Internal model control based fractional order PID controller for knee joint motion

Biomechanics is an area of research gaining lot of popularity in the recent times. In orthopedic industries, biomechanics are widely used to design orthopedic implants for various body joints, dental parts, external fixations, exo-skeletons and other medical purposes. Here, a technique for designing an internal model based fractional order PID controller for controlling the knee joint motion i.e. the movement of the shank around the knee joint, is suggested. Mathematical model is used for designing the controller and then simulation is done in simulink environment. In this technique, three out of five parameters i.e., kp, ki and kd are calculated using the conventional IMC based concept and the remaining two parameters i.e., λ and μ are obtained using trial and error method. The design technique proposed here is mathematically very simple. Moreover, better results were observed with the controller designed using the proposed designing technique as compared to the fractional controllers available in the literature so far. Using the integral error criterion robustness of the proposed controller with respect to system parameter variation is monitored and it is seen that it is better as compared to the existing fractional controllers.