Robust force controller design for an electrohydraulic actuator based on nonlinear model

This paper documents the development and experimental evaluation of a hydraulic force controller, using nonlinear quantitative feedback theory (QFT) design method. A complete nonlinear mathematical model of a hydraulic actuator interacting with an environment is used to design the controller. Uncertainties are included in the model by considering the environmental stiffness and pump pressure as unknown parameters. The Golubev method is applied to derive a family of rational linear time-invariant transfer functions, which is precisely equivalent to the nonlinear plant within the system's operating range. A robust low-order controller is designed to satisfy a priori specified tracking and stability performances. The designed controller is implemented on an industrial hydraulic actuator equipped with a low-cost proportional valve. In spite of significant actuator dynamics and under varying conditions, successful control tests are performed repetitively