Principle of combined measurement for super large gear

The combined measurement network of super large gear includes laser tracker and its measurement system, flexible joint coordinate measuring arm and its measurement system, target calibration plate, temporary reference point and a computer capable of data processing, as shown in Figure 1.

Using the characteristics of flexible joint coordinate measuring arm with high precision in a small range, the tooth surface of super large gear is measured by contact method, and the data of tooth surface measuring points are obtained. Considering that the measuring range of the measuring arm is limited, it is necessary to constantly change the position of the measuring arm to complete the measurement of all the required data of the oversize gear. The laser tracker is used for global control of the measurement network, and the frog leaping technology of flexible joint coordinate measuring arm is used. By calculating the coordinate transformation matrix between the two instruments, the point cloud data obtained by the measuring arm at different stations are registered in the laser tracker coordinate system, as shown in Figure 2.

In order to improve the measurement accuracy of the super large gear, it is more important to improve the global control accuracy of the laser tracker than to select a higher precision measuring arm. Taking Leica at960 laser tracker as an example, its global measurement accuracy is (15 μ m+6 μ m) The accuracy of angle measurement is (15 μ m+6 μ m) The accuracy of interferometric ranging is 0.5/m μ m/m。 It can be seen that the angle measurement error of laser tracker has a significant impact on its global measurement accuracy. In order to improve the global measurement accuracy of the combined measurement network, the redundancy technology and multilateral measurement method are introduced into the measurement network, and the angle measurement module is abandoned. The same temporary reference point is measured by several laser trackers whose positions are known, and the interference length measurement value is taken as the constraint condition. The spatial coordinates of the reference point are calculated by using the principle of spatial multilateral method, and then the redundant data are used to iteratively optimize the temporary reference point and laser tracker station coordinates, so as to achieve higher precision control effect.

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