雷射掃描系統與動態聚焦系統之整合與設計

The Integration and Design of Laser Scanning System and Dynamic Focus System

丁健芳(Chien-Fang Ding)

指導教授 ： 楊宏智

國立臺灣大學/工學院/機械工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.10358

摘要

近年來，隨著雷射的蓬勃發展，廣泛地應用於生醫、電子光電、光通訊、量測技術等用途，可針對材料進行切割、鑽孔、焊接、雕刻、表面處理等製程。在雷射加工系統中，常使用振鏡掃描技術來進行圖案加工，因其擁有快速且精準定位的掃描特性，再搭配不同雷射源，可以提升製程速度與靈活性。而在雷射加工過程中，雷射光束多採用高斯振福分布的型態(TEM00)，因其有較高的能量密度，此位置為雷射光束之焦點，亦即整體雷射加工系統之工作距離(working distance)。若在加工過程中，雷射光束的焦點位置不在表面上，將無法行加工或者加工效果不如預期，因此要如何掌握雷射焦點的位置技術顯得非常重要。
本論文針對雷射光束之焦點位置控制作探討，設計動態聚焦系統於振鏡掃描系統前，透過改變系統內鏡子間之相對位置，來實現對雷射光束之焦點位置控制，即成為可變焦的雷射加工系統，並於變焦範圍內加工具有高度差的工件或圖案。本論文首先利用ZEMAX光學系統設計模擬軟體分析動態聚焦系統內鏡子之配置，不同的配置將對於整體光路系統之成像品質造成影響，同時找出鏡子間相對位置與工作距離的關係，並建立一套光學元件挑選準則(criterion)，讓使用者能夠知道光學元件之間的搭配將對於雷射加工系統的影響，最後於實驗中進行驗證。
本論文發現，在動態聚焦系統中之鏡組為"平凹平凸"配置時，系統之成像品質較佳，而設計之動態聚焦系統，其變焦範圍可達25 mm。在變焦的過程中，成像品質會隨著鏡子間的相對位置而改變，發現在"平凹雙凸"配置時成像品質變化較小。再者，由雷射加工實驗中透過觀察工件之熱影響區(Heat Affect Zone)來評估系統之成像品質，發現成像品質較佳的配置，有較小且均勻的熱影響區。此外，對於本論文設計的動態聚焦系統之變焦能力測試，則透過加工45度斜面來驗證焦點位置的控制，在同樣加工高度差為25 mm之線段時，發現未使用動態聚焦系統之焦點位置控制時，其加工能力不如預期且加工線段只有一小段，理論加工長度與實際加工長度之誤差高達93 %；而有使用動態聚焦系統之焦點位置控制時，理論加工長度與實際加工長度之誤差約為3.2%左右，故可顯示本論文之動態聚焦系統能夠對於雷射光束之焦點控制作控制。

關鍵字

光學系統設計 ； 振鏡掃描系統 ； 雷射加工 ； 動態聚焦

並列摘要

In recent years, laser processing is widely used in biomedical, electronics, measurement, optical communications and other purposes with the rapid development of machining process. In the laser processing system, the galvanometric scanning technology is an important part for its advantages of fast scan speed and precise positioning. Moreover, it can enhance the speed and flexibility of the process with different types of laser. In the laser processing, it is very common to use the Gaussian distribution mode, which is TEM00 mode, due to the performance of high power density; therefore, this is also the focus position of laser beam, i.e. the working distance of laser processing system. If the focus position is not on the surface of workpiece during the laser processing, the workpiece cannot be processed or the processing result cannot be satisfied. Thus, the control technique of the focus position of laser beam is very significant.
In this thesis, we are aimed at controlling the focus position of the laser beam, and design the dynamic focus system before the galvanometric scanner system, altering the displacement of lenses within the dynamic focus system to achieve the focus position control technique of laser beam. Consequently, it becomes a varifocal laser processing system and can deal with the process which contains the height difference of workpiece or pattern. Firstly, we use the ZEMAX, which is an optical system design and simulation software, to analyze the configurations of lenses within the dynamic focus system which may caused the different image quality to the whole system. Furthermore, we can determine the relation between the displacement of lenses and the working distance of the whole system, and construct a choosing criterion of optical elements to realize the affect of the whole system; finally, verify the simulation by experiments.
This study find that when the lens configuration in the dynamic focus system is “Plano-concave & Plano-convex (PLCC-PLCX)”, the image quality of whole system is better then other lens configurations. Besides, the dynamic focus system is provided with 25 mm varifocal range. During the zooming process, the image quality of the whole system will decrease due to the displacement of lenses; but there are smaller variation of image quality in the “Plano-concave & Bi-convex (PLCC-BICX)” configuration. Next, we observe the heat affect zone of wrokpiece to evaluate the image quality by laser processing experiment, and find that good image quality will cause the smaller and uniform heat affect zone. In addition, in order to test the zoom performance of the dynamic focus system with the focus position of laser beam, we process the 45 degrees incline surface. In processing the 25 mm height difference of line, we discover that there are just a little segment instead of the complete line, and the deviation between theoretical value and actual value is up to 93% without using the dynamic focus system. However, with using the dynamic focus system to control the focus position of laser beam, the deviation between theoretical value and actual value is about 3%. It can fully display that the dynamic focus system of this thesis can control the focus position of laser beam.

並列關鍵字

Optical system design ； Laser galvanometric scanning system ； Laser machining ； Dynamic focus system

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