Sub-millimeter servo system for sample positioning based on thresholding of defocused laser spot
Accurate sample positioning and automatic sample operation can improve the performance of measuring instruments.A Sub-millimeter servo system for sample positioning based on thresholding of defocused laser spot is proposed.The effective laser spot image is extracted by thresholding of the light cone section on the sample surface.By estimating the section area and centroid of the spot,the defocus status and position of the measured sample can be acquired.A focused light cone at visible wavelength is cast onto the surface of sample,forming a marked laser spot as the indicator of the measurement point.A CCD camera is used for visual imaging,and a high-precision three-dimensional motorized translation stage is used for the accurate servo control.The marked spot is real-time monitored and processed in the platform of LabVIEW.The Autonomous Thresholding Image-Processing Algorithm(ATIPA)is proposed to detect and analyze the defocused marked spot,through which system creates a servo whereby accurate position control of the sample can be achieved.The measurement point on the sample can be accurately located by computing the center coordinates of the marked spot.And a focus function is implemented by measuring the size of defocused spot.This focus function is then used within an improved climbing search algorithm to obtain the focused sample position via moving the sample stage.Experimental results show that the system could measure the laser spot and control the sample in a robust,repeatable way within reasonable errors.The accuracy of the sample autofocus reaches 0.1 mm.
sample positioning spot detection auto-focus thresholding
Zheng Wang Liangcai Cao Enyao Zhang Guofan Jin
State Key Laboratory of Precision Measurement Technology and Instruments,Dept.of Precision Instrument,Tsinghua Univ.,Beijing,100084,P.R.China
国际会议
2013 International Conference on Optical Instrument and Technology (OIT’2013)(2013年光学仪器与技术国际会议)
北京
英文
1-6
2013-11-17（万方平台首次上网日期，不代表论文的发表时间）