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The Research on Autofocus System of Miniature Five-Coordinate Image Measuring Machine

In order to meet the high-precision measurement requirement of tested objects with tiny dimension and complex shape, a miniature five-coordinate image measuring machine, which contains three translational axes and two rotational axes , is designed and built. This machine can inspect the objects from multi-orientation and multi-posture in non-contact way. As an indispensable step of image measurement, the autofocus effect has a direct influence on the following image quality and measurement accuracy. In this paper, the composition and working principle of autofocus system are presented and discussed. Meanwhile, the path planning method for autofocus system is introduced and an autofocus method based on evaluation function of mean square deviation is proposed and discussed in detail. Finally, the experiments demonstrate the effectiveness of the method and the accuracy of autofocus system