In order to solve the problem of low precision in calibration and measurement of large size optical measuring instruments, mask, and other two-dimensional grid standards, a large size(1m × 1m) plane coordinate measuring method based on multi-axis laser interferometer is studied. Use a cube-corner prism as a reflector. Using a fixed bridge measuring machine structure, the co-planar motion is disassembled into independent X-axis movable table motion and Y-directional slider motion on the beam. Geometrical error modeling analysis is carried out on the measuring machine, and optical path spectral layout of multi-axis laser interferometry is studied. In order to monitor the deflection of the X-direction moving platform in real time, use two-channel laser interference to measure the length in the X-direction and a single-channel measurement of the Y-direction slider movement. Finally, a laser interferometry model with large plane coordinates is proposed and a motion simulation analysis is carried out for the deviation of X-axis mobile platform around Z axis, to verify the validity and necessity of real-time monitoring compensation error of double optical path for plane coordinates measurement.
Two-dimensional shape photomask is widely used to calibrate and correct optical precision measurement system like image measurement instrument and to calibrate or distortion correction of camera probe with CCD/CMOS sensor. Among all 2-D shapes, circle is adopted frequently because of its information such as size, form and position. Standard photomask with circle shape is multi-parameter calibrated by high precision laser two-coordinate standard device based on coordinate measurement method. Roundness error is assessed by least square circle method. How center coordinate, radius and roundness of a circle affected by number of measurement points, incident light intensity and optical magnification of micro probe are analyzed. Test results indicate than that standard with circle shape could be calibrated with high precision.
National working standard of two-dimensional line scale based on laser two-coordinate standard device was set up to solve the problem of the calibration and traceability of 2-D line scale optical standard and high precision photomask. The operating principle and system composition of the working standard device were introduced. The characteristics were test in special experiments. A high precision differential laser interferometer system was used for a length standard, a high magnification optical microvision system was used for precision optical positioning feedback. In order to improve the measuring accuracy, several high precision sensors were installed to measure environmental parameters for compensating the laser wavelength in atmosphere according to the empirical Edlén equation. High resolution CCD modeling and calibrating based on two-dimensional nanoscale positioning movable platform and laser interferometer were adopted to improve the pointing accuracy. Two-dimensional line scale working standard could be used to measure line spacing, point spacing, and coordinates of 2-D optical standard or photomask, with measurement range 300mm × 300mm, measurement uncertainty U=(0.1~0.3)μm, k=2. Some experiments were carried out to identify the characteristics of length measurement error, probing error, measurement repeatability and measurement reproducibility of the working standard, and measurement uncertainty was validated by the measurement experiments.
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.
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).
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