A Method for Mass Flow and Displacement Estimation in a Pneumatic Actuation System using Valve-based Pressure Sensing

This article describes a method to estimate the displacement of a pneumatic actuator based solely on pressure sensing at the control valve, which can enable low cost and remote sensing and fault detection in pneumatic actuation applications, such as in manufacturing. Pressure sensors located at the outlet ports of a pneumatic five-port two-way directional control valve are used in a generalized system model to estimate mass flow to the actuator. The approach enables observation of piston and rod displacement in real time and enables detection of motion faults without the use of displacement or proximity sensors on the actuator, which is typically located remotely from the control apparatus. The method was validated experimentally on two commercially available five-way pilot-assisted solenoid spool valves; each on two different double-acting, single rod, pneumatic linear actuators; and under different load and movement obstacle conditions. In the aggregate, the method provided a real-time estimate of actuator displacement within 7.1% error (relative to full stroke), and also provided a real-time mass flow estimate within 6.3% error. These real-time estimates are well within the accuracies suited to real-time fault detection in binary positioning systems, such as those typically used in manufacturing.