Development of precise autofocusing microscope based on reduction of geometrical fluctuations

In keeping with consumer preferences for ever more high-performance products, a requirement exists for precise autofocusing microscope systems for the inspection processes in mass production lines. Accordingly, a precise autofocusing microscope is proposed based on the reduction of the geometrical fluctuations of a laser light source, in which, the geometrical fluctuations of the laser light source are reduced via an optical diffuser. An autofocusing capability of proposed system is achieved by using position feedback signals from the centroid (x_centroid, y_centroid) of the image of the reflected laser beam captured from a CCD sensor. The experimental results show that the proposed system has a positioning accuracy of 1.5 μm with a working range of ±200 μm. Compared to conventional centroid method, it is shown that our proposed system has improved autofocusing positioning accuracy.