Micro-grippers for assembly of LIGA parts

This paper describes ongoing testing of two microgrippers for assembly of LIGA (Lithographie Galvanoformung Abformung) parts. The goal is to place 100 micron outside diameter (OD) LIGA gears with a 50 micron inner diameter hole onto pins ranging from 35 to 49 microns. The first micro gripper is a vacuum gripper made of a 100 micron OD stainless steel tube. The second micro gripper is a set of tweezers fabricated using the LIGA process. Nickel, Permalloy, and copper materials are tested. The tweezers are actuated by a collet mechanism which is closed by a DC linear motor

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

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

Optical Readout of Micro-Accelerometer Code Features

Micromachine accelerometers offer a way to enable critical functions only when a system encounters a particular acceleration environment. This paper describes the optical readout of a surface micromachine accelerometer containing a unique 24-bit code. The readout uses waveguide-based optics, which are implemented as a photonic integrated circuit (PIC). The PIC is flip-chip bonded over the micromachine, for a compact package. The shuttle moves 500 {micro}m during readout, and each code element is 17 {micro}m wide. The particular readout scheme makes use of backscattered radiation from etched features in the accelerometer shuttle. The features are etched to create corner reflectors that return radiation back toward the source for a one bit. For a zero bit, the shuttle is not etched, and the radiation scatters forward, away from the detector. This arrangement provides a large signal difference between a one and zero signal, since the zero signal returns virtually no signal to the detector. It is thus superior to schemes that interrogate the code vertically, which have a limited contrast between a one and a zero. Experimental results are presented for mock shuttle features etched into a silicon substrate. To simulate the shuttle moving under a fixed PIC, a commercially available waveguide source was scanned over the mock code