Phase-Based Impedance Control of a Powered Knee-Ankle Prosthesis for Tuning-Free Locomotion over Speeds and Inclines | CU Experts

Most impedance-based walking controllers use a finite state machine; (FSM) with dozens of user-specific parameters that need to be manually; tuned by technical experts. These parameters are only optimal near the; task (eg walking speed and incline) at which they were; tuned, resulting in decreased performance as task inevitably varies.; This paper presents a tuning-free, phase-based controller that uses a; hybrid combination of continuously-variable impedance control during; stance and kinematic control during swing to enable biomimetic; locomotion over a continuum of tasks. 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 the controller to autonomously adapt to task; variation. Experiments with an amputee participant using a powered; knee-ankle prosthesis show that our tuning-free controller 1) features; highly-linear phase estimates and accurate task estimates, 2) produces; more biomimetic joint work trends compared to a hand-tuned FSM impedance; controller, and 3) achieves lower kinematic and kinetic error than the; FSM impedance controller in 7 of 8 tested metrics. Our data-driven; control approach may allow easier clinical implementation of; variable-activity powered knee-ankle prostheses by replicating; biological behavior across tasks without expert tuning.

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