High resolution flexible 3-RRR planar parallel micro-stage in near singular configuration for resolution improvement. Part I

Abstract

The increasing level of requirements in terms of performance, accuracy, repeatability and resolution in the semiconductors industry leads to several technological problems; among them the positioning accuracy and resolution are peculiarly important. In this paper, we address the crucial issue of high resolution and fast positioning mechanisms. We propose a novel type of high resolution and fast positioning mechanism, based on a macro/micro architecture composed of two stages. We focus here on the micro-stage. It is a combination of: a 3-RRR planar parallel structure (3-RRR stands for 3 kinematic chains in parallel, each chain composed of 3 revolute joints R in a serial arrangement) with deported PRR actuation (a rod connected with two revolute joints R to a linear actuator P and to the RRR chain). This architecture provides stiffness, symmetry and interesting thermal properties; Flexible R links (which avoid the drawbacks of conventional links in terms of backlash, friction, wear, stick-slip,...); and near serial-singular configuration which results in an improvement of the resolution. A modeling of inverse kinematics for position and velocity is presented. Then, an optimization is run to find the best set of geometrical parameters for the micro-stage. An articulated kinematic scheme is finally presented.