Development of a stereo vision system for non-contact railway concrete sleepers measurement based in holographic optical elements

For railway industry, the management of finished dimensional accuracy and traceability of concrete sleepers production has become an important issue. A fast stereometric system has been developed to measure free-form surfaces of railway concrete sleepers and calculate track and rail seat dimensional tolerances. This system allows non-contact measurement of soft parts to make possible efficient inspection of post-stressed production before curing of the concrete, and speed up the digitizing process reducing some difficulties associated with stereo vision. This system integrates two holographic optical elements (HOEs), that have been developed, manufactured and tested making use of the outer intensity distribution of thin diffraction grating, to generate specific structured light consisting on a bundle of laser planes with different intensities. The experiments carried out in our study, using several precision tests and determining the error limits under specified operation conditions, illustrate the accuracy of this new system and demonstrate its relevance. (C) 2005 Elsevier Ltd. All rights reserved.