the Catia v5platform. IGRIP, one of the leading systems for robot simulation, is now incor-porated into the v5 platform as an external module. The user interface has beenharmonised to fit the Catia environment. This is a very good sales point, sinceonce the user has gotten used to working in Catia, it is a rather small step to learnIGRIP. Most functions in IGRIP use the same interactional principles as Catia andthe other v5 modules.
82
Downside of CAD integration
As mentioned earlier in section 3.2.4, this integration of simulation tools into exist-ing CAD systems does not come with out trade-offs. While this integration has itsobvious advantages in harmonised user interaction and the use of internal smartfile formats and data structures, the downside to this is that it gets harder to mixsystems from different suppliers. Using the IGRIP module in Catia to do equip-ment simulations in a layout made in LayCAD, cannot be done without modelconversions, which is time consuming and may imply some loss of data.
9.2 The demonstrator system
Focus on the early stages in layout planning
The demonstrator system developed during this project has been aimed at theearly stages in the planning of a factory layout. I have found the cooperation be-tween production engineers and operators in the improvement groups a key issue.The production engineer provides the technical foundation of the new equipment,material flow, requirements on machines in respect to cycle time and compliancewith safety and environmental regulations etcetera.
The type of simulation/visualisation addressed by the demonstrator system inthis Master´s project is less complex and is aimed more to support the collaborationbetween production engineers and operators in layout planning for equipmentchanges. One of the main objectives of the demonstrator system is to make theoperators more involved in the design process and thereby make better use of theirexpertise.
Questions about work ergonomics are difficult to address by production engi-neers alone, they are therefore depending on the expertise of the operators, withtheir knowledge of daily operations and maintenance of the equipment. As thepre-study shows, this collaboration often starts with a rough layout proposal thatis presented to the improvement group as paper based 2D drawings. The waythese 2D drawings are used by the improvement groups varies between depart-ments and is often highly dependant on interpersonal relationships.
The basic idea of the demonstrator is to provide means of simple manipula-tions of a proposed layout presented in 3D. The type of low fidelity manipulationssometimes done by cutting out machine silhouettes from paper drawings elaborat-ing with these on a bulletin board, is very powerful and the idea is to mimic theseactivities in a computer based 3D system. The simple nature of these manipula-tions makes it easy to do quick and dirty proposals which means lower cost and lessfear of making mistakes. Ideas can be tested almost immediately and alterationscan be made on-the-fly. Through iterations, wild ideas can evolve into concretesolutions fast and at a very low cost. Of course this process need not necessarilybe done on a computer, an alternate solution would be to develop a methodologyfor paper based brainstorming sessions. The benefits of using a computer based
83
system are the ability to take ideas directly back to the CAD system and by thisreduce the amount of time and effort required.
9.3 The project
This master´s project has been trying to assess the benefits of Equipment Simula-tion to Scania. The project has started by analyzing the investment/change processin order to gain an understanding on the specific needs and requirements. It wasdiscovered early that the paper based 2D drawings play an important role in thisprocess. Most work is in some way associated with the layout and the drawingsare therefore central in most discussions.
Equipment simulation is much more than just visualisation of layout proposalsand it would be interesting to look deeper into simulation systems where kinemat-ics of robots and other moving equipment are simulated.
In the last phase of this project an evaluation of the demonstrator was doneand this is an area where more work is needed. The demonstrator system includesimplementations of functions found necessary in the pre-study, yet many of theseare still not general enough to be used on arbitrary models.
84
Chapter 10
Conclusion and recommendations
The only thing to do with good advice is pass it on. It is never any useto oneself. Oscar Wilde (1854 – 1900)
10.1 General reflections
Equipment simulation is becoming more and more feasible thanks to a number offactors:
• 3D visualisation reveals details3D visualisation provides a better understanding of workplace implicationsin factory layout proposals.
• Simulation softwareSimulation software is getting integrated into CAD systems as additionalmodules. Thanks to this integration and adaptation to standard CAD soft-ware, less extra training is needed to perform simulation and fewer transla-tions between systems are needed.
• Availability of 3D modelsMore machines and equipment are being modelled in 3D, which makes equip-ment simulation easier when less extra modelling is needed.
• Complexity of manufacturing equipmentAs manufacturing equipment is becoming more complex, the benefits of equip-ment simulation increases. Simulation of kinematics as well as logic controlsystems can shorten installation time considerably.
• Support for collaborative designAs a facilitating tool for collaborative design, simulation/visualisation sys-tems may provide production engineers and operators a platform for exper-imenting with ideas of factory layout.
85
• Standard hardwareCAD software is finding its way to the standard PC. The approximate cost ofa CAD work station is now roughly 1/4 of the traditional Unix-based workstations.
• 3D graphics hardware3D graphics hardware development has literarily exploded thanks to the PCgaming industry, making high performance graphics cards available at lowcost.
• Accurate foundation drawingsDrawings of buildings and equipment models are becoming more accurate,making simulation results more reliable. There is, however, still a need tofurther
10.2 Conclusion
Engage operators in the design process
The most important outcome of this project is the definition of a method of engag-ing operators early in the layout design process.
Stimulate collaboration in layout design
Providing a simple tool for layout manipulation in 3D that is accessible in theworkshop can stimulate operators to take a more active part in layout design.
Collect ideas on potential improvements from more sources
The mobility of the system makes it easier to present design proposals and henceget feedback from more sources.
Detection of ergonomics problems in proposed layouts
The immersive exploration of a layout will provide a more realistic view of thedesign. Work positions and lift heights can be detected.
Ability to perform safety inspections earlier
3D views can reveal potential safety hazards in a layout proposal thanks to theperception of depth and height.
Presentation of layout proposals
The main advantage in presenting layout proposals in 3D is that it provides a betterand more detailed view of the equipment and the dynamic display of immersive
86
studies also makes it possible to focus the presentation on certain points and as-pects.
VRML-EAI-Java Technology
The demonstrator system developed using VRML-EAI-Java technology has showedthat it is possible to achieve a working solution with free standard technologies.However, there are trade-offs to this approach making it ill suitable for this task.The solutions is not very homogenous in that it consists of loosely coupled parts,along with a strict method of operation.
10.3 Recommendations
My recommendation for Scania on equipment simulation is:
• Re-evaluation of robot simulation softwareThe latest developments in robot simulation software and some shortcom-ings in the last evaluation in 2001, motivates a new survey and testing ofavailable systems.
• Pilot projects using simulationAn efficient way of proving benefits of new technology is by testing. Success-ful pilots will most likely increase the general interest in equipment simula-tion.
• Market surveillanceCurrently, numerous activities are taking place in development of equipmentsimulation tools and methods. Surveillance of the development in this fieldis an important task for Scania.
• Catia v5 for layout planningEvaluate the factory layout planning modules of the v5 platform in Catia.Since IGRIP now is a part of the v5 family, and migrating to this system hasstarted for all other CAD systems at Scania, it would be a good idea to evalu-ate its capabilities in layout planning as well. During the project of surveyingthe needs for Catia v5 modules at Scania, most modules are available for test-ing and evaluation.
• Standardisation of model requirementsThe specifications for 3D CAD models in Scania´s TFP needs revising. Inorder to make a relevant specification, a study of requirements for the pur-pose of layout planning is needed. These requirements need to address bothissues concerning file formats, drawing layers and level of detail.
• Building surveyStart an in-depth survey of buildings and current equipment by laser scan-ning.
87
Chapter 11
The Aftermath
Look not mournfully into the past. It comes not back again. Wiselyimprove the present. It is thine. Go forth to meet the shadowy future,without fear. Henry Wadsworth Longfellow (1807 – 1882)
This chapter discusses the future of the demonstrator system.
11.1 The heritage
The demonstrator system developed in this master´s project comprises a series ofoperations more or less separated and performed in different stages of the work-shop model assembly. This is mainly due to the constraints of using only openand freely available technologies. The greatest downside to this solution is that theprocess of assembling a workshop layout model is complicated. There are severalsteps that need to be passed in the right order to make things work and this willsurely have a negative impact on the intended users´ attitudes towards it.
11.1.1 Further work
The demonstrator system has been used to show some potential benefits of visual-isation and simple manipulation of workshop layout proposals in 3D. In additionto these benefits it has also managed to pinpoint some functionality that wouldbe desirable in a system of this kind. Examples of functionality that needs to beimplemented or added to the demonstrator include:
• Manipulation in the preview paneThe preview pane where the overview in 2D is shown should have functionsto move objects.
• Reference pointsCoordinate systems are not being dealt with properly in this implementa-tion. The machines are currently referenced as in the CAD system they were
88
exported from. This is one of the major issues in making the system work asa good tool.
• Handling of feedback from the EAI-appletThis is a matter not addressed in the demonstrator and the question remainswhether to keep this functionality within the WorkShopAssembler or an-other system (or even at all?).
• Support for notesImplementation of a “post-it”-like function is desirable to provide means ofsaving informal scribbles, like in the case of the 2D drawings.
• General VRML parsing.The VRML parsing function of WorkshopAssembler is a “quick and dirty”function that assumes imported files have been imported from AutoCAD,in its special formatting. Some models consist of other components that aretranslated into other models using a sub group and a translation. The currentparser only looks “inside” the set of points in nodes of the type IndexedFace-Set.
11.1.2 Internal communication
Another solution of the presentation module would be to let the WorkshopAssem-bler application communicate directly with the VRML plug-in using the EAI. Whetheror not this solution is possible has yet to be discovered. Meantime, the current ver-sion of the presentation module opens the VRML file for exploration in the webbrowser, without any means of feedback.
11.1.3 Alternative technology
To develop a real system based on the demonstrator, the choice of technologywould be different. VRML-EAI has its apparent strengths in its simple and opennature, but this solution also has its downsides. Viewing the scene in a standardweb browser using a third party plug-in, comprises unnecessary difficulties inhandling user feedback. The demonstrator system is in fact three separate pro-grams that communicate via EAI.
I would suggest a solution where all functions of the demonstrator system arebuilt in to one separate system, allowing import of CAD models in a standard CADexchange format. It will be a slightly more complex system, but an implementationusing OpenGL/GLUT would increase graphics performance, enable a tailor-madeuser interface and more efficiently handle user feedback and status changes in thescenes.
89
References
[1] R. Berlin, G. Bergqvist. Accurate robot and workcell simulation based on 3dlaser scanning. In Proceedings of the 33nd ISR (International Symposium onRobotics) in Stockholm, October 7 – 11, 2002.
[2] B. Bernard. Integration of Manufacturing Simulation Tools with InformationSources. Licentiate thesis, Computer Systems for Design and ManufacturingDivision, Dept. of Manufacturing systems, KTH, 2000.ISSN 1104-2125.
[3] R. Carey, G. Bell. The ONLINE Annotated VRML97 Reference Manual.Addison-Wesley, 2 edition, 1997.http://www.web3d.org/resources/vrml_ref_manual.
[4] CID – Centrum för användarcentrerad IT-design. Usor – a collection of useroriented methods. Available on: http://www.nada.kth.se/cid/usor/.Checked Tuesday, mars 4, 2003.
[5] A. Dix et al. Human-computer interaction (2nd ed.). Prentice-Hall, Inc., 1998.ISBN 0-13-239864-8.
[6] M. Fjeld, M. Bichsel, M. Rauterberg. Arbete, människa och Miljö:, chapterBUILD-IT: Intuitive plant layout mediated by natural interaction, pages49–56. Nordisk Ergonomi, 1999.
[7] M. Garland. Quadric-Based Polygonal Surface Simplification. PhD thesis,Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213-3891,May 1999.CMU-CS-99-105http://graphics.cs.uiuc.edu/~garland/papers/thesis-onscreen.pdf.
[8] H. Hoppe. Progressive meshes. Computer Graphics, 30(Annual ConferenceSeries):99–108, 1996.
[9] M. Johansson, J. Rosén. Woxénrapport nr 14: Informationssystem för virtuelltillverkning. Technical report, Woxéncentrum, KTH, 1998.ISSN 1402-0718.
90
[10] K.M. Jää-Aro. An overview of virtual environment hardware and software.Technical Report TRITA-NA-P0105, NADA, mar 2001.
[11] S. Lenman et al. Formella VR-möten. Technical report, CID - Centre for UserOriented IT Design, KTH Stockholm, 1999. TRITA-NA-DA9914.
[12] D. Luebke. A Survey of Polygonal Simplification Algorithms. Technical ReportTR97-045, 16, 1997.
[13] D. Luebke. A developer’s survey of polygonal simplification algorithms.IEEE Computer Graphics and Applications, 21(3):24–35, May/June 2001.http://www.cs.virginia.edu/~luebke/#Papers.
[14] H. McLellan. Handbook of Research for Educational Communications andTechnology: Virtual Realities, chapter 15. AECT Association for EducationalCommunications and Technology, 2001.http://www.aect.org/intranet/publications/edtech/15/index.html.
[15] C. McMahon, J. Brownie. CAD CAM. Addison-Wesley, 2nd edition, 1998.
[16] Merriam-Webster Language Center. The Merriam-Webster OnLine Dictionary.Available on: http://www.m-w.com. Checked tuesday, mars 4, 2003.
[17] C.D. Murray et al. Navigation, wayfinding, and place experience within avirtual city. Presence, 9(5):435–447, oct 2000.
[18] D. Norman. The Design of Everyday Things. Currency/Doubleday, 1990.
[19] P. Petersson. Discrete Event Simulation of Manufacturing Systems. Internaldocument, Scania CV AB, xxxx. Scania Intranet at http://scania/t/ptc/.
[20] L. Randell. On Discrete-Event Simulation and Integration in the ManufacturingSystem Development Process. PhD thesis, Division of Robotics, Department ofMechanical Engineering, Lund University, 2002. CODEN:LUTMDN/(TMMV-1054)/1-165/2002, ISBN 91-628-5319-8.
[21] Scania AB (Publ) 2002. Anual Report 2001, 2001.http://www.scania.com.
[22] VRML 2.0 Proposal. External Authoring Interface Reference. Available on: http://www.web3d.org/WorkingGroups/vrml-eai/history/eai_defacto.html.Checked 2003-08-13.
[23] A. Watt. 3D Computer Graphics (3rd edition). Addison-Wesley, 2000.ISBN 0-201-39855-9.
91
92
Appendix A
Glossary
A.1 Notions and Concepts used in this report
API Application Programming InterfaceCAD Computer Aided DesignCAM Computer Aided ManufacturingCATIA CAD systemCNC Computerised Numerical ControlDIS Distributed Interactive SimulationDXF Drawing Exchange FormatEAI External Authoring Interface (VRML/Java)HCI Human-Computer InteractionIGES Initial Graphic Exchange SpecificationLayCAD Scania’s internal name for Factory CAD from AutodeskLOD Level of DetailMDM Manufacturing Data ManagementOpenGL Graphical 3D Programming library from SGIP2000 Production 2000, part of SPS.PEIP Production Equipment Investment Process (Scania)SAI Scene Access Interface. The extension of EAI in X3D.SPS Scania Production SystemSTEP STandard for Exchange of Product model dataTPS Toyota Production SystemUSTM User Skills and Task MatchVE Virtual EnvironmentVM Virtual ManufacturingVR Virtual RealityVRML Virtual Reality Markup LanguageWRL File Extension for VRML modelsX3D Extensible 3D. Development of VRML based on XML.XML Extensible Markup Language.
93
Appendix B
Example output file
#VRML V2.0 utf8#This file was created by WorkshopAssembler 1.0 - SSSRNA#in: C:\TestMapp
WorldInfo {info [
"testing testing"]title "test"
}
DEF V1 Viewpoint {position 0 5 10orientation 0 1 0 0description "View: First"
}
Background {skyAngle [1.2, 1.57]skyColor [0 0 1, 0 0 0.6, 1 1 1]groundColor [0.5 0.6 0.3]
}
Transform {children [
Inline { url "C:\golv.wrl" }]
}
#Geometry nodesDEF root Transform {
94
rotation 1 0 0 -1.570795children [
DirectionalLight {ambientIntensity 0.5color 1 1 1direction 0 0 -1intensity 0.4on TRUE
}DEF Bana Transform {
translation 0 0 0scale 0.001 0.001 0.001children [
Inline { url "C:\BANA.WRL" }DEF PS_Bana PlaneSensor {}
]}DEF Staket Transform {
translation 0 0 0scale 0.001 0.001 0.001children [
Inline { url "C:\STAKET2.WRL" }DEF PS_Staket PlaneSensor {}
]}DEF Tvm Transform {
translation 0 0 0scale 0.001 0.001 0.001children [
Inline { url "C:\TVM.WRL" }DEF PS_Tvm PlaneSensor {}
]}DEF ABB0 Transform {
translation 0 0 0children [
Inline { url "C:\testing.wrl" }DEF PS_ABB0 PlaneSensor {}
]}
]}
DEF slider_Bana Script {
95
eventIn SFVec3f PS_positionfield SFVec3f moveSlider 0 0 0eventOut SFVec3f shifturl "vrmlscript:
function PS_position(value) {moveSlider[0] = value[0]*0.001;moveSlider[1] = value[1]*0.001;shift = moveSlider;
}"
}ROUTE PS_Bana.translation_changed TO slider_Bana.PS_position ROUTEslider_Bana.shift TO Bana.set_translation
DEF slider_Staket Script {eventIn SFVec3f PS_positionfield SFVec3f moveSlider 0 0 0eventOut SFVec3f shifturl "vrmlscript:
function PS_position(value) {moveSlider[0] = value[0]*0.001;moveSlider[1] = value[1]*0.001;shift = moveSlider;
}"
}ROUTE PS_Staket.translation_changed TO slider_Staket.PS_positionROUTE slider_Staket.shift TO Staket.set_translation
DEF slider_Tvm Script {eventIn SFVec3f PS_positionfield SFVec3f moveSlider 0 0 0eventOut SFVec3f shifturl "vrmlscript:
function PS_position(value) {moveSlider[0] = value[0]*0.001;moveSlider[1] = value[1]*0.001;shift = moveSlider;
}"
}ROUTE PS_Tvm.translation_changed TO slider_Tvm.PS_position ROUTEslider_Tvm.shift TO Tvm.set_translation
96
Appendix C
Interview answers
INTERVIEW – PRODUCTION ENGINEER
Focus according to the Contextual Inquiry
The production engineer is the person that is responsible for making layoutdrawings with objectives of optimizing material flow and make efficient use ofavailable floor space. Main focus is logistics and the order of operations withinthe production chain where the placement of machines and conveyors is veryimportant. Workplace ergonomics of operators is seen as a secondary focus.Difficulties for the production engineer includes balancing the needs of operatorsand technical aspects of layouts. The drawings are made, partly in 3D, in a CADenvironment and the production engineer has from this often a good feelingabout how the facilities will look when completed.
Questions and answers:
• In what ways are the paper based layouts used today as foundations fordiscussions? With whom, and under which forms?
– Discussions with operators about machine placement
– Foundations for decisions in discussions with management
– Discussions with surrounding departments
– Describing documents to subcontractors
– "Map of the terrain"
– Safety discussions
– Documentation in the CE-marking process
• Which aspects of the layout is discussed?
– Material flow
97
– Environmental issues
– Workplace ergonomics
– Safety distances
– Access for maintenance
– Suitability for forklift traffic
– Disturbances or noise propagation between comprising machines
• Viewpoints on paper based layouts:
– Positive
* "Easy to roll up and bring along"
* "Everybody understands"
* "Easy to manipulate with scissors and tape"
* Provides a good overview
* Flexible
* Accessible
– Negative
* 2D hides details
* Gets messy with alot of details on one level
* Physical drawings can mean problems with updating and versioncontrol
* Space consuming
– Which are the most important benefits?
* Accessability – people can gather around it and refer to it indiscussions
* They can be easily posted on bulletin boards in the workshop.
– What is lacking in the layouts of today?
* Updating modifications is awkward. It can be difficult to translateideas and notes from paper to CAD.
* Statical display means limits in information
* Freedom of choice between 2D/3D
• What are your expectations on a computer based system for layoutdiscussions/visualisation?
– "Help in making better layouts"
– "The ability to see things otherwise missed" ute efter)
– Simulation of some simpler processes
– Help in selling ideas to decision makers
98
INTERVIEW – OPERATOR
Focus according to the Contextual Inquiry
Operators do not use the paper based layouts continuously and might thereforehave some difficulties in interpret it. The operators are rarely directly involved inthe design process.The level of detail on the 2D drawings is often poorly suited for making a quickassessment of how the group machines will look when in place.The operator’s main focus is the work place. How he/her will be able to workwith machines and equipment. Accessibility of maintenance points, controlpoints, tools, storage places and workbenches are some of the aspects consideredyet difficult to see on a 2D layout.
Questions and answers:
• In what ways are the paper based layouts used today as foundations fordiscussions? With whom, and under which forms?
– Layout proposals are put up on a bulletin board
– Operators working different shifts are given the opportunity to criticizeand come up with suggestions for improvements.
• Which aspects of the layout is discussed?
– Workplace ergonomics
– Access to machines and operator panels
– Loading and unloading of work pieces and blanks
– Coffee break areas
– Quality inspection places
– Places for often used tool
– Work benches
– Adaptation for SPS
– Ease of keeping clean
• Viewpoints on paper based layouts:
– Positive
* Easy to cut and paste and manipulate
* Provides a good overview of the machines
– Negative
* They can get cluttered
* Shows no detail
99
* Does not show a realistic view
– Do feel you contribute to the design process?
* Yes, but it depends highly on the particular production engineer
– Are the viewpoints of the improvement groups taken seriously?
* Yes, if they can be motivated and presented in a clear way
• What are your expectations on a computer based system for layoutdiscussions/visualisation?
– It will provide a more realistic view of a future machine group
– Changes and improvements will be easier to see directly
100
