A electro-hydraulic position servo system based on a high speed on/off valve (HSV) and a directional valve was designed to obtain the high-precision position control of hydraulic cylinder using HSV

in existence of large parametric uncertainties and nonlinearities. Static flow characteristic of HSV was analyzed to choose appropriate experiment frequency. Nonlinear model of hydraulic system was established with friction model and the parameters of continuous differentiable friction model were identified by particle swarm optimization (PSO) algorithm. Direct adaptive robust controller (DARC) was proposed based on nonlinear projection mapping technology and back-stepping control theory. Parametric uncertainties and nonlinearities were handled by parameter online adaptation and robust feedback in DARC. Experimental results showed that the proposed controller achieved higher control performance which was better than proportion integration differentiation (PID) controller. In tracking a sinusoidal trajectory with amplitude of 5mm

frequency of 0.4Hz

the maximum tracking error was 0.638mm

average tracking error was 0.25mm

and standard deviation of the tracking error was 0.405mm during the last cycle. This method would be of valuable guiding significance to the development of digital servo control system.