Nonlinear adaptive robust control of hydraulic actuators regulated by proportional directional control valves with deadband and nonlinear flow gains

This paper studies the motion control of single-rod hydraulic actuators regulated by proportional directional control (PDC) valves with deadband and nonlinear flow gains. The boom motion control of a hydraulic robot arm driven by a single-rod hydraulic actuator is used as a case study. The experimental system dynamics are highly nonlinear. In addition, the system has large extent of modeling uncertainties such as the variation of payload and friction forces. Furthermore, the PDC valve used to regulate the control flow rate to the hydraulic actuator has a large extent of deadband and a very nonlinear flow gain coefficient right out of the deadband region. These issues make the precision control of such a system difficult. To deal with these issues, the paper presents a discontinuous projection based adaptive robust controller. Direct inverse is used to compensate for the effect of the valve deadband, and certain straight-line approximations are used to model the nonlinear flow gain coefficient of the valve. The approximation error of the nonlinear flow mapping is deal with via certain robust feedback. Theoretically, the proposed adaptive robust control (ARC) guarantees a prescribed output tracking transient performance and final tracking accuracy while achieving asymptotic output tracking in the presence of parametric uncertainties. Comparative experimental results are presented to illustrate the proposed control algorithm and the practical difficulties in controlling such a complex nonlinear dynamic system.