Stabilization of Rotary Inverted Pendulum Using Different Sliding Mode Control Techniques: An Experimental Study

Abstract

In last few decades, inverted pendulum has been considered as one of the benchmark problem in control theory. The system is highly nonlinear, underactuated, multivariable, open loop unstable and non-minimum phase. Different type of inverted pendulums is found in the literature. These are: linear inverted pendulum, rotary inverted pendulum, spherical inverted pendulum, double inverted pendulum, and mobile wheeled pendulum etc. The inverted pendulum control has been classified into three categories i.e. the swing control, the stabilization control and the tracking control. This work presents the stabilization of rotary inverted pendulum (RIP). Stabilization means keeping the inverted pendulum in the vertical upright position by applying suitable control effort on the rotary base. The conventional control techniques do not perform well in the presence of uncertainties or disturbances. Hence there is a need of robust control techniques for stabilizing of such an unstable system. The stabilization of RIP is done using different sliding mode control (SMC) techniques. These control techniques include SMC, integral sliding mode control (ISMC) and fuzzy integral sliding mode control (FISMC). SMC has two phases: reaching phase and sliding phase and it shows robustness in the presence of disturbance during sliding phase. In case of SMC the reaching phase is noise prone. This limitation of SMC can be eliminated by the ISMC technique. Both SMC and ISMC techniques are affected by the chattering phenomena which has adverse effect on the mechanical system. Therefore, FISMC technique is used to minimize the chattering effect. These control techniques have been implemented using MATLAB simulink and their results are compared with the conventional linear quadratic regulator (LQR) controller (without and with disturbance) in terms of settling rise time (tr) and time (ts). Simulation results show that the performance of LQR deteriorate with disturbance while SMC, ISMC and FISMC techniques gives better performance in the presence of disturbance. These control techniques are further validated on the real-time RIP system called QUANSER QUBE-SERVO.