Data-Driven Phase-Based Control of a Powered Knee-Ankle Prosthesis for
Variable-Incline Stair Ascent and Descent
Abstract
Powered knee-ankle prostheses can offer benefits over conventional
passive devices during stair locomotion by providing biomimetic
net-positive work and active control of joint angles. However, many
modern control approaches for stair ascent and descent are often limited
by time-consuming hand-tuning of user/task-specific parameters,
predefined trajectories that remove user volition, or heuristic
approaches that cannot be applied to both stair ascent and descent. This
work presents a phase-based hybrid kinematic and impedance controller
(HKIC) that allows for semi-volitional, biomimetic stair ascent and
descent at a variety of step heights. We define a unified phase variable
for both stair ascent and descent that utilizes lower-limb geometry to
adjust to different users and step heights. We extend our prior
data-driven impedance model for variable-incline walking, modifying the
cost function and constraints to create a continuously-varying impedance
parameter model for stair ascent and descent over a continuum of step
heights. Experiments with above-knee amputee participants (N=2) validate
that our HKIC controller produces biomimetic ascent and descent joint
kinematics, kinetics, and work across four step height configurations.
We also show improved kinematic performance with our HKIC controller in
comparison to a passive microprocessor-controlled device during stair
locomotion.