A MEMS IMU-Based Air-Propelled Positioning Ball for Small-Diameter Underground Pipeline Localization

Accurate locating of small-diameter underground pipelines (typically 20-65 mm) is crucial for avoiding or minimizing the damage during urban construction and improving maintenance efficiency. However, conventional pipeline inspection gauges (PIGs) equipped with high-grade inertial measurement units (IMUs), which are primarily designed for normal size pipeline, cannot access small-diameter or tightly curved pipelines due to their large overall size, due to the large-sized high-precision IMUs they rely on. This limitation leaves a critical gap in accurately locating such pipelines, as no effective method currently exists for their precise positioning. To address this challenge, we propose a novel method using an air-propelled inertial positioning ball (IPB) integrated with a chip-level micro-electro-mechanical system (MEMS) IMU, so as to make the device compact and lightweight enough to traverse the small-diameter pipelines. But it comes with a serious problem that the MEMS IMU chip has large sensor errors leading to fast position drift and therefore can only keep positioning accuracy for several seconds. Unlike the conventional PIGs, which are typically pulled through pipelines by steel cables at a low speed (around 1 m/s), the lightweight IPB is designed to be propelled by airflow, allowing it to fly rapidly (around 10 m/s) through the pipeline. This significantly reduces the integration time of the MEMS IMU, thereby mitigating its cumulative errors effectively. Field tests conducted in a 48-meter-long small-diameter pipe demonstrate the effectiveness of the IPB, with single-run positioning errors of 0.77 meters in the transverse direction and 1.13 meters in the height direction. By averaging the results from 4 independent runs, the maximum positioning errors were reduced to 0.36 meters (0.75% of pipe length) in the transverse direction and 0.36 meters (0.75% of pipe length) in the height direction. The proposed new approach provides a practical, efficient, and accurate solution for locating small-diameter and tightly curved underground pipelines, addressing a critical gap in underground pipeline surveying.