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

Introduction: 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. Methods: 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. Results: 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. Conclusion: 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.