Aiming at the three-dimensional positioning of pipeline robots, the sensor array methods are usually complicated in structure, large in size and difficult to realize miniaturization. In this paper, a rotating permanent magnet antenna is used as the transmitter of low-frequency magnetic signals through the pipelines, and a positioning method based on single fluxgate sensor to measure magnetic fields at multiple positions is proposed. Additionally, because of the weak magnetic field of the rotating magnet through the pipeline, the measured signal is extremely easy to be influenced by the background noise and ferromagnetic interference in the environment. In this situation, a staggered superposition method is adopted to process the signal for the positioning of pipeline robots. The signals measured by sensors at multiple positions are collected, filtered, and superimposed to the filtered signals at last moment to ensure the magnetic source signal to be extracted exactly. The experimental results show that the average absolute error of tri-axial coordinates is 0.038 m, which indicate the proposed three-dimensional positioning method can meet the requirement of pipeline robot in short-range and has the advantages of simple structure, small size, and low cost.
Pipeline robot is widely used in submarine oil pipeline inspection and maintenance engineering. When the pipeline robot detects a defect in the pipe wall or the robot's own system failure. The person outside the pipe needs to know the exact position of the robot inside the pipe. Therefore, it is important to determine the position of robot in the pipeline. However, for most subsea pipelines, the exact location and direction is often unknown. This includes horizontal pipes, vertical pipe, slope pipe and bend pipe. So it is necessary to obtain the three-dimensional position of the pipeline robot.
Because the tube wall of certain thickness has strong shielding effect on signals, soil and sea water also have strong attenuation effect on signals. At present, the extremely low-frequency (ELF, 3-30Hz) electromagnetic waves are usually used in the positioning technology of submarine pipeline robots. Based on the spatial multi-point electromagnetic signal detection method of a sensor array, the technology can be used to realized the positioning technology of mobile robots in pipes (Qi, et al. 2008). (Wei, et al. 2012) proposed the pipeline robot adaptive positioning system using a six sensors’ symmetrical structure.
