Pyrolytic Graphite Production: Automation of Material
Placement
MASSACHUS ETTS "NTMTUTE.
OF TEC HNOLOGY
by
Chase Olle
OCT 16 2014
SB Mechanical Engineering
Massachusetts Institute of Technology, 2014
LIBR ARIES
Submitted to the Department of Mechanical Engineering in
partial fulfillment of the requirements for the degree of
Master ofEngineering at
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
September, 2014
ecnology, 2014. All rights reserved
Its
C Massa s
Signature redacted
Author:...........
Chase R. Olle
Department of Mechanical Engineering
September, 2014
C tifiedby:....................
Signature redacted
David E. Hardt
Ralph E. & Eloise F. Cross Professor of Mechanical Engineering, Chairman,
Thesis Advisor
;1:t:11dby................
Ac ep
Signature redacted
........----......
David E. Hardt Ralph E. & Eloise F. Cross Professor of Mechanical
Engineering, Chairman, Department Committee on Graduate Students.
This page intentionally left blank.
2
Pyrolytic Graphite Production: Automation of Material
Placement
by
ChaseOlle
S.. Mechanical Engineering
M assachusetts I nstitute of Technology, 2014
SubmittEd to the Departmet of Mechanical Engineering September, 2014
In Partial Fulfillment of the Requi remients for the Degree of Master
of Engineering in Manufacturing
Abstract
This rsech examinestheprocess and challengesassociated with the addition of an autonomous
transfer robot to a manufacturing line for AvCarb M aertal Solutions for use in production of
pyrolytic graphite.
Development of thesystem induded thedesign and fabrication of an end-Wfector, selection of a
SCA RA robotic arm, and incorporation of avision system. The arm and theend-effector were
tested to seeif maeial would shift during transfer. Theentiresysterm wastner for
reptability and transfer time The results of thetest indicted tht the transfer system would
succusSflly reet specfications with high procss capability given by aCPI of L47.
3
Acknowledgements
First, I would like to thank my teammates Yugank Chawla and Knute Svenson. I couldn't have
possibly asked for a more friendly, intelligent and supportive team.
Thanks to my advisor Dr. David Hardt for his guidance and insights. His sharp inquiries kept
me on my toes and with his direction this project was able to far exceed expectations.
Thank you everyone at AvCarb for being friendly, open and helpful. Nearly everyone at
AvCarb has, at least once, taken time out of their day to help me. I can't possibly thank them
enough.
A special thanks to Kathryn Rutter who tirelessly supervised us. Her advice kept the project on
track and made the whole thing worthwhile.
A special thanks to Don Connors who took a risk on an unproven graduate student with no
real-world experience.
Last, thanks to my friends and family whose patience and support continue to push me to
pursue greater challenges.
5
This page intentionally left blank.
6
Contents
1
2
Introduction ........................................................................................................................... 10
1.1
Background and Motivation ................................................................................................... 10
1.2
O bjectives .................................................................................................................................. 11
1.3
Problem Statement ................................................................................................................... 13
1.4
Thesis O verview ....................................................................................................................... 13
H eat Spreader Production ..................................................................................................... 14
2.1
2.1.1
Stacking ............................................................................................................................. 15
2.1.2
Carbonization ................................................................................................................... 15
2.1.3
Graphitization ................................................................................................................... 16
2.1.4
Unstacking and Inspection ............................................................................................. 16
2.2
M aterials .................................................................................................................................... 16
2.2.1
Polyimide Sheets .............................................................................................................. 17
2.2.2
Graphite Foil ..................................................................................................................... 17
2.2.3
Heat Spreader Material ................................................................................................... 18
2.3
3
M anufacturing Process ............................................................................................................ 14
C alendering Process ................................................................................................................ 19
M achine D esign ..................................................................................................................... 20
3.1
Process O verview ..................................................................................................................... 20
3.2
Production Line D esign ........................................................................................................... 21
3.3
Transfer System O verview ..................................................................................................... 25
3.4
Robotic A rm .............................................................................................................................. 27
3.4.1
Concept Selection ............................................................................................................. 27
3.4.2
Selection of SCA RA Type and M otion .......................................................................... 29
3.4.3
A ir Lines ............................................................................................................................ 31
3.5
End Effector .............................................................................................................................. 33
3.5.1
Concept Selection ............................................................................................................. 33
3.5.2
Selection of Vacuum End Effector Type ....................................................................... 35
3.5.3
D esign of the Vacuum End Effector ..............................................................................40
3.5.4
Propagating Vacuum Effect ................................................................................................. 43
7
Contact Detection .............................................................................................................45
3.5.5
3.6
Structural Fram e .......................................................................................................................47
3.6.1
Concept Selection .............................................................................................................47
3.6.2
D esign of the Structural Fram e ...................................................................................... 47
3.7
Vision System ...........................................................................................................................52
3.8
Controller D esign .....................................................................................................................56
3.9
Control System Flow ...............................................................................................................58
3.10
Web Handling ..........................................................................................................................60
3.10.1
4
5
6
D esign of the w eb handling system ..............................................................................60
Experim entation ....................................................................................................................62
4.1
Quality M easures .....................................................................................................................62
4.2
D esign of Experim ents ............................................................................................................ 63
Results ....................................................................................................................................68
5.1
Summ ary of Results .................................................................................................................68
5.2
A nalysis of Transfer System ...................................................................................................68
5.3
Sources of Error in the Vision System ................................................................................... 71
Conclusions and Future W ork ..............................................................................................73
6.1
Summ ary of Conclusions ........................................................................................................73
6.2
Future Work ............................................................................................................................... 74
7
A ppendix ...............................................................................................................................75
8
References ..............................................................................................................................78
8
List of Figures
Figure 1: Steps of the heat spreader production process...............................................................
Figure
Figure
Figure
Figure
Figure
Figure
2:
3:
4:
5:
6:
7:
15
Material transformation through the production process..............................................17
20
The new production process with four additional steps ..............................................
22
Original layout of the inspection room ...........................................................................
CAD model of the inspection room used for experimentation.................23
24
Final layout of the inspection room including transit paths. ...................
Concept Production Line....................................................................................................25
Figure 8: Epson G6 SCARA robotic arm...........................................................................................27
Figure 9: Workspace of the robotic arm.............................................................................................30
Figure 10: End effector interaction.....................................................................................................31
Figure 11: Epson G6-451SR annotated drawing ..............................................................................
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
12:
13:
14:
15:
16:
17:
18:
19:
20:
21:
22:
23:
24:
32
Bernoulli non-contact gripper...........................................................................................37
38
Schmalz suction cup gripper lifting heat spreader material ......................................
39
Vacuum table gripping heat spreader material ................................................................
40
Vacuum end effector design ................................................................................................
41
Diffusion plate and vacuum core ........................................................................................
Exploded view of the vacuum end effector and the grip-to-arm fixtures.........42
Vacuum end effector.............................................................................................................42
Diagram depicting the effect of the propagating vacuum design..............43
44
Propagating vacuum effect. .................................................................................................
CAD model of the support structure, mounting plate and manipulator .................. 48
Finite element analysis of the mounting plate examining vertical stress..................49
Exploded view of the structural support subsystem........................................................50
51
Picture showing the final version of the structural frame ...........................................
Figure 25: Epson CV1 Vision System...............................................................................................
52
Figure
Figure
Figure
Figure
Figure
26:
27:
28:
29:
30:
Vision system setup...............................................................................................................53
Edge detection algorithm. Green arrows indicate the identified edge......................54
55
Corner detection algorithm.............................................................................................
Controller Diagram for the production line ......................................................................
56
58
Control System Flow Diagram ............................................................................................
Figure
Figure
Figure
Figure
Figure
31:
32:
33:
34:
35:
Web handling diagram....................................................................................................
Repositioning test example A ..........................................................................................
Repositioning test example B..........................................................................................
Repositioning test example C ..........................................................................................
Repositioning test example D ..........................................................................................
60
64
65
66
67
Figure 36: Charts showing the corner position of the detected heat spreader sheet..................69
Figure 37: Chart showing the angle of the detected heat spreader sheet.....................................69
Figure 38: Target and corner location ...............................................................................................
71
9
1 Introduction
This thesis will cover the introduction of a robotic manipulator into an existing production
line. Specifically, the addition of an assembly robot, which will move finished material to a film
line preceding a calendering machine.
1.1 Background and Motivation
AvCarb Materials Solutions was founded in February 2013 through an internal buyout
from Ballard Power Systems [1]. The factory, located in Lowell Massachusetts, has established
carbon material production processes. Currently AvCarb specializes in carbon fiber materials
for three main areas: friction applications (e.g. brake pads), electrochemical diffusion
applications (e.g. fuel cells), and thermal applications (e.g. heat spreaders for smartphones). [2]
The heat spreader material is principally used in consumer electronics to aid in heat
dissipation. For small consumer electronic devices (e.g. smartphones and tablets) traditional
heat dissipation systems are impractical. Classic heat dissipation systems would remove waste
heat using water coolant and air convection by fans. These were common methods for
mainframes, personal computers and laptops, however, small electronic devices have much
smaller footprints which cannot include these features. Critical components of these devices can
easily be damaged by waste heat. Therefore, small devices rely on heat spreader material
instead of traditional dissipation techniques. Heat spreader material, also called pyrolytic
graphite, is a carbon material with highly structured bonds. These bonds cause the material to
have very high thermal conductivity, as much as four times the thermal conductivity of copper.
When used in consumer electronics, this material transfers heat away from critical components
to the body of the device for dissipation. Consumer electronics are in high demand, and the
market is growing which makes the heat spreader market, which is critical to these devices, a
very appealing market to enter.
10
AvCarb is currently seeking to generate revenue by expanding their current production
portfolio. In relation to the heat spreader production process, AvCarb is scaling-up production
twelve-fold and adding a production step which will change the final form of the product
which will appeal to a wider customer base. The new production step will be the inclusion of a
calendering process which gives the heat spreader material a variety of beneficial properties,
these properties are described in greater detail in section 2.3 [Calendering Process]. AvCarb's
goal is to increase production of the heat spreader process and change the final form of the
product in order to increase their share of the heat spreader market.
1.2 Objectives
The AvCarb management team is motivated to increase production and sale of the heat
spreader material and the MEngM AvCarb team considered this motivation when selecting
topics for study. The MEngM AvCarb team, consisting of Chase Olle, Knute Svenson and
Yugank Chawla, applied research techniques in manufacturing to solve issues related to
AvCarb's business goals. To this end, the MEngM team decided to implement a fifth step to the
heat spreader production process, the process is described in greater detail in section 2.1
[Manufacturing Process].
The current production process produces sheets of heat spreader material which has not
been calendered, these sheets are placed in stacks and shipped. By contrast, the most common
method of preparing heat spreader material for use is to die-cut the material from heat spreader
rolls that have passed through a calendering process. Therefore, with the 4-step production line,
material would still need to be calendered in order to be useful. To achieve a more desirable
form-factor, a fifth step would be added to the production process. This step would first involve
inspecting material from the current process. Then heat spreader material would be placed onto
polyester film close together to approximate a continuous roll. This discontinuous roll would
then be fed through a calendering process which will reduce the thickness of the film and heat
spreader to 25 microns. After exiting the calendering machine, the entire film would be wound
into a roll and shipped.
11
These subjects were explored in greater detail by the AvCarb MEng team, each member
covered a separate topic. Yugank Chawla [3] implemented a video inspection system,
eliminating the need for operators to perform visual inspection. Previously, inspection was
done by individual operators and so to reduce errors Yugank introduced a video system which
made use of modem detection software. Material that passed Yugank's inspection process went
forward to the placement system. From there, Chase Olle was responsible for implementing an
assembly robot which places finished material onto a polyester film. This connects the end of
the AvCarb's current process with the new calender machine. Last, Knute Svenson developed
the calendering process [4], focused on understanding the physics and controls of the process.
The calendering process reduces the thickness of the material by compressing sheets between
two steel rollers. The process improves the material properties of the heat spreader sheets,
increasing their value. Together Chawla's and Svensons's work determined the effect of defects
on the material which, in turn, determines the quality of the output material. This thesis covers
the design and fabrication of a robotic assembly system.
The assembly system, or transfer robot, moves sheets of heat spreader material from a
stack to a moving line. AvCarb decided to automate the task for several reasons related to yield,
ergonomics and precision. First, the material is very delicate and susceptible to damage. Any
time a human operator must handle the material there is a risk that the material will be
damaged and rendered unusable. By removing the human factor the automated system will
have improved yield. Second, the task of picking up a sheet and putting it down on a moving
conveyer web is extremely tiresome. The line is expected to run a sheet every 30 seconds over
an 8hr work day for some 2,000 sheets. From an ergonomic perspective, this type of repetitive
motion task could negatively affect the health of a human operator. Last, sheets of the material
must be placed within a 1mm positional tolerance and a
50
angular tolerance. This would be a
difficult tolerance to achieve for a human operator on a stationary position let alone on a
moving line. By automating this process the AvCarb team can be confident that a high level of
precision is met for their output material.
12
1.3 Problem Statement
This thesis will go into detail describing the implementation of a transfer assembly robot
into the existing production process at AvCarb. The purpose of the robot is to move finished
pyrolytic graphite to a polyester film line so that both can be put through a calendering
machine. This system is necessary because manual placement would not be precise enough. The
calendering process will increase the value of AvCarb's heat spreader material. The thesis will
explain the components, machines and control systems that were used to incorporate the
assembly robot in AvCarb's production process. In addition, this thesis will describe the design
methodology that was implemented, the fabrication and assembly of machine components and
the testing procedures that were used to validate the design. The system will be considered
successful if the robotic arm can pick up and place a sheet from a stack every 30 seconds
without damaging the material with 1mm positional tolerance and +50 rotational tolerance.
1.4 Thesis Overview
This thesis has been organized into different chapters, each addressing a certain topic.
Chapter 1 presents the introduction and problem statement. Chapter 2 describes important
background information about the production process including the existing manufacturing
process, the key materials and their physical properties, the types of defects that may play a role
in determining the quality of the output material, and the background information describing
the relative benefits of the calender machine. Chapter 3 will discuss the design process
including the design methodology, the selection of key features, and the design and fabrication
of custom components. Chapter 4 will explain the testing procedures that were used to validate
the design. Chapter 5 will discuss results and Chapter 6 will cover the conclusions of the work
and suggests topics for further study.
13
2 Heat Spreader Production
This chapter describes the current process as well as the processes, materials, and defects
that will be important to the implementation of the new calendering process that will be
implemented in this thesis. The first section, Manufacturing Process [2.1], describes steps in the
four primary steps of the heat spreader production process, prior to the implementation of this
thesis. Materials [2.2] describes key materials within the production process and those material
that were to be incorporated in this thesis. The last section Calendering Process [2.3] describes
the primary step being implemented into the production process. The calendering step will
cause the heat spreader material to express desirable physical properties.
2.1 Manufacturing Process
The manufacturing process produces heat spreader material by altering the chemical
state of polyimide sheets through a two-step carbonization and graphitization process. During
this several day process, stacks of polyimide material will be exposed to temperatures in excess
of 2500*C. The end result is batch stacks of heat spreader material. The heat spreader material
produced during this manufacturing process are used, along with polyester film, as the input
materials into the production line described in this thesis.
The manufacturing process is broken into four major steps; stacking, carbonization,
graphitization, unstacking/inspection. The steps are shown in Figure 1.
14
Graphite Foil
ide Film
o. 7 me
Step 1:
Stacking
Furnace
1
Spreader
Furnace 2
Graphite Foil
Step 2:
Carbonization
Step 3:
Graphitization
Step 4:
Unstacking
Figure 1: Steps of the heat spreader production process
2.1.1 Stacking
The stacking step (Step 1) of the process begins by interlaying polyimide sheets and
graphite foil sheets. This step is completed manually. The polyimide acts as the precursor
material and will eventually be converted into heat spreader material. The graphite foil between
each sheet improves yield has a number of beneficial effects such as increased thermal and
electrical conductivity. Foreign material between layers will ruin the output material and so this
operation is performed in a clean room by trained operators. The stack housing is made from
graphite and carbon-carbon material so that the stack can withstand the extreme temperatures
used during the graphitization and carbonization steps.
2.1.2 Carbonization
In the next step polyimide film is converted into an intermediary material (Step 2). The
stacks of prepared material are put into a carbonizing furnace. The entire furnace is brought
under vacuum and the temperature is raised to over 1000'C. This induces pyrolysis in the
polyimide sheet, removing the majority of the non-carbon material. During this step the
polyimide sheets lose approximately 30% of their weight. This loss is primarily due to the
release of oxygen as CO or C02, the release of nitrogen as N2 gas, release of hydrogen as
H2
or
CH4 and the combined release of hydrogen and nitrogen as HCN [5]. A vacuum pump is used
to evacuate off-gassed material. This evacuation is tightly controlled because some of the gases
are toxic, including hydrogen cyanide (HCN).
15
2.1.3 Graphitization
In the graphitization step (Step 3) the intermediary carbonized material is converted into the
final product, heat spreader material. Stacks of material are moved from the carbonization
furnace to the graphitization furnace. Normal air is displaced by an inert gas such as argon [6]
and the environment is brought to atmospheric pressure. The temperature in the furnace is
raised to exceptionally high temperatures in excess of 2500 0C. The heat treatment refactors the
intermediary carbonized sheets into highly-crystalline and highly-oriented structures by
inducing a change in the bonding pattern of the carbon. The result is the heat spreader material,
a graphite film with very high thermal conductive properties.
2.1.4 Unstacking and Inspection
In the last step (Step 4), the finished material is separated from the graphite foil and
inspected for defects. Operators open the stack housing and manually separate heat spreader
sheets from graphite foil and place the two materials into separate stacks. While removing heat
spreader sheets, the operator will perform a visual inspection of both sides of the material.
Potential defects are described in the defects section. The graphite foil will be reused in later
production runs. The heat spreader material is weighed and sealed for transportation.
After the production line described in this thesis is installed, heat spreader material will
pass directly into the system rather than being sealed and shipped.
2.2 Materials
During the production process, polyimide material undergoes substantial chemical
changes. The following Figure 2 shows the transformation of polyimide throughout the process.
This section describes the materials involved during the process.
16
Figure 2: Material transformation through the production process
2.2.1 Polyimide Sheets
Polyimide film is the precursor material that will eventually be converted into heat
spreader material.
Polyimide film is highly desirable as the precursor for heat spreader material because of
its chemical structure. Polyimide films have an amorphous structure formed of hexagonal
carbon rings [5]. This feature coupled with the in-plane orientation of the carbon chains
improves the refactor of carbon bonds into the desired honeycomb lattice present in heat
spreader material. High heat resistant polymers which have in-plane orientation i.e. polymers
in which the molecular chains are aligned parallel to the plane give graphitic carbon upon heat
treatment. The ability of the polymers to graphitize largely depends on their in-plane
orientation, even a local difference of a degree in orientation induces non-uniform
graphitization [7].
2.2.2 Graphite Foil
Graphite foil is a form of graphite that has been produced by compressing exfoliated graphite
flakes and powder into plates [8]. For the heat spreader production process, graphite foil serves
three purposes.
17
1. Separate raw polyimide sheets.
o If two sheets of raw polyimide are in direct contact during the carbonization
stage the surfaces adhere and become marred
2. Improve thermal uniformity across polyimide sheets
o
The raw polyimide has low thermal conductivity (.37 W/ mK). Inside the
furnaces, heat propagates from the edges of the stacks inward causing nonuniform heating. The higher thermally conductive graphite foil reduces the time
the temperature takes to stabilize.
3. The graphite foil physically restricts the polyimide
o
The polyimide undergoes a large amount of shrinkage (30%) and has a tendency
to wrinkle or otherwise deform when no forces are applied. [9]
2.2.3 Heat Spreader Material
The heat spreader material is one of the two input materials that will be used in the
production line developed in this thesis. The material will be placed onto polyester film by the
robotic system described in the Machine Design section. The heat spreader material will be
input into the production system as a batch stack. The sheets are nominally 220mm x 260mm x
0.025mm and weigh 2.8 grams.
Heat spreader sheets are thin, lightweight graphite films with high thermal conductivity
when compared to the commonly used materials for dissipating heat. This material is often
used to diffuse the heat generated in electronic devices such as CPU's, processors, power
amplifiers, cameras and mobile phones. [10]
The useful thermal properties of heat spreader material are the direct result of the atomic
structure of the material. At an atomic-scale heat spreader material is dominated by two
chemical-structural regimes. Carbon rings oriented in a honeycomb lattice forms the backbone
of the structure, this is called the in-plane direction. These lattice-planes form layers held
together by Van der Waals interactions, the out-plane direction. The carbon honeycomb bonds
18
dominate the thermal properties of the lattice in the in-plane direction resulting in very high
thermal-conductivity (-1000 W/m*K) [11]. The Van der Waals interactions between layers are
comparably weaker, resulting in a much lower thermal-conductivity (-10 W/m*K).
2.3 Calendering Process
The major addition to the production process described in this thesis, will be the addition
of a calendering machine. A calendering machine reduces the thickness of input material by
compressing it between two steel rollers. The calendering process increases the thermal and
electrical conductivity of the material, and makes the less susceptible to damage. Successful
introduction of the process will improve the value of the material. This will be the last
processing step in the production line.
In the calendering process, the finished product sheet is placed on a polyester film and
fed into a calender machine which uses two steel rollers to compress the material from 90
microns to a uniform thickness of 25 microns. The process of calendering improves the thermal
conductivity of the material and causes the material to be easier to handle.
19
3 Machine Design
3.1 Process Overview
Pyrolytic graphite sees widespread use in consumer electrons and so the desirable form
factor of the material is well-defined. The most desirable form factor for the material is pyrolytic
graphite presented as sheets on a polyester film roll. This roll passes through a die cutting
process to produce forms for consumer electronics. There are very high tolerance requirements
on placement of the sheet in order to minimize waste material generated by the die cutting
process. The goal of the new process is to produce rolls of calendered heat spreader material.
Graphite Foil
*d
Polyimide Film
Step 1:
Stacking
Step S:
Visual Inspection
Heat
Fumace 1
Furnc 2
Step 2:
Carbonization
Step 6:
Placement
Spreader
Graphite Fo
Step 3:
Graphitization
Step 7:
calendering
Step 4:
Unstacking
Step 8:
RewInd
Figure 3: The new production process with four additional steps
The new process introduces four new steps. The entire process including the additional
steps are shown in Figure 3. In the first step a vision system inspects material leaving the
unstacking process. By using a computer vision system the process can eliminate the need for
20
manual inspection. This will reduce the burden on the operators and reduce variance on
acceptance rates. This step is covered in Yugank Chawla's thesis [3]
In the next step a robotic manipulator will place sheets of heat spreader material onto a
polyester film. The tolerance and repeatability requirements on placement are very high making
therefore it would not be feasible to have an operator manually place sheets. The robotic
manipulator is divided into two principal components; a robotic arm (section 3.4) and an endeffector (Section 3.5). This thesis is primarily concerned with this step of the process.
After the sheets have been placed on the polyester film the film passes through a
calendering machine. This step turns the process from a discrete batch process into a semicontinuous process. The calendering process give the heat spreader material several beneficial
properties (section 2.3). This step is covered in Knute Svenseon's thesis [4]
Last, the entire film line is rewound into a roll. The finished product is now ready for
shipment.
3.2 Production Line Design
The production line was implemented with the expectation that the line would be used
for full scale production with very few changes. For this reason, much thought went into
deciding where the production line would be located. This section describes that methodology.
There were several important considerations for the position of the production line
based on the requirements for the output material.
*
Finished rolls must be free of debris
*
Sites for adding and removing material must be easily accessible.
" The site must have access to add power, compressed air and vacuum.
" The site must be safe for operators.
The inspection room, where post-processing of the heat spreader material occurred, was
the only room in the factory that met sufficient clean room classification. In addition, the room
already has power and compressed air lines and is currently used and meets safety standards.
21
This made the inspection room the natural selection for the site of the production line. The
following diagram (Figure 4) shows the room's original setup.
Pipes
Door
Double Door
Material Carts
I
Storage Locker
Cabinets for
documentaion
]
Chairs
Workstations
Door
Material Storage
for Testing
Pipes
Racks for Miscallaneous
Equipment
Calender Machine
Cubicle
Sink
[WFE-
I
Powerbox
Power line
-
Structual Beam
Compressed Air
Figure 4: Original layout of the inspection room
Models of the room and the equipment was created to help inform the process of
locating the line. A separate contractor was given the responsibility of building the web
handling system. Based on specifications provided by the contractor a model of the web
handling system was created. The model of the entire room and production line subsystems is
shown below (Figure 5).
I
22
Web Handling System Model
Calender Machine
Figure 5: CAD model of the inspection room used for experimentation
After experimenting with several possible locations using the models, a final position for
the production line was selected. This location was selected to provide the best access for heat
spreader and polyester film entering the room, and a natural egress for finished rolls exiting the
room. Figure 6 shows the final layout and the paths of the material.
23
Material Carts
S
Ao 8
C
Workstations0
SCARA Robot
Calender
I
[I
T
Web Handling System
Figure 6: Final layout of the inspection room including transit paths. Path A indicates heat spreader
moved to inspection tables. A2 - separated heat spreader material is put input into the production line. B
-
material. Ao - material enters the room, stored on carts. Al - individual stacks are removed from carts and
polyester film rolls entering the room and input in the production line. C - finished material exits the
room.
24
3.3 Transfer System Overview
The transfer system is responsible for moving inspected heat spreader material from a
batch stack to the polyester film web. The transfer system represents the placement step of the
new process (step 6 of Figure 3). Early in the development process a concept for the production
line was produced which can be seen in the following Figure 7.
Supp0t Table
F"shed Ro
M
Guip
Calender Mcine
vTsim System
Heat Spread Sheets
Reject Pie
Figure 7: Concept Production Line
From this early concept the transfer was divided into five principal components; input
material, vision, robotic arm, grip and web. Roughly the process would occur in four steps.
1. The transfer robot picks up a sheet of input material
2. The sheet is moved to the vision system which will correct for misalignment in the sheet.
3. The robot presses the sheet into the web and the grip is released
If the computer vision detects a bad sheet the arm will instead deposit the sheet in reject
4. The arm is withdrawn and returns to the starting position
25
The sheet must be placed within a +1mm positional tolerance. This tolerance requirement
was carefully considered. To start, the sheets of the material could be offset within the stack and
the act of engaging the grip could cause sheets to shift. However, once the grip was engaged the
expectation was that the sheets would not shift relative to the body of the grip. The arm was
expected to be highly repeatable and not a source of error. Therefore, a vision system would
feedback to the arm and correct for any position errors in the sheet relative to the grip. Once the
sheet was in contact with the web, a low-tact adhesive on the web would prevent any shifting.
This would ensure that each sheet would be correctly positioned for each placement cycle.
To perform the steps described above and two meet the tolerance requirements three key
components would need to be carefully considered; an end-effector (grip), a robotic arm, and a
vision system. The following sections describe the design and selection of these components as
well as supplemental equipment.
26
3.4 Robotic Arm
lb
Figure 8: Epson G6 SCARA robotic arm
3.4.1 Concept Selection
In order to move the sheets of heat spreader material to the polyester film line a SCARA
robotic arm with a custom vacuum tale end effector was used. After review, the decision was
made to use a ceiling mounted Epson G6 series SCARA robotic arm, shown in Figure 8. The
decision to use this style SCARA robotic arm was based on several important desirable features
of the final product, and based on features of the end effector.
Key Considerations for the Robotic Arm
1. Must meet location tolerances of .5mm in x and y directions and angular tolerances of +5
2. Highly repeatable, will be required to place 5000 sheets/day
3. Material will be stored in stacks
4. System must be capable of operating the vacuum table end effector (3.5)
27
Three potential styles of robotic motion were considered.
1. 6-axis robotic arm
2. SCARA robotic arm
3. Gantry system
Six-axis robotic arms behave most similarly to a human arm. These arms have articulated
joints which allow the arm to move objects in any direction with any orientation. These arms are
the only style that is capable of changing an objects orientation. An example of this type of arm
would be the welding robots seen on an automobile production line. SCARA robotic arms are 4axis. These arms are generally made by two articulated joints and a third shaft that is capable of
motion in the z-axis and rotation about the z-axis. This allows the arm to manipulate objects in
3D and rotate objects about the z-axis. The last system, the gantry system, has only two degrees
of freedom. The system can translate left to right as well as raise or lower the end effector. This
type of system can do no rotations.
The types of arms were considered with respect to the key properties and features. The first
and most important feature was the tolerance requirements. The gantry system was
immediately ruled out because the system could only translate in two axis. As a result, the
position of the sheet on the polyester film would be determined by the speed of the line. In
order to improve accuracy, another axis of motion would be necessary to decouple the control
of position from line speed.
The next most important feature was orientation of the sheet and the input of material as
a stack. Both the sheet and the polyester film were planar structures and could be brought into
contact without rotation. For this reason the two additional rotational degrees of freedom of the
6-axis arm would go unused. In addition programming for a 6-axis arm is more complicated
than for a SCARA robot and the systems are more expensive.
The SCARA robotic arm was selected because this style was capable of performing the
desired motions and because the system was easier to use than a 6 axis arm.
28
3.4.2 Selection of SCARA Type and Motion
With the decision made to use a SCARA robotic arm an Epson G6-45SR SCARA arm
was quickly selected as the best option. The Epson brand was selected because of precedent for
the system demonstrated by Zarrouati 2008 [12]. Once the brand was selected the G6 model was
determined based on the end effector. There are five options in the Epson G-series the G1, G3,
G6, G10 and G20. The numbers identify the maximum payload by kilogram weight, so the G6 is
capable of carry a 6kg payload. When modeled, the custom end effector and fixtures was
expected to weigh 2.5kg making the G3 the natural choice. However, in the interest of
prototyping the G6 was selected to give a safety factor in the payload in the case that sensors or
actuators would be added to the end effector.
The last decision made when selecting the SCARA robot was the decision to use a
ceiling mounted unit instead of a tabletop mounted unit. This decision was informed by the
development of a workspace model. The following Figure 9 shows a birds-eye view of the
SCARA robot with the custom end effector attached. The gray shows the arms workspace. The
diagram also shows the longest possible unidirectional translation that the arm can perform.
This line of motion represents the best location for the midline of the polyester film web, by
giving the longest possible operable area. For the G6-45 SCARA the longest line of motion is
765mm.
29
SCARA Robot
Inspection
End Effector
Input
-
~-.'
C
Workspace
/
N
Reject
-~
17
C
X
Longest line of motion
Figure 9: Workspace of the robotic arm
By inspection of this model, the ceiling mounted system was shown to be the best
possible solution. In the following Figure 10, a G6-45S tabletop mount and a G6-45SR ceiling
mount are shown. During travel the end effector would have interacted with the tabletop
model's base.
30
Figure 10: End effector interaction. The grip would strike a table-top mounted arm (Left) but not a ceiling
mounted unit (Right)
3.4.3 Air Lines
The end-effector requires both compressed air and vacuum to function properly. Several
considerations were made in regards to the air-lines setup. First, the source for the compressedair and vacuum lines was selected. Electric pumps are the most common way of generating
pressure in a manufacturing setting, however, these pumps require lubricating oil which can be
ejected into the air. Any foreign material will ruin the heat spreader material and so if these
pumps were used they could not be located inside of the clean room. It was decided that the
pumps generating both compressed air and vacuum would be located outside of the room.
Pressure lines would be run from these pumps to the arm using standard pressure piping.
Another consideration was the repeatability of the system with regards to the flow valves.
Two air flow control valves were used to activate the grip. These valves must be connected to a
24V DC power source. Electrical wiring is very susceptible to damage from motion and the arm
was expected to perform up to 2000 operations per day. This fact and the fact that the G6 is
limited to a 6kg payload make it desirable to have the valves located off of the grip, in a location
31
where they won't be moved. The valves would, therefore, be located near the base of the G6
robot connected to the G6 internal pressure lines.
The Epson G6 series has internal pressure lines located near the various axis of rotations,
this reduces their susceptibility to damage from repeated motion. The pressure lines are shown
in Figure 11 as item 7 and 8. Additional air tubing was run from the tube ends located on the G6
Body (3), down through the Z-quill (4), out a gap in the adapter couple (not shown) and finally
to the inlet and outlet on the end-effector.
8
7
1
5
ITEM NO.
1
38
4~
A
PART NUMBER
G6Base
2
G6 Arm
3
G6 Body
4
Zaxis Quill
5
Upper Z-stop
6
Lower Z-stop
7
Compressed Air Line
8
Vacuum Line
6
2
Figure 11: Epson G6-451SR annotated drawing
32
3.5 End Effector
The end-effector is responsible for "gripping" the material during movement and
placement. The heat spreader material has high quality requirements and is susceptible to
damage. Therefore, special consideration was given to the design of the end-effector. Many
other design considerations were based on the successful design of the end-effector. For
example, the Epson arm described in section 3.4 was selected so that the arm would be capable
of supporting the end-effector.
3.5.1 Concept Selection
In order to move the sheets of heat spreader material to the polyester film line a SCARA
robotic arm with a custom end effector was used. The end effector will behave as the hand for
the robotic arm. After review, the decision was made to use a vacuum table end effector. The
decision to use this style of end effector was based on several important desired features of the
final product and several properties of the material itself.
Key Considerations for the End Effector
1. The material had to be placed within a certain tolerance. Location tolerances of
+1mm in x and y directions and angular tolerances of
+5 0
2. Defects will propagate in the calendering process, so high surface quality must be
maintained for the material
3. The material is very delicate and highly susceptible to creasing, tearing and
impressions
4. The material will be stored in stacks
The primary concern over the end-effector was delivering a system that could lift, move and
deposit the material while maintaining the heat spreader materials quality. Several types of
potential end-effectors were evaluated [13]. Broadly, end-effectors fall into four categories;
33
1. Impactive:jaws directly clamp and object.
2. Ingressive: pins and needles physically penetrate the surface of the material.
3. Astrictive: suction forces are applied to the objects surface.
4. Contigutive: direct contact with an adhesive.
Ingressive and contigutive end effectors were ignored because they would damage the
material. From the impactive and astrictive categories four end effector options were
considered;
1. Forcegrip: this type works by applying force between two or more points, relying on the
force of friction to prevent sliding in the unconstrained directions. Therefore, these types
of grips require rigid components with at least two planar surfaces in order to create two
opposing contact points. These grips work well on rigid components that must be
manipulated in 3D space.
2. Enveloping grippers:this type surrounds the material constraining the material's motion.
The enveloping gripper works well with irregular shapes because, unlike the force grip,
the enveloping gripper does not require two opposing contact forces. However, this type
of grip is worse at "placing" components because the parts of the component that are
enveloped cannot be accessed. An example of an enveloping gripper would be a
mechanics hand.
3. Lift grippers:this type of grip simply slides beneath a work piece and lift. These grips
constrain components in the vertical direction using gravity. Sliding is prevented using
either friction from gravity, or rigid stops. A fork lift is an example.
4. Vacuum grip: this type generates a pressure differential above the work piece, allowing
the piece to be lifted against gravity. These types of grips work best with large planar
surfaces.
Operators, prior to the implementation of the transfer system, used a modified force grip
approach to separate the heat spreader material and the graphite foil. First operators would
slide the top sheet sideways until the sheet formed a lip over the stack. The operator would then
34
pinch the sheet between the thumb and forefinger and lift, removing the sheet from the stack.
As the operator draws away from the stack their hand is reoriented from the horizontal
direction to the vertical direction so that the sheet lies with gravity. This reorientation is very
important because the sheet cannot support its own weight against gravity and so reorienting
prevents the sheet from bending and creasing.
The types of grippers were considered with respect to the current method used by
operators and other features of the material. The first and most important feature was the formfactor of the input material. Heat spreader material would enter the system as individual sheets
in a batch stack. In addition, sheets were non-rigid and delicate. For this reason, the enveloping
style was immediately ruled out because the material was neither rigid, nor irregular in shape.
The next most important feature was placement of the sheet. The polyester film was
coated in a low-tack adhesive and so the sheet must be pressed into the film in order to stick.
Both the force and lift grip types would have to have physical contact below the sheet during
placement in order to support the sheet against gravity. This would prevent the sheet from
being pressed into the polyester film until after the end-effector had been removed. By contrast,
a vacuum end-effector generates force on the upper surface of the sheet and, therefore, could
bring the sheet into contact with the polyester film with the grip still engaged. Accordingly, a
vacuum end effector was selected.
3.5.2 Selection of Vacuum End Effector Type
With the decision to use the vacuum end-effector the options were further narrowed to
three potential options.
1. Bernoulli grip
2. Suction pad
3. Vacuum table
Bernoulli grippers create lifting force by generating airflow between two surfaces. The high
velocity airstream has low static pressure. In a Bernoulli gripper, this airflow is controlled
which results in a pressure that is lower than atmospheric pressure. This low pressure zone
35
creates a partial vacuum. The lifting force is generated by airflow and so the work piece is never
brought into contact with the Bernoulli gripper. This was an important consideration because it
would help preserve the quality of the heat spreader material.
The suction pad gripper is the most common style of vacuum gripper. A low pressure
negative airflow is generated at an active site. This active site is brought into contact with the
material, blocking airflow and causing a vacuum to build up behind the material. A series of
suction pads working in conjunction lift the material and allow the system to be manipulated.
The suction pad surrounds the active site, and supports the material. If the material is partially
drawn into the active site the soft suction cup helps prevent marring.
Last, the vacuum table. This option works in the same way as the suction pad except that a
series of active sites are created across a continuous surface. With a large number of active site
this option permits the generation of a very even pressure distribution. However, this option is
more likely to cause damage to the material in high strength vacuum systems because the edges
of the active site are brought into direct contact with the material.
Each of these options was tested using available components. Based on the key
considerations, three criteria for success were created.
1. The end effector must perfectly hold the material, the material cannot slip once the
end effector is engaged. After lifting a vision system will actively correct for
misalignment. Therefore, once lifted the material cannot move relative to the end
effector or the correction will become invalid.
Test: When engaged, does motion of the end effector cause the material to
shift?
2. Use of the end effector cannot damage the material. Inspection will occur before the
material is placed into the transfer subsystem. Therefore, if the grip creates an
impression or crease when the vacuum is engaged then the inspection will become
invalid. Even if the end effector itself does not do damage the material can still
36
become damaged during motion if the heat spreader material is not properly
supported.
Test: Does engaging or moving the end effector cause visible damage to the
material?
3. The end effector must be capable of placing the material on the polyester film. This
means that the system must be capable of applying sufficient force to the sheet to
cause the sheet to stick to the film.
Test: Can the end effector be used to press the sheet into place?
The first gripper option that was considered was the Bernoulli gripper. The Bernoulli
end effector was tested using an SMC Series XT661Non-Contact 60mm Bernoulli type gripper
[14]. The gripper is shown in Figure 12. The Bernoulli gripper adequately supported the
material without damage but failed to perfectly hold the material and could not be used to press
the sheet. This type of end effector uses airflow to generate the gripping force, therefore the
work piece is never brought into contact with the end effector. This makes the Bernoulli gripper
very useful for semiconductor manipulation. However, semiconductor wafers are rigid while
the heat spreader sheets are flexible. In this case the airflow generated by the Bernoulli gripper
induced wave-like motion in the flexible sheets. This instability was considered unacceptable.
Additionally, because the sheet is never in contact with the end effector no frictional force is
generated between the two which causes the sheet to shift easily. There was no obvious way to
solve these issues and so this option was rejected.
*OOO
SMC XT"1 N=a-Cmtut BeruallGrippWr
Figure 12: Bernoulli non-contact gripper.
37
The second option that was considered was the suction cup option. This option was
tested using a custom system prepared by a Schmalz Engineering Intern. The end effector was
created using Schmalz SGP-40-HT 1-60-N035 40mm [15] suction cups and Schmalz FSTE-G1/8AG-15 spring plungers [16]. This option is shown in Figure 13 and was more successful than the
Bernoulli gripper, the suction cups could hold perfectly, press the sheet and engage without
damage. However, because the available suction cups were round they could not be brought
into perfect contact with the edge or the corners. As a result, when the end effector was moved
quickly, airflow around the corners and edges quickly caused creasing. This option was rejected
because there was no obvious way to protect the edges of the material.
Figure 13: Schmalz suction cup gripper lifting heat spreader material
The last option that was considered was the vacuum table option. Shown in Figure 14,
this option was tested using a SineSetrm S2 Vacuum plate connected to a Welch Duo Seal@
model 1402 Vacuum Pump [17]. This option was used to test the design concept but was not
considered a viable option because the weight was too much for any of the robotic arms
38
options. The design would require redesign before the end effector could be considered viable.
During testing it was shown that the vacuum table could perfectly hold, press the sheet and
move without damage. However, the material could be seen visibly deforming at the vacuum
holes. The table was made from steel with 3/16" diameter holes which would leave impressions
in the material after the vacuum was released.
VaCUUM Plate
Figure 14: Vacuum table gripping heat spreader material. The left image shows the vacuum plate and
vacuum pump. The right image shows the vacuum plate gripping the heat spreader material.
After testing we observed that there were no readily available options that would
perfectly cover the sheet and so a custom grip would be required. In addition to being the most
likely to succeed, the vacuum table had the additional benefit of being the simplest end effector
to design and fabricate.
The vacuum table end effector was selected because (with some redesign) the system
perfectly held the material, would not damage the material, and could press the material into
the polyester film and because this type of end effector was the simplest to design and fabricate.
39
3.5.3 Design of the Vacuum End Effector
Figure 15: Vacuum end effector design. SineSetTM S2 vacuum table (Left) and modified design (Right)
The design of the vacuum table end effector was based on the SineSetrm S2 Vacuum
plate system. The new design would still use holes drilled into a continuous sheet of material
with a cavity behind the sheet to create the active sites. The old and new vacuum end-effector
are shown in Figure 15. Several modifications were made to the design to reduce weight,
eliminate damage, and improve usability.
" Steel was replaced by nylon. This reduced the weight of the end effector.
" A larger number of smaller diameter holes were used. This reduced contact forces by
creating a more even vacuum pressure distribution.
*
The contact shape of the grip was created to match the shape of the heat spreader sheets.
This protected the edges of the sheet and helped eliminate damage
* Mounts were added in order to fixture the end effector to the arm.
The end effector is created by two components; the diffusion plate and the vacuum core.
The diffusion plate is made from 1/8" nylon drilled with 1mm holes. The 1mm holes are spaced
5mm apart. A 15mm border lies between the holes and the edge of the plate, fasteners are
placed in this area. When in contact with the material, force is generated by vacuum at each
hole while the sheet is supported by the nylon diffusion plate. The holes are connected to a
single vacuum cavity in the vacuum core. The core is made from 1/2" nylon and the cavity is
created by a 1/16" deep milling process. Support channels are left during the milling process
40
which prevents the diffusion plate from deflecting inward when the vacuum is engaged. The
cavity edge and the support structures were coated in epoxy and the two plates are brought
into contact with ten 4-40 machine screws that lie on the diffusion plate and cavity border. This
internal structure is shown in Figure 16. The support channels prevent the diffusion plate from
deflecting when a vacuum is drawn. The location and shape of the support channels provide
support without restricting airflow or blocking vacuum holes.
Boarders
4-40 Through Hole
with Chamfer
Diffusion Plate
Cavity
Vacuum Core
4-40 Tap Holes
Vacuum "Pull"
Extended Tabs
[j
-
Vacuum Active Site
Air
Inlet
Alternate Inlet
{ tSupport Channels
225mm
I
225mm
305mrr
Figure 16: Diffusion plate (Left) and vacuum core (Right). Combined these pieces create the vacuum
action, allowing material to be lifted
The mounting fixture is attached to two extended tabs on the vacuum core with two pairs of
1/4-20 machine screws. The border and extended tabs are used as the location for fasteners so
that the fasteners do not pierce the vacuum cavity. As a result these fasteners do not require
seals and the end effector can be disassembled easily. The mounting fixture is attached to an
EPSON tool adapter which, in turn, is fixed to the SCARA robotic arm. An exploded model
view is shown in Figure 17. The final assembled end effector is shown in Figure 18.
41
10
ITEM NO.
7
8
2
Ji l1
PART NUMBER
QTY.
1
Diffusion Ponel
1
2
Vacuum Core
1
3
Mounting Fixture
1
4
4-40 Machine Screw
8
5
1/4-20 Machine Screw
4
6
Air Flow Control Valve
2
7
1/2-20 End Cap
1
8
10-32 Flow Connection
2
9
10-32 to Male Barb
2
10
EPSON Adapter Couple
11
EPSON Tool Adapter
1
1
,5-
Figure 17: Exploded view of the vacuum end effector and the grip-to-arm fixtures (item 3, 10, 11)
Figure 18: Vacuum end effector.
42
3.5.4 Propagating Vacuum Effect
Two air flow valves lie at opposite corners of the vacuum core. These valves allow positive
and negative airflow into the cavity. These locations were selected to create a vacuum force that
would propagate across the end effector. In a system where airflow occurs evenly across a
number of active sites, there is the possibility for the material to become pinched. Figure 19
subsystem shows what happens when an evenly distributed vacuum force is brought into
contact with a slightly concave sheet of material. The two ends of the sheet are gripped first. The
vacuum force pulls the sheet flat causing excess material to be pushed towards the middle
where the displaced sheet forming a wrinkle.
At.
tttt
'It''LF
Li
Figure 19: Diagram depicting the effect of the propagating vacuum design. A- a vacuum table with evenly
distributed pressure. Al- table comes in contact with a concave work piece. A2- work piece is gripped at
both edges. A3- work piece is brought displacement propagates inward and forms a wrinkle. B- a vacuum
table with propagating vacuum design. B1 - table comes in contact with concave work piece. B2- work
piece is gripped from one edge. B3- displacement propagates from left-to-right, no wrinkle is formed.
43
The propagating vacuum effect used for this end effector prevents this from occurring. At
first, the sheet is not in contact with the end effector and negative airflow occurs only in the
corner. When the sheet comes in contact with the end effector the holes located at the corner
become blocked off causing negative airflow to be drawn from further along. By propagating
the vacuum from one corner diagonally to the other the material can be smoothed out and
brought into flat contact with the diffusion plate. This effect can be seen in Figure 20.
--
----
4
I1-
n
II
~4
U4
1071%
M-)
In
U
=4
CC
=
4~--~
-
4-
k
Figure 20: Propagating vacuum effect caused by airflow within the internal structure of the end effector.
The propagating effect can be created at any location on the surface, so long as the
airflow starts at only one location. The top left corner was selected as the starting site for the
negative airflow because the final product will be registered at the top left corner.
44
3.5.5 Contact Detection
The last consideration for the end-effector was the method for detecting contact with the
sheet and the support table. As the placement system moves sheets from the input stack to the
polyester film the stack will decrease in height. Each sheet measures roughly 25 microns in
width, because the sheets are so thin the team decided that dead-reckoning alone would not be
accurate enough to guarantee accurate pick-up. Accurately determining the height for pick-up
is critical because the material is delicate, and an overshoot could easily destroy an entire stack.
Three options were considered;
1. Force sensor
2. Light array
3. Capacitance sensor
The first option considered was the force sensor. The Epson Arm selected in section 3.4
can be equipped with a force sensor but the sensor is a non-standard component. Concern with
the force sensor option was that the grip would have to be brought into full contact with some
non-zero force to be detected. Given the delicate nature of the material any force could cause
damage. For example, in a situation where the sheet was not perfectly flat wrinkles could form
damaging the sheet (in the same way as seen in Figure 19). Concern about damaging the
material ruled out the force sensor as an option.
The second option, the light array, works by arranging a series of lights opposite a
detector such that light passes the stack. As the stack decreases in height more light will be
exposed to the detector giving a very accurate height measure. This option was determined to
be unfavorable because of the controller selected for the system (Section 3.8). The Epson RC180
controller has Ethernet and I/O communication options. I/O options can only send and receive
"go/no-go" commands and a light array necessarily needs a range of communication in order to
send non-binary height information. Therefore, the light array would have to be implemented
with a PLC through an Ethernet connection. Concerns about timing made this an undesirable
option.
45
The last option, the option that was eventually selected, was the capacitance sensor.
Capacitance sensors work by measuring electrical capacitance between the sensor and a surface.
These sensors work best with conductive material, and the heat spreader material happens to be
electrically conductive.
This option was the best of the three evaluated. Capacitance sensors can be non-contact,
therefore sheets can be detected based on proximity without generating a force [18]. Second,
capacitance sensors are available for standard I/O connections, so this option could easily be
incorporated into the Epson RC180 controller. The capacitance sensor selected was the 3-Wire
DC Metallic-Object Proximity Switch #7674K912 from McMaster-Carr.
In the interest of time, the capacitance sensors were selected but not implemented prior to
testing.
46
3.6 Structural Frame
3.6.1 Concept Selection
The structural frame is the interface between the arm and the global reference frame.
Therefore, the design was primarily dependent on the SCARA robot and secondarily on the
web handling system. The decision to use a ceiling mounted SCARA robot limited the potential
sources for framing. Of those sources, there were no frame options that could be delivered
before the SCARA robot was scheduled to arrive. In order to begin testing immediately it was
necessary for the frame to be ready before the SCARA robot arrived. For this reason, the
decision was made to fabricate a custom frame. The final version of the frame is shown in
Figure 24. Several key considerations were made when developing the design for the frame.
Key Considerations for the Structural Frame
1.
The frame must adequately support the arm without inhibiting motion
2. The placement workspace must lie within the SCARA robots z-axis range.
3. The frame must not interact with the web handling system
At the time, the design of the web handling system had not been finalized. In addition, in
order for the SCARA robot to have the largest working area the base of the SCARA robot would
necessarily be fixed over the polyester web. Considering these two issues and in the interest of
providing adequate clearance for the web, the decision was made to use a U-shaped frame. This
shape would allow the SCARA robot to rest above the polyester film without risking interaction
between the structural frame and the web handling system.
3.6.2 Design of the Structural Frame
Based on the rapid prototyping methodology the structural frame was broken into two key
features; a mounting plate and a support structure. The mounting plate would fix the SCARA
robot to the support structure which, in turn, would be fixed to the global reference frame. The
following Figure 21 shows a model view of the support structure, mounting plate, robotic arm
and end-effector.
47
Mounting Plate
-
SCARA Robot
End Effector
Support Structure
Figure 21: CAD model of the support structure, mounting plate, SCARA robot and end effector
Mounting features were cut directly into the mounting plate using a single waterjet cutting
operation. The support structure were made from 2" structural steel pipe and standardized
galvanized iron pipe fittings. Originally 80-20 aluminum extrusions were considered, however,
Epson representatives warned against the idea because the repetitive motion of the arm could
induce vibration. The mounting plate held the SCARA robot. In order to select the width of the
plate and the type of material a model was created and tested using the Von Mises Stress study
in the Solidoworks SimulationExpress toolbox (Figure 22). Based on the results 1/4" thick cast
alloy steel was selected. The Epson G6 can generate a reaction torque of 500Nm, a horizontal
reaction force of 2500N and a vertical reaction force 1500N [19]. The study in Figure 22 indicates
at the maximum reaction force specified by Epson that the plate will deflect 0.62mm with a
factory of safety of 4.82.
48
Name
T
Min
M
Stress
VON: von MStress
38856 N/m^2
Node: 17070
5.07306e+007
Node: 18459
N/mA2
VM nA Ie04An2)
4,2==,1.O
38,36
2.0
8,47.408.0
8,4B7,486.D
4,2",1 TI.D
I
I
ode 365I
Mounting Ptate-SimutationXpress Study-Stress-Stress
Name
Disptacement
Typn
URES: Resuttant Dfspiacement
Nde:93.6.
-+vi
S&WVnW
241,27S,200.C
ax
0 MM
I ode: 365
0.624185 mm
Node: 9379
Figure 22: Finite element analysis of the mounting plate examining vertical stress.
The rapid prototyping method dictated that machining steps be minimized in order to
reduce fabrication time. This would allow us to deliver a frame before the arrival of the SCARA
robot. The entire structure was fabricated using three machining steps; one waterjet cutting
operation to produce the mounting plate, one series of drills through nylon blocks to produce a
set of spacers, and one series of drills through structural steel pipe cross beams which would be
used to bolt the mounting plate to the support structure. The assembly of the frame was made
simple by the use of standardized fittings. An assembly diagram is shown below in Figure 23.
To attach the robot to the frame, first the SCARA robot was bolted to the mounting plate which
was then lifted onto the structural frame. With the mounting plate resting on the structural
frame bolts were placed through the mounting plate and the two most internal pipes, fixing the
entire structure together. The final assembled system is shown in Figure 24.
49
DETAIL B
SCALE 1 :16
13
ITEM NO.
41
75
6
1
PART NUMBER
QTY.
1
3-Way Elbow
4
2
Floor Mount Flange
4
3
60" Structual Pipe
4
4
48" Structual Pipe
2
5
Mounting Plate
1
6
Tees with Through Hole
8
7
2
8
24"
Structual
Pipe with
mounting
holes
24" Structual Pipe
9
Adjustable-Angle Tees
4
10
93827A245
4
11
1/2"-13 Grade 8 Steel
Hex Nut
4
12
M10 High-Strength Cop
Screw, 120mm long
4
13
M10 Steel Hex Nut
4
14
Spring Lock Washer
4
15
Delrin Spacer
2
6
2
Figure 23: Exploded view of the structural support subsystem
50
Figure 24: Picture showing the final version of the structural frame
51
3.7 Vision System
The vision system will be used to correct for positional errors of heat spreader sheets prior
to their placement on the polyester web. This vision system is distinct from the inspection
system described in Chawla's thesis [3]. Originally, these two vision systems were expected to
be implemented using the same camera but for timing reasons it became easier to separate the
two tasks into two separate camera systems. Chawla's inspection system will be responsible for
detecting defects (step 5 of Figure 3) and the vision system described in this thesis will be used
to correct positional errors ("Vision System" in Figure 7).
Figure 25: Epson CV1 Vision System
The vision system used for the placement system will be the Epson CV1 vision controller
and smart camera (Figure 25). The Epson SCARA robotic arm requires an Epson RC controller
to operate and so an Epson vision system was a natural choice. The vision system is intended to
aid computer guidance applications and is not designed for inspection for defects. In summary,
the CV vision system would be easy to implement but would be unable to detect defects which
is why the AvCarb MEngM team decided to separate the two tasks.
52
This vision system is only used to detect position and orientation of the sheet. The camera
is mounted vertically, oriented upward. The top of the camera lies flush with the workspace,
this reduces the chance that the camera will be damaged if irregular motion occurs. When the
arm moves a sheet above the camera system only the top left corner is visible. By viewing only
the corner the detail of the camera is increased. The top left corner was selected as the
identifying feature because the top left corner is used as the registration point for the film line.
This setup can be seen in Figure 26.
I
Robotic Alrm
End Effector
/
I
Heat Spreader Sheets
Detected Sheet
Camera/
\View/
CV1 Vision Camera
Figure 26: Vision system setup. The robotic manipulator moves heat spreader sheet over the camera. The
top left corner is used as the identifying feature.
The camera is calibrated to relate the width of each pixel to absolute coordinates. This
calibration is done using the arms internal position measurement system in conjunction with
53
identification software on the camera control. The arm is positioned above the camera such that
a registration feature is visible. The registration feature uses 9 translations of a key feature, as
detailed in the Epson Vision Guide [20]. Then, because the position of the arm is known, these
positions can be related to an absolute position.
When in use, the arm moves a sheet of heat spreader material over the camera prior to
placement. The vision system identifies the corner of the sheet using four edge detection
algorithms. The edge detection system is shown in Figure 27. The detection algorithm travels
along the green path in the direction of the green arrow until it encounters pixels that contrast
greatly indicating a transition. This system specifically identifies a transition from dark to light.
The green arrows indicate the detected point located along the edge.
Figure 27: Edge detection algorithm. Green arrows indicate the identified edge.
54
Two line detection algorithms are used for each edge which identify two points along that
edge. The two identified points are projected into a line. The intersection of these two lines is
used to estimate the position of the corner. This method is shown in Figure 28, the four squares
indicate the detected points and solid black lines are the projection. An offset is determined
based on the desired position of the corner and the observed position of the corner. The arm
uses this offset to correct the position during manipulation.
11
4
2
Figure 28: Corner detection algorithm. The enumerated squares indicate the four identified points. The
solid black lines indicated the projected edge and the intersection indicates the estimated corner position.
Angle is determined based on the vertical line, shown by 0.
55
3.8 Controller Design
Epson RC 180 Controll ?r
E
7Power
Ready
Running
0
Input
Error
Stack
User Interface
(24V DC)
Start
Stop
Reset
Recipe
Stack Ready
Emergency
stop
Robotic Arm
Vacuum
Main Safety
Power
Motion
Gripper
Control
120V AC
---
Grip Contact
Table Co
PLC
0
CVi
Controller
Web Handling
Input
Travel
Load I3
System
Figure 29: Controller Diagram for the production line
An Epson RC180 was selected to control the transfer robotic system including the arm,
the vision system, and all the auxiliary equipment such as valves and capacitive sensors (Figure
29). In order for the Epson G6 SCARA robotic arm to function properly the system must be
paired with an RC180 or RC620 controller. In addition to controlling the arm, the RC180 also
has standard I/O and Ethernet communications and the controller can be easily paired with an
Epson vision system. This made the RC180 the obvious choice for the controller for the system.
The subsystems commanded by the controller were divided into five major components.
56
1. Robotic arm
2. Gripper
3. Vision
4. Web handling
5. User interface
The RC180 controller is powered by an AC 220V single phase 60Hz power supply. The
RC180 controller has USB ports, one Ethernet and digital I/O with 16 inputs and 8 outputs. The
controller has an independent plug for connection to the robotic arm. The controller also has a
separate plug for a primary safety system that directly cuts power to the machine which was
connected to a standard emergency stop button. For testing and debugging the RC180 is
connected by USB to a computer terminal. When the command software was finalized the
connection was removed. The operators will instead use the hardwired user interface, which
will prevent modification of the software.
An Ethernet bus connects to the RC180 controller, the programmable logic controller
(PLC) and the CV1 controller. The PLC is responsible for commanding the web handling
system. The CV1 controller commands the vision system. The digital I/O is used to send and
receive signals for the gripper and for the user interface. The gripper has two outputs and two
inputs; the outputs are for the compressed air and vacuum valve, and the inputs are four the
two contact sensors. The user interface has six inputs and five outputs. The output signals
command signal lights which provide the user information about the state of the machine,
errors, and when the machine needs more input material. The input signals come from buttons
on the user interface display. These buttons will be used for typical commands such as start,
stop and reset.
57
Power
CON
Po
Ready
~Machine
OF
Error
RNningOFF
ON
Err,,,
kdle
Stack RedyS
E r.zMVEewihLn
CM
/LGTFMV
th
MS
it
~ ~
~
~
Y es
No
IF
Ero F
tac Empty
0
EDAK
MOVE-
~Rmonxg OI
esceatd
Stack
EkpEypOy
R
tLrnlt wt ie wihFl"Se
C
MOVE:
YeVaCommreOsedN,
3God
Reay
)
~~~Oe
C o nt act EOA
-
r~
LIH-IGHT
F
-
r
MVE
"IGH
esC~IGHTMOV
OVE
3.9 Control System Flow
Yes
M -
No
soao SysteFEEDBACK-
Figure 30: Control System Flow Diagram
The main controller is an RC180 using RC +5.0 control software. The controller accepts
input from buttons, two contact sensors, an inspection system, a vision system and internal
position sensors. The controller commands lights, valves and the position of the arm.
The process steps are shown in Figure 30. The process begins when power is turned on
(indicated in the top left corner of Figure 30). When power is on for both the RC180 controller
(which has an internal power supply) and the separate 24V TDK-Lambda DLP75-24-1/E power
supply then the "Power" light turns on. With power on the system begins to "Warm-Up" which
takes approximately 30 seconds. After warm-up the machine enters the "Idle" state where it
will remain until a stack of material is prepared. Once the material is put into the machine and
no errors are detected the system enters the "Machine Ready" state and the "Ready" light is
58
turned on. If the "Stack Empty" or "Error" lights are on when the machine enters the ready
state then the lights are turned off. When the start button is pushed the machine leaves the
"Ready" state and enters the "Running" state, the "Running" light is turned on.
The running state repeats the following steps, repeatedly picking and placing heat spreader
sheets from the input stack onto the polyester web. The running state starts when the arm
moves to the first position indicated by "MOVE: Start Position". The arm descends from the
starting position towards the material stack. If no material is detected the stack is considered
empty, and the machine returns to the "Machine Idle" state. If contact is detected with the
material the arm stops ("Move: Stop Descend"). While stopped, the "Vacuum" valve is opened
causing the end-effector to engage the nearest sheet. With the sheet held, the arm moves to the
"Inspection" stage. In this stage two camera systems are used; the first is Chawla's inspection
system which detects flaws, the second is the vision system described in Section 3.7 which
corrects the arms trajectory in following steps. If no material is seen the arm returns to the start
position and makes a second attempt. If the material is present but defects are detected then the
arm deposits the material in the reject pile before returning to the starting position. If the
material is good then the arm moves over the polyester film line. The web is constantly moving
at a rate of .5m/min. The arm descends in a low sweeping arc until contact is detected with the
film. Once contact is detected the sweep switches so that it is only translating with the line.
During translation the arm moves only in the direction of the web. At the same time the
vacuum is turned off, allowing the material to separate from the grip. These two steps "MOVE:
Sweep" and "MOVE: Translate with Line" are adjusted according to feedback from the pull roll
and the vision system. The vision system identifies how the end effector should be adjusted to
correct for position, while the pull roll identifies where on the web the sheet should be placed.
These two sets of feedback assure that each sheet is positioned correctly during each pass of the
placement system. Contact is detected during the "sweep" which informs the machine when to
transition to the "translate with line" step. If the contact is not detected before preselected
absolute position, then the system registers an error and returns to the "Machine Idle" state. If
the machine correctly places the sheet then the arm begins to rise. Prior to rising a separation is
created between the heat spreader sheet and the grip by opening the compressed air valve. This
59
causes a jet of air to push against the sheet, reducing the chances that the sheet will stick to the
grip during the rise step. Once the arm has risen a 10mm away from the film the compressed air
is shut off to prevent airflow from disturbing the rest of the system. The arm then returns to the
starting position to restart the running loop.
3.10 Web Handling
3.10.lDesign of the web handling system
SLdLad
CQ-2
o
GePu
CaClrL
Ro
I
L Aad CeDiA&
Figure 31: Web handling diagram
The web handling system is divided into six principal components with three load cells
providing tension feedback and three more rolls which change direction of the film. The
original web handling system design is shown in Figure 31. From beginning to end the
components are; an unwind roll, roll guide, pull roll, support, calender, and rewind roll. The
web begins with a roll of polyester film which is driven by an unwind servo. The web passes
over a directional roller and a load cell to the roll guide. The roll guide actively centers the
alignment of the web on the rollers. The roll guide is crucial for positional tolerances because
the robotic arm does not correct for positional errors in the cross web direction. If the web has
drifted 2mm sideways that error will become a 2mm position error in the final product. Next,
the web travels to a pull roll which will actively maintain tension and position in the travel
direction. Essentially, the roll guide will effect horizontal accuracy and the pull roll will effect
vertical accuracy in placement of the heat spreader sheets. The web passes another load cell to a
60
support table. The support is displaced from the web, and is only in contact when the robotic
arm is pressing a sheet into the film. The support constrains the web which prevents deflection
and reduces the effect placement has on the tension of the web. The web passes another
directional roller to the calendering machine. Last, the web passes over another load cell and
directional roller to a servo driven rewind roller.
The web handling system is separated into four tension zones. A tension zone is the area
of web between any two tension elements such as motors, or brakes. In this system there are
four elements which principally effect tension; the unwind roll, the pull roll, the calender
machine and the rewind roll. Placement can also effect tension due to the friction generated by
the act of pinching the web between the end-effector and the support table. However, the
tension generated by pinching is highly repeatable and can be eliminated by the control system.
As seen in Figure 31, a load cell is located between each of the principal tensioning elements.
Feedback from these load cells will be used to control the system.
The pull roll will govern the speed of the web. The support table is located directly behind
the pull roll because the web will be least susceptible to errors in the area after the speed
governing roll. The tension of the calendering machine cannot be changed because any change
will affect the quality of the output material. Therefore, only the unwind roll, the pull roll and
the rewind rolls will be used to control the system. The system was designed and built by an
outside contractor.
61
4 Experimentation
This chapter discusses the methods of experimentation including characteristic
measurements, measurement techniques and preliminary experimentation.
4.1 Quality Measures
The output from the production line has requirements on position and quality. Customer
requirements require the material to be defect free, positioned on the roll with a +1mm
positional tolerance and a +50 angular tolerance, and that the heat spreader material be between
25-30 microns thick.
Defects will be detected using Chawla's inspection system and the thickness will be
determined by the calendering process described in Svenson's thesis. Therefore, this thesis will
be primarily concerned with the positional requirements, on the conditions that the placement
system does not create defects or negatively affect the calendering process.
The placement system was tested for accuracy and repeatability. The grip is rigidly fixed
to the arm, and the Epson arm has well-documented measures of repeatability (the Epson
website reports that the G6-series has a x-y dimensional repeatability of + 0.015mm, a vertical
repeatability of + 0.010mm and an angular repeatability of 0.005 degrees [21].) This
repeatability represents 1.5% of the acceptable range and so we decided to ignore errors caused
by the arm. Additionally, testing during development of the end-effector demonstrated that
with the vacuum engaged sheets would not shift when exposed to normal operating forces. We
will, therefore, assume that once the vacuum is engaged the sheet does not move. The following
experiments are designed to identify and test the sources of positional error.
Measures for the experiment were taken using the Epson CV1 camera. -The camera has a
resolution of 640x480 pixels and was equipped with a 16x magnification lens. The calibration
system indicates a 0.0768 mm/pixel in the X-direction and 0.0785 mm/pixel in the y-direction.
62
4.2 Design of Experiments
Two experiments were created to test for causes of variation within the placement system.
Two conditions are assumed true: that the arm moves perfectly, and that once the grip is
engaged the sheet does not shift.
First, a "Stationary" test was used to determine if any shifting occurred during pickup, or
placement of the sheet on the testing table. The results of the test were used to determine if
errors occurring in the first test were caused by the repositioning algorithm, or the normal
shifting. To start, the arm was commanded to pick up a sheet. The arm traveled over the vision
system and a vision algorithm is run identifying the corner as described in Section 3.8. The
position was recorded. The arm then returned to the starting position and lowered until the
sheet was in contact with the worktable. The sheet was then released and the arm withdrawn.
The arm repeated the process, identifying the corner position to determine whether shifting had
occurred during pick-up or placement.
A "Repositioning" test was used to evaluate the placement and adjustment of the transfer
system. First, a sheet of material was placed randomly within a 240mm X 280mm square. The
randomness was created by releasing the heat spreader sheet from a height of 20mm, and
allowing the sheet to fall into position. The arm was then commanded to pick up the sheet. The
arm then traveled to a position over the vision system and the angle of the sheet was identified
using the vision algorithm. The sheet was then adjusted for angle by turning the grip. The
vision algorithm was then run a second time, and the sheet's position was identified. The arm
then adjusted the position of the sheet to match a pre-defined central position. The vision
algorithm was run a third time and the position of the corner and the angle of the sheet was
identified. The starting and ending positions and angles were recorded. The arm then returned
to the starting position and released the sheet. This process was repeated for 100 trials. The
following Figure 32-35 shows different position adjustments. The top image shows the original
position, and the bottom image shows the corrected position. Test A shows a sheet starting with
a top-left shift, test B shows a bottom-left shift, test C shows a top-center shift and test D shows
a bottom right shift.
63
Figure 32: Repositioning test example A. The top image shows the original random position, and the
bottom shows the corrected position. In this example the sheet starts shifted to the top left.
64
Figure 33: Repositioning test example B. The top image shows the original random position, and the bottom
shows the corrected position. In this example the sheet starts shifted to the bottom left.
65
Figure 34: Repositioning test example C. The top image shows the original random position, and the bottom
shows the corrected position. In this example the sheet starts shifted towards the top.
66
Figure 35: Repositioning test example D. The top image shows the original random position, and the bottom
shows the corrected position. In this example the sheet starts shifted to the bottom right.
67
5 Results
This chapter reports the results of the designed experiment, including both quantitative
and qualitative results.
5.1 Summary of Results
The experiments were conducted to test the accuracy and precision of the automated
transfer system.
" The transfer operation took less than 30 seconds to complete.
" After 100 trials no damage was identified on any of the placed material.
*
No shifting occurs when picking-up or placing the heat spreader material under the
testing conditions we used. The end-effector and arm are not the cause of significant
variation.
" Errors in sheet position could be corrected prior to placement using the proposed robotic
arm and vision system.
" The system met the criteria for success for position by successfully positioning the heat
spreader material within the +1mm positional tolerance and
50
angular tolerance for all
trials.
5.2 Analysis of Transfer System
The results of the experiments proposed in Section 4.2 are shown here. The ability of the
system to correct for positional and angular errors is demonstrated by the repositioning
experiment and shown in Figure 36 and Figure 37 respectively. The target position is (0,0) and
the target angle is 00. In Figure 36, the gray dots show the corner position as identified by the
edge detection software. The left graph shows the starting position of the sheets, and the right
shows the position of the sheet after the offset has been corrected. In Figure 37, the grey line
shows the initial angle, and the black line shows the angle of the sheet after correction.
68
Corrected Position
Starting Position
10
*
10
&*
*
E
%
-10
0
*
go
e
*
2
2
0
E
E
%
00,
-4
a
2
4
10
8
6
1=
-8
-6
-4
-2
I
2
4
6
8
10
0
S.
.0
-4
.
*
-60
-10
x position (mm)
-10
x position (mm)
Figure 36: Charts showing the corner position of the detected heat spreader sheet, both the starting
position and the corrected position.
Detected Angle for Random and Corrected Position Sheets
10
8
6
4
02E
be
v
2
0
-2
-4
-6
-
Starting Angle -
Corrected Angle
-8
-10
Figure 37: Chart showing the angle of the detected heat spreader sheet. The grey line shows the starting position
and the black line shows the corrected position.
69
Table 1: Test of pickup and placement shifting, offsets were not corrected. The shift was identified as the
difference between the two corner positions identified by the vision system.
Stationary Test
X Shift
Y Shift (mm)
(mm)
Mean
Range
Std Dev
-0.038
0.299
0.073
0.020
0.719
0.130
The stationary test shows that there was no significant shifting occurring during pickup,
placement, or during travel. The stationary test measured shift during pickup, travel and
placement. The difference between the starting and final position of the sheet was recorded and
the mean, range and standard deviation of this difference is shown in Table 1. The null
hypothesis was that there was no significant difference between the starting and ending
position of the sheet during the stationary test for either the x or y direction. The test was
performed using fifty samples. The result using a t-test was a p-value of 0.9884 for the xdirection and a p-value of 0.97 for the y-direction. We therefore accepted the null hypothesis. If
there was no significant difference between the starting and ending position of the stationary
test we can assume that that the robotic arm and end-effector perform the transfer operation
with no shifting.
Using the result of the stationary test indicating no shifting, we can assume that the
repositioning test is an accurate representation of the system. From Figure 36 and Figure 37, we
see that the transfer system does adequately adjust for both position and angle using the vision
system. The sheets were positioned within the +1mm and
50
tolerance for all trials. The sample
mean, sample standard deviation, Cp, and Cpk values are shown for the corrected position in the
following Table 2. These values indicate extremely good process control, we expect less the 25
parts per million to fall out of the specification limits. Figure 38 shows that corner position for
all trials were well within the specification limits. Given the very high value for Cpk for angle we
suggest reducing the specification limits for angle from 5* to 1'.
70
Table 2: Process Capability
X
Y
Angle
V (mm)
s (mm)
0.06
0.18
0.09
0.21
-0.1
0.17
Cpk
C_
1.82
1.92
1.47
1.61
10.06
10.26
Corrected Position
1
0.8
0.6
0
e
.seses
E
0
-0.8
-0.6
-0.*0 -"
0se
oe -
m
C
0
CL
@0*@
O
a
2*
0
00
e
0.2
@0*
0.4
0
0.6
0.8
-0.4
0
-0.6
0
-0.8
-1
x position (mm)
Figure 38: Target and corner location. This is the same as the corrected position from Figure 36 with a
different set of axis.
5.3 Sources of Error in the Vision System
During testing, a number of recurring problems presented themselves related to the vision
system. These errors do not occur often, but could still cause problems during a full-production
run.
71
"
Contrast:the edge detection software works best in high contrast. If the grip and the
material are similar in appearance the software will not easily detect the edge of the
material. It is important to keep the end-effector clean, particularly in a carbon-materials
facility, because debris can cause variations in contrast. Lighting is crucial, in this system
an upward-facing camera was used and overhead lights caused incorrect sources of
contrast. We had to use a shield to block light from overhead lighting.
" Local defects: the edge detection software identifies a single point of high contrast by
traveling a detection line (3.7). Because of this, if there are local defects the algorithm
will give an incorrect point. The corner is determined by projecting two lines from four
points and if one point is off the entire estimation will be incorrect. There are two ways
to avoid these errors; only use good material, use multiple redundant edge detection
lines.
" Inaccurateabsolute coordinates: after experimentation we recommend positioning the
camera in a position that naturally matches the reference frame of the robotic arm. The
vision system was turned 450 relative to robotic arm, the grip was turned to match (this
was done to reduce cycle time). However, this meant that "correction" of the position of
the grip were not the same for placement and for the over-camera position. Simply put,
the camera's x and y coordinates are relative to the end-effector, not the reference frame
of the arm. This reference frame causes some coordination issues.
*
Sheet incongruity: The heat spreader material undergoes shrinkage during processing.
Occasionally this causes some of the material to be produced with non-rectangular
geometries. The vision software used assumes a perpendicular corner and straight
edges. If either of those assumptions are not true then the correction software will be off,
particularly with regard to angle.
72
6 Conclusions and Future Work
6.1 Summary of Conclusions
A working transfer robotic assembly robot was designed and developed for use in a heat
spreader production line. The robotic system was capable of transferring a sheet of heat
spreader material, every 30 seconds within a positional tolerance of +1mm and angular
tolerance of
50
without damaging the material. This work has revealed a variety of useful
insights into the design of transfer systems for delicate, thin-film materials. The insights of
greatest interest are:
*
Robotic Arm: SCARA robots are highly effective for material transfer systems. The four
degree-of-freedom style SCARA robots balance versatility and repeatability, making
them more useful than a gantry system and more cost effective than a 6-axis robot.
Additionally, when using a large area end-effector we recommend a vertically mounted
robot to increase the size of the functional workspace. Last, if available, select a model
with internal air and electrical lines. Lines passing near or through the axis of rotation of
a joint will be much less susceptible to damage from repetitive motion.
"
End-Effector: The vacuum table style end-effector is an excellent method for
manipulating delicate, thin-film materials. The small, highly distributed set of vacuum
sites helps to prevent damage by uniformly distributing the vacuum force and the
propagating vacuum flow by preventing creases. The large contact surface protects the
edges of the sheet during motion by preventing large deflections. The smooth nylon
surface does not scratch or otherwise damage the surface of the material that the endeffector is manipulating. Last the end-effector is easy to fabricate, built from only three
components and a set of fasteners.
"
Vision: A robust vision system will be dependent on a number of factors. The most
important factor is creating high contrast between the manipulated material and the
background. The color of the end-effector should be selected with respect to the
73
material. For large sheets, a vision system limited to one corner can be an effective way
to increase precision.
6.2 Future Work
There is a great deal of additional work to be done on the heat spreader production process. The
following are a list of recommended topics for future work:
*
Incorporation:First and most important work is to incorporate the three subsystems
presented in the three AvCarb MEng thesis; "Implementation of Automatic Inspection
System" [3], "Pyrolytic Graphite Production: Automation of Material Placement", and
"The Addition of a Calender Machine to a Pyrolytic Graphite Sheet Production Plant"
[4].
*
TranslatingPlacement:The current process places sheets onto a stationary table.
However, in a full production run it is desirable to place onto a moving polyester web.
Pausing the line during placement causes marking on the calendering sheet as the
pressure from the calendering machine engages and disengages.
*
Incorporatecapacitancesensors: The starting material begins with 90micron thickness prior
to being calendered. As sheets are removed from a stack and placed on the line the
height of the stack will decrease. Active feedback from the capacitance proximity sensor
will reduce the chance that the material will be damage during pick-up.
" Placement pressure: Actual placement pressure should be measured to evaluate effects on
the effectiveness of transfer to the polyester film web. Initial testing indicated that
pressure above a certain threshold did not improve the adherence of the material to the
film. This effect should be tested and analyzed.
"
Tack and static cling for placement: Similar to the placement pressure, the low-tack
adhesive on the polyester film and static electricity could both effect the adherence of the
material to the film. Some observations were made which indicate that static electricity
is sufficient to hold the spreader material to the polyester film.
74
7 Appendix
Engineering Diagrams
1200
8.86
7.68
.20
.39
42
3.94
+=
10.43
9.25
.26
.63
______________________U
+
.®
.50
.16
.50
UNLME OTHWISE SPEC94ED:
DMENK
AREt INC-EM
"M.E
-
-
.0Q
DC
DRAV
TITLE:
XAR: MA.VIC
MM i
TWO PLAM D~CVAAd
THM RACE DEQUAL
SolidWorks Student License
INTERPRET cec/Ertc
Academic Use Only
JN N T-S
I
'lESC E PRAPPETCC
N44ERmI COMPANY NAME HEIE. ANY
REPRCLtrON N FARF OR AS A WHOLE
1.E-C
OF
OMEOI.T E MbITS ftEJUE/lSF
.4QwET COMPAKY NAMe HERE. IS
PpoiYefrio
TOEAMVG
PE:
NE
F
PCHfats
MATEVI
rfr-
AF
aA
"^NeS
RE%
SIZE DWG. NO.
A Vac. Core
An
APPICATON
ENGAP
00
NCT
SCALE CRA OINC
SCALE: 1:4 WEIGHT:
SHEET 1OF
75
12.00
5.50
R 1.57
.20
90.000
R.50
.50
.20
1.69 1.00
R.71
T
.
01
5,7
-
UNLESS OTIERWISE SPECEc:
CPMNSN ARE IN INCE
AN.k*Pi
MOA :EDSMO
THREERLACECMW
ThORarfl
MATBnutMc
SolidWorks Student License
Academic Use Only
-RH110
NAM
DATE
DRAMN
TImE-
S
i
t
neR-"^twL
ME RTCN
cRAWINCE 101 CNTNEO
S 9O >.-WYrGOF
CINERT CUPMC
NAP/E !SE. Aff
RPROCLCM
NPART OR ASA W410!E
A.ITHEO
VtWlTN PEinShONC
SERT COM PAN MA SE is
1.69
-
Nr
VI
&M
APtR
CCTo
GA
SIZE DWG. NO.
Of
NEC
APL
63
LIEO
A E.E. Fixture
ON
DO
NOT SCALE RA 'NC
SCALE:
1:4
WBGHT:
RE%
SHEET 1OF
76
1.0
6.0.0)
7 00 ".43
15
2.48
.50
62
r3.
7_50
I
.52
6-o0\
-
/2.00
2.00
.
1 0- 7.00
43
-
18 .00i
\2.50
33.00
50
-
.25
I
2.00
Ul.ES
OTHERWISE
SPECIfED:
1E4D0e AM IN INO-
NM
t---
-
.505
3.00
DAIE
DRAhM
TITLE:
ANGUk MCH -WC
1WOPLACECECAAL
1 PLACE CMAL
SolidWorks Student License
Academic Use Only
N!E
EN1G
AP
ANVG AM
ETZMEM-:
AGAM
SIZE DWG. NO.
'HOLrT
TIE !TEN
3EIEIflMPANY
NAME
E.5?
AS
A eswQLE
NEXT
PEEMSSICN
OF
.
F"ERODt.CON ft FARI OR
RE\
1
A Mt. Plate
A35Y
CC
1JO*
:
e&
iA
cCA.E
SCALE: 1:12 WEIGHT:
SHEET 1OF
77
8 References
[1] Ballard Power Systems Inc. Ballard Sells U.S. Material Products Division. 31 Jan. 2013.
<http://www.ballard.com/about-ballard/newsroom/news-releases/news01311302.aspx>. Accessed
April 4, 2014
[2] AvCarb Website. Mar. 2014. <http://www.avcarb.com/>. Accessed April 4, 2014
[3] Chawla, Y. "Implementation of Automatic Inspection System"
[4] Svenson, K. "The Addition of a Calender Machine to a Pyrolytic Graphite Sheet Production
Plant"
[5] Inagaki, M.; Ohta, N; Hishiyama, Y., "Aromatic polyimides as carbon precursors", Carbon N.Y.,
vol 61, pp. 1-21, Sept. 2013.
[6] Y. Kaburagi and Y. Hishiyama, "Highly crystallized graphite films prepared by high-temperature
heat treatment from carbonized aromatic polyimide films," Carbon N. Y., vol. 33, no. 6, pp. 773-777,
Jan. 1995.
[7] H. Hatori, Y. Yamada, and M. Shiraishi, "In-plane orientation and graphitizability of polyimide
films: II. Film thickness dependence," Carbon N. Y., vol. 31, no. 8, pp. 1307-1312, Jan. 1993.
[6] B. Confidential, "Strength in our Company GrafTech International : Overview," 2007.
[9] M. Inagaki, S. Harada, T. Sato, T. Nakajima, Y. Horino, and K. Morita, "Carbonization of
polyimide film 'Kapton,"' Carbon N. Y., vol. 27, no. 2, pp. 253-257, Jan. 1989.
[10] "Heat spreader material Sheet (PGS) Heat Spreading Material" Panasonic, Accessed: 04 Apr.
2014. <http://www.panasonic.com/industrial/electronic-components/protection/pyrolytic-graphitesheet.aspx>.
[11] E. Pop, V. Varshney, and A. Roy, "Thermal Properties of Graphene: Fundamentals and
Applications," MRS Bull. 37, 1273 (2012)
[12] Zarrouati, N. "A Precision Manipulation System for Polymer Microdevice Production",
Accessed 31 July 2014. <http://dspace.mit.edu/handle/1721.1/61927>
[13] Monkman, G.J.; Hesse, S.; Steinmann, R.; Schunk, H. (2007). Robot Grippers. Wiley-VCH. p.
62. ISBN 978-3-527-40619-7.
[14] Osborne, Mark (8 February 2010). "New Product: Bernoulli Gripper from Festo enables
'contactless handling"'. PVTech.
[15] Schmalz. Flat Suction Pads, Accessed 21 July 2014.
<http://us.schmalz.com/np/pg/produkte?hier=155-171-192-3385>
[16] Schmalz. Spring Plunger with Damping, Accessed 21 July 2014.
<http://www.schmalz.com/np/pg/produkte/ansicht?art=2153&hier=155-156-189-25&lng=en>
78
[17] SineSet. Workholding & Inspection Equipment, Accessed 3 June 2014.
<http://www.subtool.com/st/sineset-compatibilitychart.html>
[18] Lion Precision. Noncontact Sensors Technical Library, Accessed 26 June 2014.
<http://www.lionprecision.com/tech-library/technotes/cap-0020-sensor-theory.html>
[19] Epson. SCARA Robot G6 Series Manipulator Manual Rev. 13, Accessed 31 July 2014.
<http://robots.epson.com/admin/uploads/product-catalog/files/EPSONG6_RobotManual(R13).pdf>
[20] Epson. Vision Guide. Rev.5, Accessed 31 July 2014.< http://robots.epson.com/product-detail/119>
[21] Epson. Robot Controller RC180 Rev.15, Accessed 31 July 2014.
<http://robots.epson.com/admin/uploads/product-catalog/files/EPSONRC180_ControllerManual(R
15).pdf>
79