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MFE 3004 Mechatronics I

1. What is Mechatronics? 1.1 Introduction 1.1.1 A Historical Perspective The application of technology by mankind has been occurring throughout the past millennia to support human functions and activities. Right back to the time of the ancient Greeks, history is full of people who were capable of applying and advancing technology as it developed through the ages from Archimedes, to Renaissance characters such as Leonardo da Vinci, Copernicus and Galileo, to Newton, Pascal and numerous other individuals that were the precursors of the 18th century industrial revolution that completely changed the perspective of technology in everyday life. The principle driving force behind much of the change brought by the industrial revolution was the availability of a new source of power in the form of the steam engine which, when combined with developments in other technologies, made the concentration of labour into factories the most economic means of production. The demand for greater precision in the manufacture of components for steam engines in turn brought about developments in the manufacturing processes themselves leading to the development and introduction of precision lathes, boring machines and other machinery. Further developments led towards the first examples of the automation of production in the early part of the 19th century with the introduction of a system of punched cards to control the operation of an automated loom. The level of automation (a word which was only popularised in the 1940’s when Ford used it to refer to automatic machine transfer systems), continued to increase throughout the 19th century. However, the greatest development in technology at this stage was to be the introduction of electro-mechanical devices. Further developments in the early 20th century saw the introduction of motorcars, aircraft, radio and mass production and most importantly the vacuum tube valve which allowed the development of the first electronic analogue computer. By the time of the beginning of World War II, all the basic technologies were invented. Yet little interaction between such technologies existed at the time. The use of electronic systems in World War II, particularly in communication, paved the way for the establishment of electronics as a major if not dominant technology in applications that were to come. The development of the transistor and the subsequent large-scale integration of transistor circuits proved to be a major breakthrough in the application of electronics in products and processes. Such technology allowed the development of the first commercial computers, numerically controlled (NC) machines and production robots. The success in the application of VLSI allowed the development of microprocessors, giving rise to the first home computers, and digital programmable controllers for industry. Throughout the past twenty years these technologies have been developing further, giving rise to faster and faster processors. Nowadays, almost all market products and processes are being developed with some form of embedded microcontroller or microprocessor that supports in some way or another their operation. This integration of the integration of electronics and software with mechanical engineering systems is nowadays referred to as Mechatronics. The techniques and approaches devised within a Mechatronics framework offers design engineers the opportunity not only to improve the performance of existing products and systems (such as in cars and aircraft), but also in the introduction of new products such as the compact-disc player which not be achievable by conventional means.

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Figure 1.1 The evolution of Mechatronics (Mechatronics, D. Bradley et al). 1.1.2 What does the above indicate? For centuries man has always been striving to adapt technology to the benefit of humankind, mainly to improve human functionality and eventually the human way of life (some people may debate this – however we as engineers see a positive contribution to humankind through technology). The inventions of various mechanical kinematic devices, steam engines, electricity and electronic technologies have all given an impetus to the improvement in the daily life of mankind. However the foundations of the technologies we apply today have now been known for years, and what we are currently seeking is the integration of these technologies. Through such integration we aim to achieve higher efficiency and abilities in products and processes. This is one of the main driving forces in the current application of technology. The practice of improving product performance, and thus adding value can be typified by the examples shown in table 1.1 below, which indicates how integrated technologies have enhanced product performance over the years. For example, the control of temperature in early buildings was achieved by thick walls and small windows. The second generation of designs supplied ‘open-loop’ controls, where users were expected to provide the necessary feedback and close the control loop (e.g. window shutters). Further improvement occurred when closed-loop control was provided through the use of thermostat switches, thus allowing the automatic regulation of temperature. With the introduction of digital technology, through microprocessors and networked systems, great strides in control have allowed the implementation of building management systems, where not only can internal temperature be controlled, but possible apertures can be controlled via the distributed controlled system as well as ensuring efficient energy consumption within buildings. New generation systems now also include ‘artificial intelligence’ to be able to provide for even better system behaviour and optimality. The same can be said of vehicles, where initial simple controls such as suspension systems and carburettors, are now being replaced by engine and vehicle management systems, designed to improve vehicle operational characteristics. Table 1.1 Increase in technological input, increases system performance (Rzevski ed., Mechatronics, Designing Intelligent Machines, Vol. 1) Building Vehicle

Passive Control Thick walls and small windows Suspension

Open-loop Control Shutters Carburettor

Closed-loop Control Thermostat Battery charger

Embedded Information Systems

Distributed building management system

Distributed vehicle management system

Embedded Artificial Intelligence

Anticipative environment control

Route advice, monitoring distance, self-parking

Mechanical Engineering

Mechanisation Electro-Mechanical Systems

MECHATRONICS

Electronics

Information Technology and Software

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One can also look at the evolution of automation in production systems. Until relatively recently, production relied almost exclusively on rigidly structuring the manufacturing environment, typically through the use of transfer line manufacturing. Machinery was designed and programmed to perform repeatedly exactly the same operations. The need for a high product diversification, continuously changing customer demands, reduced production quantities, and reduced concept-to-market lead times, has resulted in a change in the approach adopted for manufacturing, particularly through the availability of information technology. Thus, rather than applying a rigid mass production system, production automation is relying more and more of flexible manufacturing systems which utilise relatively ‘intelligent’ machines, that can adapt much more rapidly to product changes and unforeseen process events and which are still capable of maintaining a highly efficient production. Figure 1.2 below illustrates such a manufacturing system example. Figure 1.2 A Flexible Manufacturing System illustrating how technology integration can improve production automation flexibility and adaptability. (Mechatronics, D. A. Bradley) The above indicates an added advantage in the integration of computing technology with electro-mechanical systems. Here it is possible to interconnect products into systems, capable of providing new services to customers, which would otherwise be impossible to achieve. A typical example of such systems are found in modern vehicles, such as the use of global positioning systems (GPS), which allow the vehicle user to be given route information and which, provide guidance to the user along the route. Such systems are only possible with the application of high levels of integration amongst the system components. 1.1.3 Vehicle Example To see concretely how much technological integration has been and is being introduced further and further in our everyday lives we just have to see the development of the motor vehicle over the past decades. In the early motor vehicles, no electrical element was present, not even to start the vehicle, which was initially started off by hand through the manual rotation of the crank. The electrical starter motor was the first electrical device introduced in a motor vehicle. Furthermore, until the 1960’s, the radio was the only significant electronics in a car! All other functions were entirely mechanical or electrical. No ‘Intelligent systems’ were to be found. The mechanically controlled combustion in the engine was found to be sub-optimal in terms of fuel efficiency, where modelling of the combustion process indicated that there was an optimal time for the ignition of the fuel, depending on engine load, speed, and other measurable quantities.

Production Control Inventory Control

Manufacturing Automation Protocol(MAP) Network

MAP to MAP node Robot Controller

Robot Controller

Programmable Logic Controller

Machine Controller

(MAP) Network

MAP to Fieldbus node

Sensor Actuator Logic Controller Axis Controller

Fieldbus Network

HIGH LEVELS

MIDDLE LEVELS

LOW LEVELS

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In the 1970’s the first electronic ignitions were introduced to counter this lack in efficiency, by being able to measure the crankshaft, and camshaft positions, airflow and throttle position, thus making cars substantially more fuel efficient and subsequently increasing the power to engine size ratio. The introduction of such technology proved to be one of the major reasons why Japanese car makers succeeded in setting a foothold in the USA and Europe, by providing unsurpassed quality and fuel-efficient small cars. Further developments in the late 70’s improved the vehicle braking through the introduction of the antilock breaking system (ABS) which senses the rotation of the wheels, determining whether there has been a wheel lock-up, and eventually modulating the hydraulic pressure in the braking system in order to minimise or eliminate sliding. From the ABS, further technological integration resulted in the introduction of the Traction control system (TCS) in the 1990’s, which is capable of sensing slippage during acceleration, once more through wheel rotational speed measurement, and then being able to modulate the power transmitted to each wheel in order to ensure that the vehicle is accelerating at the maximum possible rate under given road and vehicle conditions. Further application of technological integration has resulted in the Vehicle Dynamic Control (VDC) system, introduced over the past years, which is capable of improving road performance through corner steering by using a yaw rate sensor and a lateral accelerometer, together with sensors on the steering to record the driver’s intention. Nowadays, the differentiating factor amongst cars is not the type of mechanical construction of an engine but rather the additional mechatronic features introduced in vehicles, which, not only include the above mentioned features but also include other aspects such as safety systems, climate control and numerous navigational aids including telematics (which combines audio, hands-free cell phone, navigation, internet connectivity, e-mail, and voice recognition). Nowadays, one may find between 30 to 60 microcontrollers in a car, and this is only likely to increase, as the price of high performance electronic devices continues to go down. Some Examples of the application of technology integration in motor vehicles are given in the diagrams below.

Figure 1.3 Using radar to measure distance and velocity to autonomously maintain desired distance between vehicles (from, ‘Modern Control Systems’ R.C.Dorf and R.H. Bishop).

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Figure 1.4 Autonomous vehicle system design with sensors and actuators (The Mechatronics Handbook, Ed. R.H. Bishop). 1.2 So what is Mechatronics? The previous chapters have continuously highlighted the role of technological integration, and it was mentioned that Mechatronics provides a framework for this technological integration. But what is Mechatronics after all? Mechatronics was a term coined in Japan in the 1970’s by the Yasakawa Electric Company, which originally defined it as follows; ‘The word mechatronics, is composed of ‘mecha’ from mechanism and the ‘tronics’ from electronics. On other words, technologies and developed products will be incorporating electronics more and more into mechanisms, intimately and organically, and making it impossible to tell where one ends and the other begins’. Nowadays this definition has evolved in the more commonly quoted as. ‘The synergistic integration of mechanical engineering, with electronics, and intelligent computer control in the design and manufacturing of industrial products and processes’ (Harashima, Tomizuka and Fukada, 1996)’. This interrelation between the core technologies of a mechatronic system is depicted in figure 1.5. Figure 1.5 Mechatronics: the synergistic integration of different disciplines (Mechatronics Handbook, Ed. R.H.Bishop).

Electronics

Microelectronics Power electronics Sensors Actuators

Information Technology

System Theory Modelling Automation-Technology Software Artificial Intelligence

Mechanics

Mechanical Elements Machines Precision Mechanics

MECHATRONICS

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A more recent definition suggested by W. Bolton is ‘A mechatronic system is not just a marriage of electrical and mechanical systems and is more than just a control system; it is a complete integration of all of them’. It is clear from these definitions that Mechatronics does not present any new revolutionary technology. Rather, as discussed earlier, it depicts a current evolution in the application of technology, where increased benefits are obtained through the adequate integration of technology in new products and processes. Mechatronics thus represents a mode of approaching the design of products developed at the intersection of traditional disciplines in engineering and computer science. It does not in itself encompass these traditional individual technologies per se, but rather focuses on how these traditional technologies can be efficiently absorbed in the design and development of new products. This course in the area of Mechatronics will therefore not purport to provide all the fundamental knowledge in the individual traditional technological fields. Rather, it will offer a basic understanding of these technologies and how they can be brought together for the development of more successful and efficient systems. The scope is therefore that of comprehending modes of integrating technologies and not that of developing the technologies themselves. 1.3 Fundamentals of Mechatronic Systems The general structure and concept of mechatronics and mechatronic systems is represented in figure 1.6 below. This format represents two domains of interest in mechatronic systems – the information domain and the energetic or energy transfer domain. Figure 1.6 A generalised mechatronic system indicating the two principle domains of such a system (Mechatronics, D.A.Bradley et al). The energy transfer domain represents the part of the system that performs work. This domain generally incorporates the mechanical elements of the mechatronic system. The information domain on the other hand represents the part of the system that encompasses the information processing relevant to the control and management of the system’s energy transfer domain. It encompasses the

PROCESSOR

SYSTEM (Mechanics & Energy Converters) ACTUATORS SENSORS

WORLD

ENVIRONMENT

Information Domain

Energy Transfer Domain

Information Flow

Energy Flow

Human-Machine Interface

Measured Variables

Manipulated Variables

Energy flow between system and environment

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system’s ‘intelligence’, by being able to process the information received, make conclusions and take decisions. Mechatronic systems typically depict this division of an energy and information domain, with actuators and sensors serving mostly as the interfacing elements between the domains. Knowledge of the domains and the interaction between the domains is of critical importance for the successful development of such systems. What should be immediately noted at this stage is the lack of division amongst the elements into the individual conventional technologies. Indeed the key elements of a mechatronic system and its development are depicted in figure 1.7 and can be seen as being;

Figure 1.7 The Key Elements of Mechatronics (The Mechatronics Handbook, Ed. R.H. Bishop) 1. Physical system modelling – the understanding of the behaviour of mechanical/ thermal/fluid

systems through various modelling techniques, particularly mathematical, substantially helps in comprehending the mode in which the various technologies can contribute in enhancing the physical system performance.

2. Sensors and Actuators – in a mechatronic system, sensors are used to provide information about both the system and the world conditions. As the system performance increases, system information requirements increase with it, and therefore, so does the need for sensing devices. Similarly, actuators provide the interface and mode of energy transfer in mechatronic systems. Through the increase in functionality of mechatronic systems, once more, the need for cost effective actuators in such systems has been increasing.

3. Signals and Systems – information comprehension and management is of fundamental importance in mechatronic systems as highlighted above. Information understanding and comprehension ranges from the analysis of simple analogue and digital signals, to the

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management of higher level information adequate for higher levels of system control and human-machine interaction.

4. Computers and Logic Systems – the development of intelligent and mechatronic systems has been mainly supported by the increase in the performance, at reduced cost, of electronics and processing power. This has also led to the development of dedicated microprocessor based controllers, providing a backbone for information processing systems.

5. Software and Data Acquisition – the provision of properly structured software is essential to the operation of an intelligent mechatronic system as it is in the software that flexibility and capability of the system generally resides. In many applications, the cost of the software development forms a major, if not the major, cost component, requiring careful attention and control of the software definition, planning and development processes. In mechatronic systems, the software specification and design must be integrated with that of the electronic and mechanical elements, ensuring the appropriate ‘transfer of functionality’ between the individual technological domains.

1.4 Further Aspects and Functions of

Mechatronic Systems 1.4.1 Functionality Transfer We have already mentioned how motor vehicle performance has been improved overall through the application of integrated technologies. Various other examples can be mentioned to indicate how the integration of technologies has led to improved and new product functionality. For example, compared to pure mechanical realisations, the use of amplifiers and actuators with electrical auxiliary energy has led to considerable simplification in devices, such as in watches, electrical typewriters and cameras. Through the introduction of microcontrollers, further mechanical simplification has been obtained, such as in multi-axis handling systems and automatic gear systems in motor vehicles. Closed loop control systems, applicable through the introduction of actuation and sensory devices together with electronic controllers, allow the control of non-linear systems. The elimination of linearity requirement greatly facilitates the design of the mechanical element of a product, though the shifting of complexity from the mechanical to the electronic/ software element. Typical examples of such devices include modern electro-pneumatic servo valves. 1.4.2 Transparency In Systems Apart from the integration aspect, another typical feature of mechatronic systems is their transparency of operation when in use. For example, the driver of a modern car is not concerned and has no direct perception of the engine management system or TCS in his car, other than in terms of the improvements to the car performance that he can perceive. The effect of this is that the driver is now more concerned with the high level operation of the car (such as simple navigation), with the mechatronic systems providing the necessary assistance at the lower functional, behavioural level. This can be seen in various mechatronic products such as auto-focus cameras, intelligent home appliances, advanced manufacturing processes, etc. The major characteristics of a mechatronic system can therefore be summarised as; • Generally complex systems exhibiting high levels of integration, with most of the complexity

transferred to the electronic/ software element. • Increased functionality with respect to conventional systems. • Transfer of function from the mechanical to the electronics and software domains. • System assumes responsibility for process allowing operator to concentrate on high-level

procedures. • Multi-sensor environments.

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• System operation generally transparent to user. • Multi-program environment with user selection, inducing a high level of operational flexibility. Table 1.2 illustrates the additional characteristics obtained through an integrated approach to the development of modern systems as compared to more conventional designs. Table 1.2 Properties of Conventional and Mechatronic Design of Systems

Conventional Design Mechatronic Design

Added Components Integration of Components (hardware)

1. Bulky Compact 2. Complex Mechanisms Simple mechanisms 3. Cable Problems Bus or wireless communication 4. Connected Components Autonomous units

Simple Control Integration of Information Processing (Software)

5. Stiff construction Elastic construction with damping by electronic feedback 6. Feedforward control, linear (analogue) control Programmable feedback (non-linear) digital control 7. Precision through narrow tolerances Precision through measurement and feedback control 8. Non-measurable quantities change arbitrarily Control of non-measurable estimated quantities 9. Simple Monitoring Supervision with fault-diagnosis 10. Fixed Abilities Learning abilities

1.5 Information Transfer as the key to

Integration in Mechatronic Systems It has already been stated earlier on that the key to a mechatronics approach is an efficient and productive cooperation between the different engineering elements in a system design. In engineering terms, this cooperation and collaboration is achieved by the passing of ‘information’ around the system components which is called integration. In order to understand the general integration requirements it is necessary to understand the type of integration typically found in mechatronics products and processes. Fig. 1.8 shows the classical structure for such a system. Integrating the different elements of a mechatronic system together requires that each element ‘comprehends’ the information it receives and can appropriately ‘communicate’ to other elements. This is provided through appropriate interfacing of the various system elements. Table 1.3 gives details as to the type of interfacing and the typical technology involved.

Signal Conditioning Module

Input Module Signal Conditioning Module

Computer System

Signal Conditioning Module

Input Module

Actuators

Output Module

Process

Sensors

Commands

Figure 1.8 Typical Product Control set-up

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Table 1.3 Typical Integration types between control system modules. Modules Interface Type Technology

Sensors

Mechanical/ Electrical/ Chemical (various)

Various sensor types and bonding methods

Sensors Signal Conditioning

Electronic Digital and/or analogue circuitry to clean and scale signals. Mechanical or optical isolation.

Input Module

Electronic / Software Digital Input: parallel or serial Analogue to Digital Conversion, Programming of signal processing algorithms

Computer Software Programming of control algorithms

Output Module

Electronic / Software Programming of signal processing algorithms, Digital output: parallel or serial, Digital to Analogue conversion

Actuator Signal Conditioning

Electronic - Electronic Digital or analogue circuitry to scale signals. Mechanical or optical isolation

Actuator

Electrical / Mechanical Various actuator types

1.6 Further ways of integration The above basic scheme of system integration can be improved by further integration in the process. The integration in this case can be performed through the integration of the components and through the integration of information processing. 1.6.1 Integration of Components (Hardware) The integration of components (hardware integration) results from designing the mechatronic system as an overall system and embedding the sensors, actuators and microcomputers into the mechanical process as seen in figure 1.8. This spatial integration may be limited to the process and sensor, or to the process and actuator. Microcontrollers can be integrated with the actuator, the process or sensor, or can be arranged at several places. Integrated sensors and microcontrollers lead to smart sensors, and integrated actuators and microcontrollers lead to smart actuators. For larger systems, bus connections will replace cables, introducing the possibility of distributing the controller abilities throughout the system. Hence there are several possibilities to build up an integrated overall system by proper integration of the hardware. 1.6.2 Integration of Information Processing (Software) The integration of information processing (software integration) is mostly based on advanced control functions. Besides a basic feedforward and feedback control, an additional influence may take place through the process knowledge and corresponding online information processing, as seen in figure 1.9. This means the processing of available signals at higher levels, including the solution of tasks like supervision with fault diagnosis, optimisation and general process management. The respective problem solutions result in real-time algorithms, which must be adapted to the mechanical process properties, expressed by mathematical models in the form of static characteristics, or differential equations. Therefore, a knowledge base is required, comprising methods for design and information gaining, process models, and performance criteria. In this way, the mechanical parts are governed in various ways through higher level information processing with intelligent properties, possibly including learning, thus forming an integration by process-adapted software.

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Figure 1.9 Ways of Integration within Mechatronic Systems (The Mechatronics Handbook, Ed. R.H. Bishop) A typical example of how integration can occur through the integration of various levels of information processing is shown in the figure below, which illustrates in basic terms how information management occurs within a typical flexible manufacturing cell.

Figure 1.10 Information Integration at various levels within an automated manufacturing cell

Plantmanagement

computer

Operationscontrol

computer

SupervisoryInformationterminals

Operationscontrol data

elements

RawmaterialsAS/RS

controller

Deliverysystem

controller

CNCmachinecontroller

CNCmachinecontroller

Finishedparts

AS/RScontroller

AS/RSMachine

Transferdevice

MachineTool

Transferdevice

MachineTool

Transferdevice

AS/RSMachine

Transferdevice

Material and parts delivery system

Level 1

Level 2

Level 3

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1.7 To Summarise Modern manufacturing products are typified by their complexity. In order to satisfy increasing customer needs, manufacturers are designing increasingly complex customer products and using increasingly more complex manufacturing. The most significant aspect of this increase in complexity has been the introduction of digital processors as part of the design solution. By embedding microprocessors and other such devices, it has been possible to increase dramatically the performance and efficiency of a number of products. The presence of electronics and information technology in products has also permitted the development of new products, which otherwise would not have been possibly created from a purely mechanical point of view. Mechatronics offers a focus on the development of such products by emphasising the technology integration issue throughout the design and development process. The mechatronics engineer thus serves the purpose of acting as a link between specialists and provides support not only for the definition of the technologies to be used but also for the organisational structures employed, to ensure the current level and mode of technological integration.