Control of an Affordable Hand and Wrist Prosthesis

Zachary Abraham Dong Bien Kwon

zak613@gmail.com donkwo@bergen.org

Talia Solomon Michael Xie Karina Yeh

solomont@goastudent.org mxie98@gmail.com karina.yeh@lps-students.org

New Jersey Governor’s School of Engineering and Technology 2015

Abstract Different designs of prosthetic limbs

are available on the market, but the majority

of those systems are too expensive for the

average amputee. These options are also

often ineffective or require invasive

procedures for implementation.1 In this

study, a three dimensional (3D) printed

prosthesis for below-the-elbow amputees,

which was designed by a team of Rutgers

University School of Engineering

undergraduate students for their senior

design project, was paired with Thalmic

Lab’s Myo armband to provide an

affordable, practical, and convenient

experience for amputees. The Myo provided

data on muscle activity around the forearm

as well as orientation data of the arm. The

data was processed and sent to an Arduino

that was used to control servo motors

attached to the prosthetic hand and wrist,

which manipulated the digits and moved the

wrist. The prosthesis that was developed is a

functional replacement limb with an

innovative control mechanism that could

positively affect not only amputees, but also

fields such as industry and medicine.

1. Introduction Many amputees abandon their

prosthetic arms and wrists because the

weight and dimensions of various prostheses

can cause discomfort and issues with user

coordination.2 These complications often

arise when the prostheses do not fit the

amputee properly and create a demand for

customized prosthetic limbs. However,

customized healthcare is often extremely

expensive because the specifications of each

individual’s condition must be taken into

consideration.

In response to this issue, the use of

3D printers to manufacture prostheses has

been introduced. 3D printing allows for the

development of lighter prostheses that can

easily be modified to fit the amputee. It is

important to take advantage of the new

technology provided by 3D printers to make

prostheses affordable for all amputees.

Otherwise, amputees who fail to replace

their limbs may experience complications

when they rely on their opposite arm or leg,

such as overuse injuries and arthritis.3

Affordability and functionality are

also key aspects of prostheses. In this study,

a working and cost-effective prosthetic hand

and wrist was developed using 3D printing

and a Myo armband as the control

mechanism. This device acts as highly

functional but still affordable prosthesis.

Other advanced prostheses utilize

implantable myoelectric sensors (IMES),

which can easily control prostheses, but

require invasive surgery. Procedures such as

these increase both the price and recovery

time of receiving a prosthesis.3 The price,

recovery time, and the hazards of surgical

operations are incredibly important issues,

especially since 2.4 million of the 3 million

amputees in the world are from developing

countries. In these locations, it is more

difficult for patients to be able to afford

prosthetic limbs that involve expensive

medical procedures, such as operations that

implant IMES.4 The Myo is a cheaper

alternative to implanted sensors because it

requires no surgery while still providing

reliable data to control the hand.

A Myo armband combined with a 3D

printed hand and wrist has many

applications. For example, they can be used

as a prosthesis for an amputee whose

residual limb begins below the elbow. The

prosthesis can be controlled by different

forearm muscle configurations that the Myo

senses. These positions have equivalent

muscle flexions that can be taught to the

amputee in physical therapy. The prosthesis

and Myo also have applications in industry

and medicine. Researchers working with

dangerous or caustic materials could

conduct experiments from a safe distance

while manipulating the hand with the Myo.

The device could additionally function as a

remote surgical robot, which could be used

by a surgeon in the military to protect the

surgeon from the risks inherent of a combat

zone.

In this study it was tested whether a

3D printed hand controlled by the Myo

could mimic several natural hand positions

including wrist flexion and extension, digit

extension and flexion, thumb circumduction,

and grasps varying in strength.

2. Background

2.1 Myo The Myo armband, seen in Figure 1,

was created by Thalmic Labs. It has medical

grade stainless steel electromyography

(EMG) sensors and a nine-axis inertial

measurement unit (IMU) with a three-axis

gyroscope, a three-axis accelerometer, and a

three-axis magnetometer. The EMG sensors

detect muscle contractions and movements

in the arm that correspond with distinct hand

motions, such as a double tap of the index

finger and thumb, an open hand, a wave to

the right or left, and a fist.5 With the IMU,

the Myo can record the pronation and

supination, the role, of the forearm.2,5

The

data from the Myo is processed by an ARM

Cortex M4 processor. Retailing at $199.99,

the armband also comes with a modified

Bluetooth adapter to communicate with a

computer as well as a micro USB cable to

charge the device.5

2.2 Arduino Arduino is an open-source platform

that consists of a microcontroller and an

integrated development environment (IDE).

Arduino is commonly used in electronics

projects and has been popularized by its

affordability, and simplicity in usage and

language, which is a simplified form of

C++, another well-reputed programming

language. The Arduino microcontroller

easily allows the user to attach LEDs,

sensors, and other electronic pieces to

develop projects with ease.6

There are many

different types of Arduino microcontroller

boards available on the market, each with

distinct functions. For this study, the

Arduino Uno was used. The Uno was

readily available and also had a sufficient

number of pins to control the five servo

motors for the fingers and the servo motor

for the wrist.

Figure 1: The Myo Armband sits snugly

below a user’s elbow

2.3 3D Printing Current 3D printing technology

involves building three-dimensional

structures layer-by-layer with 2D cross-

sections. Machines generally use resins,

filaments, waxes, or powders to build and

fuse layers together. Industrial 3D printers

generally cost from $25,000 to $1 million

and can print up to 2 x 2 x 1 feet. More

affordable, smaller-scale personal 3D

printers use a Fused Deposition Modeling

(FDM) process, which deposits lines of

melted plastic filament in layers.7

Most personal printers use

acrylonitrile butadiene styrene (ABS) or

biodegradable polylactic acid (PLA)

filament. These filaments cost about $29 for

one kilogram at diameters of 1.75mm,

making it very available and affordable for

people who have access to personal or

public 3D printers.8

3D printing is a fast and affordable

way to prototype designs and to create

finished products within hours. This reduces

the necessity for the additional machinery

that is conventionally used to refine objects,

saving money and time. In addition, 3D

printing is used to create physical

representations of computer aided design

(CAD) files.

Furthermore, 3D printers and other

computer numerically controlled (CNC)

machines usually utilize a standard

triangulated stereolithography (STL) file

format.8 As a result, 3D printed prosthetic

limbs and other devices can be customizable

forms of healthcare. For example, in a case

study performed by Xi’an Jiaotong

University in Xi’an, China, researchers

created a “3D reconstructed freeform model

of [a] femur bone [that] conformed to the

original anatomy within a maximum

deviation 0.206mm,” and used this design to

construct a mold for a composite hemi-knee

joint substitute.9

2.4 Servos Servos are motors that consist of

gears and a shaft and can be set at specific

positions to move the fingers. The shaft can

be positioned at a degree ranging from 0-

180 degrees for typical servos, but for

continuous servos, the shaft can be placed at

any degree. Servos have three wires to

communicate with the controller board or

chip: power, ground, and signal.10

The

motors are controlled by pulse width

modulation (PWM). The width of a pulse

sent from the chip to the motor defines the

desired location of the shaft. The shaft then

rotates a number of degrees to meet the

desired position. As a result of its nature,

servo motors are used in applications that

require a setting of position.11

2.5 Microsoft Visual Studio Visual Studio is an integrated

development environment (IDE) software

created by Microsoft. The environment

allows for developers to create and build

various types of applications. Visual Studio

supports many programming languages such

as various forms of C and Java. Free

versions of the IDE are readily available

online and allow anyone to develop software

in a simple and convenient way.12

2.6 The InfinityHand

The InfinityHand, as seen in Figure

2, is a 3D printed prosthetic hand and wrist

developed for a biomedical engineering

senior design project at Rutgers University.

It has five servos in the palm that control the

movement of the fingers, and its wrist has

three degrees of freedom: flexion and

extension, pronation and supination, and

medial and lateral. It had three degrees of

freedom, because that was enough degrees

to allow the amputee to do activities of daily

living.13

3. Methods/Experimental Design

3.1 Design and Development It was decided that the prosthetic

hand and wrist would be 3D printed in order

to make the prosthesis the most affordable

and easily customizable. The design of the

InfinityHand was chosen because a printed

model of the prosthesis was readily available

for testing so the study could be focused on

the development of the control of the

prosthesis, rather than the design of the

physical prosthesis. The InfinityHand was

printed using affordable materials such

aspolylactic acid (PLA) and acrylonitrile

butadiene styrene (ABS). The Myo armband

was chosen as the control media because it

was the most cost-effective option with a

retail price of $199.99. It also had the most

natural simulation of hand motions based on

muscle movements in the arm.

An additional palm cap was designed

on SolidWorks to supplement the

InfinityHand. It was added to improve the

appearance of the hand and protect the

servos that it covered. It was designed to fit

over the InfinityHand and be attached to the

rest of the prosthesis with clips. Once the

design process was completed, it was

printed. However, it was decided that the

palm cap was too thick and made the

prosthesis unnaturally large. The original

palm cap was made thinner so that it would

be more aesthetically pleasing and

ergonomic.

3.2 Hardware The prosthesis design was based off

of a model developed by Christopher

Bargoud, Mohit Chaudhary, Julian Hsu,

Rebecca Wenokor, and James Wong. The

model designed in their project was used for

testing purposes during the first two weeks

of the project while the revised model was

being designed and printed. It was decided

that the design would be reworked so that it

was more compatible with the decided

course of research; the lowest wrist section

was removed to simplify the design and the

code that was needed to control the

prosthesis and the knuckle piece was also

curved to allow for better movement of the

rubber bands. The prosthesis utilized five

servo motors to control each individual

finger as well as one servo motor to control

the wrist. A breadboard was used to connect

the Arduino uno to the prosthesis. Both the

five volt and ground pins were wired to each

servo motor and a third pin was used as the

output pin to modulate the degree of

rotation.

The prosthesis is controlled by the

Myo armband using proprietary EMG

sensors to detect changes in the electric

potentials of one’s muscles.14

By analyzing

these potentials, the Myo can detect specific

positions of one’s hand solely based on the

muscle movement on one’s forearm. The

positions consist of an open hand, fist, wave

in, wave out, double tap of the fingers.5

3.3 Assembly Once the parts of the prosthesis were

printed, the project team began to assemble

Figure 2: The InfinityHand and circuitry

the prosthesis. Each piece needed to be

sanded so the joints would fit together with

minimal friction. Then the joints were

attached with 16 gauge and 1.25 inch nails,

and bolt cutters were used to shorten their

shaft. All of the pinkie’s joints and the distal

inter-phalangeal joint of the ring finger were

attached with 1/16 in. by ½ in. aluminum

dowel pins. The ends were then secured with

hot glue. The nails also reduced the friction

because they are metal and smooth. The

various segments were attached with

superglue where the pieces met flush.

Rubber bands were cut open and attached to

the fingers with screws screwed into holes in

the fingers. The knuckles were then

connected to the palm sides with nuts and

bolts. The palm parts, with five of the servos

screwed on, were slid into the groove in the

palm sides. Professional grade fishing line

was strung through the holes in the fingers

to the servos. The fishing line was then

connected to the servos. The finished hand is

shown in Figure 3.

Then the wrist was constructed after

printing. A gear and a servo were attached

with a rod into the wrist piece. The wrist

joint pieces were then screwed together and

additionally attached to the wrist connector

plates. Then the palm sides were attached to

the top wrist joint piece with plastic rods

that were 3D printed. After that the palm cap

was clipped together on top of the

prosthesis. Rubber cement was also painted

on top of the fingers and the palm cap to

increase the grip of the prosthesis.

3.4 Software One of the major components of the

project was the software and technological

development for the prosthesis. To program

the Arduino, the Arduino programming

environment was employed and the

executable application to send data from the

Myo to the Arduino was programmed in

Visual Studio 2013 with the C++ language.

The first major task that needed to be

completed was to be able to make the Myo

and the Arduino communicate. Due to the

fact that the Myo and the Arduino operate

on two completely separate softwares, new

code was written (an executable) to receive

the data the Myo produced, which was then

sent to the Arduino. While writing this type

of code from scratch is possible, such a task

is complex and would have used up a

significant portion of the time available for

the project. Fortunately, one of the

applications uploaded to the Myo Beta

Market, aptly named MyoDuino and

developed by Jake Chapeskie, allows for

nearly instantaneous communication

between the Myo and the Arduino.15

Once

the application was downloaded, the

Arduino Uno microcontroller accessed the

code by means of a library. The library

allowed all the MyoDuino code to be used

by people who did not write it. The

computer read the various output data from

Figure 3: The fully assembled prosthetic

hand sans palm cap.

the Myo and sent it over serial

communication to the connected Arduino.

This setup allowed for a seamless

transmission between the received Myo data

and the Arduino microcontroller.

Once the software was set up, each

servo motor on the prosthetic hand was

wired to the Arduino. Since the Myo can

only recognize five positions, five different

“cases” were coded as individual “if

statements.” For an open hand, each servo

was set to 5 degrees, and for the fist each

servo was set to 175 degrees. The reason it

was not set to 0 and 180 degrees is that the

servos start to make noise when at the limits

of their movement.

The “wave in” motion was used to

simulate a peace sign (pointer and middle

fingers extended at 5 degrees while the rest

flexed at 175) in order to test finger

movement (wrist motion was tested soon

after). Similarly, the wave out function was

used to make an okay sign (thumb and

pointer fingers flexed at 175 degrees while

the rest extended at 15 degrees).

Finally, the double tap function was

used to simulate a demo of each finger;

starting with the thumb, each finger took

turns flexing and extending. Once each

action was completed, the fingers all flexed

together to form a fist, and then extended to

form an open hand. This demo was another

way to measure the capabilities of each

finger both individually and as a unit.

After full functionality of the Myo

and the prosthesis was established, the next

step was to devise a method to modulate the

extent to which the fingers flex. Rather than

two set positions (either fully flexed or fully

extended), an adaptive prosthesis with the

capability of modulating how much each

finger flexed would give the user greater

dexterity. The problem with this type of

functionality was that the MyoDuino

executable application only allowed for the

data of the five hand positions to be sent to

the Arduino. While the Myo itself can also

measure the roll, pitch, and yaw of the user’s

arm with the Myo’s IMU, the executable

was not programmed to send over this data.

Roll, pitch, and yaw was another set of data

that was accessible to be used to control the

prosthesis have variable grip In order to

solve the problem of not having a method of

communication between the Myo and

Arduino for this data, the MyoDuino

software itself had to be modified. Visual

Studio 2013, shown in Figure 4, was used to

complete this task. Since the executable was

written in C++, Visual Studio allowed for

editing of the executable in its original

language.

After the executable was modified to

send over the data for the roll of the arm, an

example code was written to display the

corresponding variables. The variable

values were related to the number of degrees

of rotation in the arm. The variables were

assigned numeric values from 0 to 18, where

0 was the maximum roll clockwise, and 18

was the maximum roll counterclockwise. In

order to modulate the grip of the prosthesis,

the variable roll data was mapped to

correspond to the angles of the servos.

However, even though the roll of the arm

was measured from 0 to 18, the user would

need to fully stretch his arm to reach those

values. As a result, instead of being mapped

from 0 to 18, the roll was mapped from 5 to

Figure 4: The Visual Studio 2013 IDE was used

to code and edit the MyoDuino application

15. This range allowed for a more

comfortable experience when using the

Myo. The degrees of the servos ranged

from 5 to 175. By mapping the roll

variables to the degrees of the servos, the

prosthesis was capable of modulating its

grip rather than simply making a fist or open

hand, since amputees would ideally require

various levels of finger flexion when

gripping objects.

While the modulated grip functioned

properly, an issue with the movement

stemmed from the variables themselves.

Due to the fact that the range of the roll was

5 to 15, by merely changing from 5 to 6, the

degrees of the servos were increased by 1/11

(9.09%). This in turn caused the fingers on

the prosthesis to appear jerky since one

“degree” of roll translated to over 14

degrees of the servos. This motion was

smoothed out by increasing the multiplicity

factor of the algorithm within the executable

that interpreted the raw roll data.

Consequently, instead of 5 to 15, the roll

data ranged from 110 to 290. The wider

range of integers enabled the servos to move

more smoothly and allowed the flexion of

the fingers to be modulated more precisely.

Following the development of the hand, the

wrist functionality was tested. Similar to the

fingers, the wrist was controlled by a servo

motor, but rather than by pulling a string, the

motor controlled the wrist by a differential

gear system.

4. Results and Discussion

4.1 Hand Functionality and Affordability The configuration of the overall

design has each pose detected by the Myo

correspond to a predetermined gesture on

the prosthetic hand or wrist. There are

currently six gestures programmed into the

Arduino, shown in Figure 5, which can be

increased in the future.

In addition, the prosthesis will

change its fist grip strength to varying

degrees as the Myo wearer rolls their

forearm to different degrees while holding a

fist. The roll angle returned from the Myo

IMU as a user rolls his hand is shown in

Figure 6. The hand is also relatively light for

the user at 496 grams. This is because a

small infill was used. The PLA and ABS are

also much lighter materials as opposed to

the metal that other prostheses are made of.

The hand is also affordable

compared to the currently marketed

products, which generally cost more than

$10,000.16

It takes about $635 to reproduce

this prosthesis. This includes the cost of

purchasing a netbook to communicate

between the Myo and the Arduino.

However, any kind of portable computer

would be sufficient as long as it can connect

to the Arduino. This would reduce the cost

Figure 5: Gestures detected by the Myo and how they control the prosthetic hand and wrist

further. The majority of the remaining cost

covers the cost of the Myo and the servos

needed to operate the prosthesis. The rest of

the price is from the printing of the

prosthesis, as well as various pieces of

hardware required to assemble the hand and

wrist. A specific breakdown of the costs is

shown in the table in Figure 7.

4.2 Discussion From the observed capabilities of the

hand and wrist prosthesis, it is evident that

the device would be as effective as a

currently marketed artificial limb for below-

elbow amputees. A passive adaptive hand

system has “the ability of the fingers to

conform to the shape of an object held

within the hand. During grasping, the four

fingers and thumb are able to flex inwards

independently, to conform to the shape of

the object.”17

Meanwhile, an adaptive hand

can actively flex each of its fingers

individually to different degrees. A non-

adaptive hand can only fully open or fully

close its fingers.18

Therefore, the Myo-

controlled system acts as a hybrid between a

non-adaptive and an adaptive prosthetic

limb. The prosthesis designed as part of this

project is capable of flexing and extending

its fingers fully, as well as controlling each

finger individually, one at a time, to grasp

objects as an adaptive prosthetic hand

would.

In a study performed by the

Department of Rehabilitation Medicine at

the Linköping University Hospital in

Sweden, eight patients compared the

functionality and the aesthetic qualities of

nonadaptive and adaptive prosthetic hands.

The patients concluded through objective

and subjective tests that they preferred the

non-adaptive hand over the adaptive one

because it supplied more grip.18

The Myo-

controlled hand and wrist prosthesis has a

coating of rubber cement to add grip,

making it a more useful prosthesis.

Figure 6: The roll angle returned by the IMU on the Myo as a user rotates his hand back and forth

about the axis of the forearm.

Item Cost/Unit

(USD) Quantity

Cost

(USD)

Servos $14.99 6 $89.94

Myo

Armband $199.99 1 $199.99

Arduino $23.99 1 $23.99

Screws,

nuts, bolts

(misc)

$6.50 1 $6.50

Printer

filament

/cm

$100 1 $100

Netbook $200 1 $200

Fishing

Line $3.49 1 $3.49

Rubber

bands

(1/4th of

pack)

$1.99 1 $1.99

Super

Glue (1/2

bottle)

$1.50 1 $1.50

Wires $4.99 1 $4.99

Resistors

(pack) $2.10 1 $2.10

Nails

(1/5th

pack)

$0.25 1 $0.25

Rubber

Cement $1.19 1 $1.19

Total -- -- $635.93

Furthermore, the patients disliked the

adaptive hand because it weighed 595

grams, while the non-adaptive hand weighed

505 grams. Therefore, the Myo-based hand

would be extremely practical, since the hand

weighed 237 grams and the wrist weighed

259 grams, for a total of 496 grams.18

There are several options for control

of prostheses. Currently, the main categories

are body-powered and myoelectric

prostheses. However, new methods of

operating prostheses are being developed.

One of these is targeted muscle

reinnervation, where peripheral nerves are

relocated to the residual limb. These nerves

create more signals making it easier for the

myoelectric sensors to provide data for the

control of the prosthesis.1There are also

prostheses controlled by IMESs, eight of

which are surgically implanted into the

residual limb. They offer consistent signals

as well as a high level of functionality.3

Another means of operating a prosthesis is

through multi-electrode arrays that are

implanted 1-2mm into the cortex. These

innovative methods are capable of

increasing the functionality of prostheses,

yet are much more invasive. On the other

hand, myoelectric sensors can have trouble

sensing multiple signals from a residual

limb, yet have less risk. In a study

discussing which types of control devices

amputees are most interested, it was found

that amputees were most interested in

myoelectric sensors. The amputees’

responses to whether they were very

interested or not interested in more

functional prostheses did not fluctuate

between the different levels of

functionality.1 This suggests that amputees

will be interested in using the Myo as a

sensor, because it is functions well and is

noninvasive. Additionally, 74 percent of

amputees that do not use prostheses were

willing to try prostheses with better

technology and a cheaper cost. They also

wanted a large range of motion, changeable

grip strength, and the movement of multiple

joints at once.1 The prosthesis used in this

study fulfills these requests. However, it

does not answer the additional issues of

intuitive control and sensory feedback.

However with future developments these

features can be included.

The Myo is a good sensor, because it

is a easily used, noninvasive, and processes

the signals quickly. The sensors process the

Figure 7: Specific project cost breakdown

information and then it is transmitted over a

Bluetooth Smart connection to communicate

with the laptop that processes the data from

the Myo and sends it to the prosthesis.

However, the prosthesis still needs to be

attached to the laptop with wires. In the

future this information transmission can be

upgraded to a Bluetooth connection.

The prosthesis created in this study is

much more affordable than the existing

prostheses on the market and provides a

much more natural experience for the user.

The cost of the prosthesis built in this study

is $635, which is significantly less

expensive than the prostheses that use IMES

or multi-electrode arrays.

In addition to its function as a

prosthetic hand and wrist for below-elbow

amputees, the device could also be used for

industrial work to reduce the risk of worker

injuries. In factories where machinery and

hazardous chemicals are regularly utilized,

employees are frequently concerned with

health risks due to their work, and job

insecurity caused by such injuries.19, 20

For

example, out of “146 14- to 16-year-olds

who incurred an occupational injury [...],

thirty-two percent of the injuries occurred as

the result of using equipment,” showing that

machines and tools account for a large

portion of occupational hazards.21

As a

result, companies frequently assign injured

workers to safer jobs and hire subcontractors

in order to maximize work and minimize

liability costs.20

The hand and wrist

apparatus could be used to assist fabricators,

assemblers, mechanics, repairers, machine

operators, chemical workers, and employees

in various other hazardous occupations.19

Workers would use the Myo to remotely

control the hand to perform simple tasks

such as pouring chemicals, pressing buttons,

and pulling levers, which would protect

employees from prolonged exposure to

dangerous materials. This would be similar

to a laboratory glovebox, but it would be

less expensive because it is 3D printed and it

would be applicable to a wider range of

occupations. Furthermore, increased

consistency in worker productivity would

lower liability and subcontractor costs,

increasing company stability while

affordably protecting employees.

Furthermore, the appliance would be

useful for remote surgery in locations where

professional medical expertise and

equipment are scarce. In 2002, doctors

responsible for a French study “attempted

remote robot-assisted laparoscopic

cholecystectomy” with an asynchronous

transfer mode (ATM) telecommunication

system between New York City and

Strasbourg, France and experienced no

complications, and “despite a round-trip

distance of more than 14,000 km, the mean

time lag for transmission during the

procedure was 155 ms.” As a result, the

system of transoceanic surgery was

described as “perfectly reliable” and held

significant potential for remote surgery.22

Therefore, a similar but more cost-effective

system of remote transoceanic surgery could

be developed using the Myo-controlled

prosthesis and predeveloped transmission

methods.

In addition, since the Myo armband

operates based upon macro-movements of

the arm, the device could eliminate hand

tremors while surgeons are operating. This

would eliminate many issues due to a

surgeon’s age or level of fatigue,

maintaining his or her dexterity over both

short and long periods of time.22

Because the

prosthesis is inexpensive, it could be

implemented locally and remotely to

maintain consistency and efficiency in

surgeries.

With the reliability of the Myo-based

prosthesis and its ability to be applied

remotely, it could also potentially be

deployed in isolated rural areas or in

emergency situations as a fast and feasible

means of delivering assistance where

medical expertise and large, expensive

materials are unavailable. As proposed in

The New England Journal of Medicine,

time-sensitive medical care can be given

with the help of disaster-medical-aid centers,

which would provide accessible facilities for

emergency medical assistance.23

The

equipment in the medical centers or in rural

community centers could include a left and a

right Myo-controlled hand and wrist

prosthesis, along with surgical tools, a

camera, and a basic ATM system. The

system would be able to communicate with

an on-call emergency surgeon or a

specialized doctor who would be a volunteer

in another location. This method would

effectively provide people in emergencies or

remote areas with surgical assistance

without spreading medical personnel thin.

Furthermore, the ability to reach a doctor or

surgeon of a specific profession could

decrease the number of deaths following

disasters, because in the most time-sensitive

and critical injuries, “orthopedic and general

surgery skills are essential.”24

Overall, the

prosthesis could serve as a way to provide

widespread, affordable healthcare and to

increase doctor reliability.

4.3 Problems Encountered The initial challenge that was

encountered was the Myo’s Bluetooth

adapter. Once it was decided that the Myo

would be our medium of prosthesis control,

it was necessary to gain access to the data it

recorded. For this to be accomplished, the

Bluetooth adapter that came with the Myo

was needed. However, the box containing

the Myo was missing the adapter. Another

Myo was obtained; this one containing two

adapters. One adapter was a universal one

that did not include the software that was

necessary to obtain the information from the

Myo. The other was a Myo adapter that was

broken. A new Myo was then ordered with a

new adapter to allow experimentation to

begin. The challenge of not being able to use

the data recorded by the Myo delayed the

start of research because no code could be

tested and the viability of using the Myo was

undeterminable without the Bluetooth

adapter.

The appearance of the Infinity Hand

also proved to be a challenge. The

InfinityHand had most of its wiring and

servos inside the palm, exposed. It was

decided that in order to make the prosthesis

more visually appealing to an amputee a

palm cap should be designed to supplement

the Infinity Hand. A cover was designed on

Solidworks and then 3D printed. It gave the

prosthesis a better aesthetic, yet was slightly

thicker than desired. The design was then

improved to be thinner.

Another problem was the time it

required to print the prosthesis components.

For the first print a high infill percentage

was used and a low print speed. To decrease

the print time, the infill percentage was

decreased and the print speed was increased.

The decrease in the infill decreased the mass

of the hand in addition to the time. The hand

took 56 hours to print which was longer than

expected. For future use, it is advised that

multiple printers are used to shorten the

printing time.

A major technological challenge was

the limited number of poses that the Myo

armband was able to detect. As of now,

Thalmic Labs has only developed software

for the Myo armband to find five designated

poses. To add more functionality, the IMU

data was implemented. However, the data

from only one axis (roll) could be used since

the data from the other axes would interfere

with each other when the arm moved. For

increased options in the future, improved

algorithms could be created to interpret the

Myo’s EMG data. This would open

possibilities for detecting individual finger

movement and various combinations of

finger flexions and extensions. These

improved algorithms may also be able to

help the Myo detect the muscle contractions

more easily in amputees.

5. Conclusion The prosthesis that was created in

this research project is very applicable for

amputees as well as industry. The prosthesis

is innovative because it combines a new and

easy control mechanism with a well-

functioning prosthesis design. Its

affordability makes its accessible to many

people because it can be used by people who

cannot afford an expensive prosthesis. The

Myo provides a simple method of control

that does not require any invasive

procedures to implant sensors or manipulate

nerves. The design of the prosthesis can be

easily adapted because it is 3D printed. This

means that the design can be adjusted for the

size of the amputee’s residual limb or the

application the prosthesis is used for.

The objective of this project was to

create a straightforward method for

controlling the motions of a 3D printed

prosthesis. The prosthesis can alternate

between several different positions and has

the capability for future position additions. It

may be challenging for amputees to activate

some of the prosthesis positions because

their muscles have undergone trauma.

Methods to teach an amputee to manipulate

their arm muscles in different ways can be

designed in the future. Opportunities for

improvement could be based upon the data

spikes that correspond to finger movement.

Other aspects of the prosthesis and its

control system that could be upgraded in the

future are further degrees of freedom in the

fingers and wrist as well as the use easier

muscle contractions for amputees as signals.

6. Acknowledgements The authors appreciate the help and

guidance of our project mentors Julian Hsu

and Mary Pat Reiter. Julian’s and Mary

Pat’s assistance in the printing and assembly

of the prosthesis was necessary for the

completion of this project. The authors also

acknowledge Dr. William Craelius and Dr.

Kang Li for their help, resources, and

support. Resident Teaching Assistant, Kelly

Ruffenach, is thanked for her instruction.

The authors also appreciate Edmund Han’s

organization of the research projects. Ilene

Rosen and Dean Jean Patrick Antoine are

thanked for managing the Governor’s

School of Engineering and Technology. The

authors also thank the Governor’s School of

Engineering and Technology for providing

this research opportunity. The authors are

also grateful for all of the sponsors of the

Governor’s School of Engineering and

Technology. These include Lockheed

Martin, SilverlineWindows, Rutgers, the

State University of New Jersey, Rutgers

School of Engineering, South Jersey

Industries, Novo Nordisk, Pharmaceuticals,

Inc., New Jersey Resources, and the State of

New Jersey. Jake Chapeskie is thanked for

the MyoDuino library. Christopher Bargoud,

Mohit Chaudhary, Julian Hsu, Rebecca

Wenokor, and James Wong are thanked for

the design of the InfinityHand.

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