Adaptive Position Control of a Pneumatic Cylinder.

This paper deals with the adaptive position control of a pneumatic cylinder with two electro-pneumatic proportional valves. The adaptive control law consists of the following four parts : (a) stabilization of the plant by output feedback, (b) identification of the stabilized plant by the constant trace gain algorithm, (c) division of the identified model into an AR model and auxiliary system which output converges rapidly to zero when its input becomes constant, and (d) model reference adaptive control (MRAC) for the AR model. This control law is a modification of the conventional MRAC law so as to make it applicable to non-minimum phase systems.Experiments of the adaptive position control were carried out for the following cases : (1) the third and second order reference models which approximated the step response of the stabilized plant given by (a), (2) five sampling periods (25, 37, 52, 71, 107 msec), and (3) a sudden change in plant dynamics. Although the identified plant was a non-minimum phase for all cases, the behavior of the control input to the electro-pneumatic valves was stable, and the position of the load followed well the output of the reference model.