Study on Precise Displacement Control of a Miniature Hydraulic System via RBF-DOB

For compact and efficient actuation, miniature hydraulic system has overwhelming superiority in power to weight ratio. However, it always involves nonlinear interferences like variable hose volume or oil bulk modulus, which greatly restricts control performance for the actuation. In this paper, a miniature hydraulic volume-controlled actuation system is introduced and the problem of precise displacement control of the system in presence of variable hose volume caused by uncertain external load is investigated. A radical basis function-disturbance observer (RBF-DOB) hybrid control strategy based on back-stepping theory is proposed. The system and the controller are mathematically modeled and simulation to demonstrate the validity of the RBF-DOB. Comparison to proportion-integral-differential and sliding model control (SMC) methods indicates that, the system using RBF-DOB has highest displacement precision and best dynamic performance. SMC is inclined to exhibit the best robustness but inferior jitter in control command output. As far as anti-disturbance capacity is concerned, RBF-DOB control strategy falls between other two counterparts. RBF-DOB hybrid control strategy can substantially solve the problems of nonlinear interferences resulted from uncertain system parameters and different load states in miniature hydraulic actuation systems.