## 5 Autonomous Navigation Technology
### Positioning Technology
[79] pointed out that estimating the target's moving direction and structure through the maximum likelihood estimation method was found to be quite accurate. [PERSON] et al. [75] proposed a calculation method of minimizing the error of photometrics based on its weight of different texture areas, to improve the matching accuracy for images with dim and noisy points obtained from a dust-filled underground roadway. In general, the visual positioning technology is accurate in location, but as the scraper works in unique underground scenes, it still faces challenging problems, such as environmental features being insufficient, roadways being too dusty and lighting conditions varying too much, etc. Hence, how to make the system operate stably and long term will be a key problem to be solved in the future. 1. Information Fusion and Location Technology  
Single-positioning technology usually has certain limitations. Therefore, various information from different positioning technologies can be integrated to locate the scraper and improve the positioning accuracy. [PERSON] et al. [80] applied a positioning method combining dead reckoning and laser scanning positioning and determined the position and driving direction of the scraper by the articulation angle sensor, odometer and gyroscope. The result from dead reckoning was corrected by the scanning data of the roadway wall obtained through two laser scanners. The accumulated error was significantly improved compared to the ordinary dead reckoning method and the installation of other auxiliary equipment was avoided in the roadway. [PERSON] et al. [81] optimized the location and navigation algorithm based on the combination of the dead reckoning positioning and laser scanning. The simulation results showed that this method can improve the accuracy and robustness of the operating system. [PERSON] et al. [82] and [PERSON] et al. [83] combined the information obtained from both the heading gyroscope and the laser rangefinderby Kalman filtering algorithm based on a multi-sensor information fusion model and the heading angle of the scraper was accordingly determined. [PERSON] et al. [67] proposed a positioning system, which combined the UWB and laser ranging methods in the view of the long and narrow characteristics of underground tunnels and the high cost for UWB positioning systems. [PERSON] et al. [84] integrated the inertial measurement unit (IMU) and dynamic time warping (DTW) algorithms to locate the underground mine LHD and it was found to have good robust performance. The characteristics of various positioning technologies are listed for better comparison in Table 2. To sum up from Table 2 and the above-reviewed text, each single-positioning method has its own advantages and disadvantages. Even though the limitations of a single-positioning technology can be overcome and the positioning accuracy can also be improved to a certain extent when various technologies are jointly applicated in different ways, the technology still faces the problems of high cost for the equipment and complexity for the calculation. Hence, how to improve the adaptability of the positioning technologies and cut costs are the key scientific issues to be considered in future research at home and abroad.