The present apparatus scans a torch or other member in two directions contained in a scanning plane perpendicular to its advance direction. The apparatus includes means for controlling the speed of the torch in one direction and a means for controlling the position of the torch in the other direction...http://www.google.co.uk/patents/US4689469?utm_source=gb-gplus-sharePatent US4689469 - Apparatus for scanning a member in a plane perpendicular to its forward moving direction
