Mass Flow Rate-Based Control of a Digital Valve by Fuzzy Logic for Pressure Tracking in Soft Pneumatic Actuators

Digital solenoid valves (DSVs) offer a lightweight and cost-effective alternative to proportional pressure control valves (PPCVs) in pneumatic robotic systems. Pulse-width modulation (PWM) is commonly employed to manage DSVs, emulating proportional behavior. However, many existing approaches neglect charging/discharging asymmetries, transitions between sonic and subsonic flow regimes, and valve-switching delays, thereby reducing pressure-control accuracy. All these effects are considered in this work. The latter presents a mass flow rate-based model for proportional pressure regulation using a fast-response 3/2 DSV. The valve’s charging/discharging conductances and critical ratios are experimentally identified, and equilibrium and chattering pressures are evaluated as functions of duty cycle (DC) and switching frequency. Based on the identified model, a Mass flow rate-based fuzzy logic controller (FLC) has been developed. Unlike conventional approaches that directly adjust the DC, the proposed FLC generates the required mass flow rate from the pressure-tracking error. These commands are converted into DC values of the PWM by an inverse valve-flow model (IVFM). The proposed approach is experimentally validated and compared with Direct FLC on an externally reinforced soft pneumatic actuator (SPA) under sinusoidal and step pressure references. Results confirm the effectiveness of the proposed control strategy, showing more accurate tracking, lower steady-state error, and smoother control action than Direct FLC.