Tracking control of hydraulic actuators using a LuGre friction model compensation

This paper addresses the tracking control of hydraulic actuators commonly used in many hydraulically actuated robotic systems. Dynamic model of the entire actuator incorporating highly nonlinear hydraulic functions and the LuGre dynamic friction model is used to arrive at a suitable controller. The controller is augmented with adaptation laws to compensate for parametric uncertainties in the actuator dynamics, hydraulic functions as well as friction with nonuniform force variations. Furthermore, an adaptive observer is used in the controller to avoid the use of acceleration measurement. Therefore, only measurements of displacement, velocity, and hydraulic line pressures are required for the implementation of the proposed controller Stability and convergence of the control system are theoretically studied. Experimental results are presented verifying the effectiveness of the developed controller.