Proposal for Pipeline-Shape Measurement Method Based on Highly Accurate Pipeline Length Measurement by IMU Sensor Using Peristaltic Motion Characteristics

In order to prevent accidents caused by the aging of sewer pipes, it is necessary to identify the state of the pipe as well as the damage position. A pipeline diagram is required to specify the location of the damage, but pipeline diagrams are often lost. Therefore, it is necessary to measure the pipeline shape and create a pipeline diagram. We developed a robot for sewage pipe inspection that mimics the movement method of earthworms. In this paper, we propose a method for estimating the pipe shape from an inertial measurement unit (IMU) sensor mounted on the developed robot with peristaltic motion. The pipe shape is realized by a combination of distance measurement using acceleration and changes in angular velocity, and bending pipe discrimination using changes in the attitude angle of the sensor. To solve the problem in which a cumulative error occurs when the acceleration is second-order integrated in the distance measurement, the cumulative error was corrected in consideration of the periodicity of the progression and stops during the peristaltic motion; this is a unique movement method of this robot. In bending pipe discrimination, a bending pipe and a straight pipe were distinguished based on changes in the angular velocity, and the angle of the bending pipe was judged from the attitude angle of the sensor. The developed robot with an IMU was crawl on a pipe composed of multiple bending pipe and inclined pipe for pipe rise, and the pipe shape was estimated using the proposed method. In the experiments, it was possible to measure the length of the pipeline with an error of 1.42 % relative to the actual length, and it was possible to express the approximate shape of the pipeline.