線上雷射功率量測與穩定系統開發

Development of On-line Laser Power Monitoring and Stabilizing System

李孟修(Meng-Shiou Lee)

指導教授 ： 李貫銘

國立臺灣大學/工學院/機械工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.00529

摘要

自雷射被發明以來，雷射已經被應用在許多領域，如：材料加工、通訊、量測、生醫工程、國防工業等等。在雷射材料加工的過程中，雷射輸出功率是很重要的一個參數，但雷射加工時間短，而目前現有的雷射功率計因為反應時間過長，無法在短時間內精確量測出雷射的功率。為了進行雷射功率即時監測，本研究利用CMOS(Complementary metal-oxide-semiconductor)工業相機進行雷射功率線上量測系統的開發，期望能夠在雷射加工時，達到即時量測雷射功率的目的；並且針對雷射功率易受環境溫度影響而功率輸出不穩定的現象，以回授控制(Feedback control)的方式進行雷射功率的穩定控制。
本研究將經過分光、減光的雷射光束以CMOS工業相機直接擷取光點影像，計算影像中的雷射光點亮度值，利用曲線配適(Curve fitting)的方式推算雷射功率。得到即時雷射功率值後，計算量測功率值與預設功率值的誤差，以控制雷射Q開關(Q-switch)Duty time的方式，利用PID控制器進行回授控制，達到雷射功率輸出的穩定控制。
由實驗結果可知，本研究系統在連續量測模式下，平均量測誤差僅約3%，反應時間比起熱電堆式雷射功率計至少縮短3.6秒以上；利用觸發訊號的觸發量測模式下，使CMOS相機能夠同步擷取間歇式的加工出光，進行同步量測，平均量測誤差小於3%，且能夠量測最短20毫秒(Millisecond)的出光。
回授控制功能中，PID控制器能夠在1秒以內補償雷射系統之功率誤差，且過衝不到3%、幾乎沒有穩態誤差。在鍍銅PCB基板的鑽孔加工實驗中，在脈衝頻率30kHz下鑽孔，控制器能夠將孔徑長軸因功率下降的誤差由38.4%改善至1.8%，長寬比誤差由20%降至5%。在50kHz下鑽孔，控制器能夠將孔徑長軸因功率下降的誤差由100%改善至22.3%，長寬比誤差由100%降至5.8%。

關鍵字

雷射材料加工 ； 線上量測 ； CMOS相機 ； 回授控制

並列摘要

Since the laser was invented, laser has been applied in many fields such as material processing, communication, measurement, biomedical engineering, defense industries and etc. Laser power is an important parameter in laser material processing. However, since the response time of current laser power meters is too long, they cannot measure laser power accurately in a short time. To monitor the laser power in laser material processing, this study utilize a CMOS(Complementary metal-oxide-semiconductor) camera to develop an on-line laser power monitoring system. Also, this study applies a feedback control to stabilize laser power in order to solve the problem that laser power is easily affected by the environment temperature.
In this study, CMOS camera captures images of incident laser beam after it is split and attenuated. By comparing the average brightness of the beam spots and measurement results from laser power meter, laser power can be estimated. Moreover, laser power is stabilized by a PID controller which controls the “Duty time” of the laser Q-switch.
Under continuous measuring mode, the average measuring error is about 3% in average, and the response time is at least 3.6 second shorter than thermopile power meters; under trigger measuring mode which enables the CMOS camera to synchronize with intermittent laser output, the average measuring error is less than 3%, and the shortest response time is 20 millisecond.
For power stabilizing function, PID controller can fully compensate power disturbances within 1 second, the overshoot is less than 3%, and no steady-state error is noticed. In the PCB drilling experiments, the PID controller is able to reduce the error of major axis lengths of drilled holes from 38.4% to 1.8% and the error of aspect ratio from 20% to 5% while drilling at 30 kHz PRF under power disturbance. While drilling at 50 kHz PRF, PID controller reduces the error of major axis lengths from 100% to 77.7% and the error of the aspect ratio from 100% to5.8% under power disturbance.

並列關鍵字

Laser material processing ； On-line monitoring ； CMOS camera ； Feedback control

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