Evaluating Energy Consumption of an Active Magnetorheological Knee Prosthesis

This paper presents a study of energy consumption of the AMRK, an Active Magnetorheological Knee actuator developed for transfemoral prostheses. The system consists of an active motor-unit composed by an EC motor, harmonic drive and magnetorheological (MR) clutch; that is displayed in parallel to an MR brake. With this configuration, the AMRK can work as a motor, clutch, or brake, reproducing movements similar to those of a healthy knee. We used the dynamic models of the MR clutch, MR brake and motor unit to simulate the energy consumption during over-ground walking under three different situations: using the complete AMRK, using just the motor-reducer of the AMRK, to simulate a common active prosthesis (CAKP), and using just the MR brake, to simulate a common semi-active prosthesis (CSAKP). The operation strategy of AMRK uses the motor-unit only when concentric contraction is required to raise the body center of gravity during midstance. When power dissipation is required, only the MR brake operates. The results show that the AMRK spends just 14.8 J during the gait cycle, with is 3.9 times lower than the CAKP (57.2 J), while the CSAKP spends just 6.0 J.