Robotic arm for servicing nuclear steam generators

Abstract

An improved robotic arm which is capable of accurately manipulating a testing device beneath the tube sheet of the steam generator and accurately and consistently return to a selected tube location is provided. The robotic arm includes a base which is adapted to be fixedly secured to a support beam which initially positions the robotic arm within the steam generator, a first extension arm which is rotatably mounted on the base forming a primary rotation joint and which extends essentially parallel to the tube sheet. A second extension arm is rotatably mounted at the end of the first extension arm forming a secondary rotation joint and further extends therefrom. The testing device such as an eddy current inspection tool is positioned at a distal end of the second extension arm. The improvement includes a direct drive high-torque DC motor and a harmonic drive coupling being provided at each of the joints for providing a significant reduction ratio between the output of the high-torque DC motor and the rotational joint. Further, these components are of a light weight construction so as to limit the load carried by the robotic arm. A control device is provided for simultaneously independently controlling the high-torque DC motors such that the testing device can be both accurately and reliably positioned relative to the tube sheet. The robotic arm is also capable of being readily adjusted to be used in servicing various models of steam generators.