Determination of Instantaneous Center of Rotation Position of Planar Four-Bar Linkage for Knee Rehabilitation

Among all the knee-supporting mechanism devices, the four-bar linkage is mainly used as it is simple to design, provides stability to the device, and mimics the motion of the knee joint. This chapter presents a four-bar mechanism in which the coupler point mimics the knee joint motion. The position of the instantaneous center of rotation (ICR) between the femur and tibia has been determined at different knee flexion angles, ultimately giving a curve. To determine ICR at one position of crank, algebraic equations have been solved, and to trace the locus of ICR, GeoGebra (a free tool) software is used. This approach is quite simple and effective. If ICR is not considered and simply trajectories are followed by four-bar coupler point, misalignment may occur. This chapter emphasizes the importance of the determination of ICR as it is related to stability and voluntary control.