Cascaded robust nonlinear position tracking control of an electrohydraulic actuator: Sliding mode and feed forward

An approach to position tracking control based on a cascade of a nonlinear force tracking controller derived from a near input-output linearization framework and a simple feedback plus feed forward position controller is presented. The method exploits the cascade structure to employ a sliding mode pressure force tracking controller as inner-loop and the position tracking controller as an outer-loop. Furthermore, it is highlighted that Lyapunov backstepping analysis can be used to drive performance bounds and reveal trade-offs between the size of uncertainty and measurement errors and the tracking accuracy. The performance of the proposed cascaded robust controller is demonstrated with experiments and simulations on a test system that doesn't necessarily satisfy all of the assumptions made for controller derivation. In particular, a typical comparison of the robust and nominal cascade controllers shows the robust version can recover the performance of the nominal near IO linearizing controller. In addition, model simulation results are included to show the performance of the controller in the presence of some combinations of perturbations or difficult to estimate parameters such as valve coefficient, supply pressure, piston friction, and inclusion of servovalve spool dynamics.