Integrated Direct/Indirect Adaptive Robust Control of Hydraulic Manipulators With Valve Deadband

In this paper, an integrated direct indirect adaptive robust control (DIARC) algorithm is proposed for an electrohydraulic manipulator with unknown valve deadband to improve the achievable output-tracking performance. The controller design for such a system is nontrivial due to various factors, such as non-smooth static and Coulomb friction model uncertainties arising from the use of a simplified proportional-flow-valve model, and other unknown disturbances present in the system. Furthermore, when an unknown input-valve deadband is present, the controller performance can deteriorate if it is not taken care of explicitly. This paper recognizes the fact that though unknown valve deadband nonlinearity is not globally linearly parameterizable, it can still be linearly parameterized during most of the working ranges. Hence, by using an indirect estimation algorithm with online condition monitoring, accurate estimates of the unknown deadband parameters are obtained for an improved control performance. Comparative experimental results for motion control of an electrohydraulic manipulator with two different valves having deadband illustrate the effectiveness of the proposed algorithm.