Study on positioning strategy and technology at end of shearer based on ultra-wideband system

Accurate positioning of the shearer is the key to realize unmanned mining, but the localization accuracy of the shearer is low at present, which cannot satisfy the requirements of high precision positioning. Therefore, we propose that a guide rail should be respectively set up at the end of the fully mechanized mining face so that the Ultra-Wideband (UWB) base station group can move along the guide rail as a whole. When the shearer runs to the end of the fully mechanized mining face, the position coordinates of the shearer are obtained by using the UWB positioning system. After completing the current cutting, the UWB base station group migrate along the feed direction to prepare for the next positioning, achieving the positioning strategy of“one navigation one migration”, which can provide the reference for the calibration of the inertial navigation. Taking into account of the large measurement noise in the underground environment, we propose that the TOA shrinkage estimation method with the minimum mean square error criterion (MMSEC), and the observation equation is constructed based on the distance between the location terminal and the base station group, and then the extended Kalman filter (EKF) model is established to further eliminate the influence of distance residuals on the positioning accuracy and improve the position estimation accuracy of the UWB positioning system. On the basis of base station group migration device and positioning terminal mobile platform, the motion of shearer is simulated to investigate the base station group migration strategy and location algorithm of base station group migration. Experimental results showed that, MMSEC shrinkage estimation method can improve the positioning accuracy of motion trajectory, and the positioning accuracies of the third and four navigation were significantly enhanced, and the average localization errors decreased respectively from 0.341 m, 0.394 m to 0.296, 0.339 m, whose corresponding positioning accuracies were improved by 13.1% and 13.9%, respectively. After the EKF smoothing was implemented, the average positioning accuracies of the third and four navigation were further improved by 13.5% and 10.6%,respectively. As the number of base station migration increased, the average positioning error increased gradually; the average positioning error with respect to both the x and z axes increased gradually, while the average error on the y axis was basically within 0.2 m.Additionally, the positioning accuracy utilizing MMSEC-EKF approach from the first to the third navigation was less than was less than 0.2 m,which indicated that after implementing three cycles cutting, the coordinates of base stations should be re-measured, higher positioning accuracy can be obtained. The proposed positioning strategy and algorithm of “one navigation one migration” at the end of the fully mechanized mining face can provide theoretical reference for underground positioning technology, however, this strategy require to be further certified using the actual experimental verification in the underground coal mine environment.