Sliding mode control of a 2-DOF hydraulic servo system

This paper proposed an alternative control strategy for 2-DOF parallel manipulator hydraulic servo system. The mathematical model derivation and simulation of the system was presented. The aim of the study was to develop a control strategy that is able to deal with nonlinearities, and resilient to parameter changes while tracking the vertical position and angular orientation of the system. While most studies are concerned with classic linear controllers, a nonlinear sliding mode control (SMC) was investigated herein. This controller was compared to the proportional+integral+derivative (PID) controller. Simulation results showed that the SMC performs better than the PID in both the displacement and the orientation in terms of tracking error and the actuator action required. While the SMC exhibits high frequency chattering, however, it is more robust to parameter variations compared to the PID. Therefore, it is concluded that overall the SMC controller is preferred over the PID. Furthermore, since the parameters of the SMC investigated were found by iterative selection they are nowhere near optimal. Optimization techniques such as genetic algorithm can be used to fine tune the SMC parameters for better performance.