On the Observability of Pressure in a Pneumatic Servo Actuator

Pneumatic servo actuators are characterized by highly nonlinear dynamics from spool valve command to cylinder pressure, and as such are well suited to the use of nonlinear control methods requiring measurement of the full state, such as sliding mode control. This paper investigates the possibility of eliminating the pressure measurement required for nonlinear control in lieu of a nonlinear pressure observer, based on measurement of the output motion. A nonlinear observability analysis is conducted that demonstrates that such a system loses local observability in several regions of the state space, thus rendering the system unobservable.