Modelling and Control of Lower Limb Exoskeletons and Walking Aid for Fundamental Mobility Tasks

212 Pages·2012·12.36 MB·English

Modelling and Control of Lower Limb
Exoskeletons and Walking Aid for
Fundamental Mobility Tasks

by

Daniela Miranda Linares

A thesis submitted to the University of Sheffield
for the degree of Doctor of Philosophy

Department of Automatic Control and Systems Engineering

November 2016

Abstract

In the last five decades, exoskeletons have emerged as a solution to assist paraplegic and
elderly patients perform fundamental mobility tasks. The main challenge nowadays, is to
develop a device that is safe, power sufficient, seamlessly integrates with the user, while being
affordable. Several solutions have been proposed, and controllers have been identified as the
only component which can enhance integration with the user without adding weight to the
system, or increasing energy consumption. Moreover, a software platform where the
mechanical design and control techniques can be assessed, prior to experimental trials, could
save resources and decrease costs.
In this thesis, the development of humanoid and exoskeleton models, within the SimWise
virtual environment, to perform an initial validation of controllers proposed without the need
of a physical prototype, is performed. Furthermore, the selected platform is evaluated
regarding its fitness for this application.
The methodology used to generate CAD models of a humanoid, exoskeletons and a wheel
walker within the SimWise virtual environment is described, along with its integration with
MATLAB Simulink. Two exoskeleton models with their corresponding controllers were
developed, firstly, a hybrid exoskeleton with a wheel walker for restoration of walking in
paraplegic patients. And secondly, an actuated exoskeleton for assistance in standing-up and
sitting-down motions in both the elderly and paraplegic patients.
The hybrid exoskeleton uses functional electrical stimulation as actuation for knee joints
and a frame with brakes mounted at hip, knee and ankle joints to generate the walking cycle.
The wheel walker is used for support and equilibrium. A fuzzy controller for the low level and
a finite state controller for the middle level is developed. Validation of the system over
repeated walking cycles, including external disturbances, and simulation of use by humanoids
of different dimensions, is performed within the virtual environment and results discussed.
PID low level control of hip and knee joints is used to analyse standing-up and sitting-
down motions, and incorporated with an actuated exoskeleton for assisting elderly people on
performing the aforementioned tasks. A finite state middle level control is developed to
generate reference trajectories at variable velocities for the restoration of these motions for
paraplegic patients. An optimisation algorithm is used to identify low level controller
parameters for ankle joints. Finally, offline and online calculation and incorporation of zero
moment point in the control loop is performed to assess equilibrium of the system.
I
Acknowledgements

Firstly I thank God for allowing me to accomplish this goal, and giving me health and strength
to do so. I am immensely grateful with Him for each, and every blessing I have received during
the course of my life, and especially in the last 4 years.
I also wish to express my most sincere gratitude to my supervisor Dr. Osman Tokhi for
his guidance, patience, and encouragement throughout this research. For his trust, kind
commitment to his students, and for sharing his valuable experience and knowledge with all
of us.
I am grateful as well to Professor Juan Coronado, Carlos Díaz and all the guys from the
Polytechnic University of Cartagena for their collaboration, teachings and warm hospitality
during my stay.
I gratefully acknowledge the National Council for Science and Technology and the
Automatic Control and Systems Engineering Department for sponsoring my research studies.
As well as the ACSE staff, whom I have had the opportunity to meet during these years, for
their valuable advice and enthusiasm towards research.
I am indebted to all those who throughout my education life, have taught me important
lessons: lecturers at ACSE, at the ITESM-CEM and CEMA, in México, particularly those
who, beyond academic knowledge, have taught me valuable life lessons.
I am thankful to all the colleagues who have in one way or another helped ignite my
scientific curiosity, given support, advice and researched and worked by my side, especially
Normaniha, Siti Khadijah, Asnor, Ghasaq, Norafizah, Omar, Hyreil, Nafri, Abdullah, Ahmad
and all the guys from 307.
On the personal side I would like to thank my parents Alberto and Emma, to whom I am
indebted for their devotion to our family wellness and education. For teaching me so much,
challenging me to dream big, and especially for their help and understanding during the pursue
of this degree, and for being such working and loving parents and grandparents. I am grateful
too to my sister Verónica and my brother Luis for so many childhood memories, for their love,
support and inspiration.
I am also thankful to my Mexican, Brazilian, Malaysian, Nigerian, Chinese and English
friends at Sheffield and at home, for sharing your knowledge, culture and special moments
with me. Thanks especially to Nora and Janet, for their support and company during these
years.
I want to express my outmost gratitude to my husband José de Jesús for being my
colleague, my friend, and an amazing father. For providing prised advice and help in the
writing of this thesis. For being always loving and supportive, particularly during the research
journey we have gone through together, for being at my side in the past to face every challenge,
and for the hope of adventures that we are yet to share.
Finally I am thankful to my little José Alberto, since even without knowing it, he has been
my inspiration and has brighten my days with his sole existence and cute innocence. It has
been a blessing being able to witness every minute of his life.
II
Table of contents

ABSTRACT ..................................................................................................................... I
ACKNOWLEDGEMENTS ............................................................................................... II
TABLE OF CONTENTS ................................................................................................ III
LIST OF FIGURES ........................................................................................................ VI
LIST OF TABLES .......................................................................................................... X
LIST OF ACRONYMS ................................................................................................... XI

CHAPTER 1 MOBILITY IMPAIRMENTS AND EXOSKELETONS: PARAPLEGIC AND
ELDERLY PEOPLEC ................................................................................................................. 1
1.1 BACKGROUND AND MOTIVATION ............................................................................ 1
1.2 THE SOLUTION TO IMMOBILITY: EXOSKELETONS .................................................... 3
1.3 MAIN CHALLENGES .................................................................................................. 9
1.4 AIM AND OBJECTIVES ............................................................................................. 12
1.5 MAIN CONTRIBUTIONS ........................................................................................... 13
1.6 THESIS OUTLINE ..................................................................................................... 14
1.7 PUBLICATIONS........................................................................................................ 16

CHAPTER 2 MODELLING OF HUMANOID, EXOSKELETON AND WHEEL WALKER .......... 17
2.1 INTRODUCTION ....................................................................................................... 17
2.2 MOBILITY ISSUES ................................................................................................... 18
2.2.1 Spinal cord injury and paraplegia .................................................................. 18
2.2.2 Elderly muscle weakening ............................................................................. 19
2.3 EXOSKELETONS REVIEW ........................................................................................ 20
2.3.1 Sensors ........................................................................................................... 24
2.3.2 Actuators ........................................................................................................ 25
2.3.3 Power supplies ............................................................................................... 27
2.3.4 Control techniques ......................................................................................... 27
2.4 MODELLING OF HUMANOID, EXOSKELETON AND WALKING AID ........................... 33
2.4.1 Software ......................................................................................................... 33
III
2.4.2 Humanoid modelling ...................................................................................... 36
2.4.3 Exoskeleton for paraplegic patients ................................................................ 38
2.4.4 Exoskeleton for elderly and paraplegic patients assistance ............................ 42
2.4.5 Integration of models in SimWise 4D and MATLAB Simulink .................... 45
2.5 SUMMARY ............................................................................................................... 47

CHAPTER 3 LOW AND MIDDLE LEVEL CONTROL OF HYBRID EXOSKELETON AND
WHEEL WALKER FOR PARAPLEGIC GAIT IN STRAIGHT LINE ............................................. 49
3.1 INTRODUCTION ....................................................................................................... 49
3.2 WALKING CYCLE .................................................................................................... 50
3.3 MUSCLES OPERATION ............................................................................................. 52
3.4 FUNCTIONAL ELECTRICAL STIMULATION OF PARAPLEGIC MUSCLES ..................... 53
3.5 CONTROL OF PARAPLEGIC WALKING WITH HYBRID ORTHOSIS .............................. 58
3.5.1 Fuzzy control of knee joints torque ................................................................ 59
3.5.2 Finite State Control ........................................................................................ 64
3.6 VALIDATION TESTS ................................................................................................. 73
3.6.1 Repeatability tests ........................................................................................... 76
3.6.2 Stability .......................................................................................................... 78
3.6.3 Range .............................................................................................................. 81
3.6.4 Torque and energy consumption .................................................................... 82
3.7 SUMMARY ............................................................................................................... 85

CHAPTER 4 PID CONTROL OF HUMANOID AND EXOSKELETON FOR ELDERLY
ASSISTANCE ON STANDING-UP AND SITTING-DOWN TASKS……………………………….87
4.1 INTRODUCTION ....................................................................................................... 87
4.2 ASSISTIVE DEVICES FOR ELDERLY MOBILITY ......................................................... 88
4.3 ELDERLY STANDING-UP AND SITTING-DOWN ......................................................... 90
4.4 OPEN-LOOP SIMULATIONS OF STANDING-UP AND SITTING-DOWN MOTIONS ......... 94
4.5 PID CONTROL OF HUMANOID FOR TORQUE PROFILES ASSESSMENT ....................... 95
4.5.1 PID Control .................................................................................................... 95
4.5.2 Closed-loop PID control scheme .................................................................... 97
4.5.3 Tests with different gains ............................................................................... 98
4.5.4 Tests with different saturation levels ............................................................ 102
4.5.5 Tests with different velocities ...................................................................... 105
4.6 PID CONTROL OF EXOSKELETON FOR STANDING-UP ASSISTANCE ....................... 107
4.6.1 Standing-up with unactuated exoskeleton .................................................... 107
4.6.2 Exoskeleton assistance ................................................................................. 110
4.6.3 Reaction force with seat and ground ............................................................ 115
4.7 SUMMARY ............................................................................................................. 116

IV
CHAPTER 5 ONLINE TRAJECTORY TRACKING CONTROL OF EXOSKELETON FOR
PARAPLEGIC ASSISTANCE ON STANDING-UP AND SITTING-DOWN TASKS ....................... 117
5.1 INTRODUCTION ......................................................................................................... 117
5.2 EQUILIBRIUM OF MOBILE SYSTEMS .......................................................................... 118
5.2.1 Static equilibrium and-centre of mass .................................................................. 118
5.2.2 Dynamic equilibrium and zero moment point ..................................................... 121
5.3 METHODOLOGY FOR ONLINE TRAJECTORY TRACKING CONTROL ............................ 126
5.3.1 Control scheme .................................................................................................... 126
5.3.2 Finite state controller for standing-up and sitting-down ...................................... 127
5.4 OFFLINE VERIFICATION OF DYNAMIC STABILITY ..................................................... 137
5.5 IMPLEMENTATION OF ONLINE TRAJECTORY TRACKING CONTROL WITH FSC ......... 140
5.6 SUMMARY ................................................................................................................ 148

CHAPTER 6 PARTICLE SWARM OPTIMISATION OF ANKLE JOINT CONTROL PARAMETERS
FOR DYNAMIC EQUILIBRIUM DURING STANDING-UP AND SITTING-DOWN TASKS .......... 149
6.1 INTRODUCTION ......................................................................................................... 149
6.2 PARTICLE SWARM OPTIMISATION ALGORITHM ....................................................... 150
6.3 PARTICLE SWARM OPTIMISATION OF ANKLE JOINT CONTROL PARAMETERS ........... 155
6.3.1 Optimisation of ankle joint PID controller gains ................................................. 155
6.3.2 Optimisation of feet orientation PID controller gains .......................................... 158
6.3.3 Optimisation of feet orientation fuzzy control parameters .................................. 159
6.4 ONLINE TRACKING OF ZMP ..................................................................................... 160
6.5 IMPLEMENTATION OF ANKLE JOINT CONTROL ......................................................... 162
6.6 SUMMARY ................................................................................................................ 167

CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK ................. 169
7.1. SUMMARY OF CONTRIBUTIONS .............................................................................. 169
7.2. CONCLUSIONS ........................................................................................................ 171
7.3. CHALLENGES .......................................................................................................... 174
7.4. RECOMMENDATIONS FOR FUTURE WORK ............................................................... 176

REFERENCES ....................................................................................................................... 179
APPENDICIES ....................................................................................................................... 191
APPENDIX A ..................................................................................................................... 191
APPENDIX B ..................................................................................................................... 192
APPENDIX C ..................................................................................................................... 195
APPENDIX D ..................................................................................................................... 196
APPENDIX E...................................................................................................................... 197

V
List of figures

Figure 2.1 Cord Injury levels and effects, modified from (Harrison, 2006). ......................... 19
Figure 2.2 Lower limb orthosis (Hsu et al., 2008) ................................................................. 21
Figure 2.3 Exoskeletons control structure, modified from (Tucker et al.,2015) .................... 29
Figure 2.4 Humanoid model: a) Isometric, b) frontal and c) lateral views ............................ 38
Figure 2.5 a) Initial (zero) position and ranges of motion for b) hip, c) knee and d) ankle. .. 38
Figure 2.6 Exoskeleton model: a) Isometric, b) frontal and c) lateral views.......................... 40
Figure 2.7 Wheel Walker: a) Isometric, b) frontal and c) lateral views ................................. 41
Figure 2.8 Humanoid wearing exoskeleton and wheel walker: a) Isometric, b) frontal and c)
lateral views ............................................................................................................................ 42
Figure 2.9 EXO LEGS exoskeleton: a) Isometric, b) frontal and c) lateral views ................. 43
Figure 2.10 Humanoid wearing exoskeleton: a) Isometric, b) frontal and c) lateral views.. 4c4
Figure 2.11 SimWise Plant ..................................................................................................... 46
Figure 2.12 Example of Simulink implementation of SW Plant ............................................ 46
Figure 3.1 Phases of gait cycle, modified from (Hsu, et al., 2008) ........................................ 50
Figure 3.2 Joint trajectories in normal adult walking modified from (Okamoto and Okamoto,
2007)....................................................................................................................................... 51
Figure 3.3 a)Motor unit diagram b) Motor unit activation sequence, modified from
(Dictionary, 2009) .................................................................................................................. 52
Figure 3.4 FES parameters ..................................................................................................... 54
Figure 3.5 Control scheme for simulation of paraplegic walking with FES and hybrid
orthosis. .................................................................................................................................. 58
Figure 3.6 Control scheme of experimental validation of paraplegic walking with FES and
hybrid orthosis ........................................................................................................................ 59
Figure 3.7 Fuzzy membership function .................................................................................. 60
Figure 3.8 Simple fuzzy control system (Ross, 2010) ............................................................ 61
Figure 3.9 Control loop of fuzzy controller for one leg from (Jailani, 2011) ........................ 63
Figure 3.10 Knee joint references considered in a) Jailani’s work, b) Winter’s work, c)
reference proposed. ................................................................................................................ 64
Figure 3.11 Simple finite state machine ................................................................................. 65
Figure 3.12 Finite state controller of walking motion ............................................................ 68
Figure 3.13 Switching period of brakes and FES for both legs with knee orientation for
reference. ................................................................................................................................ 72
Figure 3.14 a) Exoskeleton angles and distances to floor b) Exoskeleton link lengths .......... 73
Figure 3.15 Knee joint actual orientation and reference during a complete walking cycle ... 74
Figure 3.16 Comparison of paraplegic walking with FES and hybrid orthosis vs normal
walking joints trajectories ...................................................................................................... 75
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Figure 3.17 a) Repeatability test run with incomplete step b)Zoom in of incomplete step ... 77
Figure 3.18 Repeatability test run starting step with left leg a) Complete simulation run b)
Zoom in initial steps ............................................................................................................... 78
Figure 3.19 a) Representation of disturbances applied .......................................................... 79
Figure 3. 20 System reaction to external disturbances a) Complete simulation b) Zoom in
affected time slot .................................................................................................................... 79
Figure 3.21 Travelled distance with disturbances .................................................................. 80
Figure 3.22 Test 2: System reaction to external disturbances a) Complete simulation b)
Zoom in affected time slot ..................................................................................................... 81
Figure 3.23 Test 2: Travelled distance with disturbances ...................................................... 81
Figure 3.24 Knee joint torques a) 10 seconds segment b) Zoom in initial step ..................... 83
Figure 3.25 Torque-Time integral of knee joints a) Complete simulation b) Zoom in initial

step ......................................................................................................................................... 84
Figure 4.1 Standing-up motion phases (Kralj and Bajd, 1989) .............................................. 91
Figure 4.2 Sitting-down motion phases (Kralj and Bajd, 1989) ............................................ 92
Figure 4.3 Standing-up and sitting-down lower limbs joints orientations ............................. 92
Figure 4.4 Simulation of standing-up and sitting-down motions ........................................... 94
Figure 4.5 Simulink control diagram of humanoid hip joints ................................................ 97
Figure 4.6 Simulink control diagram of humanoid hip and knee joints ................................. 99
Figure 4.7 Orientation, torque and TTI of a) hip and b) knee joints with gain combination for
minimum RMSE .................................................................................................................... 99
Figure 4.8 Orientation, torque and TTI of a) hip and b) knee joints with gain combinations
for minimum TTI ................................................................................................................. 100
Figure 4.9 Relation between TTI and 𝐾𝑑 gain for a) hip joints and b) knee joints ............. 101
Figure 4.10 Relation between RMSE and a) 𝐾𝑖 gain and b) 𝐾𝑝 gain for knee joints .......... 101
Figure 4.11 Orientation, torque and TTI of a) hip and b) knee joints with lowest torque
saturation values................................................................................................................... 102
Figure 4.12 Relation between RMSE and saturation torque for a) hip and b) knee joints... 103
Figure 4.13 Relation between TTI and saturation torque for a) hip and b) knee joints ....... 104
Figure 4.14 Relation between TTI and RMSE for a) hip and b) knee joints ....................... 104
Figure 4.15 a)Orientation, b)torque and c)TTI of hip joints for three different velocities .. 106
Figure 4.16 a)Orientation, b)torque and c)TTI of knee joints for three different velocities 107
Figure 4.17 Exoskeleton joints............................................................................................. 108
Figure 4.18 a)Orientation, b)torque and c)TTI of hip joints with unactuated exoskeleton for
different velocities ............................................................................................................... 109
Figure 4.19 a)Orientation, b)torque and c)TTI of knee joints with unactuated exoskeleton for
different velocities ............................................................................................................... 110
Figure 4.20 Simulink control diagram of hip and knee joints of humanoid and exoskeleton
............................................................................................................................................. 111
Figure 4.21a)Orientation, b)torque and c)TTI of hip joints with actuated exoskeleton for
different velocities ............................................................................................................... 112
VII
Figure 4.22 a)Orientation, b)torque and c)TTI of knee joints with actuated exoskeleton for
different velocities ................................................................................................................ 113
Figure 4.23 Standing-up and sitting-down motion with exoskeleton assistance .................. 113
Figure 4.24 a) RMSE and b) TTI of with actuated exoskeleton, unactuated exoskeleton and
humanoid alone .................................................................................................................... 114
Figure 4.25 Reaction force with a) ground and b) seat with knee orientation as reference . 115
Figure 5.1 a) Humanoid and wheel walker CoM b) CoM and centroids diagram c) CoM
during standing-up motion ................................................................................................... 120
Figure 5.2 Middle and low level control scheme ................................................................. 127
Figure 5.3 Finite state controller of standing-up and sitting-down motions ........................ 129
Figure 5.4 Feet and joints angles and distances between joints ........................................... 134
Figure 5.5 Finite State Machine of fundamental mobility tasks .......................................... 136
Figure 5.6 Robotic arm representing lower limbs ................................................................ 138
Figure 5.7 Orientation, angular velocity and angular acceleration during standing-up motion
.............................................................................................................................................. 139
Figure 5.8 Orientation, angular velocity and angular acceleration during sitting-down motion
.............................................................................................................................................. 139
Figure 5.9 Standing-up and sitting-down joints trajectories divided by state ...................... 141
Figure 5.10 Normalised orientation of a) hip joint and b) knee joint at different velocities 141
Figure 5.11 Hip joint orientation, torque and torque time integral at different velocities .... 142
Figure 5.12 Knee joint orientation, torque and torque time integral at different velocities . 143
Figure 5.13 Hip joint orientation and torque after error ....................................................... 144
Figure 5.14 Knee joint orientation and torque after error ..................................................... 144
Figure 5.15 Stick diagram of standing-up motion ................................................................ 145
Figure 5.16 ZMP and CoM during standing-up motion at average velocity compared to the
support area .......................................................................................................................... 146
Figure 5.17 Zoom in view of ZMP and CoM during standing-up motion at average velocity
.............................................................................................................................................. 147
Figure 5.18 ZMP and CoM during sitting-down motion at average velocity a) compared to
the support area b) zoom in view ................................................................................... 147
Figure 6.1 Particle swarm optimisation algorithm ............................................................... 152
Figure 6.2 PID low level control scheme for ankle joint...................................................... 156
Figure 6.3 Control scheme with feet orientation PID controller .......................................... 158
Figure 6.4 Control scheme with feet orientation fuzzy controller ........................................ 160
Figure 6.5 Middle and low level control scheme with ZMP calculation and PSO optimisation
.............................................................................................................................................. 161
Figure 6.6 Hip, knee and ankle joints orientation, torque and TTI, with feet fixed to ground
.............................................................................................................................................. 162
Figure 6.7 Hip, knee and ankle joints orientation, torque and TTI, of control scheme with
feet orientation PID and feet unfixed from ground, ........................................................... 164
Figure 6.8 Hip, knee and ankle joints orientation, torque and TTI, of control scheme with
feet orientation FLC and feet unfixed from ground, .......................................................... 165
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