Analysis of laser scanning and strategies for dimensional and geometrical control

Noncontact scanning systems are becoming more present in the industry every day. These systems allow a significant reduction in manufacturing costs, mainly due to the important decrement in the inspection time. They enable obtaining a great amount of data that provides very good levels of quality in results. In spite of the well-known advantages that these systems offer, there are also some difficulties, such as the undefined and nonstandardized accuracy when compared with traditional inspection systems based on touch-trigger probes. That is one of the reasons for the practical absence of scanning systems in metrological applications: they have not been adequately tested in terms of accuracy for geometric and dimensional tolerance control. In fact, these systems are mainly used in reverse engineering or multimedia applications. The goal pursued in this research is to analyze the applicability of scanning systems for measuring and control of tolerances. Two different scanning systems were analyzed: a laser triangulation sensor and a touch-trigger probe, both mounted on a coordinate measuring machine. Several test parts were designed, which include different canonical features: planes, spheres, cylinders, holes (outer and inner), and conical surfaces. A common alignment method was defined in order to compare the geometry generated for both scanning systems. Different scanning orientation strategies were defined for laser scanning. Besides this, features were reconstructed with several computer-aided design systems, and the correlation between the contact and noncontact geometries was analyzed to study the convergence of results among them. Finally, an analysis was carried out to compare them in terms of geometrical and dimensional tolerances, considering the contact measurements as datum. As a result, some advises are given with respect to the best strategies for scanning, estimating the deviations.