PWM Position Control of a Pneumatic Cylinder.

This paper proposes a PWM (pulse-width-modulation) control of a pneumatic single-rod cylinder positioning system. In the system, the rod chamber pressure of the cylinder remains constant, and the head chamber pressure is controlled by two solenoid valves. The valves are under PWM mode control. In synthesizing the PWM servomechanism, the solenoid valves are characterized by a static characteristic equation incorporating the nonlinear elements caused by the switching time of the valve. The proposed PWM method can assign the steady-state duty ratios of the valves to the desired locations of their flow characteristics, which makes it possible for the system to avoid the dead-zone or the nonlinear region caused by the PWM solenoid valves. Also, a threshold near the desired position is set up so that the valves are closed at steady state. An experimental study of the proposed system is performed. These experiments verify the theoretical design work, and indicate that the proposed control system is feasible for pneumatic positioning.