Abstract
The article describes issues related to the development of a sensor measuring the distance from the end of the shield support canopy to the face of the longwall panel. The sensor's task is to detect rock falls because in such a case, empty spaces in the coal seam below the roof are generated. The sensor is a part of the system which task is to predict unfavourable behaviour of the longwall roof affecting the continuity of mining. Due to an untypical workplace and difficult conditions prevailing there, it was not possible to use a typical sensor. The ultrasonic technique was used for this purpose. The next research stages related to the development of the sensor were described. Tests of various types of ultrasonic transducers, working at different parameters, were described. Only transducers with a closed structure were considered because they can operate in the presence of high dustiness and humidity. The sensor casing was adapted to a specific type of shield support. The installation location should not be accidental, as an additional hinged shield is mounted at the end of the canopy, which is an obstacle in the measuring track and can even completely cover it, making measurements impossible. The sensor is mounted close to the side edge of the shield support canopy using small free space, enabling a measurement. Structural elements of the canopy are obstacles in the measuring track and are a source of interference of the received signals. The ultrasonic transducers are built-in tubes, which direct the ultrasonic wave and amplify the received signals. The results of laboratory tests of the model of the path measurement sensor are presented. They describe the impact of analysed aspects, i.e. the type of transducers used, the structure of the surface that the wave is reflected from and the mechanical solutions on the quality of received signals. A prototype of a sensor installed on shield support is presented.
Highlights
In longwall mining systems, proper roof support, provided by powered roof support sections, determines the continuity and effectiveness of mining operations
In a publication (Rajwa et al, 2020), it has been proven that a proper geometry of the longwall support during mining operations, when the pressure induced by the roof is distributed over the entire canopy area, significantly reduces the cracking zone in the roof rock of the longwall
A smooth surface was used from which ultrasonic waves were reflected; this surface was set at an angle close to a right angle in relation to the measuring track
Summary
Proper roof support, provided by powered roof support sections, determines the continuity and effectiveness of mining operations. Uncontrolled rockfall occurs in the uncovered area between the end of the canopy of the powered roof support and the face of the longwall, causing backfilling of the conveyor, which causing interruptions in mining and putting the workers in the area at risk (Langosch and Volker, 2003; Chen et al, 2017; Andras et al, 2017; Rajwa et al 2020). In a publication (Rajwa et al, 2020), it has been proven that a proper geometry of the longwall support during mining operations, when the pressure induced by the roof is distributed over the entire canopy area, significantly reduces the cracking zone in the roof rock of the longwall. Monitoring the performance of powered roof support opens up new possibilities in terms of prediction and early warning of potential roof collapse hazards so that negative phenomena can be addressed and prevented earlier (Cheng et al, 2020; Rajwa et al, 2019). For the prediction of negative phenomena occurring in the roof, the information on the geometry of individual parts of the support through measurements with inclinometers is important (Witek and Prusek, 2016; Kalentev et al, 2017)
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