Design and characterization of precise laser-based autofocusing microscope with reduced geometrical fluctuations

Abstract

Due to consumer preference for products with ever higher performance, a requirement exists for precise autofocusing microscope systems to perform the inspection process in automated mass production lines. Accordingly, the present study proposes a laser-based microscope system in which a precise autofocusing capability is achieved using a position feedback signal based on the distance L between the geometrical center (X c , Y c ) of the image captured by the CCD sensor and the centroid (x centroid , y centroid ) of the image. The experimental results show that the proposed system has a positioning accuracy of 2.2 μm and a response time of 1 s given a working range of ±200 μm. The autofocusing performance of the proposed system is thus better than that of a conventional centroid-based system, which typically achieves a positioning accuracy of around 5.2 μm.