Model-based vs auto-tuning design of PID controller for knee flexion during gait

This paper discusses the derivation of a theoretical model of the movement of the shank, i.e. the lower part of the leg, around the knee joint. The objective is to control the angle of the shank with respect to the position of the upper leg. Subsequently, two types of design techniques are used to design a PID controller for the derived system: a model-based design method and an autotuner technique. The resulting PID controllers are compared by simulating a squat movement and a normal gait.We conclude that both PID controllers perform similar but the control effort for the auto-tuner technique presents a smoother course. However, the main advantage of the PID auto-tuner technique is that no mathematical transfer function model is necessary in order to tune the controller.