GEOMETRIC AND QUASI-STATIC THERMAL ERROR COMPENSATION OF A LASER DIGITIZER ON A COORDINATE MEASURING MACHINE

Abstract

<p>Coordinate measuring machines (CMM) are widely used in inspection and reverse engineering. There is increasing interest in using optical sensors, such as laser digitizers, to take advantage of their high data acquisition rates and the fact that they are a non-contact measurement suitable for soft materials or delicate parts. The issue to be addressed is the fact that the sensors and CMMs are made by different manufacturers, so there is no integration of the error compensation scheme. As well, unlike conventional touch trigger probes, correction of the laser digitizer pose must be explicitly incorporated. The purpose of this study was to develop a mathematical algorithm that would improve the accuracy of data collected with a laser digitizer mounted on a CMM. To this end, an algorithm was developed to compensate for the variations in digitizer pose. It compensates for both positional errors and angular errors, whether caused by CMM geometric component error or quasi-static thermal error. To implement and verify the error compensation, tests were made using a Hymarc laser digitizer mounted on a DEA Iota 1102 CMM. The thesis proposes using an optical ballbar, an adaptation of the traditional ballbar recommended by ASME Standard B89.4. The scan plane coordinates of the digitizer. the CMM axis scale positions and temperatures were recorded simultaneously in real time. The CMM error compensation algorithm was then used to post process the data to obtain improved global part coordinates. Accuracy of a laser equipped CMM is improved from 67 um to 17 um. The benefits of using optical sensors can be improved by incorporating this error compensation scheme into an integrated optical metrology system.</p>