Development of On-line Laser Power Monitoring and Stabilizing System
Date Issued
2015
Date
2015
Author(s)
Lee, Meng-Shiou
Abstract
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.
Subjects
Laser material processing
On-line monitoring
CMOS camera
Feedback control
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-104-R02522708-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):e6204a7702e65d16df8c3b8f0c74fdac