Design of a Hybrid Passive-Active Prosthesis for Above-Knee

114 Pages·2008·7.87 MB·English

Design of a Hybrid Passive-Active Prosthesis for Above-Knee Amputees
by
Bram G. A. Lambrecht
B.S. (Case Western Reserve University) 2004
M.S. (Case Western Reserve University) 2005
A dissertation submitted in partial satisfaction of the
requirements for the degree of
Doctor of Philosophy
in
Engineering — Mechanical Engineering
in the
GRADUATE DIVISION
of the
UNIVERSITY OF CALIFORNIA, BERKELEY
Committee in charge:
Professor H. Kazerooni, Chair
Professor Dennis K. Lieu
Professor Carlo H. S´equin
Fall 2008
Design of a Hybrid Passive-Active Prosthesis for Above-Knee Amputees
Copyright 2008
by
Bram G. A. Lambrecht
1
Abstract
Design of a Hybrid Passive-Active Prosthesis for Above-Knee Amputees
by
Bram G. A. Lambrecht
Doctor of Philosophy in Engineering — Mechanical Engineering
University of California, Berkeley
Professor H. Kazerooni, Chair
Every year, tens of thousands of people in the United States alone require an above-knee
leg amputation. These amputees require a prosthetic leg to regain mobility and to im-
prove quality of life. Current prosthetic knees range from simple hinges to sophisticated
computer controlled hydraulic dampers. Despite the advances in technology, above-knee
amputees still show significant deficiencies in their walking patterns, walking speed, and en-
ergy consumption. Also, without a compact energy source and small, high power actuators,
current prostheses prohibit ascending stairs step over step, and provide no assistance when
standing up. Development in powered prosthetic knees has mostly focused on the control,
with little emphasis on creating an efficient, low energy consumption, untethered device.
Thisthesispresentsthefirstenergeticallyautonomoushydraulicallypoweredpros-
thetic knee. The primary innovation of the knee is a hybrid design with two separate hy-
draulicmodesofoperation: anactivemodedrivenbyapump,andapassivemodecontrolled
2
by a variable position valve. The electrohydraulic design combines the safety, comfort, and
versatilityofastateoftheartmicroprocessorcontrolledhydraulickneewiththreenewben-
efits. First, by pumping fluid into the hydraulic cylinder, the necessary knee angle during
the swing phase of walking to clear obstacles in the path of the foot is achieved. Second,
adding power at the knee reduces hip torque required to swing the leg forward. Third, the
power added at the knee helps lift the amputee’s body weight, allowing the step over step
ascent of ramps and stairs. These benefits should reduce back and hip pain, and should
improve mobility to afford the amputee a healthier life.
i
Contents
List of Figures iii
List of Tables v
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Amputation Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Improving Amputee Quality of Life through Prosthetics . . . . . . . 2
1.2 Limitations of Current Prostheses . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Major Contributions and Outline of the Thesis . . . . . . . . . . . . . . . . 3
2 Background 5
2.1 Biomechanics Vocabulary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 A Normal Gait Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Energetically Passive Prosthetic Knees . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 Single Axis Knees . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Locking Knees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3 Stance Control Knees . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.4 Polycentric Knees . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.5 Pneumatic and Hydraulic Knees . . . . . . . . . . . . . . . . . . . . 13
2.3.6 Microprocessor Knees . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4 Transfemoral Amputee Gait Deficiencies . . . . . . . . . . . . . . . . . . . . 17
2.5 Powered Prosthetic Knee Development . . . . . . . . . . . . . . . . . . . . . 19
2.6 A Novel Hybrid Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3 Developing a Hydraulic Circuit 22
3.1 Hybrid Knee Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2 Circuit Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Hydraulic Circuit Candidates . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Hydraulic Actuator Options . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.4.1 Single Acting Cylinder . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.4.2 Double Acting, Unequal Volume (single rod) Cylinder . . . . . . . . 37
ii
3.4.3 Double Acting, Equal Volume (double rod) Cylinder . . . . . . . . . 37
3.4.4 Double Acting Rotary Vane . . . . . . . . . . . . . . . . . . . . . . . 38
3.5 Completing the Hydraulic Circuit . . . . . . . . . . . . . . . . . . . . . . . . 38
4 Hydraulic Power Unit Implementation 40
4.1 Modeling Performance Requirements . . . . . . . . . . . . . . . . . . . . . . 41
4.2 Motor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.2.1 Defining a Performance Index . . . . . . . . . . . . . . . . . . . . . . 45
4.2.2 Heat Dissipation Analysis . . . . . . . . . . . . . . . . . . . . . . . . 47
4.3 Component Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.3.1 Control Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.3.2 Hydraulic Manifold . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5 Sensing and Control 58
5.1 Control Strategy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.1.1 Control States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
5.2 Sensor Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.2.1 Knee Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.2.2 Thigh Angle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.2.3 Knee Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.2.4 Foot Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.3 Force Transducer Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.3.1 Torsion Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.3.2 Ovalizing Hole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.3.3 Shear Web Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6 Performance Evaluation 82
6.1 The Completed Hybrid Knee . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.2 Amputee Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.2.1 Otto Bock, U.S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.2.2 Otto Bock, Germany . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.2.3 Laboratory Treadmill Tests . . . . . . . . . . . . . . . . . . . . . . . 88
6.3 Testing Protocol Recommendations . . . . . . . . . . . . . . . . . . . . . . . 90
6.3.1 Measured Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.3.2 Testing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7 Conclusion 94
7.1 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Bibliography 99
iii
List of Figures
2.1 Sagittal, coronal, and transverse planes. . . . . . . . . . . . . . . . . . . . . 6
2.2 Directions of motion of the knee and hip joints . . . . . . . . . . . . . . . . 7
2.3 A single stride of the human gait cycle . . . . . . . . . . . . . . . . . . . . . 8
2.4 Components of an above-knee prosthesis . . . . . . . . . . . . . . . . . . . . 9
2.5 Knee angle, torque, and power for a normal stride . . . . . . . . . . . . . . 10
2.6 Five types of purely mechanical prosthetic knees . . . . . . . . . . . . . . . 12
2.7 Pneumatic schematic for the Endolite IP . . . . . . . . . . . . . . . . . . . . 14
2.8 Hydraulic and pneumatic schematic for the Endolite Adaptive . . . . . . . . 15
2.9 Hydraulic schematic for the Otto Bock C-Leg . . . . . . . . . . . . . . . . . 16
2.10 Abnormal hip abduction and pelvic obliquity in amputee gait . . . . . . . . 18
3.1 Hydraulic schematic for a passive knee . . . . . . . . . . . . . . . . . . . . . 26
3.2 Hydraulic schematic for an active knee . . . . . . . . . . . . . . . . . . . . . 26
3.3 Hydraulic schematic for a hybrid active/passive knee . . . . . . . . . . . . . 26
3.4 Candidate hydraulic schematics for the hybrid knee . . . . . . . . . . . . . . 27
3.5 Alternative hydraulic schematics for the hybrid knee . . . . . . . . . . . . . 32
3.6 Hydraulic schematics employing three-port controllable valves . . . . . . . . 33
3.7 Hydraulic schematics employing several multiple-port controllable valves . . 35
3.8 The implemented hydraulic circuit for the hybrid knee . . . . . . . . . . . . 39
4.1 Approximate knee angle, torque, and power for a prosthetic stride . . . . . 42
4.2 Geometry of the hydraulic actuator linkage . . . . . . . . . . . . . . . . . . 43
4.3 Pump motor performance capabilities . . . . . . . . . . . . . . . . . . . . . 46
4.4 Motor heat dissipation during stair climbing and level walking. . . . . . . . 49
4.5 Three-port controllable valve . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.6 Hydraulic manifold layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.7 Exploded hydraulic power unit . . . . . . . . . . . . . . . . . . . . . . . . . 57
5.1 Finite state machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.2 Exploded view of the knee showing sensor locations. . . . . . . . . . . . . . 64
5.3 Pressure sensor locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
5.4 Ground reaction forces for one stride . . . . . . . . . . . . . . . . . . . . . . 67
iv
5.5 Ground reaction forces in the sagittal plane . . . . . . . . . . . . . . . . . . 69
5.6 Foot load force transducer location . . . . . . . . . . . . . . . . . . . . . . . 70
5.7 Strain gage pattern for measuring shear strains . . . . . . . . . . . . . . . . 71
5.8 Torsion bar force transducer concept . . . . . . . . . . . . . . . . . . . . . . 73
5.9 Ovalizing hole force transducer concept . . . . . . . . . . . . . . . . . . . . 73
5.10 Shear web force transducer concept . . . . . . . . . . . . . . . . . . . . . . . 74
5.11 Shear web cross section dimensions . . . . . . . . . . . . . . . . . . . . . . . 75
5.12 I-beam loading in torsion and shear. . . . . . . . . . . . . . . . . . . . . . . 75
5.13 Force transducer gage placement . . . . . . . . . . . . . . . . . . . . . . . . 80
6.1 Cutaway view of the completed knee . . . . . . . . . . . . . . . . . . . . . . 83
6.2 Batteries and electronics fit under the knee cover . . . . . . . . . . . . . . . 84
6.3 Amputee walking with the hybrid knee . . . . . . . . . . . . . . . . . . . . . 89
7.1 Hydraulic circuit schematic with conservative element . . . . . . . . . . . . 96
7.2 Hydraulic circuit schematic with ankle . . . . . . . . . . . . . . . . . . . . . 97
v
List of Tables
4.1 Knee geometry parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2 Motor temperature parameters . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.1 Force transducer dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.2 Strain gage measurement isolation . . . . . . . . . . . . . . . . . . . . . . . 79
vi
Acknowledgments
First of all, I would like to thank Professor Kazerooni for recruiting me to the University
of California, Berkeley for my graduate education, and particularly for inviting me to join
the Human Engineering Laboratory. The lab has always been populated with an incredibly
talented group of staff and students working collaboratively on groundbreaking technology.
I believe you would be hard pressed to find a university laboratory anywhere else with the
same resources, wisdom, innovation, and hands-on experience.
The hybrid knee described in this thesis would not have been possible without the
help of several members of the lab. Dylan Fairbanks designed the electronics. Matthew
Rosa wrote the control and spent countless hours debugging both hardware and software
issues. Minerva Pillai prepared many drawings for manufacturing, and was indispensable
in assembling the force transducer and several other components. Thanks to all those who
paved the way through previous projects and prototypes, including, but not limited to
Adam Zoss, Sebastian Kruse, and Miclas Schwartz.
Thanks to Professor Lieu and Professor S´equin for taking the time out of their
schedules to serve on my dissertation committee.
And of course I am grateful for the support from my parents and for their friendly
ribbing about my procrastination.