Output space tracking control for above-knee prosthesis

The control of a knee joint in an active above-knee prosthesis has been designed using the Lyapunov tracking method. Locomotion was simulated to prove that the tracking control in output space is a valuable real-time control method for artificial legs. The data used for simulation were collected from able-bodied subjects while they walked on a powered treadmill. Human volunteers were braced with an ankle splint (limiting dorsi- and plantar flexion) and with a knee cage (limiting knee movements to the lateral plane). The achieved tracking of the prescribed knee motion, deviations of the thigh movement from the prescribed trajectory, maximal angular deviations from the desired trajectory, and the power consumption were studied as functions of a limited maximal knee torque and a damping constant in the knee actuator. It was found that the use of output tracking is suitable for the design of appropriate hardware and for real-time control of an above-knee prosthesis.