Design of a Lyapunov Controller for an Electro-hydraulic Actuator During Contact Tasks

In this paper, an algorithm is developed for contact task control of electro-hydraulic actuators. The goal is to design and experimentally evaluate a robust controller that allows a hydraulic actuator to follow a free space trajectory and then make and maintain contact with the environment for exerting a desired force. First, the dynamic model of a hydraulic actuator interacting with an environment is described. Then, a Lyapunov-based controller is designed, which regulates the actuator’s position and upon contact with the environment switches to a force controller. Extended Lyapunov’s second method is used for stability analysis of the developed control system, which consists of nonsmooth dynamics. The stability of the system is guaranteed by using a smooth Lyapunov function under the condition of existence and uniqueness of Filippov’s solution. The efficacy of the proposed nonlinear controller is verified via experiments. The experiments are performed on an industrial hydraulic actuator equipped with a servovalve and include motion through free space, contact with the environment and the transition between the two.