Precise autofocusing microscope with rapid response

• This study proposes a novel precise optics-based autofocusing microscope with a rapid response and no reduction in the focusing accuracy.
• In the proposed design, the variation of the image centroid position as a result of the effects of geometrical fluctuations of the laser beam is decreased by using a high-speed rotating optical diffuser. As a consequence, the focusing response of the proposed autofocusing microscope is significantly improved.
• The experimental results have shown that compared to the conventional autofocusing microscope, the proposed microscope has a more rapid response time and a comparable focusing accuracy of less than 2 μm.

The rapid on-line or off-line automated vision inspection is a critical operation in the manufacturing fields. Accordingly, this present study designs and characterizes a novel precise optics-based autofocusing microscope with a rapid response and no reduction in the focusing accuracy. In contrast to conventional optics-based autofocusing microscopes with centroid method, the proposed microscope comprises a high-speed rotating optical diffuser in which the variation of the image centroid position is reduced and consequently the focusing response is improved. The proposed microscope is characterized and verified experimentally using a laboratory-built prototype. The experimental results show that compared to conventional optics-based autofocusing microscopes, the proposed microscope achieves a more rapid response with no reduction in the focusing accuracy. Consequently, the proposed microscope represents another solution for both existing and emerging industrial applications of automated vision inspection.