Experimental Implementation of the Cascade Controller with Adaptive Dead-Zone Compensation Applied to a Hydraulic Robot

This paper addresses the trajectory tracking control in hydraulic robots by using a cascade controller with an adaptive dead-zone compensation. The hydraulic robot under research is composed of two rotational joints driven by linear hydraulic actuators. The flowrates in the linear hydraulic actuators chambers are controlled by overlapped proportional valves. The hydraulic robot mathematical model is obtained taking into account the mechanism, the actuators dynamics, and the valve dead-zone nonlinearity. The control is performed by using a cascade strategy in which the hydraulic robot is interpreted as two subsystems: a mechanical subsystem driven by a hydraulic one. Based on this interpretation, two different control laws are applied to each subsystem. In the hydraulic subsystem control law, an adaptive dead-zone compensation is added. The experimental result confirm the improvement obtained with the adaptive compensation.