A Novel Full-Digital Pneumatic Quasi-Servo Valve Design with Application to Position Control

• Main Authors: Chin-Yi Cheng, 鄭秦亦
• Other Authors: Jyh-Chyang Renn
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/00607473526145602455

博士 === 國立雲林科技大學 === 產業精密機械研究所博士班 === 102 === Nowadays, applications of pneumatic servo system have been successfully applied to many different engineering fields. In such systems, servo or proportional valve is generally the most expensive component of the systems. In order to develop an inexpensive pneumatic servo system, another digital proportional control structure comprised one or more fast-switching 2/2 on-off valves using PWM-control is employed. A significant advantage of the fast-switching PWM-control structure is the lower-cost. Its major faults, however, are noisy operation, short life cycle and steady-state error. In this paper, a novel full-digital pneumatic quasi-servo valve is proposed. The new Full-Digital Control Valve (FDCV) driven by variable current and voltage technique is applied to pneumatic rodless cylinder position control system. The FDCV consists of four parallel-connected 2/2 pneumatic on-off valves. Compared to the PWM fast-switching proportional flow control scheme, the new FDCV possesses several advantages like medium operating noise, long life cycle, ease of control and low cost. Because the resolution of the conventional binary coding system is insufficient, precise position control is difficult to achieve. To overcome such weakness, a continuous variable current and voltage input control technology will be discussed and realized. The basic idea is to reduce the opening areas of on-off valves in the FDCV by applying stepless current or voltage inputs to the solenoid. Consequently, the steady-state error and overshoot can be successfully reduced without any hardware modification. Finally, from the experimental results, it is proved that the steady-state error is significantly reduced by using the binary coding system together with the proposed novel variable current and voltage control technique. Thanks to the benefit of low cost, it is expected that the proposed FDCV will be used in place of traditional servo or proportional valves in the future.