Flexure-Based Parallel-Kinematics Stages for Passive Assembly of MEMS Optical Switches

Abstract

A key operation in assembly of MEMS optical switches is to insert fibers into U-grooves on a silicon substrate. Due to the limited positioning accuracy of the handling tool, heavy collision often occurs between fibers and the edges of U-grooves during the insertion operation. Such collisions will not only damage fibers and U-grooves but also sometimes make the fiber skidding from the handling tool. Conventional solutions to the problem involve determining misalignment using machine vision or force sensors, and then positioning fibers accurately by virtue of high precision multiaxis positioning systems (with submicron repeatability). However, such approaches are costly and difficult to implement. In this chapter, we present a cost-effective passive assembly method to solve the problem. It utilizes a specially designed passive flexure-based fixture (stage) to regulate high contact forces and accommodate assembly errors. To determine the design conditions for a successful insertion, the major problems encountered during the fiber insertion are analyzed. A systematic design method is then proposed for a 3-legged Flexure-based Parallel-Kinematics Stage (FPKS) for passive assembly applications. Experimental results show that such a passive assembly approach can effectively and automatically reduce the contact force and accommodate the assembly errors.