Data-Driven Variable Impedance Control of a Powered Knee–Ankle Prosthesis for Adaptive Speed and Incline Walking

Abstract

Most impedance-based walking controllers for powered knee-ankle prostheses use a finite state machine with dozens of user-specific parameters that require manual tuning by technical experts. These parameters are only appropriate near the task (e.g., walking speed and incline) at which they were tuned, necessitating many different parameter sets for variable-task walking. In contrast, this paper presents a datadriven, phase-based controller for variable-task walking that uses continuously-variable impedance control during stance and kinematic control during swing to enable biomimetic locomotion. After generating a data-driven model of variable joint impedance with convex optimization, we implement a novel task-invariant phase variable and real-time estimates of speed and incline to enable autonomous task adaptation. Experiments with aboveknee amputee participants (N=2) show that our data-driven controller 1) features highly-linear phase estimates and accurate task estimates, 2) produces biomimetic kinematic and kinetic trends as task varies, leading to low errors relative to able-bodied references, and 3) produces biomimetic joint work and cadence trends as task varies. We show that the presented controller meets and often exceeds the performance of a benchmark finite state machine controller for our two participants, without requiring manual impedance tuning.

Design, Kinematics and Gait Analysis, of Prosthetic Knee Joints: A Systematic Review

“…De facto, this was the first instance of an active prosthetic knee that could operate on its own power, in a subject experiment, for electrical energy regeneration. Prior training and a better experience with the prosthesis always assist amputees to better adapt to the provided prosthesis [53]. Likely, experimentation with a larger set of subjects would help to generalize the working of prostheses and make them adaptive.…”

Improving Sit/Stand Loading Symmetry and Timing Through Unified Variable Impedance Control of a Powered Knee-Ankle Prosthesis

“…We employ the approach presented in [28] to approximate the cost function in (6) with a convex equivalent. Fig.…”

“…By treating the coefficients in the δ i polynomials as independent decision variables, the cost function becomes linear in the decision variables and reduces to a convex quadratic program. As in [28], the original coefficients e 1 and e 2 can be recovered from the solution by simply approximating the rational function δ i (s)/K(s) with a fourth order polynomial (see [28] for further detail).…”

Improving Sit/Stand Loading Symmetry and Timing Through Unified Variable Impedance Control of a Powered Knee-Ankle Prosthesis

“…In this article, we extend our hybrid kinematic/impedance controller for variable-task walking [28] to also enable sitting and standing behaviors. As in our preliminary work in [15], we generate a novel, data-driven impedance parameter model based on able-bodied data that produces biomimetic joint torque during both sitting and standing motions.…”

“…In an effort to avoid the problems with discretely defined impedance parameters and to eliminate tuning, we previously developed a data-driven optimization framework to generate continuous, phase-based impedance trajectories for walking, which was validated on a powered knee-ankle prosthesis used by multiple participants [27], [28]. We recently extended this approach to sitting and standing transitions, fitting a unified polynomial impedance model to able-bodied kinematic and kinetic data [15].…”