Robust control of water hydraulic servo motor system using sliding mode control with disturbance observer

With the recent increased concerns for global environmental problems, the water hydraulic technique using pure tap water as a pressure medium has become a new drive source comparable to electric, oil hydraulic and pneumatic drive systems. However, the main problems for precise control in a water hydraulic servo motor system are steady state errors and overshoot due to its large friction torque in the low velocity range of a motor. In this research, the sliding mode control combined with the disturbance observer is applied to control the rotational angle of a water hydraulic servo motor. We examined the rotational angle control performances with these methods for load fluctuations.