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

Abstract

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 openloop results, two factors are found to be affecting PWM schemes performance, namely, the difference in the crosssectional 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.

Study on the Pressure Regulation Method of New Automatic Pressure Regulating Valve in the Electronically Controlled Pneumatic Brake Systems in Commercial Vehicles

“…The common pressure regulation methods are the PWM pressure regulation method and the on/off pressure regulation method. The PWM pressure regulation method uses PWM signals with different duty cycles to control the action of the high-speed inlet valve and the high-speed exhaust valve and to realize the regulation of the outlet pressure of the APRV [21]. PWM pressure regulation is relatively stable, but the pressure response is slow [22].…”

Research on the designing of pneumatic positioning units controlled with valves commanded in modulated pulses

“…11b) as corresponding to a driving time tap with the desired flow ̇ (fig.11a). [9][10][11][12] b. (1)…”

Dynamic vacuum pressure tracking control with high-speed on-off valves

“…Under ideal conditions of process symmetry, zero input to the PWM pulsing scheme means that the duty cycles w of the input electrical signals to the charging and discharging units in Figure 6(a) are both equal to 0.5, and the chamber pressure change rate is zero. 34 However, in reality, process asymmetry means that the chamber pressure change rate is not zero, even if both units have the same duty cycles of 0.5. The aim of the proposed asymmetric compensator is to achieve a zero pressure change rate in the case of zero input to the PWM pulsing scheme.…”