1. PRIMA
PORTFOLIO SUMMARY
Printing Myoelectric Arms
PriMA
To be completed in March 2016.
PriMA is dedicated to delivering a lower-cost prosthetic arm option with high functionality through 3D
2. PORTFOLIO ELEMENT A
PRESENTATION AND JUSTIFICATION OF THE PROBLEM
printing and sensory feedback. The product is being developed as part of an interdisciplinary
capstone design by a group of devoted Biomedical Engineering, Mechanical Engineering, and Computer
Science students. The long-term intentions for this design are to jump-start a 3D printing-based
technology company and to bring innovation to the industry.
Florida Institute of Technology, Melbourne, Florida
Project Lead, Design Engineer: Clyde Brown - clyde2012@my.fit.edu
Financial Lead, Design Engineer: Thaddeus Berger - tberger2012@my.fit.edu
Programming Lead: Nicole Ballman - nballman2012@my.fit.edu
Research Lead: Meet Pastakia - mpastakia2012@my.fit.edu
Safety Officer, Research: Taylor Atkinson - tatkinson2012@my.fit.edu
Project Advisors:
Dr. Kunal Mitra - Professor, Biomedical Engineering, Florida Institute of Technology
Mr. David Beavers - Director, Electronics Support Laboratory, Florida Institute of Technology
Acknowledgements - the following team members could not be included in this portfolio due to the team
size limit.
Austin Spagnolo: Design Engineer - aspagnolo2015@my.fit.edu
Zuhoor Yamani: Customer Relations Lead, Research - zyamani2012@my.fit.edu
Ryan Babbitt: Programming - rbabbitt2014@my.fit.edu
Justin Pavao: Programming - oavapnitsuj@hotmail.com
Danielle Goldman: Mechanical Engineering Practicum Student - DGoldman2013@my.fit.edu
Maria Vittoria Elena: Mechanical Engineering Practicum Student - melena2013@my.fit.edu
Special thanks to Tabitha Beavers (CEO, Space Coast FabLab) for manufacturing facilities.
3. I. Executive Summary
Prosthetics are becoming a more prominent part of today’s society in order to
allow amputees to still function with full limb usage in society. While prosthetics
are very common in today’s society, there are still a lot of complaints from
amputees over the devices.
This project was chosen because prosthetics are generally extremely heavy and
uncomfortable. However, with the new developments that have come from the
ability to 3D print, there is a much larger margin for development in the
prosthetic company. The goal of this project is to design a more structured
device based on the needs of consumers and clients that have been surveyed.
Through research done by the team, it is learned that there are a lot of
complaints with the current prosthetic industry. The largest complaint is that
the devices are not comfortable on the residual arm. The low comfort is due to
the fact that many parameters associated with the clients' remaining arm have
not been considered. Additionally, it is reported that many users find
prosthetics too difficult to learn to function. Lastly, the largest issues with
prosthetics are that they are not aesthetically pleasing. By using the feedback
learned from case studies and interviews had with Anna Street from Brevard
Prosthetics, we have been able to make valuable changes to the current
prosthetic designs.
By using this research, a design statement was developed for this project. Our
team must design, build and implement a 3D printed prosthetic arm in the
biomedical field. The industry is currently producing arms of poor dynamic
quality with no feedback features to induce a sense of touch. Other innovative
and cost effective ideas aren't set to hit the market until 2020 due to extensive
research and cost of development. The majority of 3D printed systems in the
industry lack structural integrity or a kinematic system. The majority of decent
working hands that are designed to last, list at a starting price of $40,000 and
up. Our design will be lower cost, 3D printed with quality, robust, structurally
sound, and it will provide kinematic motions that duplicate a real hand as well
as interface with the user to provide sensory feedback.
4. II.1 General Need for Product
II. Market Analysis Information
Prosthetics are used to replace the function lost by the removal of
appendages. In this case, the purpose of this project is to create a
prosthetic arm that is cost efficient and light weight while still having the
high functionality that a normal arm would have.
Amputations occur when a traumatic injury has occurred to a person’s
appendage. Generally, this occurs when the patient is born with a birth
defect that causes a residual arm or an injury is dramatic enough to need
the arm to be removed in order for patient survivability. As of 1996, an
estimated 1.285 million people needed prosthetics, about 1 in every 200
Americans [1]. During that time, the CDC estimates that 1,500 babies per
year are born with upper limb reduction in the United States due to birth
defects [2]. However, the population of the country has grown dramatically
since that time which would cause the total number of people with
amputations to increase as the population increases. Prosthetics are
helpful to these people because it allows them to live their lives normally as
if they still had the missing limb.
The average cost of prosthetics (depending on the quality and functionality
of the prosthetic) ranges from $5,000 – $50,000 [3], and about 85% of
Americans have insurance to cover prosthetic limbs, per the U.S. Census
Bureau [4]. Due to the projected increase in need and the rapid growth of
income inequality in the U.S., the development of an affordable prosthetic
which can be rapidly produced is necessary.
By projecting the number of prosthetics needed using the same proportion
of the population as in 1996 and multiplying by the average cost of
prosthetics, an estimated $100 billion market is predicted to exist in the
U.S. today. Typically, high-quality prosthetics are prohibitively expensive
due to the premium materials and custom machining needed, while
affordable prosthetics often have low functionality and numerous
mechanical deficiencies such as low degrees of freedom and high friction
coefficients. The advantages of 3D printing in the industry have mostly
been limited to prototyping. However, this technology can be utilized to
develop an affordable prosthetic which does not sacrifice any functionality.
The quick build time and low cost of 3D printing, combined with design
capabilities beyond normal machining offers an opportunity to undercut
the market and deliver a truly unique solution.
There is especially a need for this product due to the effect it has on people
who have a residual arm. Often times, people are stared at or cast out in
society because they are different. The biggest complaint, aside from
comfortability, with prosthetic arms is that they don’t look natural. Many
5. patients wish for their prosthetic to resemble an actual arm in order to
keep attention away from it. Additionally, they are unable to perform basic
functions in their everyday life. Between being able to pick up objects or
drive, people have a harder time functioning on their own with a missing
limb and no way to make up for the function that the previous limb had.
Prosthetics allow people with these problems to live a normal and highly
functional life.
However, even with the benefits that prosthetics supply customers, many
upper limb amputees do not wear prosthetics [5]. This is due to the low
comfortability of the device. The device is very likely to cause chafing and
additional injury due to the neglect of comfort in favor of function. Each of
the amputees who were interviewed in the case study said that in
the twenty-five years they had been an amputee, they had not worn a
prosthetic arm because it had more negative consequences than positive
attributes.
Another large issue with current prosthetics is that current
manufactuerers do not best take into consideration the desires of
amputees. The most common complaint between amputees is the fact that
a prosthetic still causes them to be stared at when they are out in society.
Instead of providing them a sense of feeling normal, they still appear robot-
like. Potential customers would ideally prefer their prosthetics to have a
more humanoid appearance in order to resemble an actual arm more
closely. For example, one man whose pseudonym in the study was Phil, had
a prosthetic that was over five years old that he preferred to wear over the
new one his doctor provided him with [5]. Even though the device was
highly functional, it was not as aesthetically pleasing as his older device.
Additionally, these devices were highly advanced but difficult to operate.
One woman for the case study (Jennifer) found these prosthetics difficult to
use, so she found it was easier to learn to function with her residual arm
rather than use a prosthetic device.
In order to obtain more information about these issues first hand, our
team contacted Ms. Anna Street of Brevard Prosthetics. A majority of our
questions had to do with the comfortability and the human factors to deal
6. with the project. She confirms that most of what the case studies
say are valid. When asked what the biggest factors to consider are, she
says the complaints she experiences that the devices are hard to use and
there is not much comfortability. However, she claimed that expense of the
prosthetic is not a big issue since insurance generally covers the price of
the device.
Due to these issues, a new prosthetic needs to be designed. The goal of
this prosthetic will be to be an easier to use, highly functional device with
the user in mind. It will be 3D printed to ensure low cost and low weight.
The socket will be designed to incorporate the user’s comfort in order to
make a device that puts the client first.
II.2 Description and Estimation of
Market Size
Prosthetics can affect anyone. There are various causes as to how
amputations can occur. One major reason a person may have missing
limbs is due to birth defects. It is estimated that four out of every 10,000
babies will have an upper limb reduction in the United States. These
children will be born without these limbs for the rest of their lives which
means they will have to use a prosthetic for the duration of their lives.
Children born without limbs have to replace their prosthetic much more
often. Since they are rapidly growing during childhood and puberty, they
have to replace their prosthetic often to keep up with the size they have
grown to. Most prosthetics are estimated to have a shelf life of three to five
years. However, a child is estimated to need a new prosthetic every two
years until they are 18. With the lifespan at 75 years, this means a person
born with an upper limb reduction will receive approximately sixteen
prosthetics throughout their lifetime if the prosthetic lasts throughout its
shelf life.
Another major way for amputations to occur is when veterans are injured
at war. During one year of the Afghanistan and Iraqi war, 15,000 soldiers
had to be removed from the warzone due to injury that was obtained
during battle. Of these soldiers, 1200 of them had to be removed due to a
battle injury that resulted in a major amputation. This was during 2014
which was the last year that military personnel were in these locations.
Troops were in Afghanistan and Iraq actively for 13 years before being
withdrawn.
According to Veteran’s Affairs, they perform approximately 7700
amputation surgeries annually. Twenty-one percent of these amputations
involve the upper limb which projects that 1600 amputations are
performed on veterans' arms every year [6]. While this is the average, this
number changes dramatically depending on the condition of the country. If
the United States is engaged in a war during that time, the number
increases dramatically. On the other hand, if the country is not actively
fighting, the number of amputations decreases.
7. During the year of 2009, 12602 surgeries were performed,and $4.8 million
was spent by Veteran’s Affair on rehabilitation and prosthetic equipment
for new amputations.
However, these are recent wars. The majority of military causalities in the
United States were during both of the world wars. During World War I, 2635
major amputation surgeries were performed. A few years later, World War
II brought more than 15000 amputations. However, a majority of
amputations are lower limb as opposed to upper limb due to the nature of
military operations [7]. However, amputees from these wars are
significantly older if they are even still living now.
It is documented that between 27-56% of upper limb amputees actually use
prosthetics. However, these numbers vary greatly and do not have a clear
literature value. Because an upper limb reduction does not affect function
the way a lower limb reduction does, it does not have as much research
done on it. One study was conducted on a population of amputees in the
North West area of the United States [8], and 72% of the people polled were
men while 28% were woman. A majority of the sample (88.88%) were
Caucasian. Fifty-five percent of the sample had a college education.
According to the same study, 56% of people with an upper limb reduction
use a prosthetic. There are many factors that contribute to prosthetic use.
Greater use was associated with marriage status while it was found that
level of education, gender, and employment status also affect use.
However, of the people polled, most upper arm reductions wear their
prosthetics for 11 hours a day for 24 days a month.
While only roughly half of the number of upper limb reductions actually use
8. III. Problem Identification
III.1 Problem Statement
prosthetics, a product that improves upon the complaints that consumers
have could cause for the number of people who actually use prosthetics.
References
There are numerous devices on the market already. However, as discussed
in the general need for this product, there are a lot of negative reviews that
consumers have about them. These devices can be uncomfortable which
decreases the number of users who are willing to wear them on a daily
basis. Additionally, if the device is not easily operated by the user, the
clients will have trouble using them which will also decrease the number of
users.
Many devices aim to provide the function for the arm that has been lost
whether through birth defects of traumatic injury. However, these
products are more likely to cause problems if the customer’s needs are not
put first. For example, one of the biggest reasons that most products are
not considered comfortable is because they do not consider future health
hazards that can happen after continued use of the product. When the
client wears the product all day, it is bound to get hot and produce sweat.
These products do not have an area to allow the sweat to escape or
evaporate. This means that the sweat just sits in the connection and rubs
the residual arm throughout the duration of the use. Eventually, the sweat
in the connection causes the residual arm to chafe which causes future
problems for the arm. Additionally, the residual arm becomes tired if it
bares too much weight for a long period of time. Customers repeatedly
wish for a
more lightweight device in order to be able to wear it for a longer period of
time. Multiple amendments need to be made to the arm in order to make
using the device a much more pleasant experience when the client must
wear it.
Another problem is how the product does not visually resemble an arm.
This makes many amputees uncomfortable because it draws more
attention to the fact they have a limb missing. Many clients wished for the
design to make them appear as normal as possible in order to make users
feel more comfortable about themselves. While younger users may like the
fact that the arm resembles what they often see in the media, older users
no longer wish for this.
The last major issue that needs to be addressed to advance this device is a
way to make it more user friendly. While features are created in order to
make the device more advanced, it turns into a disadvantage when the
functions cannot be used properly.
Therefore, these problems must be addressed in order to make a
profitable device for the market. There are endless prosthetics on the
market that have new and advanced technology. However, these devices
still cause issues because they place function as more important than the
user’s needs. In order to fabricate the best design for this device, both
function and user’s needs must be placed as equally important.
[1] Walters, Lilly. (n.d.) Statistics on Hand and Arm Loss [Web]. Available:
http://www.aboutonehandtyping.com/statistics
[2] N.A. (28 Oct. 2014) Upper and Lower Limb Reduction Defects Centers
of Disease Control and Prevention [Web]. Available:
9. 1
http://www.cdc.gov/ncbddd/birthdefects/ul-limbreductiondefects.html
[3] Mahoney, Gillian. (25 April 2013) Health Care Costs for Boston
Marathon Amputees Add Up Over Time, ABC News [Web]. Available:
http://abcnew.go.com/Health/health-care-costs-boston-marathon-
amputees-add-time/story?id=19035114
[4] N.A. (17 Sept. 2013) Health Insurance: Highlights: 2012, United States
Census Bureau [Web]. Available:
http://www.census.gov/hhes/www/hlthins/data/incpovhlth/2012/highlights.
html
[5] Rivera, Jessica C., and Johnson, Anthony E. (Dec. 2014) The Impact of
Amputation Among Veterans [Web]. Available:
http://www.aaos.org/news/aaosnow/dec14/research2.asp
[6] N.A. (07 Dec. 2014) U.S. Military Builds on Rich History of Amputee
Care [Web]. Available: http://www.amputee-coalition.org/military-
instep/rich-history.html
[7] Webster, Joseph B., Poorman, Cindy E., Cifu, David X. (24 Jan.
2014) Department of Veterans Affairs Amputation System of Care: 5 Years
of Accomplishments and Outcomes [Web]. Available:
http://www.rehab.research.va.gov/jour/2014/514/pdf/jrrd-2014-01-0024.pdf
[8] Raichle, Katherine A., Hanley, Marisol A., Molton, Ivan, Kadel, Nancy J.,
and Campbell, Kellye. (14 Sep. 2009) Prosthesis use in persons with lower-
and upper-limb amputation [Web]. Available:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2743731/
[9] Old Man with Residual Limb 2012 [Web] Available: gettyimages.com
[10] How Do You Do ... Washing Dishes? 2010 [Web] Available:
http://singlehandedsolutions.blogspot.com/2010_09_01_archive.html
[11] Rahman, Anatol. The Lego Robotic Prosthetic Arm Defines Complex
Hand and Wrist Movements Elaborately. 2012 [Web] Available:
http://thetechjournal.com/electronics/the-lego-robotic-prosthetic-arm-
defines-complex-hand-and-wrist-movements-elaborately.xhtml
[12] Westcoast Fabricates Silicone Devices in the Tampa Bay Area. 2011
[Web] Available: http://www.wcbl.com/prosthetics-2/newest-
technologies/silicone-prosthetics/
10. PORTFOLIO ELEMENT B
DOCUMENTATION AND ANALYSIS OF PRIOR SOLUTION
ATTEMPTS
2
Six types of prosthetic arms are benchmarked against each other to establish the baseline for the performance required to design a new
prosthetic arm. All of these prostheses are assessed in 12 categories: weight, size, number of joints, degrees of freedom, number of actuators,
actuation method, adaptive grip, grip force, range of motion, grasp type and motor specification. The data for these categories are obtained
through prior publications comparing and discussing the development in upper arm prosthesis. The various prosthesis models seen in this
benchmarking procedure are in the Figures IV.3.1 to IV.3.6 below.
IV Benchmarking of Competitive Products
11. Each of these prostheses are evaluated using the 12 criteria mentioned before by studying various published articles and studies carried out by a
number of other groups on these prostheses. While the product specifications listed here provide quantitative information about each product
in comparison to the other, the qualitative information of customer requirements and reviews is also mentioned in this document; Therefore,
Figure IV.3.6: The Michelangelo hand by Otto Bock (Competitor 6)
Figure IV.3.5: The Bebionic Hand v2 by RSL Steeper (Competitor 5)
Figure IV.3.4: The Bebionic Hand by RSL Steeper (Competitor 4)
Figure IV.3.3: The iLimb Pulse by Touch Bionics (Competitor 3)
Figure IV.3.2: The iLimb Hand by Touch Bionics (Competitor 2)
Figure IV.3.1: The Vincent Hand by Vincent Systems (Competitor 1)
12. The weights of prosthetic arms mentioned above are the weights of the entire system that the amputees need to carry while using the
prosthesis. In case of the iLimb Pulse and Bebionic v2 hands the total weight included controller, battery, force sensing resistors and the
distal side of the Otto Bock Electronic quick-disconnect unit. In case of the Michelangelo, the total weight included the hand with protective
sleeve, an Axon rotation wrist adapter, a large battery, and controller. For the Vincent prosthesis, the same base can be used to attach fingers
of three different sizes (distal portions), each weighing from 2-4 g.
The Table IV.3.2 below shows published kinematic and grip characteristics of the prosthetic arms studied. The three major categories: the grip
force, range of motion and grasp type determines how maneuverable the prosthesis would be, and how smoothly it would function as a
replacement for the actual arm. The grip force determines the range of forces the prosthesis can apply, which further determines the
amputee’s ability to hold and lift both heavy and fragile objects. Prostheses with wider range of grip force are better at grasping a variety of
objects, and the prostheses with lower minimum values of grasp force are better at holding fragile objects. Range of motion determines the
flexibility and accuracy with which the amputation can function. Prostheses with these values closer to actual arm serve their purpose better
than those who don’t.
Table IV.3.2: Grip and Kinematic Characteristics of Prosthetic Arms currently available in the Market
Table IV.3.1: General Properties of Prosthetic Arms currently available in the Market
The qualitative criteria studied initially between the 6 products are presented in the Table IV.3.1 below. Here, the table shows the weight of
prosthesis which is an important factor as it is the added weight that the amputee has to carry on the amputated arm, overall size of the
prosthesis which determines its maneuverability and ease of use, number of joints and degrees of freedoms which shows how closely the
prosthesis can mimic the functions of an actual arm, number of actuators, actuation method, joint coupling method and finally the function of
adaptive grip which determines the range and accuracy of force applied by the prosthesis while grabbing the objects.
this document will provide both the relative quantitative information about the 6 products studied and the qualitative requirements of the
people suffering from trans-radial amputation.
IV.3.1: Quantitative Benchmarking Data
13. Weight of the prosthesis is an important factor. An average human hand weighs about 440 g excluding the forearm extrinsic muscles, but it has
also been observed that the prostheses of similar weight are described by the amputees as heavy. Since these prostheses are supported by the
soft tissue instead of the skeleton on the amputee’s stump, the weight perceived by them is increased significantly. Hence, the weight of the
prosthesis is one of the major factors contributing to the fatigue and discomfort related to its use. An online survey of myoelectric prosthesis
users has recently revealed that 79% of the patients consider their prosthesis to be too heavy. Also, the users rated weight as 70 on the scale of
important factors (from 0 to 100) to be taken care of to make the prosthesis comfortable. Not only the total weight, but the distribution of
whatever weight the prosthesis has is also an important factor in making the prosthesis feel comfortable. Prosthesis with heavier components
like actuators and batteries placed proximal to the patient are more comfortable than those which have the heavier components placed distal to
the patient’s body. A range of 350-615 g is observed in the commercially available prostheses. These
IV.3.2: Qualitative Benchmarking of the Prosthetic Arms
The grasp force was measured on these prostheses using pinch meters for precision grasps and a grip dynamometer for lateral grasp and power
grasps. For the grip force, the Vincent and iLimb Pulse use an additional pulse mode to increase the holding force for individual finger
significantly. After a set period of motor stalls, the motor is supplied with quick pulses of power which basically ratchets the system to a higher
capable holding force than what can be achieved without the pulse mode system. An average of 69.5% increase and 91.5% increase in holding
force of individual finger was observed for Vincent hand and iLimb Pulse hand respectively because of the addition of pulse mode. The
drawback of this system is that it significantly reduces the battery life of those arms. There was a lot of variety in the designs and positions of
thumbs in the prostheses tested. Thumbs have actuated MCP and PIP, and circumduction joint that can be manually positioned in multiple
states in iLimb, iLimb Pulse, Bebionic, and Bebionic v2. The Michelangelo hand prepositions the thumb joint by a small motor prior to
performing grasps. While the main motor actuates to close the hand (palmer or lateral grasp), the small motor changes the path that the thumb
takes. In addition, the thumb also has a natural-looking resting position.
For the actuation method it was observed that five of the six prostheses tested had a proximal joint and single distal joint. The proximal joint
was similar to the human metacarpal phalange (MCP) and the distal joint was similar to the proximal interphalange (PIP) and distal
interphalange combined (DIP). Whereas the iLimb and Bebionic prostheses had distal finger segment that gave look of a functional DIP, the
Michelangelo hand consisted of single finger segment with no joints, actuated only at a single point like the human MCP joint. In case of the
iLimb, Vincent, Bebionic, and Bebionic v2 the finger joints are not actuated independently, but have fixed relative movement to each other.
Each of these prostheses have their own unique method of coupling MCP and PIP joints using a four-bar linkage. Since, the space inside the
prostheses is small, each of the models used in this study contained motors which incorporate high gear reductions. The motors were either
placed in the proximal phalanx (iLimb, iLimb Pulse, and Vincent hand using Maxon DC Series 10 motors) or in the palm (Bebionic, Bebionic
v2, and Michelangelo using Maxon GP 10A motors). The Bebionic and Bebionic v2 hands use a custom linear drive developed by Reliance
Precision Mechatronics (Huddersfield, UK). Michelangelo uses a unique system with one large custom modified brushless Maxon EC45 motor
placed at the center of the palm to control flexion/extension of all the fingers at the same time and a separate motor in proximal region for
abduction/adduction of the thumb.
Figure IV.3.7: Images of Fingers and Kinematic model joint coupling mechanism of fingers studied. (1) Vincent hand, (2)
iLimb and iLimb Pulse, (3) Bebionic and Bebionic v2, and (4) Michelangelo. Here, 1 is the angle of metacarpal phalange
joint and 2 is the angle of proximal interphalange joint.
Figure IV.3.8: (1) The Central Drive Mechanism of Michelangelo hand, (2) Placement of motor in Proximal Phalange,
rotating worm against fixed gear in Vincent hand, and (3) iLimb finger actuated in the same manner as Vincent hand, but
uses bevel gears between worm drive and motor. MCP = Metacarpal Phalange.
14. IV.4.1 US 5443525: Conductive Patch for Control of Prosthetic Limbs
IV.4 Patent Search
To further obtain the information regarding prosthetic arms and such devices in the market, five patents were studied to determine the options
currently available. All the products studied were different designs of mechanics in the prosthesis, sensory feedback devices for tactile
information about objects that are being touched by the prosthesis and myoelectric prosthesis control. These patents were studied because each
device included design elements that can be incorporated in the new myoelectric prosthetic arm design. Each of the sections below will
separately discuss about the description of the patent and about how the patents apply to the design.
numbers are quite close to the weight of an actual human arm, but still perceived heavier by the patients who use those prostheses. It is better to
have a prosthetic hand which weighs less than 400 g. Size is also an important factor for prosthetic arms. It should look almost the same as the
actual arm of an adult and hence should have length between 180-198 mm, and a width between 75-90 mm, including the cosmetic glove.
Finger kinematics which is anatomically correct is an important factor in mechanical design of the prosthetic hands. It is vital to keep a balance
between the anatomical correctness, robustness, weight, complexity and cost. To do this, a number of joints are coupled to act as a single
compound motion when powered by a single actuator. The position of actuator can be used to determine the position of all joints coupled
together. A distinct set of movements that can be described by a single parameter is considered a single DOF. Adaptive underactuation is also
used for coupling joints. Here, a single actuator controls a number of independent DOFs. Single actuator parameter cannot determine the
position of the joints as they are dependent on the contact state of each finger link with the object. This system allows multiple links to adapt to
the shape and location of an object passively using a single actuator, and hence are considered as adaptive. Nearly 40% of the human hand’s
functionality depends on the thumb, hence thumb design is a critical parameter for upper limb prosthesis. Most of the prosthetic hands studied
hear used thumb which is actuated in extension/flexion and along the circumduction axis. To alternate between lateral grasp and power grasp,
the circumduction rotation of the thumb is required. Analysis of human hand kinematics shows an average circumduction of 90.2o, achieved
through a combination of three joints at the base of the thumb. The circumduction axis of current hands is not always oriented parallel with the
wrist rotation axis. By angling this axis ventrally or dorsally, thumb flexion and circumduction rotation can be jointly approximated in a single
DOF. This can be beneficial to achieve desired hand openings and a more anthropomorphic motion for precision, power, and lateral grasp
patterns while keeping complexity low.
Grip force of the prosthesis is very important. Although most activities of daily living require fast speed and low grip forces, there are also
occasions where the patient needs low speeds and high grip forces; hence, the prosthetic arm should enable the user to perform tasks which
require both fast speed and low grip forces, and slow speed and high grip forces. It is difficult to predict the necessary grasp force required to
maintain an object within a particular grasp. The required grasp force depends on friction between the object and the fingers, the object
geometry and mass properties, the number of contact points and the relative locations of contacts. Human arm can reach up to 400 N in
power grasp and can exert 95.6 N of force in precision grasp. Based on previous studies, a grip force of 45-68 N is sufficient to perform most
activities of daily living. Based on an online survey carried out by previous researchers, about 100% of females, 76% of males and 50% of
children with amputation describe their myoelectric prosthesis to be slow. The typical speeds for everyday pick and place tasks is around 173-
200o/s, but the human hand can reach finger flexion speeds of 2290o/s if required. The finger flexion speeds of hands studied here ranged from
20o
/s to 225o
/s. The prostheses which belong to the upper portion of this range are fine, but those which belong to the lower portion of the
range are quite slow in comparison to the actual human arm. Hence, it was determined that it is adequate to have arms which have closing time
ranging from 0.8-1.5 s for most activities of daily living than anything which has closing time larger than 1.5 s.
The typical activities of daily living conducted by the amputees can be accomplished using a finite set of predefined grasp patterns. These
predefined grasp patterns include lateral, power, tripod, precision, finger point, and hook. Some researchers also consider finger counting
gesture as important besides the six gestures mentioned before. Although the full range of distinct grasps for a normal hand is greater than
thirty, these six grasps are the most important in performing typical activities of daily living for the amputees. For the prosthesis to perform the
six grasping patterns mentioned, each individual finger flexion motion must be controlled using an actuator that is independent of the other
fingers in the prosthesis. If the function of finger counting is removed, the complexity of the prosthesis and hence the requirement of multiple
actuators can be reduced.
Durability is very important for the prosthetic arms. On average, a myoelectric prosthesis user wears the device in excess of 8 hours per day.
Hence, it is very important that the prosthesis is robust and comfortable enough for the user to wear it for more than 8 hours. The designer of
prosthetic arms must consider creating a balance between durability, robustness, size, weight, and cost. To make the device robust and more
functional without making it more complex or expensive, compliant components like conforming fingertips/palmar pads, actuator design that
increases compliance, and collapsible linkage systems can be included in the design. While a normal hand performs 2500 to 3000 grasping
motions in a typical work day period of 8 hours, the prosthetic devices typically undergoes 120 grasping motions in the same period of time.
Even with low functionality of prosthetic hands compared to normal hands, they should be able to withstand a total of 300,000 grasping
cycles and maintain all of its original functionality for around 6 years of use. The current standard, which will act as the baseline, for prosthetic
devices is the lifetime of total 500,000 grasp cycles with routine servicing during the expected period of use.
15. This patent specifies a novel pad that includes an electrically conductive grid including a very large plurality of densely packed electrical
contacts embedded within a non-conductive silicone rubber matrix. The patent’s descriptions are written generally to encompass full contact of
the electrodes to the amputee’s skin at all time and to allow the detection of multitude of myoelectric signals more accurately.
The main advantage presented in this patent is the ability to detect even a small change in myoelectric signal accurately and reproducibly. Not
only can it be used for different patients reliably without making any changes, the electrode pad can be calibrated to perform at different
myoelectric signals for different patients using this device.
Weaknesses:
Acquisition of myoelectric signals may still cause the electrodes to slip away from its original position due to sweating. The signal acquisition
and processing system should be able to work with a huge amount of data coming from several electrodes which may make the prosthesis too
costly (due to high processing power), or lagging due to significant time consumed in the processing of myoelectric signals.
Strengths:
Figure IV.4.1.1: Patent No US 5443525; perspective view showing a prosthesis liner
equipped with the novel pad
IV.4.2 US 6589287: Artificial Sensibility
The general geometry of this novel pad is described as including an electrically conductive grid that includes very large plurality of densely
packed electrical contacts embedded within a nonconductive silicone rubber matrix. The unique device can be provided in any desired size and it
can preferably be bonded to the interior surface of the socket or liner for direct, conforming, non-migrating contact with the user’s skin. Since
the resistivity of this device is very small, less than 0.001 cm, it can detect even a small change in the myoelectric current. Each contact within
the grid has a size of about 0.002 inches square and the contacts are spaced about 0.005 inches apart, measured between centers. Thus, a 1-
inch square grid contains about forty thousand discrete contacts.
A multitude of myoelectric impulses can be measured through this device since it allows several pads to be placed at specific locations on the
amputee’s body. Due to the ability to easily conform the pads to the amputee’s skin and because of the high density of conductors on the pad,
the accuracy of the myoelectric signals, its reliability of detection, and its reprodicability is increased significantly. This allows for the
development of a control system capable of producing a very complete range of motions in a prosthetic hand or other prosthetic device by
helping the control system sort through and organize the complex myoelectric signals. Hence, this patented device can provide a breakthrough
in myoelectric control system by eschewing the large, metallic electrodes currently in use with several tiny electrodes that can be placed in
comfortable, non-migrating relation to the patient’s skin.
This patent for artificial sensibility of objects touched by the prosthesis when it is use. It consists of sensors applied to the left finger of the,
middle finger, and right finger of the prosthesis. These sensors are connected to a headphone unit consisting of left and right speaker, via a
signal amplifier. Whenever the a finger comes into contact with a surface, the sensor sends a signal to an amplifier which then repeats a stronger
signal to the left speaker of the headphone. This notifies the user that the left finger has moved. The process is identical for the right finger.
For the middle finger, signal is heard from both the left and right speakers equally.
16. Figure IV.4.3.1: Patent No US 20090048539; illustrates one embodiment
of the system, wherein sensors (2) are applied to a hand prosthesis or a hand
without sensation or a glove (1) and are connected to a processor (3) via
electrical or hydraulic conduits (7a), said processor (3) being connected by
electrical or hydraulic conduits (7b) to signal transducers (4), arranged on
the forearm, forming a tactile display (5).
Figure IV.4.2.1: Patent No US 6589287; shows an embodiment of the invention into a
prosthesis or hand with lost tactile sensation.
Strengths:
The main advantage is providing the patient with the ability to sense the objects touched by them with their prosthetic. Also, it has been shown
that listening to the sound from different surfaces is more stimulating, and hence a better option, than just seeing the prosthesis touch a
surface. It helps the patient recover faster from inability to detect when the prosthesis is touching a surface and what type of surface is it
touching.
Weaknesses:
A weakness of this method is that the touch feedback in the form of sound is not natural. It takes some time for the patient to learn various
cues in the form of sound while touching different objects with different textures. Also, placement of headphone distracts and impairs the
ability of patient to react to the natural sounds like someone calling his/her name, or listening to someone speaking etc.
IV.4.3 US 20090048539: System and Method for Conscious Sensory
Feedback
The system and method for conscious sensory feedback is relevant to the design of prosthetic arm as it would provide tactile feedback. In this
patent, the piezo-resistive membranes as sensors are fixed to the volar part of the fingers. These sensors produce electric signals when induced by
pressure. The signal produced by the sensors are processed and transported to a tactile display made out of vibrating motors acting as signal
transducers. They are placed parallel but clearly
separated on the volar aspect of the forearm in a transverse fashion from the medial to the lateral side. Whenever one or several fingers of the
prosthesis is touched, it induces a vibro-tactile stimulus to the skin of the forearm. The patient can easily learn and discriminate between
individual fingers and different touches without the use of vision.
Strengths:
The main advantage in this patent is providing the patient with the ability to sense the objects touched by them via their prosthesis. Since the
feedback is tactile, the patients can easily learn to differentiate various touch stimuli without much difficulties. Also, unlike the auditory
feedback mentioned above, it does not impair the patient’s ability to receive other forms of senses like sound.
17. Strengths:
Figure IV.4.4.1: Patent No US 20090048539; shows side views of the prosthetic hand
device in various positions, illustrating one configuration for parallel elastic elements in
accordance with an embodiment of the invention.
Figure IV.4.4.2: Patent No US 20090048539; an anterior view of a
prosthetic hand device in accordance with an embodiment of the invention.
Figure IV.4.4.3: Patent No US 20090048539; shows a partial cutaway view of a
section of a phalangeal portion associated with a distal end of one of the digits of
prosthetic hand device
Weaknesses:
The only weakness is that the patient has to learn to decipher various types of vibrations for various types of touches. Also, it would be better to
send sensory feedback directly to the nerve for natural response, but it is a quite difficult and invasive method.
IV.4.4 US 20120150322: Jointed Mechanical Devices
In this patent a prosthetic device includes at least one member and hand device coupled to the member. The hand device comprises of a base
and at least one digit pivotably coupled to the base. Here the digit is comprised of phalangeal portions connected by flexible joint portions.
There is at least one actuating structure with its first end coupled to the distal end of the digit, where there is an actuating structure comprising
of at least one elastic element in series with at least one non-elastic element. The device also includes at least one force actuator configured to
apply force to a second end of the actuating structure and a control system for adjusting the operation of the force actuator based on at least
one actuation input, an amount of given force, and an amount of displacement generated by the force. The prosthetic device also comprises of
electromyogram (EMG) sensors for generating control signals from the residual limb of the user.
The prosthesis further comprises of a computing device that can detect if certain part of the prosthesis is in contact with an object and can
operate force actuators, using the motion control mode and force control mode, based on the amount of force and displacement. The device
consists of at least one restorative element which applies force opposite to the actuator force.
The main advantage is that the prosthetic hand can detect a variety of signals and use them to operate the actuators like muscles in a real hand.
The patient wearing this prosthesis can detect when the prosthesis is contact with an object and can operate the actuators accordingly. This is
done directly by a processor using the feedback obtained from the sensors in the hand. Compliance characteristics of the device are
automatically calibrated by having the hand slowly close and open without grasping an object while the motor current and position are
monitored to create a position/force map in the absence of an object.
18. Figure IV.4.5.1: Patent No US 20130046394; simplified illustration of an embodiment of a
myoelectric prosthesis control system
Figure IV.4.5.2: Patent No US 20130046394; simplified illustration of a
portion of a gel liner
Weaknesses:
The only weakness is that although the prosthesis can detect its position and contact with an object, it does not send tactile feedback to the
patient directly. In fact, the feedback is taken by the processor and necessary changes in actuation are made directly by the processor. Also,
because of several sensors in the hand the processor driving the prosthesis should be powerful enough to perform several computations and real
time changes based on the position of the prosthesis. This could also reduce the battery life because many computations require the processor
to draw more power from the battery.
The idea behind this patent is to provide a myoelectric prosthesis control system that includes a gel liner that has layers and a plurality of leads
at least partially positioned between layers. The leads can be partially positioned between the layers and coupled to electrodes.
Moreover, the electrodes can include an electrode pole that may be configured to contact the residual limb via the gel liner. The electrode poles
can be configured to detect electromyographic signals and at least some of the electrodes and at least some of the leads can be manufactured
from a compliant conductive material.
A gel liner, for use with myoelectric prosthesis control systems, is assembled from a non-conductive fabric and electrodes. Leads are positions
between the electrodes and a thermoplastic elastomer beneath the gel. The layer of thermoplastic elastomer can also be coated over the outer
layer so that at least one electrode will partially protrude from the layer of thermoplastic elastomer.
IV.4.5 US 20130046394: Systems and Methods of Myoelectric Prosthesis
19. Figure IV.4.5.3: Patent No US 20130046394; simplified illustration
showing an embodiment of a distal end of the gel liner of Figure
IV.4.5.1, including a signal-conditioning electronics module and a distal
end connector
IV.5 Opportunities for Competitive Advantage
Weaknesses:
Strengths:
The main strength of this patent is that the there are several electrodes that can measure small changes in the myoelectric signal. Due to the
involvement of the several electrodes, the reception of false signals are significantly reduced, providing more accurate control over the actuators
operating the prosthesis. Each electrode can include a pole that may be configured to contact the residual limb when the gel liner is worn. The
electrode poles can be configured to detect electromyographic signals. Some of the electrodes and leads can be manufactured from a compliant
conductive material.
One of the weaknesses of this patent is that the placement of electrodes and leads is very complex. This could affect the reparability of the
system by compounding small problems. The complexity of the design can increase the cost of manufacturing compared to other, simpler
designs.
While there are many prosthetic arm designs currently on the market, there are three needs that current models do not address: excessive
weight, lower maneuverability, and high cost. Many prosthetic arms on the market have great strength, are durable, have decent battery life, and
are robust enough to be used both indoors and outdoors; therefore, there is very little room for innovation to improve the basic functions of the
prosthetic arms. Prosthetic arms designed for increased maneuverability, such as the ones with several degrees of freedom and a range of grip
force studied in the benchmarking exercise are quite numerous but expensive. Also, they lack basic sensory feedback mechanisms that provide
the tactile information about objects which the prosthesis contacts. What is currently missing from the prosthetic arm market is a device that
improves the comfort, provides sensory feedback, and serves as a low cost option for high maneuverability and natural functioning which mimics
the actual human arm.
Too many users feel that the prosthetic arms are too uncomfortable and slow to use like normal hands and end up not wearing them. While
prosthetic arms are meant to be used for assistance, hence they should function like a normal hand without causing much discomfort to the
user. Due to this, there is opportunity for a new prosthetic arm design that reduces or completely removes discomfort and increases
maneuverability. Lower lag time between the muscle stimulus and action performed by the prosthesis and sensory feedback from the prosthetic
arm can greatly solve the problem of users feeling that the prosthesis is just additional weight. As discussed, the number of amputees who feel
that it is better to have no prosthesis than to have one with partial functionality is alarmingly high. This problem can be solved by designing a
prosthetic arm which is inexpensive, lightweight, comfortable and life like in appearance and functions.
An aesthetically pleasing prosthesis design is also a major area for competitive advantage. Many individuals with amputated arms resist using
their prosthetic arm because they believe that it makes them look different from other people. There is a need for prosthetic arms that provide
the user with high functionality of hands but donot look like a traditional medically issued artifact. It should blend
with their body so that no person can tell the difference. We suggest a design of prosthetic arm which falls in the category of arms that function
similar to the actual arm and has price which is close to the traditional body powered prosthetic arms. A device that falls into this category would
have a large competitive advantage because there are currently no products in this space. Taking of this gap in the market would ensure that our
design attracts customers that would otherwise lack interest in our solution.
There is no question that any new design would have to meet a standard for stability, maneuverability, safety, durability, height adjustability,
and indoor/outdoor dual usability. Our prosthetic arm design will have to function at the same level as the baseline established through
benchmarking in order to be a viable option as an assistive device. However, the design team’s goal is to make a higher performing prosthetic
arm at an affordable price that suits most people’s pockets. We are focused on making a prosthesis that encourages people to use it in their daily
life without concerns of discomfort or damage to their remaining portion of the arm. The new prosthetic arm design will be light and
cosmetically attractive as well as functional so that the users will enjoy using their prosthetic device.
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24. The following design requirements are divided into Top Priority, Priority, and Additional
Requirements. Top priority and priority requirements are all disqualifying requirements, meaning that a
design concept which cannot satisfy the requirement will be discarded. The distinction is that priority
requirements have been determined through industry contacts and customer survey to be the most
critical to creating a successful, competitive product. Additional requirements would improve the design,
but are not absolutely necessary.
1) The solution should approximate the capabilities of a human arm and hand. This is a functional
requirement. The human hand can reach speeds of up to 40 rad/s and grip force of 400 N (all fingers
closed). Everyday tasks involve angular speed in the range of 3-4 rad/s and grip force of 0-67 N, which is
the minimum amount of force the prosthetic arm should achieve. Force/pressure sensors will be needed
to monitor the forces the solution is applying on objects, as well as relay information about the nature of
the object (soft/hard, strong/weak). A human wrist and forearm can achieve 85-90ºof supination, 85-90º of
pronation, 30-45º of ulnar deviation; 15º of radial deviation, 80-90º of wrist flexion, and 70-90º of wrist
extension [1]. Our prosthetic arm will need to come close to these values. All of the major prosthetic arms
in the market are custom made, based on the measurements of the amputee’s able hand and have size of
approximately 180-198 mm in length and 75-90mm in width. Hence, the prosthetic arm being designed will
be within the same range of length and width. An average human hand weighs about 400g and the major
prosthetic arms commercially available range from 350-615 g [2]. The prosthesis we are designing should
be towards the lower end of the range so that the amputee can comfortably carry it all day. The optimum
weight is less than 400g, as 79% of amputees describe 400g prosthesis as being too heavy to carry for the
entire day [3]. Additionally, our prosthesis will be designed such that most of the weight (particularly the
battery) is located proximal to the stump and does not produce excessive torque on the residual limb.
2) The solution must be comfortable. This is a functional requirement. Beyond the previously mentioned
factor of weight, the materials which contact skin must feel comfortable. Sweat buildup and blood
stagnation must be prevented, and ideally, muscle stimulation and temperature control should be
V.1 Top Priority Requirements
V. Solution Product Requirements
25. incorporated into the design.
3) The solution must be composed of materials which are compatible with human skin, non-allergenic,
and strong. This is both a functional and safety requirement. To avoid the need for extensive disclaimers
and the possibility of legal issues, the materials which contact skin cannot be irritating or contain
allergens. Structural, printable materials can be chosen from a variety of thermoplastics to meet these
requirements while incorporating high material strength. Smaller, weaker parts will need to be molded, as
molding will increase the material strength. This is because a mold results in a continuous solid, while
printing results in a layered material where the strength of the laminate becomes a limiting factor. Two of
the most readily available printable plastics are PLA (polylactic acid) and ABS (acrylonitrile butadiene
styrene). PLA has a higher tensile strength (approx. 7,000-9,500 psi) than ABS (approx. 5,000-5,500 psi),
while ABS can withstand higher temperatures [3].
4) The solution product must meet FDA standards and include all necessary labels in accordance with
current medical device legislation. This is a regulatory requirement. Legislation states that a statement
of identity of the device must be listed on the principal display panel which includes the common name of
the device, statement of its intended action, and indications of its use [4]. The Food and Drug
Administration also requires approval for any implantation device. According to the FDA, an implant is a
device that is placed inside or on the surface of the body to replace body parts, monitor the body, and/or
help organs increase function [5]. This prosthesis is therefore classified as an implant, so meeting FDA
standards is necessary to market the solution.
5) The solution will need adequate storage and processing capabilities. This is a functional
requirement. Storage must be at least 1 MB in order to collect muscle tension data from the amputee and
learn the appropriate gestures based on varying levels of tension. Smaller amounts of storage will be
needed for temperature data and force data as well as collecting data to monitor the electronic and
mechanical systems to prevent failures. Processing power will need to be high enough to execute all
functions quickly and simultaneously.
6) The solution must be capable of operating in normal conditions for a "full" work or school day. This is a
functional requirement. A battery of at least 10 amp-hours will be required. Batteries should ideally be
able to be recharged without being removed from the arm. The solution should be able to operate for a
full 8-9 hour work or school day, so as not to be an inconvenience to the amputee.
7) The solution must use safe batteries/power sources which also fulfill the above power requirement.
This is a safety requirement. The current best option to meet the power requirements while being safe
are nickel-metal-hydride (NiMH) batteries. Ventilation will be needed to prevent the batteries from
blowing.
8) The solution must operate at a peak voltage no higher than 7 volts. This is a functional
requirement. The majority of electronic components which will be used have a 7 V peak voltage, and most
affordable, small batteries on the market currently work in this range. This peak voltage will add to the
safety of the system, as 7 V is not dangerous to humans due to the high resistance of skin [1].
9) All wires must be either housed internally or protected with wire channels through the necessary parts.
This is both a functional and safety requirement. Internal housing in the forearm will provide ample
protection for most wires. For those leading to sensors in the fingertips or to electrodes (for myoelectric
sensors), channels must be designed through these subsystems for wires to travel such that they will not
potentially touch skin, which could be a concern if wires become stripped and/or exposed, especially in
wet conditions. While the peak voltage should not harm skin (see requirement 8), wire channels will
mitigate any risks.
10) The solution's electronic components must fit in the volume of a forearm. This is a functional
requirement. The available room can be approximated as an 8-inch tube which tapers from a 2.5-inch
inner diameter down to a 2-inch inner diameter. The electronics should fit in a significantly smaller space
than this so that heat sinks can be incorporated and so the solution can be scaled down in size to fit
children.
11) A learning process must be developed for the user to "break in" the arm and so the arm can learn
gestures from the amputee's muscle tension. This is a functional requirement. Gestures will be tested
using a distance accuracy task, object relocation task, and dexterity task as success criteria. Such
procedures should be contained in a product handbook when the solution is introduced to the market. In
the distance accuracy task, the amputee will be tested on the greatest distance and accuracy he/she can
achieve by throwing a bean bag into a target zone in least amount of time. This test will show the
solution's ability to grab an object from a container by lifting it vertically up and releasing it at a desired
time to be able to throw it exactly on the target. The goal is to be able to throw up to 120 bags per minute
on the desired spot for at least 90% of the time. For the object relocation task, the amputee will be timed
adding and removing objects from a small container. This test will show the solution’s ability to
consistently lift objects of varying weights, sizes, and shapes, move them laterally, and to be able to move
object in and out of a container. The objects to be moved include CDs, pencils, a pack of index cards,
V.2 Priority Requirements
26. notebooks, 500 mL water bottle, ruler, roll of masking tape and 2 inch vinyl kick ball. The objects should be
moved a distance of 60 cm in 7.5 seconds 90% of the time. For the dexterity task, the amputee will place
and secure as many nuts and bolts as possible. This task demonstrates the solution’s ability for fine
motor control. The solution is successful if the amputee is able to secure 1 nut and bolt in 37 seconds 90%
of the time [3].
12) The solution should include temperature sensors with a range of -20 to 100 degrees Celsius. This is a
functional requirement. This temperature range is broad enough to include all temperatures that the
solution will normally experience, and includes some hot temperatures which would be potentially
damaging, allowing a control system to cause the arm to let go of and recoil from hot objects. Any
temperatures outside the range of the sensors should be recognized as potentially harmful. This is not a
disqualifying requirement because, in the worst case, the amputee could most likely identify potentially
harmfully hot or cold objects by visual inspection rather than using sensors.
13) The solution's temperature feedback should be done using LEDs (light-emitting diodes) for quick and
easy recognition and minimal power consumption. This is a functional requirement. This could be done by
simply using a red and blue LED, where red denotes "too hot" and blue denotes "too cold" so that the
amputee knows when he/she is contacting a dangerously hot or cold object. Using LEDs to designate
dangerous temperatures serves two purposes. It would use minimal amounts of power and generate
negligible heat, and it would also be a very easily and quickly recognized signal to the amputee to pull their
arm away from the dangerous object. This is not a disqualifying requirement for the same reason as
requirement 12 and because other notification systems could be used, although they may take more
power.
14) The solution should have manual fail-safes in case of motor failure or locking. This is both a
functional and safety requirement. The solution should be designed to be manually forced out of an
undesired position into a desired position if the motors fail or lock or if the arm loses power. This is not a
disqualifying requirement because lack of these manual fail-safes would not be hazardous to the amputee
or have a significant negative effect on the product life-cycle.
15) Mechanical and electronic stops should be added to the solution in order to prevent movement
beyond the nominal range of motion. This is both a functional and safety requirement Mechanical stops
would be a way to improve the strength of the joints while preventing undesired motion which could
cause mechanical failures. Electronic stops would allow the arm to know when to stop moving. Calibration
systems would be needed to fulfill this subset of this requirement, allowing the arm to track its own
motion. This is not a disqualifying requirement because the solution can still function properly without
these fail-safes.
16) The solution should have customizable colors and finishes in order to accomodate customers'
aesthetic preferences. This is a non-functional requirement. In particular, children may want various
colors and finishes to be applied to the materials. Adults may desire artificial "skin" coverings for the arms.
Some amputees may desire an arm which they can custom paint or color. All of these solutions can be
delivered, and would increase the value and marketability of the arm. However, this is not a disqualifying
requirement as it has no effect on the overall functionality of the solution.
17) The solution should be designed at a cost of no more than $2,500. This is a non-functional
requirement Currently, prosthetic arms range in price from $3,000 for lower functionality to $30,000 for
top-of-the-line prosthetics featuring premium materials and high functionality [6]. A low price allows the
solution to fill a middle ground in the market as a low-cost, high-functionality option which customers and
insurance companies would be more willing to pay for. Like requirement 16, this would improve the value
and marketability of the arms. Also, the low cost would mean that arms could be produced on a larger
scale more quickly, and with less start-up capital. While cost is a factor, it is not a disqualifying
requirement because it does not directly effect the functionality of the solution.
References
V.3 Additional Requirements
27. PORTFOLIO ELEMENT D
DESIGN CONCEPT GENERATION, ANALYSIS, AND
SELECTION
The following references were used in this section.
[1] N.A. (21 Oct. 2003) Nickel Metal Hydride Batteries Handling Precautions [Web].
Available:<http://www.tayloredge.com/reference/Batteries/Ni-MH_Precautions2.pdf>.
[2] Belter, Joseph T., Segil, Jacob L., Dollar, Aaron M., and Weir, Richard F. (5 Nov. 2013) Mechanical
design and performance specifications of anthropomorphic prosthetic hands: A review [Web].
Available:<http://www.rehab.research.va.gov/jour/2013/505/page599.html>.
[3] Weir, Richard F. (n. d.) Design of Artificial Arms and Hands for Prosthetic Applications [Web].
Available:<http://smpp.northwestern.edu/downloads/Design%20Of%20Artificial%20Arms%20And%20Han
ds%20For%20Prosthetic%20Applications.pdf>.
[4] N. A. (Aug 1989) Labeling Regulatory Requirements for Medical Devices [Web]. Available:
<http://www.fda.gov/downloads/medicaldevices/deviceregulationandguidance/guidancedocuments/ucm0
95308.pdf>.
[5] N.A.(26 April 2012) Implants and Prosthetics, FDA [Web]. Available: <http://www.fda.gov/
MedicalDevices/ProductsandMedicalProcedures/ImplantsandProsthetics/>.
[6] Turner, Rhoda (30 May 2009) Prosthetic Cost, Disabled World [Web]. Available:
<http://www.disabled-world.com/assistivedevices/prostheses/prosthetics-costs.php>.
28. VI. Biomedical Engineering
VI.1 Arm Connection
The most important component of biomedical engineering in this project is finding a way to make the
connection to the patient the most comfortable. As stated in part A about why the project is produced in
the first place, comfortability in prosthetics is one of the biggest complaints. The team worked to engineer
a socket that would work efficiently for the user, be able to consolidate space, and be comfortable for long
days.
The possibilities for the connection are narrowed down to four main options.
Arm Clamp: A method that would clamp the prosthetic down to the residual arm. This method would take up space where the
clamp is concerned. The clamp may dig into the user’s skin after wearing it for a long period of time.
Sling: This method would attach the device using an across the body sling.
Suction: A suction would connect to the patient’s arm completely. It would be covered by a prosthetic sleeve.
Sleeve: The sleeve is a design that would allow for the arm to be inserted into it much like an elbow brace would be worn. The
design incorporates a thermoplastic to allow for additional strength as well as a hollow screw to allow room for wires.
The criteria for the arm connection is factored down to four main issues from the problem statement.
Comfort: The connection to the arm needs to be comfortable after extended usage for the patient. It needs a way to minimize
chafing due to sweat. It should be worn for extended hours a day and not make the arm too sore to wear the next day.
Ease of Use: The device needs to be user-friendly. There should not be a complex mechanism to lock the device onto the arm
that clients may not be able to understand.
29. Strength: The attachment should be strong enough to allow for the connection to hold the prosthetic arm throughout the day
without the possibility that the arm would not be able to provide its function.
Space: The connection should not weigh too much. It should allow for ample enough space for the circuits and boards within
the arm.
The sleeve pictured above was the design that was produced that solved the largest issues in the problem
statement. The major issues with the connections were they took up a lot of space, they were not easy to
use, and they were not comfortable. This design was able to fulfill the criteria to improve upon the three
problem areas in this department.
In order to consolidate space, the sleeve had a hollow screw at the end of it. This allows for less space to
be taken up by a connection in the actual prosthetic. All wires from the device that must connect to the
sleeve (ie, the wires from the myoelectric sensors that must be attached to the residual limb) are weaved
through the hollow part of the screw and attached according to the arm.
This design also made the device easier to use for the client. As opposed to a complex clamp or a sling
over the body, the design is a sleeve that is custom made to fit over the residual arm of the user. There
will be markings to show which side faces up versus down. Once the sleeve is securely on the arm, the
prosthetic can be secured onto the hollow screw on the sleeve and used immediately.
The last improvement from the problem statement is the comfort for the patient. The design sleeve is
made of a COOLMAX sleeve which has high ratings from users. The sleeve closest to the screw would then
be made with a thermoplastic that would not affect the comfort of the patient but allow for a higher
strength in the sleeve to hold the arm up properly. Additionally, within the sleeve, there is a silicon ring
where the sleeve connects to the residual arm. Silicone gel is reportedly very comfortable to wear for an
extended time period. Silicon allergies are extremely rare which make it a material that can be
30. used commonly.
The silicon ring will ideally prevent chafing after extended wearing of the arm. Normally with prosthetics,
the residual arm sweats throughout the day where the connection between the sleeve and the residual
arm. As the client moves during usage, the sweat and sleeve rubs along the residual arm which causes it
to become red and irritated. The ring will allow for the sweat to move around while minimizing the area
that the residual arm is touching the bottom of the arm.
This design allowed for the team to understand a way to minimize the problems that are normally
associated with prosthetics in the industry while keeping the functionality that was aimed for.
The team also determined that a way to stimulate the blood was needed for the residual limb. There were
two possible designs that were considered for this.
Small Shocks/Sensors: These small shocks would stimulate the blood to keep it from remaining stagnant.
The shocks would be very low voltage and current so the person would barely be able to perceive it, let
alone feel as though it is painful. It would also take up little space.
Fluid System: The system would pump fluids through the connection in order to stimulate the nerves in
the residual arm. This could be problematic if a leak were to occur. It would also make the device heavier
and taken up a lot of space.
The following components were chosen to make the decision concerning the best way to stimulate the
blood flow.
Space: The system must take up the least amount of space and weight possible
Safety: Since the system would have direct contact with the patient’s skin, the patient’s safety is vital to the
system chosen.
Efficiency: The system should efficiently stimulate the nerves.
The sensors were chosen as a better method due to their conservation of space. Additionally, they are
considered safer compared to the liquid system that could potentially leak into the wiring of the device.
31. II. Mechanical Engineering
While the biomedical engineering team focused on how the arm would connect to the patient in the
design process, mechanical engineering spent most of the time designing the actual prosthetic (including
the arm, hand, and fingers) as well as how to physically connect the various components of the device in
order to make one functioning design.
There were two designs considered for the wiring of the arm.
Shell: The shell would allow for the wires to be hidden away from view.
Wires Exposed: Wires could be seen throughout the arm.
The following were the components that went into this decision.
Ease of Use: The goal was to find the device that was easiest to use for customers so that they would be
more likely to purchase the device.
Safety: There are many possible dangers that could come from the wiring. Examples of these dangers
include electrical shocks and clipped wires.
Aesthetics: This factor just attempted to find the design that would be most visually appealing for the
user.
II.1 Mechanical Designs
This design was chosen as the best because it is aesthetically more appealing and looks more human like
whereas wires exposed would look more robotic. Additionally, with wires hidden in a shell, the wires are
much less likely to become clipped and cause possible injury for the user.
There were many different design considerations made about the project dealing with materials. The first
major discussion for the team was the uses of a removable, rechargeable battery versus a charging port
within the arm. A rechargeable would allow for a shorter battery lifespan but would allow for more
mobility because additional batteries could be charged and placed into the battery port when one was
dead. A charging port would allow for a longer battery lifespan, but the arm could not be used once the
battery went dead.
When trying to incorporate both designs into the arm, the removable battery was much more difficult to
incorporate because of the potential dangers it could cause to the user when they had to interfere with
the electronics and the wires to remove the battery. Additionally, there would have had to be a way to
open up the shell to retrieve the battery. A charging port would take up much less space because it would
not require this port. It would also require less work of the user because the purchase of additional
batteries would not be necessary. It would also be safer for the user at the end of the day because it
32. The components that went into picking the proper battery were as follows:
Battery Life: The battery life is important because it must be able to power the arm
for the lifespan of the arm since the arm has a rechargeable port.
Energy Density: The energy density determines the daily number of hours the
device can be operated.
Toxicity: This factor determines how safe the battery is for the user if it were to
explode.
Weight: The weight of the prosthetic is directly proportional to how comfortable it is
for the client.
1
would not require the electrical part of the arm to interfere with replacing the battery. The team
ultimately chose to go with a charging port based on these conditions and the longer battery life.
Once the charging part was decided on, the team had to decide on the type of rechargeable batteries to
use. There are four most common rechargeable batteries. These four types are Nickel Cadmium, Nickel-
Metal Hydride, Lead Acid, and Lithium Ion. Each of these batteries has unique features that bring both
positives and negatives to this project.
The team chose to pick Nickel-Metal Hydride based on this matrix. While both the option picked and the
Lithium Ion had the most positive attributes, battery life was sacrificed for a safer battery. Additionally,
prosthetics only usually have a shelf life of approximately five years before a new one must be purchased
due to the changes in the residual arm. The small battery life roughly lines up to this timeline which makes
it fit the device that must be made more safely. Additionally, Lithium Ion batteries are still relatively new
and the full consequences they possess have not been fully discovered by usage yet.
III. Computer Science
The computer science team works with how the device is coded to perform its various functions.
III.1 Coding
The main design conception that computer science had to deal with hardware that would allow for the
most efficient coding.
The system chosen was Arduino Mega 2560 for all hardware coding for the motors and sensors. This
system was chosen because its ability to easily store data on the system. The goal with the project would
be for the program to learn. Once the arm performs a motion, it should learn the signals that are
33. required to create this movement and be able to repeat the movement more easily in the future. This
hardware also had the most memory out of all the possibilities. This would mean that the arm would be
able to store much more data for future movements. Additionally, this would allow for the boards to
become stackable which would improve the amount of space within the arm.
35. PORTFOLIO ELEMENT F
CONSIDERATION OF DESIGN VIABILITY
Over the period of project requirements, definitions, research, and design modeling; elimination and
refinement took place repetitively to bring PriMA to its final design model. The architecture of the system
is fabricated to aid the customer in daily life experiences and shorten the technological gap keeping
prosthetics from acting as real human extremities, and flesh. Starting in a chronological order the process
begins with muscle movement in the residual below elbow limb of the patient. Myoelectric sensors are
positioned on top of specific muscle groups in this area. These sensors recording micro muscle
movements and convert them into a single analog digit such as (1,2,3,4,5). This number is the sent
through the circuit within the prosthesis to the processing board where it is interpreted. The number
passes through verifications for hand gesture patterns in the programming code until it finally falls into a
criterion to perform an operation. The processing board then sends a signal to the linear actuator design
motors located in the wrist and fingers to conduct a motion which will illicit a gripping pattern; thus giving
the user the ability to use their brain to control the motion of their prosthesis.
VII. Consideration of Design Viability
VII.1 Design
36. To make the system more user friendly and comfortable a secondary system of sensors and equipment
are positioned to simulate the sensation of feeling the objects being touched. Force Resistor Sensors are
placed on the fingertips of the hand along with temperature sensors. They are left in an open loop circuit
with 4 vibrating motors located back against the skin of the patient above the elbow. A voltage is sent to
the sensors and when an object is gripped it alters the voltage and sends the remaining electricity to the
user. Essentially the patient can feel hard they are gripping an object because of the flocculation in
vibration of the motors receiving the remaining power from the sensors. The temperature resistors will
detect if the object in contact is hot or cold and light a red or blue LED to alert the user if the temperature
is in a damaging range. Finally a Pelteir Cooling device is located just above the elbow as well to
temporarily cool the patient’s blood flow and reduce anxiety of wearing a prosthetic.
In the biomedical industry, it is of importance to maintain similarity to humanoid appendages when
designing prosthetics; therefore, the first, and most important, design consideration for PriMA is
developing a functional arm that looks as close to a real arm as possible. To establish realistic
characteristics, we mapped each of our own arms proportions as well as performed extensive research
into the case studies of gender, race, and age group arm and hand size. With these parameters, we were
able to develop a generalized model for any elbow down amputee that we may work with. Further, we
have determined that it is important to aesthetically design the exterior of the prosthetic to resemble the
skin tone and texture of the amputee. Thus, we have determined that the final product will include a skin
sleeve to better disguise the mechanical nature of the prosthesis. Given that 75% (citation) of people
prefer not to wear prosthetic arms they own, for a variety of reasons, which includes appearance, this will
allow us to better support the desires of more amputees.
Figure 1: Assembly of the PriMA final CAD
model.
Given the viability of manufacturing low cost, mechatronic, prosthetic arms, we have determined that the
best avenue for driving our system is with micro DC motors, control boards, batteries, and sensors that
are currently readily available to the public.
Motors
Wrist Motors
For the wrist, it quickly became clear that a dual shafted motor design would be necessary. The wrist will
feel a lot of torsion when the fingers or hand are exposed to a force, inducing a moment or torque.
Having one mechanism driving the rotation of the wrist, as well as support it, would not be ideal for this
type of situation. At this point, we began searching for motors with multiple shafts and satisfactory
holding torque to fit in the forearm. Stepper motors are the best choice with this form of application, but
after research, they are very heavy, large, and expensive. The weight of one of these devices large enough
for the application would make it very uncomfortable to wear. This led us to search for alternative
options that would still be able to hold various radial positions. The company Tamiya manufactures small
and cost effective gearboxes for robotic applications. We have selected to their small, 72004 dual shaft
gearbox that utilizes a standard DC motor with a worm gear on its shaft. This worm gear then drives a
gearbox, which increases the torque drastically. The assembly can be setup with a 216:1 or 336:1 gear
ratio. Again, this is another feature that will allow versatility in our design.
Thumb Motors
To keep the assembly hardware unified and simple, we came up with a way to use an analogue of the
same N20 motors to drive the thumb. The lead screw is again connected to a threaded slider, but this
slider will reside in the body of the thumb itself. To replicate the many degrees of freedoms of the thumb,
we will use a second N20 motor to allow the thumb to traverse across the palm. This N20 motor will not
have a lead screw, but will rather have a standard motor shaft. A worm gear will be pressed onto this
shaft. The proximal portion of the thumb will have gear teeth printed onto the body for connecting to the
worm gear. This will allow for precise movements of the thumb, as well as great holding torque when not
in motion.
VII.1.1 Appearance and Modularity
VII.1.2 Determining Platform
37. 3: Tamiya DC motor Parallel Axis
Gearbox.
Figure 2: Lead Screw N20
Brushless DC Motor
Figure.
Electronics
Sensors
While assessing how the user interface could be innovated from previous models in the market to provide
more accurate human gestures, senses and mobility the team determined that the use of sensory
technology was essential. The main factor one would consider when thinking of a human hand is the
sense of touch. This is broken down into the actual contact between the skin and a surface regarding
pressure and temperature. The best way for our team to reproduce these capabilities in a dynamic
prosthetic is to plant force and temperature sensors at specific locations within the extremity so that it
may benefit the user when in use. The 2.5 Kilo Ohm force resistors will be placed in the distal finger digits
of the thumb, pointer and middle fingers. Extensive case studies (Citation) have shown that these three
fingers apply the majority factor of force when gripping objects by some 80% of the time. By placing force
resistive sensors in these locations a code can be put in place that reduces the chances of squeezing
objects too hard or too light when being lifted. These sensors work as a resistor in a circuit that reduces
the voltage coming in based on how much pressure is applied to the sensor pad (seen below in figure 4).
The temperature resistive sensor (seen below in figure 5) will be placed in the distal finger digits of the
pink and ring finger to gather a general temperature gage for any object in which the user may come in
contact with. The software is designed to release any objects that will begin to deform finger tips or
sections of the arm as well as light a blue or red LED based on whether the object would be hot or cold to
the human touch.
Figure 4: Temperature sensor. Figure 5: Force-sensitive resistor.
Finger Motors
After searching through many variants of micro motor types and configurations we decided to rule out
the use of stepper motors, servomotors, and linear actuators as the driving force for our system. Stepper
motors require more electrical wiring and processing power from a control board than all other motors.
Due to the size limitations of our project, the use of more control boards would have been negatively
affected the space capacity of the forearm as well as the overall weight of the assembly. Servomotors
were not an option because they cannot be used for any application that does not use wires and pulleys
as the driving mechanism. This driving method provides substantially less torque, and it limits the
degrees of freedom of the actuating force. Linear actuators, while still likely the most powerful, are very
large, and they are very expensive; the smaller the size, the higher the price. Considering the possible
options, we set out to find a solution that would advocate our plans of having a high functioning,
lightweight arm.
After extensive research, we concluded that converting a micro DC motor to a linear actuator, by use of a
lead screw, is the best compromise between all types of motors. To better match the torque capabilities
of a linear actuator, the DC motors need to be geared down significantly. Given these parameters, we
quickly discovered the N-20, micro DC motor with M4 lead screw shaft (as seen in Fig.) exceeded our
requirements. In addition, these motors are available in many different gear ratios and operate within a
voltage range of 3-12 V. A threaded slider, guided by a pathway in the knuckles, pushes and pulls a
connecting linkage that joins the proximal finger digit to the slider.
38. Myoelectric
To allow the human intuition to power the bionic prosthesis, sensors must be utilized to pick up brain or
muscle activity that is directly correlated with the maleficent arm. While implanting the human body
would be the most effective way to receive neural electrical pulse from the remain intact nervous system
it is highly regulated and still deep in the research and development stage. Thus the most viable option
for PriMA was to select the Myoelectric Muscle Sensor V3 technologies. These systems are cheap, readily
available on the market and easy to use. The system is comprised of a microcontroller along with 3
electrode sensor pads hooked to an analog Jax cable. The system takes all muscle movement through the
skin at which it is attached and records it as a sinusoidal wave. This wave is then transmitted to the
microcontroller which is preprogrammed to refine the signal into single analog digits for the processing
board to read. To effectively record motion for all five fingers and wrist control the final model will
incorporate two microcontrollers with a total of 6 electrode sensors.
Figure 6: Myoelectric Muscle Sensor V3 electrode pads
and microcontroller.
Batteries
The power supply for the entire system will consist of 1.2V Sub C class Tenergy Nimh batteries wired in
series together to produce a 6V charge going into the boards and breadboards of the system. First the
allows for the batteries to be spaced throughout the system so that weight is evenly distributed
throughout the structure and so that space can be reserved. This set up will allow the interface to
function for a time constant of 5500 mAH. The table below shows the approximate use of each electronic
piece of the system and how many Amps it will draw per hour, showing a final estimated time for daily use
in a typical work environment of 8 hours. The Tenergy C cell batteries are also non memory forming cells
and have a recharge life of up to 1000 charges. These NiMh batteries were chosen because they pose the
least biological harm to the user and provide the best power per space of any robotic battery source.
Figure 7: Tenergy Nickel
Metal Hydride 1.2V
battery cell.Table 1: Daily battery usage table.
Circuit Board
When addressing the shear amount of electronics in our final model, PriMA needed a processing board
capable of supplying enough power, and data to each component in a timely and affordable manner.
While searching through a large majority of boards, microcontrollers and processors we determined the
best option was to select the Adruino uno (seen below in Figure 4). This board most importantly is
39. essentially one of the few boards that fits within the electrical core design space for our forearm. The
board is installed with an ATMEGA328 8 bit microcontroller processor with 32KB of ISP flash storage. This
allows the Uno to be used for a variety of purposes which fit the requirements of our sensory and
mechanical system. The system was also selected for its unique stack compatibility with the arduino
motor shield V2. The Uno contains 6 Analog pins, 14 digital pins with 6 PWN pin outputs. The system takes
an input voltage from 6-12V and regulates it so that the processor and board runs on 5V. Given that we
have, 3 force resistors, two myoelectric sensors (2 pins each), and 2 temperature resistors the arduino
must be modified with a DAC (digital to Analog Pin Converter) so that all of the sensors can be run
properly and efficiently.
Figure 8: Arduino Uno circuit board.
Arduino Motor Shield V2
In able to run the majority of the electrical components within the prosthesis, microcontrollers must be
installed between the motherboard and their respective extremities in order to operate and control them
in the proper manner. PriMA’s final design prosthesis contains 7, bi-directional, DC motors which will all
need to operate independently from each other. The most effective way to produce these characteristics
with in our interface is to use two Arduino Motor Shield V2 microcontrollers. These microcontrollers are
most importantly stackable with the Arduino uno, which brings the digital and analog pins from the
motherboard up to the microcontroller so sub systems can still be operated (seen below in figure 7). The
Motor Shields are capable of running 2 stepper motors or 4 DC motors bi-directionally. Since these units
are stackable we can stack one motor shield on top of another to gain access to 8 bi-directional DC
motors all independently operated.
Figure 9: Stackable Arduino Motor
Shield V2 microcontroller.
VII.1.3 Structure
Fingers
Four-bar linkages and linear actuators will drive the fingers. They are designed to be as slender and lifelike
as possible and while replicating the strength and gripping abilities of human fingers. The tips of the
fingers will contain force and pressure sensors set into holes designed into the tip sections. Current finger
prototypes are hollowed to fit the linkages and wires. Future iterations will seek to minimize the hollow
space through the middle of the fingers in order to improve structural strength while still housing the
wires and linkages. While the current prototypes are smooth, the gripping surface may be textured in
future iterations to improve the fingers’ gripping ability. Ultimately, however, skin-like coverings will be put
over the entire arm, possible negating the need for a roughened gripping surface. To further improve
material strength, finger sections in future iterations may be cast. This improves the material strength by
eliminating the layer separation inherent in many 3D printing processes.
