Variable Structure Control of a Pneumatic Actuator

In an effort to overcome the nonlinerities associated with a pneumatic system the variable structure control (VSC) technique has been employed to control the position of a pneumatic actuator. To accomplish this a model of a pneumatic actuator was developed to allow the control systems to be studied via simulations. The results from the simulations indicated that the VSC technique can position the actuator rapidly, via first-order trajectory, in response to a step input. An experimental study of the VSC control system was then performed. These experiments verified the simulation work, and demonstrated that inherent system delays and the quantisation of the control signals can cause and uncontrollable oscillatory behaviour; stability limits were established for three of the system parameters. It was also found, that the actuator could be placed within ±5 mm of the desired position.