Design of controller for single axis knee using MR Damper

Human gait is characterized by periodic repetitions of two phases: a stance phase in which a foot is in contact with the ground, followed by a swing phase in which the lower limb swings through after toe-off. The functional necessities of above-knee prostheses are to provide knee locking during the stance phase and damping during the swing phase. Most of the conventional above-knee prostheses are based on passive mechanisms with constant mechanical properties such as friction, spring and damping coefficients. However, these designs are unstable while mimicking the natural gait, due to lack of active knee joint control. On the other hand, active type prostheses, such as those with hydraulic actuation (C Leg, Otto Bock) and a magnetorheological (MR) brake (Rheo Knee, Össur) can produce a gait similar to that of normal persons effectively, but they are expensive, heavy and consume significant energy. Therefore, in this paper a platform for designing semi-active type above-knee prostheses using MR damper is aimed at, as it has the best features of passive and active systems. The MR damper is designed with the objective of controlling swing-phase damping in above knee prosthesis. The knee is modeled as a single axis knee with an MR damper as shown in Figure 1. Figure 1: The amputee's swing leg model. l1 I1, m1 θ1 a1 Y