Nonlinear Model Based Coordinated Adaptive Robust Control of Electro-hydraulic Robotic Arms via Overparametrizing Method

This paper studies the coordinated motion control of robotic manipulators driven by single-rod hydraulic actuators. Compared to conventional robot manipulators driven by electrical motors, hydraulic robot arms have a richer nonlinear dynamics and stronger couplings among various joints (or hydraulic cylinders). This paper presents a physical model based adaptive robust control (ARC) strategy to explicitly take into account the strong coupling among various hydraulic cylinders (or joints). To avoid the need of acceleration feedback for ARC backstepping design, the property that the adjoint matrix and the determinant of the inertial matrix could be linearly parametrized by certain suitably selected parameters is fully exploited and overparametrizing method is used. Theoretically, the resulting controller is able to take into account not only the effect of parametric uncertainties coming from the payload and various hydraulic parameters but also the effect of uncertain nonlinearities. Furthermore, the proposed ARC controller guarantees a prescribed output tracking transient performance and final tracking accuracy while achieving asymptotic output tracking in the presence of parametric uncertainties only. Simulation and experimental results on a three degree-of-freedom (DOF) hydraulic robot arm (a scaled down version of an industrial backhoe/excavator arm) are presented to illustrate the proposed control algorithm.