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Functional Surfaces in Mechanical Handling of Microparts
Povilas Pocius, s021524
Supervisor: Prof. Leonardo De Chiffre
Co-supervisor: Ph.D. student Asta Gegeckaite
IPL publication
December, 2006
Abstract The present thesis investigates functional surfaces on a mechanical gripping device, in
order to improve the handling of micro objects. The projects will focus on different
techniques for surface modifications with the applications on micro handling and
assembly. The gripper had been tested on robot MELFA RV-1A/ Mitsubishi for handling
operation of micro-specimens. Functional surface of gripper was measured by several
optical measuring machines, evaluated with powerful image metrology programs and the
conclusions had been drawn regarding the suitability for the gripping devices for the
micro applications.
Analysis of functional surfaces for mechanical handling of microparts is needed in order
to evaluate the impact of tacking surface area ration and different surface parameters.
These parameters can strongly affect the functional behaviour of handling process of
microobjects. For this reason it is a need to develop different techniques for surface
modifications.
Mechanical grippers are traditional used for manipulating large objects. Due to this
scaling behaviour manipulation in microscale is completely different from manipulation
in the macro scale. Adhesive forces between gripper and object can be significant, if
compared to the gravitation force. These adhesive forces arrives primary from
electrostatic attraction, van der Waals and surface tension forces. The balance between
these forces depends on the environmental conditions, such as humidity, temperature,
surrounding medium, surface condition, material and relative motion.
Design, mathematical modelling and surface structure of griper grasping parts must be
developed in order to avoid or decrease influence of surface, material and motion.
Preface
The thesis has been prepared as the requirement of the Master Science Degree in
Department of Manufacturing Engineering and Management at Technical University of
Denmark.
The work has been carried out during the period June 1st, 2006 to December15th, 2006 at
IPL-DTU under supervision of Prof. Leonardo De Chiffre and Ph.D. student Asta
Gegeckaite. During the project I have become indebted to number of people whose
help I could not have been without. Firstly, I would like to thank my supervisors
Professor Leonardo De Chiffre and Ph.d. student Asta Gegeckaite for the input to the
thesis work and a great supervision.
Special thanks are for Ph.D. Giuliano Bissaco for huge support in experiment task and
preparation of experiments equipment. Thanks to René Sobieski for his help, suggestions
for metrology, evaluations and his kind advice.
Thanks to all people who have contributed significantly to the present work and
especially I would like to thank the: Peter, Giudo, Jimmy, Rasmus, Tomasso, Chistoffer.
I would like to thank my friends and colleagues Danila and Vladimir for comprehensive
help and great time we had together and the friendly atmosphere accompanied our days.
Finally it is very important to me to thank to all IPL staff for grate atmosphere and a lot
of advice.
Kgs. Lyngby, December 2006 Povilas Pocius
Nomenclature Symbol Description Standard Unit Ref-
ere-nce
Amplitude parameters: Sa Roughness Average DIN 4768 [nm] Sq Root Mean Square ISO 4287/1 [nm] Ssk Surface Skewness ISO 4287/1 Sku Surface Kurtosis ANSI B.46.1 Sy Peak-Peak ISO 4287/1 [nm] Sz Ten Point Height ANSI B.46.1 [nm] Hybrid Parameters: Ssc Mean Summit Curvature [1/nm] [6] Sti Texture Index [7] Sdq Root Mean Square Slope [1/nm] [6] Sdr Surface Area Ratio [6] Functional Parameters: Sbi Surface Bearing Index [6] Sci Core Fluid Retention Index [6] Svi Valley Fluid Retention Index [6] Spk Reduced Summit Height DIN 4776 [nm] Sk Core Roughness Depth DIN 4776 [nm] Svk Reduced Valley Depth DIN 4776 [nm] Sdcl-h l-h% height intervals of Bearing Curve ISO 4287 [nm] Spatial Parameters: Sds Density of Summits [1/mm2] [6] Std Texture Direction [deg] [6] Stdi Texture Direction Index [7] Srw Dominant Radial Wave Length [nm] [7] Srwi Radial Wave Index [7] Shw Mean Half Wavelength [nm] The table lists the roughness parameters by their symbol, name, corresponding 2D standard and unit.
Povilas Pocius Functional surfaces in mechanical handling of microparts
Table of contents Table of contents........................................................................................................................ 1 1. Micromanufacture and microhandling. Review of gripping devices................................. 2
1.1. Gripping principles .................................................................................................... 3 1.2. Factors, influencing microhandling ........................................................................... 4
1.2.1. Room conditions ................................................................................................ 5 1.2.2. Gravitation ......................................................................................................... 6 1.2.3. Van der Waals force........................................................................................... 7 1.2.4. Electrostatic force .............................................................................................. 7 1.2.5. Surface tension................................................................................................... 8 1.2.6. Comparison between the forces ......................................................................... 9
1.3. Classification of gripping devices............................................................................ 10 1.4. Requirements for gripping devices .......................................................................... 11 1.5. Gripping design of devices and handling process performance ............................... 12
1.5.1. Design of mechanical gripping devices ........................................................... 12 1.5.2. Adhesive gripper.............................................................................................. 14 1.5.3. Vacuum gripper ............................................................................................... 15 1.5.4. Gripper employing the Bernoulli effect........................................................... 16
1.6. Microobjects ............................................................................................................ 17 1.6.1. Definition of the microobject........................................................................... 17 1.6.2. Design .............................................................................................................. 17 1.6.3. Factors influencing handling process............................................................... 18
2. Microassembly with mechanical gripper ......................................................................... 22 2.1. Definition of mechanical grippers ........................................................................... 22
3. Mathematical modeling ................................................................................................... 24 3.1. Modeling of part and gripper interaction ................................................................. 24 3.2. Equilibrium forces ................................................................................................... 26
4. Design and manufacturing of the gripper surfaces .......................................................... 36 4.1. Existing gripper: Study on functional surfaces in gripper ....................................... 36 4.1. Existing gripping device ............................................................................................... 37 4.2. Development of new gripper functional surfaces .................................................... 38
5. Metrology......................................................................................................................... 41 5.1 Robot limits and uncertainty analysis ............................................................................ 41
5.1.1. Error analysis ................................................................................................... 43 5.1.2. Measurement uncertainty evaluation ............................................................... 45
5.2. Existing gripper functional surface evaluation ........................................................ 46 5.3. Grippers evaluation by optical measuring machine................................................. 50 5.4. Measuring procedures with De Meet....................................................................... 53 5.5. Roughness Parameters ............................................................................................. 54 5.6. Results...................................................................................................................... 58
6. Experiments. Testing of gripping devices ....................................................................... 60 6.1 Experiment procedure and results.................................................................................. 60
7. Conclusion ..................................................................................................................... 101 References.............................................................................................................................. 102
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1. Micromanufacture and microhandling. Review of gripping
devices
Micro handling and assembly is as the discipline of transportation, positioning,
orienting and assembling of micro-scale components into complex micro systems and
covers. In this chapter a review of possible techniques for handling and assembly, as
well as review of gripping devices will be given.
This report consists of seven chapters. Chapter 1 gives a general introduction to
microhandling problem and all influence factors which performed with them and description
of microobjects.
Chapter 2 describes mechanical grippers, process of handling microparts and suitability of
microapplication. There main task is to define and specify the requirements of the mechanical
gripper fingers (for micro applications), by using many different methods for gripping device.
This has been done by performing mathematical modelling of the micropart. So, the purpose
of chapter 3 is a mathematical modelling of handling operation influencing factors and
method of theoretical calculation. Chapter 4 experimental parts to evaluate existing gripper
functional surface, develop new grippers for microapplication. There additional profile was
provided in form of design and manufactured gripper surfaces. Represented development and
modification of new gripper functional surface.
Chapter 5 represents metrological point of view. All measurement and evaluation what occurs
in the project are represented in this chapter. Mostly all the measurement was done by optical
measuring machines: UBM, DeMeet, Stemi 200C Microscope and evaluated by SPIP and
Dix/microscope programs. Surface values related to microhandling problem are evaluated and
analyzed for father suggestions. There is also going to be performed evaluation of functional
surfaces of the grippers, their repeatability, compatibility and variability concerning
appropriate micro parts.
Chapter 6 represents experiments of handling of microobjects, robotic programming,
alignment, handling process and results of suitability and repeatability.
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The purpose of chapter 7 is discussion and conclusion of the results. There will be find
suggestions to what could be done to improve micro handling processes.
1.1. Gripping principles
Handling of micro parts is an issue facing new problems that were not encountered in
conventional size production. However, an increasing number of micro components
based on different materials and with complex geometries need to be handled with
micrometer precision. A significant number of specialized micro grippers are
developed for specific applications, but a homogeneous strategy for specification and
selection of the grippers seem to be missing. Manual placement of micro mechanical
parts by contact and non-contact gripping devices is extremely slow, troublesome and
inaccurate. The need for highly flexible automatic solutions is therefore evident
although they usually require large investment in tooling.
In this paper, micro handling is defined as the handling and subsequent assembly of
micro mechanical parts of dimensions below 1 millimeter as well as parts larger than 1
millimeter with denned microstructures of sub-millimeter size [1].
These main parts will be discussed in this paper:
• The object,
• The handling functionality
• The gripping principle.
The object is defined by means of dimension, geometry, material and weight. The
handling functionality is an attempt to describe the handling situation and the related
necessary operations. Handling scenario consists of the sequential steps of picking,
transportation, orientation and releasing. Furthermore, in order to focus on a possible
assembly operation coming immediately after the physical handling, the assembly process
is considered as a part of the handling functionality. Finally, the gripping principle is
described [2].
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The methodology for choosing a gripping principle based on the object geometry and a
handling functionality would be the following:
• Define the micro object characteristics (weight, material, geometry, dimensions);
• Choose the functionality of the micro handling process.
The functionality of the micro handling process depends also on the number of the micro
object to be manipulated, that gives a beed to define and plan the handling strategy. One
of the important factors is the speed of operation, as precision and control of the process
can be easily lost with high speeds. After all the factors, influencing the micro handling
process are summarized and consideration of the properties of the micro object itself are
done, the qualified micro gripping principle can be selected among the list from known
principles.
1.2. Factors, influencing microhandling In this paragraph of factors, influencing the microhandling will be summarized. A survey
of the forces influencing microobject during the handling will be presented. A particular
attention will be on the forces, working at the microscale.
For the parts with masses of several grams, the gravitational force usually will dominate
adhesive forces and parts will drop when the gripper opens. When parts to be handled are
very small (relative diameter less when 1 mm) adhesive forces between gripper and object
will become larger than gravitational forces. Then the object will adhere to the gripper
and after the gripper will be opened will not drop down, but has to be removed by specific
techniques. These surface forces can be used in grippers as an adhesive force to pick up
the object. These forces are almost not controllable and they are more likely to disturb the
process rather than improve it. It shows that grippers using adhesive forces to pick up
objects have been developed.
Adhesive force arises primarily from:
• van der Waals forces;
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• electrostatical forces;
• surface tension.
These adhesive forces arise primarily from electrostatic attraction, van der Waals forces
and surface tension. The balance between these forces depends on the environmental
conditions, such as humidity, temperature, surrounding medium, surface condition,
material, and relative motion [2],[3]. In the figure 1.1 it is shown common pick and place
operations.
Figure 1.1: Pick-and-place operation with micro-parts. Due to sticking effects, parts may be attracted to the gripper during approach and release phase, causing inaccurate placement [4]
1.2.1. Room conditions In a high humidity environment, or with hydrophilic surfaces, there may be a liquid film
between the spherical object [4]. Figure…
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vv Figure 1.2: Micro-gripper holding spherical objects
γπrFtens 4= ( 1.1 )
where r is the object radius ,γ is the surface tension ( γ =73 mNm-1 1 for water).
Assuming hydrophilic surfaces and a separation distance much smaller than the object
radius.
1.2.2. Gravitation Gravitation is a physical force that is responsible for interactions between objects with
mass. For a spherical part of silicon the gravitational force is:
gsrF igrav ρπ 3
34
= ( 1.2 )
where isρ = 2300Kgm-3 is the density of silicon. For accurate placement, adhesion forces
should be an order of magnitude less than gravitational forces. More about gravitation
force will be discussed in chapter 2.1.
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1.2.3. Van der Waals force Van der Waals force is a force that arises from the instantaneous polarization of atoms
and molecules into dipoles when they are set close. Even if van der Waals force is much
weaker than other intermolecular forces, like ionic interactions, hydrogen bonding or
permanent dipole-dipole interactions, it is able to hold together many molecules that are
too stable to become an integral part, as noble gases. The van der Waals force between a
sphere and a flat gripper can be approximated by [5] and [6]:
28 zhrFvdw π
= z<<r (1.3)
where H is the Hamaker constant, z is the distance between the surfaces and r is the radius
of the sphere. This formula is assuming atomically smooth surfaces. Severe corrections
need to be made for the rough surfaces. In fact the van der Waals force falls off very
rapidly with increase of distance between two surfaces, but it is only significant for gaps
less than about 100 µm.
Since the tolerances on the billetare r 6 µrn, the distance between the lateral surface of the
billet and a cylindrical bore cannot be kept less than 0.1 µm, for this reason the van der
Waals force results prevented.
1.2.4. Electrostatic force
The electrostatic forces arise from charge generation (triboelectrification) or charge
transfer during contact. Consider the force between a spherical object and a plane (such as
one finger of the grippe). The approximate force between a charged sphere and a
conducting plane is given by:
( )2
2
24 rqFelec∈
=π
(1.4)
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where q is charge, ∈ is the permittivity of the dielectric, and r is object radius. The
assumed charge density is approximately 1.6 x 10-6 Cm-2.
The attractive force per unit area between two parallel plates is [5]:
εσ
ε22
1 22 SEp == ( 1.5)
where p is the pressure in Pascal, ε is the permittivity of the air, E the electric field
strength and σs the surface charge density. At atmospheric pressure and centimeter-size
gaps, the breakdown strength of the air (about 3-106 V/m) limits the maximum surface
charge density to about 3x10-5C/m2. Such a value of the surface charge density sets a limit
to the pressure at about 50 Pa[6].
When a gap is very small (in the order of 10µm) maximum fields of gap can increase by
one order of magnitude or even more.
For the specific process to be performed, no relevant charging affects are considered or
easily achievable: therefore, the electrostatic force was not comprised between the
eligible methods for billet gripping.
1.2.5. Surface tension
When two objects are exposed to the environment, a thin film of water or contaminant
(e.g. oil, lubricant, etc .) is formed on their surfaces. When they are brought together very
closely, the films touch and melt together. In this way the two objects stick because of the
surface tension. This attractive force increases because of high humidity environment,
large radius of curvature, long contact time and hydrophilic surfaces. The force can be
calculated through the following expression [5]:
dA
Ftens)cos(cos 21 θθγ +
= (1.6)
where: γ is the surface tension, A is the shared area, d is the gap between surfaces and θ1 ,
θ2, are the contact angles between the liquid and the surfaces.
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1.2.6. Comparison between the forces Adhesive forces and the gravitational force are compared in Figure 1.3 [reference]. It is
assumed that the object is a silicon sphere picked up by a gripper with flat jaw surfaces.
Forces are expressed as a function of the object radius.
For accurate gripping, adhesive forces should be an order of magnitude higher than
gravitational forces. From the comparison, it can be highlighted that surface tension
forces are the biggest ones. For this reason the attention was focused on these surface
tension forces, considered as the most stable, repeatable and accurate.
On the other hand, van der Waals forces can start to be significant when spheres of radius
>100µm have to be handled. Similarly, electrostatic forces can be of interest task for the
manipulation when operating with parts less than 10 µm in size.
Figure 1.3: Gravitation, electric, van der Waals and surface tension forces
Capillary forces dominate and must be prevented to allow accurate placement. Van der
Waals forces start to be significant (with smooth surfaces) at about 100 µm radius and
generated electric charges from contacts could prevent dry manipulation of parts less than
10µm in size.
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Figure 1.3 shows electrostatic to be the least significant force except for gravity, it can be
argued that it is actually the most significant force for grasping and manipulation of W/m
to 1 mm parts [4]. First, van der Waals force is only significant when a gap is less than
100nm, unless objects surface is very smooth. Then the effective distance, between the
object and the gripper will be large except at a few points of contact. Finally, the
electrostatic forces can be active over ranges of the order of the object radius. Surface
roughness is much less important for electrostatic forces than for van der Waals.
1.3. Classification of gripping devices Gripping devices, depending on the principle used to hold the micropart, can be divided
into two categories:
• Contact;
• Non-contact.
Contact grippers are a group of grippers which have direct contact with the object.
Contact grippers especially gripers for micro assembly can be divided in categories
depending of work principle:
• Mechanical gripper;
• Vacuum gripper;
• Adhesive gripper;
• Biological gripper;
• Distributed motion gripper.
Non-contact grippers are a group of grippers which have no direct contact with the object;
it means that handling process is without any direct contact with the object. That is
important when it is needed to avoid a damage of microobject (due to very small
dimensions of the object or resistance of the object material). Micro non-contact grippers
are divided into following categories depending of the working principle:
• Magnetic gripper;
• Electrostatic gripper;
• Optical gripper;
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• Bernouli effect gripper
1.4. Requirements for gripping devices Requirements for the gripping devices are to match related gripping application. In our case
will be examined a gripping devices for micro application.
Many micro-operations demand sensor control in the execution to compensate for several
types of errors like part dimension variations. It might be possible to compensate for
inaccuracies in part gripper relations in this way as well.
When diminishing part dimensions, the influence of adhesive forces increases.
Electrostatic force fields are known to be disturbing in the pick-and-place cycle. In
particular when direct physical contact exists between gripper and part, surface tension
forces and van der Waals forces may play a role as well. The sensitivity for adhesive
forces needs therefore to be considered when selecting a griping principle. The part
weight, e.g. the relative importance of adhesive forces compared to gravity, is essential
here. Measures can be taken to diminish the effect of adhesive forces, e.g. drying the
environment or adding hydrophobic coatings to parts reduces the influence of surface
tension forces. Adding surface roughness reduces the influence of van der Waals forces
and electrostatic forces can be reduced by using conductive materials. Other approaches
can be: overcoming the surface forces during the release task such as for example by
gluing the component at the right place, using dynamic release using a needle blowing
away the handled component
The mechanical micro grippers have to fulfil these requirements [3]:
• Parallel opening or closing of the gripper tip:
• Non planar design of the gripper:
• Small dimension of the gripper;
• Relatively high surface roughness for easy gripping of micro structures;
• Material according to the applications of the gripper device.
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1.5. Gripping design of devices and handling process performance One of the main difficulties in production of microsystems is handling and assembly. These
process steps of the fabrication sequence are predominantly done manually by skilled human
operators. The automation in this area by assisting the human operator in picking-up
microscopically small structures, holding them and placing on the right position improves
the operators working conditions, decrease the production costs, increase both, the process
reliability and the product quality after assembly [7]. In this section the important designs of
micro-grippers and micro-assembly process solutions will be presented.
1.5.1. Design of mechanical gripping devices Microgripper is robotic tool used for microhandling or microassembling operation to
grabb or manipulate microobject. Generally defined for grabbing a product with
dimensions in the micrometer range.
Mechanical grippers is group of grippers where handling process is performed by using to
the grasping force. Forces acting in this micro-environment will be properly discussed in
chapter 2.1. Many different kind of microgrippers have been developed.
One of the examples is electrostatically driven mechanical gripper which has a total
length of 400µm and a thickness of 2.5µm (see Figure 1.4) [8]. The gripper closes
completely by applying a voltage of 45V. The maximum force is equal to 0,1µN and it is
reached at 50V. The gripper has been used to pick up microscopic objects, such as 2.7µm
diameter polystyrene spheres. However, sticking problems have been observed.
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Figure 1.4: Electrostatic microgripper [1].
Suzumori et al. [7] developed a pneumatically or hydraulically driven gripper. In such a
gripper, one of the jaws is a flexible chamber, while the other is a rigid jaw. When the
flexible chamber is pressurized, it bends towards the rigid jaw. The prototype is 8 mm
wide, 18 mm long and has a gripping force of 2N.
Keller et al. [11] made a thermal gripper, based on differential thermal expansion. By
pushing the elastic structure which holds the jaws, a longitudinally expanding beam
element allows the opening motion (see Figure 1.5). It can be provided with different
types of tweezers tips, depending on the application. The gripping device is about 2 mm
wide and 9 mm long.
Figure 1.5: Thermal microtweezers [16]
1.5.2. Adhesive gripper Adhesion is the molecular attraction between the two bodies in contact. Adhesive gripper
is based on this principle. As it is described in the section 1.2 sticktion or adhesion also
can be used to build a gripper. In this case, objects are picked up by means of surface
tension forces. This kind of forces, arising from air humidity, can be controlled by
incorporating a microheater in the gripper [6]. In the cold condition, the object can be
picked up simply by touching it.
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To release the object, the heater evaporates the moisture layer that keeps the object stuck
to the gripper. Instead of using natural moisture layers, some adhesive grippers have a
dispenser that forms a small drop at the gripper's surface. When the gripper is brought in
contact with the object, the surface tension centers the component to the surface of the
gripper. The disadvantage of such gripper is that the spreading of the drop takes some
time and the micro part has to be resistant to the liquids.
1.5.3. Vacuum gripper A vacuum gripper is a very simple gripper, as it consists mainly of a thin tube or pipette
connected to a vacuum pump. This makes this kind of gripper cheap and easy to replace.
The suction principle enables the grippingg of objects with different shapes, dimensions
surface quality and material. (see figure 1.6).
Figure 1.6: Vacuum gripper
The vacuum gripper and the working platform, carrying the microstructures, should have
the same electric potential (grounding) to avoid electrostatic loading between the gripper
and handled microstructures. After sputtering, the glass-pipette is connected with the
holder and the vacuum controller. Due to the fact that we have used for experiments
pipettes with different dimensions, a direct connection with the vacuum controller was not
possible. To solve this problem a polymer-microloader was used (as shown in Fig. 10),
enabling at the same time mechanical flexibility between the glass-pipette and the
connection of the vacuum controller. To handle larger structures (>500 µm), very fine
medical injection needles (e.g. with 0,3 mm diameter) can be used as metallic vacuum
grippers (Fig. 1.6) [4] and [8].
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1.5.4. Gripper employing the Bernoulli effect Bernoulli's principle states that for fluid (or air) flow an increase in velocity occurs
simultaneously with decrease in pressure. That means that the only cause of the change in
fluid velocity is the difference in pressures either side of it. Due to difference between
pressures specimen will be lifted without any touch with gripper. This type of grippers
can lift and transport delicate silicon wafers (or similar 2½D microobjects, e.g.
membranes, etc.). The gripping device mainly consists of a circular plate with a hole
through which the air is blown. It lifts the wafers by blowing gently on the wafer upper
surface so that the aerodynamic lift is created (see Figure 1.7).
Figure 1.7 - Bernoulli effect employing gripper [12].
By blowing through the central hole, the air flows radially between the circular plate and
the wafer. The air high velocity induces a dynamic pressure decrease (Bernoulli effect)
that leads to an attractive force between the wafer and the circular plate.
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1.6. Microobjects
1.6.1. Definition of the microobject
Microobject is an object with dimensions in the micrometer range, or object that has structures
in the micro range, which have affect for handling or assembly of a product. Due to consideration of the micro object classification, many different aspects have to be
taken into the account. The object which is going to be handled is the main part of the
handling and assembly process, so it is critically important to classify micro parts. The
literature study about the micro products shows that there is no clear classification and
united system to separate the micro objects into the specifics classes [10].
In order to have a better understanding, why different products require specific handling
process, the classification has to be done. In the microobject classification, the different
properties will be explained, by introducing the different object characteristics and
concluding how these characteristics influence the micro handling and assembly process.
1.6.2. Design A design of the micro product is closely dependent on the required functionality of the
product, specifications and final tolerances of the separated components and the final
products. While designing a micro product, the different functionalities are related to the
different, components, which are optimized to the specific function, with respect to shape,
weight, materials, dimensions and surface properties. These properties will be examined
in the following section .
The approach of the design would be the desired functionality of a product, resolved into
a logical structure. The easiest way to do it is to decompose the product into the separate
objects and to prospect separate parts of the process and object itself. An extreme case in
functionality integration is the monolithic design, where the micro product is constituted
of only one component, having all the functionalities, with the displacements obtained
only through the flexibility of its features. When designing a microproduct, the
specification meets the specified requirements for a product, thus controlling the design
process [9].
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Several constrain due to the incompatibilities of materials, processes and geometries have
to be considered while defining a manufacturing sequence. Since each process step
influences the results of both the previous and the following process steps the process
sequence has to be checked and incompatibilities has to be identified.
1.6.3. Factors influencing handling process
Geometry Geometry of the micro product is one of the critical parameters which influence the
handling and assembly process. From a geometrical point of view micro products can be
organized into three groups [9]:
• Two-dimensional structures (2D). Examples of the products could be different
types of optical lenses or micro mirrors.
• Two- dimensional structures with a third dimension also called two and a half
dimension (2½D). Examples could be: fluid sensors where the structure of the
channel system itself is two-dimensional, but since the channels have a finite depth
they can be characterized as 2½D|.
• Real three-dimensional structures (3D). Typical examples of 3D structure can be
components of various shapes, found for example in hearing aids [8] or in micro
motors [10].
Dimensions Depending on the dimensions of the microobject, these are separated into these groups:
<lmm (real micro products);
>lmm, but having micro structures, which can effect handling process.
Importance of dimensional classification is to explain the definition of the microobject
and to show the differ ence between micro object and the "macro" object with the micro
structures.
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Materials A full understanding of the properties of the materials, used for micro applications is
important in order to future develop the micro components. Depending on the
functionality of the microparts, material characterization may take the form of evaluation:
mechanical, optical, etc. Material properties also influence the handling process. While
going to the smaller sizes of the products, from macro to micro and even to the nano
sizes, it very important to choose the right material for the product, as it is probably one
of the easiest things to change. Depending on the specific properties, existing materials
can be divided into groups of:
• Ceramic and glasses;
• Metals and alloys;
• Polymers and elastometers
• Hybrids: composites, foams and natural materials
Ceramics and Glasses.
A generic term of so called earth materials: (clay. sand, etc.) processed by firing, or
baking. The classification includes pottery, earthenware, glass, abrasives. Chemically
materials of this class have a combination of metallic (light blue) and non- metallic
aterials. Predominantly ionic bonding is influencing the properties, mainly because of the
Coulomb interaction between the positive and negative ions. The difference between
Ceramic and glasses is a morphologic structure: Ceramic has crystalline and glasses has
amorphous structure. The most commonly used ceramics is silicon. It is a semiconductor
material used to fabricate most transistors and integrated circuits. Pure silicon is used to
make almost all the semiconductor chips currently sold on the market. Silicon is not the
only semiconductor which can be used to make integrated circuits, but it does have many
properties that make it quite a bit better for this purpose than the other known
semiconductors. It has been separated from ceramics, as silicon is one of the materials
which is mostly used in the micro technology [15].
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Metals and alloys.
About 80% of the known elements are metals. Any of a class of chemical elements that
have a luster and can conduct heat and electricity. In water quality, these elements (in
high enough concentrations) can be considered toxic. Specific physical property of
metals is metallic bonding (positive ions in the soup of the valence electrons) [10] and
[13].
Polymers and elastometers.
High molecular weight, chemical compounds formed by repeated linking of smaller
chemical units called monomers. Polymers from which fibers are made are long chain
molecules in which the monomers are linked end-to-end linearly. Synthetic polymers used
for carpet fibre include nylon-6,6 and nylon-6 (polyamides), polyester, polypropylene and
polyacrylonitrile (acrylics). In popular terminology, polymers are also called plastics or
resins.
Mechanical properties of the materials influencing the final properties of the material are:
• Stiffness - elastic modulus or Youngs modulus (MPa);
• Strength - yield, ultimate, fracture, proof, offset yield measured as stress (MPa);
• Ductility - measure of ability to deform plastically without fracture - elongation,
fracture:
• Strain toughness, resilience - measure of ability to absorb energy (J/m3);
• Hardness - resistance to indentation/abrasion (Various scales, e.g.: Rockwell.
Brinell, Vickers).
Weight The weight of the part can be defined as a the vertical force exerted by a mass as a result
of gravity. A model for a weight calculation is introduced for a product, having few parts,
connected in together. Each part has a weight associated with it which the engineer can
estimate, or calculate, using Newton's weight equation:
w = m x g (1.7)
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where w is the weight, m is the mass, and g is the gravitational constant which is 9.8 m/s
in metric units. The mass of an individual component can be calculated if we know the
size of the component and its chemical composition.
Every material has a unique density. Density r is defined to be the mass divided by the
volume v:
r = m/v (1.8)
If we can calculate the volume of the component, then:
m= r x v (1.9)
The total weight of the part W is simply the sum of the weight of all of the individual
components [12].
The weight of the micropart is important, to know, as it is used later in the calculations of
the gripping devices and also it can influence the handling and assembly principle. Also
gravity force depends on the weight of the microobject.
Topography Surface properties plays an important role in determining the applicability of a griping
principle. For instance, in case of applying the van der Waals principle, the surface
roughness is determining for the force value [15, 16]. Another example is if surfaces can
easily be damaged, direct physical contact between the gripper and the part may be
undesirable. In this case it is better to use non-contact gripping devices.
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2. Microassembly with mechanical gripper
2.1. Definition of mechanical grippers Mechanical grippers is group of grippers where handling process is performed with the
help of grabbing force. Force generated from motor through the drives is transformed to
two or more jaws, when jaws are compressed in interaction between them emerge grasp
force. This force is calculated:
drgg knNG ⋅⋅= (2.1)
here: - grasp force; gG
– one jaws grasp force ; gN
n – number of jaws;
- empirical coefficient due to jaws material; drk
Mechanical grippers are based on the friction principle (see Figure 2.1) and they are
generally used for manipulating large object. In the microworld, mechanical grippers have
to deal with these problems:
• too high forces damage the object or the object may jump away and be lost;
• too low forces lead to lose the object.
Therefore, the force applied by the gripper has to be precisely controlled [1].
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NgNg
Ffr Ffr
Figure 2.1: Main forces, friction principle
Gs
ss mgG ⋅= (2.2)
( )tenselecvdwfrgs FFFFNG ++++< µ2
(2.3)
where: -gravitation force of the specimen; sG
- friction force between specimen jaw surface; frF
- van der Waals forces; vdwF
- electrostatic forces; elecF
- surface tension forces; tensF
- mass of specimen; sm
µ -friction coefficient between the object and jaw; The best way to grasp micro-objects is to use a microgripper where grasp force and jaws
size match the requirements.
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3. Mathematical modeling The force analysis of manipulation systems for robots has two points of consideration:
• the control of the robot in particular industrial environment [16], [17] and [18],
• the second point, which can be considered from design point of view [19].
It is necessary to control the actuated joint force and torques in case of force control based
upon the information of external environment forces. The force control might be
associated with a non-deformation grasping. Link dimensions, bearings, motors and other
elements have to be chosen during the design of the robot, based on the knowledge of the
external load and the reaction forces obtained in the joints. In many cases the external
load might be considered as static or as a function of the position of the end-effector of
the robot.
3.1. Modeling of part and gripper interaction
Grippers are the object of considerable research. The kinematics and force control
problems engendered by these devices here will be analyzed. Force control for this system
requires the specification of contact forces between the fingers and the gripped object.
Fgrav
Ffr
Fvdw, Ftent, FelecFvdw, Ftent, Felec
T
Figure 3.1. Model of interaction between the object and the gripper functional surface
An equilibrium forces are the forces required to maintain the object in equilibrium
without squeezing it. The interaction force between two fingers is defined as the
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component of the difference of the finger contact forces along the lines joining the two
contact points. The equilibrating forces have no interaction force components.
Fgrav
Ffr
Fvdw, Ftent, Felec
Fvdw, Ftent, Felec
Fvdw, Ftent, Felec Figure 3.2. Model of the objevct and gripper interaction, if the gripper would have three fingers. In a legged locomotion system or a walking machine it is essential to compute the support
forces required at the feet to maintain equilibrium with the force of gravity and the inertial
forces [22], [24]. The support forces are equilibrating forces. They are similar to the
scalar internal forces which characterize the pinch between two jaws [20].
Instead, a suboptimal solution to this problem is proposed in this paper. This method is
attractive in its speed and efficiency. Contacts are modeled as point contacts [20] which
means that a finger can apply any three force components but no moments. A quasi-static
approach to the problem has been adopted. That is, the load wrench, which is the resultant
of the inertial forces on the object and all external forces excluding the finger forces, is
always balanced by the finger contact forces.
Formulation
Let Xe-Ye-Ze be a reference frame fixed with respect to the earth. Consider a reference
frame Xg-Yg-Zb with the origin at the grasp centroid, the centroid of the support/contact
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points, (Exi, Eyj, Ezj,), and the Zb axis parallel to the wrench axis [25]. The leading
superscripts e and b refer to the earth and body (object) fixed reference frames
respectively.
This problem of determining the contact forces may be decomposed into two sub-
problems:
a) Determination of the forces required to maintain the equilibrium of the gripped body
assuming that the finger interaction forces are absent.
b) Determination of the interaction forces needed to produce the finger forces computed
in step a) without violating the friction angle constraints.
The following sections elaborate on procedures for steps a) and b).
The force analysis of manipulation systems for robots has two points of consideration: the
control of the robot in particular industrial environment [3], [6] and [7], and the second
point, which can be considered from design point of view [5]. It is necessary to control
the actuated joint force and torques in case of force control based upon the information of
external environment forces. The force control of the robots might be associated with a
non-deformation grasping [1]. Link dimensions, bearings, motors and other elements have
to be chosen during the design of the robot, based on the knowledge of the external load
and the reaction forces obtained in the joints. In many cases the external load might be
considered as static or as a function of the position of the end-effector of the robot.
3.2. Equilibrium forces The force distribution must satisfy the six equations of equilibrium (see eq.3.1, 3.2). It is
convenient to decompose this system of equilibrating forces into two force fields. One
force field consists of forces parallel to the load wrench axis (parallel to Zb) and the other
is comprised of forces perpendicular to the load wrench. Two methods of solving the two
problems to find the equilibrating forces are described in the following subsections.
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(3.1)
(3.2)
It will be presented as methods:
A. Method I
The set of six equations in (3.1) can be decomposed into two sets of equations. Three out
of the six equations of equilibrium, involving the x and y components may be written as
(3.3)
where Fix and Fiy are the x and y components of Fi and the xi and yi, coordinates refer to
the i-th finger contact point. The matrix equation (3.3) represents an undetermined set of
equations with only three equations in 2n unknowns. There are clearly 2n-3 degrees of
freedom in this system. However, in accordance with the definition of the equilibrating
forces, the vector difference between any two contact forces should have no component
along the line joining the two contact points [24]. Mathematically, this condition is
expressed as
(Fi - Fj) • (pi -pj) = 0, i, j = 1 ,•••,n (3.4)
The matrix equation (3.3) can now be solved subject to the restriction (3.4) and this yields
a simple solution given by
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(3.5a)
(3.5b)
where
The forces on the X-Y plane are thus given by (3.5a) and (3.5b) and it is easy to verify by
substitution that they satisfy (3.3) and (3.4). All forces are perpendicular to the
corresponding position vector
(Fixi+Fiyj) • pi = 0. (3.6)
This force field is analogous to the velocity field of a rigid body where the velocity of any
point is perpendicular to the position vector if the origin is coincident with the velocity
center [24]. Thus the centroid of the contact points may be introduced as a force center
similar to the velocity center in instantaneous kinematics.
If (3.3) is rewritten as
Gr = w (3.7)
where G is the 3* 2n coefficient matrix, r is the 2n * 1 unknown force vector, and w is a
known 3*1 vector, then this system of equations can also be solved by taking the Moore-
Penrose Generalized Inverse of G [26]. If G+ is the pseudo-inverse of G, then for a full
rank matrix (one in which the rank of G is the minimum of the number of rows and the
number of columns)
G+=GT(GGT)-1 (3.8a)
and r can be found from the equation
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r = G + * w. (3.8b)
In the event G is not of full rank, the pseudo-inverse can still be found by using the LU
decomposition scheme or the Householder algorithm [26]. In this case, the pseudo-inverse
can be analytically derived and it is interesting to note that the solution thus obtained from
(3.8a) and (3.8b) is identical to (3.5a) and (3.5b).
This, in fact, provides a physical interpretation of the pseudo-inverse. The null space of
the coefficient matrix G consists of all possible interaction force vectors and the row
space of G comprises of all the equilibrating force vectors with zero interaction force
components. The pseudo-inverse seeks the solution vector with the least Euclidean norm
(length) and hence the force vector which lies completely in the row space of the
coefficient matrix (which has no interaction force components). A rigorous proof for the
general case, in which all three components of forces are considered, is presented
elsewhere [25], [26].
Having found the finger forces in the x and y directions the three remaining equations of
equilibrium, (3.1) can be applied to solve the second subproblem involving the z
components
(3.9)
The F^ and Fiy quantities on the right-hand side in (3.9) are known quantities (see (3.5))
and it should be noted that (3.3) has to be solved before the right-hand side of (3.9) is
known—the two sets of equations are not decoupled. This system of three equations and n
unknowns can be solved again by using the pseudo-inverse which serves to minimize the
norm of the Fz vector. (A physical interpretation for the pseudo-inverse can be made in
terms of the fingers having equal compliances in the Z direction.) The zero interaction
force hypothesis is not used here as it would require all the z components to be equal and
would thus overconstrain the problem. The Fiz force field obtained by the pseudo-inverse
is described by a planar force distribution and is of the form
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Fiz=A+B(xi-xs) + C(yi-ys). (3.10)
This is because the pseudo-inverse solution has to belong to the row space of the
coefficient matrix in (3.9). The coefficients A, B, and C can be obtained by Gaussian
elimination performed on a 3 x 3 system of equations. Alternatively, analytical
expressions can be written for the three constants
where
This completes one method for finding the equilibrating forces (step a).
Method II
This method decouples the problems of finding forces parallel to the x-y plane and forces
parallel to the wrench axis completely. This time, (3.l) are used to solve for Fix and
Fiy.
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(3.11)
The pseudo-inverse solution can be obtained with some algebraic manipulation
(3.12)
(3.13)
where
The z components of the forces are found by considering (3.1) through. The terms ΣziFix
and ΣziFiy in (3.9) are zero by (3.11). Again, an analytical inversion for (8) is possible and
the Fiz are given by:
(3.14)
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Equations (.12) and (3.13) do not describe a force field with zero interaction forces ((3.4)
does not hold). The interaction forces on the x-y plane can be found to be
(3.15)
Unfortunately, this quantity is not zero, unless the contact points are all on the same plane
perpendicular to the wrench axis or along the same line parallel to the wrench axis. But,
on the other hand, the complete decoupling of (3.9) and (3.11) which are required to find
the two force fields is an advantage. It is difficult to say which of the two methods is
better as in either case, the solution is suboptimal.
It should be noted that the forces computed by either of these two methods are not really
equilibrating forces. However, as mentioned earlier, the pseudo-inverse solution is
identical to the equilibrating force solution in the general case. Thus both these method
yield solutions which are, in fact, approximations to the equilibrating force vector.
The forces computed by either of the two methods described earlier are Fiz(i = 1, , n)
which are parallel to the wrench axis Fix, Fiy(i = 1, ... , n) which lie on plane perpendicular
to the wrench axis. It is assumed that method I is used and the resultant of the forces Fix
and Fiy is perpendicular to the vector p, (see Fig. 2). Let the total interaction force exerted
by the ith finger on the object be Ffl. Then
(3.16)
(3.17)
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The net resultant of the interaction forces has to be zero for equilibrium to be maintained.
It is easy to see that for a two-fingered grasp, the interaction forces must be equal and
opposite in direction. For a three-fingered grasp, the interaction forces must be coplanar
and concurrent [24]. If the number of fingers are greater than 3, it is not easy to arrive at
such simple conclusions. However, if the lines of action of the interaction forces pass
through a point of concurrence, (3.17) is automatically satisfied. The condition of
concurrency is a necessary and sufficient condition for n < 3 but only a sufficient
condition for n > 3.
Nevertheless, this condition yields useful simplifications in the procedure of
determination of interaction forces. The desired situation is one in which the lines of
action are along the normal to the surface of the gripped object at the contact points. In a
practical situation, the normal at the contact points are unknown and, in general, are not
concurrent. It is proposed that the point of concurrence be chosen as the centroid of the
contact of points, namely, the origin. This choice is merely a convenience and, in
principle, any other point could be chosen. The reader is requested to bear with this gross
assumption—its validity is discussed later. Now the unit normals et at all the « contact
points are given by
eix=xi/di eiy=yi/di and eiz = zi/di (3.18)
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(3.19)
For n = 3, (3.19) is a system of three homogeneous linear equations in three unknowns
and the only solution seems to be a trivial one. This is not the case since the rank of the
system of three equations in (3.19) is only 2. This is because any three points and their
centroid are coplanar, and hence, the determinant of the coefficient matrix formed by the e/'s
is always zero for n = 3. Thus (3.19) has only one degree of freedom. If n = 4 there are three
independent equations (in general the points are not coplanar, unless the grip is planar, and
the rank is 3) and again there is one degree of freedom. For n > 4 there are n - 3 degrees of
freedom. In Fig. 3.2, if
Fit = Fixj+ Fiyj
then
Fi = Fit + Fiz + Fil.
The net contact force Fi may be resolved along the normal et (postulated normal) to get
Fin and on to the plane perpendicular to the normal to get Fin.
The friction angle, at the i-th contact point is defined as
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(3.20)
In (3.20) it has been assumed that (3.6) is satisfied. That is, Fit is perpendicular to ef
which is true only if method I is adopted. If method n is used Fit has to be resolved along
and perpendicular to ei and accordingly (3.19) and (3.20) are modified.
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4. Design and manufacturing of the gripper surfaces
The design of production systems is generally based on economic considerations, which are
related to certain technical criteria, such as capacity, availability, and reliability. To realize a
cost-effective design, these technical and economic criteria should be considered in their
mutual coherence during the conceptual design process.
This chapter focuses on a productivity of model, which is related to this subject. This model
allows an opinion to be formed about the technical and economic performance of conceptual
robotic assembly cells, during the process of design. First, the system design process is
discussed in brief, after which the productivity variables are presented. All models are used to
assess the technical and economical behaviour.
4.1. Existing gripper: Study on functional surfaces in gripper
130°
1.29±0.01
2
Measuring directions
Figure 4.1. Surface roughness measuring direction by stylus instrument
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Figure 4.2. Gripper surface roughness. After filtering surface error.
Figure 4.3.Rough profile. Exsisting gripper functional surface. (see appendix)
4.1. Existing gripping device
Existing gripping device is shown in the following picture
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The design of the gripping devices and the experimental setup is represented in the following tables
4.2. Development of new gripper functional surfaces
Figure 4.4. Existing gripping device
Povilas Pocius Functional surfaces in mechanical handling of microparts
Table 4.1. Plan of the experiment gripper’s testing GRIPPER \ SPECIMEN
Cylindrical surface
Plane surface (polished)
Plane surface (rough)
LBM surface
EDM horizontal surface
EDM vertical surface
Shape
R1.15
0.1Ra
Ra≈0.28µm
Ra
Ra≈1.2µm
0.120.06
0.02
0.05
0.07
0.04
0.05
0.07
0.03
Sketch of grabbing
Plastic specimen
No
+
+
+
No
+
Micro screw
+
+
+
+
+
No
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Page 40
Table 4.1 . Gripper/ Specimen
Cylindrical surface
Plane surface (polished)
Plane surface (rough)
LBM surface
EDM horizontal surface
EDM vertical surface
Shape
R1.15
0.1
Ra
Ra≈0.28µm
Ra
Ra≈1.2µm
0.120.06
0.02
0.05
0.07
0.04
0.05
0.07
0.03
Manufacture procedure
Preparation
milling
milling
milling
milling
milling
milling
Modification
milling
-
-
LBN
EDM
EDM
Surface finish
polishing
polishing
-
polishing
-
-
Contact area
100 %
Measuring and evaluation equipments
UBM
UBM
UBM
UBM, DeMeet, Stemi 2000C
UBM, Stemi 2000C
Povilas Pocius Functional surfaces in mechanical handling of microparts
5. Metrology
5.1 Robot limits and uncertainty analysis The most important characteristic for our object is accuracy and repeatability. This defines
and estimates the robot ability of coming back to the same position within coordinate system
with the same movements made n-times, is a measure of variability of measuring results
when the same quantity is measured more times. Usually that the parameter that estimates the
repeatability is defined in a statistic mode, using for example the deviation standard, often the
interval that define the repeatability
Another characteristic of the robot performance the quality of robot performance is accuracy:
it is the error between the nominal position and the average of the obtained positions.
The standards do not specify what type of instrumentation shall be used for the test.
With the data of test we can evaluate the pose accuracy in 3D so:
APp= 222 )()()( ZcZYcYXcX −+−+−
Xc = commanded position
APp= position accuracy
Xai= position attained
X = average of attained positions
And the pose repeatability so :
RP1= l±3Si
li= ( ) ( ) ( )222ZZYYXX aiaiai −+−+−
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l = ∑=
N
iil
N 1
1
Sl=( )
11
2
−
−∑=
N
llN
ii
For a linear test the accuracy become:
accuracy
APp = ( )cXX −
with
∑=N
iXN
X1
1
Thus, the differential change in length ln,1, caused by position errors, (Dx, Dy, Dz), is
obtained as:
( ) ( ) ( )212
12
11, ZZYYXXl pppn −+−+−=
Then, by following the same procedure, two additional measurements at point (xp, yp, zp),
are
, where is the length measured by LVDT. 1,1,1 na lll −=∆ 1.al
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5.1.1. Error analysis There are many reasons for which a robot does not reach the position or orientation wanted.
In this section is presented an overview of all possible error sources and a several manners
how these errors appear, in particular considering the circular test. After considering the main
errors a mathematical model to evaluate and correct these errors: this part is not present in
this section.
Mechanics Kinematics Dynamics
gear errors:
backlash,
compliance
static, dynamic
and thermal
deformation
angle transmission error
link length
deviation
displacement of
axes
zero error
dynamic of the
real system
following error
simplified joint
controller
Table 5.1 Summary of main error sources.
Geometric errors.
This type of errors depends mainly by inaccuracy of the robot mechanic structure as arm
length arm, axis position, zero position and by the components for movement like motors,
bearing, stiffness of the drive…it’s possible remove to them only by increasing the accuracy
of working phase. They appear like translation, rotation, parallelism or squareness error. The
effects that produce angular errors are the most heavier because the arm length enlarge these
arms giving large position errors.
Dynamic errors.
These error origin from dynamic forces or mechanic resonances driven by movement. Often
these are only present during the transitory phase and depends by the length of this phase. To
remove these errors the robot needs a computer-power bigger than actually used in industries.
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Thermal errors.
Are due from thermal expansion of metal. The sources can be internal(motors, bearing) or
external(environment causes). These errors produce a non-linear effects on the structure, very
hard to analyze.
System errors.
This categories includes all errors that come from a bad calibration, control algorithms and
non-synchronism between the measurement system and robot controller, errors in the basic or
system software, in particular considering a circular path errors of interpolation,
imperfections from the sensors, death band or transmission components. Only identifying the
sources of these errors it possible remove these ones.
Instrumentation/equipment.
Some errors can derive from inaccuracy, positioning and human errors.
The robot’s joints are all revolute joints, thus in particular it is possible to recognize some
particulars errors like:
• Tumbling: imperfections in the roundness of the axis, the bearings, and shells will
introduce a motion of ideally in itself moving axis;
• Errors at the encoder: this depends by resolution of encoder
• Link deflection: is directly related to link extension and causes inclinations of and of
each link;
• Human errors: adherence to all recommendations and instructions for use the robot or
the measuring instrumentation, inaccuracy of robot positioning, inexperience etc…
• The loads that the robot carries and moves influences this performance: there are two
types of load to be considered : static load(weight of workpiece etc…) and dynamic
(force due acceleration).
• Vibrations are divided in two types: self-exited vibrations(e.g. by eccentric load),
forced vibration(e.g. stimulation by other machines or robots via foundation) and
chatter(stimulation of the robot by automatic process).
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5.1.2. Measurement uncertainty evaluation
All types of measurement are subjects to some uncertainty. A measurement is complete only
if it is accompanied by an estimate of uncertainty. There are a lot of uncertainty sources as
equipment uncertainty, from operator, environmental influence etc. This parameter is
evaluated using statistical analysis following definite rules.
The complete sequence of passages in order at an estimate of the uncertainty is the following:
Identifications of the influence components: environment of measurement, reference element
of measurement equipment, measurement equipment, measurement setup, software and
calculation, metrologist, object to be measured, measuring procedure, physical constant and
conversion factors.
Modelling: this operation consist of express in mathematical terms the dependence of output
quantity (Y) on the input quantity (X)
Correction: defined the systematic error model a correction can be carried out. Error sources
which can not be corrected will contribute to the uncertainty of measurement.
Analysis of uncertainty sources: is needed to know these sources, uncertainties of a
measurement process are a mix of a lot of contributors
First type of evaluation of standard uncertainty: this type of estimate is applied when several
independent observations have been made for one of the input quantities under the same
conditions of measurement; if s is the deviation standard of our sample the uncertainty u
equal to s : s=u
Second type of evaluation of standard uncertainty: is associated with an estimate xi of an
input quantity Xi by means other then the statistical analysis of a series of observations. The
standard uncertainty u(xi) is evaluated by scientific judgement based on all available
information (from literature or past experiences) about the variability of Xi . This type of
standard uncertainty is obtained assuming a density function based on the degree of belief
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that even will occur. The density function usable are the Gaussian(normal), triangular,
rectangular, U-shaped.
Calculate the combined standard uncertainty u(c): is the standard uncertainty of an output y
obtained from the values of a number of other quantities. Is the results of the combined
variance obtained from all variance and covariance components; if the quantities are not
correlated
if the quantities are correlated
Calculate the expanded measurement uncertainty: the object of this parameter is to provide an
interval about the results of a measurement that may be expected to encompass a large
fraction of values that could be reasonable to attribute to the measurand. Expanded
uncertainty is a multiplying the combined standard uncertainty u(c) by a coverage factor k .
U=k*u
The standard coverage factor is k=2 that presents a level of confidence of 95,45%.
5.2. Existing gripper functional surface evaluation
Analysis of topography can be based on two or three dimensions. Since the topographies of the project case are inherently three-dimensional, the focus in the following will mainly be on three-dimensional surface topography analysis.
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Various methods for quantitative and semi-quantitative topography analysis have been established as reviewed in reference [?]. These methods include: • Height distributions and Abbott curves • Topography parameters • Fourier transform analysis (FT analysis) • Fractal methods • Wavelets • Motif analysis • Change trees Despite their appeal FT analysis, fractal methods, wavelets, Motif analysis, and change trees do not have the same industrial importance as topography parameter. The Abbot curve, also known as bearing area curve, illustrates the relationship between height and the bearing area of the surface. The Abbott curve also corresponds to a cumulative height distribution. In the two-dimensional regime topography parameters are well established and standardised as in ISO 4287. A similar body of standards have not yet been established for three-dimensional parameters. Fourier transform analysis involves decomposing the surface into a series of sinusoidal and calculating the root-mean-square height for each wave [6]. The resulting FT spec shows the relationship between wave frequency and root-mean-square height (see 3.5). For noncyclical topographies, FT analysis has less intuitive appeal, but can provide useful information [9]. Topographical evaluation could also be based on topography-dependent functional properties such as friction or roughness. Typically, such topography-dependent functional properties also depend on other factors and we would not expect universal relationships between topography and functional properties. The definition of parameters able to characterize and quantify the microgeometry of the surface has been a topic of great interest in the last decades. The availability of 3D data, allowed by the new generations of measuring instruments, has stimulated research in many fields. One of the most impressive achievements has concerned the visualization techniques and image manipulation able to provide realistic representations of the surface. The usefulness of such an approach for a qualitative characterization is well recognised [5], [12]: often the image inspection, possibly aided by some enhancement techniques, can be assumed as the only aim of the analysis. Indeed, the image conveys a vast amount of information, which can be easily interpreted by an experienced observer. When quantitative information is required, the adoption of parameters becomes essential. But parameters are inherently synthetic and can not completely describe the complex reality of a surface; each parameter can give only information on some specific features of the microgeometrical texture and requires a sound interpretation. In this work 2D parameters are those that are calculated from a single profile, while parameters calculated over an area are referred
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to as 3D, with a further subdivision into areal parameters, derived by 2D parameters, and uniquely 3D parameters. At present, 3D surface texture measurement is not yet covered by international standards, but it is the object of on-going research projects in Europe and abroad; standards concerning this area are expected to appear in the future. In the research carried out within the European Program [12] a set of fourteen 3D parameters has been proposed (Table 5.2). These parameters are denoted by "S" instead of "R" to indicate that they are calculated over a surface. Strictly speaking, most of the parameters of the set are derived from the corresponding 2D parameters, while only three are uniquely devised for surface characterisation. The definitions of these latter are below: Table 5.2: The primary parameter set proposed in [5].
SQSZSsqSku
SdsStrSalStd
SqSscSdr
SbiSciSvi
Surface bearing indexCore fluid retention indexValley fluid retention index
Functional parameters
Hybrid parametersRoot mean square slopeArithmetic mean summit curvatureDeveloped surface area ratio
Density of summitsTexture aspect ratioFastest decay autocorrelation lengthTexture direction
Amplitude parametersRoot mean square deviationTen point heightSkewness of height distributionKurtosis of height distribution
Spatial parameters
While the main objectives of the these efforts originally were there to create network reproductions of the surfaces in three dimensions, several features as coloured plots, extensive filtering facilities, computation of three-dimensional parameters, as well as volume and area computation facilities, ftnave been added and are now in use in different [7] Two groups of surface parameters have been found to be most relevant: (i) Sa, St and Ssk that are related to the general roughness of the surface, and (ii) Spk, Sk, Svk, which are related to specific functional properties - primarily tribological properties. These parameters, which correspond to the two-i dimensional parameters Ra, Rt (DIN), Rsk, Rpk, Rk and Rvk, are defined in.
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Another set of parameters that are under development comprises surface high peaks count, furrow and pit identification, furrow separation and other texture identification entities. SPIP™ is a comprehensive product containing many generic analytical and visualization tools that can be applied on various types of images and curve data, for example images from electron-, interference-, and optical microscopes. In particularly SPIP™ has specialized tools for correcting and analyzing Scanning Probe Microscope (SPM) data including force curve analysis and Continuous Imaging Tunneling Spectroscopy (CITS). Fourier Measurement The Measure tab of the Fourier menu is used for measuring systematic periodicities in the image by analysis of the associated Fourier peaks at sub-pixel level. Periodicities are most often part of the true surface in which case we may want to use SPIP to detect and measure the lattice structure and maybe perform a calibration when the reference values are known. However, periodicities may also originate from coherent noise or vibration problems during the scanning process, in which case you can use SPIP to diagnose the problem and determine the time domain frequency in Hz. Fourier analysis The Fourier transform is a powerful tool for image analysis. This is true in particular for analysis of repeated patterns such as pitch standards and molecular or atomic structures. Fourier images reflect repeated patterns as narrow peaks, the co-ordinates of which describe their periodicity and direction. Such peaks are easy to detect by image processing without any pre-knowledge of the features form or periodicity. Furthermore, the repeat distances can be measured very accurately by determining the Fourier peak co-ordinates at sub-pixel level.
Pict. Fourier
1D Fourier Analysis
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The Fourier transform of a profile is calculated when right clicking on one of the Fourier functions in a profile window. The 1D Fourier window has strong tools for analyzing periodic structures and diagnosing noise or vibration problems. To achieve the highest accuracy it will be an advantage to apply the Fourier X 16 (Requires the Calibration Module) function of the Profile context menu. The cursors can be used to measure a periodic distance (pitch) by moving a cursor to the first harmonic peak. Then the corresponding wavelength is calculated and written in the text field of the window and next the first cursor, see example below. The MX/M1 fields are used for testing the harmonic numbers; SPIP automatically divides the wavelength of the different cursors with the wavelength of curser M1. In this example, M1 points to the first harmonic, i.e., the pitch, M2, M3 and M4 are pointing to the 2nd, 3rd and 4th harmonics respectively, which is confirmed by the M2/M1, M3/M1, and M4/M1 fields. The higher harmonics can be used for getting a statically estimate of the pitch by multiplying the wavelength values by their harmonic numbers.
5.3. Grippers evaluation by optical measuring machine Influencing factors in optical measuring machine
Results influencing measurement in optical measurement machines
Measurement Strategy
•Evaluation criteria•Probing method
•Number of sampling points•Distribution of sampling
points•Filter
Measuring Instrument
•Measuring range•Algorithms
•Coordinate system•Measurement and evaluation
software•Probing system
Operator
•Planning•Alignment
•Probe configuration•Tidiness
Workpiece
•Material•Size•Color•Gloss
•Roughness•Waviness
•Value of form deviation•Type of form deviation
Environment
•Humidity•Temperature
•Temperature evaluation•Vibration
•Dirt particles
Results influencing measurement in optical measurement machines
Measurement Strategy
•Evaluation criteria•Probing method
•Number of sampling points•Distribution of sampling
points•Filter
Measurement Strategy
•Evaluation criteria•Probing method
•Number of sampling points•Distribution of sampling
points•Filter
Measuring Instrument
•Measuring range•Algorithms
•Coordinate system•Measurement and evaluation
software•Probing system
Measuring Instrument
•Measuring range•Algorithms
•Coordinate system•Measurement and evaluation
software•Probing system
Operator
•Planning•Alignment
•Probe configuration•Tidiness
Operator
•Planning•Alignment
•Probe configuration•Tidiness
Workpiece
•Material•Size•Color•Gloss
•Roughness•Waviness
•Value of form deviation•Type of form deviation
Workpiece
•Material•Size•Color•Gloss
•Roughness•Waviness
•Value of form deviation•Type of form deviation
Environment
•Humidity•Temperature
•Temperature evaluation•Vibration
•Dirt particles
Environment
•Humidity•Temperature
•Temperature evaluation•Vibration
•Dirt particles
Figure 5.1. Influencing factors on the results of coordinate measurement
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Figure 5.1.shows the basic factors for coordinate measuring machines and the results of their measurements. All these factors are usually divided into two parts, de-pending on the source of the factor. The factors coming from the machine and from the machines systems are called internal source errors. In this case, the measuring instru-ment and all factors in this part are coming from internal sources. The coordinate system most significant internal factor consists in the deviations of the real coordinate system with regard to the ideal machine coordinate system. These deviations are caused by distortions in the shape and orientation of the guideways and relative parts. OMM have a control unit and computer with special algorithms to handle the readings and to introduce corrections, calculate distances and all geometrical features. The algorithms that carry out these functions can have unexpected behavior if they are used near their validity range. Another type of factors that are showed in Fig.xx are the external factors. Tem-perature is the most difficult factor to control. Temperature modifies the shape of the parts base of a OMM, and alters them configuration. Temperature changes in time in a determined place or has different values according to each place. The reference temperature for all kinds of di-mensional measurements is 20ºC. Environmental humidity also influences the result of a measurement. It can expand the volume of the granite table. Dusts can rest on the ob-ject or the measuring probe and change the results of a measurement too. Earthquakes are transmitted to the machine through the foundations. The atmosphere can also transmit vibration. Light Among the external factors, influencing the accuracy of measurement is the operator. He can misrepresent the results of the measurements for any reason (i.e. competence, tiredness etc.). In addition, the operator can have very big influence on the temperature and dimensions of an item if he touches the object. Limitation The optical measuring systems (UBM, De Meet, Stemi 2000C microscope) of coordinate measuring machines have more limitations of measurement, compared with mechanical probing system. The factors that were described in section 1.4.1 are valid for optical probes too. However, optical sensors have more factors that mostly are coming from external source. Table 5.3.
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RV 1-A Mitsubishi Axis movemets 6 Speed 2.2m/s** Load capacity 1.5Kg Repeatability* ± 0.02 Arm weight 19Kg Max.P-point 418mm Allow movement 1.44Nm Using Pallet insertion assembly
Dimension The length measurement uncertainty u is specified in a simple form as a length – dependent parameter (VDI/VDA 2617): There A, K and B are constants, and L is measured length. This equation can be represented in the graph called the length measurement uncertainty diagram The environmental conditions have a significant influence on the error source of a OMM. All these conditions from measurements of a reference artefact are to be re-corded and taken into account as reference environment condition for assumption the OMM deviation as measuring uncertainties. The limits of difference between reference and real measurement conditions shall be stated in the calibration certificate. The calibration using the error synthesis method usually consists of three steps: The firs step is estimation of the OMM’s parametric errors. These errors can be assessed for each of the axes (Table5.4) of the machine six degrees of freedom: three rotational and three translational errors. During this estimation, only the error sources that are active and have influence for the specific measurement task need to be estimated. Usually this involves the assessment of the geometric and probing errors of the OMM and their response to variations in the environmental conditions as specified in certificate. Second step is calculations of the errors for the measured coordinates of each measured point specified in the measurement strategy, as obtained using a well-known probing strategy, under specified environmental conditions. These errors are obtained by superposition of the parametric errors. Table 5.4 specification of scale GB – A /2.1/
Measuring range 50 – 475 mm Smallest readable value 0,1 micrometer Accuracy ± 1 to 3 micrometer (depends on measuring area) Measuring axis Diameter 2 mm Total length Measuring area + 100 mm
The standard uncertainty of y is obtained by appropriately combining the standard uncertainties of the input estimates x1, x2... xn. This combined standard uncertainty of the
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estimate y is denoted by u(y) and it can be find from positive square root of the combined variance , which is given by/16/: ( )yuc
2
( ) 2
1)(
ix
n
i i
uxfyu ⋅
∂∂
= ∑=
The total standard uncertainty of measurement is calculated by equation: kuU ⋅= Where ‘k’ is the coverage factor .
5.4. Measuring procedures with De Meet
1. Planarity between basic and functional plane (two distance); 2. Holes for pins and screw hole measuring (diameter, tolerance); 3. Holes in gripper plate measuring (5 holes 3mm diameter, 2 with 2 mm diameter); 4. Distance between holes in gripper plate ( corresponding to drawing);
• if hole axis is alignment;
5. Distance between holes in grippers heads ( corresponding to drawing); [see drawing] 6. Alignment between hole axis on gripper head and basic axis ( on gripper plate), find
angle α
α
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Figure 5.2 angle 7. Alignment between the holes on gripper plate (claiming holes of gripper head) with
basic axis (find angle γ)
γ
Figure 5.3. angle
8. Alignment between basic axis and gripper head sharp angle line (and distance); 9. Gripper head dimensions (just shown in the figure);
Figure 5.4. Gripper
5.5. Roughness Parameters Most parameters are general and valid for any M ´ N rectangular image. However, for some parameters related to the Fourier transform we assume that the image is quadrangular (M=N). Before the calculation of the roughness parameters we recommend carrying out a slope correction by a 2nd or 3rd order polynomial plane fit. Note, also that roughness values
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depends strongly on measurement conditions especially scan range and sample density. It is therefore important to include the measurement conditions when reporting roughness data. The Roughness Average, Sa , is defined as:
|),(|1 1
0
1
0µ−= ∑∑
−
−
−
−lk
N
l
M
ka yxz
MNS R 1
Where µ is the mean height:
),(1 1
0
1
0lk
N
l
M
k
yxzMN ∑∑
−
−
−
−
=µ
The Root Mean Square Sq, is defined as:
[ ]21
0
1
0),(1 µ−= ∑∑
−
−
−
−lk
N
l
M
kq yxz
MNS
Note, that the mean value µ is not subtracted from the height values before squaring. It is therefore necessary to perform a proper plane correction or high pass filtering of the image before calculating the Sq. The Peak-Peak Height, Sy, is defined as the height difference between the highest and lowest pixel in the image. minmax zzSy −= The Ten Point Height, Sz , is defined as the average height of the five highest local maximums plus the average height of the five lowest local minimums:
, 5
)()(5
1
5
1∑∑−−
−+−= i
vii
pi
z
zzS
µµ
where zpi and zvi are the height of the ith highest local maximum and the ith lowest local minimum respectively. Only positive maximums and negative minimums are valid. When there are less than five valid maximums or five valid minimums, the parameter is not defined.
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The Surface Skewness, Ssk , describes the asymmetry of the height distribution histogram, and is defined as:
[ ]∑∑−
−
−
−
−=1
0
1
0
33 ),(1 M
k
N
llk
qsk yxz
MNSS µ
If Ssk = 0, a symmetric height distributions is indicated, for example, a Gaussian like. If Ssk < 0, it can be a bearing surface with holes and if Ssk > 0 it can be a flat surface with peaks. Values numerically greater than 1.0 may indicate extreme holes or peaks on the surface. The Surface Kurtosis, Sku , describes the peaked-ness of the surface topography, and is defined as:
[ ]∑∑−
−
−
−
−=1
0
1
0
44 ),(1 M
k
N
llk
qku yxz
MNSS µ
For Gaussian height distributions Sku approaches 3.0 when increasing the number of pixels. Smaller values indicate broader height distributions and visa versa for values greater than 3.0. Hybrid parameters There are three hybrid parameters. These parameters reflect slope gradients and their calculations are based on local z-slopes. The Mean Summit Curvature, Ssc, is the average of the principal curvature of the local maximums on the surface, and is defined as:
∑−
⎟⎟⎠
⎞⎜⎜⎝
⎛+⎟⎟⎠
⎞⎜⎜⎝
⎛−=
n
tsc y
yxzx
yxzn
S1
2
2
2
2 ),(),(2
1δ
δδ
δ
for all local maximums where dx and dy are the pixel separation distances. The Root Mean Square Slope, Sdq , is the RMS-value of the surface slope within the sampling area, and is defined as:
∑∑−
−
−
−
−−⎟⎟⎠
⎞⎜⎜⎝
⎛ −+⎟
⎠⎞
⎜⎝⎛ −
−−=
1
0
1
0
21
21 ),(),(),(),(
)1)(1(1 M
k
N
l
lklklklkdq y
yxzyxzx
yxzyxzNM
Sδδ
R 8
The Surfaces Area Ratio, Sdr , expresses the ratio between the surface area (taking the z height into account) and the area of the flat xy plane:
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, %100)1)(1(
)1)(1(2
0
2
0
yxNM
yxNMAS
M
k
N
lkl
dr δδ
δδ
−−
−−−⎟⎠
⎞⎜⎝
⎛
=∑∑−
−
−
−
where
( )( )2
11122
12
2111
221
2
)),(),(()),(),((
)),(),(()),(),((41
++++
++++
−++−+
⋅−++−+=
lklklklk
lklklklkkl
yxzyxzyyxzyxzy
yxzyxzyyxzyxzyA
δδ
δδ
For a totally flat surface, the surface area and the area of the xy plane are the same and Sdr = 0 %. Functional parameters for characterizing bearing and fluid retention properties The functional parameters for characterizing bearing and fluid retention properties are described by six parameters. All six parameters are defined from the surface bearing area ratio curve shown in the figures below.
Figure 1: Bearing curve illustrating the calculation of Surface Bearing Index, Core Fluid Retention Index and Valley Fluid Retention Index
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5.6. Results
0,0E+00
1,0E+03
2,0E+03
3,0E+03
4,0E+03
5,0E+03
6,0E+03
7,0E+03
LBM EDM Cylindrical Plane-Polished
Existing Plane rough
Functional surface
Spk,
Sk,
Svk
[nm
]
SpkSkSvk
0,0E+00
5,0E+02
1,0E+03
1,5E+03
2,0E+03
2,5E+03
3,0E+03
3,5E+03
4,0E+03
LBM EDM Cylindrical Plane-Polished
Existing Plane rough
Functional surface
Spk,
Sk,
Svk
[nm
]
SpkSkSvk
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0,0E+00
5,0E+02
1,0E+03
1,5E+03
2,0E+03
2,5E+03
LBM EDM Cylindrical Plane-Polished
Existing Plane rough
Functional surface
Sa, [
nm]
0,0E+00
5,0E+02
1,0E+03
1,5E+03
2,0E+03
2,5E+03
LBM EDM Cylindrical Plane-Polished
Existing Plane rough
Functional surface
Sq, [
nm]
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6. Experiments. Testing of gripping devices
6.1 Experiment procedure and results
Methodology of experiment. The methodology of experiment is formed in order to select the
appropriate and optimal plan of experiment from the viewpoints of time, precision of results,
price and technologies. It means that it is needed to assess how to perform that in
technological way in order to obtain the needed results, how to eliminate the undesirable
factors from the experiments that they would not influence the results, the number of tests
regarding to the relation of the precision of results and time, the price of experiments, this is
the ratio of price of experiment operations (equipments, materials, operator’s time) and time
required to perform the needed experiments.
Assessing all these factors while testing and changing some of the parameters (it was
observed how much time it takes, how to perform it better, how to decrease the influence of
outside factors and etc.) it was performed the methodology of experiment plan. The results
showed that it was purposeful to use the slightly different sequence of handling operation
experiments for different micro-specimens. It is almost the same experiments only there are
used different “hole” positional plates for different micro-specimens and the number of
experiments differs too. The latter dimension changed because of the complexity of
operation, the number of occurring mistakes and time needed to perform one operation.
Alignment of positions in the “hole” plate
Plan of experiment is to assess the handling operation while taking a plastic specimen for the
ending specimen part of small diameter and putting it into a positioning hole in the plate
mentioned above. In this way it is to prepare the plastic specimen to assembly operation with
micro-screw. Our investigated micro-specimens can be assembled by cranking the micro-
screw into plastic specimen part of small diameter.
Experiment was performed at the “hole” position plate, which dimensions and data of holes is
(see Picture 6.1)
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Y
X
P1
P12P3
2*4stk. ø2
4stk. ø1.9
P10
15
15
Picture 6.1 “Hole” position plate
For this reason the handling of plastic specimen operation over small diameter ending part
due to high deformation was cancelled and the priority was given to the handling operation
for the main part. In this experiment there was used twelfth hole positioning plate (see above).
Four positions x-axis direction and three y-axis. Diameters of the holes are 1.9mm in first
position for each line of operation and 2mm respectively.
. Farther there follows the sequence according to the experiment plan:
• The robot program is written according to the experiment handling operation that was
determined in advance.
• The plastic specimens are putted manually with tweezers to every position. Also the
small diameter part should be above. This helps to perform the alignment of position
plate in original x, y-axis of the robot, as the external diameter of plastic specimen is
similar to the diameter of the hole. Also the small part hole of specimen is of the
similar diameter as the calibration stick angle, and the central axis of specimen’s small
part hole coincides with the axis of position hole. This makes it easy to determine the
exact position of holes in the robot’s positions measured position plate in three
marginal positions of x, y- axis (xx) and are recorded and converted in computer
positioned list.
• Calibration stick mounted on the robot jaws
• Then it is compared with the robot’s original x, y axis and the alignment of position
plate is performed after the above indicated coordinates are checked several times;
• Putting gripper on the robot jaws;
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• With mounted gripper all the positions are checked, and then it is adjusted if needed.
For positioning we used grippers with plane (rough) surface and small diameter ending
specimen.
Plane (rough) surface gripper is defined by a functional surface unmodified after it’s
manufacturing. During manufacturing surface of this gripper was milled with high speed, as
it’s aluminum alloy material allows such high speed operations. Due to this fact functional
surface of gripper has uniform grooves.
Experiments performed with plane surfaces showed the following results:
Conclusion. The more pressure grippers applied to the plastic specimen (forced influenced)
the more difficult it is to remove the specimen from its position (hole) in the plate. This leads
to increase in error numbers, which can be explained by deformation of the plastic specimen
due to the exceedingly strong forced influenced.
We observed that adhesive force (stickiness) is not dependant of “hole” position alignment
(on the position plate). The experiments show us that the error frequency is the same for
experimental operations for on all 4 different lines. At the same time we observed a high level
of dependence from how good specimen placement was in second position in each line. Good
specimen placement in this case means placement without specimen falling out or sticking
effect, which causes misalignment. After that the program needs to be stopped in order to
correct position of the specimen, otherwise misalignment makes it very difficult to continue
with proper insertion of the specimen into the next position.
Conclusion. Experiment shows that increasing specimen position in one operation
summarizes uncertainty for each position.
The higher position in the row (see Picture 6.1) the more frequently we observe specimen
stickiness to the functional surface of gripper.
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Heavy deformation influence due to elasticity and force relations. Specimen endings with
small diameter and thin walls elasticity too big for handling force. This leads to deformation
of this part, which increases touching with gripper surface size. This explains more frequent
stickiness of deformed specimens to gripper surface.
This project task is to evaluate of grippers different functional surfaces influence in the
handling process of these specimens, so that is not our part to found optimal procedure of
assembly. For this reason handling operation with the small diameter ending plastic specimen
is not enough related to project goal.
For the future handling evaluation was used a new positioning hole plate with smaller hole
diameters.
Experiment was performed using plastic specimen to evaluate plane-surface grippers. The
platform for experiment was a plate with 12 positions. (see Picture 6.2)
Y
X
P1
P12
P3
4 stk ø1.3x0.6
2 * 4 stk ø1.3 * 0.7
P10
15
15
Picture 6.2 Positions “hole” plate with 12 positions
Alignment of two gripper “holding” surfaces.
The two gripper functional surfaces must be aligned to each other in order for gripper to
properly grab the specimen. The functional surfaces must be parallel to each other to avoid
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premature release of the specimen. The lower ends of the grippers must be on the same level,
e.g. z-axis’ value of these ends must be equal in order for gripper to touch plate properly.
Gripper functional surface alignment is done by performing the following steps:
1) Gripper is lightly fixed with screws to the robot jaws
2) A G-block is placed between two gripper functional surfaces
3) Gripper closes and the G-block is held tightly by it. Due to lightly fixed screws and
automatic force control (constant load) this action aligns the gripper functional
surfaces in planar positions
4) Gripper moves carefully down in z-axis direction to a G-block put on the plate. This
corrects the gripper with parallel position of the hole plate.
5) The screws are then tightened in this two alignment positions
Experiment plan
Experiment for plastic specimen evaluation consisted of following steps: (see picture 6.3)
1) Open gripper jaws
2) Move gripper to first position (in each line), which is described in position list *.pos
3) Gripper grabs the specimen
4) Gripper arches the specimen to a point above second position
5) Gripper opens jaws (releases the specimen)
6) Operator evaluates, whether adhesive force effect is present
a. If present then error is marked. Program must be stopped and alignment must
be corrected.
b. If not present then experiment continues
7) Move gripper to second position
8) Gripper grabs the specimen
9) Gripper arches the specimen to a point above third position
10) Gripper opens jaws (releases the specimen)
11) Operator evaluates, whether adhesive force effect is present
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a. If present then error is marked. Program must be stopped and alignment must
be corrected.
b. If not present then experiment continues
12) Gripper moves to next line or positions and experiment is repeated
Picture 6.3. Experiment plan for plastic specimen evaluation
Experiment for micro screw specimen evaluation consist a similar step. Due to cost of
operation and high frequency of occurring handling errors there is two positions and two
line of handling operation. Experiment operation is represented in picture below (see
Picture 6.4).
Picture 6.4 Plan of experiments for micro screw specimen evaluation
In order to prepare for the experiments operator performs the following steps:
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• Checks all positions on the plate
• Checks the gripper jaw handling program
• Places specimens into 1st position of each line of the plate
Conditions of experiment
To limit the impact of temperature and humidity on experiments all experiments must be
performed in temperature controlled room. In the room where all handling operation
experiments were performed a temperature controlling device is present. But due to strong
deviations in the atmosphere of the room temperature control was insufficient to completely
avoid temperature and humidity impact. For this reason the temperature and humidity levels
were recorded prior to each experiment.
Certain corrections are done to position the holes of the plate more precisely. Operator does
this by changing appropriate coordinates in the robot positioning program.
This process was performed in order to avoid gripper manufacturing uncertainty. It was
observed that after the alignment procedure of gripper position mostly in z-axis direction was
changed. This can be explained by gripper manufacturing uncertainty, e.g. in hole centricity.
In this experiment the temperature of 21.1oC and humidity level of 51% were recorded in the
robot laboratory.
Grippers with plane (rough) surface.
Experiments performed with plane (rough) surface grippers showed the following results:
Repeatability of handling experiment was 100%, when distance between the gripper and
position hole plate is 0.5 or 1 mm. Accuracy of the experiments decreased rapidly, when
distance was increased to 2mm and more. During the course of all experiments z-axis position
of the gripper (distance from the plate to gripper) did not affect the adhesive force and/or
stickiness effect on the specimen held by the gripper. This fact was observed in all
experiments, regardless of the functional surface of the gripper used in the given experiment.
For all further experiments the distance between the gripper and positioning hole plate was
chosen to provide the operator with optimal conditions for observing the release phase of the
Master thesis Page 66
Povilas Pocius Functional surfaces in mechanical handling of microparts
handling procedure, at the same time minimizing the possible error due to “falling” distance
[See picture 6.3].
“Falling” distance error can be explained by specimen turning during the fall and only
touching the hole with one side, e.g. asymmetrically. The kinetic force accumulated by the
specimen during the fall becomes potential force on the moment of impact with the plate. If
the potential force is stronger than specimen’s gravitational force (Fspec.pot.> Gs), the specimen
bounces off the surface of the positioning plate. In cases with specimen falling
asymmetrically, it turns further and does not properly fit into the positioning hole, e.g. falls
out of it. Following the handling program must be stopper and the operator has to place the
specimen into the correct position manually.
To avoid this disturbance several trials were performed prior to the experiments. During those
trials it has been determined that the optimal distance between the gripper and the position
place is from 0.75 to 1 mm. Therefore all experiments with plastic specimens were performed
with 1mm distance.
Following to the same logic and trials as above with the plastic specimens, the distance
between the gripper and the position plate was set to 2mm for experiments with micro-
screws.
There appeared a question as to which influence caused this effect. We suppose that this is, as
well as in the aforementioned paragraph, an effect of electrostatic force relations of plate and
gripper. It could also be influence of elasticity of specimens and potential force, (which
occurs due to kinetic force of falling specimen) after bouncing off the surface.
Plane (rough) surface of gripper with plastic specimen.
From the beginning handling process showed 100% repeatability, but after some time during
experiment adhesive force effects appeared. This processes cannot be explained by anything
else than electrostatic force influence. Because other parameters which have influence the
handling process were unchanged during subsequent experiments. Electrostatic force could
be conducted to plate or gripper by the human operator during the manual placement with
tweezers of specimens into first position in each line. This can affect generation of different
electrostatic charges between gripper and position “hole” plate.
Master thesis Page 67
Povilas Pocius Functional surfaces in mechanical handling of microparts
Load number 15
The experiment using gripper with rough surface had several errors in repeatability of
handling operations. Grabbing the specimen from the first positions in each operation was
100% accurate. However steps following the first release were in some cases erroneous. This
can be explained by severe roughness and uniform profile errors due to milling, as peaks on
rough functional surface grab the specimen in ununiformed manner (from different unaligned
angles and varying touching surface areas). During this experiment stickiness effect was not
observed. Adhesive force influence occurred several times but without clear pattern. Results
represented in table bellow (see Table 6.1).
Table 6.1
1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 80 70 70 77 74,3 5,1Third 66 60 50 50 56,5
76,9 19,3
Stiching occasion 1
Plane-Rough - plastic specimen (load number 15)
Correct operation percentage in all positions %Operation line on the position plate
Ope
ratio
n
posi
tions
Of all positions7,9
Plane-Rough - plastic specimen
40,0
60,0
80,0
100,0
1 2 3
Position in each line
Rel
ease
, % load 15load 20load 25
Figure 6.1 Plane-Rough-plastic specimen
Load number 20.
Master thesis Page 68
Povilas Pocius Functional surfaces in mechanical handling of microparts
The results of experiment with load number were similar. However the overall number of
errors has decreased (26.7%’ received when minus successfully numbers of handling
operation). This result can be explained by higher load force lightly deforming the specimen
and creating more stable touching surface area. (see Table 6.2)
Table 6.2
1 2 3 4 Mean value St.DevFirst 90 100 90 100 95,0 5,8Second 77 64 70 80 72,8 7,2Third 55 50 55 48 52,0
73,3 19,1
Stiching occasion 3
Ope
ratio
n
posi
tions
Of all positions
Operation line on the position plate
Plane-Rough- plastic specimen (load number 20)
Correct operation percentage in all positions %
3,6
Load number 25.
Experiment with plane (rough) surface grippers with load number 25 and plastic specimens
was different from the previous ones, as there was a higher number of errors (35.2%).
Stickiness effects were observed several times. This can be explained by a higher level of
specimen deformation, increase of touching surface area due to this deformation and profile
error (waviness). (see Table 6.3)
Table 6.3
1 2 3 4 Mean value St.DevFirst 80 90 90 90 87,5Second 55 50 60 60 56,3 4,8Third 58 50 50 44 50,5
64,8 17,6
Stiching occasion 7
Operation line on the position plate
Ope
ratio
n
posi
tions
Of all positions
Plane-Rough - plastic specimen (load number 25)
Correct operation percentage in all positions %
5,0
5,7
Experiments with plane (polished) surface grippers with load number 15
Master thesis Page 69
Povilas Pocius Functional surfaces in mechanical handling of microparts
Plane (polished) surface of gripper was produced by polishing the previous plane (rough)
surface with 4000 quality sandpaper.
Experiments performed with plane surfaces showed the following results:
Load number 15.
The experiment using gripper with polished surface gave good results and repeatability
during the first attempts. However after several handlings adhesive force effects started to
occur. Adhesive force effect can be explained as the electrostatic force influence. We can
conclude this because no deformation or other force influences was observed. Due to
significant roughness of plastic specimen there could not be influence by other forces such as
Van der Waals force. Surface tension can also be neglected due to light load.
The most likely source of the electrostatic force conduction, as in the previous experiments,
could be the human operator. This explains the cumulatively growing adhesive force
influence with repeating number of handling operations during the experiment.
Load number 15
However after several handlings adhesive force effects started to occur. Adhesive force effect
can be explained as the electrostatic force influence. We can conclude this because no
deformation or other force influences was observed. Due to significant roughness of plastic
specimen there could not be influence by other forces such as Van der Waals force. Surface
tension can also be neglected due to light load.
The most likely source of the electrostatic force conduction, as in the previous experiments,
could be the human operator. This explains the cumulatively growing adhesive force
influence with repeating number of handling operations during the experiment. (see Table
6.4).
Table 6.4
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Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 3 4 Mean value St.DevFirst 100 90 100 100 97,5 5,0Second 80 90 70 77 79,3 8,3Third 66 66 50 50 58,0
78,3 18,3
Stiching occasion 8
Operation line on the position plate
Ope
ratio
n
posi
tions
Of all positions
Plane-Polished - plastic specimen (load number 15)
Correct operation percentage in all positions %
9,2
Plane-Polished - plastic specimen
40,0
60,0
80,0
100,0
1 2 3
Position in each line
Rel
ease
, %
load 15load 20load 25
Figure 6.2 Plane-Polished-plastic specimen
Load number 20
With increased load the effects of adhesive force became more frequent, as additionally to the
electrostatic force influence the touching surface area has increased. This can be explained by
higher load deforming (squeezing) the plastic specimen. Though the level of deformation
with this load could not be visible by eye. (see Table 6.5)
Table 6.5
Master thesis Page 71
Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 3 4 Mean value St.DevFirst 90 100 90 100 95,0 5,8Second 77 80 70 80 76,8 4,7Third 55 50 60 48 53,3
75,0 18,5
Stiching occasion 6
Operation line on the position plate
Ope
ratio
n
posi
tions
Of all positions
Plane-Polished - plastic specimen (load number 20)
Correct operation percentage in all positions %
5,4
Load number 25.
Plane (polished) surface of gripper and plastic specimen showed slightly higher adhesive
force effects, compared to the previous load. At the same time the effects of deformation of
the plastic specimen became clearly visible. Such relatively low increase of adhesive force
influence compared to the large increase in the touching surface area and can be explained by
rapid increase in the tension force of the plastic specimen. (see Table 6.6)
Table 6.6
1 2 3 4 Mean value St.DevFirst 100 100 100 90 97,5 5,0Second 60 50 55 60 56,3 4,8Third 44 50 37 44 43,8
65,8 24,4
Stiching occasion 7
Of all positions
Ope
ratio
n
posi
tions
Plane-Polished - plastic specimen (load number 25)
Correct operation percentage in all positions %Operation line on the position plate
5,3
Conclusions:
• Grippers with plane (polished) functional surface can be used for handling operations
with plastic specimens, however conduction of electrostatic force from external
“generators” must be eliminated.
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Povilas Pocius Functional surfaces in mechanical handling of microparts
• This experiment has clearly showed the influence of load force on handling
operations, because there no other significant forms of influence were present
Plane (polished) surface of gripper with chamfer surface of microscrew
In order to better evaluate fitting of the plane (polished) surface gripper for handling
operations with microscrew, the process was divided into two different holding techniques.
• Gripper grabs the chamfer surface of screw head;
• Gripper grabs the cylindrical surface of the screw head
The test was performed on the new position hole plate (see figure 6.3) with 4holes ø0.6x1.5
dimensions, because diameters of holes in the plate must be related to screw diameter.
Y
X
P3
P2P4
2*2 stk ø0.6x1.5P1
15
15
Figure 6.3 Position “hole” plate for micro-screw handling operation
Load number 15.
This experiment showed mediocre handling operation quality with some errors in holding, as
well as adhesive force influence. No deformation on plane (polished) gripper surface or
microscrew chamfer surface was visible. Results represented in table bellow (see Table 6.7).
Table 6.7
Master thesis Page 73
Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 Mean value St.DevFirst position 80 80 80,0 0,0Second position 55 60 57,5 3,5
68,8 13,1
Stiching occasion 6
Operation line
Of all positions
Chamfer screw surfaceCorrect operation %
Plane-Polished - micro-screw (chamfer)
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
1 2
Position in each line
Rel
ease
, %
load 15load 20
Figure 6.4 Plane-Polished microscrew (chamfer).
Load number 20.
With load number 20 there appeared significant visible deformation on functional surface of
the gripper. However the number of proper handling operations has also significantly
increased. This can be explained by deformation providing an “optimal” level of touching
surface area, e.g. not too large to graven adhesive force influence, but large enough for proper
holding. (see Table 6.8)
Table 6.8
1 2 Mean value St.DevFirst position 80 88 84,0 5,7Second position 70 77 73,5 4,9
78,8 7,5
Stiching occasion 2
Chamfer screw surfaceCorrect operation %
Of all positions
Operation line
Master thesis Page 74
Povilas Pocius Functional surfaces in mechanical handling of microparts
Load number 25.
Further increase in load rapidly escalated the level of plane (polished) gripper surface
deformation. After several handling the surface area was completely worn down, preventing
further handling operations.
Plane (polished) surface of gripper with cylindrical surface of microscrew.
Load number 15.
The experiment with the cylindrical surface of the microscrew operated with plane (polished)
surface of the gripper was conducted under the same conditions as the one with chamfer
surface of microscrew. In the same way, as with previous experiments with different gripper
surfaces, the coordinates were changed in the gripper operating program in order to avoid
using the part of gripper’s functional surface damaged by experiments with the chamfer
surface of the microscrew.
In this case, comparing to the experiments with the chamfer part of the microscrew, the
handling operation error margin became generally lower with no adhesive force influence.
However the microscrew was slipping relatively more often out of the grip. (see Table 6.9)
Table 6.9
1 2 Mean valueSt.DevFirst position 70 70 70,0 0,0Second positio 60 50 55,0 7,1
62,5 9,6
Stiching occasion 0
Operation line
Of all positions
Cylindrical screw surfaceCorrect operation %
Master thesis Page 75
Povilas Pocius Functional surfaces in mechanical handling of microparts
Plane-Polished - micro-screw (cylindrical)
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
1 2
Position in each line
Rel
ease
, %
load 15load 20
Figure 6.5 Plane-Polished-micro-screw (cylindrical).
Load number 20.
In the first handing operations with load number 20 the results were very good. However
deformation started occurring to the functional surface of the gripper. After more repetitive
operations the plane (polished) surface of the gripper became completely deformed and could
no longer function. (see Table 6.10).
Table 6.10
1 2 Mean valueSt.DevFirst position 66 70 68,0 2,8Second positio 85 77 81,0 5,7
74,5 8,3
Stiching occasion 0
Cylindrical screw surfaceCorrect operation %
Of all positions
Operation line
No experiments with load number 25 were conducted, as the functionality of the gripper was
completely disabled.
Conclusions:
• During experiments with plane (polished) surface of gripper best results were
achieved when handling chamfer surfaces of the microscrews with load number 20.
• Handling experiments with cylindrical surface of microscrews also showed very good
results with load number 20, but due to the soft material of the gripper surface
repeatability was limited by durability of gripper surface.
Master thesis Page 76
Povilas Pocius Functional surfaces in mechanical handling of microparts
• In order to achieve optimal microscrew handling results harder material should be
used for gripper with plane (polished) surface.
LBM and plastic specimen
When carrying out the experiment for the evaluation of the handling operation of plastic
specimen with the functional surface of the modified LBM (Laser beam machining) gripper,
the robot load number 15 was used in the first case.
Load number 15
The test was performed on the same position “hole” plate as in the analogous experiment. In
this case, the results have shown that gripping mistakes occur at the moment of holding
operation, which was not observed before (see Table 6.11). This could be explained by
insufficient squeezing force of the gripper – i.e., the micro-object was simply not gripped
with enough force. Also, some mistakes were observed at the point of release operation: the
tested micro-object falls out at a wrong time. One presumes that electrostatic and van der
Waals forces might contribute to this. Their total values are not sufficient to ensure stable
stickiness effects to the gripper functional surface, but are enough to offset the influence of
the elasticity force of the specimen. The total amount of mistakes does not exceed 21.9%.
Table 6.11
1 2 3 4 Mean value St.DevFirst 90 100 90 100 95,0 5,8Second 80 60 70 70 70,0 8,2Third 60 70 77 70 69,3
78,1 14,0
Stiching occasion 1
LBM - plastic specimen (load number 15)
Correct operation percentage in all positions %Operation line on the position plate
Ope
ratio
n
posi
tions
Of all positions7,0
Master thesis Page 77
Povilas Pocius Functional surfaces in mechanical handling of microparts
LBM - plastic specimen
40,0
60,0
80,0
100,0
1 2 3
Position in each line
Rel
ease
, %
load 15load 20load 25
Figure 6.6 LBM-plastic specimen.
Load number 20
The experiment, using the robot load number 20, is performed in the same way as the
previous one. The results demonstrated that the handling operation is performed in a much
more exact way. Moreover, in comparison to the previous experiment, no cases of the object
falling out due to insufficient grip were observed. Repeatability of holding operation from the
first position in each line was at the 100% level during the experiment. However, there were
mistakes in the second and third operation positions. Also, several cases were observed with
the stickiness effect. This can be explained by the increased influence of the adhesive force.
When the squeezing force is bigger, the elastic plastic specimen deforms which leads to an
increased touching surface between it and the gripper surface and the reduction of roughness.
That leads to the increase of van der Waals and surface tension force and its influence to the
micro-specimen handling operation. (see Table 6.12).
Table 6.12
Master thesis Page 78
Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 80 60 60 50 62,5 12,6Third 50 77 70 62,5 64,9 11,5
75,8 20,0
Stiching occasion 5
Of all positions
Operation line on the position plate
LBM - plastic specimen (load number 20)
Correct operation percentage in all positions %O
pera
tion
posi
tions
Load number 25
The experiment, using the robot load number 25, showed that results were poorer compared
with the load number 20 test. Due to the increased influence of the forces, mentioned in the
description of the previous experiment, the number of mistakes grew, and the influence of the
stickiness effect was observed more frequently. (see Table 6.13).
Table 6.13
1 2 3 4 Mean value St.DevFirst 90 80 90 90 87,5Second 77 50 70 50 61,8 13,9Third 60 77 50 42 57,3 15,1
68,8 17,7
Stiching occasion 14
Of all positions
LBM - plastic specimen (load number 25)
Correct operation percentage in all positions %Operation line on the position plate
Ope
ratio
n
posi
tions
5,0
Conclusion. The results of this experiment have shown that the best results of handling plastic
micro-specimen are achieved with the load numbers 15 and 20. The difference is that, using
load 15, there is not enough force to fully grip the specimen consistently, while at load 20, the
influence of the adhesive force manifests quite strongly.
The use of the functional surface of modified LBM gripper (using such modification
parameters), despite quite good observed results, is not expedient.
Master thesis Page 79
Povilas Pocius Functional surfaces in mechanical handling of microparts
LBM – Screw
Chamfer profile of screw.
Evaluation of handling operation while using chamfer surface of a screw head with a LBM
gripper. (Theoretical touching surface of a rectangle. See Chapter 3)
Load number 15.
During handling operations chamfer surface of microscrew head with LBM gripper stickiness
not occurred most of the times. (see Table 6.14). Mostly this happened due to adhesive force
influence. At the same time light deformation of the gripper functional surfaces took place,
due to hard microscrew material and soft gripper surface. This means that functional surface
area increased slightly from nominal.
Table 6.14
1 2 Mean value St.DevFirst position 90 60 75,0 21,2Second position 60 66 63,0 4,2
69,0 14,3
Stiching occasion 0
Chamfer screw surface
Operation lineCorrect operation %
Of all positions
LBM - micro-screw (chamfer)
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
1 2
Position in each line
Rel
ease
, %
load 15load 20load 25
Figure 6.7 LBM-micro-screw (chamfer).
Master thesis Page 80
Povilas Pocius Functional surfaces in mechanical handling of microparts
Load number 20.
Stickiness occurrence not frequency between chamfer surface of microscrew of head and
LBM gripper remained on the same level during handling operations with load number 20, if
compared to ones with load number 15. (see Table 6.15). But due to the aforementioned
differences in material hardiness of microscrew and grippers the level of gripper surface
deformation has greatly increased. The total touching surface area increased respectively.
Increase in the total touching surface and the unchanged level of stickiness shows us that
adhesive force influence has reduced. This happened due to increase of touching surface
profile error and roughness, because each microscrew makes handling process scratches or
deformation.
Table 6.15
1 2 Mean value St.DevFirst position 80 77 78,5 2,1Second position 70 60 65,0 7,1
71,8 8,9
Stiching occasion 1
Chamfer screw surfaceCorrect operation %
Operation line
Of all positions
Load number 25.
Frequency of stickiness occurrence between chamfer surface of microscrew head and LBM
gripper has reduced during handling operations with load number 25, when compared to
previous loads. Adhesive force influence was not recorded. This can be explained by high
level of set deformation occurring due to high pressure on the small surface. After that the
gripper surface “received” form of wear scar, shaped as the head of the microscrew. (see
Table 6.16).
Table 6.16
1 2 Mean value St.DevFirst position 70 50 60,0 14,1Second position 77 50 63,5 19,1
61,8 13,9
Stiching occasion 1
Chamfer screw surfaceCorrect operation %
Operation line
Of all positions
Master thesis Page 81
Povilas Pocius Functional surfaces in mechanical handling of microparts
Furthermore, due to positioning error and increased roughness of the gripper’s functional
surfaces, gripper had less touching with microscrews surface. Wear scar radius became
greater than the microscrew head and their contact surface was due to peak of roughness. This
explains the low level of stickiness and inexistent adhesive force effect.
Conclusion. The increased surface deformation during trials with load 25 has reduced the
influence of the adhesive force. In the following operations screw handling error margin
became even higher.
Cylindrical profile of screw with LBM gripper functional surface
Evaluation of handling operation while using cylindrical surface of screw head with a LBM
gripper (theoretical touching profile line. See Chapter 3.2.)
For this experiment the positioning coordinates in the gripper operating program were
changed, due to deformation caused to the LBM gripper by previous operations with the
chamfer surface of microscrews. The coordinates for the functional surface of LBM gripper’s
contact with the microscrew were moved by 0.75mm from the original gripper axis. This
could be done, because the width of functional surface of the LBM gripper is 2mm. In
essence this means that a “new” gripper surface was used for the experiment, in order to
avoid influence of the deformation caused by the previous experiment. (see picture 6.5 below)
Picture 6.5 LBM gripper functional surface after the handling operation
Master thesis Page 82
Povilas Pocius Functional surfaces in mechanical handling of microparts
Load number 15.
During handling operations cylindrical surface of microscrew head with LBM gripper
percentage of error while handling the microscrew after the first position in the line was very
high (%). However when the handling process was proper neither stickiness, nor adhesive
force influence was observed. This can be explained by very small touching surface size.
During the course of this operation some level of gripper LBM surface deformation occurred.
This effect was similar to the one described in the above section regarding the chamfer
surface of the microscrew. (see Table 6.17).
Table 6.17
1 2 Mean valueSt.DevFirst position 70 60 65,0 7,1Second positio 80 88 84,0 5,7
74,5 12,2
Stiching occasion 2
Cylindrical screw surfaceCorrect operation %
Operation line
Of all positions
LBM - micro-screw (cylindrical)
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
1 2
Position in each line
Rel
ease
, %
load 15load 20
Figure 6.8 LBM-microscrew (cylindrical).
Load number 20.
During handling operations cylindrical surface of microscrew head with LBM gripper
percentage of error while handling the microscrew after the first position in the line was even
Master thesis Page 83
Povilas Pocius Functional surfaces in mechanical handling of microparts
higher (%). Handling of cylindrical microscrew has become much more difficult, due to
increase in LBM gripper surface deformation with this load.
In continuation of the same experiment handling it has become virtually impossible to
successfully grab and move the microscrew, as the microscrew was slipping out of the gripper
all the time. (see Table 6.18).
Table 6.18
1 2 Mean valueSt.DevFirst position 55 50 52,5 3,5Second positio 40 48 44,0 5,7
48,3 6,2
Stiching occasion 0
Cylindrical screw surfaceCorrect operation %
Operation line
Of all positions
Further operations with load number 25 were not performed, due to anticipated high level of
further deformation of the LBM gripper surfaces without positive handling results.
Conclusion. LBM gripper surface is insufficient for grabbing the cylindrical surface of the
microscrew, due to too small touching area. For this reason frequent slipping was observed.
Friction coefficient is very small and adhesive force effects were not observer. Also the level
of deformation caused to the functional surface of the LBM gripper while operating
cylindrical surface of the microscrew was higher than the one caused with the same loads
while operating the chamfer surface of the microscrew.
EDM vertical modified functional gripper surface with plastic specimen.
This experiment was performed in order to evaluate influence of EDM (electro-discharge
machining) in vertical direction (See Chapter 4.3) gripper surface on handling operations with
plastic specimens.
The same “hole” plane plate was used for this experiment, as the one used for grippers with
plane surface.
Master thesis Page 84
Povilas Pocius Functional surfaces in mechanical handling of microparts
Load number 15.
In the course of this experiment handling operations with plastic specimen by EDM vertical
gripper functional surface showed very good results. Handling was correct and precise both
with holding and releasing the plastic specimen, though sticking effect occurred just a one
times. (see Table 6.19).
Table 6.19
1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 90 90 100 88 92,0 5,4Third 80 70 90 77 79,3
90,4 10,3
Stiching occasion 1
Ope
ratio
n
posi
tions
Of all positions
Correct operation percentage in all positions %Operation line on the position plate
EDMvert. - plastic specimen (load number 15)
8,3
EDMvert. - plastic specimen
40,0
60,0
80,0
100,0
1 2 3
Position in each line
Rel
ease
, %
load 15load 20load 25
Figure 6.9 EDM vertical-plastic specimens
Load number 20.
Handling operations were similar with load number 20 with even smaller number of handling
errors, compared to load number 15. (see Table 6.20).
Table 6.20
Master thesis Page 85
Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 100 90 100 90 95,0 5,8Third 90 80 90 88 87,0
94,0 6,8
Stiching occasion 0
Ope
ratio
n
posi
tions
Of all positions
Operation line on the position plate
EDMvert. - plastic specimen (load number 20)
Correct operation percentage in all positions %
4,8
Load number 25.
During handling operations with load 25 the error margin during the release phase of the
handling operation was higher than with the previous loads (see Table 6.21).
Table 6.21
1 2 3 4 Mean value St.DevFirst 100 100 100 100 100,0 0,0Second 90 88 77 77 83,0 7,0Third 80 70 66 70 71,5
84,8 13,1
Stiching occasion 0
Ope
ratio
n
posi
tions
Of all positions
EDMvert. - plastic specimen (load number 25)
Correct operation percentage in all positions %Operation line on the position plate
6,0
At the moment of the release by gripper plastic specimen fell down out of “hole” position.
This can be explained by tension force of the plastic specimen generated due to high pressure
load of the EDM surface of the gripper. Theoretically in this case the tension force of the
specimen should be equal values and moving in opposite (180o) direction. In our case the
micro-peaks on the parallel gripper surfaces made by EDM are not aligned with each other
(See Picture 6.6 below).
Master thesis Page 86
Povilas Pocius Functional surfaces in mechanical handling of microparts
FSTFT
FT
∑∑→→
≠ STST FF FSTFT
FT
∑∑→→
= STST FF
FST FT
FTFT
FT
Picture 6.6 Representation of how tension force is generated
These micro-peaks generate tension force to different directions. The summary tension forces
in both sides are not parallel with each other, due to this fact the plastic specimen did not fall
down straight into the position hole.
Conclusion. Handling plastic specimen with EDM vertical surface gripper shows very good
results and repeatability. We can conclude that EDM vertical surface gripper provided the
best results out of the gripper surfaces used this far in the experiments. For this gripper
surface type the optimal load force number is 20. With EDM vertical surface only light
adhesive force influence was observed with load number 15, but in load number 20 that was
made obsolete with light tension force. Load number 25 is too high for this type of gripper
functional surface due to occurring undesirable force (tension force etc).
EDM vertical modified functional gripper surface with micro-screw.
This experiment was performed in order to evaluate influence of EDM (electro-discharge
machining) in vertical direction (See Chapter XX) gripper surface on handling operations
with microscrew. During this experiment the external temperature in the robot room was
21.1oC and humidity level was 50%.
Master thesis Page 87
Povilas Pocius Functional surfaces in mechanical handling of microparts
Chamfer profile of screw with EDM vertical surface gripper.
Evaluation of handling operation while using chamfer surface of microscrew head with an
EDM vertical modified gripper surface.
Load number 15.
The experiment with handling operations with chamfer surface of microscrew by EDM
vertical gripper showed quite good results with both grabbing and holding percentages
(62,0%). However the margin of correct releases was very low due to high stickiness level (9
times). (see Table 6.22). After occurrence of such stickiness the operator had to stop the
handling program and to remove the microscrew from the gripper functional surface. Set
deformation appeared on the peaks of EDM vertical surfaces of the gripper, where chamfer
area of the peaks was completely smashed.
Table 6.22
1 2 Mean value St.DevFirst position 90 80 85,0 7,1Second position 30 48 39,0 12,7
62,0 27,9
Stiching occasion 9
Operation line
Of all positions
Correct operation %Chamfer screw surface
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Povilas Pocius Functional surfaces in mechanical handling of microparts
EDMvert. - micro-screw (chamfer)
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
1 2
Position in each line
Rel
ease
, %load 15load 20
Figure 6.10 EDM vertical-microscrew (chsmfer).
Load number 20.
The handling with load number 20 showed better results compared to those with load number
15. This was especially significant during the release phase of the operation, as the stickiness
effect has disappeared. However it became more difficult for the gripper to hold and raise the
microscrew in the beginning of the operation due to increased heavy damage to the EDM
vertical modified surface. (see Table 6.23).
Table 6.23
1 2 Mean value St.DevFirst position 50 50 50,0 0,0Second position 55 48 51,5 4,9
50,8 3,0
Stiching occasion 1
Of all positions
Chamfer screw surfaceCorrect operation %
Operation line
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Povilas Pocius Functional surfaces in mechanical handling of microparts
Cylindrical profile of screw with EDM vertical surface gripper.
Evaluation of handling operation while using cylindrical surface of microscrew head with an
EDM vertically modified gripper surface.
In the same way, as with the experiments performed with LBM surface gripper (See above),
the level of deformation sustained during experiments with chamfer surface of the
microscrew was too heavy. Analogically the coordinates for the functional surface of EDM
vertical gripper’s contact with the microscrew were altered by 0.75mm.
Load number 15.
The experiment with handling the cylindrical surface of the microscrew had fewer stickiness
occurrences than respective experiment with chamfer surfaces (See Table 6.24). The lower
level of stickiness can be explained by relatively smaller touching area of the cylindrical
microscrew surface compared to the chamfer one. At the same time the number of errors with
holding was about the same.
Table 6.24
1 2 Mean valueSt.DevFirst position 60 44 52,0 11,3Second positio 30 21 25,5 6,4
38,8 17,0
Stiching occasion 3
Of all positions
Cylindrical screw surfaceCorrect operation %
Operation line
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Povilas Pocius Functional surfaces in mechanical handling of microparts
EDMvert. - micro-screw (cylindrical)
20,0
25,0
30,0
35,0
40,0
45,0
50,0
55,0
1 2
Position in each line
Rel
ease
, %load 15load 20
Figure 6.11 EDM vertical microscrew (cylindrical).
Load number 20.
Handling operation with EDM vertical surface gripper and load number 20 on cylindrical
surface of microscrew showed worse results than those shown with load number 15 for same
surface, as well as number 20 with chamfer surface of the microscrew. This is explained by
heavy deformation, as after several repeated handling operations the gripper functional
surface was no longer functional, e.g. handling operation could no longer be performed. (see
Table 6.25).
Table 6.25
1 2 Mean valueSt.DevFirst position 55 37 46,0 12,7Second positio 20 44 32,0 17,0
39,0 14,7
Stiching occasion 3
Of all positions
Operation line
Cylindrical screw surfaceCorrect operation %
Note on load number 25.
In cases with both chamfer and cylindrical surfaces of microscrew further operations with
load number 25 were not performed, due to anticipated high level of further deformation of
the EDM vertical gripper surfaces without improved handling results.
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Povilas Pocius Functional surfaces in mechanical handling of microparts
Conclusion. Best results were showed in experiments with chamfer surface of the microscrew
and load number 20, as well as cylindrical microscrew surface and load number 15. In general
usage of EDM vertical modified gripper surface is not suitable for handling microscrews in
all possible ways. There is large difference in hardiness of metals and the fragile triangular
peaks of EDM surface are easily destroyed.
For this reason usage of EDM gripper surface modification on such metal type during
microscrew handling operations is too expensive and not reasonable.
Cylindrical profile surface gripper and plastic specimen
No handling experiments with cylindrical profile surface gripper and plastic specimen,
because no expedience to increase tacking surface area for handling operation of the plastic
micro-specimen. Also the diameter of gripper cylindrical functional surface and plastic
specimen not related.
Cylindrical profile surface gripper with micro-screw.
All dimensions and reason for this experiment was explained in chapter 4. Cylindrical profile
of the surface gripper is made with the same radius as the diameter of microscrew. Because of
that gripper with this surface type can only be used in experiments with microscrews and not
with plastic specimens. In order to properly handle the microscrews this gripper needs to be
especially properly aligned.
Alignment of two cylindrical profile functional surfaces of gripper.
Two cylindrical profile functional surfaces of gripper must be aligned to each other in order
for gripper to properly grab the specimen. These surfaces must be parallel to each other to
avoid premature release of the specimen and radius centers on cylindrical curves must be in
the same point. Also the lower ends of the grippers must be on the same level, e.g. z-axis’
value of these ends must be equal in order for gripper to touch plate properly.
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Povilas Pocius Functional surfaces in mechanical handling of microparts
In order to achieve the abovementioned conditions the operator must perform the following
steps:
1) Gripper is lightly fixed with screws to the robot jaws
2) Take a bore with the same diameter as the cylindrical microscrew profile
3) A hole in position plate is covered with multiple levels.
4) The bore is put through the tape and thereby fixed vertical position. The tape makes it
possible to move the bore in all three axes
5) Two G-blocks are placed on both sides of the bore tip
6) Grip closes with high load and the bore is held tightly by it. Due to lightly fixed
screws and automatic force control (constant load) this action aligns the gripper
functional surfaces in planar positions
7) Gripper moves carefully down in z-axis direction to the two G-blocks put on the plate.
This sets the gripper tips on the parallel level with the position hole plate
8) The screws are then tightened in this two alignment positions
All further experiment preparation procedures are the same as in the previous experiment. To
reduce manufacturing uncertainty of gripper all positions of holes on the plate must be
checked and corrected in the position list of the handling program by the operator.
Experiment cylindrical profile surface gripper with microscrew.
Load number 15.
During the experiment with cylindrical profile surface gripper and microscrew handling
operation frequent errors were observed in grabbing and holding phases of the process. Upon
release of the screw stickiness occurred frequently (10 times). (see Table 6.26). The two
possible reasons for such large amount of errors are:
• Theoretically large touching area, compared to the previous experiments
• Possible error in radius of cylindrical gripper profile or in diameter of microscrews
No deformation to the gripper surface was observed.
Table 6.26
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Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 Mean value St.DevFirst position 50 60 55,0 7,1Second position 20 24 22,0 2,8
38,5 19,6
Stiching occasion 10
Operation line
Of all positions
Cylindrical screw surfaceCorrect operation %
Cylindrical func. surface - micro-screw
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
1 2
Position in each line
Rel
ease
, %
load 15load 20
Figure 6.12 Cylindrical functional surface –microscrew.
Load number 20
In comparison with the previous, lighter load this handling experiment provided superior
results, especially in holding procedure. However the level of stickiness to the cylindrical
surface of the gripper has increased.
This can be the effect of higher load, which negated the influence of errors in radius of
cylindrical gripper profile and in diameter of microscrews.
Another reason for that is the deformation of cylindrical gripper surface. As a result the
microscrews in handling started rotating under the load force thus increasing their touching
surface with the touching surface of the gripper and by that stabilize the position in the hold.
This supported the stickiness effect. (see Table 6.27).
Table 6.27
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Povilas Pocius Functional surfaces in mechanical handling of microparts
1 2 Mean value St.DevFirst position 80 88 84,0 5,7Second position 55 40 47,5 10,6
65,8 22,2
Stiching occasion 12
Of all positions
Correct operation %Operation line
Cylindrical screw surface
Conclusions
• Handling microscrews with cylindrically surfaced gripper was best with load number
15
• The large circular touching area did not guarantee the microscrew turning away from
the original axis
• Too large touching surface proves to have negative effect on handling operation in
form of high stickiness level
• The soft gripper material was relatively quickly and lightly deformed allowing the
screw to turn into erroneous position
• Using cylindrically surfaced gripper made of this kind of material for handling
microscrews is inefficient
Existing gripper
The existing gripper is the griper, which was built at IPL by supervision of Asta Gegeckaite.
And used in all the previous experiments before this project. For more information about it
see in the chapter 4.
Existing gripper evaluation test is performed in order to ascertain the existing relevance
degree of gripper for micro-handling process with samples that interest us. Also to compare
how much the handling process has improved or worsened while leveling with newly
produced and modified functional surfaces of grippers. Existing gripper handling operation
experiment with plastic micro-specimen was performed applying the analogous procedure as
for the experiment of grippers of new design.
Experiment with existing gripper surface with load number 15 and plastic specimens showed
results with a high number of errors (30.6%). (see Table 6.28).
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Povilas Pocius Functional surfaces in mechanical handling of microparts
Table 6.28
1 2 3 4 Mean value St.DevFirst 80 90 90 80 85,0Second 70 60 70 70 67,5 5,0Third 55 48 60 60 55,8
69,4 13,5
Stiching occasion 4
Ope
ratio
n
posi
tions
Operation line on the position plate
Of all positions
Correct operation percentage in all positions %
5,8
5,7
Existing gripper - plastic specimen
40,0
60,0
80,0
100,0
1 2 3
Position in each line
Rel
ease
, %
load 15load 20load 25
Figure 6.13 Existing gripper-plastic specimen
The test was performed on the same position “hole” plates as in the analogous experiments.
In this case, the results have shown that gripping mistakes occur at the moment of holding
operation. Plastic specimen stickiness to the existing gripper surface is possible to explain by
too great touching surface influencing gripper functional surfaces geometry. It is of triangle
shape with the cut with 130 degrees angle, thus while taking the element it touches to four
planes of the gripper (see picture 6.7). This increases the grabbing area by a long way
comparing with the flat surface of the gripper.
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Povilas Pocius Functional surfaces in mechanical handling of microparts
Picture 6.7 Functional surface of existing gripper
Some mistakes were observed at the point of release operation: the tested micro-object falls
out at a wrong time. One presumes that electrostatic and van der Waals forces might
contribute to this. Their total values are not sufficient to ensure stable stickiness effects to the
gripper functional surface, but are enough to offset the influence of the elasticity force of the
specimen.
The experiment, using the robot load number 20, is performed in the same way as the
previous one. The results demonstrated that the handling operation is performed in a much
more exact way.
Repeatability of holding operation from the first position in each line was at the 100% level
during the experiment. However, there were mistakes in the second and third operation
positions. Also, several cases were observed with the stickiness effect. This can be explained
by the increased influence of the adhesive force. When the squeezing force is bigger, the
elastic plastic specimen deforms which leads to an increased touching surface between it and
the gripper surface and the reduction of roughness. That leads to the increase of van der
Waals and surface tension force and its influence to the micro-specimen handling operation.
(see Table 6.29).
Table 6.29
1 2 3 4 Mean value St.DevFirst 90 90 90 80 87,5Second 60 50 55 50 53,8 4,8Third 50 50 60 66 56,5
65,9 16,9
Stiching occasion 6
Of all positions
Ope
ratio
n
posi
tions
Correct operation percentage in all positions %Operation line on the position plate
5,0
7,9
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Povilas Pocius Functional surfaces in mechanical handling of microparts
The experiment, using the robot load number 25, showed that results were poorer compared
with the load number 20 test. Due to the increased influence of the forces, mentioned in the
description of the previous experiment, the number of mistakes grew, and the influence of the
stickiness effect was observed more frequently. (see Table 6.30).
Table 6.30
1 2 3 4 Mean value St.DevFirst 90 80 90 80 85,0Second 40 50 48 55 48,3 6,2Third 44 38 50 42 43,5
58,9 20,0
Stiching occasion 11
Ope
ratio
n
posi
tions
Of all positions
Operation line on the position plateCorrect operation percentage in all positions %
Existing gripper - plastic specimen (load number 25)
5,8
5,0
The plastic specimen stickiness with existing gripper surface can be explain due to
immoderate touching surface area with four points gripper functional surfaces.
Micro-screw handling operation with existing gripper experiment was performed applying the
same methodology and on the analogous hole position plate. Experiments of the load number
15 and 20 showed the analogous results, thus here they are analyzed together. Results
indicated that only 3 operations out of 40 were successful. This is explained by the total
variance of geometrical functional surfaces of both gripper and micro-screw. From the
viewpoint of geometrical sense the common grabbing of gripper of lozenge profile totally
misfits the grabbing of chamber micro-screw surface. The grabbing of micro-screw of
cylindrical surface is possible only under certain favorable conditions. These conditions mean
that the micro-screw position, to be precise, the turning of micro-screw cap has to be ideally
proportional regarding the existing functional surface of the gripper.
In opposite case the different asymmetric forces will affect the functional surfaces of the
gripper. Knowing that the width of grabbing surfaces is very small, alignment of micro-screw
xy plane is very easily vulnerable. And in this case it is overbalanced by the affecting
asymmetric forces, thus the micro-screw merely slips out of the existing gripper functional
Master thesis Page 98
Povilas Pocius Functional surfaces in mechanical handling of microparts
surface. In this way the impropriety of the existing gripper for the micro-screw handling
operation is explained.
Conclusion is that existing gripper with its triangle functional surface misfits for the plastic
specimen handling operation because of too great area of the touching surface. Thus too great
adhesive forces having negative influence for handling operation operate there. But this
geometrical solution of form of functional surface of existing gripper has it own advantages.
Grabbing by four points on the cylindrical or spherical surfaces performs the automatic
alignment of position (that is very important). (see Picture 6.8)
Picture 6.8 Geometrical solution
Also after the automatic alignment the grabbing of the object is performed by four
symmetrical points (when the specimens are cylindrical or spherical surfaces) with regard to
each other and applying the proportional forces. This means that if there is a different
structure or material of functional surface of existing gripper when influence of van der
Waals, electrostatic and surface tension forces is decreased to minimum, then it would the
optimal solution from the geometrical point of view for handling operation specimens with
cylindrical or spherical surfaces. Existing gripper with its own triangle functional surface
totally misfits the micro-screw handling operation because of the geometrical inadequacy.
The modification of surface or selection of other material would not solve the problem of the
micro-screw handling. It would require the functional surface of gripper of totally other
design and geometry.
Master thesis Page 99
Povilas Pocius Functional surfaces in mechanical handling of microparts
50
60
70
80
90
100
LM EDM Plane-Polished
Plane-Rough Existing
Functional surface
Rel
eas
(%)
load nr 15load nr 20load nr 25
0
10
20
30
40
50
60
70
80
90
LBMchamfer
LBMcylind
EDMchamfer
EDMcylind
Cylindrical Plane-Polishedchamfer
Plane-Polishedcylind
Plane-Rough
chamfer
Plane-Roughcylind
Functional surface
Real
es (%
)
load nr 15load nr 20load nr 25
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Povilas Pocius Functional surfaces in mechanical handling of microparts
7. Conclusion
Analysis of functional surfaces for mechanical handling of microparts was presented in theis
thesis. In was done in order to evaluate the impact of tacking surface area ration and different
surface parameters. These parameters can strongly affect the functional behaviour of handling
process of microobjects. For this reason it is a need to develop different techniques for
surface modifications.
These grippers were important to be investigate, as the ones working at the macroscale,
cannot be used in the microscale
Design, mathematical modelling and surface structure of griper grasping parts are developed
in order to avoid or decrease influence of surface, material and motion.
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Povilas Pocius Functional surfaces in mechanical handling of microparts
References
1. Petrovic, D., Popovic, G., Chatzitheodoridis, E., Medico, O., Almansa, A., Sümecz, F., Brenner, W., Detter, H. 2002 Gripping tools for handling and assembly of microcomponents Proc. 23rd. International conference on microelectronics (Miel 2002), Vol. 1., Yugoslavia, 12-15 May 247- 250
2. Petrovic, D., Popovic, G., Chatzitheodoridis, E., Del Medico, O., Almanasa, A., Detter, H., Brenner, W. 2001 Mechanical gripper system for handling and assembly in MEMS Micromachining and microfabrication process technology VII. SPIE P. 151-155
3. Bleuler H., Clavel R., Breguet J., Langen H., Belleouard Y. 2001 Applications of microrobotics and microhandling First Japan-Switzerland Bilateral Symposium on Science and Technology in Micro/Nano Scale issue 36 26-28 microrobotics and microhandling
4. Fearing R.S., 1995 Survey of Sticking effects for micro parts handling IEEE 212-217
5. Zhou Y., Nielson B.J. 1998 Adhesion force modeling and measurement for micromanipulation Part of SPIE Conference on microrobotics and micromanipulation 169-180
6. Weck, M., Petersen, B. 2001 Adhesion problems during handling of micro parts- vibration assisted release of objects Euspen international conference 148-151
7. Dechev, N., Cleghorn, W.L., Mills, J.K. 2004 Microassembly of 3-D microstructures using a compliant, passive microgripper Juornal of microelectronical systems, vol. 13, no.2 176-189
8. Development of tools for handling and assembling microcomponents J Ansel, Y., Schmitz, F., Kunz, S., Gruber, H.P., Popovic, G. 2002 . Micromech. Microeng. 12 430- 437
9. Austin, B.M. 1969 Handling miniature parts; Automation 66-69 micohandling 10. Alting L., Kimura, F., Hansen H.N., Bissacco G. 2003 Micro engineering Annals
of CIRP vol. 2003 11. López-Sáncez, J., Miribel- Catala, P., Montare, E., Puig- Vidal, M., Bota, S.A.,
Samitier, J. 2001 High accuracy piezoelectric- based microrobot for biomedical applications IEEE 603- 609
12. Miller A.T. Allen P.K. 2004 Grasp it! A versatile simulation for robotics grasping IEEE 110-122
13. Fleischer, J., Bouchholz, C., Weule, H. 2003 Automation of the powder injection moulding process for micro mechanical parts Annals of the CIRP Vol. 52/1 419- 422
14. Rollot Y., Régnier S., Giunot J.C. 1999 Simulation of micro-manipulations: adhesion forces and specifics dynamics models International journal of adhesion and adhesives nr. 19 35-48
15. Liu Y., Starr G., Lumia W.R. 2005 Spatial grasp synthesis for complex objects using model-based simulation Industrial robot: an international journal 24-31
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16. Ikonomopoulos A., Dritsas L., Force control in Robot Finishing, Proc. of 25th ISIR, Hanover, Germany, 1995
17. Shim S., Kramer B., A Force-controlled Approach to Robotics Deburring, ASME Press, New York, 1988
18. Whitney D. E., Quasi-static Assembly of compliantly Supported Rigit Parts, Trans. ASME I. Dyn. Syst. Meas Control, 104. (3), 1982, pp. 65-77.]
19. Shahinpoor, M., A Robot Engineering Textbook, Harper and Row, Publishers, New York, 1987.
20. J. K. Salisbury and B. Roth, "Kinematic and force analysis of articulated mechanical hands," J. Mech. Transmiss. Automat, in Des., vol. 105, pp. 35-41, Mar. 1983
21. W. Holzmann and J. M. McCarthy, "Computing the friction forces associated with a three fingered grasp,'' in Proc. 1985 IEEE Con/, on Robotics and Automation (St. Louis, MO, 1985), pp. 594-600. Also IEEE J. Robotics Automat., vol. RA-1, pp. 206-221, Dec. 1985.
22. C. A. Klein, K. W. Olson, and D. R. Pugh, "Use offeree and altitude sensors for locomotion of a legged vehicle over irregular terrain," I, 1983.
23. R. B. McGhee and D. E. Orin, "A mathematical programming approach to control of joint position and torques in legged locomotion systems," in Theory and Practice of Robots and Manipulators, A. Morecki and K. Kedzior, Eds. New York, NY: Elsevier, 1977, pp. 225-232.
24. K. J. Waldron, "Force and motion management in legged locomotion, IEEE J. Robotics Automat., vol. RA-2, no. 4, pp. 214-220, Dec. 1986.
25. K. H. Hunt, Kinematic Geometry of Mechanisms. Oxford, UK:Clarendon Press, 1978.
Master thesis Page 103
Apendix content: WRITE HEADING 1....................................................................................................................................................... II
PLANE SURFACE (ROUGH) ................................................................................................................................ II EXISTING GRIP (ALL SURF)............................................................................................................................... III EXISTING GRIP (SMALL AREAS) .......................................................................................................................IV LBM SURFACE WITHOUT POLISHING (ALL SURF) ..........................................................................................V LBM SURFACE WITHOUT POLISHING (SMALL AREAS) .................................................................................VI LBM SURFACE POLISHED (ALL SURF)............................................................................................................VII LBM SURFACE POLISHED (SMALL AREAS)...................................................................................................VIII EDM VERTICAL SURFACE (ALL SURF).............................................................................................................IX EDM VERTICAL SURFACE (SMALL AREAS)......................................................................................................X CYLINDRICAL SURFACE (ALL SURF) ...............................................................................................................XI PLANE SURFACE POLISHED (ALL SURF) .......................................................................................................XII
WRITE HEADING 1....................................................................................................................................................XIII LBM – PLASTIC SPECIMEN..............................................................................................................................XIII LBM – MICRO-SCREW..................................................................................................................................... XIV EDMVERT. - PLASTIC SPECIMEN ................................................................................................................... XV EDMVERT. - MICRO-SCREW........................................................................................................................... XVI CYLINDRICAL FUNCTIONAL SURFECE........................................................................................................ XVII PLANE-POLISHED - PLASTIC SPECIMEN.................................................................................................... XVIII PLANE-POLISHED - MICRO-SCREW.............................................................................................................. XIX PLANE-ROUGH - PLASTIC SPECIMEN ........................................................................................................... XX EXISTING GRIPPER - PLASTIC SPECIMEN.................................................................................................. XXII EXISTING GRIPPER - MICRO-SCREW ......................................................................................................... XXIII
WRITE HEADING 1
Plane surface (rough) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1145 1254 1177 1195 1205 1195,2 40,01 Sq [nm] 1385 1484 1405 1396 1455 1425 42,49 Ssk 0,0663 0,0446 0,0643 0,0553 0,0601 0,05812 0,01 Sdr % 3,94 4,1 4 4,2 3,84 4,016 0,14 Spk [nm] 1349 1202 1349 1349 1349 1319,6 65,74 Sk [nm] 3965 4215 3995 3785 4365 4065 226,83
Svk [nm] 800 746 810 804 780 788 26,04
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1164 1168 1214 1150 1210 1181,2 28,93 Sq [nm] 1389 1381 1348 1421 1358 1379,4 28,59 Ssk -0,165 -0,145 -0,151 -0,148 -0,154 -0,1526 0,01 Sdr % 2,5 2,22 2,35 2,2 2,3 2,314 0,12 Spk [nm] 1428 1095 1227 1295 1287 1266,4 120,71 Sk [nm] 3474 3423 3488 3412 3444 3448,2 32,45
Svk [nm] 1229 1192 1212 1183 1210 1205,2 18,05
Existing grip (all surf) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1497 1294 1304 1340 1471 1381,2 95,83 Sq [nm] 1883 1672 1848 1741 1683 1765,4 95,87 Ssk -0,0686 0,18 0,051 0,14 -0,02 0,05648 0,10 Sdr % 7,02 4,02 5,35 6,2 4,3 5,378 1,26 Spk [nm] 1883 1862 1827 1895 1887 1870,8 27,35 Sk [nm] 4802 4811 4488 4512 4344 4591,4 206,63
Svk [nm] 2158 2131 2212 2183 1910 2118,8 120,51
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 1026 768 1014 850 810 893,6 119,05 Sq [nm] 1368 978 1148 1021 1199 1142,8 154,83 Ssk 0,622 0,623 0,524 0,553 0,708 0,606 0,07 Sdr % 4,3 2,3 2,95 3,2 4,1 3,37 0,83 Spk [nm] 2216 1516 1527 2195 1857 1862,2 342,12 Sk [nm] 2863 2346 2488 2612 2700 2601,8 197,71
Svk [nm] 1369 761 1112 1183 910 1067 237,16
Existing grip (small areas) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 479 398 427 448 425 435,4 30,15 Sq [nm] 655 550 601 590 612 601,6 37,94 Ssk 0,215 0,476 0,284 0,366 0,401 0,3484 0,10 Sdr % 1,56 1,34 1,5 1,41 1,39 1,44 0,09 Spk [nm] 1036 939 1011 983 949 983,6 40,88 Sk [nm] 1319 1142 1340 1101 1228 1226 105,27
Svk [nm] 831 569 801 562 760 704,6 129,48
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev Sa [nm] 891 724 789 812 825 808,2 60,44 Sq [nm] 1182 884 1008 943 1113 1026 121,74 Ssk 0,0809 0,477 0,342 0,105 0,376 0,27618 0,17 Sdr % 2,89 1,43 1,34 2,5 2,64 2,16 0,72 Spk [nm] 1632 1080 1458 1514 1109 1358,6 249,35 Sk [nm] 2536 2232 2337 2520 2302 2385,4 135,67
Svk [nm] 1422 477 887 946 1102 966,8 343,58
LBM surface without polishing (all surf) Measuring values [nm] [nm] Surface
parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 5179 4768 4018 4850 3920 4547 551 Sq [nm] 6604 5974 5142 6021 5349 5818 583 Ssk 0,0568 0,152 0,278 0,0539 0,178 0,14374 0,09 Sdr % 22,8 2,3 2,95 3,2 4,1 7,07 8,82 Spk [nm] 8177 7216 6927 8026 7852 7639,6 540,94 Sk [nm] 15700 12486 12518 14212 13709 13725 1335,10
Svk [nm] 6212 5765 4178 5133 4945 5246,6 782,07
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 3082 4079 3141 3210 3367 3375,8 407,28
Sq [nm] 3782 3210 4242 4079 4352 3933 457,68 Ssk -0,811 -0,121 0,278 0,041 -0,231 -0,1688 0,41 Sdr % 12,3 10,1 7,95 13,2 16,3 11,97 3,16 Spk [nm] 3418 2516 3227 3698 4151 3402 605,08 Sk [nm] 8761 8414 6218 11210 8711 8662,8 1770,53
Svk [nm] 4475 4178 3165 5121 4692 4326,2 734,51
LBM surface without polishing (small areas) Measuring values [nm] [nm] Surface
parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 3126 2646 4000 2812 3226 3162 524 Sq [nm] 4128 3327 4957 3943 4153 4102 583 Ssk 0,746 0,527 0,737 0,525 0,676 0,6422 0,11 Sdr % 20,6 14,8 16,8 2,5 2,64 11,468 8,39 Spk [nm] 8549 5110 8331 7214 8009 7443 1399 Sk [nm] 7460 7275 10473 8520 8202 8386 1275
Svk [nm] 3388 1838 1731 2446 2100 2301 668
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 2592 3491 2646 3126 2817 2934,4 374,40 Sq [nm] 3372 4824 3327 3327 3943 3758,6 650,21 Ssk -1,15 -1,95 0,527 -0,68 0,746 -0,5014 1,14 Sdr % 15,3 20,3 14,8 17,2 15,9 16,7 2,20 Spk [nm] 3086 1328 5110 2573 3497 3118,8 1379,66 Sk [nm] 6040 5930 7275 6824 6192 6452,2 575,66
Svk [nm] 5589 10214 1838 4485 6731 5771,4 3074,79
LBM surface polished (all surf) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 485 478 479 398 512 470,4 42,77 Sq [nm] 862 836 755 712 894 811,8 75,91 Ssk -4,98 -2,84 0,284 -1,62 0,476 -1,736 2,28 Sdr % 1,26 1,41 0,0246 1,34 2,4 1,28692 0,84 Spk [nm] 1134 1242 1011 983 1036 1081,2 106,37 Sk [nm] 1266 1142 1340 1298 1228 1254,8 75,32
Svk [nm] 1446 1395 1516 1435 1527 1463,8 56,12
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 786 894 679 755 812 785,2 78,66 Sq [nm] 1196 1242 1136 1145 1011 1146 86,66 Ssk -3,61 -2,84 0,954 -2,62 -0,432 -1,71 1,90 Sdr % 2,84 3,41 0,848 2,54 3,54 2,64 1,08 Spk [nm] 1076 1042 1671 987 9,26 957,05 597,97 Sk [nm] 2193 1842 2140 2298 1947 2084 185,84
Svk [nm] 1905 2195 1716 1853 2159 1965,6 205,35
LBM surface polished (small areas) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 339 340 287 331 398 339 39,53 Sq [nm] 425 422 358 452 470 425,4 42,58 Ssk 0,254 0,343 0,215 0,348 0,284 0,2888 0,06 Sdr % 0,814 0,811 1,34 0,544 0,734 0,8486 0,30 Spk [nm] 721 870 892 765 741 797,8 77,92 Sk [nm] 1042 1136 1011 1198 1036 1084,6 79,21
Svk [nm] 324 305 284 365 287 313 33,19
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 705 606 699 768 679 691,4 58,22 Sq [nm] 895 782 888 812 864 848,2 49,29 Ssk -0,435 -0,7 2,68 0,0243 0,457 0,40526 1,35 Sdr % 2,47 2,09 1,34 2,21 1,94 2,01 0,42 Spk [nm] 995 821 1023 874 995 941,60 88,66 Sk [nm] 2093 1753 2077 1843 1942 1941,60 147,09
Svk [nm] 1015 1069 1140 1097 1014 1067,00 54,19
EDM vertical surface (all surf) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 1984 1888 1915 2153 1810 1950 129,45 Sq [nm] 2242 2478 1975 2121 2199 2203 184,30 Ssk -0,0542 -0,0864 0,0524 -0,214 0,08 -0,04444 0,12 Sdr % 5,41 6,3 5,95 5,6 5,1 5,672 0,47 Spk [nm] 1127 1016 1241 1195 1051 1126 94,49 Sk [nm] 6211 6044 4678 5612 6700 5849 761,69
Svk [nm] 1203 1351 1112 1183 1110 1191,8 98,24
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 2003 1942 1978 2124 1976 2004,6 70,18 Sq [nm] 2262 2046 2375 2401 2104 2237,6 158,69 Ssk -0,0528 -0,0971 0,0213 -0,194 0,03758 -0,057004 0,09 Sdr % 5,44 4,72 4,98 5,22 5,85 5,242 0,43 Spk [nm] 1152 1095 1246 1167 1051 1142,2 74,21 Sk [nm] 6161 6027 5671 5912 6746 6103,4 401,78
Svk [nm] 1213 1035 1182 1267 1294 1198,2 101,28
EDM vertical surface (small areas) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 1033 1344 1152 1279 1221 1205,8 119,84 Sq [nm] 1318 1693 1456 1594 1498 1511,8 141,82 Ssk -0,903 -0,949 0,0253 -0,9412 -0,652 -0,68398 0,41 Sdr % 7,45 4,77 7,62 6,34 5,11 6,258 1,31 Spk [nm] 560 1197 784 946 897 876,8 232,75 Sk [nm] 2749 2316 2314 2687 2704 2554 219,35
Svk [nm] 2196 3564 3145 3013 2265 2836,6 590,01
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 1224 777 1164 945 1034 1028,8 178,07 Sq [nm] 1500 999 1452 1367 1294 1322,4 197,31 Ssk -0,552 -0,761 -0,194 0,0487 -0,0971 -0,31108 0,34 Sdr % 6,02 4,56 4,21 5,33 6,04 5,232 0,83 Spk [nm] 405 713 527 634 551 566 116,08 Sk [nm] 3645 1619 2434 2264 2931 2578,6 758,64
Svk [nm] 1669 1710 1730 1645 1634 1677,6 41,33
Cylindrical surface (all surf) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 1314 1355 1278 1362 1426 1347 55,63 Sq [nm] 1827 1875 1768 1794 1867 1826,2 46,02 Ssk 0,531 0,458 0,376 0,675 0,464 0,5008 0,11 Sdr % 6,39 6,47 6,12 6,75 5,94 6,334 0,31 Spk [nm] 3036 3108 3204 3123 3009 3096 76,98 Sk [nm] 3451 3534 3462 3514 3442 3480,6 40,86
Svk [nm] 2052 2140 2002 2134 2167 2099 69,19
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 965 960 945 976 931 955,4 17,62 Sq [nm] 1315 1296 1276 1304 1379 1314 39,03 Ssk 0,535 0,344 0,366 0,434 0,513 0,4384 0,09 Sdr % 4,23 4,11 3,94 3,76 4,35 4,078 0,23 Spk [nm] 2185 2152 2046 2246 2234 2172,6 80,25 Sk [nm] 2828 2827 2714 2768 2887 2804,8 65,93
Svk [nm] 1571 1627 1594 1616 1647 1611 29,44
Plane surface polished (all surf) Measuring values [nm] [nm] Surface parameters
[units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 287 281 346 372 296 316,4 40,32 Sq [nm] 374 368 476 501 397 423,2 61,23 Ssk 0,0929 0,1 0,24 0,076 0,149 0,13158 0,07 Sdr % 0,698 0,673 0,631 0,449 0,864 0,663 0,15 Spk [nm] 519 528 587 603 632 573,8 48,77 Sk [nm] 853 833 954 978 828 889,2 71,24
Svk [nm] 404 389 492 426 356 413,4 50,78
Measuring values [nm] [nm] Surface parameters [units] 1 2 3 4 5 Mean value St.Dev
Sa [nm] 474 465 368 467 385 431,8 50,95 Sq [nm] 639 612 544 586 633 602,8 38,88 Ssk -0,377 -0,58 0,064 0,0741 -0,247 -0,21318 0,28 Sdr % 1,7 1,7 1,1 0,94 1,54 1,396 0,35 Spk [nm] 604 604 566 542 522 567,6 36,70 Sk [nm] 1334 1316 1298 1235 1364 1309,4 48,21
Svk [nm] 911 858 824 876 801 854 43,18
WRITE HEADING 1
LBM – plastic specimen LBM - plastic specimen (load number 15)
Correct operation percentage in all positions % Operation line on the position plate
1 2 3 4 Mean value St.Dev
First 90 100 90 100 95,0 5,8
Second 80 60 70 70 70,0 8,2
Ope
ratio
n po
sitio
ns
Third 60 70 77 70 69,3 7,0
Of all positions 78,1 14,0
Stiching occasion 1 LBM - plastic specimen (load number 20)
Correct operation percentage in all positions % Operation line on the position plate
1 2 3 4 Mean value St.Dev
First 100 100 100 100 100,0 0,0
Second 80 60 60 50 62,5 12,6
Ope
ratio
n po
sitio
ns
Third 50 77 70 62,5 64,9 11,5
Of all positions 75,8 20,0
Stiching occasion 5 LBM - plastic specimen (load number 25)
Correct operation percentage in all positions % Operation line on the position plate
1 2 3 4 Mean value St.Dev
First 90 80 90 90 87,5 5,0
Second 77 50 70 50 61,8 13,9
Ope
ratio
n po
sitio
ns
Third 60 77 50 42 57,3 15,1
Of all positions 68,8 17,7
Stiching occasion 14
LBM – micro-screw LBM - micro-screw (load number 15)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean value St.Dev 1 2Mean value St.Dev
First position 90 60 75,0 21,2First position 70 60 65,0 7,1
Second position 60 66 63,0 4,2
Second position 80 88 84,0 5,7
Of all positions 69,0 14,3 Of all positions 74,5 12,2
Stiching occasion 0 Stiching occasion 2
LBM - micro-screw (load number 20)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean value St.Dev 1 2Mean value St.Dev
First position 80 77 78,5 2,1First position 55 50 52,5 3,5
Second position 70 60 65,0 7,1
Second position 40 48 44,0 5,7
Of all positions 71,8 8,9 Of all positions 48,3 6,2
Stiching occasion 1 Stiching occasion 0
LBM - micro-screw (load number 25)
Chamfer screw surface Cylindrical screw surface -no recorded resultsCorrect operation %
Operation line
1 2Mean value St.DevFirst position 70 50 60,0 14,1Second position 77 50 63,5 19,1
Of all positions 61,8 13,9
Stiching occasion 1
EDMvert. - plastic specimen EDMvert. - plastic specimen (load number 15) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 100 100 100 100 100,0 0,0 Second 90 90 100 88 92,0 5,4
Ope
ratio
n po
sitio
ns
Third 80 70 90 77 79,3 8,3 Of all positions 90,4 10,3 Stiching occasion 1 EDMvert. - plastic specimen (load number 20) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 100 100 100 100 100,0 0,0 Second 100 90 100 90 95,0 5,8
Ope
ratio
n po
sitio
ns
Third 90 80 90 88 87,0 4,8 Of all positions 94,0 6,8 Stiching occasion 0 EDMvert. - plastic specimen (load number 25) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 100 100 100 100 100,0 0,0 Second 90 88 77 77 83,0 7,0
Ope
ratio
n po
sitio
ns
Third 80 70 66 70 71,5 6,0 Of all positions 84,8 13,1 Stiching occasion 0
EDMvert. - micro-screw EDMvert. - micro-screw (load number 15)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean value St.Dev 1 2Mean value St.Dev
First position 90 80 85,0 7,1First position 60 44 52,0 11,3
Second position 30 48 39,0 12,7
Second position 30 21 25,5 6,4
Of all positions 62,0 27,9 Of all positions 38,8 17,0
Stiching occasion 9 Stiching occasion 3
EDMvert. - micro-screw (load number 20)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean value St.Dev 1 2Mean value St.Dev
First position 50 50 50,0 0,0First position 55 37 46,0 12,7
Second position 55 48 51,5 4,9
Second position 20 44 32,0 17,0
Of all positions 50,8 3,0 Of all positions 39,0 14,7
Stiching occasion 1 Stiching occasion 3
EDMvert. - micro-screw (load number 25)
No experiments due to high deformation
Cylindrical functional surface Cylindrical func. surface - micro-screw (load number 15) Cylindrical screw surface
Correct operation % Operation line
1 2 Mean value St.Dev First position 50 60 55,0 7,1Second position 20 24 22,0 2,8
Of all positions 38,5 19,6 Stiching occasion 10 Cylindrical screw surface (load 20)
Correct operation % Operation line
1 2 Mean value St.Dev First position 80 88 84,0 5,7Second position 55 40 47,5 10,6
Of all positions 65,8 22,2 Stiching occasion 12
Plane-Polished - plastic specimen Plane-Polished - plastic specimen (load number 15) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 100 90 100 100 97,5 5,0 Second 80 90 70 77 79,3 8,3
Ope
ratio
n po
sitio
ns
Third 66 66 50 50 58,0 9,2 Of all positions 78,3 18,3 Stiching occasion 8 Plane-Polished - plastic specimen (load number 20) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 90 100 90 100 95,0 5,8 Second 77 80 70 80 76,8 4,7
Ope
ratio
n po
sitio
ns
Third 55 50 60 48 53,3 5,4 Of all positions 75,0 18,5 Stiching occasion 6 Plane-Polished - plastic specimen (load number 25) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 100 100 100 90 97,5 5,0 Second 60 50 55 60 56,3 4,8
Ope
ratio
n po
sitio
ns
Third 44 50 37 44 43,8 5,3 Of all positions 65,8 24,4 Stiching occasion 7
Plane-Polished - micro-screw
Plane-Polished - micro-screw (load number 15)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean value St.Dev 1 2Mean value St.Dev
First position 80 80 80,0 0,0 First position 70 70 70,0 0,0
Second position 55 60 57,5 3,5Second position 60 50 55,0 7,1
Of all positions 68,8 13,1 Of all positions 62,5 9,6
Stiching occasion 6 Stiching occasion 0
Plane-Polished - micro-screw (load number 20)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean value St.Dev 1 2Mean value St.Dev
First position 80 88 84,0 5,7 First position 66 70 68,0 2,8
Second position 70 77 73,5 4,9Second position 85 77 81,0 5,7
Of all positions 78,8 7,5 Of all positions 74,5 8,3
Stiching occasion 2 Stiching occasion 0
Plane-Polished - micro-screw (load number 25)Experiment not succeed
Plane-Rough - plastic specimen Plane-Rough - plastic specimen (load number 15) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 100 100 100 100 100,0 0,0 Second 80 70 70 77 74,3 5,1
Ope
ratio
n po
sitio
ns
Third 66 60 50 50 56,5 7,9 Of all positions 76,9 19,3 Stiching occasion 1 Plane-Rough- plastic specimen (load number 20) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 90 100 90 100 95,0 5,8 Second 77 64 70 80 72,8 7,2
Ope
ratio
n po
sitio
ns
Third 55 50 55 48 52,0 3,6 Of all positions 73,3 19,1 Stiching occasion 3 Plane-Rough - plastic specimen (load number 25) Correct operation percentage in all positions % Operation line on the position plate 1 2 3 4 Mean value St.Dev
First 80 90 90 90 87,5 5,0 Second 55 50 60 60 56,3 4,8
Ope
ratio
n po
sitio
ns
Third 58 50 50 44 50,5 5,7 Of all positions 64,8 17,6 Stiching occasion 7
Plane-Rough - micro-screw (load number 15)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean valueSt.Dev 1 2Mean value St.Dev
First position 70 66 68,0 2,8 First position 60 66 63,0 4,2
Second position 66 60 63,0 4,2Second position 70 80 75,0 7,1
Of all positions 65,5 4,1 Of all positions 69,0 8,4
Stiching occasion 2 Stiching occasion 0
Plane-Rough - micro-screw (load number 20)
Chamfer screw surface Cylindrical screw surfaceCorrect operation % Correct operation %
Operation line Operation line
1 2Mean valueSt.Dev 1 2Mean value St.Dev
First position 80 77 78,5 2,1 First position 66 50 58,0 11,3
Second position 55 50 52,5 3,5Second position 50 66 58,0 11,3
Of all positions 65,5 15,2 Of all positions 58,0 9,2
Stiching occasion 4 Stiching occasion 2
Plane-Rough- micro-screw (load number 25)
Experiment not succeed
Existing gripper - plastic specimen Existing gripper - plastic specimen (load number 15)
Correct operation percentage in all positions % Operation line on the position plate
1 2 3 4 Mean value St.Dev
First 80 90 90 80 85,0 5,8
Second 70 60 70 70 67,5 5,0
Ope
ratio
n po
sitio
ns
Third 55 48 60 60 55,8 5,7
Of all positions 69,4 13,5
Stiching occasion 4 Existing gripper - plastic specimen (load number 20)
Correct operation percentage in all positions % Operation line on the position plate
1 2 3 4 Mean value St.Dev
First 90 90 90 80 87,5 5,0
Second 60 50 55 50 53,8 4,8
Ope
ratio
n po
sitio
ns
Third 50 50 60 66 56,5 7,9
Of all positions 65,9 16,9
Stiching occasion 6 Existing gripper - plastic specimen (load number 25)
Correct operation percentage in all positions % Operation line on the position plate
1 2 3 4 Mean value St.Dev
First 90 80 90 80 85,0 5,8
Second 40 50 48 55 48,3 6,2
Ope
ratio
n po
sitio
ns
Third 44 38 50 42 43,5 5,0
Of all positions 58,9 20,0
Stiching occasion 11
Existing gripper - micro-screw
Existing gripper - micro-screw (load number 20)
Cylindrical screw surface
Correct operation %
Operation line
1 2 Mean value St.Dev
First position 20 10 15,0 7,1
Second position 0 0 0,0 0,0
Of all positions 7,5 9,6
Stiching occasion 0
Recommended