Machine vision calibration for a nuclear steam generator robot

Inspection and repair of pressurized water reactor steam generators are among the most costly and schedule-critical activities of a refueling outage. These. tasks are highly automated with robots and special tools. This paper describes a method of improving the calibration of a steam generator robot by adding a machine vision computer to the existing tool-head monocular video. The steam generators are heat exchangers containing several thousand tubes ranging from 20 to 40 m in length. Each tube is 1 to 2 cm in diameter with a wall thickness of {approximately} 1 mm. The tubes are welded into a thick tube sheet that caps a hemispherical or quarter-sphere plenum. Practically all work must be performed robotically because the plenum is a high-radiation area. A robotic arm with precise positioning capability must enter the plenum through a 40-cm passageway. Most arms are anchored to either the passageway or the tube sheet. The arm must identify each of the thousands of tubes by row and column number based on the measured robotic joint angles and the calibrated arm-to-tube sheet spatial transform.