A Generic Model Based Tracking Controller for Hydraulic Valve-Cylinder Drives

The control of hydraulic valve-cylinder drives is still an active subject of research, and various linear and particularly nonlinear approaches has been proposed, especially in the last two-three decades. In many cases the proposed controllers appear to produce excellent tracking ability due to robust- and/or adaptive functionalities, but also often rely on full state feedback and/or cumbersome and elaborate parameter designs. Also, such sophisticated control approaches often lack tuning methods which, together with the lack of proven reliability, is likely to be the reason why such approaches generally has failed to break through in industry. This paper discusses the dominant properties necessary to take into account when considering position tracking control of hydraulic valve-cylinder drives, and presents two generally applicable, generic control design approaches that combines non-linearity compensation, feed forward control and linear control. The generic properties of the proposed control structures arise with the fact that the designs are based on analytic considerations and rely on meaningful design rules. This also means that the proposed design approaches does not utilize conventional model based linear analysis tools such as bode plots, root loci etc. in order for the controller parameterizations to be realized. However, the analytic approach presented takes offset in such analyzes, but in a generalized fashion. The proposed control structures are focused on industrial applicability, and are therefore constrained to utilize only measurements of the piston position, the valve spool position, the transmission line pressures and the supply pressure, as feedbacks. The control structures are generally targeting a high bandwidth of the controlled cylinder drive and accurate tracking ability in the entire range of operation, rather than reducing stationary errors, and may be parameterized from the desired gain margin, as well as linear model parameters. The proposed control design approaches are evaluated in an experimentally validated, nonlinear simulation model of a hydraulic valve-cylinder drive, and the results demonstrate the excellent tracking effort realized with the proposed design approaches.