On the control of pneumatic positioners and the case of the inverted pendulum

In a previous paper (see Proc. IEEE Ind. Automation Conf., Toronto, Canada (1990)), the authors applied a model-based control strategy to a system consisting of a rodless cylinder with a 12.5 mm bore, 250 mm stroke and 1.2 kg load. Though previous studies have demonstrated that attractive accuracies and positioning times can be obtained with pneumatic systems under digital control, they were achieved with expensive control valves that provided an air flow proportional to a variable control signal. The present paper describes an investigation of the potential of pneumatic systems controlled by low cost on-off control valves. A pulse-width relay LQR driven controller has been successfully applied to the on-off control of a pneumatic inverted pendulum. The results provide a convincing demonstration of the potential of digitally controlled pneumatic positioners