Optimal Design of Magnetorheological Damper for Prosthetic Ankle

MR fluid is being used, of late, in several applications such as vibration isolation, prosthetics and haptic devices. Application of a magnetic field controls the rheological properties of the MR fluid enabling pressure drop, high shear stress, and reversibility of these properties. The present work aims at designing a prosthetic ankle and utilizes a pressure drop formulation using the Bingham model. Subsequently, magnetostatic analysis is done for solving an approximate parametric magnetic model (PMM) assuming linear magnetic systems. The usage of PMM reduces the computation time. Finite element magnetostatic (FEMS) validation of PMM for fluid parameters has been done. Finally, the design parameters of the MR valve are optimized with a multi-objective genetic algorithm (MOGA). The selection of design parameters has been done considering anthropometric constraint of a below-knee amputee. The objective functions chosen for the optimization are to: (a) maximize pressure drop and (b) minimize mass of the damper valve, thus reducing the mass of the prosthetic ankle. The optimization results indicate effective trade-off solutions between pressure drop and mass of the damper. The most optimal design is arrived at by awarding higher priority to the mass of the MR damper.