Abstract
The measurement of longwall retreat and creep displacements is of great significance for the safety production of a coal mine. In order to reliably and accurately obtain the longwall retreat and creep displacements, this paper proposes an ultrawideband (UWB) radar imaging method. The bolt plates fixed in the roadway coal wall are imaged as the target points. First, a signal model is built, and a modified nonlinear chirp scaling (NLCS) imaging algorithm is designed to obtain the high-resolution image. Then, the retreat and creep displacements are estimated based on the imaging results. Finally, simulation and experiment are performed. The simulation results show that the radar imaging method is theoretically feasible to measure the retreat and creep displacements. The measurement errors in the experiment are 0.058 m and 0.040 m, respectively. In the experiment, the radar velocity fluctuation and signal attenuation cause the target azimuth and range errors in the imaging results, which makes the measurement errors in the experiment larger than that in the simulation. This method requires no additional roadway information except for the bolt plates fixed in the coal wall. In addition, the signal propagation of UWB radar is rarely affected by the dust and moisture in the harsh environment.
Highlights
At the end of the roadway, a shearer, an armored face conveyor (AFC), and a roof support system are installed across the back of the panel, creating the longwall face. e shearer moves back and forth along a rail associated with the AFC to cut the coal seam, while the roof support system supports the coal seam roof
The AFC is pushed along the retreat direction by the larger hydraulic push arms attached to the roof support system for the cutting cycle [3, 4]
The interaction between the coal seam and equipment in variation pressures leads to the sideway slippage of equipment across the longwall face, called the longwall creep. is prevents the retreat of longwall face. e longwall creep displacement refers to the difference of AFC position along the moving direction between the adjacent cutting cycles shown in Figure 2. erefore, it is necessary to monitor the longwall retreat and creep displacements
Summary
At the end of the roadway, a shearer, an armored face conveyor (AFC), and a roof support system are installed across the back of the panel, creating the longwall face. The AFC is pushed along the retreat direction by the larger hydraulic push arms attached to the roof support system for the cutting cycle [3, 4]. A cutting cycle refers to the process in which the shearer moves the whole length of the longwall face.
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