DOE OSTI2012
The December 2010 version of the guide, ORNL/TM-2008/159, by Jeff Bunn, Josh Schmidlin, Camden Hubbard, and Paris Cornwell, has been further revised due to a major change in the GeoMagic Studio software for constructing a surface model. The Studio software update also includes a plug-in module to operate the FARO Scan Arm. Other revisions for clarity were also made. The purpose of this revision document is to guide the reader through the process of laser alignment used by NRSF2 at HFIR and VULCAN at SNS. This system was created to increase the spatial accuracy of the measurement points in a sample, reduce the use of neutron time used for alignment, improve experiment planning, and reduce operator error. The need for spatial resolution has been driven by the reduction in gauge volumes to the sub-millimeter level, steep strain gradients in some samples, and requests to mount multiple samples within a few days for relating data from each sample to a common sample coordinate system. The first step in this process involves mounting the sample on an indexer table in a laboratory set up for offline sample mounting and alignment in the same manner it would be mounted at either instrument. In the shared laboratory, a FARO ScanArm is used to measure the coordinates of points on the sample surface ('point cloud'), specific features and fiducial points. A Sample Coordinate System (SCS) needs to be established first. This is an advantage of the technique because the SCS can be defined in such a way to facilitate simple definition of measurement points within the sample. Next, samples are typically mounted to a frame of 80/20 and fiducial points are attached to the sample or frame then measured in the established sample coordinate system. The laser scan probe on the ScanArm can then be used to scan in an 'as-is' model of the sample as well as mounting hardware. GeoMagic Studio 12 is the software package used to construct the model from the point cloud the scan arm creates. Once a model, fiducial, and measurement files are created, a special program, called SScanSS combines the information and by simulation of the sample on the diffractometer can help plan the experiment before using neutron time. Finally, the sample is mounted on the relevant stress measurement instrument and the fiducial points are measured again. In the HFIR beam room, a laser tracker is used in conjunction with a program called CAM2 to measure the fiducial points in the NRSF2 instrument's sample positioner coordinate system. SScanSS is then used again to perform a coordinate system transformation of the measurement file locations to the sample positioner coordinate system. A procedure file is then written with the coordinates in the sample positioner coordinate system for the desired measurement locations. This file is often called a script or command file and can be further modified using excel. It is very important to note that this process is not a linear one, but rather, it often is iterative. Many of the steps in this guide are interdependent on one another. It is very important to discuss the process as it pertains to the specific sample being measured. What works with one sample may not necessarily work for another. This guide attempts to provide a typical work flow that has been successful in most cases.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗