| 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
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%, 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 22.3% and the error of the aspect ratio from 100% to5.8%
under power disturbance.
Keywords: Laser material
processing, On-line monitoring, CMOS camera, Feedback
control
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