Design, Modeling, and Simulation of Low-Cost Magnetorheological Fluid-Based Prosthetic Leg

This paper deals with designing and modeling a prosthetic leg with MR damper to control the knee joint for above-knee amputees. A four-bar mechanism has been selected for the knee joint of the prosthetic leg. A twin-tube MR damper was chosen for this work because of its better performance compared with other dampers, mainly due to the mobility of the magnetic core. The MR fluid selected for the purpose was the commercially available MRF 140CG. The entire modeling and simulation (motion analysis) of the prosthetic leg were done using SOLIDWORKS. This was done using the various relations of the natural human gait cycle. To find out the torque required to walk appropriately, dynamic analysis was done on a natural human leg’s free body diagram (FBD). A curve was obtained between torque at knee and hip angle by combining the results of FBD and SOLIDWORKS simulation FBD and SOLIDWORKS simulation results. To understand the behavior of the MR damper, magnetic analysis, and CFD was done using COMSOL and ANSYS, respectively. Various results like variation of the magnetic field with coil wire diameter, variation of pressure, and velocity were obtained. Using these obtained results, a relation between the yield stress and current was obtained. This will further be used to obtain a relation between required torque and current. The control strategy for this leg is the use of a PID controller. The obtained relation between hip angle and current will be stabilized using a PID controller by tuning suitable gains.