Visual measurement is one of the important measurement methods for pinion gears. The measurement principle and the systematic structure of a pinion gear visual measuring system were given. Pixel equivalent is the key parameter in the visual measurement system, which needs to be calibrated before dimensions evaluation. A glass dot calibration plate was applied in the system calibration. Pixel equivalent calibration experiment, LED brightness experiment, edge compensation experiment and multi-position edge compensation experiment was carried out. The parameter pixel equivalent is determined by the comparison between the physical size of center distance of adjacent mark circle in the glass dot calibration plate and its pixels number obtained by the visual system. The center distance of adjacent mark circle was chosen to avoid the affection of the brightness of light source and the sub-pixel technology was used. The proper brightness condition of LED light was selected in the LED brightness experiment. Under this condition, the compensation of edge deviation was obtained by analyzing the edge position deviation in the diameter measurement of the mark circle of the calibration plate. The experimental results show that the pixel equivalent is 5.59522μm/Pixel, and the compensation of edge deviation is 0.54μm. 49 diameters of the circular marker were measured in edge compensation experiment, the largest difference between the measured diameter in central vision after compensation and its physical dimensions is 0.3um, which is 0.2um in muti-position edge compensation experiment. The calibration methods and the experimental research are important for the designed visual measurement system for pinion gears.
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