Automatic 3D Joining in Microassembly

In this paper, we propose an automatic control strategy to perform joining tasks in microassembly of three-dimensional (3D) micro-electro-mechanical-system (MEMS) structures, using a robotic workstation equipped with a microscope and a passive microgripper. In the proposed automatic joining scheme, the reoriented micropart, which is often not parallel with the focal plane of the microscope, is localized in 3D space with pattern matching and an auto-focus method. The joint features in the micropart and MEMS chip are aligned with a two-stage strategy. In the first stage, the MEMS chip is placed in a lower position than that of the reoriented micropart. The positions in x-y plane (parallel with the focal plane of microscope) of the joint features are determined with pattern matching method. Visual servo control is employed to align the joint features in two different parallel planes with sub-micron accuracy. In the second stage, the joint features are aligned in the z direction (along the optical axis of the microscope) with assistance of vision. The contact status of joint features is detected with the gray value of the image in the surrounding area of the tips of micropart, which changes due to the deflection of the joint feature. Experiments demonstrated the efficiency and validity of the proposed 3D joining strategy.