of applied science - university of toronto t-space€¦ · sheiia hubbard for her suggestions,...
TRANSCRIPT
Deveiopment of A Paediatric Prosthetic Hand with A Two-Degree-of-Freedom Thumb
Paul Xue Bang Hu B.A.Sc.
A thesis submitted in conforrnity with the requirements of the Degree of
MASTER OF APPLIED SCIENCE
in the University of Toronto
O Hu, 1997
Depanment of Mechanical and Industriai Engineering Institute of Biomedical Engineering
University of Toronto
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ABSTRACT
A new paediauic prosthetic hand with multiple grasping patterns was presented in this
thesis. The purpose of this new design was to improve performance of conventionai cMd
prostheses by providing a more hct ional hand. Some speciai mechanisms were designed,
which allowed the thumb of the new hand to be set in different positions. These positions
correspond to common grasping pattern of the naturai hand : palmar, lateral, and
cylindrical/sphericd. A three dimensional cornputer simulation mode1 was built to obtain
proper initial positions of the thumb and fingers. A working prototype was fabncated.
Initial tests focused on the mechanical properties of the hand. Test result indicated that
this new hand met design requirements.
A preliminary hct ional evaluation was carried out with a chiid dternatively wearing a
conventional prosthetic hand and the experimental hand. The purposes of this
investigation were to examine the performance of the new hand and to determine
additionai fiindonal benefits derived fkom using the hand. Results ffom the clinicai
evaluation indicated that the new hand performed as weii as a conventional hand. It had
added functionai benefits in that compensatory body movements were minimired, and a
larger variety of objects could be held with increased stability.
Contributions of this work include development of the first childsized prosthetic hand in
which the thumb can be placed in different positions. A novel mechanism was designed
and built to ennire locking of üiumb rotation during the performance of grasping
activities.
I wouid l i e to first thank Dr. Stephen Naumano for his guidance, encouragement,
support, and for having the confidence to take me on as a graduate student. 1 would also
like to thank Dr. Denise Reid for her encouragement and for help regarding the dinical
evaluation. Speciai thanks go to Ihsan Al-temen for his enthusiasm, expertise,
encouragement and wihgness to help out whenever necessary. Thank you aiso to Dr.
Wfiam Cleghom for his supe~sion and encouragement.
Other major contributon to this work include:
Sheiia Hubbard for her suggestions, clinical contributions and experience;
Sandra Ramdial for her clinicat assistance;
Zigmond Chong and John Hancock for their machining and suggestions in the
creathg of a working mode1 of the experimental hand;
Clients of BlooMew MacMillan Centre who volunteered their t h e ;
My coileagues Kim Parker and Aian Moms for their assistance;
Ail sta f f in the Rehabilitation Engineering Department for providing a
wonderfùl environment;
In addition, 1 would like to thank my family: my d e Doris , rny parents and my parents-
in-law, who always provided emotional impiration and genuine encouragement.
My appreciation for financial support goes to the Rehabilitation Engineering Department
of Bloorview MacMillian Centre and the Naturai Sciences and Engineering Research
Councii of Canada .
TABLE OF CONTENTS
. . ABSTRACT ................................................................................................................... il
... ACKNO WLEDGEMENT S ............................................................................................ III
TABLE OF CONTENTS ............................................................................................... iv ... LIST OF FIGURES ............................ ,.. ................................................................ wii
LIST OF TABLES .......................................................................................................... x
1 . THESIS OVERVIEW ............................................................................................... 1
1.1 INTRODUCTION ................................ .., ........................................................... 1
1 -2 HYPOTHESIS STATEMENT ............................................................................... 3
1.3 GOALS OF THESIS .............................................................................................. 3
1.4 OVERVIEW OF =SIS ..................................................................................... 5
.... 2 . REVLEW: ANATOMY AND MECHANICS OF THE UPPER EXTREMITY 7
2.1 INTRODUCTION ..................................... ... ................................-....--............*...*. 7
2.2 FUNCTIONAL STRUCTURE OF THE NATURAL HAND ................................. 8
......................................................................... 2.2.1 Hand and Its Anatomicai Plane 8
2.2.2 Bones and Joints of the Natural Hand ............................................................. 11
2.2.3 Functiod Activities of the Hand .................................................................... 14
2.2.4 Mechanicd Anatomicai Basis of Prehension Patterns ...................................... 16
........................................................................................................ 2.3 SUMMARY 18
3 . FUVIEW: UPPER EXTREMITY AMPUTATIONS AND THE USE OF
PROSTHETIC PREHENSORS ................................................................................ 19
3.1 INTRODUCTION ............................................................................................. 19
..... ..................................................... 3 -2 UPPER EXTREMITY AMPUTATIONS ... 19
............................................. 3 .2.1 Classification of Upper Extremity Amputations 19
..................................................................................... 3.2.2 Levels of Amputation 21
........................................................... 3.2.3 Estimates of Ann Amputee Population 22
.................... 3 .2.4 Prosthetic Requirements of the Unilateral and Bilateral Amputee 22
............................................................... 3 -3 UPPER EXTREMITY PROSTHETICS 24
.......................................... 3 .3.1 Purposes of Fitting an Upper Extremity Prosthesis 24
........................... .................. 3 -3 -2 Classification of Upper Extremity Prostheses .. 25
3.4 PROSTHETIC PREHENSORS AND RELATED RESEARCH ........................... 28
..................................................................................... 3 .4.1 Prosthetic Prehensors 28
.............................................................. 3.4.2 Presently Available Prosthetic Hands 30
3 .4.3 Areas of Current Research .............................................................................. 35
3.5 SUMMARY ..................................................................................................... 38
........................................... . 4 DESIGN PARAMETERS FOR THE NEW DESIGN 40
............................................................................................... 4.1 INTRODUCTION 40
......................................................................... 4.2 DEFINTNG THE USER GROUP 41
.................................................................... 4.3 FUNCTIONAL CONSIDERATION 43
.................................... 4.3.1 Defrning Proper Thumb Positions for the New Design 44
................. .......... 4.3.2 Digital Adaptations Which Vary the Prehension Pattern .. 46
........................................................................................ 4.3.3 Hand Biomechanics 48
....................................................................... 4.4 COSMETIC CONSIDERATIONS 50
.................................... 4.5 GEOMETRIC AND MATERIALS CONSIDERATIONS 51
........................................................................... 4.5.1 Anthropometnc Dimensions 51
........................................................................................ 4.5.2 Choice of Materials 52
.............................................................. 4.6 OPERATIONAL CONSIDERATIONS 54
...................................................................................... 4.6.1 Motor and Gear Box 54
..................................................................................... 4.6.2 Openingklosing Rate 55
....................................................................................................... 4.6.3 Reliability 55
............................................................................. 4.7 OTHER CONSIDERATIONS 55
4.8 SuMMARY ......................................................................................................... 56
................................................................................................. 6.4.3 Questionoaire 84
............................................................................................................ 6.5 RESULTS 85
........................................................................................................ 6.5.1 WNB test 85
....................................................................................... 6.5 -2 Additional Activities 86
.......................................................................................... 6.5.3 The Questionnaire 90
............................................................................................ 6.6 DISCUSSION ..... ..... 91
................................................................................. 6.6.1 Limitations of the Smdy 91
.................................................................................. 6.6.2 Analysis of Test R e d t s 92
6.7 SUMMARY ...................................................................................................... 95
..................................................................................................... . 7 CONCLUSIONS 96
............................................................. 7.1 SIGNIFICANCE OF THE RESEARCH 96
................................................ 7.2 RECOMMENDATIONS AND FUTURE WORK 97
............................................................................................... 7.2.1 Design Aspects 98
...................................... 7.2.2 Recommendation for Future Clinid Investigations .. 99
........................................................................................................ REFERENCES.. 100
........................................................................................................... APPENDICES 103
..................................................... APPENDIX A: MOTOR CHARACTERISTICS 104
.......................... APPENDIX B : ANALY SIS OF SY STEM SPEED REDUCTION IO5
............................................. APPENDUC C: ANALYSIS OF SYSTEM TORQUE 112
............................... APPENDIX D: ANALYSIS OF CONTACTING LOCATION 114
.................................................... APPENDIX E: ETHICAL CONSIDERATIONS 121
APPENDE F: QUESTIONNAIRE FORM FOR CLINICAL EVALUATION OF
..................................................... THE EDERIMENTAL HAND 129
APPENDIX G: SOME IMPORTANT DRAWNGS OF TEE EXPRIMENTAL
HAND ........................................................................................... 134
LIST OF FIGURES
......................................................................................... Figure 1 . 1 Myoelecuic hand 2
........................................................................................ Figure 2- 1 h t o m i c a l planes 10
........................... ...................... Figure 2-2 Bones and joints of the hand (volar view) ... 11
.................................................... ......... Figure 2-3 Joints and joints axes of the h g e r ... 13
............................................................... Figure 2-4 Joints and joints axes of the thumb 14
Figure 2-5 Six basic types of grasping patterns, as defined by Schlesinger ..................... 15
....................... Figure 3- 1 Classification of upper extremity amputations ..... .................. 20
.................................................. Figure 3-2 Upper limb functional levels of amputation 21
................................................. Figure3-3 Classification of upper extremity prostheses 25
Figure 3-4 Cosmetic hand ............................................................................................. 26
Figure 3-5 A body powered, cable dnven prosthesis ................................................. 27
Figure 3-6 Hook prosthesis ........................................................................................... 28
................................................................ Figure 3-7 Anthropomorphic hand prosthesis 29
Figure 3-8 Hybrid of body-powered elbow and EMG controlled prehensor ............... .... 30
......................................................................................... Figure 3-9 Otto Bock Hands 32
................................................. Figure 3- 10 Variety Ability System Inc . (VASI) Hands 33
Figure 3-1 1 Hugh Steeper Hands ................................................................................. 34
........................................................................... Figure 3- 12 The Southampton Hand 36
................................................................................... Figure 3 - 1 3 The Montreal Hand 37
........................................................... Figure 4- 1 The laterd posture of a natural hand 44
...................... Figure 5- 1 Opedclosing mechanism of a conventional prosthetic hand ... 59
Figure 5-2 The simplified mechanism of the new design ................................................ 60
....................................... Figure 5-3 The thumb locking mechanism .......................... .... 62
................................................................................. Figure 5-4 Various finger designs 64
................................................................ Figure 5-5 Actuator and its reduction system 66
.................................. Figure 5-6 A three dimentional mode1 of the expenmental hand 69
................................ Figure 5-7 Three basic grasping patterns of the experimental hand 71
Figure 6- 1 Functional cornparison between a conventional hand and the experimental
............................................................................................................ hand 87
... Vlll
Figure 6-2 Functional identification of the experimental hand ..................................... 89
Figure 6-3 Score comparing the aspect of Spontaneity of Prosthetics Function ........... -92
Figure 6-4 Score cornparhg the aspect of Skiil of Prosthetics Function ......................... 93
......................................................... Figure B - 1 Traction drive planetary reduction 105
Figure B - 2 Gear planetary reduction ......................................................................... 106
......................................................... Figure B - 3 Spur gear and bevel gear reduction 108
Figure B - 4 Bevel gear and spur gear reduction for the thumb ................ .... ................ 109
Figure B - 5 Bevel gear and spur gear reduction for the rest fingers ............................ 110
Figure B - 6 Sirnplifïed structure of thumb and index finger ......................................... 114
Figure B - 7 Simplified structure of index finger for purpose of geometricai analysis ... 1 16
Figure B - 8 Simplified structure of the thumb for purpose of geometrical analysis ...... 117
1.1 INTRODUCTION
Prosthetic hands are artificial devices designed for people with upper extremity
amputations to provide them some basic functions of natural hands. A survey published in
1988 estimated the number of arm amputees in the United States at 90,000 with about
fi@ percent choosing to Wear prostheses'.
Currently, several commercial prosthetic devices are available. They range fiom passive
cosmetic hands, body harness powered split-hooks, myoelectric hooks, and myoelectric
hands. Despite dEerences in their mechanical systems, control strategies, socket systems
and power sources, most devices only offer a single degree of freedom in the form of a
pincer type fuoction. In contrast to natural hands, these commercial devices are
functionally very simple2. Figure 1- 1 shows a typical myoelectric hand where surface
electrodes on the amputee's residual lirnb pick up myoelectric signals which are amplified
and conditioned to aliow the opening and closing of the hand. It contains a single motor
to allow fingers and the thumb to opedclose in opposition, and thus has one degree of
fieedom. The functional performance of one degree of freedom hands is very limited.
Clinical experience has shown that they do not fulfill the requirements of many amputees3
The lirnited function fiequently results in the prosthesis not being used at all, or being used
only as a cosmetic replacement for the lost limb. More functionality would considerably
improve the utilkation of these devices.
1
Figure 1-1 Myoelectric handz
The concept for developing more fundonal hand prostheses that would allow different
grasping patterns has been in progress for two and a haif decades. Several experimental
hands with more fùnctiom than those avaiiable commercially have been designedJv5. The
challenge, however, has been how to apply these concepts to juvede amputees. In fact,
major prosthesis manufacturers have not adequately addressed the issue of providing
young arnputees with more fùnctionai prostheses. An improved functional ability would
enable them to perform a wider variety of activities.
This thesis presented a unique approach to develop a more functional hand. It involved a
study of major hand grasping patterns of a nahiral hand. It investigated children's
developmental characteristics and their control abilities and determined suit able functions
that are age related. It specified the design requirements of the experimental hand. A
novel design concept was then generated. Cornputer simulation, an effective aiding tool,
was applied to ver@ this design solution. An experimental prototype was fabncated.
Initial tests focused on the mechanical properties of the haad. Test result indicated that
this new hand met design requirements.
A preliminary functionai evaluation was carried out with a child wearing a conventional
prosthetic hand and the experimental hand. The methodology emplo y ed consisted of the
standardized UNB, an analysis of activities, and a questionnaire. Results from these
methods identified additional hctionai benefits of the experimental hand.
1.2 HYPOTHESIS STATEMENT
Providing a t h 6 that c m be positioned by the user of a pros~hetic hand will
remit in greater rrpper limb functional peflormunnc
1.3 GOALS OF THESIS
The goals of thesis were to:
determine the most frequentiy used grasping patterns of the natural hand and
define the motions of the fingers and thumb related to these patterns.
investigate functional requirements and control ability of different age groups
and determine the age group that would most benefit fiom a more functional
hand prosthesis.
spece the design requirements for the expenmentai hand.
develop a design concept and generate special mechanisms for this concept.
build a three dimensional computer mode1 to ver@ this design solution.
fabricate a prototype and perform initial bench tests on this experimental hand.
perform a preliminary cluiical evaiuation to iden* both performance and
funaional improvements of this experimental hand.
1.4 OVERVIEW OF THESIS
Chopter 2 - Review: Anatomy and Mechanics of the Upper Extremi~,
Chapter 2 provides a brief review of hand anatomy, grasping patterns, and
basic phases of hand prehensioa.
Chapter 3 - Review: Wpper Extremity Amputations and the Use of Prosthetic Prehemors
Chapter 3 reviews information reiating to upper-extrernity amputatioas,
current prehensors, methods of control, and provides an overview of current
research.
Chapter 4 - Design Parametersfor the New Design
Design parameters and functionai requirements of the experimental hand are
specdïed in this chapter. This infornation provides the necessary groundwork
for Chapter 5.
Chapter 5 - Design and Deveiupment
In this chapter, ai l procedures involved in the design of the experimental hand
are discussed. The major topics covered are: hardware design, the building
of a three dimensionai computer mode1 and initial tests on the experimental
haad.
Chapter 6 - Preliminary Clinicul Evaluation of the fiperimental Hand
Chapter 6 describes the procedures involved in clinical evaiuation. It details
methods for this clinical investigation and also discusses results obtained
fiom the clinical evaluation and their implications.
Chuper 7 - Conclusiom
Chapter 7 details the significance of this work and recommeodations for
ftture research.
2. REVIEW: ANATOMY AND MECHANICS OF THE
UPPER EXTREMITY
2.1 INTRODUCTION
The skeletai and neuromuscuiar structures of the shoulder, arm, forearm, and hand
constitute the upper extremity. Clearly, this is a biological system of such complexity that,
if it were to be considered fiom all possible points of view, volumes would be required to
describe its anatomy, physiology, and manifold performances. The central point of this
thesis, however, is to design a prosthetic hand with more hnctional ability. Discussion in
this study is therefore directed towards problems related to design of prosthetic hands and
its clinical implication. Consequentiy, anatomicai, physiologicd, and performance data
have been selected ody where they are pertinent to this issue. It should be recognized
that, in meeting the stated objectives, the h c t i o n of the wrist is ignored. Although wrist
and hand movements are CO-ordinated, they can be analyzed independently. In the human
hand, wrist position is important for grip strength. Because of the mechanics of the
prosthetic hand, where wrist position is not correlated to gnp strength, it became
unnecessq to discuss wrist position.
The natural hand is in many ways a perfect instrument. It embodies multiple degrees of
6eedom and is capable of integrated fùnction. Power storage is part of the efficient
physiological system and the actuators have optimal features. It is unredistic to think that
al1 the cnteria and performance specifications of the normal hand could be reproduced in a
7
manmade device3. However, it is possible to downgrade and compromise from such ideal
specifications and to design a realistic hand prosthesis. The main purpose of this chapter
is to analyse the fhctional ability of a natural hand and to determine the hand's most
cornmon grasphg patterns fiom an infinite variety of pattern.
2.2 FUNCTIONAL STRUCTURE OF THE NATURAL HAND
2.2.1 Hand and Its Anatomical Plane
The hand consists of five digits: thumb, index finger, midde finger, ring finger, and little
finger. These digits may alternatively be divided into two parts: fingers, and the thumb.
Fingers consist of joints and bones which have similar charactenstics. The thumb has
slightly dEerent characteristics and is disnissed in Section 2.2.2.
The hand's anatomy consists of 27 bones and over 20 joints, and its kinesiology involves
the use of over 33 different muscles6. Each factor plays a dflerent role in the hand's
functional activities. Bones are respoosibie for rigidity within a segment of a hand, joints
provide the freedom of movement, and muscles serve to move ngid segments on each
other. Since a great part of hand prosthesis design is associated with the motion of the
human hand and the range of motion of a human hzad is restricted by the freedom of joints
rather than activity of musculature7, the study of bone and joint movements will help
designers to determine basic grasping patterns of the natural hand.
In order to analyze the motion of the hand, it is necessary to dehe the anatomical planes
(Figure 2-1). In Figure 2-14 the rotations of limb segments are defined relative to the
matornical planes. Flexion and extension occur in the sagittal plane, abduction and
adduction in the coronal plane, and extemal and internai rotation in the transverse plane.
In Figure 2-1B, the anatomical planes are shown in relation to the body in the standard
position Note that the hands are not aligned with the anatomical planes. In Figure 2- 1 C,
the plane of the palm is the coronal plane. The plane perpendidar to the coronal plane
running the length of the hand is the saginal plane, and the third plane, which is
perpendicular to both the coronal and sagittal planes, is the transverse plane. In the
resting or neutral position, the thumb sticks out fiom the p a h and is not oriented with the
anatomical axes.
Figure 2-1 Anatomical planes"
A) the rotations of limb segments are defined relative to the anatomical planes; B) the anatomical planes are shown in relation to the body in the standard position; C) the anatomical planes are shown in relation to hand in the standard position -
2.2.2 Bones and Joints of the Natural Hand
The hand
The bones of the hand, shown in Figure 2-2 and iisted in Table 2- 1, naturally group
themselves into the carpal bones, comprising of eight bones which make up the wrist and
root of the hand, and the digits, each composed of its metacarpal and phalangeal
segments7. The carpal bones are arranged in two rows, those in the more proximal row
articulating with the radius and uha. Between the two is the intercarpal articulation. The
bony conformation and iigamentous attachments are such as to prevent both lateral and
dorsal-vola (the palm of the hand) translations and also to d o w participation in the major
wrist motions. These are either wrist extension and flexion in the sagittal plane or
abduction and adduction in the coronai plane.
Figure 2-2 Bones and joints of the hand (volar view)'
Carpal bones GM, Greater muitanguiar N, Navicular L, Lunate Tl Tnqueîrum p, Pisifo rm LM, Lesser muitangular Cl Capitate H, Hamate Metacarpal bones M-1, II, III, IV, V First phaiangeal senes FP-1, II, III, IV, V Second phaiangeal series SP-1, II, IIIl IV, V Third phalangeal senes TP-1, II, IIIl IV, V Rc, Radiocarpal IC, Intercarpal CMC(CM), Carpometacarpal MCP(MP), Metacarpophalangeai P R Proximal int erphalangeal DIP, Distd interphalangeai
Joints
Table 2-1 Bones and joints of the hand and wrist'
In each of the fingers, the matornical design is essentially the same. Each finger consists
of four bones (Figure 2-2): metacarpal bone, fxst phalanx bone, second phaiam bone,
third phalanx bone, and four joints (Figure 2-3): carpometacarpal (CM),
metacarpop halangeal (MP), proximai interphalangeal (PIP) and distai interphaiangeal
(DIP). The CM joints of the hge r s are gliding joints and virtudy immovable. The MP
joints are condyloid joints which allows for motion about two axes (Figure 2-3). The
range of motion for flexiodextension is about 90 degrees in the sagittal plane, and 20 to
40 degrees for abductionladduction in the coronal plane, depending on the finger. The
PIP and DIP joints are single axis hinge joints which are capable of dowing
flexiodextension through 90 degrees.
-
Figure 2-3 Joints and joints axes of the fînger6
The thumb
The thumb consists of three joints: CM, MP, P (Figure 2-4) and three bones: metacarpal,
first phalangeal, and third phalangeal. The CM joint of the thumb has two axes of rotation
which aiiow much greater fieedom of movement (Fig. 2-4). The first finger axis runs
through the base of the metacarpai and slants toward the base of the ring finger;
abductioxdadduction occurs £tom metacarpal rotation about this axis. The second axis
runs through the base of the metacarpal but at approximately right angles to the palm;
flexion/extension occurs fkom metacarpai rotation about this axis. In addition to these
pure actions: abductiodadduction , flexion/extension, the CM joint dows for actions
known as opposition and reposition. These actions are not pure actions, but rather
combinations of the four pure actions: opposition = flexion + adduction, and reposition
= extension + abduction.
Figure 2-4 Joints and joints axes of the thumb6
2.2.3 Functional Activities of the Hand
The hand is used in two functional ways. The less common and completely unspecialized
form of usage is as a fixed object on a mobile base with the hand simply being a passive
trammitter of force. An example would include a flattened palm. This form comprises
approximately 20 percent of usage patterns8. The more cornmon skilied use is as a mobile
organ on a mobile Iimb (80 percent of usage patterns).
CYLtNORICAt GRASP
HOOK or SNA?
Figure 2-5 Six basic types of grasping patterns, as defined by chl le singe?
in prehensile use, the band is considered to have two parts, the thumb and the rest of the
digits. Most activities combine the thumb and hgers prehension. It is evident equally
fiom a study of the bone-joint anatomy and fiom observation of the postures and motions
of the hand that an infinite variety of prehension patterns are possible. For purposes of
analysiq however, it suffices to describe the principal types. Seeking a logical basis for
defining the major prehension patterns, ~eller'' found that the object-contact pattern
furnished a satisfactory basis for classification. For photographic observation of
prehension patterns naturally assumed by iodividuals when (a) picking up, and (b) holding
for use common objects, three types were selected fkom among those originally classified
by schIesinge?. These, shown in Figure 2-5, are palmar, laterai and tip grasping pattern.
In palmar prehension, the thumb opposes the palmar surfaces of the index and middle
fingers, comprising a type of
used in daily living activities.
"three jaw chuck. This type of prehension is most ofien
In lateral prehension, the thumb opposes the lateral surface
of the index finger. This position is notably of benefit for holding flat objects such as keys
and cards. The tip grasping pattern is especialiy usefil in picking up srnail objects, such as
toothbrushes and pencils. The hct ional performance of tip grasping is often overlapped
with the palmar pattern. The frequency with which each of these types occurred in the
investigation cited is given in Table 2-2. WMe the relative percentages differ in the two
senes of action, the order of fiequency with which the prehension patterns occurred is the
same. The predominance of "three jaw chuck pdmar prehension in activities of daily
living is the reason that most commercial options of hand prostheses are designed with the
thumb in opposition to the second and third hgers. Both cylindrical grasp and sphencal
grasp are functionaily necessary in grasping cylindncal shape of objects or spherical shape
of objects, since they provide the largest holding surface of the hand, which presents the
most stable grasping ability.
1 Series 1 Palmar 1 Tip 1 Lateral 1
Table 2-2 Frequency of prehension patterns'0
Pick up Hold for use
2.2.4 Mechanical Anatomical Basis of Prehension Patterns
It is convenient to analyze digital mechanics in terms of flexiodexteasion variations in the
digits and thumb postures. The foiiowing descriptions are taken fkom Taylor and
Schlesinger (1 95 5)'.
(%) 50 88
("A) 17 2
("A) 33 10
Individuation of Digital Flexion-mension
Insertion of the flexor and extensor muscle system dong the proximal-distal axis provides
a variety of flexiodextension patterns (Figure 2-3). There are three muscles that act on ail
four digits at once: two of them are flexors, and the third is an extensor. This unequal
distribution of muscles results in more strength in ciosing a hand than when opening it.
Each muscle has one tendon going to each of the four hgers. Each tendon is acted upon
by a separate group of muscle fibers, making it possible to flex and extend the fingers
individudy or as a group. This is important because it means that hgers are somewhat
independent, but not totaiiy since there is common musdature. Two common prehension
patterns; palmar prehension and tip prehension, are related to these fiexion/extension of
digits.
Thu rnb versatility Panernr
The versatility of the thumbs lies, first in the variety of its flexion/extension pattems
(Figure 2-4) and , second in the adjustable rotatory transverse plane in which
flexiodextension can take place. The first of these is directly d o g o u s to the digital
system for the other four digits, in that for any given metacarpal position there are
numerous possible positions of the phalanges. The second effect is due to the relative
mobility of the carpometacarpal joint, which allows the thumb to act in any piane
necessary to oppose the digits. The principal oppositions are semi-direct, as seen in
palmar, tip, and spherical prehensions. Actually, in these cases, the plane of the thumb
action is inched 45 to 60 degrees to the palmar plane. In lateral prehension, the plane is
approximately pardel to the palmar plane.
Hand Movemenis
The three major fiinctional applications of the hand are (1) slow to rapid movement with
controlied rate, intensity, and direction (e.g. playing the guitar, writing, or sewing); (2)
ballistic, or rapid repetitive, rnovement (e-g. typing or piano playing); and (3) the most
specialized use, fixation of the digits including CO-contractions yielding prehensio$.
2.3 SUMMARY
The hand is an organ with an intricate anatomy. It is unrealistic to design a hand
prosthesis according to its natural prototype. The only possible design solution is to set
modest and realistic goals. This chapter bnefly summarizes the characteristics of the
natural hand, determines the most important grasping patterns, and provides a basis for
hand prosthesis design.
3. REVIEW: UPPER EXTREMITY AMPUTATIONS AND
THE USE OF PROSTHETIC PREHENSORS
3.1 INTRODUCTION
This chapter provides a bnef overview of upper-extremity amputations, prosthetic
prehensors, methods of controi, as well'as areas of curent research-
3.2 UPPER EXTREMITY AMPUTATIONS
3.2.1 Classification of Upper Extremity Amputations
Upper extremity amputations are classified as either acquired or congenital (since binh),
involving one or both arms (unilateral or bilateral respectively). Further classification is
according to the level of the amputation (Figure 3- 1).
Figure 3-1 Classification of upper extremity amputations
Acquired amputations are where previously sound upper limbs were removed due to either
trauma or disease. Traumatic acquired amputations are most common among working
age individuals, due to war or industrial accidents. Disease acquired amputations could
happen at any age. The congenital amputee is born with the limb either missing or
incompletely forrned". Approximately three percent of ail amputees are born with
congenital limb absence. Generaily, most adult amputees are traumatic and the majority of
child amputees are ~on~eni ta l '~ .
3.2.2 Levels of Amputation
Levels of amputation are ïiiustrated in Figure 3-2.
(1) interscapdo-thoracic
(2) shoulder disarticulation
(3) humeral neck
(4) above elbow
(5) elbow disarticulation
(6) short below elbow
(7) medium below elbow
(8) long below elbow
(9) wrist disarticulation
( 10) partial hand
Figure 3-2 Upper limb functional levels of amputatiod2
3.2.3 Estimates of A m Arnputee Population
Every year in the United States, a large number of persons lose a hand or an ami due to
trauma or conqenital deficiency. Estimates place the number of arm amputees in the
United States at 90,000 in 1988, with about fifiy percent choosing to wear prostheses'.
Of the f3ly percent wearers of a m prostheses, levels of amputation were estimated as
follows:
Shodder, 5%
Above elbow, 23%
Elbow, 3%
Below elbow, 57%
W r i s h d , 12%
.A more recent survey at The Bloorview MacMillian Centre found ttiat 83% of the children
clients in the Powered Upper Extremity Prosthetic Programme were below-elbow
a n ~ ~ u t e e s ' ~ . Another study also showed that only about twelve percent of al1 amputees
are bilateral arnputees14. The largest population of upper-extremity prosthesis wearers
was that of unilaterai., below-elbow amputees.
3.2.4 Prosthetic Requirements of the Unilateral and Bilateral Arnputee
Since the primary purpose of supplying an amputee with a prosthesis is to provide some
basic hand function, the therapist must first determine the amputation level of an arnputee
and then decide what kind of prosthesis can meet his needs. The level of amputation to a
certain extent determines the prosthetic result. More proximai amputations make wearing
and controlling a prosthetic device increasingly difIicult resulting in a reduction in the
function that can be restored. People with amputations such as partial hand, and wrist
disarticulation are oflen able to rotate their forearrns and also their prostheses. Therefore,
functional restoration will be greater. Below-elbow amputees wearing a prosthesis do not
have the ability to rotate their foreanns but are able to flex and extend their elbows.
For higher level amputees such as shoulder disarticulation, humerai neclg and above
elbow, hctional restoration is often very Illnited.
The prosthesis' fiinctional requirements for unilateral and bilateral amputees are very
different. Because of fiinctionai limitation and lack of tactile sensation with m e n t
prosthetic hands, a unilateral amputee tends to use his natural hand in the dominant role,
while the prosthetic hand is used ody in a supporthg role. It has been observed that a
task that requires oniy one hand will be performed by the natural hand even when the task
is in the worlang range of the prosthetic handlO. The prosthetic hand is used only for
tasks requiring both hands. in such tasks, the prosthetic hand is used in a non-dominant
role mch as holding or positioning an object, while the naturai hand manipulates it15. The
prosthesis' hctional requirements for bilateral amputees are much greater, since bilateral
amputees must rely on the prosthetic hands to perform tasks.
3.3 UPPER EXTREMITY PROSTHETICS
3.3.1 Purposes of Fitting an Upper Extremity Prosthesis -
Loss of a limb through trauma or congenital deficiency can be devastating to a certain
extent. Fortunately, recent advances in technology provide amputees with more prosthetic
options. The purposes for fitting a prosthesis are as foll~ws'~:
To provide an opportunity for an individuai with upper extrernity amputation to
explore ways in which the provision of a prosthesis might enhance his abilities
vocationaliy, in recreafion and in the domestic environmeiit.
To restore or add some functions which are not present because of a lack of part or al1
of the upper limb.
To restore an intact and bilateral body image. It is important to many people that they
look 'complete' to a casual observer. Paradoxicaily, i f h e cosmesis is difficult to
detect, sudden discovery, for instance, when shaking hands, may aiso cause -
embarrassment .
To supply some bilateral nuictional capabiiity. For instance, a prosthesis may be used
as an assistant to the remaining functional hand by holding tools or other objects which
require a two-handed grasp, or as a support against which objects can be held securely
without reliance on an adapted environment.
To produce weight symmetry about the spine. Disturbance to the trunk and spinal -
muscles over a long penod may cause degenerative changes such as scoliosis which
are diflEicult to reverse.
To provide a prosthesis which can be used as an instrument of social communication.
Good cosmesis is ody part of this restoration. It is aiso necessary to attempt as far as
is possible to retain or restore movement and grace to the prosthesis in order to mirnic
the intact upper limb.
3.3.2 Classification of Upper Extremity Prostheses
Prostheses can be classified into the broad categories as shown in Figure 3-3.
1 Upper limb prosthesis 1
Passive a Active a Figure303 Classification of upper extremity prostheses''
Passive prostheses are fked devices and have no controllable action. Some amputees
value appearance so much that they would rather have a cosmetic, passive prosthesis
(Figure 3-4) than any fùnctional prosthesis that is compromised in appearance. Cosmetic
prostheses are not used a great deai, but are very important to those amputees who do use
them, since these hands are more anthropomorphic than any other hands. Functionai
passive prostheses are cornmonly used in recreational activities where durability and a
specific shape of prosthesis are required.
Figure 3-4 Cosmetic hand"
Since passive prostheses have no controllable action, the use of these devices is very
limited. In order to obtain more ftrictions, active prostheses were developed. Active
prostheses have moving components that are controiiaôle by the users. They are either
body (cable) or externally (battery, e.g.) powered. Ifthe prosthetic user has reasonable
body strength, joint mobility, and is motivated, a body powered, cable driven prosthesis
(Figure 3-6) is a reasonable low cost optioni5. The usual 'motor' for a high force/large
excursion requirement is bi-scapular separation Typically this cable powered method is
used to operate forearm flexion andfor hand functional gripping devices. With the advent
of micro-rnotors, high power density rechargeable batteries, and miniature low power
electronic components, the possibilities for prosthetic design have increased considerably.
Routine prosthetics practice can now provide electricdy powered hands and grippers.
Although the control systerns may differ in detail, they aU have certain similarities. A
sensor detects some electromyogram (EMG) change due to muscle contraction in the
residual limb. The sensor signal is fed into a control package and in turn generates an
output which controls a motor. The motor actuates a mechanism which provides motion
to the prosthesis under control (see Figure 1- 1). This strategy is known as myoelectric
26
control, and is the most cômmon method of control of extemal powered prostheses. In
additional to EMG cuntrol, other mtegies such as odoff switch control, force sensitive
resistors controi, and capacitive touch plates control are also used to control
el&tromecb.nical prostheses.
The major benefit to the use of providing extemal power is that effort is considerably
reduced. Since the amount of grip or iifk is limitai by the power which can be applied to
the body powered systems, ody small control forces are required fiom electrical systems.
ln addition, the hamess can be eliminated or . . . and the support loads transferred
to the socket where this is aiiproprïate, and pogtioniog the prosthesis in space is &O
generaiiy easier. The costs ofemploying these techniques are finsinciai, increase in weight,
higher complexity and probable reduction in speed.
Figure 3-5 A body powered, cable driven prosthesis15
3.4 PROSTHETIC PREHENSORS AND RELATED RESEARCH
3.4.1 Prosthetic Prehensors
Prehensors are the termimi devices siîuated on the end of arm prostheses. They can be
hooks, anthropomorphic hands or hybrids12.
Hooks are the simplest of the three (Figure 3 -6). Most of the hooks are of the 'split '
variety, with one stationary and one movable finger giving lateral prehension. They are
cable-operated and have a standard threaded shafl for connection to the prosthetic wrist.
The grasping pattern of these hooks is a three-jawed chuck or palmar prehension. The
advantages of these hooks are durability, simple structure, and low cost. The negative
aspect is the lack of cosmetic appeai.
Figure 3-6 Hook prosthesisu
The purpose of antfiropomorphic hands is to combine hction and cosmesis (Figure 3-7).
These prostheses typicaily have only a single degree of fieedorn with the index and the
middle finger acting together to oppose the thumb. They can be either body or externally
powered and have cyhdricai and tri-digital grasping patterns. The ring and little fingers
are only cosmetic with no functional purpose. The advantages of these hands are that they
are natural hand-like and provide more hction. Negative aspects are cos, lack of
durability and relative complexity.
Figure 3-7 Anthropornorphic hand prosthesis12
As with most prosthetic devices, there are trade-offs in the use of hands and hooks.
Hands are usually preferred when appearance is more important, and hooks are usually
preferred where function is more important. Some amputees choose to use hands and
hooks interchangeably, depending upon the occasion. When working in the garden or
garage, for example, the amputee may select to use the hook: when going out to dinner or
the theatre, the amputee may select the hand.
Because no one prosthesis is a perfect replacement for the human limb, the prescription of
upper-limb prosthetic components is always a compromise between attributes such as
hct ion versus appearance, hook vernis hand, body powered versus externaiiy powered.
For some amputees, a hybrid prosthesis may be the best answer. An example of this is an
above-elbow prosthesis with a body controfled prosthetic elbow and an EMG controlled
prosthetic hand (Figure 3-8). in this case, the amputee may have insufncient body power
for both components or may simply prefer the easier-to-use EMG controlled hand.
Figure 3-8 Hybrid of body-powered elbow and EMG controlied prehensor12
3.4.2 Presently Available Prosthetic Hands
Below-elbow amputees represent the largest group in the upper extremity amputee
population. A myoelectric prosthesis offers these users good cosmesis, fieedom from
hmessing, and superior pinch force when compared to a voluntary-opening hook or
conventional prosthesis. At present, there are only limited Merent myoelectric prosthetic
hands cornmercially avaiiable. The different manufachvers are: Otto Bock (German),
Variety Ability Systems Inc. (VASI) (Canada) and Hugh Steeper (England).
Otto Bock Hands
These hands have become the maiostay of rnyoelectridy controlled terminal devices
(Figure 3-9). They are avdable in four different adult sizes and three child sizes. The
2000 hand, which is the child range of hands, is specidy designed for children ages 3-6
and 5-9 years. The smaller child size hand cornes with duai motor control and is low in
mass(about 120 grams). Pinch force is approximately 51b. which is enough for typical
activities of this age group. The larger child size hand (about 2 10 grarns) is approximately
twenty percent larger than the smaller hand and provides up to 81b. phch force. The 6 ?4
in. hand is for preteens, but will suit some petite women as weil. The 7 !4 in. size hand is
meant for ladies, but can also be used by young men The 7 ?4 inin. hand is meant for the
average patient, whereas the 8 in. hand will provide a better match for males with large
hands. The hand chassis of the 7 % and 8 8. hand are the same; the difference in size is
made up in the inner cosmetic hand and @ove only.
The Otto Bock hands have major parts, such as the chassis and the hgers, made fiom
stampings and therefore WU not stand up to hard work such as farmiag, logging, or even
gardening12. In addition, the PVC @oves, which have not been improved in 30 years, are
easily stained by n e w s p ~ t , dye f?om new clothing, etc. Children in the preschool group
3 1
are these with the highest number of @ove replacements. Based on a recent study at
B ~ O O M ~ W MacMillan Centre, the average preschool child requires 1.7 gloves per
Figure 3-9 Otto Bock Hands
A) Otto Bock 2000 haod without cosmetic glove; B) Otto Bock adult hands
V&t@ Ability System Inc (YASI) Han&
The Variety Ability Systems hc. lightweight W 0-3 myoelectric hand (Figure 3- 1 OC) is
designed to meet the functional needs of very young children in the age range of 1-3 years.
Some children have been fitted at less than 1 year of age. The hand features injection-
molded reùiforced plastic body and hger parts to achieve a low mass of 1 3 0g. This hand
provides approximately 3 A b . pinch force which is enough for this age group of users.
The W2-6 hand is designed to meet the needs of children in the age range of 2 - 6 years.
The pinch force is about 51b. which is acceptable. The W5-9 hand is 20 percent larger
than the W 2-6 hand, and incorporates aii its features. This hand provides 6.5 1b.- 9 lb.
pinch force. The VAS1 hands are known to have outstanding quality and reliability. The
total modular design of the Variety hands makes for simple maintenance. The plastic
fingers and thumb are easiiy replaced, and electronic and mechanical drive syaems are
packageci to aüow easy removal and replacement.
A B C
Figure 3- 10 Variety Ability System Inc (VASI) Hands
A) W 5-9 hand; B) W 2-6 hand; C) W 0-3 hand
Hugh Steeper Hm&
Hugh Steeper hands are available in five different sizes. Two sizes have been available for
several years and are intended to serve children of ages 6 - 8 and 8 - 10 years (Figure 3-
L 1). The other three hands are for adults. AU hands can be used with a myoelectnc
control system. The mass for the srnailest hand is about 270g. This is umecessarily high
and does not compare favorably with the next largest hand, the Otto Bock larger child
hand, which has a mass of 2 10 g, and the W2-6 hand, which has a rnass of only 186 g.
The cosmetic appearance of the hand is also lacking, and the hand body is simply too long
and out of proportion. The overall cosmetic appearance is less than satisfactoryt2.
Figure 3-1 1 Hugh Steeper Hands
Despite individual Werences in design, aii these hands have a cornmon feature in that they
have only a singie degree of fieedom with the index and the middle finger acting together
to oppose the thurnb. Clinical experience has shown that they do not £LEU the
requirements of many amputees3. The limited function fiequently results in the prosthesis
not being used at all or being used only as a cosmetic replacement for the lost limb.
Additional functionality would considerably improve the utilization of these devices.
3.4.3 Areas of Current Research
Development of muitifirnctional prostheses has been in progress for two and a half
decades. Two typical experimental h d s with more complex mechanisms than those
avaiiable commerciaiiy have been designed. These are the:
Southampton Hknd2.
Montreal Fland4.
The Southampton Hand
This experimental hand was designed at the M o r d Orthopaedic Engineering Centre,
Oxford, United Kingdom (Figure 3-12). It is comprised of four DC motors, nine sensors
and control algorithms which are written for a microcontroiler. The design ailows the
hand to perform tip grasphg, palmar grasping, as weil as, lateral grasping, where the
thumb opposes the side of the index hger. The hand is designed to look and move in an
anthropomorphic way to provide a pleasing cosmetic appearance. It was designed to fit
four motors within the natural envelope of the hand. This hand improves the grasping
capabilities of an artificial device, and led to a design which was easily controlled by a user
as it mimics the control system of the natural hand.
C
Figure 3-12 The Southampton Hand
A) Tip grasping; B) Lateral grasping; C) Palmar grasping
The Montreal Hand
This hand was the result of a joint research effort between L'Institut de Montreal and
L'Ecole Polytechnique de Montreai. The design of this hand focuses on the essential
thumb movements (Figure 3- 13). It allows the hand to perform a tri-digital prehension
with two fingers, and a lateral prehension. A preliminary functional evaiuation has shown .
the following advantages4:
it rninimizes the use of body and am compensatory movements during al1 the phases
of prehensioa
it greatly improves the visibiiity of the object.
it dows a better orientation of the object held for use.
Figure 3- 13 The Montreal Hand
Regardless of Merences in design, the Southampton Hand and the Montreal Hand have
two common characteristics: Firstly, both hands can provide more than a single degree-
of-fieedom which improves thw grasping capabilities. Secondly, they are more
anthropomorphic than other designs, providing a wider range of grip postures, under any
control philosophy. These two desigm present the closest resemblance, so far, to the
fùnctional ability of a reai hand. Both designs are a step beyond anything practical that has
been proposed previously or tried for the mature prosthesis user. Both hands are stU in
the development stage and there are many challenges remaioing such as low reliabilïty,
kigh maintenance cost and increased mass, wbich require solutions before they can be
regarded as commerciaiiy viable. In addition, these hands are designed for aduit users.
This represents a problem in scaling d o m the devices to fit into the much smder package
required by a child.
3.5 SUMMARY
In this chapter, a broad ovwiew of upper extremities and prosthetic prehensors has been - presented. Because the terminal device is the most important component of a prosthesis,
it is necessary to choose a control technique that provides the appropnate actuation of that
device. It is thought that myoelectric control provides the most physiologically natural
source of control, and that whenever possible, it should be given con~ideration'~. It is
M e r thought the majority of individuals with upper iimb deficiencies generdy prefer a
hand as a t e r d device. In many cases, this desire may be purely psychological. As -
professionals, however, we need to respond to that need. The majonty of individuals with
upper limb deficiencies are unilateral, with the prosthesis becoming the non-dominant side.
Therefore, it is important that the prosthesis fust meet an individual's psychological needs,
and secondly, that it be easily controlled and provide adequate prehension for stabiliring
objects, which is the prirnary h c t i o n of the non-dominant side during bilateral hand
activities. This would seem to indicate using myoelectric control which best uses the - residual neuromuscular system.
Limited types of myoelectric hand prostheses are commercidy available today. They
offer a single grasping pattern and have potential advantages over earlier body-powered
prostheses. However, clinical experience has s h o w that they do not meet the
requirernents of many amputees3.
Muitifiinctional hand prostheses have potential advantages to provide more prehension
patterns and better cosmetic appearance. They could improve the funaional restoration
and rehabiiitation of inaividuals with upper limb deficiency. However, this type of hand
prosthesis is stdl in the development stage and there are many questions which require
m e r s before it can be regarded as a commercial option. In addition, these hands are
being developed for adult users only. Simple scaling down of the adult version wili not
produce a child shed hand. The development of more functional children's hands will not
only improve cosmetic appearance and quality of grasping, but wifl dso meet their
psychological needs.
4. DESIGN PARAMETERS FOR THE NEW DESIGN
4.1 INTRODUCTION
The human hand is one of nature's most intricate mechanisms. Its loss, therefore, while
presenting one of the most difficult problems in hctional repiacement, imposes upon the
individual a severe handicap both physicaiiy and psychologically. For this reason, therz
has been a great need to develop hand substitutes which in utility and appearance might
bring to the upper limb amputee a new measure of satisfaction and confidence.
As previously discussed, prehension, or the ability to grasp, is the primary fùnction to be
sought in the hsnd design. Many prosthetic designers have been able to devise a hand
replica capable of providing many fùnctions. Complex problems involved in prostheses
designs have led to the development of commercial myoelectric hand prostheses as simple
substitutes offering only one type of prehension "three jaw chuck" prehension. It is clear
that these single degree-of-fkeedom hands are hctionally unsophisticated but reliable and
lightweight. To improve their fimctioaal ability, severai experimental adult hands with
more functional abilities than these avaiiable commerciaily have been designed. Up to now
there has been one major obstacle to develop more functional children's hands: the failure
to scale down an adult version hand to fit into the much smaller package required by a
child. In addition, a number of other factors such as complicated mechaoisms, larger hand
size, increased mass and sophisticated control methods indicate that these adult hands are
not suitable for chiidren.
40
The purpose of this discussion is to determine the possibiiity of mechanisnu which can
replace some of the grasping abiiity of which the n a t d hand is capable. The airn is to set
proper design requirements that could lead to develop a new hand with increasing
h c t i o n The aspects of discussion are divided into the following five broad headings:
defining the user group
fiinctional considerations
cosmesis
geometric and materia considerations
operational considerations
DEFlNlNG THE USER GROUP
Children, as they grow, are physicdy and psychologicdy different in each growth penod.
It is not sufficient to provide every age group of children withthe same type of prosthetic
hand. They mut be provided precisely when appropriate for the abilities and rnaturity of
the childrenlg. Therefore, a keen appreciation of the normal development sequence of
human maturation is needed to provide effective prosthetic interventions during different
growth periods. Table 4- 1 summarizes typical cognitive and psychological milestones and
suggests specific prosthetic interventions for each developmental stage.
Upper fi* u = w j i K - acrivitiesadioordaa&r liend *Acrivi~ebod>.pawered
camiarldnriecrwknchrld brrdl I iamyih
*
Table 4-1 S~ecifk prosthetic interventions for each developmental stagezu
From Table 4- 1, the author concluded that the prosthetic success is not solely dependent
on the type of prosthesis, but rather upon the harmony between the interventions offered
and the developrnental needs and abilities of the particular age group. Curent pincer type
WO-3 and W2-6 hands require iittle operational skiiis and are well niited for users up to
six years of age. There is a need to provide children older than six years of age who have
already developed sufficient physical ability and operational skills with more functional
hands.
Prosthetic replacement of a hand must first of d be based upon a consideration of the
structure and activities of the normal mechanism. It has become evident that
proponionate prosthetic regain is srnalier for the hand than for any other amputation
loss2'. It is therefore vital to ensure that maximum utilization be planned for the person's
remaining abilities. In principle, increased function could corne from an increased number
of independent motionsP. A prosthetic hand with a two-degree-of-fieedom thumb
provides more independent motions. These increased motions contribute more grasping
abiiity which should provide more fùnctional benefits. The objective of this section is to
define what are the proper thumb positions, digital adaptations, and hand biomechanics
needed to increase fùnction.
4.3.1 Defining Proper Thumb Positions for the New Design
The Nonmanipulative Function of a Naturai Hand
As descnbed in Seaion 2.2.3, one of the major nonmaaipulative fùnctions of a natural
hand is to fix hand posture in a tlat geometry and function with the arm/wrist to transfer
force or to support the body in case of falling d o m Occasionally children require these
uses of the hand. When it happens, the hand's laterai posture is important, since the fuily
opened five digits and palm present the largest contacting d a c e of a natural hand
(Figure 4- 1). Pincer types of prosthetic hands Iack their lateral/resting position. The
contact sdace is either the tip of the thumb or part of the hand body, and are limited in
providing a safe support. There is thus a need to set one of the thumb's positions (Pl) on
the lateral side of the experimental hand.
Figure 4-1 The lateral posture of a natural hand *
The Mmipulaiive Funetion of a Nizturd Hmd
The manipulative funclion of a hand is related to its grasping ability. The grasping
patterns are most easily understood by reference to the shape, size, and form of the objects
which the hand is adapted to grasp. Figure 2-5 shows some basic pattern. Almost all
these patterns are related to the position of the thumb. Among these patterns, the
predominant pattern is palmar grasping, making it the pattern of first choice in hand
design. The palmar pattern of a prosthetic hand is aiso used to peiform some tip grasping,
since the functionai performance of these two patterns often overlap in the naturai hmd.
It has be seen that ail the pincer type of prosthetic hands have been designed on this basis.
One of the thumb positions (P2) of the new design will thus be set to allow for palmar
gr= P.
No doubt the palmar grasp is the moa important grasping pattern. In pradce, however,
this type of prehension result in an artificial hand which is not particularly effective in
some situations. The hand cm obscure the user's view, and vision is so important when
there is no sensation in the artScid hand. In addition, the positioning of the thumb makes
it difficult to grip and pick up flat shaped objects from a flat surface, a difficulty which is
funher compounded by the rigidity of the gripping surfbces of the average artificial hand24.
Visibility of an object to be picked up or held is needed for efficient prehension This can
be achieved by using a lateral movement of the thumb against the side of the index finger.
In the artificial hand, provision of a 'key' pinch has several advantages: firstly, the user can
see both the object and the thumb action readily; secondly, the thumb moves in a plane
much more nearly aiigned with the horizontal; thirdly, it provides a good base for a 45
suitable grip and can d o w a long object such as a card, to be held satisfactorily.
Therefore, this position should not be neglected in any prosthetic hand design2O. Position
1 defined in Section 4.3.1 is also used to perform the lateral grasping pattern.
Both the cylindrical grasping pattem and spherical grasping pattern are tùnctiondy
important. They provide the most stable grasping fûnction when grasping cyliadricai
objects or spherical objects, since all digits make contact with the surface of the object.
To restore t h function., the thumb of the experûnental hand should have a position (P3)
opposite to the rniddie and ring fhgers.
4.3.2 Digital Adaptations Which Vary the Prehension Pattern
No discussion of the functionai potentiaiities of the naturai hand can omit mention of the
digital movements, whether carried out singly or in innumerable pattern other than simple
prehension. So varied are the possibilities that there is no accepted classification of finger
movements based upon digital mechanics. The problem of digital mechanics in the
artifïcial hand is chiefly one of determinhg how m q digits can be made operable. Three
methods have been used20.
In the first, flexible finger coupling has been employed to permit conformable grasp of
irregular objects. In prehension, each finger flexes until it lodges solidly against the object
or the palm of the hand. Theoretically, such a pattern emulating the conformable
prehension of the natural hand is desirable, but in practice mechanical operation of such a
46
system bas been unsatisfactory. Failure has been rnostly due to the generally slow
operation of the fingers, since each mua flex into a stable position before grasp is certain;
in addition, the flexible couplings necessary for such an operation are difncult to make
mechanicaiiy efficient.
The second method, which is the mon used method so far, is to make digits II and III,
close coupled in action, while digits IV and V are passively flexible "floaters". T hus,
palmar prehension and tip prehension are secured by opposition of the thumb to digits II
and III, while the flexible and elastic character of digits N and V permits a satisfactory
approach to progressive flexion The comparative views of the sound hand and the hand
designed by this method, show the extent to which ths type of artificiai hand can
satisfactonly be designed to meet both fiuictional and cosmetic goals. The only weakness
of this method is the lack of contact surface, since the digits IV and V are passive1 y
flexible "floaters" .
In the third method, the four digits are rigidly interco~ected so that they flex as a unit on
the simulated metacarpophalangeal articulation. This arrangement avoids the instability of
the first design and increases the contact surface of the second design. This feature is also
important to a natual-appearing grasp and fllnctionaily necessary to support the thumb in
Position 3. The disadvantages of applying such a method are increased manufacturing
costs and the greater mas of the prosthetic hand.
Since the third method shows more advantages than the others, the author decided to
apply this method in the design study.
4.3.3 Hand Biomechanics
In determining the forces of grasp which should be provided in the artificial hand,
knowledge of the forces requires in everyday living tasks, and of the forces possible in the
natural hand, is usehi. Moreover, the adjustment of strength of grasp to the job
requirements (graded prehension) and the maintenance of grasp (isometric prehension) are
natural features which should have their counterpart in the &cial hand.
Prehension Force Requirements
Measurements of prehension forces required in the manipulation of common objects and
other activities of everyday M g have been reported by ~eller". A strain gauge placed
over the paimar pad of the thumb served to register the forces. Examples are given in
Table 4-2. From the design point of view, the average pinch force for children's hand
prostheses shouid be about 4 Ib. to 8 lb.
1 Doorknob (survey of 13)
/ Pulling on sock i
r- i Manipulation of screw cap i f I
B
Holding tablespoon
3-in. diameter, fïli with
water, total weight, 0.7 lb.
2.2-in. average diameter;
average torque to operate,
3.1 in.-lb.
Prehension of folds of sock
Conventional toothpaste
tube; 0.5-in screw cap
Spoon weight, 0.121b., held
as for drinkùig soup
Table 4-2 Prehension force* in manipulation of common objectsLO
* Minimal force necessary to perform the activities
Isometric and Graded Prehension
An important characteristic of the natural neuromuscular mechanism is its ability to
maintain grasp over long penods of time without undue strain. Replacement of this
fiinction in the artificial hand is a special problem which has been met in Merent ways by
prosthetic hand manufacturers. Of many design attempts, the method applied in the VAS1
hand is weil accepted and considered as one of the most successful design solutions. The
core of this method is to instail an aoti-roilback mechanism at the output shaft of the gear
box. Grasp of an object can be maintained and the digits are prevented fiom rolling back
even if the motor is turned o t i
In the design of the artificial terminal device, another feature of natural prehension
requires special attention1'. It is that the naturai hand, by utiliring sensory feedback fiom
weight and slippage mes, is able to quickiy and adequately correct prehension forces to
the necessary value for firm grasp. But feedback mes are sensed very imperfectly by
transmission through the artificial mechanism or by vision where using a prosthesis. The
author will not consider this aspect within this study.
An artifïciai hand, in order to be bctionai, must be on continuous display. Because it can
not be hidden, cosmesis is an a very important element in patient acceptance (see Section
3.5). Whiie the amputee would like to have a nanird arm and hand, if this is not possible
one would prefer to at least appear normal, or to attract the least attentionz5. Cosmesis in
a limb, however, is not just 'static cosmesis', Le., the appearance of the prosthesis when at
rest, but includes a much more important component, and one which is difficult to
simulate: the appearance of the prosthesis when in motion, a feature which has been called
' dynamic cosmesis'.
This interdependence of cosmesis and a movement pattem is not a simple issue. It is made
up of both the pattern of movement, which should correspond to a normal movement
pattern, and the spatial configuration or positions taken by the Werent parts of the hand,
arm or shodder under the influence of outside forces, such as gravity, or intemally
50
occurring forces, such as those arising fkom inertia. In previous prosthetic design, very
tittle attention was paid to this factor. It is often the absence of an appropriate grasping
pattern, which destroys any illusion based purely on static cosmesis.
An alternative approach, common in prosthetic design over many years, is to provide an
artScid hand with a glove covering (see Figure 3-4). This only improves the 'static'
cosmesis of the prosthesis but not its 'dynamic' cosmesis. To avoid unnatural,
compensatory body movements and thereby to irnprove both 'static cosmesis' and
'dynamic cosmesis' of the prosthetic band, the hand's design should incorporate at l e s t al1
three basic grasping patterns: laterai, palmar and cylindncaVsphencal grasp.
4.5 GEOMETRIC AND MATERIALS CONSIDERATIONS
4.5.1 Anthropornetric Dimensions
The cosmetic acceptance of a prosthetic hand is not only related to its shape, but also to
its size. Ideally, the size of an appropriate prosthetic hand should be as ciose to a natural
hand as possible. The uiformation on average anthropomeuic dimensions of a natural
hand for various popuIations is availab~e~~. Table 4-3 shows a list of such data. This set
of data was taken fiom average sizes of chiidren ages 6.5 - 8.5 years and was used as a
reference for the design work. The challenge for the author was how to incorporate
structurai and mechanical components into this size limitation.
L
1 , Thumb length 4.8 i 0.4 1 t
/ Thvmb diameter i
1.54 0.9
1
Index finger length 5 -3 0.3 1 l
F
Index finger diameter i 1.19 0.8
Middle finger length s
1 J
Table 4-3 Anthropometric data for children ages 6.5 to 8.5 24
I I 5 -9 L i 0.4
I
4.5.2 Choice of Materials
1 Middle finger diameter -
The selection of the best material for hand fabrication involved - a compromise of several
factors: feeling and weight, processability, se~ceability and permanence. No single class
of materials now known represents the optimum in ail four respects. It is of interest,
therefore, to d y z e the characteristics of various available materials in the light of these
factors and to draw conclusions as to the material representing the best compromise.
1.22 0.7
Feeling and Weiglt
Since a prosthetic hand is usually used daily, a heavier hand would more likely to be
rejected by users. Keeping the weight of this type of temiinal device within acceptable
iimits is one of the major goals in hand design. Ideaily, materials should be as light as
possible. The thermal conductivity and heat capacity of nich materials should be low so
that they wiIi present to the touch a mturdy warm feeling.
"Processability" refers to the ability of a material to be formed into a hand. Considering
the complex shape of the hand, a matenal that can be easily formed into a desired shape
without shrinkage is considered as a suitable material.
"SeMceability" implies durability of a material. As indicated before, the average life of a
paediatnc prosthetic hand is about two years. Although the durability of a hand does not
completely depend on its matenal, a hand made of durable materiais wiii help minimize the
mechanical failure.
"Permanence", that is, retention of the original characteristics for a reasonable time under
service conditions, is almost too obvious a requisement to need mention, yet it is a most
dinicult quality to achieve. In some cases, permanence of mechanical properties, such as
strength and shape, cm be gained ody at the expense of tirne. Both shape and mechanical
properties of such a materid should be retained in spite of exposure to sunlight, heat, and
cold, etc.
4.6 OPERATIONAL CONSIDERATIONS
4.6.1 Motor and Gear Box
ln order to s impw the design, the author used the available VAS1 5-9 motor and gear
box. The specifications of the motor are listed in Appendix A- The motor shaft is also the
input shaft of the gearbox. The gear box contains two planetaq reduction systems. The
first system is a fixed ratio planetary traction drive system. This system reduces the
rotational speed by a factor of 8.34: 1, while increasing the system torque by the same
factor. Simiiariy, the second planetary drive fùrther reduces the rotationai speed and
increase the system torque by 5.08: 1. The combined reduction factor is thus 42.32: 1.
Further stages of gear reduction are discussed in Chapter 5.
4.6.2 Openingklosing Rate
T heoretically, increasing the opening/closing speed wili increase the ability to grasp -
abjects quickly for the amputee. However, the motor and reduction system limit the
product of torque and rotational speed. If the opedclosing rate is rnaximized, the result is
a low pinch force; in nûn, if the pinch force is maximized by large speed reduction, the
open/closing speed is low. Until new, higher torque moton are produced, this
compromise will remain. For this design, the author set an acceptable cycling time corn
maximum open to maximum closed at about 1 second. -
4.6.3 Reliability
Generally, a prosthetic hand should be able to cycle 250,000 times without breakdown in
order to operate maintenance free for one yea,?. The experimental hand designed by the
author undenvent such a reliability testing .
4.7 OTHER CONSIDERATIONS
In addition to the specific problem aiready outiined, other factors such as total mass,
operating noise level, maintenance and repair also need to be considered. Generally, a
more functional hand rnay require increased mass, since more parts may be used in the -
design. A mass of 275 gram is considered acceptable for a child prosthetic hand".
4.8 SUMMARY
The goal of this section was to define the design parameters for a more functiond
prosthetic hand than those currently available. in principle, increased function could corne
from an increased number of independent motions20. A prosthetic hand with a two-
degree-of-fieedom thumb facilitates grasping pattern which provide more functional
benefits and improve both 'static cosmesis' and dynamic cosmesis' of the prosthesis.
Specific design requirements are:
The thumb has two-degrees-of-freedom. It can perforrn the opening/closing function
with fingers in a plane, and it is also able to change the orientation of the plane by
moving to different positions perpendidar to the first plane. It can be set manually in
three difEerent positions within this second plane. Position 1 (Pl) is related to the
band's nonmanipulative fûnction, lateral grasping pattern and 'static' appearance.
Position 2 (P2) provides palrnar grasping pattern. Position 3 (P3) provides cylindncal
grasping and spherical grasping pattern.
The thumb should rotate fieely when it is moved to any position in the positional
plane, and will be locked in position when the thumb pelforms holding/closing fùnction
with fingers in the fhctional plane.
Ali hgers will be comected to the same shaft (hger shaft) to perform action
together.
The p h and fkger segments should resemble the human mode1 (age group 6.5 to 8.5
years) in both configuration and proponion.
The opening distance should gradudy increase from P 1 to P3, as the size of objects
held increases.
The hand should be powered by a single motor.
The gearbox unit should be taken fiom a VASI hand drive which is self-locking.
The experimental hand should be able to cycle 250,000 times without fadure.
The minimum open/closing tirne should not exceed 1 second.
The pinch force should be 4 lb. - 8 lb.
The total mass should not exceed 275 grams.
The hand should be modular in design, easiiy allowing for replacement of components.
The materials used for fabrication should foIiow the conditions tisted in Section 4-52,
5. DESIGN AND DEVELOPMENT
5.1 INTRODUCTION
In the surnmary of Chapter 4, the author specifïed all the necessary design requirements
for the new experimental hand. In this chapter, the author presents the design approach to
meet these requirements. This chapter consists of three major areas: a) design hardware;
b) construction of a three dimensional model; c)initial tests on the mechanicd aspect of
the experimental hand. The main goal of this chapter is to introduce readers to a unique
design solution to meet the design requirements indicated in Chapter 4.
5.2 HARDWARE DESIGN
5.2.1 Method for Obtaining Different Grasping Patterns
As indicated in Section 4.3, a prosthetic hand is considered as fùnctionally sufficient if it
can provide three basic grasping pattern positions: palma-, lateral and cylindedspherical.
Since ali these patterns are related to the position of the thumb, a possible design solution
is to design a hand with a two-degrees-of Ereedorn-movement thumb.
Before starting to design such a hand, the question of "how to position the thumb?" has to
be answered. Since there are strict limitations on mas, size and energy consumption,
only a single motor is used in the design. The only function of this motor is to perform
58
openingklosing of the hand. Positionhg the thumb would be through passive control
such as using the other band to push the thurnb into position.
The remaining challenge is how to maintain the hmd's opening/closing function with the
thumb in each different position.
The conventional hand uses two pairs of spur gears to t rader rotation firom the motor to
the thumb and fingers. Since the thumb and fingers only have one-degree-of-freedom,
bey are limited to move in one plane (openinglclosing plane). Their gears are able to
mesh with the motor output gear all the tirne. Rotation of the motor output gear drives
the thumb and hgers to opedclose simultaneously (Figure 5-1).
Figure 5-1 Open/closing rnechanism of a conventional prosthetic hand
UnWre this one-plane of movement the thumb of conventional hand, the thumb of the
experimental hand has to be moveable in two different planes: openingklosing in the same
plane as the conventional hand, and in a plane perpendicular to that plane (see Chapter
59
4.8). Cleariy, this rquires a different design approach. A simple solution wodd be to
use bevel gears to achieve this tw~plane of movement thumb (Figure 5-2). The
characteristic of a bevel gear is its capability of meshing together when the direction of
rotation is changed The thumb bevel gear is able to rotate mund both shaft x-x and
SM y-y. Rotation around shaft x-x results in the thumb changing its orientation with
respect to the paim, and rotation around shaft y-y produces openinglclosing of the thumb
with respect to the fhgers. Ali hgers are connecteci with the same SM z-z and are able
to rotate around sh& z- t By meshing the finger gear with the motor output shaft and the
thumb bevel gear with driving gear, the thumb and fingers are able to opcn/c!ose
simdtaneousl y.
RING FINGER- ,-MIDDLE FINGER
F 1 NGER GEARS
MOTOR OUTPUT
HOTOR IiUTPUT
1 NGER
I I I \
Figure 2-2 The simplifed mechaniam of the new design
5.2.2 Method for Securely Holding Objects
An important characteristic of the naturd neuromusdar mechanism is its ability to
maintain grasping over long periods of t h e without undue strain. To replacement this
feature, the author designed a special thumb-locking mechanism to lock the thumb into its
position and appiied the available anti-rd back mechanism to prevent the thumbhgers
nom rolling back. The combination of these two mechanisms ensured the secure
grasping of objects.
Thurnb-Locking Mechanism
One of the design requirements is that the thumb cm be moved to different positions
manuaiiy. The force that pushes the thumb to its positions cornes fiom the aid of other
hand or other objects. Since the thumb bevel gear meshes with driving gear al1 the M e ,
the force required to rotate the thumb bevel gearhhumb around shaft x-x t3erefore is very
small, which is good for young users.
During the hand's closing/holding period, even a s m d i fiction force between objects and
the thumb will easily cause the thumb to slip from its position. To prevent this, the author
designed a speciai mechanism which proved to be an effective method to lock the thumb in
position without any movement during the holding period.
This thumb-locking system has two basic features: when the hand is fully open (fully
abduction), the thumb can be moved into dserent positions by a very small force in
positionai plane, and when the hand is closing or holding, the thumb is locked in its
position and is not ailowed to move in this plane.
The mechanism of this design is shown in Figure 5-3. When the hand is fully open (fùlly
abduction), the locking pin disengages from the thumb fiame. This allows for rnovement
of the thumb in the positional plane.
Figure 5-3 The thumb locking mechanism
When the hand is closing , the rotation of the motor bnngs the rotation of the sh& to a
locking position. The locking cam attached to this shift also rotates. The rotation of the
cam drives the locking pin to move upward into a hole located in the thumb frame, which
causes locking of the thumb.
A spring-bail set is instalied in the hand body with its bal1 end touching the positioning
hole in the thumb fiame. There are three positioning hole in the thumb frame which
represent the three positions of the thumb. The feanire of using this spring-bal1 set is to
dlow the thumb to move in the these positions like a ratchet.
Anti-Roll Back Mechanism
Another design requkement is that once the hand's pinch force reaches its maximum
torque, the electric circuit will automaticaiiy switch off the motor. This prevents the
motor fiom overheating and aiso reduces the consumption of battery energy. Since the
motor is reversible, once the motor stops working, the pinch force pushes the
fingers/thumb back, which causes the lose of grasp. The thumb-locking mechanism is only
good at locking the thumb in the position, however, it can not prevent reverse rotation.
To avoid ths, the author applied the VAS1 hand's anti-roll back mechanism (built in the
motor-gear box) in the new design, which eliminates this reverse rotation.
5.2.3 Design of the Thumb and Fingers
A good deai of attention has been given to the development of the thumb and fingers to
permit as much versatility in prehension operations as possible and yet maintain a normal
appearance. Robotic research has developed to replace several fùnction-specific industrial
grippers with a single dexterous prehensor capable of grasping and manipulation objects
with a variety of shape and size. Related topic include finger contact m o d e ~ s ~ ~ ~ ~ , grasp
~tabili ty~~, and sliding theoV3'. In the field of prosthetic design, many designs, ranging
fiom simple one-piece fingers to those with interiinked, articulated fingers have been
fabricated and t e ~ t e d ) ~ (Figure 5-4).
Figure 5-4 Various finger designs3*
Of these designs, the author decided to constmct monocoque fingers. These fingers
provide lateral stability and are capable of retaining objects without the tendency to propel -
them out. Al1 four hgers in the experimentai hand were arranged to operate together to
reduce instabiiity. The thumb used a geared articulated design which appears to offer a
number of advantages, not only because it can be used to reduce speed but also because it
has a tendency to force into the optimum position of grasp any object contacted in the
prehension operation.
5.2.4 Method for Obtaining Proper OpeninglClosing Rates and Pinch Force
In order to meet the design requirements listed in Chapter 4, the author used the following
gear reduction systems to obtain an appropriate pinch force and a one second
opening/cIosing rate. Options for choosing the motor and its gear reduction system were
either to use a powemil large motor with î low gear ratio or a srnall motor with a high
gear ratio. The motor used in the new hand is a VAS1 hand motor (see Section 4.6.1 ).
This is a srnall motor with high speed. To reduce the speed and increase the output torque
, two major steps of reduction were used in the new hand: firstly, a motor-gearbox
reduction section built into the VAS1 motor; and secondly, a gear reduction system
designed by the author to obtain the proper pinch force and openinglclosing rate. Figure
5-5 shows a flow chart of the total reduction system. Detailed analyses of the gear ratio
and pinch force are presented in Appendix B and Appendix C respectively.
1 Motor 1
Traction Drive n Gear Planetary Reduction n
Reduction
Bevel Gear Reduction Spur Gear Reduction
Spur Gear and Bevel Gear Finger Shaft
Figure 5-5 Actuator and its reduction systern
5.2.5 Contacting Points
Since the thumb and fingers rotate independently in different planes at different speeds, it
is necessary to determine the location of the thumb and fingers at any given tirne to ensure
that the location of the thumb matches the location of fingers at their end points to form
each grasping pattern. Using the formula listed in Appendix D, the author obtained the
proper contacting location of both the thumb and fingers.
This hand's openingklosing consias of two difTerent rotations: the rotation of the fingers
(represented by the index finger in this analysis) and the rotation of the thurnb. The
cdculation for the rotation of the index finger is relatively simple, since the finger only has
one-degree-of fieedom. The anaiysis of the thurnb involves two steps: rnoving the thumb
to each position, and opening/closing the thurnb. The coordinated rotation of the thumb
and the finger creates these patterns which are similar to basic grasping patterns of a
sound hand. The detailed analysis is presented in Appendix D.
5.2.6 Materials Used in the Design
A nurnber of different materials were available, none of which had the optimum propenies
listed in Section 4.5.2. Since the material requirernents for different segments of the hand
are different, the materials selected here represent the best compromise available at the
time.
-
The hand body was made fiom delron. This material d o w s for consistent dimensional
control of the finished product. The thumb's cover, which protected the imer
components, was made hom aluminum. Fingers and thumb were fabricated from Zytel
ST8O 1, which is a 'super-tough' plastic providing excellent impact resistance. NI the
gears were made fiom s t d e s s steel which provides high strength and high Wear
resistance.
5.3 THE APPLICATION OF CAD IN THE DESIGN OF THE
PROSTHETIC HAND
5.3.1 Introduction
A cornputer software package, I-DEAS~~, was used to model the hand in a three
dimensional form. This geometric mode1 was then used for mass properties calculation,
interference studies, stress anaiysis, and manufacturing planning. This three dimensional
model is shown in Figure 5-6. By checking the geometry, the relative motions of the
fingers, thumb, and the possibility of interference, the author was able to obtain proper
hger lengths and joint angles corresponding to the different grip pattern. The application
of this technique was expected to shorten the design time and reiiuce the manufacturing
cost by allowing correct choices to be made.
5.3.2 Construction of the Hand Morphology
The geometnc dimensions of the h g e r s and the paim were based on selected average
values of the natural hand for the selected age group. Points and lines were used to
generate a two dimensionai structure. This was then converted to a solid to obtain the
extemal shape of the experimental hand. Fingers and thumb positions were then adjusted
and orientated to their flexion planes and angles in order to visualize the obtained grasping
patterns. Successive trials were used in order to obtain a physiological prehension without
interference. Finaily, the proper initial positions and joint angles for al1 segments were
determined.
Figure 5 4 A three dimentional mode1 of the experimental band
A) Palmar grasping patterns; B) Tip grasping pattern; C) Lateral pattern
5.4 INITIAL TESTING OF THE EXPERIMENTAL HAND
5.4.1 Introduction
M e r the design concept was verified by the 1-DEAS software, a prototype of the new
prosthetic hand was fabricated at the BlooMew MacMillan Centre. Initial tests on the
experimental hand focused on measuring the performance of various parameters that affect
fiinctionality of the prosthetic hand without involving users. The purpose for these initial
tests was to determine if the new hand met the design requirements listed in Chapter 4.
Any functional tests involving the users are discussed in Chapter 6.
The initiai testing of the new hand was divided into the following four broad headings:
finctional aspects
geometric aspects
operational aspects
'static' cosmesis aspects
5.4.2 Functional Aspects
The thumb has two-degrees-of-freedom. The thumb cm be manually set in three dserent
positions to form the major grasping patterns of lateral, palmar and cylindncal/spherical
grasp. Figure 5-7 shows these three thumb positions. The thurnb can be easily rotated
and is M y locked in the position when the hand starts to closehold. Al1 fingers are
coupled when opening or closing. The coordinated performance of the thumb and fingers
achieves grasping patterns simiiar to those of a sound hand.
Figure 5 7 Three basic grasping patterns of the experimental hand
A) cylindricaUsphencal position; B) palmar position; C) lateral position
5.4.3 Geornetric Aspects
Geometric parameters are those that are primarily based on the extemai dimensions of the
prosthesis. Ideally, the size of an acceptable prosthetic hand should be as close to the
natural band as possible. The average anthropometric dimensions of the natural hand for
ages 6.5 to 8.5 years are listed in Table 4-3. The measurement data on the new hand are
iisted in Table 5 -1. Clearly, the anthropometnc dimensions of the experimental hand are
quite close to the natural hand with the exception of thumb length. In addition, hrther
refinement is needed for the shape of the hand palm and some segments.
13.6 1 12.7
r
i Hand breadth i
b / Thumb length
i T
i 6.4 6.37 4
i --- ?
6.2 1 4.8 I i
1 Thumb diameter
I
f 1.54 1 -44 !
I
! Index fhger length
t
1
5.3 5.34 f
j
/ Index fhger diameter
1 Middle finger diameter
---y 1.19 1 .O3 i
i Middle b g e r length
f
Table 5 1 Anthropometric dimensions of the experimental hand and the natural hand
! 5 -9 5.42
I
5.4.4 Operational Aspects
T e h g of operationai aspects focused on three areas: mechanical reliability,
openingklosing rate and pinch force.
Mechanical reliability of the experimentai hand was carried out by performing long-term
bench tests. The new hand underwent 10,000 cycles in the lateral position, 10,000 cycles
in the palmar position and 5,000 cycles in the cylindricalI sphericai position. The total
number of cycling was 25,000, about a tenth of the average life span of a prosthetic hand.
The method for measuring the opening/closing rate was to set the thumb in different
positions. In order to obtain accurate rate, the experimentd hand was cycIed 500 cycles
in the three different positions. The author obtained the followhg information:
in the lateral position,
Total time = 420 sec.
Opening/closing time = 420/500 = 0.84 sec.
in the palmar position,
Total time = 482 sec.
Opening/closing time = 4821500 = 0.964 sec.
in the cylindncal I spherical position,
Total time = 528 sec.
Opening/closing t h e = 5281500 = 1 .O6 sec.
These three openingklosing times meet the design requirements.
The method for obtaining pinch force was to place a special gauge between the thumb tip
and finger tip and close the hand. The gauge reading indicated the pinch force of the
expenmental hand. The pinch force 3 .O lb. which appears to be much smaller than a VAS1
hand's 8 lb. The major reason for this smali force is the limited power output of the VASI
motor, since the length of the new hand's fingers are aimost twice as long as those of a
VAS1 hand, and because the opening/closing speed of the expenmental hand is faster than
the VAS1 hand on average by eight percent. The only way to increase pinch force is to
replace the current motor with a more powerfùl motor.
5.4.5 Casmesis
The testing of 'static' cosmesis aspect is focused on two areas: the shape of the
experimental hand and the mass of this hand.
As a successful bio-device, both size and shape of a prosthetic hand should be as close to
the natural hand as possible. Table 5-1 indicates that the size of this new hand is
reasonable. The appearance of this new hand is shown in Figure 5-7. This shape could be
considered as a natural morphological appearance, aithough some further improvements
are still needed.
The mass of this expenmentd hand is about 267 grams which is heavier than the VAS1
haod's 221 grams. Since the experimental hand cornes with four moving fingers which is
two more moving fingers than the VAS1 hand, the mass increase should include the
additionai two cosmetic fingers of the VAS1 hand.
Mm h d = 267 gram
MvAsr h d = 22 1 gram
M V A ~ -=mic = 1 1 gram
M,, = 267/(22l+ll) = 1.15
From the design point of view, this tifteen percent mass increase is reasonable, since this
new design has a more complicated mechanism than that of a VAS1 hand. The hand body
is responsible for most of the increase mass, due to its method of construction. Since this
hand is a first prototype, it was made by machining which requires much more material
than if made by injection moulding.
5.5 SUMMARY
A prosthetic hand with a three position thumb was presented in this chapter. Some special
mechanisms and their theoretical analyses were presented. The author applied 1-DEAS
software as a design tool to build a computer model, which aiiowed the author to visualize
the model for different angles, scales, and colors. By checkhg the geometry, the relative
motions of the hgers, thumb, and the possibility of interference were detemiined to
obtain proper h g e r lengths, initial positions and joint angles corresponding to the
different grasping pattern. This graphical representation and animation of different
segments helped the author to better understand of the problem and saved time in the
design process.
A prototype of the new design was fabricated at the Bloorview MacMillan Centre. The
initial tests on this hand showed that it meets most of the design requirements listed in
Chapter 4.
The author is aware that any engineering solution of a hand substitute would necessady
be based on many compromises. A clinical evaluation is the only way to ensure that
acceptable compromises and solutions have been chosen.
6. PRELlMlNARY CLlNlCAL EVALUATION OF THE
EXPERIMENTAL HAND
6.1 INTRODUCTION
As indicated in Chapter 5, an engineering solution of a hand substitute is based on many
compromises. One way to test that the compromises are acceptable is to perform a
c h c a l investigation. The investigator cm test how well functional requirernents of the
new hand have been met, by using the hand to perform certain tasks related to these
requirements.
Since the petformance of certain fùnctions of a given prosthesis can only be evaluated
when integrated with the user, variability in user motivation, problem solving skills, and
other uncontrollable variables makes hctional testing unsuited for cornparhg individuai
prosthesis scores between users. In most cases, scores of performance of diEerent
prostheses can only be compared for the same user. Changes in performance between
prostheses can oniy be compared with other participants of the test to determine whether
there is a trend34.
The basic elements involved in this experimental evaluation are:
subject selection
training and instruction
testhg
results
discussion
6.2 SUBJECT SELECTION
Idedy, it would be desirable to include subjects representative both in number and
charader of the group who could use the equipment being tested3'. However, the author
did not have large numbers of subjects available. An aiternate method used was to select a
çubject who represented the characteristics of the group of amputees with regard to age,
years of amputation, and personal attitude towards the prosthesis.
6.2.1 Selection Criteria
Ai1 variables that might be important must be considered in the selection of a suitable test
subject. Users who fuifil1 the foiiowing selection criteria were considered as ideal
candidates for this research.
Age is considered to be an important factor. As discussed in previous chapter, this hand is
designed for ages 6 and up. In this age group, users now begin to "operate on
operations," which means they can conceptualize and problem s01ve~~.
The penod shce amputation is also sigiilficant. An experienced myoelectric wearer has
the kinesthetic ski11 to isolate muscular contractions of cornand muscles. It requires
practice to develop this s u . This indicates a level of sophistication which permits an
understanding of the process, control and learning to control a complex prosthesis, and the
capacity to adapt to those changes a new situation may create.
Personal attitude towards this shidy wili directly influence the research results. A
potential subject must be intelligent and motivated. He must aiso be realistic in his
expedations of the functioning of the new hand and understand the limitations and the
capabilities of the prosthesis.
Parents play an important role. The parents' attitude toward the experirnental hand could
affect their child's degree of acceptance.
6.2.2 Subject Profile
With the help of the prosthetic group of the Bloorview MacMillan Centre, an ideal
candidate was selected among from the clients. With the support of his parents, the
subject was invited to this clinical study. Table 6-1 lists the profile of this subject.
1 Age: 1 l2
1 Level of amputation; 1 BeIow elbow I
Sex:
Side of amputation:
Male
Left
Date of fitting a prosthetic hand: 2 months afier birth L
Date of fitting current hand: 2 years ago (Otto Bock 7 1/4
How many days a week is a prosthesis worn? Everyday
How many hours in a day is a prosthesis worn?
Table 6-1 The subject profile
More then 12 hours
Prosthetic hand used for activities of daily living?
6.3 TRAINING AND INSTRUCTION
Yes
M e r the subject was selected, he was invited to participate in this preliminary evaluation.
Since he was a long tirne user of a prosthetic hand and had already established patterns of
prehension with his device, it was expected thaî this may influence the test results with the
experimental hands. Idedly, a subject should be dlowed to use the experimental hand for
a period of t h e , undergoing any testing. This was not possible within the tirneframe. The
altemate solution was to give the subject brief instmctions and let him decide which
strategy should be used for a given task. Prior to testing, the subject was informed that:
1. The experimental hand has three grasping patterns related to the position of the
thumb.
2. Positioning the thumb is accomplished by passively rotating it with the other sound
hand. The thumb can be moved to different positions only when the band is hlly open.
3. The subject was told to decide by himself, which type of grasping pattern was most
suitable when performing each required task.
As indicated in Section 6.1, the purpose of this evaluation was to determine the
performance of the experimental hand and to identify any additional functional benefits.
To achieve this goal, three methods were used. The U N 3 test was used to compare the
fûnctional performance of the experimental band with the prosthetic hand used by the
subject, an Otto Bock 7 314 hand. Secondly, activities were videotaped to identify
attributes of the experimental hand' performance. These activities were those that could
either not be performed by the conventional hand or could be performed by the
experimental hand with greater ease. Thirdly, the subject was asked to fil1 out a
questio~aire regarding initial impressions of the experimental hand.
6.4.11 The UNB test
The UNB test was developed by Sanderson and Scott in 1 9 8 ~ ~ ' . This is the only validated
method for evaluating the fùnctional performance of children with upper limb prostheses.
The UNB test is comprised of activities which would normaliy be encountered by a child
in daily Me. They are selected to be age appropriate and readily avaiiable. Al1 items are
80
norrnally carried out with two hands penorming either symmetrical or assisting fùnctions.
With careM attention to the creation of a relaxed atmosphere, the examining therapist is
able to determine how the child would actually use the prosthesis in performing bimanual
activities of daiiy living at home or at school.
An important and unique feature of the UNI3 test is the use of a dual rating scale, for skill
and for spontaneity of prosthetic funaion. Skill refers to the users' ability to open and
close the terminal device to grasp and release objects of dflerent sizes and shapes with
confidence speed and consistency. Spontaneity is defined as the users' tendency to use the
prosthesis to assist with the task. This innovation arose from the observation that many
individuals possess sufficient sM1 to use a prosthesis very well but show little tendency to
do so. W~thout this inner spontaneity, the child is unWtely to continue using the prosthesis
when the therapist or parents are not available to remind him or her. Dextrous use of the
prosthesis on request only is not enough to ensure good function. This dual rating scale
addresses the need for separate measures of ski1 and spontaneity. Table 6-2 shows the
rating scale for the UNB test.
Spontaneity of Prosthetics Function Score
Immediate, automatic, consistent use of terminal device for active grasp.
Slight delay or inconsistent use of terminal device for active grasp.
V e q delayed, occasional or "last resort" use of the terminal device.
Use of prosthesis proximal to terminal device only.
Prosthesis not used or used only on request.
Ski11 of Prosthetic Function
Active use of terminal device is quick, skilled and smooth. Grasp is
consistently rnaintained.
Active use of terminai device, shows some degree of awkwardness,
slowness or uncertainty. Grasp is readily regained when lost.
Active use of terminal device is attempted, but looks very slow or
awkward. Grasp is fiequently lost or regained with difficulty.
No active terminal device function, although terminal device or some other
part of prosthesis may be used passively to stabilize or suppon.
Prosthesis not used
score
Table 6-2 Rating scale for the UNB test
The procedure for the UNI3 test was to let an experienced therapist select 10 age
appropnated activities fiom the test manual and administrate the test processing. These
10 activities, listed in Table 6-3, were performed by the subject who wore both hands
altemately. A video camera was used to record the performance of the subject using the
hand. To assess the reliability of test results, these subtests were rated by an experienced
therapist on a scale fiom O to 4 points based on the guidelines for scoring s h o w in Table
6-2. Results from the test were then converted to bar charts to depict the results(see
Section 6.5 for details).
6.4.2 Videotaping
One of the characteristics of the UNB test is that al1 tasks are preset in the manual and are
able to be performed when using any prosthetic hand. There was therefore a limit on what
functional activities could be examined. To complement this investigation, videotape was
used to andyze additionai tasks not contained in the UNE3 test, and which are described in
Figure 6-1 and Figure 6-2. The feature of these activities is that these tasks can either not
be performed using the conventionai hand or show great functional improvements when
using the experimentai hand. The purpose of this study was to idente additional
functional benefits of the experimental hand
Data anaiysis consisted of comparing the results using the two hands. Table 6-3 lists a
number of positive functional charactenstics of a functionai prehensor? Results from
this test are analyzed in Section 6.5.
Secure and stable grasp
Functiond Characteristics
Once an object is grasped, it does not easily change orientation within the grasp or fdl out of the
Descriptions
in hand 1 prehensors to attain a secure and stable grasp. Easy to abgn object to grasp
Excessive effon is not required to determine exactly where the object should be contacted to fom a
prosthesis. Objects do not have to be perfectly aligned in the
Objects can be held in many stable grasp. Objects cm be aligned in several directions within
orientations for use Minimize required pre-
the hand depending upon the purpose of the grip Slight variations of initial wrist orientation will not
alignment of wrist Able to hold variety of object
impair the ability to grasp an object. Regular and more complex shapes are easily grasped
shapes Able to grasp large objects Able to grasp smaii objects
being grasped 1 hand and object to be grasped are visible and the
by the prosthesis.
The hand does not impose excessive size limitations
Good visibility of objects on what can be grasped. When grasping an object, the grasping surface of the
Minimal compensatory
force ( enough force is applied to hold an object without so
prosthesis does not obscure the line of vision. Objects can be grasped without umatural
movernents Good control of gripping
compensatory actions of the arm, torso or head. The user can control the gripping force so that
Grasp force feed back much force that the object could be damaged. User can tell how much grasping force is being
Grasp !ooks naturai
1 quickly and reliably.
applied by visual, audible or other means. Able to grasp and hold items in a natural looking
Quick release of grasp
Table 6-3 Description of functional characteristics
mamer. In hazardous situations, the grasp cm be released
6.4.3 Questionnaire
The third assessrnent method used in this study was to ask the subject to fil out a
questionnaire on initial impressions of the experimental hand. The questionnaire is
presented in Appendix F and was aimed at assessing the overall chara~tenstics of the
experimental hand. Its content covered general aspects of the prosthetic hand such as
cosmetic appearance, functiond ability and operational performance. This questionnaire
was arranged to be filied out at the end of the clinical investigation. Results of this
questionnaire are presented in Section 6.5.
6.5 RESULTS
6.5.1 UN8 test
The 10 activities selected from the UNB Test are listed in Table 6-4. These activities were
performed when using both the Otto Bock hand and the new experimental hand
altemately, and were scored on a scaie from O to 4 points according to the guidelines for
sconng shown in Table 6-2. These score results were converted to the bar charts of
Figure 6-3 and Figure 6-4. An analysis of the performance of both hands is presented in
Section 6.6.
Act ivities
Wrap a parcel:
a) cut paper to size
b) use scotch tape dispenser
c) tie up parcel
Sew on a button:
a) cut length of thread
b)thread needle
c)sew button on shirt
Cut meat with knife and fork
Wash and dry dishes
Sweep floor
Sweep up pile of dust
To tals
Score (Otto Bock Hand)
A B
2 1
Score ( New Hand)
A B
2 I
Table 6-4 Activities selected from the UNB Test and their scores
A) Spontaneity of Prosthetic Function; B) Ski11 of Prosthetic Function
6.5.2 Additional Activities
Benefits of the experimental hand that were observed from videotaped activities are listed
in Figure 6-1 and Figure 6-2. These are activities that could not be performed by the old
hand or when performed by the experimental hand showed functional irnprovement. The
performance of these activities was contrasted with the results from the LMB test. The
fùnctional improvements of the experimental hand were then identified from the analysis.
The VASI hand
The experimental hand
The merimena hand The VAS1 hand
The experimental hand The VAS1 hand
AU com&ercial available prosthetic hands
only offer one palmar grasping pattem
which requires more pinch force to hold a
cyiindricai object .
The experimental hand provides a
cylindrical grasping pattem (position 3)
which results in a more secure and stable
grasp with a smaiier pinch force.
The experimental hand is able to hold
objects in the same orientation as a
conventionai hand.
~ h e experiiental hand is also able to hold
objects orientated better for use than most
prosthetic hands.
Figure 6-1 Functional cornparison between a conventional hand and the experimental hand
ne more grasping patterns, the easier it is to perfom
more tasks. The experimentd hand minimi7.e~ required
pre-alignment of the wrist and improves the visibility of
objects being grasped. A typical example is insertion
of a disk into a drive by using lateral grasping.
Like moa prosthetic hands, the experimentd hand is
also able to grasp small objects such as thread by using
the palmar grasping pattern (Position 2).
To carry out this floor sweeping task requires a high
pinch force for moa commercial hands, since only two
of their four fingers participate in performing the task.
Ail four hgers of the expenmental hand work togethel
to provide a stable grasp with low pinch force.
Udke most hands, the thumb of the experimental hand
has three positions which makes aiigning objects to
grasp easier.
Figure 6-2 Functional identification of the experimental hand
The experimental hand is able to hold a greater I
variety of object shapes and is also capable of holding
much larger objects than a conventional hand.
Using the conventional hand's pattern method to grasp
a smaü cube requires compensatory movements of the
shoulder and a m -
Jshg one of the experimental hand's patterns
nuiimizes the compensatory movement of should and
um, and also improves the 'dynamic' cosmesis of the l
rrosthetic hand. I
dost commercial prosthetic hands do not provide a
iteral posture which negatively impacts their 'static'
users with a more natural looking prosthetic hand.
6.5.3 The Questionnaire
Results fkom the questionnaire are shown in Table 6-4. These initial impressions obtained
from the nibjea indicated areas of acceptance for the experimental band and areas
requiring fkther improvement. Discussion of the results is presented in Section 6.6.
1- In your opinion, what is the importance of the moveable thumb:
a) Functiodly? High X , moderate , little
b) Cosmetically? High X , moderate , little
2- In your opinion, do you think this new hand will improve your hand's grasping ability? y e s X no
3- Are you satisfied with the following aspects of the new hand:
a) The dimensions of fingers(exc1ude thumb)?
b) The thumb is longer?
C) The hand overail dimensions?
4- Are you satisfied with the following characteristics:
The weight of the prosthesis?
a) Is the closing and opening speed?
c) 1s the grasping force sufficient?
d) 1s the hand opening sufficient?
too srnail Too big
too long too short
just right 2 Acceptable2
too long
too big
too small
just right X
Acceptable too heavy
too high too low just n g h t x
Yes n o 2 maybe
Yes X no
5- 1s the thumb's three position toggle mechanism easy to use? Yes X no
6- 1s the thumb's locking mechanism stable and functional? yes X no
Do you wish to make some other cornments on this hand? I would like to 6e the-first person to use this new hand
Table 6-5 Initial impressions of the experimental hand
6.6 DISCUSSION
6.6.1 Limitations of the Study
Several factors infiuenced the test results. One major factor was that the subject had
wom his prosthetic hand for a much longer t h e than he was able to Wear the experimental
hand before test. Control patterns for operathg subject's usually hand and attitudes
formed over a long wearing period had to be considerably more fixed and inflexible than
when wearing the experimental hand. This would seem to bias results.
Another limiting factor is that only a single subject was used and therefore the results only
provide an indication of the hand's performance.
Some tasks selected f?om the UNB test manual were not suited for this subject. For
instance, sewing a button on is a very rare activity for a 12-year old boy, and does not
fully show the user's ability when using a prosthetic hand.
The hand's smail pinch force, the lack of a glove and extemal attachent of the electronic
control circuit of the experimental hand also could have intluenced the test results. A
smali pinch force would increase the difficulty in grasping objects. The Iack of a high
fiction @ove may lead to fùrther instability when grasping, and the extemai electronic
circuit disturbed the subject's concentration when performing tasks. Because of these
factors, score results may not tmly indicate optimal performance with the experimentai
hand .
6.6.2 Analysis of Test Results
Resuits fiom the UNB test showed that both hands scored highiy in spontaneity of the
Prosthetics Function aspect (see Table 6-4). The higher the score, the more iikely users
accept the prosthesis. The overali score for the Otto Bock hand was 36/40 and 35/40 for
the experimental hand. The high score for the experimental hand indicates that the hand
compares well with the Otto Bock hand.
EOtto Bock Hand
I Experimental Hand
Figure 6-3 Score comparing the aspect of Spontaneity of Prosthetics Function
.Otto Bock Hand
Experimental Hand n
Figure 6-4 Score comparing the aspect of Skill of Prosthetics Function
Results f?om the IMB test also showed that there was a score difference in the aspect of
ski11 of prosthetic function (Figure 6-4). The skill score refers to a user's ability to grasp
and release objects with confidence, speed and consistency. Because the subject has
worn the Otto Bock hand for almost two years and had never tned the expenmental hand
before, a big score dflerence was expeaed. The fact that the overall score for the Otto
Bock hand was 32/40 and for the experimental hand it was 29/40, indicates only a srnail
difference between the two hands. Among these 10 tasks, five task scores of the
experimental hand were the same as those of the Otto Bock hand, and one task scored
higher. This is encouraging, since s k t y percent of the task scores were the same for both
hands without any user's practice with the experimental hand.
It is noticeable that in one task, 'use tape dispensers', the scores of the experirnentai hand
in both spontaneity and skiU aspects were higher than those of the Otto Bock hand.
However, the experimental hand scored lower in cutting, sewing and holding a dust pan,
which implies that M e r improvements are still needed for tbis hand. Lncreasing pinch
force of the experimental hand could improve the scores of these activities.
An analysis of the videotaped activities, presented in Figure 6- 1 and Figure 6-2, indicated
the following bct ional advantages of the experimental hand:
both 'static' and 'dynamic' cosmesis were improved
a greater variety of object shapes could be held.
compensatory movements of arm and shoulder were minimized.
grasp appears more natural
objects could be oriented dBerently to suit the panicular task
required pre-alignment of the wrist was minunized
a stable grip with a lower grasping force was provided
Initial impressions of the experimental hand were obtained fiom the questiomaire and
were listed in Table 6-5. Hence, the subject indicated that this experimental hand provided
improved function and cosmesis. The shape and size of this hand were acceptable and the
hand rnechanism was also easy to operate. The only weakness of this hand is its low
pinch force which must be improved in the fbture.
6.7 SUMMARY
Three methods were used to clhically evaluate the experimental hand. These methods
focused on different aspects of the hand. The UNB test examined performance aspects of
the hand. Videotaping emphasized additionai functional benefits denved fiom using the
hand and the questionnaire highlighted initiai impressions of the hand. Despite the fact
that the subject had never used the new hand before, the testing indicated that this
experimental hand improves not only the hctional ability of the user but also the hand's
cosmesis.
Since this study is only a preliminary clinicai investigation, many of the factors associated
with the new hand are stili unknown, and fùrther experimentation is still needed to identiS,
them. There are severai factors which negatively impacted the test results, and the score
obtained in this study is probably lower than it should be. It is possible that the score for
this experimental hand would be improved d e r a period of practice with it.
7. CONCLUSIONS
An experimental hand with a moveable thumb was designed and a preliminary ciinical
evaluation of it was undertaken. Section 7.1 reviews the significance of this research.
Section 7.2 proposes recommendations and future avenues of investigation that have
resulted fiom this work.
7.1 SlGNlFlCANCE OF THE RESEARCH
The consequences of an upper limb amputation may be descnbed in terms of impairment,
Le. the loss of hand funetion. It may also be described in terms of disability, Le. loss of
ability to perform certain activities2. The aim of rehabilitation is to reduce the
consequences of amputation by providing users with prosthetic devices that maximize
function. In principle, one method to increase fùnctions is to increase the number of
degrees of freedom. Unlike one-degree-of-freedom conventional hands, the expenmental
hand has two-degrees-of -fieedom and is therefore able to form more grasping patterns.
Results fiom a preliminary clinical investigation showed that the new hand not only
performs as well as conventional hands but has added fùnctional benefits.
The acceptance or rejection of a prosthetic hand depends on the balance between the
benefit derived fiom it and the 'nuisance factor' associated with the use of the prosthesis3'.
96
The benefit may depend on increasing grasping fundons or the ability to perforrn manual
activities, and on cosmetic aspects. Since prosthetic requirements, operational skills and
control abilities for every age group are dinerent, prosthetic hands with the same
mechanism and controi method will never be a good solution for ali users. The
experimental hand presented in this study is specially designed for users aged six and up.
Even though this hand is only an expenmental prototype, clinicd investigation showed
that it was already acceptable to the subject who tried it out.
Standardized activities are important in the analysis of the general performance of a
prosthesis. The UNB test is the only standardized test for this purpose. There is a need to
develop other test methods that can iden* additional aspects of hand prosthesis usage.
The suppiementary methods used in this ciinicd study complement the UNB test.
In conclusion, the prototype prosthesis designed by the author shows some advantages
over the conventional prosthesis.
7.2 RECOMMENDATIONS AND FUTURE WORK
Further work is needed in two major areas: design aspects and clinical evaluation.
Improvement to these two aspects wil1 iead to development of a more functional
prosthetic hand.
7.2.1 Design Aspects
The pinch force of the experimental hand is only 3 .O lb. which is much less than a VAS1
hand's 8 Ib. of force. The major reason for this small force is the Limited power output of
the motor. The possible solution for increasing the pinch force is to replace the current
motor with a more powehl motor.
One of the controversial designs of this new hand is the thumb locking system. The
mechanism presented in this thesis is an automatic locking system which means that the
position of the thumb wiil be locked once the hand starts to close. Only when the hand is
hlly opened can the position of thumb be changed (see Chapter 5). Although this locking
method will prevent thumb slippage when the hand holds an object, it obviously is
different to the characteristic of the naturai thumb since the natural thumb cm change its
position during action. A suggestion to overcome this problem is to use a manual locking
system. The disadvantage of using this is that it rnakes the control of the hand more
complicated and can not be used for bilateral hand amputees. Ideally, a hand with both
locking systems would be desirable.
Another aspect of the experirnental hand is the design of the fingers. The fingers used
were ngid bodies. It may be beneficial to redesign these fingers to be flexible and thus
close to natural fingers. The thumb in this design also is much longer than in the natural
hand and needs to be redesigned.
The experimental hand is heavier than currently commercially available hands. Most of the
increase in mass is due to the hand body. The hand is a first prototype and was made by
machining, which requires much more matenal than if it had been made using injection
moulding. To become attractive, the shape of hand body needs to be further shaped.
Finally, if it is possible, incorporating tactile control in the experimental hand should
M e r improve it.
7.2.2 Recommendation for Future Clinical Investigations
As indicated in Chapter 6, the clinicd evduation presented in this study is only a
preiiminary examination and not a pure assessment. Many of the factors associated with
the use of the hand are still unknown, and there is need to conduct fûrther evaluations to
idente them.
Since the sample size for this evaluation was limited to one individual, definitive
conclusions about the hand cannot be made. In future testing, three factors should be
considered: (a) users should Wear the hand for a penod time before undergoing testing.
(b) the sample size should be increased. (c) abjects should be selected who represent the
charactenstics of the group for whom the hand was designed with regard to variables such
as number of years since amputation, type of prosthesis used, etc.
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32 Fletcher, M., Humrm Limbs and ïheir Substitutes (edited by Klopdteg. P. EJ, Hafner Publishing Company, New York, pp.223-237, 1968.
33 Mark H. Lawry I-DE4S Master Series, Structural Dynarnics Research Corporation, Milford, Oh, 1993,
34 Jacques, G., Powered Prosthetic Hand Function: Design h e s And Visual Feedback, M. A. Sc. Thesis, University of Toronto, 1994.
3 5 Feeney, R J., EvaZuatzon of Upper fitremity Prostheses, Prosthetic and Ortho tic Practice, Edward Arnold (publishers) Ltd., London., 1969 pp. 405-4 10.
36 Pulaski, M. S. Understanding Piaget, An lnlroduction to Chzldren 's Cognitive Development. Edward Arnold (publishers) Ltd., London., pp7- 1 1, 1982.
37 Sanderson, E.R., Scott, RN., W B Test ofProsthetics Function, Bio-Engineering Institue, University of New Brunswick, pp. 1-3 3, 198%
38 Roeschlein, R A, Dom hok, E., Factors ReZated to Successful Upper Exlremity Prosthetic Use. Prosthet. Orthot. Int., 13, pp 14- 18,1989.
APPENDICES
Motor (MicroMotor* 1 624 T 4-23} Charactenstics
Input Resistance R, = 4.00 Ohm +/- 12%
Input Voltage Vi = 4.5 Volt
No Load Speed n,, = 9900 rpm +/- 12%
No Load Current &, = 0.0220 Arnp +/- 50%
Rated Torque T, = 1.5 mNm
Stall Current 1, = 1.125 Amp.
Max. Mechanicd Power Pm = 1.2166 Watt
M M constant 16 = 2243.8044 rpdvolt
Torque Constant Tc = 4.2560 mNdA
Stall Torque T, = 4.6944 mNm
Friction Torque Tf = 0.0936 mNrn
Max Efficiency n, = 75.4630%
Speed at max. e E N, = 8772 rpm
Rated Current 1, = 0.3744 Amp.
Rated RPM N, = 6737 rpm
Working Efficiency n, = 62.6693%
Maximum Angular Accel. A, = 54.605* 10-3 rad/s2
*Micro Mo Electronics Inc. 1488 1 Evergreen Ave., Clearwater, FL 34622-3008
APPENDIX B: ANALYSIS OF SYSTEM SPEED REDUCTION
Trocton Drive Planetary Reduction
1 MOTOR INPUT
Figure B - 1 Traction d h e planetary reduction
ALL LINKS X RPM
FIX 4 GIVE 1 Y RPM
Table B - 1 Traction drive planetary reduction chart
NET
X
Y
X + Y
X
- Y * DlD2
X - Y"Dl/D2
X -
-Y * DI/D3
X
O
X - Y* D1/D3 X
H o u s i n g is f i x e d :
S p e e d R a t i o :
For: D l ( d i a m e t e r o f g e a r 1 ) = 0 . 0 5 9 i n .
D 3 ( d i a m e t e r o f g e a r 3 ) = 0 . 4 3 2 8 in .
Gem Plmelary Reduction
1 INPUT X I
-
Figure B - 2 Gear planetary reduction
Table B - 2 Gear planetary reduction chart
ALL LINKS X RPM
FIX 4 GIVE 1 Y RPM
NET
H o u s i n g 3 i s f i x e d :
S p e e d R a t i o :
1
X
Y
X + Y
F o r : N l ( n u m b e r o f t e e t h o f g e a r 1 ) =
N 3 ( n u m b e r o f t e e t h o f g e a r 3 ) = 5 3
2
X
-Y*Nl /N2
X - Y*Nl/N2
3
X
-Y*Nl /N3
X - Y* Nl/N3
4
X
O
X
Spur Geat and Bevel Geor Reduction
Figure B - 3 Spur gear and bevel gear reduction
For Spur Gear:
N 1 (the number of teeth of spur gear 1) = 16
N2(the number of teeth of spur gear 2) = 38
N3(the number of teeth of spur gear 3) = 40
For Bevel Gear:
NB l(the number of teeth of bevel gear 1) = 36
NBZ(the number of teeth of bevel gear 2 j 72
Speed Ratio for Spur Gear:
N1 N 2 - N I - 16 R s = - x - - - - - N2 N 3 N 3 40
Speed Ratio for Bevel Gear:
Total Speed Ratio:
Gear Ratio:
Bevel Gear and S p r geat Reàùction for the Thutnb
Figure B - 4 Bevel gear and spur gear reduction for the thumb
For Spur Gear:
N l(the number of teeth of spur gear 1) = 24
N2(the number of teeth of spur gear 2) = 6 1
N3(the number of teeth of spur gear 3) = 45
N4(the number of teeth of spur gear 4) = 52
For Bevel Gear:
NB l(the number of teeth of bevel gear 1 ) = 36
NB2(the number of teeth of bevel gear 2) = 36
Speed Rat10 for Spw G e x
Speed Ratio for Bevel Gear:
Total Speed Ratio for Thurnb:
Rthumb = RS x RBCVCI = 0 -34
Gear Ratio:
Spur Geur Reduction for the Red Fingers:
Figure B - 5 Bevel gear and spur gear reduction for the rest fingers
For Spur Gear:
Nl (the number of teeth of spur gear 1) = 25
N2(the number of teeth of spur gear 2) = 72
N3(the number of teeth of spur gear 3) = 40
N4(the number of teeth of spur gear 4) = 50
Speed Ratio for Spur G e x
Speed Ratio for Fingers:
Gear Rati O:
Total System Reduction for the numb:
Tot& System Reduction for the Rest Fingers:
APPENDIX C: ANALYSE OF SYSTEM TORQUE
The specification of motor(Micromotor-1624) was listed in Appendix A.
Vrated = 4.5 volts
Ramiam =4.00R k12%
V i i = 6.0 volts
Twistari~ =4.256011NmlA=.603 oz-in/A
Tni~tarstall =IniotcsstalxT~=1.50~.6û3=.904 oz-in
Gear reduction fiictor tbrough planetary systerns and fint super gear and bevel gear reduction:
Gear Ratio = GR1 x GR2 x GR3 = 8.34 x 5.08 x 5 = 21 1-60
Stall torque at 1W! efficiency through diese rechiction:
Tstau = Tmtastall x Gear Ratio =.904 x 2 1 1 -60 = 19 1 -29 oz - in
Since: Tstau = Tfingernall +Trh*
Ffinsa(the finga force) = Ftlumib(the thumb force) = F
Tfigastall= Ffmger x L r i t h e lengdi of finga) x Rfia
= F x Lfmger x R r i e r
Tauimhnall= Fthtrmb x -the length of thumb) x Rihurnb
=FxLthdxRthumb
L f i g a = 2.8 in. L t f i ~ b = 2.9 in,
191.285 = F x 2.8 x 0.2 + F x 2.9 x 0.340479
F = 123.61 oz.= 7.72 Ib.
APPENDIX D: ANALYSIS OF CONTACTING LOCATION
Figure B - 6 Simplified structure of thumb and index finger
Lf represents the length of index finger
Lt represents the length of thumb
a represents the length between shafl two (S2) and sh& three(S3)
c represents the length between shaft one (S 1) and shaft three(S3)
o l represents the speed of angular rotation of sh& one, whch is
available fiom previous gear ratio analysis
02 represents the speed of angular rotation of thumb shafi one, which is
available from previous gear ratio analysis
This hand's opening/closing consisted of two dflerent rotations: rotation of the fingers
(represented by index h g e r in this analysis), and rotation of the thumb. The calcuiation
for the rotation of the index finger was relatively simple, since the index finger oniy
rotated around shaft S 1 by the speed of o 1. Rotation of the thumb involved two steps:
both the thumb and linkage were rotated around shaft S3 by a certain angle 8, and then the
thumb rotated around shafl S2. The purpose of the first rotation was to move the thumb
and thumb kame into position corresponding to one of the three desired grasping patterns
by manually rnoving it . M e r the thumb was in position, the second rotation took place.
The Geometricaf Analysis of Index Finger
Figure B - 7 Simpiified structure of index finger for purpose of geometrical anaiysis
Since 0 = o * t (time of rotation)
For tip's location of index finger in X axis
For tip's location of index finger in Y axis
For tip's location of index finger in Z axis
x = o
y = L f * sine
= Lf * sin (a*$)
Y = ~ f * COS e
= Lf * cos (o*t)
The Geometrical Andysis of the mrnb
Figure B - 8 Simpiified structure of the thumb for purpose of geometrical analysis
a represents the angle between plane P0"A and plane ZOX.
The location of O is (0,0,0).
The location of O' is (O,O,-C)
The calculation of the location of thumb' s tip consisted of three steps:
(1 ) The thumb has k e d angle a between the linkage a and itself.
(2) Both thumb and its linkage rotate around Z axis by P degrees.
(3) Only the thumb rotates around its Y" axis by a* t degree.
Known factors: Lt (the length of thumb)
a (the length of thumb linkage)
a , 6 , P (initiai angles of thumb)
0 2 (the speed of angular rotation of gear)
The following steps are needed to denve the equation for P(X. Y, 2)
a) Lnitial position: (P = 0, a2 =O)
ED A P - arctan - 0 2 = L D 0 " E = arctan-- EO" EO"
L t x s i n 6 = arctan = arctan
Lt x c o s 8 x c o s a c o s d x C O S a
\ c o s ' a . - -
S o :
NOTE TO USERS
Page(s) not included in the original manuscript are unavailable from the author or univerçity. The manuscript
was microfilmed as received.
UMI
c) rotate both thumb linkage and Lt around Z axis
when t (operation time) is hown, the location of the thumb's tip and index finger's tip
cm be calculated fiom the above equation.
The experimental process to evaluate the functional ability of the new prosthetic hand was
subjected to review by Bloorview MacMillan Centre's ethicai review cornmittee. The
approved document, found below, included the following:
Subjea Information Letter
Subject Consent Form
Letter of Collaboration
Release forrn for videotaping / photography
FUNCTIONAL COMPARISON BETWEEN A NEW MOVEABLE THUMB PROSTaETIC BAND AND A CONWNTIONAL PROSTHETIC HAND
Information Forrn: Subiect, Parent or Guardian
Principal investigator: Paul Hu, B.A.Sc.
Academic Supervisors: Stephen Naumann, Ph.D., P.Eng.
William Cleghom, P b D., P.Eng.
Denise Reid, Ph.D., O.T.
Introduction
A natural hand is capable of holding a large variety of objects with different shapes by
changing its thumb position. Current prosthetic hands are reliable and lightweight, but
have oniy one thumb position. The holding abilities of these hands are limited. To
improve the functional performance of prosthetic hands, the author designed a new hand
with a rnoveable thumb. Theoretically, this hand should provide more functional benefits
than the current hand. The purpose of this study is to determine how the new design
differs fiom these currently used hands with respect to meeting needs in a practical
environment.
In this study, we wili evaluate the functional performance of your child's current
prosthetic hand with the new hand by asking your child to perform a series of task. We
will also ask your child to fil1 out a questionnaire on hisfher impressions about the two
hands.
We hope that this information will lead us to design a more functional hand.
The Studv
If your child decides to participate, you and/or your child will be asked to attends a one-
hour session at Bloorview MacMillan Centre, MacMillan site.
During the session, we will ask your child to perforrn the UNB test when wearing borh the
new hand and the VAS1 5-9 hand altemately. You chiid will be asked to pick up a variety
of different shaped objects. Two video cameras in the room will record your child's
performance. The purpose of the study is to compare the performance of both hands. We
wiil not be comparing your child's performance with that of other research subjects. We
will also ask your chdd for an opinion about how the two hands' fùnction compares.
Risks and Discornforts
There are no know risks or discornforts associated with participation in this research
project.
Expected Benefits
Your chdd may not receive any direct benefits from participating in this study at this time.
However, once we have examined data collected from ail the participants in this study, we
may be able m o w the m e n t hand design to generate a better design with improved
performance.
Al1 information collected during the study will be considered confidentid. No information
which might identiQ the participants will be included in any reports, presentations or
publications which result fiom this without your expressed written approval.
Feedback
Your questions and comments regarding the project are encouraged and will be accepted
at any time. You / your child may decline to participate or may withdraw From the study
at any time without risk your involvement with the Centre.
If' you should wish, you may discuss the results of your test with us.
Please direct your comments and questions to Paul Hu (41 6-425-6220 Ext.5 15)
FUNCTIONAL COMPARISON BETWEEN A NEW MOVEABLE TBUMB PROSTBETIC BAND AND A CONVENTIONAL PROSTHETIC BWND
Consent Form: Subiect. Parent or Guardian
Principal investigator: Paul Hu, B.A.Sc.
Academic Supentisors: Stephen Naumann, PbD., P-Eng.
William Cleghom, Ph-D., P.Eng.
Denise Reid, Ph.D., O.T.
Has your child been involved in research in the past ? Yes - No -
1s your child currently involved in another research study? . Yes - No -
The name of this study or investigator is
I have read and understood the information form related to this project, al1 my questions
so far have been satisfactorily answered and I hereby consent to participate in the study.
The details of the study were explained to me by:
1 understand that 1 rnay withdraw my consent and discontinue participation at any time
without prejudice to current and further treatment or involvement at Centre.
I f at any time 1 need further information 1 know 1 may contact Paul Hu (4 16-425-
6220x5 1 5).
Signature of Participant / Parent 1 Guardian Name in Block Letters
Date Signature of Investigator
THE HUGH MACMILLAN REHABILITATION CENTRE
To: Dr. Jeff Jutai
From: Sandra Ramdial, S heila Hubbard
Subject: Research study by graduate student Paul Hu
Date: September 9, 1996
The Powered Upper Extremity Prosthetic team hereby acknowledge that we will assist in
recruiting candidates for the study: Functioaal Cornparison Between A New Moveable
Thumb Prosthetic band And A Conventionai prosthetic Hand, to be adrninistered by Paul
Hu, a graduate student fiom The University of Toronto. We will also assist in evaluation
of the videotaped results. We are f d a r with the purpose and procedure of the study
and agree with its administration.
Subjects for the study will be selected fiom current clients of the Moelectric Prosthetic
Program at Bloorview MacMillan Centre. We hope to recmit three iefi hand subjects
based on type of prosthesis used, good functionality with their prosthesis. abilitv to follow
simple instructions, and avadability. Each of the subjects will be a current prosthetic Hand
user and will be fit with the new hand. The subjects will partiqate on a volunteer basis.
The study will uphold subject anonymity and confidentiality.
Solicitation for subjects wili commence upon permission by the Ethics Review Cornmittee
and conclude by the end of December 1996.
S andra Ramdid C .P. (C) Sheila Hubbard, P.&O.T., B.Sc.
Coordinator, Powered Upper Extrernity Powered Upper Extremity Prosthetics
Prosthetics Program Program
THE HUGH MACMILLAN REHABILITATION CENTRE
To : Dr. Jeff Jutai
From: Stephen Naumann, Ph.D., P-Eng
Subject : Research study by graduate student Paul Hu
Date: September 9, 1996
Paul Hu is a graduate student in the Institute of Biomedical Engineering and Department
of Mechanical Engineering at the University of Toronto, working towards the degree of
Master of Applied Science under my supervision. He will be administering a clinical
evaluation entitled: Functional Cornparison Between A New Moveable Thumb Prosthetic
Hand And A Conventional prosthetic Hand, as part of his master's thesis entitled: The
Development Of A New Prosthetic Hand With A Moveable Thumb.
Subjects for the study will be seiected from current clients of the Myoelectric Prosthetic
Program at BlooMew MacMillan Centre. Three left hand subjects will be recruited based
on type of prosthesis used, good hnctionality with their prosthesis, ability to follow simple
instructions, and avadability. Each of the subjects will be fit with the prosthetic hand and
the new hand. The subjects will participate on a volunteer basis. The study will uphold
subject anonymity and confidentiality.
Stephen Naumanq Ph.D., P. Eng.
Associate Director, Rehabilitation Engineering Department
APPENDIX F: QUESTIONNAIRE FORM FOR CLlNlCAL EVALUATION OF THE EXPERlMENTAL HAND
A PROSTHETIC HAND WITE MULTT-GRASPING PATTERNS
OUESTIONNAIRE
This questionnaire applies to subjects who participate in the research study: Funrtional
Cornparison Between A New Moveable Thumb Prosthetic Band and A
Conventional Prosthetic Hand. Its main goal is to obtain users' initial impressions of
the new hand.
File No:
Age :
Sex:
Date of fitting prosthetic hand:
Date of fitting current hand:
Side of amputation: ieft , right , bilaterai
Level of amputation: B/E other
how many days in a week do you wear your prosthesis? DfiV
how many hours in a day do you wear your prosthesis? HA3
Do you use your current prosthetic hand:
a) for activities of daily living
b) for recreational activities
Yes-
** - if yes, speciQ:
INITIAL IMPRESSION OF TEfE NEW HAND
1 - In your opinion, what is the importance of the moveable thumb:
a) Functionally? high , moderate , little
b) Cosmetically? high , moderate , Iittle
2- In your opinion, do you think this new hand \vil1 improve your hand's grasping ability'?
3- Are you satisfied with the following aspects of the new hand:
a) The dimensions of fuigers(exc1ude thumb)?
too big too small
too Lon9 too short
just right
b) The thumb is longer?
acceptable
too long
C) The hand overall dimensions?
too big
too small
just nght
4- Are you satisfied with the following characteristics:
a) The weight of the prosthesis? acceptable
too high
b) 1s the closing and opening speed?
too high
too low
just ri&
c) 1s the grasping force sufficient?
Yes
no
maybe
d) Is the hand opening suficient?
5- Is the thumb's three position toggle mechanism easy to use?
6- 1s the thumb's locking mechanism stable and functional properly?
7- Do you wish to make some other comments on this hand?
J :.' DRAFT ONLY
Bugh MacMiflan Rehabilitation Centre
InnderstandthattbesephotographsTiges will b e M in a sbatrelodon that w3.I protecttheprivaq of the pmon photographed anil mat they wilI be kept for the time paiod roqaired by law or outlined in the pliaes of the Hu@ Mac- Rehab'itation Came-
S--tue of Client or Person Legally Authorized to Consent:
Signature of Witness:
APPENDIX G: SOME IMPORTANT DRAWINGS OF THE
EXPRIMENTAL HAND
I c H m A
136
CHANGES1 A NEW
DATE1 DFTSi DESIGNER1 PAUL HU APPDI SUPSD BYi SUPERCEDESI
MATERIAL1 1
COATINGi
HEAT TREATI
HARDNESSl
ER- R E v x m s E m.
THE HU%H MacMILLAN REHAB, CENTRE REHABILITATION ENGINEERING
IR8 UNIT1 NA ME^ THE EXPERIMENTAL HAN
SHEET OF SCALE1
NOMINAL INCH
,XX I d l 0 , X X X I ,005
,005
SURFACE FINISH 6v ANGLES * 30'
D m m
DIMENSIONAL TOLERANCES (UNLESS OTWERWISE STATED)
CORNER R A D I I
INTERNAL MAX. EXTERNAL MAX,
B R E A K S H A R P EDGES MAX, HOLE DEBURR DEPTH MAX.
