Autofocus for automated microassembly under a microscope

A motorized microscope is used as optical sensor for automated microassembly. To achieve the required resolution range an automated autofocus system is indispensable. Since we are equipped to acquire and process microscopic images we follow a passive approach to autofocusing based on image processing. In a typical microassembly situation there are non-planar objects and several different focal planes. In our autofocus system, focal planes are determined by means of an image power measure and coarse/fine tuning. Position markers are employed to assign non-planar objects a well defined focal plane. For the identification of the different focal planes we make use of our a priori knowledge about the assembly process and the objects to be observed. In this way we are able to distinguish single, well defined focus locations. This approach to autofocusing is particularly valuable for applications in microscopy going beyond the conventional sample inspection.