01 prima_detaildesignreport

PRIMADETAILED DESIGN REPORT

BIOMEDICAL ENGINEERING DESIGN 1 & 2: BME 4292 & 4293FALL 2015 - SPRING 2016

FLORIDA INSTITUTE OF TECHNOLOGY

TEAM MEMBERS:CLYDE (DOUG) BROWN - TEAM LEADER

THADDEUS BERGER - FINANCIAL LEADERTAYLOR ATKINSON

RYAN BABBITTNICOLE BALLMANMEET PASTAKIAJUSTIN PAVAO

AUSTIN SPAGNOLOZUHOOR YAMANI

MARIA VITTORIA ELENADANNIELLE GOLDMAN

PROJECT ADVISORS:DR. KUNAL MITRA

MR. DAVID BEAVERS

EXECUTIVE SUMMARY

A low-cost, highly functional prosthetic arm design has been developed by the PriMA senior design team at Florida Institute of Technology. The group has found a way to provide a novel medical device which could become a competitive product on the market. The device is strong, lightweight, and non-invasive, and has a wide array of sensory capabilities and a novel system for tactile feedback which can be used to drive the hand.

ACKNOWLEDGEMENTS

PriMA would like to thank all advisors and supporters to this project. Special thanks to our advisors, Jennifer Schlegel, the Kern Entrepreneurial Engineering Network, and Tabitha Beavers and Project Based Learning.

CONTENTS

Executive Summary......................................................................................................................................................1

Acknowledgements......................................................................................................................................................1

Figures......................................................................................................................................................................... 3

Tables...........................................................................................................................................................................5

1: Introduction.............................................................................................................................................................6

1.1: Problem being addressed..................................................................................................................................6

1.2: Motivation........................................................................................................................................................6

1.3: Global, social, economic, and contemporary impact........................................................................................6

1.4: Final problem statement...................................................................................................................................6

2: Background..............................................................................................................................................................7

2.1: Literature Review..............................................................................................................................................7

2.2: Patent Search....................................................................................................................................................7

2.3: Research Required to Design and Build Prototype..........................................................................................12

2.4: Current State of the Art..................................................................................................................................15

2.5: Regulatory and Economic Constraints.............................................................................................................20

2.6: Ethical, Safety, and Liability Issues..................................................................................................................20

2.7: Client Survey Synopsis.....................................................................................................................................21

3: Preliminary Designs................................................................................................................................................22

3.1: Appearance/modularity..................................................................................................................................22

3.2: Determine Platform........................................................................................................................................22

3.3: Motors............................................................................................................................................................23

3.3.1: Wrist Motor.............................................................................................................................................23

3.3.2: Thumb Motors.........................................................................................................................................23

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3.3.3: Finger Motors...........................................................................................................................................23

3.4: Electronics.......................................................................................................................................................24

3.4.1: Sensors.....................................................................................................................................................24

3.4.2: Myoelectric..............................................................................................................................................24

3.4.3: Batteries...................................................................................................................................................25

3.4.4: Processing Board......................................................................................................................................26

3.4.5: Arduino Motor Shield V2 microcontroller................................................................................................26

3.6: Structure.........................................................................................................................................................27

3.6.1: Fingers......................................................................................................................................................27

3.6.2: Palm.........................................................................................................................................................27

3.6.3: Thumb......................................................................................................................................................28

3.6.4: Wrist.........................................................................................................................................................28

3.6.5: Forearm....................................................................................................................................................28

3.6.6: Neoprene Connection Sleeve...................................................................................................................29

3.7: Materials.........................................................................................................................................................30

3.7.1: Polymer Selection....................................................................................................................................30

3.7.2: Dampening...............................................................................................................................................30

3.8: Size Restrictions.............................................................................................................................................30

3.9: Human Factors................................................................................................................................................31

3.9.1: Health & Safety........................................................................................................................................31

3.9.2: 3D scanning and mold impressions..........................................................................................................31

3.9.3: Blood circulation......................................................................................................................................31

3.10: Failure Factors...............................................................................................................................................33

3.11: Manufacturing..............................................................................................................................................34

3.11.1: Methods: 3D Printing vs. Casting...........................................................................................................34

3.12: Analysis of Functionality................................................................................................................................35

3.12.1: Stress analysis........................................................................................................................................35

3.12.2: Thermal Analysis....................................................................................................................................35

3.12.3: Watertight and Corrosion Resistant System...........................................................................................36

4: Final Design............................................................................................................................................................36

4.1: Final Solution Principles..................................................................................................................................36

4.2: Functional Analysis..........................................................................................................................................36

4.3: Parameters and Constraints............................................................................................................................36

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4.4: Design Analysis................................................................................................................................................38

4.4.1: Linkage.....................................................................................................................................................38

4.4.2: Palm/Knuckles..........................................................................................................................................39

4.4.3: Fingers......................................................................................................................................................39

4.4.4: Forearm....................................................................................................................................................40

4.4.5: Thumb......................................................................................................................................................40

4.5: Decision Analysis.............................................................................................................................................40

4.6: Quality Function Deployment (QFD)...............................................................................................................42

5: Prototype Development and Testing.....................................................................................................................43

5.1: Bill of Materials (BOM) and Rationale for Use.................................................................................................43

5.2: Prototype Fabrication Process........................................................................................................................44

5.3: Assembly.........................................................................................................................................................45

5.4: Prototype Testing Protocol.............................................................................................................................46

5.5: Tests Performed and Results...........................................................................................................................47

6: Conclusions and Future Work................................................................................................................................48

6.1: Implications of Results....................................................................................................................................48

6.2: Future Work and Improvements.....................................................................................................................48

6.3: Errors..............................................................................................................................................................48

6.4: Final Evaluation of Design...............................................................................................................................48

7: References.............................................................................................................................................................49

FIGURES

Figure 1: Patent No US 5443525; perspective view showing a prosthesis liner equipped with the novel pad.............8

Figure 2: Patent No US 6589287; shows an embodiment of the invention into a prosthesis or hand with lost tactile sensation......................................................................................................................................................................9

Figure 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................................................................................10

Figure 4: 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)....................................................................10

Figure 5: 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.. . .10

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Figure 6: Patent No US 20090048539; an anterior view of a prosthetic hand device in accordance with an embodiment of the invention....................................................................................................................................11

Figure 7: Patent No US 20130046394; simplified illustration of an embodiment of a myoelectric prosthesis control system........................................................................................................................................................................12

Figure 8: The iLimb Hand by Touch Bionics (Competitor 2)........................................................................................18

Figure 9: The Vincent Hand by Vincent Systems (Competitor 1)................................................................................18

Figure 10: The iLimb Pulse by Touch Bionics (Competitor 3).....................................................................................18

Figure 11: The Bebionic Hand by RSL Steeper (Competitor 4)...................................................................................18

Figure 12: The Michelangelo hand by Otto Bock (Competitor 6)..............................................................................18

Figure 13: The Bebionic Hand v2 by RSL Steeper (Competitor 5)...............................................................................18

Figure 14: 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, θ1 is the angle of metacarpal phalange joint and θ2 is the angle of proximal interphalange joint...........................................................................19

Figure 15: (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......................................19

Figure 16: Tamiya DC motor parallel axis gearbox.....................................................................................................23

Figure 17: Lead screw N20 brushless DC motor.........................................................................................................23

Figure 18: Force-sensitive resistor.............................................................................................................................24

Figure 19: Myoelectric sensor kit...............................................................................................................................24

Figure 20: Temperature resistor................................................................................................................................24

Figure 21: Tenergy NiMH battery cell........................................................................................................................25

Figure 22: Arduino Uno circuitboard..........................................................................................................................26

Figure 23: Stackable Arduino V2 Motor Sheild...........................................................................................................26

Figure 24: Open hand gesture....................................................................................................................................27

Figure 25: Closed hand gesture..................................................................................................................................27

Figure 26: Palm and knuckles separated....................................................................................................................27

Figure 27: Palm and knuckles connected...................................................................................................................27

Figure 28: Wrist connection.......................................................................................................................................29

Figure 29: Forearm and wrist assembly.....................................................................................................................29

Figure 30: Schematic of electrical components to be built into the sleeve................................................................30

Figure 31: Neoprene sleeve with PriMA logo.............................................................................................................30

Figure 32: Basic below-elbow disarticulation amputation and human anatomy.......................................................32

Figure 33: Synthetic lab testing arm with artificial muscles, veins, and nerves..........................................................32

Figure 34: Dual-axis extrusion 3D printer...................................................................................................................34

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Figure 35: Layer ridges and separation......................................................................................................................34

Figure 36: Finger assembly simulation.......................................................................................................................35

Figure 37: Knuckle simulation....................................................................................................................................35

Figure 38: Linkage bar simulation..............................................................................................................................35

Figure 39: Slider joint simulation...............................................................................................................................35

Figure 40: Schematic of four bar linkage driving fingers............................................................................................38

Figure 41: Palm and knuckles.....................................................................................................................................39

Figure 42: Fingers.......................................................................................................................................................39

Figure 43: Forearm attached to hand.........................................................................................................................40

Figure 44: QFD spreadsheet.......................................................................................................................................42

Figure 45: Full newest version arm assembly with sleeve connection.......................................................................45

Figure 46: Sleeve connection subassembly................................................................................................................45

Figure 48: Subassemblies of the hand, finger, and forearm.......................................................................................46

Figure 47: Test conducted of motors driven by EMG signals.....................................................................................47

TABLES

Table 1: General properties of prosthetic arms currently available in the market.....................................................16

Table 2: Grip and kinematic characteristics of prosthetic arms currently available in the market.............................17

Table 3: Daily Battery Power Consumption................................................................................................................25

Table 4: Failure Factors..............................................................................................................................................33

Table 5: Blood flow stimulation decision chart..........................................................................................................41

Table 6: Arm connection decision chart.....................................................................................................................41

Table 7: Battery decision chart...................................................................................................................................42

Table 8: Bill of Materials............................................................................................................................................43

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1: INTRODUCTION

1.1: PROBLEM BEING ADDRESSED

Prosthetic arms have been in existence since the antiquity, with the technology evolving from rudimentary materials to the current field of robotics. While prostheses are vital in enabling amputees to lead somewhat normal lives, they are responsible for causing acute pain to their users due to bad fit and complex features. Existing prostheses are cumbersome, hence causing painful blisters or sores that add to the discomfort of amputees (Schweitzer). Furthermore, the manufacturers make standardized prostheses that do not account for the different dimensions or location of the nubs, making discomfort the primary cause of the stoppage in the use of prostheses.

1.2: MOTIVATION

The motivation for addressing the discomfort problem stems from numerous complaints from customers regarding bad fit, heaviness, and exorbitant prices of prostheses. The crux of the issue is the failure of manufacturers to customize prostheses to the requirements of every individual. Furthermore, manufacturers add extra features on the devices as a ploy to charge inflated prices. Some prostheses cost as high as $100,000, making it impossible for most amputees to afford (CostHelper Health). The introduction of low-cost prosthetic arms in the market will, therefore, meet the existing demand.

1.3: GLOBAL, SOCIAL, ECONOMIC, AND CONTEMPORARY IMPACT

Today, the global arena is riddled with warfare, terrorism and arterial diseases that increase the incidence of amputations. The prevalence of arterial diseases that impede proper blood circulation in the limbs are the leading causes of amputation, followed by conflicts involving the use of guns and explosives (DisabledWorld.com). The rising cases of amputees indicate the possible victims of pain caused by poorly designed prostheses. The result will be a massive decline in the popularity and use of the devices in the market. On a social level, the pain arising from the bulkiness of prosthetic arms increase the physical and mental distress of amputees, thus negating the goal of medical care. Thus, acute depression is likely to result, leading to the loss of the productive capacity of the victims, while increasing their dependency level. On an economic level, the manufacture of prosthetic arms acts as a source of revenue for manufacturers and paves the way for innovation and employment. However, the exorbitant prices charged on the devices, coupled with costly repairs and stringent warranty restrictions will reduce their popularity in the market (Schweitzer). The result will be fewer profits and tax revenue for both the manufacturers and the government respectively. Lastly, contemporary societies want not only high-tech prostheses but also devices that resemble actual limbs. Thus, the cosmetic trend of arm prosthetics is likely to persist in the years to come.

1.4: FINAL PROBLEM STATEMENT

Comfort must be a priority for all manufacturers if prosthetics are to survive in the market. Therefore, this paper focuses on how to create an inexpensive technologically-advanced prosthetic arm that is both lightweight and comfortable.

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2: BACKGROUND

2.1: LITERATURE REVIEW

Preliminary study on the products currently available in the market indicated that the weight of the prosthesis is one of the crucial deciding factors that determines if the amputee would use the prosthesis or not. Even though the prosthesis may weigh the same as the actual arm of the patient, it acts as an additional object that is perceived by the amputee as heavy because it does not naturally belong to the body. Another important factor of the prosthesis is its size. It plays a vital role in how comfortable and accurate prosthesis is by determining its maneuverability and ease of use. It also determines how comfortable and accurate the prosthesis is for use in daily activities. Other factors that are important in the prosthesis design to determine how closely it mimics the functions of an actual arm are number of joints, degrees of freedom, range, accuracy of force applied, actuation method and number of actuators.

Research on previously made prostheses indicated that grasp type, range of motion, and grip force are additional factors that determine the maneuverability and smoothness function of the prosthesis that replaces the lost arm. The range of forces that the prosthesis can apply determines the amputee’s ability to hold and lift either heavy or the fragile objects, which in turn is dependent on the grip force. Hence, a prosthesis that can apply a wide range of grip forces is optimal for grasping a variety of objects. It is good for the prosthesis to apply as much minimum value of force as possible to hold a fragile object. In a similar manner, it is better for the prosthesis to apply as much high value of force as possible to hold a heavy object. The range of motion is also an important aspect for the prosthesis to mimic an anatomical arm as it affects the flexibility and accuracy. Overall, the closer these factors are to the actual arm, the better the prosthesis will serve its purpose. Some other important factors that make the prosthetic arm similar to anatomical arm are the robustness, battery life, cosmesis, and sensory feedback of the prosthetic arm.

Another factor that needs to be taken care of while designing the prosthesis is its weight. An average human arm weighs about 440 g when the forearm extrinsic muscles are excluded. Studies conducted in the past have shown that prosthesis which are designed to be around 440 g are perceived by the patients as heavy as it is supported by the soft tissue on the residual arm and is not directly connected to the skeleton itself. In addition, more weight is put on a small area if the residual arm is small and hence heavier the prosthesis is perceived if attached to it. So, a significant increase in the perceived weight of the prosthesis is observed with decrease in the size of residual arm. Hence, if the weight is large, the prosthesis can contribute to fatigue and discomfort, and if it is small, it can be useful as a replacement arm without causing these problems. Online surveys previously conducted on prosthesis users showed that approximately 80% of the users perceive prosthesis to be too heavy. The users rated weight as 70 on the scale of 0 to 100 in terms of factors that are important for comfort.

2.2: 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.

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US 5443525: CONDUCTIVE PATCH FOR CONTROL OF PROSTHETIC LIMBS

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 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 Ω 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 reproducibility 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.

STRENGTHS:

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.

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Figure 1: Patent No US 5443525; perspective view showing a prosthesis liner equipped with the

novel pad.

US 6589287: ARTIFICIAL SENSIBILITY

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 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.

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.

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Figure 2: Patent No US 6589287; shows an embodiment of the

invention into a prosthesis or hand with lost tactile sensation.

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.

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Figure 5: 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 3: Patent No US 20090048539; shows side views of the prosthetic hand device in various

positions, illustrating one configuration for parallel

Figure 4: 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.

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.

STRENGTHS:

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.

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.

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Figure 6: Patent No US 20090048539; an anterior view of a prosthetic hand device in accordance with an

embodiment of the invention.

US 20130046394: SYSTEMS AND METHODS OF MYOELECTRIC PROSTHESIS

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.

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.

WEAKNESSES:

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.

2.3: RESEARCH REQUIRED TO DESIGN AND BUILD PROTOTYPE

Six types of prosthetic arms were benchmarked against each other to establish the baseline for the performance required to design a new prosthetic arm. All of these prostheses were 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 were 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 2.3.1 to 2.3.6.

Each of these prostheses was 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, this document

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Figure 7: Patent No US 20130046394; simplified illustration of an embodiment

of a myoelectric prosthesis control system.

will provide both the relative quantitative information about the 6 products studied and the qualitative requirements of the people suffering from trans-radial amputation.

The qualitative criteria studied initially between the 6 products are presented in the Table 2.3.1. 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.

The Table 2.3.2 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.

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.

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.

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

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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.

QUALITATIVE BENCHMARKING OF THE PROSTHETIC ARMS

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 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 showed 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

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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.

2.4: CURRENT STATE OF THE ART

Current state of the art devices are extremely advanced, but not suited for customers’ needs. One form of competition is known as the WPI Prosthetic Arm [53]. This arm is also a lightweight, low cost design that was very similar to ours. Instead of using metals like normal prosthetic arms, this design also uses plastics to keep it light and cheap. However, our design differs because one of our primary objectives is comfort on top of the lightweight and low cost materials. Additionally, our project will incorporate more temperature and pressure sensors in order to operate the prosthetic arm like an actual arm would work.

Another similar item currently on the market is the Michelangelo arm [54]. The Michelangelo arm has a very sensitive touch and is one of the most advanced systems on the market. This product has larger degrees of

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freedom than a majority of products on the market. However, because of that, the product is very expensive and costs over $73,000. Ideally, our team would like to take similar technology from this device and use it in our design to make it efficient while still be inexpensive.

Finally, our last major competitive product is the Bebonic arm [55]. The arm is very cutting age and smaller than the normal prosthetic arm which means more lightweight. It has a high grip pattern and is the cheapest product on the market with the most advanced technology. However, its cost is still extremely high compared to our budget. Normally, this item is on the market for $11,000.

Table 1: General properties of prosthetic arms currently available in the market.

Hand Competitor 1 Competitor 2 Competitor 3 Competitor 4 Competitor 5 Competitor 6

Weight (g) - 450-615 460-465 495-539 495-539 ~420

Overall Size - 180-182 mm long, 75-80 mm wide, 35-41 mm thick

180-182 mm long, 75-80 mm wide, 35-40 mm thick

198 mm long, 90 mm wide, 50 mm thick

190-200 mm long, 84-92 mm wide, 50 mm thick

-

Number of Joints

11 11 11 11 11 6

Degrees of Freedom

6 6 6 6 6 2

Number of Actuators

6 5 5 5 5 2

Actuation method

DC Motor with Worm Gear



DC Motor with Lead Screw

DC Motor with Lead Screw

-

Joint Coupling Method

Linkage spinning MCP to PIP

Tendon Linkage MCP to PIP

Tendon Linkage MCP to PIP

Linkage spanning MCP to PIP

Linkage spanning MCP to PIP

Cam design with links to all fingers

Adaptive Grip Yes Yes Yes Yes Yes No*

*Adaptive grip in Competitor 5 is accomplished through adaptive mechanical coupling, and in others through electronic torque control.Here, DC = direct current, MCP = metacarpal phalange, PIP = proximal interphalange

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Table 2: Grip and kinematic characteristics of prosthetic arms currently available in the market.

Hand Competitor 1

Competitor 2

Competitor 3

Competitor 4

Competitor 5

Competitor 6

Grip Force

Precision Grasp (N)

- 10.8 - 34 (tripod) 34 (tripod) 70

Power Grasp (N)

- - 136 75 75 NA

Lateral Pinch (N)

- 17-19.6 - 15 15 60

Range of Motion

MCP Joints (o) 0-90 0-90 0-90 0-90 0-90 0-35

PIP Joints(o) 0-100 0-90 0-90 10-90 0-90 NA

DIP Joints (o) NA ~20 ~20 ~20 ~20 NA

Thumb Flexion (o)

- 0-60 0-60 - - -

Thumb Circumduction (o)

- 0-95 0-95 0-68 0-68 -

Thumb Circumduction Axis

Parallel with Wrist axis





Compound Axis

Grasp Type

Finger/Grasp Speed

- 200 mm/s 1.2 s in power grasp

1.9 s in power grasp, 0.8 s in tripod, 1.5-1.7 s in key grasp

0.9 s power grasp, 0.4 s tripod grasp, 0.9 s key grasp

-

Achievable Grasps

Power, precision, lateral, hook, finger point





Opposition, lateral, and neutral mode

Here, DIP = distal interphalange, MCP = metacarpal interphalange, PIP = proximal interphalange and NA = not applicable

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Figure 11: The Bebionic Hand by RSL Steeper

(Competitor 4).

Figure 12: The Michelangelo hand by Otto Bock (Competitor 6).Figure 13: The Bebionic Hand v2 by

RSL Steeper (Competitor 5).

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Figure 14: 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, θ1 is the angle of metacarpal phalange joint and θ2 is the angle of proximal interphalange joint.

Figure 15: (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.

2.5: REGULATORY AND ECONOMIC CONSTRAINTS

Prosthetics fall under the Food and Drug Administration (FDA). The FDA claims that medical implants are devices that are placed inside or on the surface of the body. In order to allow our device to be on the market, the FDA requires it must go through numerous stages of testing. Once the device is fully developed, it would still take months to be able to go onto the market. However, it would ensure that our device is completely safe for the people who may purchase it.

The advantage of the device economically though is the fact that it would undercut almost every single other prosthetic device on the market. Most upper limb prosthetics are well over $10,000 per device. Our device would be highly customizable for each individual patient while still only costing approximately $1000 to produce. This is significantly lower than the average price of these products on the market.

2.6: ETHICAL, SAFETY, AND LIABILITY ISSUES

The main ethical issue is the idea that people would purposely jeopardize themselves in order to gain the same advantages that they feel that someone with a prosthetic would have. Ethicists fear at one point that the amount of advantages that may come from a prosthetic could make an average person become drastic enough to do something in order to receive those same advantages. Now that there is an Olympic winning runner who has a prosthetic, it raised the idea that maybe the prosthetic made it easier for the winner to compete in the race. They feel a prosthetic should have just as many features as it takes to mimic an actual arm without too many mechanical advantages.

Safety issues for this product should be minimal. Myoelectric sensors must be connected to the client’s arm, however these can send small shocks to users. In order to combat this from happening in our product, the sensors will be tested repeatedly to minimize errors. Additionally, sensors will be sewn into the sleeve, so the amount of direct connect they will have will lessen. The device runs at such low power, if someone were to get electrocuted from it, they would experience an extremely small shock. The maximum voltage this arm will run at is 7 Volts which is small. These should be the only major electrical issues. For the mechanical side, the main safety issues would be the pinch points. However, the product has been designed specifically to minimize these in order to keep clients safe.

For prosthetics, the probability of liability is higher than that of medicine or nursing especially as the industry is becoming more popular during times of war. Device malfunction can occur which could result in injury. However, this is most common in leg prosthetics because if they fail during use, it could cause the client to fall and experience serious injury. For a prosthetic arm, there is a much lower risk. The prosthetic may give a small shock or pinch someone if not used properly, but otherwise it should not be able to hurt the user in malfunction. Additionally, the computer science team intend to add a safeguard that would cause the arm to power down totally in case of a malfunction. If the product were to go on the market, the team would create a liability waiver. However, a core goal of this experiment is the make the device as user friendly and safe as possible.

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2.7: CLIENT SURVEY SYNOPSIS

In order to obtain more information about these issues first hand, our team contacted Ms. Anna Street of Brevard Prosthetics. A majority of the questions had to do with the comfortability and the human factors to deal with the project. She said confirmed most of what the case studies said were true. When asked what the biggest factors to consider are, she said the complaints she experienced was 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.

The team also gained the ability to talk to more potential clients through the experience at the KEEN conference in Tempe, Arizona. Clients liked the idea of having an arm centered on features that people wanted as opposed to having something that was unnecessarily complex. The biggest complaint for most people is the fact that these devices tend to be hard to use for the people that the devices are created for. Additionally, the devices are more concentrated on the idea of getting more features developed as opposed to comfortability and aesthetics. After discussing with the various clients who may be interested in this product, the main focuses the team made was make the hand as life-like as possible (ie, aesthetically pleasing, temperature and pressure sensor to understand what they are touching), comfortable, and easy to use.

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3: PRELIMINARY DESIGNS

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 elicit a gripping pattern; thus giving the user the ability to use their brain to control the motion of their prosthesis.

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 5 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 how hard they are gripping an object because of the fluctuation 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 Peltier 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.

3.1: APPEARANCE/MODULARITY

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.

3.2: DETERMINE PLATFORM

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.

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3.3: MOTORS

3.3.1: WRIST MOTOR

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.

3.3.2: 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.

3.3.3: FINGER MOTORS

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.

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Figure 17: Lead screw N20 brushless DC motor. Figure 16: Tamiya DC motor parallel axis gearbox.

3.4: ELECTRONICS

3.4.1: 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. 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.

3.4.2: 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 remaining 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.

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Figure 19: Temperature resistor.

Figure 18: Force-sensitive resistor.

Figure 20: Myoelectric sensor kit.

3.4.3: 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.

Table 3: Daily Battery Power Consumption

Electrical Component Quantity mAh Total mAh Percentage Used per hr

Total Amps per work day

N20 Motor 6 120 720 54% 3000

Force Resistor 3 0.136 .408 100% 3.264

Temperature Resistor 2 0.0915 .183 100% 2.916

Tamiya Gear Box Motor 1 120 120 41% 393.6

Arduino Uno 1 50 50 100% 400

Arduino Motor Shield V2 2 30 60 100% 480

Vibrating Coin Motors 4 70 280 54% 302.4

Peltier Cooling Device 2 200 400 12% 384

Myoelectric Controller and Sensors

2 30 60 100% 480

Total mAh 5446.18

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Figure 21: Tenergy NiMH battery cell.

3.4.4: PROCESSING 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 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.

3.4.5: ARDUINO MOTOR SHIELD V2 MICROCONTROLLER

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.

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Figure 23: Stackable Arduino V2 Motor Sheild. Figure 22: Arduino Uno circuitboard.

3.6: STRUCTURE

3.6.1: 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.

The fingers move using four-bar linkages and linear actuators. The actuators push the base sections while the linkage moves along a curved path designed into the middle section of each finger. The current design uses spring-loaded fingertips, which are pre-loaded, in a partially flexed position (essentially a torsional spring). As the hand grips objects where use of the fingertips will become critical, the spring will extend and provide additional gripping strength.

3.6.2: PALM

The palm is the housing for the driving mechanisms of the fingers and thumb. This requires it to be sturdy and durable while remaining light. It was made possible to fit five motors directly onto the palm. Without the separation of components, pathways would be necessary to squeeze the motors into place ultimately creating many locations of stress concentration across the palm. Since we strayed away from one solid part, strong structural ribs can be implemented axially down the palm.

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Figure 24: Open hand gesture.

Figure 25: Closed hand gesture.

Figure 26: Palm and knuckles connected. Figure 27: Palm and knuckles separated.

The knuckles are also able to be much stronger and supportive of the motors. The pathways for the threaded sliders would not have been possible without the extra build volume in the knuckles. These pathways are designed to be rectangular which provides structural reaction moments on the sliders. The motors bolt directly to the knuckles, and then bolts are used as the fasteners between the knuckles and the base. When the knuckles and palm base are fastened together, the motors will be safely enclosed from the wearer of the prosthesis. Further, the motors can be submerged into the structure of the palm. There is a lot of room for potentiometers, wiring, and other hardware within the shell due to this. The base will also feature an enclosed wrist connection, which will give a streamlined look and protect the wires from the control unit. The support material for the wrist connection is used for connecting the thumb traversing motor. The worm gear and gear teeth will not be exposed to the skin covering the mechanisms.

3.6.3: THUMB

The opposable thumb is one of the most complicated joints seen in nature. To be able to realistically replicate the ability of an opposable thumb, the prostheses thumb will utilize two of the previously described N20 motors. One of the N20 motors will be used as a worm drive system to allow the thumb to traverse across the palm. This will end up having a larger lateral range of motion than a human thumb for the user to learn and take advantage of. The worm drive system will prevent the thumb from being pushed out of any location set by the user without deforming the PLA itself. The second N20 motor will function similarly to the fingers using the M4 lead screw to convert the rotational motion to linear motion with a threaded slider.

3.6.4: WRIST

The wrist will only have one degree of freedom allowing rotation. This is sufficient for the goal of creating an affordable, feature full arm and allows for the wrist to accomplish its primary functions. The previously described Tamiya worm gearbox will be used for connecting the forearm and palm together as well as controlling the motion. A hinge joint is used around the gearbox, completely concealing it and encasing the wires. This design has a nice appearance, and looks similar to a human wrist.

3.6.5: FOREARM

In order to keep the operating software, boards and electronics in a safe environment for the user to use as well as in an easy location to be manually worked on for maintenance and updates it had to be designed into a core structure. Essentially the batteries, boards, microcontrollers, heat sinks, and beard board are located in this area as seen in the figure below. This core is printed or cased similar in PLA just like the other pieces of the arm and contains 3 natural heat transfer fins between the top and bottom layer. The outside surface will be coated in a silicon dampening material to reduce all residual and large vibrational forces, which may be exerted on the system at any point during its use. Having the electronics in a central core location allows the subsystem to be waterproofed so that the customer cannot damage the electronics if any damp or wet materials come in contact with the prosthesis as well as allowing it to be operated in extremely humidified locations. Given the idea of performing maintenance of the system it must obviously be able to detach from the electrical system remaining in the structure of the arm with ease and without damaging the system. The only way to elicit these properties is to have wire connection pins located at the inlets and exits of the core which allow the microcontrollers and boards to separate from their outside extremities.

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The forearm will also contain the Tamiya DC brushless Motor dual shaft gearbox, which will be located in the front half of the final design. The gearbox motor is in position to power the wrist motion that the prosthesis is designed for. The back side of the forearm will contain the receptor connection for the neoprene sleeve that will attach to the user along with the cable inlets coming from the myoelectric sensors, coin motors, and Pelteir cooling devices also located in the sleeve.

3.6.6: NEOPRENE CONNECTION SLEEVE

As discussed in previous sections of the portfolio the retro fitting of the prosthesis to the patient is one of the most difficult and crucial aspects of the design process. This involves the sensitivity of the patient’s residual limb, structural integrity of the entire weight of the final design and the process of sensor control. To ensure that all of these factors were covered the only viable solution for the system was the use of a custom made, skin tight, suction style neoprene sleeve. These sleeve as seen below will be tightly pulled onto the customer’s residual limb and three quarters of the way up the bicep muscle. Inside the neoprene sleeve and advanced network of electronics will be sewn into a stationary place in the material. The myoelectric sensors will be located in the lower section of sleeve around the forearm so that accurate readings can be gathered and transmitted to the processing board. On the Bicep and Tricep portions of the sleeve, four coin motors will be position in a anatomical arrangement to allow the user to comprehend then sensation of touch when the force resistor sensors located in the fingers come in contact with an object. Finally closer to the elbow, two Pelteir cooling devices will be positioned around critical arteries so that blood flow going towards the bottom of the residual limb can be cooled in its pathways. On the Joint end of the sleeve a simple key way joint with pressure relieve ball socket is located in the center along with a circular cut out for all electrical conduits to pass through. This will allow for a seamless connection between the two separate component assemblies.

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Figure 28: Wrist connection. Figure 29: Forearm and wrist assembly.

3.7: MATERIALS

3.7.1: POLYMER SELECTION

3D printing, for practical applications, utilizes polylactic acid (PLA) or acrylonitrile butadiene styrene (ABS). ABS is a more difficult to print as it must be extruded at a higher temperature than PLA; therefore, it is also more prone to warping during manufacturing. Our group selected PLA as the primary working material due to how readily available it is in the market as well as that most affordable 3D printers only use it its filament source. This can be an issue as it drastically decreases the durability and strength that the material would normally have if cast molded as a solid part.

3.7.2: DAMPENING

In order to ensure that our final product will last as long as its electrical are designed for we must reduce the amount of vibrations that each board will undergo during the average day a user is wearing it. In order to do this a dampening material must be placed between the electrical core and the outer structure of the forearm. The company 3M supplies a viscoelastic dampening sheet which contains the properties we need to keep the system from being damaged and also contains a sticky surface so that it can be applied to anything necessary.

3.8: SIZE RESTRICTIONS

Size is one of the most difficult restrictions to overcome while designing this arm. Only so much can fit into a confined space that is small in volume to begin with. The forearm houses the control unit for the arm, so the forearm has to be designed to be at least as big as the necessary control boards while remaining at least as small as to look normal on an amputee. Luckily, the Arduino Uno with necessary expansion boards fits into the dimensions of an average human forearm. However, the current design is only applicable to adults. It is planned to attempt to shrink the system to the applications of children, but it is not considered for the first prototypes. The palm also runs into a minimum size issue since it houses six N20 motors. As before, it would not be ideal to have the palm noticeably larger than what the amputee originally had.

3.9: HUMAN FACTORS

3.9.1: HEALTH & SAFETY

PINCH POINTS

Pinch points are locations, usually hinged points, that skin or other extremities can get stuck in and sheared. In the case of large machinery, these can be very dangerous; however; the worst that could happen with this prosthetic, if it does happen, would only be an uncomfortable pinching sensation. This is still not desirable, so the joints will be shielded as best as possible from the user. The wrist joint is completely concealed from human contact. The finger joints are not as concealed as the wrist, but they should have no ability to pinch. Further, the artificial skin sleeve that is intended to go over our own will eliminate any chances of the user contacting a pinch point during everyday use.

ALLERGIES

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PLA is derived from corn, but during the production of PLA the allergen, Profilin, is theorized to be destroyed and or rendered inactive. There is no direct scholarly research behind this, but there is also no known human allergic reaction to PLA. It is known, in many cases, that people with food allergies can eat food possessing the allergen they’re allergic to after being cooked because the allergen is denatured. This is true for corn; therefore, it is assumed to be true for PLA due to having never afflicted anyone and the heat required to produce it. However, we recommend that patients with a corn allergy use caution due to the ambiguity of knowledge. The processes used to create this arm can easily supplement PLA for another material. This is recommended unless a doctor confirms that PLA will not cause a reaction with a corn sensitive amputee.

3.9.2: 3D SCANNING AND MOLD IMPRESSIONS

Below elbow disarticulation patients come from a variety of backgrounds, ages and genders such as battlefield injuries, birth defects, or illness related surgeries. To account for the wide range of sizes and ligament proportions one must develop a method to retrofit the prosthesis in a simple and productive manner. The most efficient way to do this with a 3D printed system involves using a conventional 3D scanner. This technique allows the provider to scan the patient’s residual limb and fit the prosthesis to the exact size necessary to provide optimal appearance and comfort.

3.9.3: BLOOD CIRCULATION

In order to test our hypothesis on providing sensory feedback to the user based on what they may touch with the force resistors and the peltier cooling apparatus which both will be embedded in the sleeve. The most efficient way of testing this theory is to one use the arm seen below in figure 1 as the main synthetic human device. The apparatus contains all of the arteries, veins and muscle structures that any ordinary human extremity would have. Then using the procedures documented in figure 3 one would perform the same below elbow disarticulation surgery to the dummy arm. By re-creating a patient's surgically removed arm, one would then be able to apply the sleeve presented in the final draft and test the original hypothesis. Essentially, the every time the force resistive sensors come in contact with an object they will send the remaining voltage through the circuit to the Coin motors in the sleeve which when then vibrate to the level of voltage coming in. This would ultimately provide the user with the sensation of touching objects with a non-human hand, as well as provide a level intensity for how hard the fingertips are grasping something due to the variable voltage coming from the force resistors. This technology also acts as a system which will circulate the blood of the patient within their respective attachment sleeve; ensuring that blood will not stagnate in the outer walls of the remaining limb. This quality is essential to the customers because it prohibits their limb from developing dead spots, and also keeps the muscle in the area healthy with fresh proteins and oxygen so that they can trigger effective signals into the myoelectric sensors located further down the remaining limb.

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Figure 32: Basic below-elbow disarticulation amputation and human anatomy.

The second important aspect of the sleeve is the two Pelteir Thermoelectric Cooling devices located just above the vibrating motors. In normal prosthetic limbs where a user is provided with an attachments sleeve, not only does the blood of the customer stagnate but it also perspires into the surrounding material. This effect is a hazard one must avoid when developing this system for multiple reasons. First the patient will begin to become extremely uncomfortable wearing the prosthesis if it promotes sweat and heat build-ups in the surround extremity. Secondly, when sweat is trapped between a foreign material and skin it typically begins to develop rashes and dead skin areas. This is the worst scenario that can happen to a customer, as they will actually not be able to use their equipment while the sore heals. Finally, if the sweat were capable of leaking into the surround electronics it could potentially damage the interface of the system or corrode it over time. The best way to avoid this is to position these micro heat exchangers just above the vibrating coin motors in the sleeve. This area of location will ensure that all blood coming from the heart and distant arteries is cooled before entering the lower sections of the remaining limb. To control this, a temperature resistor will be also place in the sleeve so that In the event that the arm rises above a normal homeostasis it will automatically switch on and begin to cool the area by up to over 20 degrees in a period of five minutes. There will also be a temperature switch so that should the user begin to become anxious of the heat within their sleeve they can manually switch the cooling devices on to their digression.

When performing the lab testing, mass flow sensors and thermocouples will be placed at the inlet of the sleeve at the top of the remaining limb, the bottom of the remaining limb, and the exit of the sleeve. Then

Perfluorocarbons or synthetic blood will be added to the system at the same rate in which a heart would pump blood to the extremity any typical human arm. These data collection devices will first record the system when the cooling and blood circulating devices are NON-active to get a control. Then they will record at multiple levels of

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Figure 33: Synthetic lab testing arm with artificial muscles, veins, and nerves.

vibrational intensity and cooling parameters to find the most effective and healthy circumstances for a patient's arm.

3.10: FAILURE FACTORS

Table 4: Failure Factors

Function Potential Failure Potential effects from failure

Cause of Failure Problem Addressed

Criteria(100 scale)

Electrical Command System

Short Circuit Switch Failure Sensory Failure

Electrical system stalls or breaks Electrical System stalls of breaks Non -responsive electrical system Sporadic Involuntary movement Use of System outside of Parameters

Broken Soldering conduits Broken Soldering conduits Sensors have worn or blown as well as bad soldering at the board connection port.

yes yes yes

7 2 8

Gestures

Lifting Gripping Pulling

Dropping object being lifted Object being gripped slips of falls Pulling of an object fails

Force is larger than specified restraints Force is larger than specified restraints Force is larger than specified restraints

yes yes yes

15 15 15

Sleeve Joint Connection

Extensive Load Dislocating from limb

Force is larger than specified restraints

yes 15

Wrist Connection

Extensive Load Wear and Tear

Wrist structure breaks or deforms Pathway Jams/ stops movement

Force is larger than specified restraints Material wears down

yes yes

6 2

Daily Use Bumping Falling

Electronic/ structural failure over time

Arm experiences frequent small forcesImpact is larger

yes yes

4

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Complete structural and electrical failure

than designed for 3

Motor Drive System

Motor Stall Failure Mechanical system seizes

Force applied is larger than factory specifications.

yes 8

3.11: MANUFACTURING

3.11.1: METHODS: 3D PRINTING VS. CASTING

SLA VS. FDM

There are currently two types of 3D printing techniques used in the entry level prototyping industry. The more developed and common method is the Fused Deposition Modeling (FDM) 3D printing. This method simply heats up a nozzle that melts down polymers from a spool as it is fed into the nozzle. The nozzle then “prints” out the 3D model layer by layer. The process can print virtually any geometry with many different types of polymers, but PLA is common and easy to use with this method. For further production of the arm, more polymers can be experimented with if desired. See the figure below for a visual representation of FDM printing surface cannot be printed. The layer-by-layer process creates ridges that can be seen and felt on the final product. An example is shown below.

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Figure 34: Dual-axis extrusion 3D printer.Figure 35: Layer ridges and separation.

3.12: ANALYSIS OF FUNCTIONALITY

3.12.1: STRESS ANALYSIS

The below Stress Analysis demonstrate Von Mises Stress simulation in Solidworks Edition 64. The color scale seen in the figures has been increased by 300-400% to give a more visually stimulating example.

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Figure 37: Finger assembly simulation. Figure 36: Knuckle simulation.

3.12.2: THERMAL ANALYSIS

Given the robust electronic nature of PriMA’s final model, thermal characteristics of the product must carefully be considered before entering a safe customer market. The entire mechanical arm will be fitted into a synthetic glove that is aesthetically identical to the patients other extremities. This presents issue when determining where excess heat produced by the batteries and all other electronics will be disbursed to. To counter these effects the electrical

core

located in the forearm as well as the palm and joint connection sleeve must be designed to release this heat into the ambient surroundings. To begin with the electrical core where all of the boards, batteries and microcontrollers are located will be filled with heat sinks which will draw the heat out of the system and into the synthetic glove which will emit heat in the same manner skin will through pores or voids in the synthetic. The palm will also contain heat sinks, which will pull heat from the motors in the knuckles out of the device and again into the synthetic silicon glove. Finally the sleeve will consist a neoprene synthetic material, which is unique in its ability to pull moisture and heat from the inner surface and out the ambient surroundings.

3.12.3: WATERTIGHT AND CORROSION RESISTANT SYSTEM

The prosthesis will not be watertight from an exterior standpoint due to relative heat transfer concepts such as pressure build-ups due to temperature differences. PLA is not water-soluble, therefore the material grade is not threatened by humidity, rain etc. However, each electrical subsystem in the prosthesis will be coated in 3M’s electrical sealing resin spray. This spray is used widely in the electrical industry to keep electrical systems water tight and resistant to humidity or corrosion.

4: FINAL DESIGN

4.1: FINAL SOLUTION PRINCIPLES

The final solution was designed to address all the customer issues regarding comfort, price, and functionality within a robust and aesthetically pleasing electromechanical platform. Furthermore, the systems were designed to be scalable to accommodate customers of various sizes. The goal was for the solution to mimic the abilities of the human anatomy with regard to motion and sensory capabilities, and to mimic the sizes and shapes found in

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Figure 38: Linkage bar simulation.Figure 39: Slider joint simulation.

nature. Lastly, the solution was designed to be safe, user-friendly, and capable of withstanding a wide range of practical uses.

4.2: FUNCTIONAL ANALYSIS

The solution should hold up well to everyday use due to the excellent qualities exhibited so far through the design process. The hand should have considerable strength due to the use of what are essentially worm drives – the lead screws must be stripped for the grip to fail. The limiting parts in the arm will be the driveshaft on the wrist gearbox and the linkages driving the fingers. Electronically, the arm currently does not have a desirable battery life. However, with higher quality batteries (available with more funds), the arm could certainly work for an entire work/school day on one charge, which was the original goal. Also, since LiPo batteries have a separate charging cable, a charging port can be designed into the arm for simplicity.

4.3: PARAMETERS AND CONSTRAINTS

The distribution of weight on the entire structure of the prosthesis another major factor besides the overall weight that determines the comfortability of the prosthesis. It was found that if heavier components of the prosthesis are placed proximal to the patient’s amputated arm, the prosthesis became more comfortable when compared to the situation in which the heavier components are placed distal to the patient. Most of the prosthetics currently available in the market weigh approximately 350-615 g. These values on paper seem almost the same as the weight of an anatomical arm; however, the amputees still perceive such prostheses to be heavy as they hang on the soft tissues of the residual arm. So, it is always better to have prosthesis that weighs less in comparison to the 400 g benchmark that is the average weight of an anatomical arm. Size, as mentioned before, is also equally important factor for prosthesis to function properly and be comfortable to use. On average, the prosthetic arm’s palm region should be of the same size as the anatomical arm with length and width of the palm between 180-198 mm and 75-90 mm respectively with the prosthetic glove on it.

Apart from the size and weight, the kinematic of fingers is also important for the prosthesis to be anatomically correct. Studies on the biomechanics of palm have shown that nearly 40% of hand’s functionality is dependent on the thumb. Hence, the function of thumb is important, and a vital parameter to consider while designing the prosthetic arm. This factor is vital as it determines the how mechanical prosthetic arm would function in comparison to the anatomical arm. Due to the combination of three joints at the base, the thumb has an average circumduction of 90.2o when analyzed for its kinematics. Besides these major parameters and requirements, it is also important to achieve more anthropomorphic motion and desired hand openings for various grasp patterns while keeping the complexity low. Hence, it was important for the team to create a prosthesis that keeps a balance between weight, anatomical correctness, complexity, cost, and robustness.

Grip force is another important factor that needs to be taken care of to make sure that the prosthesis functions in a desired manner. As mentioned before, researchers have found that the amputees need high grip forces with low speeds under specific situations and fast speed with low grip forces for most of the normal day-today activities. Hence, it is important to make sure that the prosthesis that is designed should enable the amputees to work with a range of grip forces and both high and low speeds. The friction force between the object and the fingers, the object’s geometry and its weight determine the gripping force required to hold that object. Besides these, the relative location of contacts and the number of contact points also determine the amount of grip force required to hold an object. An average anatomical hand produces grasping forces ranging from 95.6 N in precision grasp to 400 N in power grasp; however, a grip force of 45-68 N is sufficient enough to perform normal activities of daily living.

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It has been found that 76% of the men, 50% of the children and almost 100% of the women in an online survey consider myoelectric prosthesis to be slow, with delay in the time of response from the time amputee gives the command to do a particular activity.

Studies have also shown that human fingers have flexion speed of about 173-200 o/s for normal everyday tasks of lifting and putting back objects, but can reach up to a flexion speed of 2290o/s if required. The prosthesis currently available in the market have finger flexion speeds ranging from 20o/s to 225o/s. Out of these, while the ones on the upper portion of this range are comparable to anatomical hands, the ones on the lower end are noticeably slow for the amputees to use them like their anatomical arms. Another limitation of these prostheses is that they cannot reach the speed of 2290o/s under rare circumstances even if they belong to the upper end of the flexion speed range. Research has also shown that it would be adequate to design prosthesis with finger closing time of around 0.8-1.5 s for most day-to-day activities. So, it is an important parameter that should be incorporated in the prosthesis.

A normal anatomical arm can perform a range of more than 30 distinct grasping patterns. Out of these, predefined grasping patterns like tripod, hook, power, finger point and precision are the major grasping patterns that can accomplish typical activities of daily living. Finger counting another important gesture that can be useful if predefined. Durability of the prosthesis is also very important factor for it perform like a normal arm. All the myoelectric prostheses that are currently available in the market set 8 hours of battery life per charge as a target to achieve for the prosthesis to function as a replacement for the anatomical arm. It is assumed that the arm should ideally work for this period per charge every day of the week as the normal work day for most people is approximately 8 hours. Hence, the prosthesis should be comfortable and robust enough to be used for at least 8 hours per day for it to replace an amputated anatomical arm. Previous studies have also shown that an anatomical arm performs 2500-3000 grasping motions on an average workday of 8 hours. However, these numbers are pretty high and in case of prosthesis the number of grasping motions performed comes down to 120 on a typical 8 hours of work day. This can be considered as the minimal target to achieve, with target set on achieving 2500 grasping motions on a normal workday of 8 hours. Considering the lower end of achieving 120 grasping motions, the prosthesis should still be robust enough to maintain its optimum functionality for approximately 6 years with a total of 300,000 grasping cycles taking place. Most of the prostheses available in the market with routine servicing have set a baseline standard of 500,000 grasp cycles for the time they mention the prostheses is expected to function properly.

Therefore, research on the biomechanical properties of the anatomical arm and currently available prostheses in the market revealed that the prosthetic arm when engineered should create a balance among size, cost, weight, robustness and durability. It will be better to offer a prosthesis that costs less and outperforms all the products currently available in the market even though the cost is not a matter of concern as prostheses are covered by the insurance companies.

Cost of the prosthesis is not a concern, but is still better to make the prosthesis which is inexpensive and available to a wider spectrum of patients. This can be achieved by using 3D printing technology that can be used make prosthesis of desired size quickly and effectively using custom CAD design for individual patients. It is also necessary to keep the system calibrated when the battery of the prosthetic arm completely discharges. Hence, it is important to find possible solution to make sure that the prosthesis remain calibrated even if the user completely discharges the batteries while working with the prosthesis. Patients with amputations have shown to have positive reviews about the ideas of tactile feedback from the prosthetic arm and about the capability to prevent mechanical and temperature related damages to the prosthetic arm. Hence, to include force and temperature

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sensing capabilities is very useful for aesthetic and safety purposes. Additionally, attachment of the prosthesis to the residual arm should be strong, and seamless enough to make it aesthetically pleasing for the amputee. Research has shown that amputees want the prosthesis to attach with the residual arm in a manner that makes sure that it is biocompatible, comfortable, and is supportive of both the exchange of heat and moisture to the surroundings. It should also be connected to the residual arm in such a manner that it looks like a real and single entity from the shoulder to the tip of the fingers. Therefore, in addition to the numeric parameters mentioned before in this document, it also important to give consideration to small things mentioned in this paragraph to make the prosthesis functional, aesthetically pleasing, and comfortable for the amputee so that he/she can wear it for at least 8 hours of the normal workday.

4.4: DESIGN ANALYSIS

4.4.1: LINKAGE

In our final design, the volume has been reduced drastically making for a hand and arm that is comparable to our own arms. Achieving such a milestone required redesigning the finger driving linkage system to be optimized for the newer parameters. The above sketch is what we came up with and provides a range of motion and performance better than that of a human finger.

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Figure 40: Schematic of four bar linkage driving fingers.

4.4.2: PALM/KNUCKLES

While the original idea of having the palm and knuckles separated was great, the desire for a smaller product pushed us away from the design. It is possible to keep the parts one rigid structure while making an even more durable part. Ultimately, this saves weight and time while increasing strength motor speed. Further, the line of action of the motor shaft which drives the fingers is at a much more adequate position now. The torque applied has doubled since the preliminary design. Lastly, the overall thickness is half of the initial design. This allows for a 3d scanned hand to be made into a cover for all of the mechanics and wires.

4.4.3: FINGERS

The fingers have remained the same mechanically for the majority of the project; however, they have been completely redesigned with aesthetics in mind. As seen below, the fingers are round in appearance now. Also, a simulated fingernail appearance is in the works.

Figure 42: Fingers

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Figure 41: Palm and knuckles.

4.4.4: FOREARM

The forearm was originally larger than it needed to be and intended on using a slide in housing for the electronics. This has changed completely. A 3d scan of one of our arms was used to create a solid shell in solidworks, and then a cover was cut out with mounting holes placed into the base. While looking more realistic, this arm also allocates the allowed volume for electronics in a great way.

4.4.5: THUMB

The thumb is the hardest part to design while maintaining 2 degrees of freedom (DOF). It is found that the solution involves using a removable gearbox that can be assembled independently of the hand. The thumb casing is to be made from a 3d scan of a thumb which will line up perfectly with that of the hand. A cable driven system connected to a motor within the forearm drives the remaining DOF and allows for perfect gripping of objects.

4.5: DECISION ANALYSIS

Based on the patient’s requirements, the prosthetic arm should be: easy to use and functional, lightweight, aesthetically pleasing, and inexpensive.

To make the prosthetic arm easy to use, it will be provided with some predefined gestures for common actions like: hook, finger point, power grasp, precision grasp, and lateral pinch. These are common everyday functions that a fully functioning arm would be able to do. For ease of use the prosthetic arm will also be provided with actuators that provide a wide range of grip force (6.3-67N) [5]that can: hold even a fragile object at low grip force and pick up heavy objects using high grip force, without dropping them. Pulse mode will be included to hold heavy objects for longer time.

Each finger will be connected to an individual motor and the thumb with a pair of motors so that they can move quickly (0.8-1.5s flexion) [6], independently, and with several degrees of freedom. A four-bar linkage will be used to couple MCP and PIP joints of fingers for adaptive gripping of objects like anatomical fingers. Touch and temperature sensors will also be included to detect the physical characteristics and temperature of the surface in contact with the prosthesis. These sensors will send the information to the processor, which would send signals to the vibrating motors, providing tactile feedback to the user’s forearm. A dense grid of myoelectric sensors can be included to increase the sensitivity and accuracy of myoelectric signals used to run the actuators in the prosthesis.

To reduce the weight to less than 400 g and to increase durability of prosthesis, it would be fabricated via 3D printing using ABS or PLA. Collapsible linkages can also be included to increase the compliance. To increase

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Figure 43: Forearm attached to hand.

comfortability, the prosthetic arm will be connected to a sleeve made of COOLMAX rolled on the stump to reduce sweating and infection, and to increase breathability for the skin. Using the method of 3D printing and inclusion of materials like ABS, PLA and COOLMAX will also reduce the cost of manufacturing significantly.

Our group used design matrices as a method of deciding which component part would be most efficient for our project. The team came up with criteria for each individual selection in order to understand which of the parts worked best for our system. The following is an example how we chose one of the components for our system.

The following of components that are being considered for a way to increase blood flow in the residual arm.

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.

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.

Table 5: Blood flow stimulation decision chart.

Space Safety Efficiency

Sensors + + +

Fluid System - - +

This method was repeated for each major design made by the team about the project. The components are determined by whether they meet the criteria (+) or they do not (-). The following decision matrices are for the arm connection and battery types.

Table 6: Arm connection decision chart.

Comfort Ease of Use Strength Space

Arm Clamp - - + -

Sling - - - -

Suction + - - +

Sleeve + + + +

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Table 7: Battery decision chart.

Battery Life Energy Density Toxicity Weight

Nickel Cadmium + - - +

NiMH - + + +

Lead Acid + - - -

Lithium Ion + + - +

4.6: QUALITY FUNCTION DEPLOYMENT (QFD)

The quality function deployment chart shows the relations between the various factors, with a 0 being strong negative, 1 being mild negative, blank being no relation, 2 being mild positive, and 3 being strong positive. Each requirement was rated with numerical priorities from 0 (minimum) to 3 (maximum).

Figure 44: QFD spreadsheet.

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5: PROTOTYPE DEVELOPMENT AND TESTING

5.1: BILL OF MATERIALS (BOM) AND RATIONALE FOR USE

Table 8: Bill of Materials

Material Rationale

11.1V LiPo Batteries The batteries were selected due to excellent recharge capability and power at their size

Arduino Mega The main board to run all non-motor functions

Arduino Motor Shields 2 were needed to run the motors

N20 DC Motors Motors used to drive the fingers and thumb

Tamiya Gearbox Used to drive the wrist

Fasteners Pins, nuts, screws, and bolts hold the arm together

Neoprene Used to construct the sleeve

Myoelectric Sensors Used to control motors

Force Sensitive Resistors Used for feedback loop

Vibrating Motors Used for feedback and blood circulation

Arduino Uno Additional board used to run the feedback loop

Paint Plasti-Dip and gloss paints to be used for showcase

Watlow 97 This is a feedback system that allows for the heating of the water bath in order to ensure that the system is uniformly at the same temperature throughout.

Artificial Tissues The artificial tissues are sewn together in order to mimic a residual arm to give accurate test that would give results similar to that of an actual residual arm.

Cartridge Heater The cartridge heater is used in order to heat the water bath in order to have a constant temperature to the set up throughout.

Thermocouples The thermocouples are used in order to take the temperature readings at a variety of spots on the artificial arm.

Latex Tubing The latex tubing is used to mimic the vessels inside the body that the blood flows through.

PLA As well as being the material of which the arm is composed, PLA is used to print the peristaltic pump that attaches to the stepper motor. The tubing is

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then threaded through the 3D printed piece in order to cause suction as the stepper motor is turned on. The blood was then able to flow using the suction.

Alginate The alginate is used to create a hydrogel to mimic the inside of the arm tissue. It has similar thermal properties of the actual inside of an arm.

Thermal Camera The thermal camera is going to be used in order to take a visual images to demonstrate the flow of heat through the arm. The use of this will be vital in order to show the difference between the regular heat transfer in blood flow versus the heat transfer when a cooling device is used.

Thermocouple Connectors The connectors were used to connect to the thermocouples for the sensor to connect to the Watlow 97 in order to allow for a temperature feedback system.

Step Motor The step motor is used to drive the pump in order to allow for the flow of the blood.

Red Food Coloring This is used to dye the water in order to have the same optical properties as the blood.

Needle and Fishing Line This will be used to stitch the artificial tissues together in order to resemble an actual residual arm.

These materials were all used in order to prove the concept that the cooling devices would do their job. The goal would be to show the results of the experiment through the temperature readings given by the thermocouples as well as the visual images given by the thermal camera.

5.2: PROTOTYPE FABRICATION PROCESS

Once the CAD files are updated as desired, they all are meshed into individual stereolithography (.STL) files that can be converted into gcode for 3d printers. The .STL files are then opened into a 3d printing software, with a slicing program, of choice. Printer settings and support material layout is specified within the printing software. For our prototype, we use 100 micron layer resolution. The slicing software properly distributes the .STL file into toolpath data to be sent to the printer. Once the printer is running, only waiting is required. In this situation, we use fused deposition modeling (FDM) printers

The parts left on the print bed at the completion of the print have to be cleaned of any support material used for maintaining complex geometries or tight tolerances. Conveniently, newer 3d printing softwares are coded for breakaway support. This makes removing support almost as simple as just peeling it off. Some more finishing with a razor blade or dremel is required to remove rough edges. While the parts could be applied to the arm in this state, we do more post processing for appearance and performance. The parts are all lightly media blasted with 220 grit aluminum oxide. After this, a wash in warm water and soap is applied to remove all oils and residue. Wet sanding with 2000 to 3000 grit pads follows for a glossy finish that eliminates any trace of the 3d printing process. A gloss white paint followed by a clear coat is then applied to the finished parts. Finger and hand parts will dry and then be masked off for a rubber coating for increased friction and grip strength.

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5.3: ASSEMBLY

Unfortunately, due to software malfunctions with the CAD program Solidworks 2015, drawing views with accurate dimensional analysis could not be produced from our project. The team will do everything in its power to resolve the issue and submit said drawings at the soonest available date.

Figure 45: Full newest version arm assembly with sleeve connection.

The Assembly of the hand is modeled directly after one of our own teammates who serves as a very average build for the common male adult in modern day society. 3D scanning was used to pull direct models of his forearm, fingers and hand so that an accurate model could then be modified into a prosthesis. Therefore, all dimensioning of the arm is directly related to his body part proportionalities. The length of the forearm from the longest finger at full extension to the fartherst section of the forearm measure around 20.4 inches. The largest width of the forearm measure to be roughly 3.56 inches at a depth of 3.4 inches. All other relevant data will be produced in the late submission of CAD drawing files once the software malfunction is resolved.

Figure 46: Sleeve connection subassembly.

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Figure 47: Subassemblies of the hand, finger, and forearm.

5.4: PROTOTYPE TESTING PROTOCOL

The prototype is currently being tested by the computer science team. Their tests include largely calibration and increasing the number of gestures which the hand can perform. Mechanically, the M.E. group will conduct material tests by finding or generating a stress vs. strain curve for 3D printed (layered) PLA, and then use these material properties in SolidWorks to run simulations. The BME team will use artificial tissues and blood vessels to conduct blood flow and thermal tests to examine the effects of the vibrating motors in the feedback loop and the thermoelectric cooling devices.

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5.5: TESTS PERFORMED AND RESULTS

Simulations of the mechanical components have been previously run in SOLIDWORKS; however, these simulations used standard material properties for polylactic acid (PLA). 3D printing alters these properties substantially based on which orientation the layers are printed. To account for this, tensile tests will carried out to determine the mechanical aspects of PLA after printing. This will allow for betting fitting and more accurate simulations of the hand.

Myoelectric signals have been characterized by reading signals from our arms while performing gestures. A library of simulated signals can be used to test our working prototype without actually connecting the arm to a human. As of now, full hand gestures have been performed and all fingers are functional.

Rudimentary strength tests have been performed such as carrying a backpack with each finger. Under most circumstances, the fingers could support a static 15 pound load. After repeated loading, or fatigue, the finger linkages would fail as predicted in our earlier simulations.

An artificial residual arm was created using artificial tissues purchased and sewed together using a needle and fishing hook. Within the arm, an alginate hydrogel was created in order to mimic the inside of the arm. The tubing was placed within the hydrogel inside the artificial tissue. This mimics the vessel through the arm. The rest of the tubing is pushed through the peristaltic pump which was attached to the top of a stepper motor. This allows for a suction to be created for the blood to flow through the experiment.

The set-up was placed in a hot water bath heated by the cartridge heater connected to the Watlow 97. This device is a feedback system so the thermocouples are also attached to the device. Once the setup is heated to 37 degrees throughout the system, the blood is allowed to flow throughout the set up. The thermocouples were used to measure the temperature as the blood flows throughout the system. The thermal camera will also be used to take a picture of the system to show the transfer of heat through the setup.

After the control were tested, the cooling devices from our device were placed on the artificial residual arm. The tests were then ran again using the cooling devices in order to observe the differences compared to a regular residual arm data. This allows for the proof of concept for the cooling devices and how well they work in our device.

The device in question is currently being set up in the Space Coast FabLab. Conclusive testing results from this test have not been conducted yet. Testing will occur the week of March 7th - 11th so results can be compiled together for the final poster that will be presented at Senior Design Showcase.

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Figure 48: Test conducted of motors driven by EMG signals.

6: CONCLUSIONS AND FUTURE WORK

6.1: IMPLICATIONS OF RESULTS

The final solution should provide an innovative, competitive product to the prosthetic market within the next two years. Currently, the arm could function as a low-level medical device, but would be limited by its lack of exposure and by the FDA's requirements regarding clinical tests for medical devices. Regardless, the system used in this solution will constitute a significant improvement to the prosthetic industry.

6.2: FUTURE WORK AND IMPROVEMENTS

The team intends to conduct more testing in the coming weeks, as well as making aesthetic improvements. The mechanical and electrical systems are nearly finalized, with the only remaining modifications being the thumb (which will be completed by March 12th) and potentially adding temperature sensing and thermoelectric cooling. The model at showcase will feature a hand sprayed with Plasti-Dip for extra grip, and a buffed, polished, and painted arm with embossed PriMA logos, as well as user manuals and packaging.

6.3: ERRORS

There are a few potential sources of error in the analysis of this design. One of those is in the estimation of the material properties of the printed PLA. In these situation, empirical data shows that estimating a layered material as a continuum is inaccurate. However, making an accurate estimate for the material strength of a layered material is very difficult to do analytically. The best option for this is to use experimental data, which may have relatively large errors by percentage. Compounding the errors is the fact that, with the fingers flexed, there will be laminates running in several directions at once, through which forces and stress are propagating.

Another potential error is in the analysis of the product life cycle. With a large number of small, moving parts, and with the uncertainty in the material strength, a large amount of error is then propagated to life cycle calculations, as fatigue on the materials will likely be the limiting factor. Overall, it is likely that the life cycle for the product with its original components will be fairly short due to the extensive use of plastics. However, this is addressed by using standardized, replaceable parts as much as possible.

6.4: FINAL EVALUATION OF DESIGN

This design should prove to be excellent once it is completed. It has garnered the interest of KEEN and others both inside and outside the industry. The systems used are truly novel and will result in a significant improvement in prosthetics. The price will also bring quality to those who could previously not afford it, improving overall quality of life for amputees. Mechanically, the design is reasonably robust, and is standardized enough that weaker parts can be replaced easily and affordably. Biomedically, the solution should be very safe for human use, as it is non-invasive and made of a non-harmful material. The arm will also have some rehabilitative qualities due to the emphasis on stimulating blood flow. Electronically, the arm constitutes a step along the larger path in science and technology of increases in the amount of sensory devices included in new engineering developments.

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