Ultra-Precise Assembly of Micro-Electromechanical Systems (MEMS) Components

摘要

This report summarizes a three year effort to develop an automated microassembly211u001eworkcell for the assembly of LIGA (Lithography Galvonoforming Abforming) parts. 211u001eOver the last several years, Sandia has developed processes for producing surface 211u001emachined silicon and LIGA parts for use in weapons surety devices. Some of these 211u001eparts have outside dimensions as small as 100 micron, and most all have submicron 211u001etolerances. Parts this small and precise are extremely difficult to assembly by 211u001ehand. Therefore, in this project, we investigated the technologies required to 211u001edevelop a robotic workcell to assembly these parts. In particular, we 211u001econcentrated on micro-grippers, visual servoing, micro-assembly planning, and 211u001eparallel assembly. Three different micro-grippers were tested: a pneumatic probe, 211u001ea thermally actuated polysilicon tweezer, and a LIGA fabricated tweezer. Visual 211u001eservoing was used to accuracy position two parts relative to one another. Fourier 211u001eoptics methods were used to generate synthetic microscope images from CAD 211u001edrawings. These synthetic images are used off-line to test image processing 211u001eroutines under varying magnifications and depths of field. They also provide 211u001ereference image features which are used to visually servo the part to the desired 211u001eposition. We also investigated a new aspect of fine motion planning for the micro-211u001edomain. As parts approach 1-10 (micro)m or less in outside dimensions, 211u001einteractive forces such as van der Waals and electrostatic forces become major 211u001efactors which greatly change the assembly sequence and path plans. We developed 211u001ethe mathematics required to determine the goal regions for pick up, holding, and 211u001erelease of a micro-sphere being handled by a rectangular tool. Finally, we 211u001eimplemented and tested the ability to assemble an array of LIGA parts attached to 211u001etwo 3 inch diameter wafers. In this way, hundreds of parts can be assembled in 211u001eparallel rather than assembling each part individually.