Experimental tests on position control of a pneumatic actuator using on/off solenoid valves

Abstract

A position-controlled pneumatic actuator using pulsewidth modulation (PWM) valve pulsing algorithms is described. The system consists of a standard doubleacting cylinder controlled with two three-way solenoid valves through a 12-bit A/D PC board. The mechatronic system has the advantage of using o d o f f solenoid valves in piace of more expensive servo valves and it may be applied to a variety of practical positioning applications. A proportional integrative (PI) controller with position feedforward is successfully implemented. Several experimental tests are carried out to evaluate the robustness of the control system and the performances of a novel pulse-width modulation algorithm implemented. The actuator's overall performance is comparable to that achieved by other researchers using servo valves.

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

“…Therefore, the valves' duty cycle falls between d min and d max , which are the minimum and maximum valve duty cycles, respectively. d max is given by [14]:…”

“…To avoid these nonlinearities, in some PWM schemes, valves' delays are taken into account, e.g., T don is added to the duty cycle of both valves [2,3,14] and their duty cycle is limited to T PWM −T doff [2,14]. Considering whether or not to apply these delay times, the performance of the system would differentiate accordingly.…”

“…Shih et al [2] and Gentile et al [14] took into account both of the valves' "on/off" delays to develop new PWM schemes. In [2], a modified differential PWM (M-D-PWM) scheme accompanied by a fuzzy method was established to control the position of a rodless pneumatic cylinder.…”

“…They indicated that incorporating the M-D-PWM scheme had created a more linear relationship between the chambers' pressure difference and the duty cycle ratio compared to the differential PWM (D-PWM) scheme. In [14], a PI controller was employed with a new PWM scheme, in which a maximum "on" time of solenoid valve was limited during a duty cycle.…”

Improving dynamic performances of PWM-driven servo-pneumatic systems via a novel pneumatic circuit

“…Regarding the control aspects of PWM-driven servo-pneumatic systems, some papers used PID based controllers with empirical tuning [7], but others were mainly concerned with modeling and/or controller design. Some efforts for analytical modeling of pneumatic actuators, valves and friction can be found in [8][9][10][11][12][13].…”