Nonlinear adaptive robust control of electro-hydraulic servo systems with discontinuous projections

This paper studies the high performance robust motion control of electro-hydraulic servo-systems. The dynamics of hydraulic systems are highly nonlinear and the system may be subjected to non-smooth and discontinuous nonlinearities due to directional change of valve opening, friction, and valve overlap. Aside from the nonlinear nature of hydraulic dynamics, hydraulic servo systems also have large ea;tent of model uncertainties. To address these challenging issues, the recently proposed adaptive robust control (ARC) is applied and an ARC controller based on discontinuous projection method is constructed. The resulting controller is able to take into account the effect of the parameter variations of inertia load and cylinder and the uncertain nonlinearities such as uncompensated friction forces and external disturbances. Non-differentiability of the inherent nonlinearities associated with hydraulic dynamics is carefully examined and addressing strategies are provided. Compared with previously proposed ARC controller, the ARC controller in the paper has a more robust parameter adaptation process and is more suitable for implementation.