Optimal design of flow mode semi-active prosthetic knee dampers

Magnetorheological (MR) fluid devices operate in a variety of modes, including flow, shear, squeeze, and pinch. Among these, the flow mode is the most efficient one and produces large field-induced pressure differences. Although shear mode is the least effective, it is the most commonly utilized in many applications, including prosthetic knee, due to its ease of construction. In this study, two flow mode designs which are twin rod and rotary vane MR dampers are optimally designed for prosthetic knee application. A multi-objective optimization problem with damping force or equivalent torque and mass as the objectives is formulated and the optimal designs are fabricated and experimentally characterized. The twin rod MR damper is found to produce a damping force of 1020 N at 1 A with an optimal mass of 0.71 kg. The rotary vane MR damper is determined to produce a maximum torque of 33 Nm at 1 A with an optimal mass of 1.1 kg. Finally, the designs are compared with many MR fluid based prosthetic knee design configurations. Based on the results, twin rod MR damper is identified as the optimal design configuration for prosthetic knee application.