A Robotic Lower Limb Prosthesis for Efficient Bicycling

Abstract

A controller for a powered transfemoral prosthesis is presented, which can coordinate power delivery at the knee with the motion of the crankshaft on a bicycle. The controller continuously estimates the lengths of a four-bar linkage model through the application of a recursive least squares algorithm. The link lengths are used to estimate the angle of the bicycle crankshaft. With this measure, the delivery of knee torque is coordinated with the motion of the user. The controller is implemented on a prosthesis prototype and assessed on a transfemoral amputee subject ( N = 1). The subject exhibited a bilateral work asymmetry of 83.5% when cycling with his daily use prosthesis in a free-swing mode. When 60-N·m peak assistance was provided by the powered prosthesis, the bilateral work asymmetry was reduced to 11.4%. The subject's metabolic energy rate was measured for speed and power-matched cycling while the powered prosthesis provided zero assistance (i.e., turned of f and providing its back-drive resistance) or 30-N·m peak assistance. Subject's metabolic energy rate decreased by 16.5% when receiving powered assistance relative to the zero-assistance condition.