Technology using on-off solenoid valves is currently being applied in controlling pneumatic actuators to replace the use of the pneumatic proportional/servo valves. However, controlling the pneumatic actuators using on-off solenoid valves is often difficult due to the low switching frequency of these valves and the high nonlinearity of the pneumatic system. In this paper, we first re-evaluate a controller proposed by Truong in 2020 [B. V. Truong, Study on accurate control of pneumatic cylinder using on-off solenoid valves, Bachelor thesis, Fluid Power and Automation Eng. Dept., School of Transportation Eng., Hanoi University of Science and Technology, Hanoi, Vietnam, 2020], in which four pneumatic on-off valves were used. We then modify the Truong's controller by dividing the desired position input of the cylinder into two controlled position intervals and each interval will use a separate control law. Seven operating modes of the four on-off solenoid valves combined with the Pulse Width Modulation method (PWM) are used. The experimental research method is carried out. The modified controller is evaluated by comparing it with the Truong’s controller and a controller for a pneumatic system using pneumatic proportional valves at the same conditions of the desired position inputs. Comparison results verify the usefulness of the modified controller.
Keyword
position control, pneumatic cylinder, on-off solenoid valve, pulse width modulation
