應用最佳UIO改善CNC工具機軌跡精度

Abstract

在精密製造工業中，切削過程的加工精密度扮演重要的地位。然而，由於 外界負載擾動（如切削力、摩擦力）或系統參數的變化，而影響 CNC工具 機的加工精度。因此，如何降低外界負載擾動對伺服系統的影響，將是一 重要的課題。在近二十幾年來，UIO以廣泛被探討其存在且必要的條件， 很少有應用在實際系統。本文，主要以廣義結構UIO為基礎，利用 2-delay output的方法，推導出穩定的UIO，以適用在含有有非最小相位 零點的實際系統。當系統受到程序或量測雜訊干擾時，本文推導出最佳穩 定 UIO，使估測誤差方程式的變異數(variance)為最小。在實驗上，本文 針對四種控制器（ P, CCC, ZPETC, CCC+ZPETC），加一額外的荷重於 X- Y位置平台。利用最佳穩定UIO 估測其所受負載擾動大小，以轉矩補償器 補償其干擾效果，實驗結果證實輪廓和位置誤差均獲得改善，所以本文所 提的方法在運動控制上是可行的。 In precise manufacturing industries, the accuracy of machin- ing process is the most important requirement. However, In prac- tice, the cutting torque and friction act as the external distu- rbance which decreases the accuracy of machining process badly. Therefore it is crucial to reduce the influence of external disturbance in the precise motion control. In recent two decades, major studies focus on deriving the necessary and sufficient conditions for the existence of unknown input observer (UIO). Few of them have been used for real appli- cations. In this reaaacher, by appling the 2-delay output method to the genernal-structured UIO, a stabilized UIO (S-UIO) is der- ived for non-minimum phase system to estimate both states and unknown inputs. When plant process and measurements are disturb- ed by noises, an algorithm for constructing aaaan optimal S-UIO is derived to minimize the variance of estimation errors. In the present experiments, an external load is added to the X-Y position table with four different controller's structures (P, CCC, ZPETC, CCC+ZPETC). The Optimal S-UIO estimates disturb- ance for compensating torque so that the effect of external disturbance can be reduced. Experimental results show that both the contouring and tracking errors have been successfully degraded and prove that the proposed method is suitable for motion control.