Design and Testing of a Servo Controller for Pneumatic Cylinders

Abstract

A closed-loop method of controlling a pneumatic cylinder is proposed where the cylinder can respond to varying position demands from an external source. The method uses a state space design technique involving the experimental identification of a dynamic model for the cylinder and valve combination. Data for the identification are obtained from an initial phase in which the valve and cylinder are excited by an operator. The controller constants are then derived using a pole placement design technique. The model and control constants are derived within the controller, resulting in automatic tuning. Experimental data are presented in response to step and ramp inputs. With moderate closed-loop bandwidths the response is well damped but as the designed bandwidth increases, lightly damped oscillations occur in the response, probably caused by differences between the responses of the experimental system and its model. If greater closed-loop bandwidths are required further work needs to be done on the form and order of the model.