Automated micro-assembly of hydrogel modules based on defocus feature

Acquisition of target location and depth information under microscale is the precondition to achieve automated microassembly. To obtain accurate location, we need to utilize focused image for image processing under optical microscope. However, there´s no unified standard to evaluate the clarity of an image acquired by manually focusing. This paper presents an auto-focusing method to automatically determine the focal plane of target and depth information through the algorithm to evaluate the clarity of target image. The automated microassembly of donut-shaped microstructure was achieved based on the auto-focusing method and the tip of micromanipulator was detected in 3D space. Experimental result shows that the auto-focusing method achieved accurate focusing with error less than 4.1 μm and high speed focusing within 10 s. The detection success rate of the donuts is around 99.8% and the determined depth information between donut and micromanipulatoris within 5 μm.