Closed-loop volume flow control algorithm for fast switching pneumatic valves with PWM signal

In this paper, a closed-loop volume flow PWM control algorithm of fast switching pneumatic solenoid valves is studied on the basis of experimental results of fluid flow valve characteristics. Dynamic nonlinear behavior of fast switching valves is analyzed using state-of-the-art mass flow sensors. Minimal Pulse Width Modulation (PWM) pulse width and nonlinear flow characteristics depending on pulse width and pressure difference are observed. Based on experimental data, different approaches to mathematically describe correlation of volume flow, pressure difference and pulse width are given. Bilinear interpolation is found out to have the best correlation and is used to develop a closed-loop control algorithm. The algorithm was tested with controlling of Pneumatic Artificial Muscle (PAM) contraction/position with two fast switching valves and minimal PLC / microcontroller requirements were determined.