Position Control of a Pneumatic Servo Cylinder using Fuzzy-Sliding Surface Controller

Abstract

In this paper, both the PID and fuzzy-sliding surface controller are applied to the position control of a proportional- valve-controlled pneumatic rodless cylinder. Because of the highly nonlinear basic equations of pneumatic systems, the modelling of such a pneumatic servo is excluded from this paper. Besides, it is usually quite difficult to obtain a satisfactory position control of a pneumatic rodless cylinder because an apparent dead-zone in the response curve during the starting phase always appears. The dead-zone signifies a serious response delay. One reason for such a response dead-zone is the stick-slip friction and the nonlinear deadband of the proportional valve. In this paper, therefore, the chattering output of sliding mode control is introduced to reduce the effect of stick-slip and the nonlinear fuzzy-logic-controller is employed to control this unmodelled and highly nonlinear system. Accordingly, the fuzzy-sliding surface controller is proposed, which is exactly the combination of the fuzzy-logic-controller with the sliding mode controller. There are two key features of this control scheme. One is the easier implementation of the controller as compared with that of the conventional fuzzy-logic-controller because the number of controller input is reduced by half. The other is the ability to reduce the response dead-zone during the starting phase. Finally, a series of experiments are carried out and the experimental results prove that the fuzzy-sliding surface controller is superior to the conventional PID controller.