Abstract: The invention relates to a system for detecting and locating surface discontinuity by a light beam; it is more particularly intended for detecting any discontinuity forming a line on this surface, or any discontinuity forming two opposite lines on this surface. In the latter case, this discontinuity may, for example, be the join defined by the opposite edges of two metal sheets to be welded.

Abstract: The invention relates to an automatic and self-adapting process for fusion-welding a joint between two surfaces, with the aid of a welding head which essentially comprises a joint detector and a torch supported by a carrier mobile along the joint. This welding head is mobile in rotation about a main axis related to the carrier and substantially perpendicular to the plane tangential to the surfaces to be welded at the location of the joint, and mobile in translation along this main axis. The torch and the detector are mobile in rotation about a secondary axis related to the head and parallel to the main axis and the torch is able to pass through the main axis in the course of its rotation about the secondary axis.A reference direction for all the degrees of freedom of the head is defined when the above-mentioned axes as well as the axes of the torch and the detector are in the same plane.