Degenerated Degree of Freedom Sensing Without Loss of Accuracy While Estimating the Rigid Body Parameters for the Calibration of a Two-Axis Robotic Arm for Prototype Fast Breeder Reactor, Steam Generator Inspection System

The Prototype Fast Breeder Reactor (PFBR) has eight Steam Generators (SG), each with 547 tubes connecting top and bottom headers. The integrity of these tubes is ascertained using periodic In-Service Inspection (ISI) procedures. Two-Axis Tube Locator Module (TLM) is a robotic manipulator designed to be used to precisely locate all 547 tubes. The difference in the device work plane and the tube sheet plane is mainly due to error from tolerances in fabrication and error due to mounting the device. These errors hinder the accurate positioning of inspection device over the tubes for inspection. In this work, a novel approach to calibrate the TLM is attempted by using motor encoder as sensors, to calibrate the TLM without using any external calibration devices. In this work, a three-point calibration is used to compute transformation matrix using two-axis motor encoder as sensors, for measuring the displaced position of calibration point tubes and using SVD on the correlation matrix formed from the original and transformed points. Even though three independent measurements (x, y, z axis) are required to spatially ascertain the positioning error of the probe with respect to calibration point tube, it proved that planar 2D measurement using readily available servo motor encoder sensors itself is adequate for the calibration of TLM without much loss of accuracies. The degenerated sensing reduces the cost, effort, and time for calibrating the TLM for use in inspection.