MCHE 484 Senior Design Final Report Rev_8

MCHE 484 Final Design Report
Instructor: Dr. Christopher Dalton
Advisor: Dr. Joshua Vaughan
Authors: Daniel Newman, Jonathan Orta, Joel Weber,
Tyler Kragle

1.0 EXECUTIVE SUMMARY
The project defined in this report consist of a Cable-Drive Parallel Robot, ( CDPR). There are many
different configurations, constraints and degrees of freedom that can applied to these robots. A
CDPR design consist of a frame with various motors that drive cables operated by a control
sequence to accurately maneuver a central module; Skycam is an example of this application. With
the time allotted, the best interest of the group was to choose a 2D planar application because of time
and monetary means. Design consisted of using a microcomputer to control the speed and direction
of the motors while using a micro-stepper to provide vibration control to the motor. Other aspects
of the design included necessary static and dynamic calculations in order to select the appropriate
motor torque. Upon completion the CDPR consist of one motor, able to move in 2D planar motion
The objective is to eventually apply this 2D planar design into a more versatile 3D application.
TABLE OF CONTENTS
Page
1.0 Executive Summary...........................................................................................................................1
1

2.0 Introduction........................................................................................................................................3
3.0 Background Research........................................................................................................................4
3.1 Versaball..........................................................................................................................................................5
3.2 Stepper Motor/Microstep Driver................................................................................................................6
4.0 Design Process....................................................................................................................................6
4.1 Design Criteria...............................................................................................................................................6
4.2 Design Evaluation Process...........................................................................................................................7
4.3 Designs Created.............................................................................................................................................7
4.4 Design Selection............................................................................................................................................8
5.0 Final Design Details..........................................................................................................................9
5.1 Mechanical Design......................................................................................................................................10
5.1.1 Motor Selection............................................................................................................................................10
5.1.2 Design of Fabricated Components...............................................................................................................10
5.1.3 Aluminum Structure Design......................................................................................................................11
5.1.4 Pneumatics...................................................................................................................................................11
5.1.5 Constraint of the Versaball..........................................................................................................................12
5.2 Electronic Design.........................................................................................................................................13
6.0 Design Testing and Results...........................................................................................................14
6.1 Structure Construction...............................................................................................................................14
6.2 Motor Testing...............................................................................................................................................14
6.3 Pneumatics Testing.....................................................................................................................................14
7.0 Cost Analysis....................................................................................................................................14
7.1 Vendor Breakdown.....................................................................................................................................14
7.2 Labor Breakdown........................................................................................................................................15
8.0 Conclusions.......................................................................................................................................16
9.0 Appendix...........................................................................................................................................18
9.1 Appendix I – Motor Calculations.............................................................................................................18
9.2 Appendix II – Structure Calculations......................................................................................................20
9.3 Appendix III – Fabrication Drawings.....................................................................................................24
9.4 Appendix IV – Design Tools ....................................................................................................................28
9.4.1 House of Quality..........................................................................................................................................28
2

9.4.2 Function Tree...............................................................................................................................................29
9.5 Appendix V – Parts List..............................................................................................................................32
10.0 References.......................................................................................................................................34
LIST OF ILLUSTRATIONS
Page
Figure 1 - Morphological Chart (a)........................................................................................................7
Figure 2 - Morphological Chart (b).......................................................................................................8
Figure 3 - Design Evaluation Matrix.....................................................................................................9
Figure 4 - NEMA 34 Motor Torque Curve.........................................................................................10
Figure 5 - Versaball Constraints..........................................................................................................13
Figure 6 – Beaglebone Black................................................................................................................14
Figure 7 - Vendor Cost Breakdown.....................................................................................................15
LIST OF TABLES
2.0 INTRODUCTION
The field of cable-driven robotics possesses vast capabilities and opportunities. Over the past several
decades, a number of studies have shown that this field of robotics has great potential. Simply put,
the cable-driven robot referred to here is a set of n cables loaded in tension by n motors. These cables
are arranged such that they can be wound or unwound to manipulate a focal object called the end-
effector. These types of robots are considered in many ways to be better than the previous option –
serial manipulators – which are made using a rigid set of links and joints. The most common
example of this device is a robotic arm. Cable driven robots have advantages such as higher
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acceleration, lower mass, greater range of motion, and adaptability. Their shortcomings include the
lack of a cable’s ability to provide negative (compressive) tension. This means that a cable can pull
an object, but not push it without the interference of other mechanisms.
Cable-driven robots are used in many applications today such as construction, rehabilitation, and
entertainment. Because of its wide range of uses, there are numerous different designs and theories
in this field. Since this is a fairly new field of robotics, cable-driven robots are still being designed
and tested in different forms of industry. With this new technology, these industrial settings can
hopefully be made safer and more efficient.
Our current design project is to analyze and design the interface of all components involved in
this cable-driven robotic process, as well as implement a grasping mechanism to be transported by
the cables. Our specific objectives are the following:
• Create a simple & lightweight design
• Utilize a Versaball®
• Lift objects of various shapes and sizes
• Operate in a 10ft X 2ft X 8ft workspace
• Single user operation via connection as well as online interface
• Operate through a 110V ordinary outlet
• Implement the recording of user commands, location, & cable movement
• Programmable movement
We focus our research and design based on using these robots to enhance an inside
manufacturing environment. The following article shows or research, process, and design towards a
cable-driven robot that will accomplish these goals and objectives.
3.0 BACKGROUND RESEARCH
The focus of selecting how to design a cable-driven parallel robot is to eliminate the constraints of
rigid parallel robots. These robots are applicable for factory settings, astronomical observation,
structure building devices, rescue, rehabilitation, etc. The advantages cable-driven parallel robots
have are large workspace, ease of reconfiguration, high speed motion, and high payload to weight
ratio [1]. The cable-driven parallel robots fall into two categories: fully-constrained and under-
constrained [2]. The fully-constrained cable robots can control all its motions solely by cable forces,
while in the under-constrained situation, gravity is necessary to serve as the constant external force
that controls the end-effector’s degrees of freedom [3]. A control scheme must be implemented in
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order to control the cable length, where a feedback control in the cable length is used for
coordination to realize the desired cable length corresponding to a desired position of an end-
effector [4]. As far as how the cable will be displaced, one of the more successful ways of achieving
this is by using motorized drums that can coil or uncoil the cables [5]. Since cables can only pull and
not push, n+1 cables must be used for n degrees of freedom [6]. One thing that has not been done
before is regarding the fully-constrained design where cables provide the downward force. The
current way to achieve the downward force is, as stated, by using cables or by relying on
gravitational forces, which limits workspace by having additional cables and adds constraints to
current designs. Similar projects include the Arecibo Observatory, the world’s largest single largest
aperture telescope. A system of 18 static cables, reinforced by three towers, suspends a 900-ton
platform above the dish that all act as the support system of the dish [7]. Cable-driven parallel robots
can serve as the end-effector of a camera robot, which offers a valuable solution for viewing over the
sky [8]. Other potential areas of employment for these robots include airplane part assembly, giant
ship assembly, and rocket launch simulation [9]. A low gravitation application has been used to
simulate motion in low gravity conditions, which is helpful in aerospace engineering, especially in
simulating docking, launch, and landing processes [10]. The use of these robots has been
implemented in rehabilitation assisting patients with medical issues. Two types of robots are used
for this application where a traction-type is used for example to suspend a broken arm by using
cables [11] while the other method is an exoskeleton-type robot to assist and accelerate the healing
process with the same injury [12]. One application that is similar to our design is FALCON-7. This
project uses four motors that control the lengths of the four separate cables to move an end-effector
around in a three-dimensional space [13].
3.1 Versaball
For the end effector used in the design of our cable-driven parallel robot, a robotic gripper,
VERSABALL, is to be used to pick up objects and translate them in an operational space. This
particular robotic gripper uses a method of jamming granular materials by vacuum-packing. The
way this phenomenon, called jamming transition, works is that granular materials or particles can
flow and act like a fluid when loosely packed, but the materials interlock to become rock-solid when
packed together. This gripper takes advantage of this behavior so that when the gripper is soft, it can
be pressed against an object, conforming to take the object’s shape. Preceeding this step is when the
gripper vacuum-hardens to grasp the object firmly [14].
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3.2 Stepper Motor/Microstep Driver
A stepper motor is a type of brushless DC motor that divides a full rotation into a number of
equal steps. The motor’s position can then be commanded to move and hold at one of these steps
without any feedback sensor, like an open-loop controller. The important property of a stepper
motor is that in converts input pulses into a precisely defined increment in the shaft position. These
pulses move the shaft through a fixed angle. Inside the motors are multiple toothed electromagnets
arranged around a gear-shaped piece of iron. To control the electromagnets, a microcontroller is
typically used. By having a higher number of teeth in the electromagnets allows for a higher
resolution in the motor, and by having a higher resolution, the precision of the shaft increases. For
the application of the robot, having a stepper motor with a high resolution is ideal since operating
the VERSABALL to move to precise locations in the operating space is one of the more focused
design criteria. To increase the resolution of the motor, a microstep controller is used to smooth out
the motor operation. This microstepping process is done by approximating a sinusoidal AC
waveform. Although, the accuracy drops by using a microstepper, the mechanical noise is reduced,
mechanical actuation is gentler, and resonance problems are reduced. The real advantage to using
this device is that by maintain synchronization of the system will provide less wear and tear on the
motor [16].
4.0 DESIGN PROCESS
4.1 Design Criteria
The task of providing a cable-operated means of lifting, transporting, and releasing various objects
using an 110V outlet was given. Under this objective specific crieteria was given to implement into
the design. The most essential requirements of this cable robot were the following:
• Remotely operable via internet interface
• Ability to record user commands, location, and cable movement
• Cable movement prompted by pre-programmed or manual input commands
• Include limiting and kill switches
Through these objectives, as well as other customer requirements, a House of Quality was created.
This was used to organize and relate the customer requirements and functional requirements of our
specific project. All criteria was then weighted based on suggested importance. This was the first
step in the design process and showed the importance of certain restraints versus others.
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4.2 Design Evaluation Process
The next step in the design process was to use this House of Quality to create a Function Tree. The
purpose of the function tree was to consolidate all the functions of the robot into more simple sub-
functions that can be accomplished. The first level of sub-functions included transportation, user
interface, and data recording. These three sub-functions contain all needed functions in the entire
project. The sub-functions in the Function Tree would then simplify and direct the remaining design
process.
4.3 Designs Created
After these sub-functions are created, they can be used to begin the various designs of the cable
robot. This is initiated by a Morphological Chart. A Morphological Chart is simply a table that
displays the resolutions of each sub-function through various designs. Since no designs have been
chosen yet, this should include all possible solutions. Each separate sub-function was then matched
to create alternative design concepts.
Figure 1 - Morphological Chart (a)
7

Figure 2 - Morphological Chart (b)
Four separate design concepts were created. The main difference between them was each method of
grasping an object. These methods included a Versaball, mechanical claw, and magnet. The other
important differences were its specific motor usage and process of user interface/control. Other
requirements were met very similarly based on prior instructions from the customer such as Python
and PC-based Datalogger.
4.4 Design Selection
With alternative design concepts created, the next task was to then decide on the most optimum
design. This was accomplished using an Evaluation Matrix. The Evaluation Matrix gives a means to
rate each concept based on its execution of the customer requirements. Through the three levels of
rating, the under- constrained Versaball concept was found to best satisfy theour objectives and
requirements set by this design. This is proven by its accomplishment of the most important needs.
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As shown in the Evaluation Matrix, the under constrained Versaball concept met the highest
weighted requirements such as transportation, user interface, and safety.
Figure 3 - Design Evaluation Matrix
5.0 FINAL DESIGN DETAILS
After the building blocks of the final design were selected, the final design for this prototype was
realized. Two primary elements of this design fall under the scope of the project: electronic control
and mechanical structure. An important distinction must be made for the final design of this
project. Where the previous design documentation dictated a three-dimensional operational space,
the design that follows assumes a prototype assembly that will operate in a plane. This design is
meant to serve as a proof-of-concept where the initial objectives will not all be met, but given the
constraints of budget, time, and engineering know-how, a baseline can be created from which future
teams can build and improve to ultimately meet those objectives.
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5.1 Mechanical Design
Two constraints were initially given with respect to the mechanical design: the 3.5” Versaball must
be used and 80-20 aluminum frame will create the structure. Additionally, two solenoid valves and
their associated fittings and hose were purchased prior to the commencement of this design. The
pneumatic control of the Versaball would originate from a compressed air source in the lab where
the structure would be constructed.
5.1.1 Motor Selection
With these constraints in place, the first major design selection was the motor that would power the
cable assembly. A calculation was performed to determine the required torque on the motor to lift
and accelerate the Versaball. See Appendix I for the associated calculation. It was concluded from
this calculation that a motor with an available torque in excess of 800 oz-in would be necessary. A
NEMA 34Y Stepper motor from Anaheim Automation was selected. This motor is part of a package
sold by the vendor which is meant to be a complete solution to power and control the motor. The
available documentation from the vendor indicates that this motor has access to the torque
necessary at rotational speeds that are reasonable for the desired application (Figure 11
).
Figure 4 - NEMA 34 Motor Torque Curve
5.1.2 Design of Fabricated Components
1
PKG-342-MBC12-PS-CBL System Diagram And Specifications, Anaheim Automation
10

For this design, multiple components needed to be fabricated as opposed to being purchased from a
vendor. These components include adapters that allow mounting of the motors and valves to the
frame as well as an adapter that allows for additional ballast to be added to the Versaball. In order
to confidently send design drawings to a fabricator, the appropriate components were modeled in
Autodesk Inventor and dimensions were confirmed. Appendix III shows the final design drawings
for the three components that were fabricated for this design.
5.1.3 Aluminum Structure Design
A number of 1” extrusions of aluminum T-Slotted frame2
were supplied for the construction of the
prototype. Given a design area of 10’x8’x2’, a method of assembling the frame needed to be
evaluated. The primary loads considered were the motors and the tension evaluated per Appendix
I. The main concern for the structure would lie in the cross member where the motor and hoses
were supported. With most of the weight of the assembly lying in the Versaball, the motors were
designed to be located as close to the L-Brackets as possible. This location will serve to alleviate any
excess moment and therefore any excess displacement and stress in the assembly. Per calculations
in Appendix II, it was concluded under the assumptions of this design that the modeled structure
would be acceptable. An understood complication is the potential deflection in the frame. Given
time and budgetary constraints, the risks of deflection would be acceptable.
5.1.4 Pneumatics
The pneumatic control of the Versaball was also a major design concern for the prototype. The
facility in which the prototype would be built contains a pressurized air outlet which would supply
the pneumatic force required to operate the Versaball. Additionally, several fittings, valves, and
lengths of hose were supplied to the team. Once again, an analysis of the 3D CAD model assisted in
gaining an understanding of the pneumatic components. Given the very large operational area
along with the fact that two lines of hose would need to be supplied to the Versaball, it was decided
to use coiled lengths of hose from the top cross-member of the frame to the Versaball outlets. These
coiled hoses would be mounted to a linear bearing on that member, which would allow them to
2
McMaster P/N 47065T101
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transverse its length as the Versaball moves. A Filter/Regulator was purchased to help regulate the
input air, and several fittings were purchased to allow for the hose to run from the regulator to the
valve.
5.1.5 Constraint of the Versaball
The constraint of the end-effector in a cable-controlled design is a huge concern. For the prototype
specified by this design, time and budget were once again strong factors in the decision to move
forward with an under constrained design (Figure 5). As the figure below shows, the two cables
that will run from the motors will give stability in the X and Y directions while also providing a
small restoring moment in the Y and Z directions. By further analyzing the Versaball, it becomes
apparent that the interaction between the assembly and the force of gravity is a stable one, meaning
that a force in the Z direction (out of the page) or a moment along the X direction will be restored by
gravity. A full vibration analysis would allow for a more thorough understanding of the stability of
the assembly and increase the effectiveness of a controller. Regardless, it is apparent that while this
system is technically stable within a certain limit, severe limitations will exist in its effectiveness and
application.
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Figure 5 - Versaball Constraints
5.2 Electronic Design
Two main aspects of the design needed to be controlled electronically: the Versaball and the motors.
To gain this control, the Beaglebone board was chosen (Figure 6). The Beaglebone is a
microcomputer that readily accepts Python scripted code and can be used to control several inputs
and outputs. A Raspberry Pi and PiFace Digital were initially considered for this purpose, but when
it was discovered that this hardware would not be able to generate an output signal in the range of
frequencies that the motors would require, a decision was made to change to the Beaglebone. Using
Python scripted code on this board would be facilitated by the fact that a Pulse Width Modulation
(PWM) function library is readily available.
13

Figure 6 – Beaglebone Black
6.0 DESIGN TESTING AND RESULTS
6.1 Structure Construction
6.2 Motor Testing
6.3 Pneumatics Testing
7.0 COST ANALYSIS
7.1 Vendor Breakdown
TIn this section contains a detailed report of all monetary expenditures recorded in the design
project. The project followed a typical design sequence where all design was formally completed
and analyzed before any purchases were made. Major expenses like the Versaball, Stepper motor
system and 20x20 framing were supplied by Dr. Vaughan. BOSCO Machine Shop also donated
three fabricated parts. These items are included in the budget but were not directly ordered by the
team. McMaster was the supplier of choice for most remaining parts. McMaster made it simple to
14

choose parts with nice CAD filesdiagrams and part numbers for every item. Depicted below is a
PDF of every item included in the project including part number, estimated cost and vendor.
Figure 7 - Vendor Cost Breakdown
The project came to a total of about $6,000. If this designe group were to have involved abuilt the
3D Cable Drive Robot, withhaving four motors, the estimated cost would come out to $8,000. The
reason the cost is not significantly more is because for the 3D version only needs two additional
motors and a bit more hardwarecouple of brackets. The 2D planar model we currently havebuilt in
this design is not hardwould rather easily be modified to revise into incorporate three dimensional
movement. A comprehensive list of purchased components can be found in Appendix V.
7.2 Labor Breakdown
Month Total time
January 41
February 25
March 54
April 93
May 0
Total Hours 213
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8.0 CONCLUSIONS
While the design operated as projected, there were also some limitations that were unforeseen. The
operation of the motors via microcomputer performed without incident by providing proper coding
to control the according motor speed and direction. However, due to monetary limitations, only one
motor was available to use, essentially eliminating the proposed two-dimensional application.
Adding another motor and altering the code would allow for the two-dimensional movement
desired. Although two-dimensional movement was limited, success was still achieved because the
project’s objectives were completed. As far as future work for this design, it is on the right path to
taking the succeeding steps into two-dimensional and three-dimensional designs that are more
practical in real-world applications.
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17

9.0 APPENDIX
9.1 Appendix I – Motor Calculations
18

19

9.2 Appendix II – Structure Calculations
20

21

22

23

9.3 Appendix III – Fabrication Drawings
24

25

26

27

9.4 Appendix IV – Design Tools
9.4.1 House of Quality
28

9.4.2 Function Tree
29

30

31

9.5 Appendix V – Parts List
32

33

10.0 REFERENCES
[1][2][3] X. Tang “An Overview of the Development for Cable-Driven Parallel
Manipulator,” Advances in Mechanical Engineering, vol. 2014,
http://www.hindawi.com/journals/ame/2014/823028/
[4] S. Kawamura, H. Kino, and C. Won, “High-speed manipulation by using parallel
wire-driven robots,”Robotica, vol. 18, no. 1, pp. 13–21, 2000.
[5][6] S. Kawamura et al. Development of an ultrahigh speed robot FALCON using wire
driven system. In IEEE Int. Conf. on Robotics and Automation, pages 215-220, Nayoga,
25-27 May 1995.
[7] http://en.wikipedia.org/wiki/Arecibo_Observatory.
[8] http://www.skycam.tv.
[9] X. Tang “An Overview of the Development for Cable-Driven Parallel Manipulator,”
Advances in Mechanical Engineering, vol. 2014,
http://www.hindawi.com/journals/ame/2014/823028/
[10] http://en.wikipedia.org/wiki/Rendezvous_Docking_Simulator.
[11] G. Rosati, M. Andreolli, A. Biondi, and P. Gallina, “Performance of cable
suspended robots for upper limb rehabilitation,” in Proceedings of the IEEE 10th
International Conference on Rehabilitation Robotics (ICORR '07), pp. 385–392, IEEE,
June 2007.
[12] G. Yang, H. L. Ho, W. Chen, W. Lin, S. H. Yeo, and M. S. Kurbanhusen, “A
haptic device wearable on a human arm,” in Proceedings of the IEEE Conference on
Robotics, Automation and Mechatronics, vol. 1, pp. 243–247, December 2004.
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[13] S. Kawamura et al. Development of an ultrahigh speed robot falcon using wire
driven system. In IEEE Int. Conf. on Robotics and Automation, pages 215-220, Nayoga,
25-27 May 1995.
[14] Eric Brown et al., Universal robotic gripper based on the jamming of granular
material, Proceedings of the National Academy of Sciences, 2010, DOI:
10.1073/pnas.1003250107
[15] http://www.micromo.com/microstepping-myths-and-realities
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