Overview of Active AFOs

156 Pages·2011·6.55 MB·English

by  Kira Barton

THE DESIGN AND CONTROL OF ACTIVE ANKLE-FOOT ORTHOSES

BY

KENNETH ALEXANDER SHORTER

DISSERTATION

Submitted in partial fulfillment of the requirements
for the degree of Doctor of Philosophy in Mechanical Engineering
in the Graduate College of the
University of Illinois at Urbana-Champaign, 2011

Urbana, Illinois

Doctoral Committee:

Associate Professor Elizabeth Hsiao-Wecksler, Chair
Professor William Durfee, University of Minnesota
Professor Karl Rosengren
Associate Professor Srinivasa Salapaka
Dr. Geza Kogler, Georgia Institute of Technology
UMI Number: 3479345
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Abstract
Ankle foot orthoses (AFOs) can be used to ameliorate the impact of impairments to the
lower limb neuromuscular motor system that affect gait. Existing AFO technologies include
passive devices with fixed and articulated joints, semi-active devices that modulate damping at
the joint and active devices that make use of a variety of technologies to produce power to move
the foot. Emerging technologies provide a vision for fully powered, untethered AFOs. In this
dissertation, a novel portable powered ankle-foot orthosis (PPAFO) cabable of providing un-
tethered assistance during gait is presented. The PPAFO provides both plantarflexor and
dorsiflexor torque assistance via a bi-directional pneumatic rotary actuator. The system uses a
portable pneumatic power source (compressed CO2 bottle) and embedded electronics to control
the motion of the foot. Experimental data from two impaired and five healthy subjects were
collected to demonstrate design functionality. The impaired subjects had bilateral impairments to
the lower legs that caused weakness to the plantarflexors, in one case, and to the dorsiflexors in
the other. Data from the healthy walkers demonstrated the PPAFO’s capability to provide
correctly timed plantarflexor and dorsiflexor assistance during gait. The results from the
impaired subjects demonstrated the PPAFO’s ability to provide functional assistance during gait.
Additionally, this dissertation presented a modeling and control approach to address limitations
present in the PPAFO through the introduction of a new hardware configuration and new control
architecture. A combined model consisting of both the PPAFO and the human foot and shank
segments was first derived and validated. Next, the current and the new PPAFO system
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configurations were evaluated both in simulation and experimentally during three simplified
functional gait tasks: (1) motion control of the foot at the start of the gait cycle, (2) plantarflexor
torque assistance during late stance, and (3) dorsiflexor position control of the foot during swing.
The resulting analysis showed that the new system configuration both outperformed and was
more efficient than the current PPAFO configuration. The stringent design requirements of light
weight, small size, high efficiency and low noise make the creation of daily wear assist devices
challenging, but once such devices appear they will present new opportunities for clinical
treatment of gait abnormalities.

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Dedication
To Kira, Adelynn and my fantastic family!
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Acknowledgements
This work was supported by National Science Foundation grant #0540834 and the Center
for Compact and Efficient Fluid Power, an NSF Engineering Research Center. I would also like
to thank Professor Andrew Alleyne, Professor Eric Loth, Professor Tim Bretl, Kira Barton, Yifan
(David) Li, Emily Morris, Aaron Becker, Henry Kohring, Jason Thomas, Joel Gilmer, Anastasia
Borok, Richard Kessler, Enric Xargay, Dave Hoelzle, Louis DiBerardino, my HDCL lab mates,
my committee members, and the investigators in the Comparative Neuromechanics Laboratory at
Georgia Tech (Prof. Young-Hui Chang, Megan Toney, and Jasper Yen) for their assistance with
this work.

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Table of Contents
LIST OF TABLES……………………………………………………………………………….ix
LIST OF FIGURES………………………………………………………………………………xi
CHAPTER 1 INTRODUCTION ................................................................................................ 1 
1.1 Motivation ...................................................................................................................... 1 
1.2 Dissertation Overview .................................................................................................... 3 
CHAPTER 2 TECHNOLOGIES FOR POWERED AFOS: POSSIBILITIES AND
CHALLENGES* ............................................................................................................................. 5 
2.1 Introduction .................................................................................................................... 5 
2.2 Motivation ...................................................................................................................... 6 
2.3 Normal and Pathological Gait ........................................................................................ 7 
2.4 Existent Passive and Active AFO Designs................................................................... 11 
2.4.1 Passive AFO Designs............................................................................................... 11 
2.4.2 Active and Semi-Active AFO Designs ...................................................................... 18 
2.5 Discussion..................................................................................................................... 28 
CHAPTER 3 A PORTABLE POWERED ANKLE-FOOT ORTHOSIS FOR
REHABILITATION * ................................................................................................................... 35 
3.1 Introduction .................................................................................................................. 35 
3.2 Methods ........................................................................................................................ 38 
3.2.1 PPAFO System Description ..................................................................................... 39 
3.2.2 Empirical Testing of PPAFO Functional Performance during Gait .............................. 46 
3.3 Results .......................................................................................................................... 49 
3.3.1 PPAFO System Performance Characteristics ............................................................. 49 
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3.3.2 Functional Walking Results...................................................................................... 52 
3.4 Discussion..................................................................................................................... 56 
3.5 Conclusion .................................................................................................................... 60 
CHAPTER 4 EXPERIMENTAL EVALUATION OF THE PPAFO ...................................... 62 
4.1 Introduction .................................................................................................................. 62 
4.2 Methods ........................................................................................................................ 64 
4.2.1 System Description Hardware and Control ................................................................ 64 
4.2.2 Subject Information ................................................................................................. 65 
4.2.3 Experimental Procedure and Data Collection ............................................................. 66 
4.2.4 Data Analysis .......................................................................................................... 68 
4.3 Results .......................................................................................................................... 73 
4.3.1 Results from the Healthy Walkers............................................................................. 73 
4.3.2 Results from ISubPF ................................................................................................ 83 
4.3.3 Regions of Deviation Analysis ................................................................................. 86 
4.3.4 Results from ISubDF ............................................................................................... 88 
4.4 Discussion..................................................................................................................... 92 
4.5 Conclusion .................................................................................................................... 96 
CHAPTER 5 MODELING, ANALYSIS AND CONTROL OF A POWERED
ANKLE-FOOT ORTHOSIS ......................................................................................................... 97 
5.1 Introduction .................................................................................................................. 97 
5.2 Modeling, System Identification, and Model Validation ........................................... 100 
5.2.1 PPAFO System Hardware ...................................................................................... 100 
5.2.2 Modeling of the PPAFO-Leg System ...................................................................... 102 
5.2.3 PPAFO-Leg Model Validation ............................................................................... 112 
5.3 Model-Based System Analysis and Control Design .................................................. 114 
5.3.1 Description of Functional Tasks Required for Gait................................................... 115 
5.3.2 PPAFO Control Design.......................................................................................... 118 
5.3.3 Experimental and Simulation Results ...................................................................... 120 
5.4 Discussion................................................................................................................... 125 
5.5 Conclusion .................................................................................................................. 126 
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CHAPTER 6 CONCLUSIONS AND FUTURE DIRECTION.............................................. 128 
6.1 Conclusions ................................................................................................................ 128 
6.2 Future Work................................................................................................................ 131 
6.2.1 Improving the Efficiency of the Current System ...................................................... 132 
6.2.2 The Next Generation PPAFO System...................................................................... 132 
6.2.3 Improved Control of the PPAFO ............................................................................ 133 
6.2.4 Continued Subject Testing ..................................................................................... 135 
LIST OF REFERENCES ............................................................................................................ 136 
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List of Tables
Table 2.1 A comparison of weight, torque, advantages, disadvantages, performance metrics, and
effectiveness of the novel passive AFO designs described in Section 2.4. ...................................... 33 
Table 2.2 A comparison of weight, torque, advantages, disadvantages, performance metrics, and
effectiveness of the novel Active and Semi-Active AFOs designs described in Section 2.4............... 34 
Table 4.1 Healthy subject joint range of motion, mean (and standard deviation), for each speed and
footwear condition. N unitless ROM symmetry index (SI) between the bilateral joint pairs was
calculated for each joint pair. A negative SI indicates that the parameter value for the left side
was greater than the right. ........................................................................................................ 74 
Table 4.2 Healthy subject, mean (and standard deviation), values for step length, cycle time, stance
time, and step width for all speed and footwear conditions. A unitless symmetry index (SI) was
also calculated for the bilateral parameters. A negative SI indicates that the parameter value
for the left side was greater than the right. ................................................................................ 75 
Table 4.3 Peak moment and powers and associated % gait cycle timing for the left ankle joint. ............. 76 
Table 4.4 Peak moment and powers and associated % gait cycle timing for the right ankle joint. ........... 77 
Table 4.5 Mean (and standard deviation) values of complexity and variability separated by body
segment, side of the body, and footwear condition at the normal walking speed. ........................... 81 
Table 4.6 Mean (and standard deviation) values of complexity and variability separated by body
segment, side of the body, and walking speed for shoe walking. ................................................... 82 
Table 4.7 Mean (and standard deviation) values of complexity and variability separated by body
segment, side of the body, and walking speed for PPAFO assisted walking. .................................. 83 
Table 4.8 ISubPF joint range of motion, mean (and standard deviation), for shoe and PPAFO
footwear conditions. A symmetry index (SI) between the bilateral joint pairs was calculated
for each joint. A negative SI indicates that the parameter value for the left side was greater
than the right. .......................................................................................................................... 84 
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