Research on Design and Precision Positioning of a Servo Pneumatic Control System

• Main Authors: Kei-Ren Pai, 白凱仁
• Other Authors: Ming-Chang Shih
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/91083900035365096493

博士 === 國立成功大學 === 機械工程學系碩博士班 === 94 === Servo pneumatic systems have the strong nonlinear and time-varying characteristics that are associated with high air compressibility, the friction force of the system, nonlinear behavior of the air flow rate through the valve at the null position of the valve, and the stick slip effect. These complicated nonlinear phenomena make accurate position control of pneumatic servo system difficult to achieve. So, how to reject those nonlinear effects is the most effective method to improve the positioning precision. In the paper, two control methods using digital valve and servo valve are applied to control pneumatic precise positioning system. On digital valve control hand, the tradition digital valve composed of two 3/2 solenoid valves is used to excite the pneumatic positioning control by regulating the pressures of two chambers of the pneumatic cylinder. When the system arrives the balance point, this digital valve must be still switched continuously to hold the pressures of two chambers. It causes the rippling pressure so that the precise positioning is difficult to achieve. And, it will also effect the lifetime of the solenoid valves. So, a new proportional flow digital valve composed of four small 2/2 solenoid valves is designed to improve these drawbacks. The characteristic of the designed digital valve is tested and measured. The designed digital valve with tradition Fuzzy control strategy is applied to control the pneumatic positioning systems. Because the digital valve has enough small flow resolvability to excite the tiny step control, the positioning precision of the pneumatic servo system can be greatly advanced without the complicated controller. For using servo valve to control the pneumatic servo system, the main affecting factors for the precise positioning such as the nonlinear flow characteristic of the air flow rate through the control valve at the null position of the valve and the friction force of system are discussed. Two controllers are designed to control the pneumatic servo system. First, the conventional Fuzzy controller with a dither compensator is designed to control the pneumatic servo system. The dither compensator is designed to overcome the stick-slip effect of the pneumatic table. This method is effective not only to overcome the stick-slip phenomenon of the cylinder but also to improve the positioning accuracy of the pneumatic servo system. Another, owing to the strong time-varying characteristics of the pneumatic system, the pneumatic position system lacks the robustness. Therefore, a self-tuning fuzzy sliding mode controller (SFSMC) is designed to execute the precise positioning control. Besides, a dead-zone compensator and a load compensator are designed to compensate the dead zone of the system and to reject the external load, respectively. Those compensation signals are directly added to the designed controller to improve the positioning precision and the robustness of system simultaneously.