Calibration of the set of laser profilers with an application to real time measurement of the injection molded parts geometry

Abstract A laser profiler is a device used to acquire object profiles based on laser triangulation. It enables reconstruction of the three-dimensional surface of a moving object, for example one transported on a conveyor belt. To scan an object from multiple directions and minimize dead zones occurring in concave regions, a set of profilers can be employed. In this article, we propose a calibration method that allows independent positioning of profilers at arbitrary locations, without constraints on their spatial configuration. The calibration is based on a three-dimensional pattern with circular reference markers, whose reliable detection is ensured through the combined use of the height map and the intensity image. The method was experimentally validated using a stand composed of a conveyor belt equipped with a high-resolution encoder and four laser profilers LJ-X8400 with resolutions of 75 μm laterally (X/Y) and 3.6 μm vertically (Z). It achieved a calibration precision of 0.1 mm across 20 experiments comparing 780 reference points seen by all four profilers. The method has been implemented in industry, as part of an optical inspection system for geometry control of polymer components.