Simulation of the motion of a four bar prosthetic knee mechanism fitted with a magneto-rheological damper

A comprehensive study on the application of magneto-rheological (MR) damper in above knee prosthetic is introduced. The stance phase and the swing phase were studied. The knee model was composed of four-bar prosthetic knee mechanism with an MR damper. The equations of motion, of the model, were obtained using Newton's second law at the sagittal plane. To avoid the difficulties of the inverse dynamics, due to the damper’s nonlinear characteristics, a simplified approach was suggested for the Spencer model. This simplified approach was used to calculate the input voltage to the damper to obtain the desirable control force. The input data was obtained from the experimental work by sticking surface land marks to the artificial leg and filming it during performance of the daily activity. The Stream pix, AVI Edit, and WINanalyze software were used to calculate the global kinematics, for the required surface land marks, at each frame of the recorded motion. The model results represent the voltage required for the MR damper, during most daily activities, of a person who uses this kind of an artificial leg. The results showed that the required voltage depends on displacement, velocity and calculated force.