C2F: Coarse-to-Fine Vision Control System for Automated Microassembly

In this paper, authors present the development of a completely automated system to perform 3D micromanipulation and microassembly tasks. The microassembly workstation consists of a 3 degree-of-freedom (DOF) MM3A® micromanipulator arm attached to a microgripper, two 2 DOF PI® linear micromotion stages, one optical microscope coupled with a CCD image sensor, and two CMOS cameras for coarse vision. The whole control strategy is subdivided into sequential vision based routines: manipulator detection and coarse alignment, autofocus and fine alignment of microgripper, target object detection, and performing the required assembly tasks. A section comparing various objective functions useful in the autofocusing regime is included. The control system is built entirely in the image frame, eliminating the need for system calibration, hence improving speed of operation. A micromanipulation experiment performing pick-and-place of a micromesh is illustrated. This demonstrates a three-fold reduction in setup and run time for fundamental micromanipulation tasks, as compared to manual operation. Accuracy, repeatability and reliability of the programmed system is analyzed.