Optimal design of ow mode semi-active prosthetic knee dampers

Magnetorheological (MR) fluid devices operate in four modes: ow, shear, squeeze, and pinch. Among these, the flow mode is the most efficient one and results in large field-induced pressure differences. Despite being the least efficient, shear mode is the most commonly used in numerous applications, including prosthetic knees, due to its ease of construction. Additionally, shear mode designs require larger shear areas and reduced fluid gap tolerance compared to their ow mode counterparts, resulting in a complex design such as the commercially available multi-plate MR brake. Therefore, in this study, two ow mode designs, twin-rod and rotary vane MR dampers, are optimally designed for prosthetic knee application. The optimal designs obtained from solving a multi-objective particle swarm optimization problem are fabricated and experimentally characterized for various harmonic excitations of varying amplitudes, frequencies, and currents. The optimal designs are compared with many MR fluid-based prosthetic knee design configurations. Based on the results, a twin-rod MR damper with a mass of 0.71 kg and a damping force of 1020 N at 1 A is identified as the optimal design configuration for prosthetic knee application.