Abstract
Passive prosthetic legs require undesirable compensations from amputee
users to avoid stubbing obstacles and stairsteps. Powered prostheses can
reduce those compensations by restoring normative joint biomechanics,
but the absence of user proprioception and volitional control combined
with the absence of environmental awareness by the prosthesis increases
the risk of collisions. This paper presents a novel stub avoidance
controller that automatically adjusts prosthetic knee/ankle kinematics
based on suprasensory measurements of environmental distance from a
small, lightweight, low-power, low-cost ultrasonic sensor mounted above
the prosthetic ankle. In a case study with two transfemoral amputee
participants, this control method reduced the stub rate during stair
ascent by 89.95% and demonstrated an 87.5% avoidance rate for crossing
different obstacles on level ground. No thigh kinematic compensation was
required to achieve these results. These findings demonstrate a
practical perception solution for powered prostheses to avoid collisions
with stairs and obstacles while restoring normative biomechanics during
daily activities.