Conoscopic holography-based long-standoff profilometer for surface inspection in adverse environment

One of the more challenging applications of optical metrology is real-time dimensional control and surface inspection in industrial applications, where strong requirements of cost, setup, and applicability in adverse environments greatly limit the number of applicable technologies. This work shows an optic profilometer developed specifically for this purpose, the algorithms developed for efficient and accurate distance map calculation, and an example of its use in a harsh steelmaking environment. This device, based on conoscopic holography, is able to obtain a distance profile of a target in a single shot, works at long distance standoff (700 to 1200 mm), and still keeps good resolution (under 0.2 mm) with a very easy and reliable setup. The second part of the work focuses on a real example of this technology applied in an on-line inspection system in steel continuous casting funded by the European Coal and Steel Community, and which is currently working in the Aceralia LDA steelmaking factory in Asturias (Spain). The system is placed in the process line and performs on-line detection of surface defects over hot steel slabs (above 800 degrees C in the inspection point) from a distance of 1200 mm. 100% of the production can be inspected without interfering with the process and without adding any delay. (c) 2006 Society of Photo-Optical Instrumentation Engineers.