Position control of a pneumatic actuator under the influence of stiction

The paper presents a new control scheme which is applied to pneumatic servo system. It consists of two parts, an analog P controller part (inner loop) and a digital PI controller part (outer loop). The inner loop is used to stabilise the system, which initially contains an integrator, and to reduce the effects of the nonlinearities present in the system. Therefore, the identification of the plant and the controller design become easy to perform. The outer loop is used to specify the characteristics of the whole system, and to cope with the problem caused by the stick-slip friction. The proposed method allows the limit cycles to be eliminated in a progressive manner by decreasing the integral gain of the PI controllers. A series of experiments are performed to show that the control performance is satisfactory, in both tracking and regulation.