Proc. SPIE. 9671, AOPC 2015: Advances in Laser Technology and Applications
KEYWORDS: Microscopes, Metrology, Calibration, Image processing, Atomic force microscopy, Scanning electron microscopy, Data processing, Signal processing, Precision measurement, Charge-coupled devices
Grating is an important sensor widely used in CNC machine or equipment for length measurement with high precision.
Special line scales with dense and micro lines are also widely used for the calibration of length measurement instrument.
All the pitches of grating and spaces of dense lines of line scale are needed to be calibrated for a good measurement
application. General methods for measurement of dense and micro lines include digital image processing method by
CCD Microscope or line scanning method by AFM or SEM, and laser distraction method. There are some disadvantages
to measure a long length grating with high precision and efficiently in these methods. A dynamic method based on
Photoelectric Microscope is introduced, the lines of grating to be measured is moving uniformly when measuring, and
the working distance is a bigger 65mm, the zoom of objective is low 10X. The principle of this dynamic method is
discussed and the distortion of line signal is analyzed. The way to decrease the affection caused by distortion of line
signal is also described. A special glass grating line scale with length 10mm, space 10μm and width 5μm is measured to
verify the method. The measurement result and the uncertainty analysis demonstrate the expand measurement
uncertainty (k=2) is less than 0.1μm.
With the development of laser technology, the laser wavelength has been the primary standard of length measurement. The measurement of laser wavelength is studied widely in the world. In fact, the accuracy is different when measured in the air and vacuum. The measurement accuracy of laser wavelength is high when measured in vacuum, such as beat frequency method, its precision can meet 10-15 order of magnitude. However, most of length measurement are taken place in air which influenced by environmental factors such as temperature, pressure, humidity and air ingredient. The research of how to enhance the measurement precision in air is meaningful. There are many general methods for measurement of laser wavelength include Edlen empirical formula method, the extraction method (the refractive index interferometer), F-P etalon method, and grating diffraction method, etc. By comparing and analyzing these methods, among them the Edlen formula method is the most simple and practical, the measurement result and analysis demonstrate the measurement method can achieve the precision of 3× 10-8.
Combining laser interferometric comparator with high precision inductance sensor, a novel measuring device for step gauge was developed. A high precision laser interferometer system was used for a length standard; a zero-crossing trigger signal of inductance sensor output voltage was used for the aiming signal. In order to improve the measuring accuracy, several high precision sensors were installed to measure environmental parameters for compensating the laser wavelength according to the Edlén empirical equation. A rotating mechanism was designed. Two key problems, probe obstacle avoidance and aiming repeatability, were solved. Experimental analysis of the contact force and speed of influence on measuring probe repeatability, and a segmented control method of the movement speed was established. The experiment indicates that the system has a high accuracy of measurement, which can be used for contact measurement of other one dimension length standard.
Automatic interference comparator (AIC) is a high precision one-dimensional length measurement machine for investigation and calibrations of line scales, linear encoders and length gauges. This paper emphasizes a novel electronic subdivision method for the AIC to realize precision measurement, which is composed of integer fringe counting, fraction fringe counting and electronic strobe. The realization of the whole system is based on FPGA. A standard line scale has been calibrated by this method on the AIC of the National Institute of Metrology(NIM) in China. The experimental results show the measurement repeatability is less than 7.5 nm, which demonstrates the feasibility of the new signal processing method.
Line sensing is key for line scale measurement. Different methods for line sensing are suited to different Line Scales.
Line sensing methods such as CCD microscope and slit photoelectric microscope currently mainly used in the world are
introduced. This paper presents a new method based on laser line scanning technique, which is widely used in laser bar code scanner. The basic sensing principles, the precision can be obtained with different methods and the advantages and disadvantages of the methods are also discussed. An experiment device based on laser line scanning was built to measuring the ordinary line scale such as square rules, steel tapes. In order to get a good reproducibility for line sensing, the line signal processing is studied. The line position is calculated as mass center of certain areas above minimum value of each line signal, the experiment result shows that when measuring 1mm interval of an ordinary steel ruler in scanning interval 10μm, the reproducibility is less than 1μm.
Composition and principle of 2m laser automatic interferometric comparator were introduced. A novel contact aiming system based on high precision inductance sensor was designed. The zero-cross trigger signal of inductance sensor output voltage was treated as the aiming signal. A rotating mechanism was designed and a segmental shifting motion control model was established. Two key problems, avoiding probe crash and aiming repeatability, were solved. The one dimension end standards such as gauge block, step gauge could be measured directly by this means. The data of test revealed that aiming repeatability was less than 0.2μm.
Photomask is a kind of 2-D optical standard with etched orthogonal coordinates made of a glass substrate chrominged or
filmed with other metal. In order to solve the problems of measurement and traceability of ultra precision photomasks
used in advanced manufacturing industry, 2-D photomask optical standard was calibrated in high precision laser two
coordinate standard device. A high precision differential laser interferometer system was used for a length standard, a
high magnification optical micro vision system was used for precision optical positioning feedback. In this paper, a
image measurement model was purposed; A sampling window auto identification algorithm was designed. Grid stripe
image could be identified and aimed at automatically by this algorithm. An edge detection method based on bidirection
progressive scanning and 3-sigma rule for eliminating outliers in sampling window was found. Dirty point could be
removed with effect. Edge detection error could be lowered. By this means, the measurement uncertainty of 2-D optical
standard's ruling span was less than 0.3 micrometer (k=2).