End effector position and identification system for steam generator servicing machine

Apparatus for servicing a steam generator tubesheet in which an end effector is mounted on the free end of a support member cantilevered, at selected angular positions in a plane parallel to the tubesheet, from a platform member of a carriage movable along an arm which rotates in a plane which is also parallel to the tubesheet, the improvement comprising:

• signal generating means comprising at least two sensor elements mounted on one of said members, each of said sensor elements being operative to generate an electrical signal when triggered, and at least two trigger elements mounted on the other member, each of said trigger elements being operative to trigger a sensor element when aligned therewith, said sensor elements and trigger elements being arranged on the respective members to generate, through the alignment of trigger elements with selected ones of said sensor elements, a discrete pattern of electrical signals for each of a plurality of angular positions of the cantilevered support member on the platform member, and means responsive to said pattern of electrical signals to position said arm and carriage relative to said tubesheet to align the end effector with a selected location on the tubesheet.