High-precision target location for industrial metrology

Many industrial metrology applications require accurate and real or near-real time measurement tools in often adverse conditions. Over the past three years, the Industrial Alignment Project (IAP) has been focused on the development of precise measurement techniques for use with large rotating machinery. This paper highlights some results using digital array cameras which have been shown to be well suited for many applications. Limited camera resolution and high accuracy point positioning requirements have required the development of specialized targets. Retro-reflective targets are used to reduce the varying effects of lighting/shadows since this material exhibits maximum reflection in the direction of the light source. Using sub-pixel edge detection techniques with the pre-defined targets, it is possible to obtain accuracies of 1/20th a pixel or better. In addition, employing multiple camera stations with an appropriate imaging geometry, the three dimensional coordinates of the point of interest can be obtained by establishing photogrammetric techniques. The results of test projects are given to illustrate the viability of such a measuring system.