Piston position estimation for an electro-pneumatic actuator at standstill

• A parallel between electro-pneumatic actuators and PMSMs is drawn.
• The observability of the piston position is analyzed at standstill.
• A signal injection method is proposed to make this system observable.
• A non-linear observer is synthesized to reconstruct the piston position at standstill.
• A Lyapunov function is proposed to demonstrate the system global stability.

In this paper, a first strategy to reconstruct the piston position of a pneumatic cylinder supplied by two servovalves is proposed using only the chambers pressure measurements. This work focuses on the position observation at standstill. Starting from a classical model of this actuator, a transformation of the inputs is used. This way, for the first time, a link is established between electro-pneumatic actuators and Permanent Magnet Synchronous Motors (PMSM). This allows to apply PMSM zero speed observation strategies to electro-pneumatic actuators. Thus, following an observability analysis, a signal injection based methodology is used to ensure the observability of the electro-pneumatic system. A non-linear position observer is synthesized and a Lyapunov function is provided to ensure the global stability. Experimental results confirm the proposed strategy efficiency. The proposed technique constitutes a first step toward sensorless position control of electro-pneumatic actuators.