Air Muscle Artificial Limb Second Generation P09023edge.rit.edu/edge/P09023/public/DesignPacket.pdf · P09023: Air Muscle Artificial Limb Design Review October 24, 2008 Page 3 Project

P09023: Air Muscle Artificial Limb Design Review October 24, 2008

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Air Muscle Artificial Limb – Second Generation

P09023

Detailed Design Review

Multidisciplinary Senior Design I

Rochester Institute of Technology

Friday, October 24, 2008

“Design and build an artificial limb capable of moving in all directions of freedom of a human hand”

https://edge.rit.edu/content/P09023/public/Home


Page 2

Table of Contents Project Summary ........................................................................................................................................... 3

Customer Needs & Specifications ................................................................................................................. 4

Design Metrics versus Customer Needs ....................................................................................................... 5

Team Structure ............................................................................................................................................. 6

Faculty, Advisors, and Customer ................................................................................................................... 7

Human Hand Anatomy .................................................................................................................................. 8

Air Muscles .................................................................................................................................................... 9

Air Muscle Data ........................................................................................................................................... 10

Mesh Materials ........................................................................................................................................... 13

Spring and Air Muscle Sizing ....................................................................................................................... 14

Overall Concept ........................................................................................................................................... 15

Hand Design ................................................................................................................................................ 16

Controls Design ........................................................................................................................................... 17

Controls Algorithm ...................................................................................................................................... 18

Prototype .................................................................................................................................................... 20

Reactions to the Concept Design Review ................................................................................................... 21

Customer Feedback .................................................................................................................................... 22

Preliminary Schedule .................................................................................................................................. 23

Appendix A – Detailed Design Risk and Progress Assessment .................................................................... 24

Appendix B – Bill of Materials ..................................................................................................................... 27

Appendix C – Drawings ............................................................................................................................... 28

Hand Design ............................................................................................................................................ 28

Finger Design ........................................................................................................................................... 29

Joint Design ............................................................................................................................................. 30

Disk Design .............................................................................................................................................. 31


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Project Summary

This is a second generation project aimed at developing a scalable air-muscle actuated robotic

hand. The first generation of this project created three fingers with complete range of motion but did

not complete the pinky, the thumb, or motion of the palm. Eventually the hand could be scaled down

for microsurgery or scaled up for deep sea maintenance applications. The primary objective of this

project is to improve upon the first generation of the project through the design and build of an artificial

limb capable of moving in all directions of freedom of a human hand. The mechanical design and the

controls system should accurately imitate motions of the human hand, and the design should be easily

repeatable, robust, and easy to use. At the end of this project, the customer will be presented with a

hand meeting all of the set criteria and an optimized control algorithm.

Objectives:

Gain understanding of work from the first generation

Make the current design more robust

Update the controls scheme

Determine joint/muscle attachment methods

Implement design

Expected Benefits:

Reinforce the bioengineering program at RIT

Teaching and prospective student recruitment tool

Platform for future senior design projects

Benefits in prosthetics field

Possibility for remote surgery

Potential Problems:

See Appendix A – Detailed Design Risk and Progress Assessment


Page 4

Customer Needs & Specifications

Need Description Importance

Air Muscle Safety Air muscles cannot explode 1

Cable Safety Cables cannot break 1

Controls Safety Control system exhibits safe motion 1

Follow Regulations Project follows all RIT rules 1

Distal Interphalangeal Joint Motion Range of Motion of Distal Interphalangeal Joint 1

Proximal Interphalangeal Joint Motion Range of Motion of Proximal Interphalangeal Joint 1

Metacarpophalangeal Joint Motion Range of Motion of Metacarpophalangeal Joint 1

Robust Hand cannot break 2

Scalable Project must be scalable for future generations 4

Mechanical Optimization Improvement from current system 2

Software Optimization Improvement from current system 2

Ease of Use Must be easily operated 4

*Needs ranked on a scale from 1 to 5 with 1 being the most important


Page 5

Design Metrics versus Customer Needs


Page 6

Team Structure


Page 7

Faculty, Advisors, and Customer


Page 8

Human Hand Anatomy

Figure 1: Hand Anatomy

Figure 2: Joint Directions of Freedom


Page 9

Air Muscles

Figure 3: Air Muscles

Air muscles consist of a flexible, expandable tube covered in a separate meshed tube.

The two tubes are clamped off at one end, and air pressure is allowed to enter at the other end.

When the tube is pressurized, it expands, and that forces the mesh to expand.

Since the surface area of the mesh must be conserved, the length of the tubes decreases.

This air muscle contraction is an attempt to mirror biological muscle contraction and control.

P08023 performed extensive air muscle research which we will utilize and work forward from. We will

be confirming their test results for our design purposes, but we will not be re-evaluating air muscles or

looking into any alternatives for this project.


Page 10

Air Muscle Data

The charts below were developed by the previous senior design teams. The first four charts

testing two different lengths of air muscles as well as two different materials. The PET mesh is

Polyethylene Terepthalate.

Figure 4: 2.5 Inch PET Mesh Change in Length

Figure 5: 2.5 Inch Mylar Mesh Change in Length

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70

Co

ntr

acti

on

(in

che

s)

Pressure (psig)

2.5 inch PET Mesh - 1/8 inch Tubing

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70

Co

ntr

acti

on

(in

che

s)

Pressure (psig)

2.5 inch Mylar Mesh - 1/8 inch Tubing


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Figure 6: 5 Inch PET Mesh Change in Length

Figure 7: 5 Inch Mylar Mesh Change in Length

From the charts above, it is apparent that there is a significant difference

between PET mesh and mylar. More testing must be done to validate these tests

for our application.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60 70

Co

ntr

acti

on

(in

che

s)

Pressure (psig)

5 inch PET Mesh - 1/8 inch Tubing

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 10 20 30 40 50 60 70

Co

ntr

acti

on

(in

che

s)

Pressure (psig)

5 inch Mylar Mesh - 1/8 inch Tubing


Page 12

The chart below is from team P08024. They tested several air muscles of

different lengths. This chart shows that longer air muscles do contract more, and

over the region of tube lengths, the maximum contraction seems linear. Again,

more testing must be done to validate these tests.

Figure 8: P09024 Air Muscle Data

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2 3 4 5 6 7 8

Delt

a L

en

gth

(in

)

Original Tube Length (in)

Tube Length vs Maximum Delta

Muscle A

Muscle B

Muscle C


Page 13

Mesh Materials

PET Polyethylene Terephthalate

Material Specifications

Strength & Abrasion

Tensile Strength PSI 85000

Abrasion Resistance H

Tenacity gms/denier 4.5

Typical Elongation

Break 15

3g/denier 5

Specific Gravity 1.38

Metallic Mylar® is braided from .010" monofilament made from PolyEthylene Terephthalate, with a

continuous operating temperature of -103°F to 257°F. Its melt temperature is 446°F and is offered in 2

dramatic colors: Gold and Silver. Mylar sleeving is a mildly conductive polyester film that helps with

electrical insulation and shielding. It is also compliant with European Union's Restrictions on the use of

Hazardous Substances (RoHS) Directive.

Flexo Chrome (CH) Flexo Chrom is engineered by braiding heavy gauge 5 mil metallized polyester film (Mylar®) in combination with our clear polyethylene terepthalate (PET), we've produced a tough, durable and attractive solution for a wide range of applications, especially cosmetic ones. Even though it is very similar to our Mylar® product, it is heavier and has a much better abrasion resistance. The metallized Mylar® component is conductive, allowing Flexo Chrome to be used in shielding applications, as well as applications where the temperature exceeds 400° F.

This strong and attractive product is both practical in electronic applications and decorative on the wires and hoses of high end show cars and motorcycles. Flexo Chrome is more durable than our Mylar® and more abrasion resistant, but they basically look the same.


Page 14

Spring and Air Muscle Sizing

Springs will be used to pull the fingers straight. The spring constants need to be determined as

well as the air muscle forces. The springs will be sized after conducting a force analysis on the hand. Jim

Breunig and Alex Bird have been working on the force analysis.

Each phalange is separated, and a free body diagram is drawn on each phalange. The forces in

the vertical direction (using global coordinates) are then summed, and the sum must be greater than

zero. This will allow for acceleration in the vertical direction, allowing the fingers to straighten. This

method produces four equations, and eight unknowns.

The phalanges are then divided up differently. The distal phalange and middle phalange are

modeled as 1 body. Then the distal, middle, and proximal phalanges are modeled as one body. The

distal, middle, proximal phalanges and metacarpal bones are then modeled as 1 body. The middle and

proximal phalanges are also modeled as one body. This produces four more equations, and no more

unknowns.

The two sets of equations can then be solved for the tension force. This is still being solved.

Matlab will be used so that it can be implemented by future senior design teams. If the design changes,

the user would change the mass and change the geometry dimensions using matlab.

This analysis will also be used to determine the force required for the air muscle. The air muscle

must be able to overcome the spring force. The spring and air muscle deflection can be calculated using

simple geometry. With the force and deflection, the spring constants can be determined for the springs.

This analysis should be completed by the end of week 9.


Page 15

Overall Concept

Figure 9: Overall Flow Chart

*See Appendix B for Bill of Materials, Appendix C for Detailed Design Diagrams, and Appendix D for Detailed Controls

Schematics


Page 16

Hand Design

One of the problems from both P08023 and P08024 was the manufacturing of the hand was difficult and time consuming. One of the main criteria for this project is that it must be easy for someone else to replicate, and in order to meet this criteria, the hand’s design incorporates as many off-the-shelf parts as possible.

Figure 18: Full Hand Assembly

*See Appendix C for more detailed drawings about the hand assembly and individual components


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Controls Design

“VACCUUM”

PLENUM

ATMOSPHERE

MANIFOLDMANIFOLD

MANIFOLD

MANIFOLD

MANIFOLD

MANIFOLD

MANIFOLD

MANIFOLD

AIR MUSCLES

DIGITAL

PRESSURE

GAUGE

ELECTROMECHANICAL SYSTEM

P09023: ARTIFICIAL AIR MUSCLE LIMB

MECHANICAL

PRESSURE

REGULATORS

SOLENOID

ON/OFF

VALVES

WALL

PLENUM

WALL

SUPPLY

DIGITAL

PRESSURE

GAUGE

Figure 10: Controls Design


Page 18

Controls Algorithm

USB DAQ

1

USB DAQ

2

USB DAQ

3

RELAY BOARD

1

RELAY BOARD

2

RELAY BOARD

3

RELAY BOARD

4

p1

p2

p3

[23,1]

E

[23,1]

R

r1

r2

r3

~

~

~

r4~

~

~

~

Ri = Ri-1

CONTROLS ALGORITHM

IF ERROR IS POSITIVE

TOO MUCH AIR IN MUSCLE

BEGIN RELEASING AIR

IF ERROR IS ZERO

JUST ENOUGH AIR IN MUSCLE

STOP ANY ACTION

IF ERROR IS NEGATIVE

NOT ENOUGH AIR IN MUSCLE

BEGIN FILLING AIR

1

-1

-sgn(φi+τ)

φiττ

[23,1]

P

[23,1]

D

P

D

E

~

[46,1]

R

R

~R

Concatenated Vector of Potentials Read from DAQs 1200 Times Per Second.

User Input Vector Relating to ASL Letter Predetermined Finger Positions (Potentials)

Error Vector, Pure Difference

Thresholded Error Vector (Result), Still Only Related to Potentiometers

Adjusted Resultant Vector Transformed to Value for All Valves, Not Just At Potentiometers


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time

[ms]

Potential

[V]

αANGLE/POTENTIAL

FACTOR

φfinal

φstop

φopen

φ0

time

[ms]

Potential[V]

αi4φfinal

φstop

φopen

φ0

αi3αi2

αi1

EXPERIMENT FOR PRESSUREi

αi = Average(αij),

A

jφf3φs3φf2

φs2φf1φs1

tclose tstop

1

-1

-sgn(φi+τ)

φiττ

τ = f(α)

THRESHOLDING

α = f(PRESSURE)

αi = CONSTANT | PRESSUREi


Page 20

Prototype

The book Robots Androids and Animatrons by John Lovine details how what the air muscles are, how to

make them, and how to assemble an actual robotic hand using the “Amazing Arm” toy. While the

resulting product clearly does not meet all criteria for this project, it is similar enough to the chosen

design that it will be immensely helpful in proving the design concepts set forth thus far. This will also

give our team practice in air muscle use and construction, while providing a quick and basic

understanding of our system’s structure and function as we finalize our design and testing.

Figure 11: Awesome Arm Prototype


Page 21

Reactions to the Concept Design Review

The concept design review held at 8:00 am on Friday, October 3, 2008, alerted the team to many

potential concerns. Because of the progress the team had made up until that point, the concept design

review quickly morphed into a preliminary design review, and many of the concerns brought up there

have since been addressed or identified in detail as suggested.

Concern Countermeasure

The team had no way of benchmarking because

preliminary risk assessment does not contain

enough quantitative factors.

The team created the "Detailed Design Risk and

Progress Assessment" document, which includes

many more quantitative factors.

Air muscles proved to be unreliable in the last

iteration of the project, so pairing them does not

seem like the best idea.

A spring will be paired with each air muscle as a

passive way of returning the fingers to their neutral

positions, if viable.

The springs may not be able to return all parts of the

fingers to the neutral position without some help.

Testing will show which springs are not capable, and

those springs will be replaced with air muscles. The

design will have room for all air muscles.

Air muscle discharge is not linear or predictable.

A vacuum will be attached to a plenum at the exit

for the air muscles and extensive testing will be

done to identify the system response as much as

possible.

The team did not seem to have much data from the

first generation of the project.

The team located all old files and had Chappy sort

through them. The team will be confirming the old

data through testing.

The team seemed too focused on the speed of the

muscle's reactions and not on anatomical accuracy.

The team consulted with the customer and has

decided that speed is not as important as

anatomical accuracy.

The mechanical design presented at the concept

design review seemed hard to manufacture.

The design has been revamped using mostly off-the-

shelf components.

The team seemed to lack knowledge of how a

human hand really works.

The team visited Dr. Doolittle in the cadaver lab and

has started a free body diagram.

Time delays in the control system seemed imminent,

unpredictable, and uncontrollable.

The team decided that the hand will always start at

pre-defined and tested neutral position. All test data

will therefore remain relevant throughout

operation.


Page 22

Customer Feedback

Thus far the customer, Dr. Lamkin-Kennard, has been pleased with the team’s concepts and progress.

Degrees of Freedom

The main focus of this project is to maintain the same directions of freedom of this human hand.

Dr. Lamkin-Kennard has been keeping us on track throughout the project so that we can be as accurate

as possible.

Modular Mechanical Design

Dr. Lamkin-Kennard likes the idea of having off the shelf parts in the design. She said that a

previous team of hers spent a lot of time machining parts. By using a modular, off the shelf design, parts

can be swapped out quickly, the design can act as a platform, and overall mechanical assembly is faster

and easier.

Controls Design

The controls team has held meetings with Dr. Lamkin-Kennard. We showed her the flow charts

for the controls scheme, and she is very happy with the direction that we are going.

Platform Design

Dr. Lamkin-Kennard has helped the team maintain focus throughout the project. Every major

design decision has been discussed with Dr. Lamkin-Kennard. One aspect of this design is the need for it

to act as a platform for future senior design teams. This design should be able to be built on and

improved for future generations of the project.


Page 23

Preliminary Schedule

Item Completed by Date

FBD Analysis Jim & Alex 10/24/2008

Valve Test Program Eva 10/27/2008

Order Hand Parts Design Team 10/31/2008

Valve Testing Eva 10/31/2008

Order control system parts Controls Team 11/05/2008

Air Muscle Test Rig Eva 11/07/2008

Hand Completely Assembled Design Team 12/19/2008

P08023 Air Muscle Test Validation Controls Team 12/19/2008

Air Muscle Fill Time Testing Controls Team 12/19/2008

Order Air Muscle Supplies Controls Team 12/19/2008

Air Muscle Production Controls Team 01/09/2009

Air Muscle Attachment Controls Team 01/09/2009

Spring Selection Eva 01/16/2009

Finger Spelling Program Tommy 01/16/2008

Spring Strength & Capability Testing Controls Team 01/23/2009


Page 24

Appendix A – Detailed Design Risk and Progress Assessment

*Highlighted rows indicate that a countermeasure has been chosen

Problem Countermeasure Quantification Category

1

The cables used for tendons stretched

through regular use and frequently need

to be replaced

The fishing line used could be pre-

stretched prior to installation on the

hand

Cable cannot stretch more than .25”

once installed Maintenance

1

The cables used for tendons stretched

through regular use and frequently need

to be replaced

A different material could be selected

for the cable

Cable cannot stretch more than .25”

once installed Maintenance

2 Some air muscles exploded because the

clamps were not strong enough

Use hose clamps instead of “crimpable”

clamps

0 of the air muscles can explode once

installed on the hand

Air Muscle

Quality Control

2 Some air muscles exploded because the

clamps were not strong enough

Perform a quality control check on all air

muscles prior to installation

0 of the air muscles can explode once

installed on the hand

Air Muscle

Quality Control

3

Passive finger position control needs to

be replaced frequently. Rubber bands

dry-rot very quickly and rubber tape

needs to be replaced every couple of

weeks.

Use air muscles to control the fingers'

movement back to the hand's neutral

position

Hand should not need to be serviced

more than 1 time per month Maintenance

3

Passive finger position control needs to

be replaced frequently. Rubber bands

dry-rot very quickly and rubber tape

needs to be replaced every couple of

weeks.

Use springs to pull the fingers back to

the hand's neutral position. If the air

muscle can be controlled at partial fill

levels, only one muscle is needed to pull

the finger down.

Hand should not need to be serviced

more than 1 time per month Maintenance

4 Air muscles leak, and it is difficult to

keep them filled at a constant volume

Use barbed fittings at the ends of the air

muscles instead of the push-connect

fittings

Air muscles cannot cause fingers to

move more than 10 degrees away from

the target position

Hand

Performance



Vent the exhaust valves to a vacuum

chamber to control the air muscle

deflation



the target position

Hand

Performance


Page 25



Use softer material for the hoses, which

will conform to the fitting rather than

just sitting on top of the stem



the target position

Hand

Performance

5 Having a large number of air muscles

will be bulky and difficult to package

Reduce the number of air muscles

required

Use springs to pull the fingers back to

the hand's neutral position. If the air

muscle can be controlled at partial fill

levels, only one muscle is needed to pull

the finger down. This will reduce the

number of required air muscles to 23

Aesthetics


will be bulky and difficult to package

Design the packaging around the size of

the final assembly Aesthetics


will be bulky and difficult to package Package the assembly into a mannequin

If we go this route, we need to define

the size of the mannequin Aesthetics

6 The previous hands do not have any

motion in the palm

The design team will design a system of

air muscles to move the palm

*We need to find out if there is a chart

documenting palm motion capabilties

Anatomical

Accuracy

7

The fingers on previous hands are not

able to accurately represent the

potential rotation in a human finger

Chris came up with a new concept for

the design of the fingers

The fingers must be able to move as

specified in Jim's chart

Anatomical

Accuracy

7




Use ball and socket joints instead of pin

connections



Anatomical

Accuracy

7




Use a pre-made skeleton of the human

hand



Anatomical

Accuracy

8 The cables may bind up if they have to

wind through the fingers

Attach the cables to the outside of the

fingers just like tendons connect to bone

in an actual hand



Anatomical

Accuracy

9

The fingers in Chris's design might be

too heavy for the air muscles to move

them

Make the fingers hollow The fingers must be able to move as


Anatomical

Accuracy

10

The fingers in Chris's design might not

be able to accommodate for the cables

running through them

Make the fingers hollow The cables can never bind up Manufacturability

10

The fingers in Chris's design might not

be able to accommodate for the cables

running through them

Attach the cables to the outside of the

fingers just like tendons connect to bone

in an actual hand

The cables can never bind up Manufacturability


Page 26

11 Springs may not be able to return all the

fingers to their neutral positions

Test and figure out if some portions of

the fingers need to have air muscle

assistance for their return to the neutral

position



Anatomical

Accuracy

12 The air muscles are sometimes slow to

fill, causing a delay to finger motion

Use valves with a larger minimum orifice

size



Anatomical

Accuracy

13 The larger the valves are, the more

expensive they get

Prove that motion is possible with

largest valves allowed by budget

Valve cost must be less than $20 per

valve Cost

13 The larger the valves are, the more

expensive they get

Allow for future generations to hook up

larger valves to our design

Valve cost must be less than $20 per

valve Cost

14 Current control system is ineffective,

complex, and difficult to operate

Program a very reliable, easy to use

interface Controls

15 Current control system is not easily

modifiable for future generations

Create a program for the control system

which is easily modifiable by future

generations of this project

Controls

15 Current control system is not easily

modifiable for future generations

Clearly document how and why

everything with the program was done Controls

16

Files from the past generation of this

project are not easily decipherable and

not easily accessed

Clearly document how and why

everything was done

Future

Generations

16

Files from the past generation of this

project are not easily decipherable and

not easily accessed

Leave Dr. Lamkin-Kennard all of our lab

books and a clearly organized CD with all

of our files

Future

Generations

17

Current hand layout is messy and not

aesthetically pleasing for

demonstrations

Aesthetics

18 Hand must be easy to replicate

We must leave behind lots of

documented drawings and notes about

the design

It cannot take more than a week for

someone to replicate our hand Manufacturability

18 Hand must be easy to replicate We will make lots of annotated drawings It cannot take more than a week for

someone to replicate our hand Manufacturability

19 USB relay boards might not like being

chained together

Test to figure out what the reaction is

for the USB relay boards being chained

together?

Either the boards work or they don't Controls

19 USB relay boards might not like being

chained together Mix PCI cards with the needed relays Either the boards work or they don't Controls


Page 27

Appendix B – Bill of Materials


Page 28

Appendix C – Drawings

Hand Design

Figure 12: Full Hand Assembly


Page 29

Finger Design

Figure 13: Pinky Finger Assembly


Page 30

Joint Design

Figure 15: DIP and PIP Female Joint Figure 14: DIP and PIP Male Joint Figure 22: Universal Joint


Page 31

Disk Design

Figure 23: Disk

Documents

Air Muscle Artificial Limb Second Generation P09023edge.rit.edu/edge/P09023/public/DesignPacket.pdf · P09023: Air Muscle Artificial Limb Design Review October 24, 2008 Page 3 Project