Positioning technology for stepwise underground robots
Pipeline robots, borehole robots or exploring robots that work in underground environments can be classified as underground robots. When an underground robot takes a task, tracing and mapping the track of the robot is very important. This project addresses the development of a positioning technique for stepwise underground robots, which have been developed in Durham University. This research is expected to provide a general benefit to stepwise robotic positioning systems rather than a particular robotic or other situation. The initial period of this project was the most difficult. After a few months of literature searching, no suitable positioning technique had been found. Existing techniques are suitable for surface robots, undersea robots or airborne robots but are far away from the application requirements for underground robots. Positioning technology depends on sensor techniques and measurement technologies. The underground environment restricts the use of absolute measurement technologies. Consequently, underground robotic positioning systems heavily rely on relative measurements, which can cause unbounded accumulation of the positioning errors. Moreover, underground environments restrict the use of many high precision sensors because of restricted space and other factors. Hence, the feasibility of developing high, long-term, accuracy underground robotic positioning systems was problematic. Since it was found that there was a lack of research on underground robotic positioning, fundamental investigation became necessary. The fundamentals include the dominant error and the characters of the accumulation of positioning errors. After the investigation of the fundamentals the difficulty and feasibility of developing a high long-term accuracy positioning system was understood more clearly and the key factors to improve the accuracy of a positioning system were known. Based on these, a novel parallel linkage mechanism based approach was proposed. This approach has flexibility in terms of geometrical structure and provides the possibility to improve long-term accuracy of a positioning system. Although parallel linkage mechanisms have drawn a great deal of attention from researchers in passed years, this is the first time a parallel linkage mechanism has been applied to a robotic positioning system. Consequently, new problems were generated by this application of parallel linkage mechanisms. In this project, a Principal Component Analysis (PCA) method is applied to solve the positioning problems and a particular case has been used to show how to solve these problems. Through this case, the advantages of this approach and the feasibility to improve the positioning accuracy is presented. The methodology that can be used to solve the problems for different particular cases can also be used to carry out study for general situations, which have also been illustrated. Many problems still need to be solved. At the end of this thesis, some further problems are discussed. The author of this thesis believes that the proposed approach can be applied to industrial projects in the near future.