Design and Validation of a Polycentric Hybrid Knee Prosthesis With Electromagnet-Controlled Mode Transition

A hybrid knee prosthesis is proposed in this letter, which consists of a polycentric structure in passive mode for low-torque activities and a single-axis structure in active mode for high-torque activities. A novel mode transition mechanism controls self-holding electromagnets for switching modes between the four-bar linkage and single-axis structure. Compared with the conventional single-axis hybrid knee, the four-bar polycentric mechanism with varying instantaneous center of rotation (ICR) can enhance the geometric stability and increase the toe clearance in passive mode. For active mode, we developed a custom embedded electric system, employed torque control for stance and position control for swing. The results of bench tests indicated that the bandwidth of the controller was suitable for locomotion. The clinical test of level-ground walking without sudden buckling and stumble was validated by three subjects. Regarding climbing stairs, a typical high-torque activity in daily locomotion, all subjects reach the maximum knee torque around 0.95 Nm/kg comparable to the able-bodied.