Moire-based positioning system for microrobots

Abstract

For all microrobot handling, a so called "Global Positioning system" must give the position of the robots to the robot control. At the University of Karlsruhe a position sensing system called "<i>MPS</i>" is currently being developed. With a resolution of 1 &#956;m and a turn-around-time of 0.2s this system is very exact and fast. Working touchless, its measurement principle works two-staged: the first approximation step is using the photogrammetrical principle, these results based on interferometrical effect delivers the mentioned resolution of 1 &#956;m. The freely movable robot is equipped with three marks working both as a photogrammetrical and as a Moire-based mark by having three of four coincidental cosinusodial shaped full circles printed upon it. A high-resolution CCD-camera is watching the whole scene permanently. Because of the Moire-effect, there are two grids needed to generate the Moire-fringes which have to be analyzed by the connected computer with the developed software. The first grid is the grid on the robot marks. The second grid, which is fixed to the working plate, is virtually created inside the computer (this grid is also circular and cosinusodial shaped). Merging the CCD-picture (after some image processing) with the virtual grid, the Moire-effect will appear. With a overspecified linear equation system, the centre point of the mark can be calculated then.