Integrated direct/indirect adaptive robust motion control of single-rod hydraulic actuators with time-varying unknown inertia

This paper studies the precision motion control of single-rod hydraulic actuators with accurate parameter estimations. An integrated direct/indirect adaptive robust controller (DIARC) is proposed to take into account the inherent nonlinearity, parametric uncertainties and uncertain nonlinearities associated with the hydraulic systems. Compared with existing direct ARC controller designs, the proposed DIARC controller not only achieves a better output tracking performance, but also provides better parameter estimations, which can be used for other purposes such as the higher level trajectory planning and the system and component health monitoring. These stronger theoretical results are made possible through the use of the new design philosophy of separating parameter estimation dynamics from the tracking error dynamics. Theoretically, in the absence of valve dynamics, the proposed DIARC controller achieves a guaranteed transient performance and final tracking accuracy in the presence of both parametric uncertainties and uncertain nonlinearities, while achieving asymptotic tracking in the presence of parametric uncertainties only. Practically, experimental results on the precision motion control of a single-rod hydraulic cylinder with time-varying unknown inertia verify the excellent output tracking accuracy and good parameter estimation of the proposed integrated ARC design