Abstract
The precice and flexible motion control has been recently required for also the pneumatic driving mechanism. Some types of electro-pneumatic servo system which enable the continuous position control by means of the servo or proportional valve have been provided. However such valves contain the disadvantages to be expensive and extremely sensitive to a dust in the operating air.
In this study, the PWM mode electro-pneumatic servo system is proposed in which the position of piston is controlled by the PWM driving an on-off two way valve. The control system is constructed by use of inexpensive automobile-type fuel injection valves as the valve driven in the PWM mode. The characteristics and performance of the system are analyzed and discussed to obtain the following results.
1) The theoretical model of pneumatic driving part and the method of identification of system parameters (friction, damping ratio, etc.) based on the static characteristics are given.
2) The influence of sliding friction on the position control performance is clarified, and proved the effectiveness of Coulomb friction to stabilize the response and to rapidly stop a piston.
3) The proposed system can provide the enough satisfactory performance for the usual application of the pneumatic driving. The trial system can realize the repetitive positioning precision, ±0.06mm.
This control manner has the advantage in which the PWM valve with so large cross section is not required because the PWM mode is adapted only in the vicinity of desired position.
