Toward balance recovery with leg prostheses using neuromuscular model control

Abstract

Objective: Lower limb amputees are at high risk
of falling as current prosthetic legs provide only limited func-
tionality for recovering balance after unexpected disturbances.
For instance, the most established control method used on
powered leg prostheses tracks local joint impedance functions
without taking the global function of the leg in balance recovery
into account. Here we explore an alternative control policy for
powered transfemoral prostheses that considers the global leg
function and is based on a neuromuscular model of human
locomotion. Methods: We adapt this model to describe and
simulate an amputee walking with a powered prosthesis using
the proposed control, and evaluate the gait robustness when
confronted with rough ground and swing leg disturbances. We
then implement and partially evaluate the resulting controller
on a leg prosthesis prototype worn by a non-amputee user.
Results: In simulation, the proposed prosthesis control leads to
more robust walking than the impedance control method. The
initial hardware experiments with the prosthesis prototype show
that the proposed control reproduces normal walking patterns
qualitatively and effectively responds to disturbances in early
and late swing. However, the response to mid-swing disturbances
neither replicates human responses nor averts falls. Conclusions:
The neuromuscular model control is a promising alternative to
existing prosthesis controls, although further research will need to
improve on the initial implementation and to determine how well
these results transfer to amputee gait. Significance: This work
provides a potential avenue for future development of control
policies that help improve amputee balance recovery.