Comparison of SMC and PID Controllers for Pneumatically Powered Knee Orthosis

The study aims in the design and implementation of suitable controllers for the knee joint of a pneumatically actuated orthosis, which is intended for rehabilitation and assistive purposes. Pneumatically powered orthosis, when compared with electrically driven orthosis, is lightweight in structure and also cost-effective. The knee and hip joints of the orthosis should follow the desired angle trajectory so that subject can move and stabilize efficiently. The role of controllers is crucial for the effective functioning of the limb to achieve the desired angle and velocity. Controllers like SMC and PID are integrated in the driving mechanism of the limb, and the characteristics are determined. The gain constants of proportional-integral-derivative controller (PID) are tuned manually to get the optimal response. Sliding mode control (SMC), basically a nonlinear control method is implemented for better performance. The prototype of below hip orthosis is fabricated, and the kinematic equations of the system are determined which is used to choose the optimum trajectory for the knee joints. The dynamics of the system are determined using Lagrange Euler Method, and the actuator torque required for both the joints is calculated. The performance of both controllers is compared, and SMC controller proved to be efficient in tracking the different types of reference inputs of the pneumatic assistive limb.