應用於雷射振鏡掃描畸變補償之系統控制設計

Abstract

本論文旨在研究振鏡掃描式雷射加工的畸變失真問題與解決方法。 由於系統中包含了轉動掃描振鏡與聚焦透鏡等非線性元件，雷射加工過程會產生畸變失真的問題。雷射振鏡主要用於控制雷射行進方向，決定雷射加工圖形，而聚焦透鏡目的為集中雷射功率、調整光斑大小，是影響雷射加工準確性的重要元件，這兩個元件分別會在雷射掃描時造成枕狀畸變與桶狀畸變的問題。此外，當雷射進行高速掃描加工時，振鏡馬達的定位速度也是決定掃描畸變的重要關鍵。若振鏡的穩定時間太長，穩定時間無法追趕上掃描移動的時間，也會造成嚴重的影像失真。 為了解決畸變失真的問題，針對振鏡與聚焦鏡的光路原理進行推導，找出畸變圖形與理想圖形的關係方程式，進而設計適當之修正方程式以抑制狀畸變。另一方面，透過振鏡系統動態方程式的推導與系統判別的方式完成系統轉移函數。為了進行系統判別，本研究使用PSD（Position Sensing Diode）元件建構一個雷射訊號動態量測系統，用以偵測雷射振鏡系統的動態特性，透過振鏡系統動態方程式的推導與系統鑑別的方式將實際的動態系統轉換成數學模型以進行畸變分析，而後設計適當之控制方法縮短振鏡轉動的穩定時間，使其小於轉動時間，以達到畸變補償。 實驗結果顯示，在畸變補償部分，20×20mm2大小的正方形，其畸變誤差可小於8μm。而在3.5度的偏轉角度時，到達穩態的時間小於200μs，大幅改善振鏡掃描時的畸變情形。

In a variety of laser processing method, the galvanometer scanning laser is one of the major processing systems. However, comprising non-linear components such as the rotating scanning galvanometers and the focusing lens in system result in many distortion problems. To decides the graphics of processing, galvanometer scanners control the laser travel direction which. And the focus lens is used to focus the laser power and adjust the spot size, which is an important component to affect the accuracy of laser processing. But these two parts will cause pillow distortion and barrel distortion when laser scanning. Furthermore, the positioning speed of the scanning motor is also a huge factor of distortion when operating high-speed scanning. In order to solve the aberration, the distortion theory, compensation and improvement are investigated in this thesis. We analysis the laser travel route of scanning mirror and focus lens to find the relation function between distortion and ideal graphics, then design appropriate controller to suppress generation of the barrel or pincushion distortion. On the other hand, distortion analysis will be achieved by investigate the system transfer function through system identification method. In order to determine the system, we construct a signal measuring system using the PSD component. The dynamic characteristic of laser galvanometer scanning system and the coefficient of transfer function can be obtained by calculating experimental data. Hence the laser galvanometer system model of laser scanning system has been identified. Then design the controller according to target speed, and reduce the oscillating time of scanning mirror. The results show that, after compensation, the distortion error of less than 8μm when scanning 20 × 20mm2 square. And the time reaching steady state is less than 200μs when the deflection angle is 3.5 degrees. The distortion situation is significantly improved.