Sliding mode PID-controller design for robot manipulators by using fuzzy tuning approach

In this paper, a chattering free sliding mode control (SMC) for a robot manipulator including PID part with a fuzzy tunable gain is designed. The main idea is that the robustness property of SMC and good response characteristics of PID are combined with fuzzy tuning gain approach to achieve more acceptable performance. For this purpose, in the first stage, a PID sliding surface is considered such that the robot dynamic equations can be rewritten in terms of sliding surface and its derivative and the related control law of the SMC design will contain a PID part. The stability guarantee of this sliding mode PID-controller is proved by a lemma using direct Lyapunov method. Then, in the second stage, in order to decrease the reaching time to the sliding surface and deleting the oscillations of the response, a fuzzy tuning system is used for adjusting both controller gains including sliding controller gain parameter and PID coefficient. Finally, the proposed methodology is applied to a two-link robot manipulator including model uncertainty and external disturbances as a case study. The simulation results show the improvements of the results in the case of using the proposed method in comparison with the conventional SMC.