Accurate motion control of a servopneumatic system using integral sliding mode control

Abstract

Pneumatic systems are a simple and readily available technology that presents high force to volume ratios. Their use is nevertheless restricted to simple motion tasks, given the complexity in its modelling and control. One of the main aspects contributing to this panorama is the difficulty in accurately predicting friction forces. In fact, although it is possible to find in literature complex friction models that suit well a particular experimental set-up, its practical use becomes hindered given the diversity of pneumatic actuated systems found in industry. This paper presents a new controller that achieves very good results even without a friction model. The controller architecture includes a robust motion control loop and a non-linear state feedback pneumatic force loop. The motion controller law is based on integral sliding control and takes into account the pneumatic dynamics, using it as a natural filter of the discontinuous part of the control law. Experimental results show that the proposed approach leads to low tracking and positioning errors. These results are obtained without including a friction model and even in the presence of parameter disturbances caused by a fivefold payload change, without any controller retuning or excessive control action activity.