The Role of Pressure Sensors in the Servo Control of Pneumatic Actuators

Pneumatic servo actuators are characterized by highly nonlinear dynamics, and as such are well suited to the use of nonlinear control methods requiring measurement of the full state, such as sliding mode control. The requirement of pressure measurement, however, is particularly burdensome, due in large part to the high cost of pressure sensors relative to other components of the servo system. Since the cylinder pressures are states of the dynamic system, the possibility exists of eliminating the pressure sensors in lieu of a nonlinear observer. Through the construction and rank test of a nonlinear observability matrix, it is shown that significant singular points exist in the system that, for most practical purposes, renders impractical the use of a nonlinear observer to reconstruct pressure states.