Strategies to reduce the configuration time for a powered knee and ankle prosthesis across multiple ambulation modes.

Recently developed powered lower limb prostheses allow users to more closely mimic the kinematics and kinetics of non-amputee gait. However, configuring such a device, in particular a combined powered knee and ankle, for individuals with a transfemoral amputation is challenging. Previous attempts have relied on empirical tuning of all control parameters. This paper describes modified stance phase control strategies - which mimic the behavior of biological joints or depend on the instantaneous loads within the prosthesis - developed to reduce the number of control parameters that require individual tuning. Three individuals with unilateral transfemoral amputations walked with a powered knee and ankle prosthesis across five ambulation modes (level ground walking, ramp ascent/descent, and stair ascent/descent). Starting with a nominal set of impedance parameters, the modified control strategies were applied and the devices were individually tuned such that all subjects achieved comfortable and safe ambulation. The control strategies drastically reduced the number of independent parameters that needed to be tuned for each subject (i.e., to 21 parameters instead of a possible 140 or approximately 4 parameters per mode) while relative amplitudes and timing of kinematic and kinetic data remained similar to those previously reported and to those of non-amputee subjects. Reducing the time necessary to configure a powered device across multiple ambulation modes may allow users to more quickly realize the benefits such powered devices can provide.