Development of kinematic coupling preload guidelines through design and testing of an adjustable micromanufacturing fixture

Abstract

In the growing field of non-lithographic micromanufacturing, the ability to properly align a workpiece to a machine limits the attainable tolerances in micro-electro-mechanical-systems (MEMS) prototyping. This limit has created the need for a standard adjustable base for implementation into multiple precision machines, allowing for six-axis adjustment and alignment of workpiece stages that are moved between these machines. Such a fixture--a hybrid positioning fixture (HPF)--has been designed, fabricated, and tested. This HPF has demonstrated <50 nm and <1.5 [mu]rad 2[sigma] (95% confidence) static positional repeatability over 1000 separation-engagement cycles and equivalent 2[sigma] (95% confidence) path-following accuracy when used as a dynamic nano-stage. The HPF has also demonstrated adequate stiffness to ensure <50 nm positional accuracy over an adjustment range of ±5 [mu]m and ±100 [mu]rad in response to 2 N normal and lateral forces during micro-milling operations. The HPF is based upon a kinematic coupling concept, and experiments have been completed that show highly repeatability coupling can be obtained by loading the Hertzian kinematic contacts of the HPF past the fully plastic half-groove material limit. This is a novel result that allows for stiffness increases of ~2.5 and load capacity increases of ~15.5 over conventional kinematic couplings, which are typically loaded to the sub-surface elastic limit.