Tracking And Locating Technology Of In-pipe Mobile Robot

The tracking and locating of in-pipe mobile robot is a technology to detect the position of robot by measuring outside the pipeline. This technology decides the further developments and practical applications of pipeline nondestructive tests and in-pipe operations, etc. As the normal electromagnetic methods can not be applied in pipeline engineering, because of the intense shielding effects of metallic pipe wall and buried pipeline environment. So, the wireless, reliable, fast, even the global tracking and locating technology is one of the key technologies to improve the system performance and practical application value of in-pipe mobile robot. Based on the projects"Seabed in-pipe mobile robot and inspection technology"and"Tracking and locating technology of pipeline robot based on ultra-long electromagnetic wave", this thesis studies the tracking and locating theory and system applications of in-pipe mobile robot.The thesis presents the completed design methods of the tracking and locating system of the in-pipe mobile robot, and analyzes the working process and requirements of the system. The specific structure and performance of the in-pipe emitter system and the outside sensor system are described in detail.In order to solve the shielding problem by metallic pipe wall and buried pipeline environment, which is a great bottleneck for the application of tracking and locating technology, the extreme low frequency (ELF) magnetic field is applied to realize the communication between inside and outside of pipeline. Based on the Maxwell electromagnetic theory, the analytical propagation model of the ELF magnetic field in the buried pipeline environment is presented. The thesis studies the affects of the geometric sizes and electromagnetic parameters of the pipeline environment on the propagation character of the ELF magnetic field and the optimum emitting frequency. In order to simply the analysis of the tracking and locating algorithm, the thesis presents an equivalent magnetic dipole model to approximately describe the propagation of the ELF magnetic field. The imitation error is reduced to minimum by the structural optimum design of the emitting coil. The actual propagation performance of the ELF magnetic field is tested by various experiments, and the results show that the ELF magnetic field is practicable in the tracking and locating technology of the in-pipe mobile robot.Tracking is roughly estimating the position of in-pipe mobile robot with low accuracy. There are two tracking methods are presented in the thesis, i.e. (1) single axis emitting and point measure, (2) three axes emitting and point measure. The first method can only estimate the rough position of the in-pipe robot by concluding the propagation character of ELF magnetic field in various pipeline environments. The estimation precision of position is low and this method wastes time a lot. The second method is based on the orthogonal rotations of the emitting vectors and the receiving vectors. The relative position and orientation between emitter and sensor are calculated respectively. This tracking algorithm adopts the energy of the sensor's output, which is helpful for the dynamic tracking of robot. It also solves the problem of low sensor to noise ratio (SNR) when the relative distance between emitter and sensor is too long. The two methods are verified by field tests. It is concluded that the first tracking method is suitable for the visible pipeline, the specific distribution pipeline, or unknown distribution but the moving speed of robot is low enough. With little estimation error, the second method is verified practicable for tracking of in-pipe mobile robot, and satisfies the requirements of pipeline engineering.As the propagation distance of ELF magnetic field is limited, the thesis presents a global tracking and locating concept in order to improve the practical application value of the tracking and locating technology. The static locating algorithm, which is applied when defects on pipe wall are inspected or there is something wrong with the robot, is presented based on the sensor array. The sensor array is help to improve the detection area of ELF magnetic field and the accuracy of the locating algorithm. According to the number of axis and sensor, linear and nonlinear algorithms are presented, respectively. The first algorithm is based on the matrix transformation method and the second one is based on the optimum theory. With theoretical analysis, it is shown that the second method is simple and more suitable for practical application, and requires fewer sensors. The principle of motion inductive noise of sensor is analyzed and some methods have been presented to reduce the affects. The static locating algorithms have been verified by experiments. It is concluded that the locating algorithms and the locating system satisfy the requirements of pipeline engineering.