Design of a robotic thumb for prosthetic application

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Dipartimento di Ingegneria Informatica MSc. Bionics Engineering

Design of a Robotic thumb for prosthetic application.

Supervisors:

Prof. Christian Cipriani Prof. Marco Controzzi Dr. Leonardo Cappello External supervisors: Prof. Giovanni Vozzi

Presented by:

Punith Reddy Vanteddu

Anno Accademico 2018/2019

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hs HvAsihi mMdm gCc c।(sanskrit quote) Has shvasihi mamdam gachchha ch. Smile, Breathe and Go slowly I dedicate this to my family, my friends, my teachers and all the well wishers who have mentored, stood by me and encouraged me through thick and thin. Without you all... this journey wouldn't have been the same.

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4 Design evaluation 25 4.1 semi-passive abduction . . . 25 4.1.1 Design 1 . . . 25 4.1.2 Design 2 . . . 25 4.2 Passive abduction . . . 26 4.2.1 Design 1 . . . 27 4.2.2 Design 2 . . . 27 5 Performance evaluation 28 6 Conclusion 29 6.1 Future work . . . 29 Appendices 30 A Appendix A 31 A.1 Introduction . . . 31 A.1.1 Assumptions . . . 31

A.2 The Problem . . . 32

A.2.1 flexion . . . 33

A.2.2 Abduction . . . 37

A.2.3 Hyperextention . . . 37

A.3 Geometrical parameters . . . 39

A.4 Results . . . 41

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List of Tables

2.1 Table weightage for prerequisites . . . 13

2.2 Comparison of the Hands . . . 15

A.1 Table depicting the known Geometrical parameters . . . 40

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List of Figures

1.1 Human hand skeletal structure. . . 1

2.1 Different grap patterns. . . 7

2.2 House of Quality. . . 14

3.1 Motions of thumb . . . 17

3.2 Axes of rotation of fingers . . . 18

3.3 Mechanisms a)worm gear b)fourbar linkage. . . 19

3.4 Mechanisms a)Planetary gear b)Geneva mechanism c) Friction wheel mechanism. 19 3.5 Concept comparison and evaluation. . . 20

3.6 CAD model of design 1 a) Rear view to highlight the gear meshing of Abduction b)Front view to understand the rachet paul mechanism c) Magnified view of ratchet paul mechanism. . . 21

3.7 CAD model of design 2 a) Rear view to highlight the friction bearing for Abduc-tion b)Front view to understand the rachet paul mechanism c) Magnified view of ratchet paul mechanism. . . 22

3.8 CAD model of design 1 a) Full assembly of the thumb with the button b)trigger mechanism . . . 23

3.9 CAD model of design 1 a) Full assembly of the thumb with the pin b)Detailed sectional view of the pin . . . 24

4.1 Design2 3D printed assembly model . . . 26

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5.1 a) the full assembled model of design b) the indented abduction block c) Pin

engaged to the abduction block . . . 28

A.1 Forces acting during flexion. . . 32

A.2 Forces acting on ratchet and pinion with the coreesponding vectors. . . 34

A.3 Abductionshaft. . . 36

A.4 Stresses acting on the pinion shaft. . . 41

A.5 Stresses acting on the abduction shaft. . . 41

A.6 Stresses acting on Ratchet. . . 42

A.7 Stresses acting on Pinion. . . 42

A.8 Diameter with respect to change in Twist. . . 44

A.9 Bending Stress with respect to deflection. . . 44

A.10 Shear stress with respect to twist angle . . . 45

B.1 hub . . . 47 B.2 baseblock . . . 48 B.3 Index . . . 49 B.4 Pinshaft . . . 50 B.5 Flange . . . 51 B.6 Shaft . . . 52 B.7 Assembly . . . 53

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Abstract

The replacement of a missing human hand with a prosthetic has become a denitive need recently. The prosthetic hand shall serve as a proper replacement both in terms of cosmetic and functional aspects. The functional aspects of the prosthetic hand have seen a range of developments and innovations in the past 40 years from passive wooden hands to multifunctional electronic hands. This research is still ongoing as the need to eectively compensate for the functionality of the human hand still exists.

The thumb plays a prominent role in the hand allowing it to perform a variety of tasks. It is also considered the evolutionary paradigm shift in terms of limbs functionality. Hence, there is a dire need to restore and improvise the functionality of the thumb in the prosthetic hand. The diculty arises in the design of thumb due to its unique geometry and movements compared to the other ngers. The thumb can change its orientation from opposable to lateral position depending on the need. The thumb also performs the exion/extension movement like the other ngers, but the range of motion is greater, as this motion can be coupled with the thumb ab-duction/adduction. Therefore, the thumb has two separate axes of rotation and the challenge in the prosthetic thumb is to obtain both these movements maintaining the dexterity but not com-promising with other geometrical concerns such as weight and size of the thumb. Hence, eorts are made to perform both these movements with a single actuator by realizing a mechanism. The design of the mechanism has been approached by setting a set of prerequisites that dene the boundaries to explore design inspiration. The prerequisites have been divided in terms of quantitative and qualitative parameters. The primary dierence between them is that the quan-titative parameters can be measured directly, and the quanquan-titative parameters need a dierent mode of measurement. The quantitative parameters are

Size- The size of the prosthetic thumb must be comparable to the standard human hand and is considered as a very important prerequisite

Weight- Weight is an important feature in terms of user comfort and shall be made to be as close to the human hand

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tradeos. As we increase one, the other is compromised. Therefore, the speed of the thumb shall be less important than the rest of the prerequisites.

Nonback-drivability- This feature enables to hold the position and allows to maintain the force without the continuous supply of power. This is an essential feature in the prosthetic as it can help with fatigue and power concerns.

The quantitative parameters are Adaptability- this feature determines the adaptable nature of the thumb with respect to the holding object. This cannot be directly determined. Hence, it is realized as a resultant feature of an adaptive grasp mechanism. This feature is not considered as a very important feature.

Complexity- the level of complexity employed in the prosthetic thumb determines the level of innovation. When the need to encapsulate both the exion/extension and abduction/adduction movements into one single mechanism, the complexity arises. Therefore, this feature is consid-ered, yet kept as a less important feature.

Reliability- The reliability of the prosthetic thumb reduces with increases with an increase in the number of parts employed in the mechanism. The more the number of parts in the mechanism, the more risk of them failing and resulting in a critical failure. Therefore, this feature is consid-ered very important

Dexterity- As already proclaimed, the most intriguing feature of the thumb is its dexterity, and it can be measured by checking the number of grasps achievable.

Keeping these design prerequisites, a dierent state of the art prosthetics was studied and com-pared. The comparison was made on the basis of mechanisms used and its resultant performances. The state of the art was divided as commercial prosthesis and research prosthesis. The com-mercial prosthesis was a design that has been successful and has been engaged with the market that gives denitive feedback. The research prosthesis explores dierent innovations and can give scope for the betterment. These hands were compared by type of mechanism, type of actuation technique and evaluated against the design prerequisites proclaimed previously by using quality function deployment in House of Quality.

1) Ilimb 2) Bebionic 3) Vincent 4) Manus 5) Smarthand

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6) Vanderbilt 7) SSSA-MyHand.

Using the data obtained from comparison from the House of Quality four designs were proposed. The designs were classied as semi-passive and passive abduction mechanisms. The semi-passive designs have an abduction/adduction movement assisted by the actuator in only one direction. The opposite direction shall be realized manually. The passive abduction mechanism operates independently without any assistance from the actuator and only relying on the external manual force.

Design 1- The design utilizes a worm gear mechanism to perform the exion motion. Due to the use of the worm gear mechanism, the nonback-drivability is an inherent property of the mech-anism of exion/extension. The abduction/adduction mechmech-anism is performed by a gear that engages with a toothed abduction block when the thumb performs a hyperextension and under-goes abduction mechanism. The Cad model for the mechanism was presented and the meshing of the gears with precision was a huge problem and the design was not presented further. Design 2- The design has a similar feature as to design 1 and performs exactly in the ex-ion/extension movement. The abduction/adduction movement is realized by a friction wheel attached as an extension to the back of the thumb and engages with abduction block when the thumb performs hyperextension. The rotation of the motor continuous the abduction movement in one direction. The nonback-drivability of the abduction/adduction is ensured by employing a ratchet and pawl mechanism. The opposite return of the thumb is performed by hyperadduction and engages a snap mechanism that returns the thumb to its primary opposition position Design 3- The design is a passive abduction/adduction mechanism. It uses the same worm gear mechanism for exion but for the abduction/adduction movement it uses a button trigger that releases the position and allows it to adjust the desired position. This trigger can be accessed manually of also using an external constraint such as pressing against an object. The disadvan-tages of the mechanism were the amount of friction that developed and trying to x an accessible position for the trigger button. Design 4- This mechanism keeps the exion mechanism same as previous but for the abduction uses a pin that engages and disengages due to an external force. The mechanism is very simple yet, eective and complies with all the prerequisites eciently.

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cover and other electronics. This is close to 1/5th of the weight of the natural human hand. The reliability fares high too due to its simplistic mechanism and the minimal number of parts. The thumb exhibits 22.7 N of force during exion.

The design 2 even though has some disadvantages due to the stresses developed can be further developed and presented an optimal solution for the prosthetic thumb. This work shall be carried out in the future.

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Chapter 1

Introduction

The articial hand is a term that can be tricky since, it is even though conceptualized with a combination of existing and innovative technology, it is always parameterized to function as a replacement of a human hand. Hence, the hand should be able to perform eectively comparable to a natural human hand. The articial hand must compare closely with missing a human hand. This imposes a need to understand the human hand thoroughly to replicate and also compare the performance of the articial hand. The Fig.1.1 shows the total number of bones and joints

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the hand to be oriented in multiple positions allowing the hand to achieve its gold standard dexterity. Hence, it is a dicult task to implement such an intricate mechanism into an articial hand, such that its behavior is identical to that of a human hand. The intricacies of the human hand can be categorized as the following

1)Independent nger exion 2) Thumb position

3) Wrist orientation

The articial hand that shall be developed will approach these three design categories indepen-dently, yet to keep these aspects synchronous with one another. The thesis presents exclusive design methodology employed for an articial thumb capable of both exion and abduction movements independently and also providing enough room for the other two design aspects for a complete human hand.

1.1 Background

The thumb has two digits and must provide eective prehension while grasping and also ma-nipulation and release of the object. There is a signicant amount of literature corresponding to the articial hand design with emphasis on the thumb.

1.1.1 Literature survey

The emphasis on the functionality of articial hand comparable to a human hand has been ef-fectively made by [17]. The article gives the timeline of the design innovations occurred in hand prosthesis and comments on the substantial development of myo-prosthesis by introduction of the myo-electrically powered prosthesis for children developed by Sorbye and this innovation led to the advanced electrically powered multiple degrees of freedom prosthesis such as the tendon driven Belgrade arm[16], UTAH arm[15], Stanford hand/JPL hand[18]. The design objectives mentioned in this article are to increase the number of grasp patterns achievable using the current prosthesis and improvement in the visual feedback of an object in hand. Additional to these, the design constraints that need to be incorporated are the cosmetic appearance, weight of the hand, limiting the power consumption, modularity, speed, size. The thumb is responsible for the extended dexterity of the hand and its opposable function a very fundamental aspect of the prehensile capability of the hand. The thumb consists of 5 DOF. The exion of the thumb is

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possible by the MCP joint which has to be held stable during the grasping of objects and also the nine motor muscles along the skeletal joints are intricate in the grasping kinematics of the hand. By the help of the biomechanics study of the thumb the 5-DOF system has been simplied into a 2-DOF system.

The research present in [10] tries to incorporate a curl of the digits along with the exing of the ngers called the adaptive grasp allowing the users with a better gripping mechanics. It employs a 6-link mechanism for the ngers where links 1,2,3 are 3 segmented straight links connected in series and links 4,5,6 are placed strategically in between 1,2,3 so as to drive the ngers and achieve an anthropometric exion. Link 6 also acts as driving link to cause the exion Inde-pendent exion of the ngers can achieve a close adaptive grasp to the object yet the ngers ending position shall be dierent relative to each nger depending on the object. The paper discusses the principle of actuating all the ngers using a single motor using springs. The design of the thumb has been performed by use of cable and the abduction movement has been achieved manually. The thumb exion is achieved by a 4-bar linkage driven by cable looped over a pulley and connected to the link 4. The abduction of the thumb is monitored by providing a rotational shaft that rotates along with the pulley to allow exion in all the planes of grasp.

[19] explained the importance of underactuated mechanisms that can enable the hand design to achieve higher dexterity with a simple mechanism. The underactuated mechanisms have an advantage in grasping as the geometrical conguration of the ngers is determined by external constraints related to the geometry of the object. The thumb mechanism presented in the re-search has two digits similar to the human hand and performs exion and extension by using a cable driven underactuated mechanism. The adduction and adduction is performed by a four-bar linkage mechanism.

[21] presents an innovative mechanism embedding a geneva wheel for the abduction and adduc-tion. It presents the various guidelines that need to be considered while designing a human hand and also presents their level of importance in achieving a better functional design. The ngers are presented as a martensitic uniform structure that is driven by a single actuator.

[6] gives a description of a cybernetic hand with adaptive grasp, and non-back drivability using dierential mechanisms. The design and importance of a nonback drivable system are explicitly

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instead of rigid mechanical joints and provides an experimental evaluation of the performance of the hand compared to the rigid existing robot arms. [8] uses a semi-independent mechanism to implement the abduction and adduction motion along with exion and extension movements of the thumb using a single actuator. The design implements a geneva mechanism to switch from the exion/extension mode and abduction/adduction mode. Due to its innovative mechanism and limited use of actuators, the weight and size characteristics of the human hand are achieved without losing the functionality.

The detailed study of these designs has provided further insight into various existing mecha-nisms and their advantages and disadvantages. [20] explains the importance of opposable thumb in daily manipulation activities and can also reduce the need to rely on independent long ngers. [2] gives us detailed guidelines to help design thumb with anthropomorphic and functional com-parisons to the human hand. The article consists of a detailed study of various tests performed to obtain the parameters to compare and exploit in thumb design. Also,[23] gives us an anthro-pomorphic study and provides the guidelines for the design of the thumb. [1] provides a review of all the hand prosthesis available and provides with a methodology to compare them. This article enables to set a benchmark for the design guidelines based on the state of art available.

1.2 Organisation of the thesis

The literature survey gives us a detailed understanding of the research methodology and various segments that need to explore in order to realize an eective design of the robotic thumb. Since the emphasis of the research is on the design of a robotic thumb with both exion/extension and abduction/adduction properties, the thumb shall be explored anatomically and functionally. The structure of the thesis is presented by rst exploring and discussing the design requirements. These describe the various parameters that need to be considered and compared in order to nalize and establish tradeo and prerequisites for the design. The next chapter shall focus on the design methodology where the prerequisites are employed in a constructive manner to obtain design concepts. These concepts are evaluated and nalized for further development. These designs are evaluated in the next chapter by using the same comparison we employed for design requirements. These designs are then developed further to understand the performance evaluation to understand the functionality of the design. The thesis is then concluded by sharing

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the results and insights for the research. Finally, the document is ended with the addition of appendices which contain the numerical and design work performed to give the thesis a holistic view.

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Chapter 2

Design requirements

The design of a robotic thumb requires a specic set of prerequisites to enable a worthwhile comparison with a human thumb. In order, to achieve this, the anatomy of the human hand must be studied thoroughly both in terms of geometry and functionality. The design must comply with certain essential parameters, such as the weight, size, etc and these parameters must be embedded into the design to be comparable to that of an actual thumb to be used in Activities of Daily Living(ADLs). The insight into the kinematic design of the robotic hand is presented in [12], the article discusses the importance of a hand in terms of grasping and manipulation of objects and the signicance of individual ngers for the task. This leads us to a practical approach for designing a DLR Hand Arm system using a series of medical tests and grasping tasks. The paper further analyses the basic skeletal design of the hand and its role in the grasping kinematics based on the number of joints and degrees of freedom achievable. Furthermore, it categorizes the grasping action as a result of two principal components, the ngers, and the thumb. The importance of thumb can be realized in two contradictory grasping actions such as as

1) Key grasp 2) power grasp

Both these grasps have been the primary requirements of our design of the articial thumb. Firstly, the kinematic component of these two grasping movements has been explored including the eort to meet the geometrical requirements of the human hand. The article [2] provides a deeper insight into the thumb and emphasizes on the importance of three major aspects of designing a robotic thumb comparable to the human thumb. The article discusses an approach

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Figure 2.1: Dierent grap patterns.

considering 1)Biomechanics 2)Anatomy 3)Surgery

These provide the guidelines for the proposed eective design. Using this research a specic set of prerequisites of design have been considered in the development of the design.

2.1 Prerequisites

Based on the guidelines a set of prerequisites have been chosen for the thumb design. These prerequisites consist of both the kinematic and dynamic properties of the thumb. These prereq-uisites can be categorized into

1)Quantitative Parameters 2)Qualitative parameters

2.1.1 Quantitative parameters

The quantitative parameters of the design can be dened as the parameters that can be measured and modied accordingly to obtain the required design parameters. These parameters can be controlled to enhance the performance of the design.

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Size

For an anthropomorphic prosthesis, it is natural for the envelope of the hand to replicate the size and shape that is natural to the user. Since prosthetic hands are sized according to human hand measurements, the prosthetic hand structure, including cosmetic covering, should have a length between 180 and 198 mm and a width of 75 to 90 mm to match normal human hand size. Therefore, this is considered a mandatory prerequisite

Weight

The human hand has an approximate weight of 400 g or 0.6 percent of the total body weight for men and 0.5 percent for women[3, 22]. However, prosthetic terminal devices of similar weight have been described by users as being too heavy. Since the forces from the device are borne by the soft tissue instead of the skeleton, the perceived weight in the terminal device is increased. In addition to the overall weight of the device, the weight distribution aects the perceived weight of the system. For this reason, the weight of the prosthesis must be as close to or within the connes of the human hand weight and it is extremely essential in the design

Grip force

Most activities of daily living (ADLs) require fast speed and low grip force (e.g., typing, ges-turing). However, tasks that require low speeds and high grip force occur often enough that a prosthetic hand must enable the user to perform such tasks (e.g., opening a door with handle, unscrewing jar lid). The grip force able to be exerted by a hand on an object is largely a func-tion of the hand posture, object geometry, and transmission method. The necessary grasp force to maintain an object within a particular grasp is also dicult to predict because it is largely dependent on the friction between the ngers of the hand and the object, the number of contact points, the relative locations of contact, and the object geometry and mass properties. In a precision grasp, the human hand can exert an average of 95.6 N of force. In power grasps, the forces can reach up to 400 N[26]. According to Heckathorne [14], a grip force of only 68 N is required to carry out ADLs .

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Speed

Although the human hand can exhibit nger exion speeds of 2,290 deg/s, the typical speeds for everyday pick and place tasks are 172 to 200 deg/s[14, 26]. There are numerous ways the speeds have been described. What is of most concern to the end user, however, is the amount of time it takes to acquire an object in dierent possible grasp congurations. Some groups, therefore, present grasp speed as a measure of time to open or close the hand. Presenting hand speed data in terms of total time to acquire an object is problematic since the metric is dependent on the size and shape of the object. In fact, closing speeds that are too fast can be a substantial negative because many myoelectric control schemes rely on the user to stop the hand at the right closing position while it's moving (i.e., no direct position control), excessive closing speed makes that substantially more dicult.

Non-back drivability

A transmission mechanism is dened as non-back-drivable when motion can be transmitted only from the input to the output axis and not vice-versa. Such property enables the actuator to deliver a stall torque without energy consumption, therefore the possibility to switch o the power, once a desired position of the hand or grasp stability has been achieved [7]. Many of the hands incorporate nonback-driveable mechanisms (NBDMs) between the motor and the exion of the ngers. The most common NBDMs include lead screws, worm drives, and roller clutches.

2.1.2 Qualitative parameters

These parameters are the functional parameters that make the design eective. These parameters cannot be measured in traditional means but can be determined as a consequence of the kinematic and dynamic traits of the design.

Adaptability

The design needs to be adaptable in order to grasp various shapes and also must be able to make easy transitions between the grasps. Therefore this trait is a result of an adaptive grasp system.

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Complexity

The design must be less complicated in order to ease up the manufacturing and installing pro-cess. The hand complexity can be easily correlated with the type of mechanism and number of actuators necessary to implement the mechanism. This complexity increases when we strictly adhere to the design connes of hand weight and size. As we increase the number of actuators the weight increases too as a result and if we try to reduce the number of actuators, the resultant mechanism that should perform the dexterous manipulations become more and more complex. Hence there is a need to optimally consider the number of actuators.

Reliability

The reliable design is a very highly desired parameter. This parameter shall be given higher importance throughout. The number of joints and moving parts in a mechanism increases the reliability of the design decreases as the overall reliability of the design is a result of the cumulative reliabilities of individual parts both in terms of function and geometry. Therefore the number of moving parts must be minimal in order for the design to be highly reliable.

Dexterity

The typical ADLs conducted by an amputee can be accomplished using a nite set of predened grasps. These grasp patterns include power (used in 35 of ADLs), precision (used in 30 of ADLs), lateral (used in 20 of ADLs), hook, tripod, and nger point[4]. Some researchers consider certain gesturing to be important. The full range of distinct grasp types for the able hand is greater than 30[9]. In order for a hand to accomplish all seven grasping patterns (six standard grasps plus nger counting), each individual nger exion motion must be controlled with an independent actuator that is not coupled to the other ngers. However, removing the requirement for nger counting can reduce this to a smaller number, particularly if external interaction is permitted, such as a common feature for thumb circumduction axis to be passive and changed by the user. A passive thumb mechanism requires an external force to maneuver the thumb into distinct postures and cannot be moved by the device.

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2.2 A brief comparison of available designs

There is a need to study thoroughly the various state of the art articial hands that can provide valuable design input. The dierent hands available can be divided into

1)Commercial prosthesis

2)Research prosthesis Study of these two dierent types of prosthesis provides a good balance between innovation and eective designs

2.2.1 Commercial prosthesis

There are various dexterous and reliable models available in the market. These designs have been developed considering both the innovative cutting edge technology and the commercial elements as manufacturability, batch production, and customer satisfaction.

I-limb[24]

I limb developed by Touch bionics weighs 460-465 gms has 11 joints and 6 DOF and 6 actuators. Actuated using DC motor coupled with a worm gear and the joints are linked using tendon mechanism linked form MCP to PIP. The thumb circumduction axis is parallel to the wrist and multiple numbers of grips can be achieved. Can be considered as a golden standard for the commercial prosthesis. The motors are placed in the ngers and the thumb abduction motors in the wrist.

Be-bionic[25]

Bebionic developed by RSL Steeper now owned by Ottobock weighs 550 gms has 11 joints and 6 DOF and 5 actuators. Actuated using DC motor coupled with a leadscrew and the joints are linked using kinematic linkage linked from MCP to PIP. And has compliance due to a slot provided at the MCP. The thumb circumduction axis is parallel to the wrist and multiple numbers of grips can be achieved. The motors are placed in the wrist.

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provided at the MCP. The thumb circumduction axis is parallel to the wrist and multiple numbers of grips can be achieved. The motors are placed in the wrist.

2.2.2 Research hands

Research hands are mostly designs that serve as a proof of concept with a limited emphasis on the commercial aspects of the design. Yet they have very innovative solutions to the design optimization of the problems. Most of the designs presented in the research hands are complex mechanisms but provide an innovative and reliable solution.

Manus Hand[21]

Manus Hand was developed by researchers of Spain, Belgium and Israel, and weights 1200 gms. It has 9 joints and 2 actuators one for thumb and others for the four ngers. Also, a Geneva mechanism to switch from exion of the thumb to thumb abduction. It has no adaptive grasp and the thumb abduction axis is toward the thumb at 45 from the wrist. Has very limited dexterity.

Smart hand[5]

Smart hand developed by ARTS laboratory Pontedera, having 16 Joints and has 4 actuators. They are actuated by means of a tendon/spring coupling method. The hand weighs 520 gms. The axis of the thumb abduction axis is at 40 towards the little nger from the wrist. The hand has motors in the palm and has bevel and worm gears giving it a non-back drivable advantage

Vanderbilt[27]

Vanderbilt hand developed by Vanderbilt university weights 580 gms and has 16 joints and 5 actuators. It uses a cable to actuate the hand and has a single cable for each nger. Also has the thumb abduction and the axis is a 15 towards the little nger from the wrist. The motors are embedded in the wrist and the digits have an adaptable grasp. An NBDM is used inside the gear train and coupled to the motor.

My-hand[8]

The SSSA My hand was also prepared by ARTS lab in Pontedera and weighs 478 gms. It has 10 joints and 4 actuators with a Geneva mechanism to shift the exion of the index nger and the

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abduction of thumb. It is an innovative technique called the TISIT. It uses a four-bar mechanism for the ngers and the thumb encompasses the motor used for its exion motion. The thumb is rigid and has no degrees of freedom in the digits. The other ngers have the adaptable grasp.

2.3 Quality function Deployment

The design prerequisites are used to grade and compare the above mentioned hands in order to evaluate and innovate a mechanism for the design. The prerequisites are rst provided with a weight and then the state of the art are compared and scored with respect to these prerequisites.

Table 2.1: Table weightage for prerequisites

Parameter Importance Value

Size Very important 9

Light weight Very important 9

Limited complexity Less important 1

Adaptability Less important 1

Non-back drivability Very important 9

Speed Important 3

Dexterity Very important 9

Grip force Very important 9

Reliability Very important 9

As it has been pointed out that the quantitative parameters can be numerically compared but the qualitative parameters need a dierent means to compare. Hence, these have been compared indirectly by comparing the number of joints, number of grasps achievable and the availability of the thumb abduction/adduction mechanism and the type of mechanism.

Table 2.2 shows us the comparison of hands with respect to the design parameters. As it can be seen the size and weight of all the hands are close to that of the human hand except for the MIT Manus which has been designed as a proof of concept but as a result, has a high

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check the achievable grasps to understand the dexterity. With the above comparison, individual mechanisms of the hand are taken into consideration and again compared against each other with the design prerequisites to come up with an innovative solution

2.3.1 House of quality

The individual mechanisms are compared with each other with the design prerequisites providing the weight for an innovative design mechanism. This comparison is done by using a House of quality approach which prerequisites on the left and the mechanism on the top and individual scores are realized. Also, a comparison is made such that which two mechanisms can co-exist together to solve the exion and abduction movements simultaneously. The design prerequisites are also compared against each other such that we understand the trade-os. The gure?? shows that with the comparison performed the lead screw and worm gear mechanism agree with the prerequisites and also they can be combined with other mechanisms to achieve a holistic design. The mechanisms such as friction coupling, Geneva mechanism, clutch, ratchet and pawl also can be added to these mechanisms.

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Table 2.2: Comparison of the Han ds del

Size, mm, long, wide, thic

k W eigh t, gms Sp eed, deg/sec Num b er of join ts Num b er of actu-ators Th um b ab duction Num b er of grasps Force, N Non- bac k driv- abilit y tu m 180- 182,75 , 35-41 460-465 110 11 6 Av ailable, axis parallel to wri st axis 5 10.8 Y es 198,90 , 50 495-535 95 11 6 Av ailable, axis parallel to wri st axis 5 34 Y es olu tion 50 th per-cen til e 500 103 11 6 Av ailable, axis parallel to wri st axis 5 25 Y es 1200 103 9 2 Av ailable, axis 40 deg to-w ards th um b from wrist axis 4 60 Y es 12 m m longer 520 103 16 4 Av ailable,axis 40 deg to-w ards littel n ger from wrist axis 6 17 Y es hand 190,75 580 225 16 5 Av ailable, axis 15 deg to-w ards th um b from wrist axis 5 20 Y es 200,84 478 175 10 4 Av ailable,axis 40 deg to-w ards littl e n ger from wrist axis 5 20 Y es

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Chapter 3

Design Methodology

Drawing insight from the above techniques to highlight the concepts that can be used in the design a design methodology has been formulated in the design development. From the result of Quality function deployment, the mechanisms that can be implemented to satisfy all the pre-requisites shall be explored and analyzed. These mechanisms shall be conceptualized and some design variants will be developed based on the kinematic and functional requirements of the thumb. These concepts will be evaluated to conclude on a nal design. These designs are then further developed and checked for proof of concepts and then designed for manufacturing after performing a design evaluation. To initiate the process, a brief comparison of the actual hand shall be carried out in order to understand the morphology of the design. The thumb design has been categorized into two stated of motions in terms of functionality which shall be considered under the geometrical constraint of size and weight. The two states are

Flexion-Extention

This is the most utilized movement of the ngers while performing any type of activity. The grasp motion requires the thumb to ex in unison with the ngers depending on the grass. The average range of motion of the thumb exion is 90deg _{with the axis of rotation normal to the}

palm of the hand. The reverse motion is called extension where the thumb is moving away from the ngers. The thumb has the capability to hyperextend for 10 − 12deg_.

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Abduction-Adduction

the ability of the thumb to change its orientation makes it its unique feature and also provides added dexterity in handling tasks. The ability to position the thumb in opposition to the ngers is an abduction. The normal range of motion of this is 98deg_{. As discussed above, this movement}

allows performing additional grasps such as power grasp and cylindrical grasp. The opposite motion of the thumb to return to the lateral orientation along with the ngers is called adduction. The thumb can undergo a hyperadduction motion of about 5deg_.

Figure 3.1: Motions of thumb

3.1 Mechanism inspiration

The fusion of both thumb exion/extension(FE) movements with abduction/adduction(AbAd) movements is particularly dicult as the challenge persists in enveloping both these axes of motions such that the size and weight of the design must not be compromised. Both these motions have perpendicular axes of rotation and in order to obtain complete control over these axes of rotation, there is a need for an innovative mechanism that can switch between these motions. This mechanism has to exploit the nonback-drivability too in order to have an eective grip with ecient power distribution.

3.2 Concept development

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Figure 3.2: Axes of rotation of ngers

and hand overall. Hence, there is a need for a switch from one movement to another when necessary. This prospect is kept in consideration while developing the mechanisms for individual movements.

3.3 A few mechanism concepts

the mechanisms that comply with the prerequisites have been already seen in the Quality function deployment and the house of quality diagrams. The mechanisms that have been truly reliable and have been thoroughly implemented and tested are

1) worm gear

2)four bar linkage operated by crank shaft

these two mechanisms can ensure a good grip force along with maintaining a nonback-drivability, serve exclusively for an ecient FE motion. The AbAd motion needs a separate mechanism yet should not hinder the FE and must be able to make a smooth transition between the Fe and AbAd mechanisms by implementing a switch. The motor controlling the FE should also control the AbAd motion hence the motor should function with two perpendicular axes. some of the mechanisms that can be envisaged for this are

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Figure 3.3: Mechanisms a)worm gear b)fourbar linkage.

2)Geneva wheel 3)Friction wheel

several concepts have been explored by combining these two dierent set of mechanisms including

Figure 3.4: Mechanisms a)Planetary gear b)Geneva mechanism c) Friction wheel mechanism.

the switch. The concepts have been too complicated or too big in size, challenging the complexity and size prerequisites of the design. since the inspiration of the design was realized as my hand the design for FE was decided to remain the same as the MyHand design and for AbAd two approaches were realized. Since the AbAd motion with a nonback-drivability and a switch has

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prerequisite in order to improve reliability.

3.4 Concept evaluation

Four dierent concept designs were imagined, Two with a semi-passive AbAd and two concepts with passive AbAd. These designs were realized by developing the 3d models in CAD software and then compared with each other in terms of the prerequisites and then the best two designs were then 3d printed for proof of concept. After testing these designs are nally sent for full-scale manufacturing.

Figure 3.5: Concept comparison and evaluation.

3.5 Design description

3.5.1 Semi-passive AbAd

Two dierent designs were envisioned by using the similar worm gear mechanism used in MY-Hand. For the AbAd as decided to develop a semi-passive mechanism which used the same worm gear rotation in order to accomplish the AbAd in one direction.

Design 1

This mechanism used an extra gear with an axis perpendicular to the worm wheel and meshed to the lead screw. the FE motion is performed as usual by the worm and screw and the after a complete extension the screw is disengaged with the worm and the other gear attached to

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the screw is engaged with gear and the continuous motion of the screw is responsible for the AbAd motion. Once the nger has performed the abduction completely the motor rotates in the opposite direction enabling into disengage from the AbAd movement gear and re-engage with the worm wheel. The nonback-drivability of the AbAd mechanism is ensured by a ratchet and pawl mechanism that holds 3 individual positions of the thumb in between opposition position and inline position of the thumb. the opposite motion in the AbAd is achieved by applying force to perform hyperabduction which disengages the pawl from ratchet and the nger snaps back into opposition position of the thumb.

Figure 3.6: CAD model of design 1 a) Rear view to highlight the gear meshing of Abduction b)Front view to understand the rachet paul mechanism c) Magnied view of ratchet paul mech-anism.

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AbAd base block. The rotation of the lead screw ensures the movement of the AbAd.and after reaching the motion is nished, the lead screw re-engages with the worm. The nonback-drivability is ensured by the similar mechanism of the ratchet and pawl mechanism including the snap action to get the thumb back into opposition position.

Figure 3.7: CAD model of design 2 a) Rear view to highlight the friction bearing for Abduc-tion b)Front view to understand the rachet paul mechanism c) Magnied view of ratchet paul mechanism.

3.5.2 Passive AbAd mechanisms

To completely eradicate the complexity of including both the FE and AbAd motions in the same actuators, completely passive AbAd designs have been envisioned. These mechanisms have the partial nonback-drivability as they snap position with respect to a certain force applied and can also use geometrical constraints to switch positions.

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Design 1

This mechanism uses the same worm gear mechanism for the Fe but the AbAd mechanism is performed manually by engaging or disengaging a lever using a push button embedded in the design. Also, this mechanism can be snapped by using excessive force to switch between positions.

Figure 3.8: CAD model of design 1 a) Full assembly of the thumb with the button b)trigger mechanism

Design 2

This has the same design parameters of the design 1 but instead of a lever, uses a pin shaft that slides along an inner hole and engages and disengages with the base block. The base block is indented to trap the pin at various positions. This pin can be shifted with a certain amount of excessive external force.

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Figure 3.9: CAD model of design 1 a) Full assembly of the thumb with the pin b)Detailed sectional view of the pin

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Chapter 4

Design evaluation

As seen above the CAD models of the individual designs have been realized and were analyzed. The evaluation of the corresponding designs are presented below

4.1 semi-passive abduction

the two designs were subjected to a preliminary evaluation

4.1.1 Design 1

The CAD model of the design 1 was studied closely and the following issues were reported 1) The possible issues with the meshing of the gears in the abduction block

2) The precision issues with the rotation of the gears which in turn might lead to the meshing issues of the gear

3)the friction and stress issues associated with irregular meshing and continuous rotation of the second gear

considering these issues the design was not developed further.

4.1.2 Design 2

The design 2 seemed to have removed the issues associated with the gears in design 1. The CAD model was further sent for 3d printing and checked for proof of concept. The design worked as

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in the fracture of certain components.

To address these issues, dierent materials such as poly-urethane skin was used to absorb the stresses developed by the friction wheel. This proved to be ineective after certain cycles of usage oo. Other techniques such as using compliant members and reinforcing with composite materials were also explored. All these methods were either too complicated to implement or cost ineective.

Figure 4.1: Design2 3D printed assembly model

Figure 4.2: Dierent types of friction couplings manufactured

4.2 Passive abduction

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4.2.1 Design 1

The 3d printed model was realized and then tested. The performance was impressive and eec-tive. The design presented no fractures or any other aberrations. But the design had a primary aw of accessing the trigger button. The design was made to shift its position using a trigger button or by use of excessive force. It presented issues in these primary aspects.

1) The access to the trigger button was not an easy task while the grasping was occurring. 2) The force required to change the position was greater than realized and was though can produce stresses and heat that might lead to the internal of the mechanism.

Figure 4.3: Trigger mechanism

4.2.2 Design 2

The design 2 was realized and the performance was impressive in all the terms. The design was simplistic and presented no challenges during its transition of positions. This encouraged us to proceed to the design for manufacture stage and the required components were manufactured and assembled.

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Chapter 5

Performance evaluation

The manufactured components were assembled. The weight of the total assembly resulted in 58.6g which is impressive as it is 1/5th the weight of the human hand. Also, The thumb was easily able to transition into dierent positions and with limited force. The design was simplistic and fares well the prerequisites of adaptability due to its 4 dierent positions, reliability due to its minimal number of moving parts, and dexterity. The design was assembled with a motor DCX 10L 6V which exhibits around 22.7N at 7.2 V which is a impressive grip force for a single thumb.

Figure 5.1: a) the full assembled model of design b) the indented abduction block c) Pin engaged to the abduction block

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Chapter 6

Conclusion

The eort to design a prosthetic thumb in the connes of the design prerequisites has been achieved. The parameters of the performance are satisfactory. The thumb can be utilized for the purpose of prosthetic at dierent levels of amputation due to its elegant and simplistic design. It can be integrated with other prosthetic hands easily too due to its design features.

6.1 Future work

The design shall be developed further for implementing the feature of active abduction system. The design 2 in semi-passive abduction system shall be developed further too since its promising performances except for the stress and friction issues.

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Appendix A

A.1 Introduction

The thumb has to perform both exion/extension and abduction/adduction movements using the same actuator. The thumb shall be designed to overcome the moments during exion and abduction movement, also the stresses developed during grasping of an object. The thumb has been designed for 50th _{percentile male hand. The abduction movement has 3}

positions-a) Position 0- this is the default position where the thumb is in fully extended and in opposition used for power grasp and to hold heavier and objects with bigger sizes.

b) Position 1- in this position the thumb has performed adduction, it is used to hold objects with relatively smaller sizes compared to position 0.

c) position 2- this is the extreme end of the adduction position used for key grasp.

Based on these positions some assumptions can be made about the dynamics about the thumb.

A.1.1 Assumptions

The following are the assumptions for the problem to reduce the complexity

1)The weight of the holding object in position 2 is very less when compared to the weight of the object during the position 0. As an extension of the assumption, we can say that the size and the weight of the object are directly proportional.

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A.2 The Problem

The problem can be divided into three parts

1)Flexion- In this stage only the forces acting during the exion motion of the thumb are con-sidered.i.e the forces acting during grasping and the forces due to ratchet but the torque due to motor is neglected.

2)Abduction- In this stage the forces acting during abduction are considered, the motor torque and force due to the abduction spring and also the forces action on the friction rod.

3)Hyper-extension- In this phase the forces acting on the friction rod due to the hyper-extension and their respective moments.

To begin with the problem, we consider the exion phase and the corresponding free body diagram is given in gure A.1

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A.2.1 exion

During exion the xobject remains consistent but yobject and zobject shift along the yz plane

according to the exion position. As per the assumptions made the size and the weight of the body are directly proportional. Hence, for simplicity the object is assumed to be big enough that the nger is in fully extended position while holding it. For generalization, the position vectorRobject shall be consistent irrespective of the exion position due to the uniformity in the

motion along yz plane. Similarly, for the forces in ratchet as the hub rotates along the y-axis, considering this rotation of the axes as local transformations, all the three components remain consistent. Using the FBD and the following assumption we carry out the balancing of the moments and obtain the following eqn A.1. With this result the problem can be subdivided and the stresses developed in indiavidual parts can be analysed seperately.

Robject = q (yobject)2+ (zobject)2 Rr= p (yr)2+ (zr)2 Wobject∗ Robject= Fr∗ Rr Fr = Wobject∗ Robject Rr (A.1) Ratchet

The force Fr imparts stresses on the ratchet. The ratchet shall be realized as a rectangular beam

for simplicity and by using the bending moment equation the stresses developed are realized. the distribution of forces can be obtained from the gure 2.1. Using this we can obtain eqnA.2

Iratchet= b ∗ t3 3 σratchet= Mratchet∗ e Iratchet σratchet= 1.5 ∗ Fr∗ e b ∗ t2 (A.2)

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Figure A.2: Forces acting on ratchet and pinion with the coreesponding vectors. Fp = Fr∗ r2 r1 (A.3) σpinion= 1.5 ∗ Fp∗ r2 b ∗ t2 (A.4)

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Pinion shaft

The pinion shaft can be considered as a cantelever beam with a circular cross section and an uniform distributed load due to the Fr and Fp. Hence, the bending force can be derived as

Wudl= s Fr sin θ 2 + Fp2 .

Let, the diameter of the shaft be dpinion, then the stress in the shaft is obtained as in eqn A.5

σpinionshaf t=

32 ∗ Wudl∗ b

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Abduction shaft

Using gure 1.1 as reference we can understand all the forces acting on the abduction shaft and the moment being caused. In this, we also accomodate the self weight W0 acting on the shaft

which shall be considered as a UDL. The various moments acting on the shaft are listed below and can be comprehended from gure A.3

Figure A.3: Abductionshaft.

1) Moment due to weight Mob= Wobject∗ Robject

2) Moment due to ratchet Mr= Fr∗ Rr

3) Moment due to self weight M0 = W_4l02cd[2l + (d2(2c + d)2]

the total stress developed shall be due to the sum of all moments and assuming the diameter of the abduction shaft as dabdshaf t we get eqn A.6

ΣM oment= q M2 ob+ Mr2+ M02 σabdshaf t= ΣM omentdabdshaf t 2IShaf t σabdshaf t= 32ΣM oment (A.6)

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A.2.2 Abduction

The abduction motion triggers the spring force and also as we use friction coupling, the friction force between the friction rod driven by the motor and the surface are responsible for the motion. For the analysis the position 2 is considered as it has the maximum deection of the spring. and also as the assumption was made the weight of the object held in this position is much lighter and considered negligible compared to the torque and spring forces. Therefore,

Ff ric =

M otorT orque dfricrod

and balancing the moments we get eqn A.7

Ff ric∗ dfricrod + Fspring∗ Zspring = Fr∗ Rr

Fr=

Ff ric∗ dfricrod + Fspring∗ Zspring

Rr (A.7)

substituting this result in eqns A.2 to A.5 and in eqn A.6 the moment due to weight shall be replace by moment due to spring force.

A.2.3 Hyperextention

During the hyper extension the friction rod comes in contact with the friction plate. This ensues a beding moment on the shaft and also die to friction there shall be torque acting on it. By observation, it can be postulated that the maximum bending force and the twist occur at position 2 and can be understood that maximum deection and counter twist occur here. Hence, we can design for the strength of the shaft to with stand the stresses. considering the force acting on the beam as Fnormal

maximumdef lectionδmax =

Fnormall3_{f ric} 3EI I = h 4 3 − πd4_{f ricshaf tf} 32 Fnormall3

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P olarM omentof InertiaJ = h 4 12 − πd4_{f ricshaf tf} 64 γmax= T lf ric G[h₁₂4 −πd 4 f ricshaf tf 64 ] (A.9)

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Using A.9 and allowing the maximum twist possible we can obtain the diameter of the friction shaft and substituting this and the maximum allowed deection into A.8 we can obtain the Fnormal which can dive is the stress developed in the shaft.

σbending= Fnormallf rich₂ h4 3 − πd4 f ricshaf tf 32 τ = T h 2 h4 12− πd4 f ricshaf tf 64

where Torque acting is the resultaint of motor torque and torque due to spring and we get

σtot =

r σbending

2 + τ

2 _(A.10)

A.3 Geometrical parameters

In this section we dene all the parameters used known geometrical parameters and solve the equations. Using the data in table A.1 calculations are carried out for a varying weight of the object.

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Table A.1: Table depicting the known Geometrical parameters

Denition Symbol used value

Distance of object from origin Robject 55mm

Distance of ratchet from origin Rr 8mm

Length of ratchet section b 4mm

thickness of ratchet section t 1.5mm

moment distance e 5mm

Angle of force acting with respect to the x axis θ 40deg

Diameter of the pinion shaft dpinion 2mm

Weight of the object Wobject Varying from 0 to 3 kg

Self weight W0 100gms

Length of the abduction shaft l 6mm

length of the UDl d 3mm

distance of the UDL grom the xed end c 1mm

Diameter of the abduction shaft dabdshaf t 3mm

Nominal Motor torque M otortorque 95N − mm

Diameter of the friction rod df ricrod 7mm

Spring force FSpring currently assumed 4N

moment arm of the spring from origin zapring 1.5mm

Maximum deection in friction shaft δmax varying from 0 to 0.5mm

length of the friction shaft lf ric 12mm

side of the square section h 2

Diameter of the circular section in the square df ricshaf t varying with respect to the

strength of the material

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A.4 Results

Using the varying weight of the object as input, the variation of stresses can be calculated accordingly and compared to understand and choose the required material to be used for the design. The variation of stresses in pinion shaft and abduction shaft can be seen in gs A.4 and A.5. Also the stresses that are developed in the ratchet and the pinion can be seen in gs A.6 and A.7

Figure A.4: Stresses acting on the pinion shaft.

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Figure A.6: Stresses acting on Ratchet.

Figure A.7: Stresses acting on Pinion.

Following the results and forllowing the prerequisite that the σ ≤ 0.3σyieldand σ ≤ 0.18σultimate.

Except for abduction shaft the stresses developed in the rest of the elements are fairly less. The possible material that can be used to manufacture these elements can be observed in table2.2, or atleast the type of material that have similar properties.

The elements with lessesr stresses can be manufactured with materials similar to alluminium alloy as the weight to strength ratio is a favorable attribute. Also for abduction shaft, a materail similar to steel should be a good choice and if possible a material with lesser density and similar properties to steel will be even a better choice. Now using the properties of ASTM514 steel alloy to design the friction shaft in hyper-extension phase. based on the geometrical parametres in tableA.1 and the eqns A.8, A.9 andA.10 , we can obtain the results seen in gsA.8, A.9 and

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Table A.2: Table depicting the Material properties Material Youngs Modu-lus(E),Gpa Shear Mod-ulus(G), Gpa Yield Stress(σyield), Mpa Ultimate stress (σultimate), Mpa Alluminum alloy 70 26 400 455 Steel, high strength al-loy ASTM A514 200 80 690 760 ASTM A36 steel 200 80 250 400 Stainless steel AISI 302 â cold-rolled 200 80 520 860

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A.10.

Figure A.8: Diameter with respect to change in Twist.

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Figure A.10: Shear stress with respect to twist angle

The results show that there will be a lot of sresses developed during hyper-extension and can-not be xed just by using material s with adequate strength but should try to employ compliance in design to allow deformation and provide stress release.

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Appendix B

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C C 105° 195° 150° R5.5 R8 2x 2.5 H7 through 6.5 3 through R2 8 R1 R1 4H7 through 4 ₂ (13.66) 2H7 4 0.5 through 75° 31.65 39.65 R1 22.15 27.65 225° R2 M1.6 through

Artificial Hands Area

The BioRobotics Institute - Scuola Superiore Sant'Anna

Part. N. 5 Denominazione: HUB Materiale: ERGAL Complessivo Denominazione: Passive Thumb Foglio: 1/1 Gruppo Denominazione: Scala: 2 Sottogruppo Denominazione: Data: Sep-18-18

Tolleranze generali UNI ISO 22768 Trattamenti speciali:

Disegnato

Quantità: 1 Controll. Sostituisce il: il Approvato Arch. N°: A B SECTION C-C A(5.000) B(4.000)

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A A B B _17.5 26 6 2.5 2 2.5 2.5 20 3 4x 2 through 4x 4x90 1 2.5 13.75 4x 2 through 4x 4x90 1 R0.5 R0.5 2.5

Part. N. 1 Denominazione: BASEBLOCKNEW Materiale: ERGAL Complessivo Denominazione: Passive thumb Foglio: 1/1 Gruppo Denominazione: Scala: 3 Sottogruppo Denominazione: Data: Sep-18-18

Disegnato

Quantità: 1 Controll. Sostituisce il: il Approvato Arch. N°: = = = = SCALE 3.000 SECTION A-A SECTION B-B Figure B.2: baseblock

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C C B B 8H7 3 R0.5 4 through 14 14 2xR0.5 2.5 1.5 0.5 0.75 5 2.5 7 7 M2 3 1.6 3.8

Part. N. 3 Denominazione: PINASSEMBLY Materiale: ERGAL Complessivo Denominazione: Passive Thumb Foglio: 1/1 Gruppo Denominazione: Scala: 5 Sottogruppo Denominazione: Data:

Tolleranze generali UNI ISO 22768 Ttrattamenti_speciali

Disegnato

Quantità: 1 Controll. Sostituisce il Approvato Arch. N° Detail X Y Depth a 1.83 5.12 through b 1.59 8 see detail A c 2.94 10.71 see detail A d 5.53 12.3 see detail A e 8.56 12.27 see detail A f 11.21 10.54 through a b c d e f = = origin SECTION C-C A SECTION B-B

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0.15 45° 0.15 45° 1.5 4.75 5.5 SR0.75 1.5 2 4.5

Part. N. 1 Denominazione: PIN Materiale: ERGA: Complessivo Denominazione: Foglio: 1/1 Gruppo Denominazione: Scala: 20 Sottogruppo Denominazione: Data: Nov-28-18

Disegnato

Quantità: 1 Controll. Sostituisce il: il Approvato Arch. N°: SCALE 20.000 Figure B.4: Pinshaft

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A _A 8H7 3 2.5 2.5 2 x 1.6 through ₁₄ 3.46 2.79 R0.5 14 4.2 through 5 12.17 8.88 M2 3 1.6 3.8 7 7

Part. N. 2 Denominazione: FLANGE Materiale: ERGAL Aluminium Complessivo Denominazione: Passive thumb Foglio: 1/1 Gruppo Denominazione: Scala: 5 Sottogruppo Denominazione: Data: Sep-17-18

Disegnato

Quantità: 1 Controll. Sostituisce il: il Approvato Arch. N°: = = SCALE 4.000 SECTION A-A

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13.5 4 9.5 3g6 4g6 3g6

Part. N. 6 Denominazione: SHAFT Materiale: ERGAL Complessivo Denominazione: Passive Thumb Foglio: 1/1 Gruppo Denominazione: Scala: 10 Sottogruppo Denominazione: Data: Sep-19-18

Disegnato

Quantità: 1 Controll. Sostituisce il: il Approvato Arch. N°: SCALE 10.000 Figure B.6: Shaft

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Part. N. Thumb assembly Denominazione: PINASSEMBLY Materiale: WRGAL Complessivo Denominazione: Passive Thumb Foglio: 1/1 Gruppo Denominazione: Scala: 3 Sottogruppo Denominazione: Data:

Tolleranze generali UNI ISO 22768 Ttrattamenti_speciali

Disegnato

Quantità: 1 Controll. Sostituisce il Approvato Arch. N° SCALE 3.000 SECTION XSEC0001-XSEC0001 SCALE 3.000

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Design of a robotic thumb for prosthetic application