Common path optical design for 2D inspection system with the capability of auto-focusing

Abstract

This paper developed an optical design approach to combine the auto-focusing and image sensing in the 2D inspection system. The focusing principle here employed the chromatic confocal microscopy due to the one-shot focusing capability. The system held a special issue that the chromatic confocal microscopy has the higher optical dispersion characteristic than the 2D image sensor which captures a clear image for the optical inspection. Hence, the system here must be designed to be characterized with both the higher and lower optical dispersion, which was called as the common path optical design in this study. That is, an optical approach must be developed to divide and switch the above totally different dispersion conditions. Accordingly, the higher dispersion device, the chromatic confocal sensor, examined the object surface height to vertically vary the focused position of the 2D inspection system. Furthermore, the lower dispersion device, the 2D image sensor, can be adjusted to focus onto the object surface so that a clearly focusing image can be acquired. The experimental results were also provided to ensure this approach can automatically focus the object surface and then the clear image can be captured to perform optical inspection to obtain the position, dimension or area.