Abstract
To realize a continuous fine motion control with a pneumatic actuator, the electronical intelligent control is required, in which an electro-pneumatic conversion is essential. In this study, by introducing a Pulse-Code-Modulation (PCM) technique into this conversion, the microcomputer controlled digital pneumatic servo system with a pneumatic cylinder and on-off solenoid valves is proposed. Its positioning performance is experimentally examined to obtain the following results.
1) The PCM technique enables the continuous control with only on-off solenoid valves, in which the control signal directly corresponds to the binary signal. Therefore this method is suitable for the microcomputer control and much practical as a digital control method of a pneumatic actuator.
2) In the repetitive positioning, the learning control modifying the reference input based on the preceding positioning error is much effective to eliminate the unpredictable errors due to the sliding friction and so on.
3) Under some conditions the nonlinear friction makes the stopping manner change to largely decrease the positioning accuracy. When unchanged, the scattering amount of the repetitive stopping position almost agrees with the minimum resolution distance in the PCM. The experimental system can realize the positioning accuracy of about ±0.25mm.
4) In the PCM control, the maximum piston speed must be constrained for the satisfactory positioning accuracy. To prevent the positioning time increasing due to this constraint, the positioning method added the open-loop controlled high speed region is proposed and its effectiveness is proved.
