High Precision In-Pipe Robot Localization with Reciprocal Sensor Fusion - 19516

Manual measurement of U-235 deposits in uranium enrichment piping is a costly, time consuming, and labor-intensive process that is a well-known cost and schedule driver. Autonomous, robotic innovation enabled by this research is revolutionizing the measurement speed, quality and safety of this important operation. The huge advantage is the robot's ability to measure from inside the pipes. The upside is sensing the geometry, appearance and radiometry directly. The downside is the inability to know precise, absolute position of the measurements in very long pipe runs. This paper develops the unprecedented localization required for this purpose. This paper presents the precise localization method designed for in-pipe radiation measurement robots. Unlike other in-pipe localization methods, this approach achieves millimeter-level accuracy in hundred-foot runs and does everything on one robot without relying on tether cable or communicating devices out of pipe, which is an important feature for nuclear in-pipe robot. It overcomes challenges usually encountered by in-pipe localization such as long travelling distance and operation time, narrow view angle, and featureless environment. The robot is equipped with encoders embedded in tracks which can record travelled distance, but encoder odometry drifts unacceptably due to slip and non-linearity. The robot also incorporates a laser range finder measuring the absolute distance, but range finder in long pipes has many misleading false measurements that are difficult to filter. The innovation here is to use one to filter/calibrate the other so that data used from the two sensors improve each other iteratively and reciprocally. The survey measurements accuracy of this localization method is proven by experiments comparing to ground truth and 'Zippering error' experiments that compare measurements to fixed features in pipes. (authors)