氣壓控制系統由於氣體的可壓縮性、系統的摩擦力、閥體中位點的非線性特性及系統黏滯滑動等現象，使氣壓伺服系統為一時變及高度非線性系統，欲精密控制不易，以致於使氣壓系統難以獲得高精密之位置控制。因此如何有效克服氣壓控制系統非線性特性對精密定位的影響，將是提升氣壓伺服定位精度的一個研究課題。
在本文的研究中，主要針對使用伺服氣壓數位閥控及伺服氣壓比例式流量閥控兩種控制方法來對所建構之氣壓運動平台作精密定位控制。首先在伺服氣壓數位閥控方面，傳統使用兩個3口2位電磁閥結合脈寬調變(PWM)來控制氣壓系統兩氣室的壓力，以達到定位的目的，此等控制方法易造成系統於目標值附近兩高速電磁閥體仍須不斷地切換，以維持壓力平衡，因此對於氣壓精密控制，易因電磁閥體不斷地切換，而造成兩端氣室壓力產生微小變動現象，使系統不易平穩定位，因而難以達精密定位的控制，此外，電磁閥的不斷切換易造成閥軸過熱，影響電磁閥的使用壽命。因此，本文開發設計一種使用四顆微小2口2位電磁閥(流量係數 )結合具時間補償脈寬調變控制方式之伺服氣壓數位閥來取代一般傳統昂貴伺服閥或比例閥，並將所設計之數位閥體結合傳統模糊控制來對氣壓運動平台作精密定位控制，因所設計之數位閥體有足夠小之流量解析來對氣壓伺服系統作精密微小穩定的運動控制，因此不需複雜控制器便能有效大大提升伺服氣壓數位閥控精密定位的技術。
對於伺服氣壓比例式流量閥控方面，本文首先分析及探討影響定位精度甚巨之控制閥體閥軸中位無感應區及零點飄移與系統摩擦力等非線性因子，然後設計一些非線性的補償策略，來克服氣壓伺服系統非線性現象對精密定位的影響。本文中設計兩種氣壓精密定位的控制器：其一，以傳統模糊控制器作為氣壓伺服位置控制法則，並針對克服非線性動摩擦力及黏滯滑動現象，提出新的補償方法，即於控制訊號中輔以一比系統自然頻率大的顫振訊號，來消除氣壓缸粘滯摩擦力所衍生滑動(Stick-Slip)效應得現象，並將此顫振訊號直接加諸於伺服閥控制訊號中，以改善氣壓缸摩擦力的影響，並達成氣壓運動平台精密定位控制。其二，由於氣壓系統為時變系統，系統控制變數易隨時間而產生變動，造成系統難有一較好之強健性，因此本文另設計一具負載補償器之自調式模糊滑動控制器，來使氣壓運動平台可達成精密定位控制下又能有效提升控制系統之強健性。

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.

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