Adduction Assistance from Powered Hip Exoskeleton Enables Modulation of
User Step Width During Walking
Abstract
Abstract-Using wearable robotics to modulate step width in normal
walking for enhanced mediolateral balance has not been demonstrated in
the field. We designed a bilateral hip exoskeleton with admittance
control to power hip abduction and adduction to modulate step width.
Objective: As the first step to show its potential, the objective of
this study was to investigate how human’s step width reacted to hip
exoskeleton’s admittance control parameter changes during walking.
Methods: Ten non-disabled individuals walked on a treadmill at a
self-selected speed, while wearing our bilateral robotic hip
exoskeleton. We used two equilibrium positions to define the direction
of assistance. We studied the influence of multiple stiffness values in
the admittance control on the participants’ step width, step length,
and electromyographic (EMG) activity of the gluteus medius. Results:
Step width were significantly modulated by the change of stiffness in
exoskeleton control, while step length did not show significant
changes. When the stiffness changed from zero to our studied stiffness
values, the participants’ step width started to modulate immediately.
Within 4 consecutive heel strikes right after a stiffness change, the
step width showed a significant change. Interestingly, EMG activity of
the gluteus medius did not change significantly regardless the applied
stiffness and powered direction.
Conclusion: Tuning of stiffness in admittance control of a hip
exoskeleton, acting in mediolateral direction, can be a viable way for
controlling step width in normal walking. Unvaried gluteus medius
activity indicates that the increase in step width were mainly caused
by the assistive torque applied by the exoskeleton.
Significance: Our study results pave a new way for future design and
control of wearable robotics in enhancing mediolateral walking balance
for various rehabilitation applications.