Nonlinear force control of an electro-hydraulic actuator

In this paper, a Lyapunov-based control algorithm is developed for the control of an electro-hydraulic actuator. A first order nonlinear model for the actuator is developed from first principles. The servovalve used to control the actuator is modeled as a third order linear system and the controller uses model reduction to a first order system. Using Lyapunov-based techniques, a controller is developed which compensates for the modeled nonlinearities in the actuator. Additionally, parametric model uncertainties are compensated for by the inclusion of a gradient parameter adaptation scheme. The controllers are implemented on a simple force tracking problem, representative of several manufacturing processes, and the results are compared with typical linear controllers found in industrial practice. The comparison is carried out in simulation. The nonlinear controllers, although requiring additional state information, perform much better than the corresponding linear controllers.