The impact of different alignment strategies on the overall performance of a white light scanner according to sphere spacing error specified in VDI 2634

摘要

System alignment strategies impact the overall performance of white light scanners, in particular affecting the uncertainty that is determined using the sphere spacing error specified in the VDI 2634 guideline. This paper addresses the accuracy of optical white light or so called "topometric" scanners. In almost any application of such scanners it is necessary to put together scans from different directions: from a couple of scans to a couple of hundred scans. Accuracy for the scanner itself can usually be well described for a single scan. However, the accuracy for assembled data sets from many scans is harder to estimate and specify as it depends on many more parameters as well as on the alignment strategy being used. This paper will describe different alignment strategies including the use of robots, tracking systems, and targets, as well as best fitting methods. The impact of these methods on the resulting overall accuracy is described and demonstrated using real test examples. In addition, different methods of achieving these accuracy numbers will be presented including using guidelines such as provided in VDI 2634. This paper will briefly touch on the basic principles of white light scanning to understand the potential as well as to illustrate the limitations of these techniques. This paper is intended to provide a useful guideline for engineers or quality managers who want to establish or learn more about new scanning technologies, with special attention given to the accuracy issues.