An experimental comparison of PWM schemes to improve positioning of servo pneumatic systems

Distinct advantages of the combination of the pneumatic actuated plants with “on/off” solenoid valves have motivated many researchers to conduct research in this scope. Pulse-width modulation (PWM) is a tool to use such combination in servo tasks. This paper studies the most frequent and well-reported PWM schemes. These PWM schemes have been applied for positioning tasks of the pneumatic actuators using solenoid on/off valves. In this study, the positioning performance of the servo pneumatic system, utilizing different PWM schemes, is investigated through several experiments with step and sinusoidal reference inputs. Rise time, overshoot, and steady-state error, in step input tests, and tracking performance in sinusoidal tests demonstrate the effectiveness of the deployed PWM schemes in the pneumatic system behaviors. Moreover, the closed-loop results demonstrate that the system robustness against the increase of the system’s mass is associated with the applied PWM scheme. Based on the open-loop results, two factors are found to be affecting PWM schemes performance, namely, the difference in the cross-sectional areas on each side of the piston and the piston position, in which these factors have not been considered in the design procedure of the former studies. Taking into account the former factor, a modified version of the PWM schemes is proposed. Steady-state errors in closed-loop tests verify the effectiveness of the developed modified PWM schemes.