A welding position detecting apparatus provided on a welding torch which forms an arc between a welding wire and a groove face on a work piece. The apparatus has an optical system for irradiating the groove face with a converging ray at a point in advance of the point of the arc so as to form a groove...http://www.google.de/patents/US4667082?utm_source=gb-gplus-sharePatent US4667082 - Welding position detecting apparatus
