The Impact of Phase Variable Accuracy on Continuous Controller Performance for Knee-Ankle Prostheses: A Case Study

Robust and effective control algorithms are essential for advancing powered lower-limb prostheses from laboratory settings to broader commercial use. Continuous controllers, which estimate an individual's gait progression to determine desired joint actuator outputs, have recently shown great promise. However, their success relies on accurately estimating the individual's progression through the gait cycle to ensure proper actuator behavior. This study investigates and quantifies how two gait estimation methods using only the global sagittal thigh angle for a knee-ankle prosthesis user impact controller performance. Two controllers were tested with each gait cycle estimation algorithm: a joint-level impedance controller and a task-level center of mass controller, extended to the kneeankle configuration herein. Experiments were conducted with an individual without amputation walking on a knee-ankle prosthesis. Higher linearity in gait estimation ($\mathrm{R}^{2}=0.984$ vs. $\mathrm{R}^{2}=0.980$) using the improved method resulted in lower shank velocity ($>25 {\%}$), better symmetry of shank velocity ($\sim 75 {\%}$), and lower impact into the mechanical hardstop during knee extension in swing for the impedance controller.