Optimal geometry of the powered roof support’s operation

Monitoring the working parameters of powered roof support is an area for improvement in hard coal mining. The phenomena occurring during the operation generate many risks from difficult geological and mining conditions, leading to undesirable events. In addition, improper use of machinery and equipment results in a high accident rate in mining. Thus, monitoring the operation of machines in mining reduces accidents and losses resulting from stops and prevents unforeseen failures caused by operational and external factors. The paper presents the research results on the optimal geometry of the powered roof support operation in the mining wall. The research included the powered roof support’s essential elements’ operation. Sensors constituting the measuring system were installed on these elements. The measurements made by the sensors made it possible to determine the working height at a given stage of the section’s operation. The research was carried out in three sections, which were part of the powered roof support. The measurements were taken during actual changes occurring in the coal mining process.


Introduction
The powered roof support is part of the mechanised wall complex, the task of which is directly processing the rock mass and transporting the mining product from the forehead zone [1,2].The powered roof support's function is to secure the working space and support the work of the entire mechanised complex [3], as well as close cooperation with the dog heading, which secures the sidewalls [4,5].Thus, the role and importance of powered roof support significantly impact the safety and efficiency of the entire mining production process [6,7].That is why it is so important from the perspective of mining development to constantly improve the design and operation of the entire roof support, that is, both powered and gallery-type roof supports.For powered roof support, which is built of independent sections, it is imperative to control [8,9] the operating parameters of these sections and, therefore, the entire roof support.The powered roof support protects the working space from the rock mass and must provide adequate space to operate other machines and ensure ventilation safety [10,11].This is especially important from the point of view of caving excavations, which, as a porous medium, also affect the powered roof support and the ventilation system [12,13].The risks in the mining production process, especially natural ones, place very high demands on the entire powered roof support.They mainly result from the deformation effect of the rock mass on the powered roof support.That is why extensive powered roof support research is carried out.
Due to its functions, the correct operation of the powered roof support is fundamental to ensure the continuity and safety of the entire mining production process [14][15][16].Currently, powered roof supports used in Poland are widely varied regarding their mechanical parameters, structures and systems controlling working parameters [17][18][19].This means that for virtually every wall, different sets and systems are used that make it difficult or even impossible to effectively and efficiently supervise the powered roof support's operation, thus limiting the possibilities for improving the powered roof support's work.Also, deteriorating working conditions, resulting from the increasing depth of operation and the associated increase in various hazards, make it increasingly necessary to work on reducing workers' participation in powered roof supports operation.One such direction of research and development of powered roof support is automatic control systems [20,21].Such a solution should affect the continuity and flexibility of the powered roof support, and limit workers' participation in the exploitation.However, the development of such a system requires a lot of knowledge, work and a lot of research [22,23].
This paper addresses this important and current topic.It presents the results of studies on powered roof support sections at the workstation under real exploitation conditions.The study covered three sections of the powered roof support during their work in 4 days.The purpose of these studies was to analyse the geometry of the section during its operation and, in particular, to determine its height during the coal mining cycle.The research and its results are part of the extensive work on the development of a control system for sections of powered roof support in the field of analysis of their geometry.

The method of measuring the work of the longwall support.
The tests were carried out based on a measuring and recording system, which made it possible to measure the geometric parameters of the powered roof support section.The slope parameters of the individual structural elements of the tested sections and their height during operation were defined.The results obtained by the sensors system developed and installed on the sections constituted the basis of the analysis.These sensors were installed on the essential elements of the powered roof support, i.e. foot piece, cap piece, shield and lemniscate, communicating with each other wirelessly.The method of their construction was determined based on bench and model testing.The sensors were installed on innovative mounting brackets designed for this purpose, which were mounted on the tested elements of the section.The sensor consisted of a base, which was also its handle, a globe and a battery.A measuring device using MEMS technologies was installed under the globe.The battery provided power for the sensor.The communication diagram of the individual elements of the measuring system is shown in Figure 1. 3 The sensors communicated wirelessly by sending data to a converter that changed the signal from wireless to wired.The signal was sent to the underground computer located in the longwall.In the underground test stand, there was the possibility of archiving and processing data and visualizing the operation of the powered roof support, taking into account geometric parameters and pressure in the props.The signal was subsequently transmitted via the underground infrastructure to the server room on the surface, where the data was also analysed based on data processing and visualisation systems.
The layout included the measurement of three sections of the powered roof support.The sections were equipped with 12 measuring sensors.Each of the sensors measured the transverse and longitudinal angles of the main elements of the powered roof support.We determined the working height of the section's operation in the wall excavation based on the angles.The height was determined based on the sum of the working heights of the three powered roof support areas, shown in Figure 2. The accepted method of determining the height of sections during work is a new authorial method used in research.The method of measuring the height of the section during operation is shown schematically in Figure 2.
. To determine the height (H1,2,3), trigonometric functions were used, where the total height (H) was determined based on the working conditions of the powered roof support's elements and the geometric parameters of the sections).The measurement was burdened with a relatively low error, thanks to installing four sensors on the floor base, conopy, shield and lemniscate.The prototype of the measuring system and the adopted calculation method allowed for objective monitoring of the operating cycle of the powered roof support in underground conditions.

Tests in real longwall exploitation conditions with the use of a measuring and recording system.
The research station was located in a wall excavation, where several sensors were built on three sections, constituting the measuring and recording system.The location of the sensors is shown in Figure 3.The arrangement of the sensors was developed based on bench tests, tests using the finite element method (MES) and the experience of constructors and mining engineers.The mining wall where the research was carried out was on deck 510, with a mass ranging from 8.8 m to 10.8 m.The layers in this area collapsed at an angle of approx.6° southwest.The mining and geological conditions of the wall excavation, in which sections were built, are presented in Table 1.
Tab.1.Longwall parameters.The presented waveforms show the height of the work of powered roof support in the wall excavation.The sections were located side by side.Based on the data obtained, it is possible to determine the stage of work of each section under study and to pre-diagnose the reason for the changes in the height of its operation.The changes in the powered roof support's working height result from how it is controlled during its working cycle and from difficult geological and mining conditions.A lower height of the powered roof support's operation on the 3rd day of the analysis (sample 18001-18022) could result from incorrect operation while moving towards the unmined coal.This graph shows a low height, which difficult geological and mining conditions, technological procedures or incorrect use of the powered roof support may cause.

Summary
Maintaining the correct geometry of the powered roof support section by monitoring its position during operation improves the safety of the underground operation process.Monitoring the geometric parameters of the individual structural elements of the section and the physical parameters of its work gives a wide range of possibilities to control and respond to disturbances in its operation.The measuring system allows quick identification of any type of deviation in the setting of each section of the powered roof support.The result of these actions is to ensure the optimal and safe operation of each section.Firstly, obtaining quick information about emerging irregularities in the setting of the section will limit further deterioration of its cooperation with the rock mass and other machines of the complex.The measuring system's essence is monitoring geometric changes, but it can cooperate with the commonly used pressure monitoring system in hydraulic props.This allows you to comprehensively monitor the parameters of the section's operation comprehensively and thus identify and quickly respond to dangerous conditions.The correct geometry of the powered roof support significantly reduces geotechnical hazards in underground coal mining.The obtained information about the

Hc_34
Hc_35 Hc_36 geometry of the powered roof support section allows us to evaluate its operation and determine the relationship between its state and the phenomena occurring in the rock mass.Using this system provides opportunities to control cooperation with rock mass, which should result in rapid remedial action in case of such dangerous symptoms.This, in turn, gives a high chance of eliminating many events, such as rock falls or roof collapses, resulting from incorrect cooperation of the powered roof support with the rockmass.

Figure 1 .
Figure 1.Diagram of communication of the system for monitoring the geometrical parameters of the longwall support, where: 1 -wireless communication of sensors installed on section elements in the longwall excavation, 2 -underground position in the longwall excavation, 3 -control room on the surface of the mining.

Figure 2 .
Figure 2.The method of determining the total height of the powered roof suport.
analysis made it possible to determine the changes in the height of the powered roof support for 4 days.The research was carried out during fundamental changes in the coal mining cycle.Figure41295 (2024) 012005 IOP Publishing doi:10.1088/1755-1315/1295/1/0120055shows the recorded changes in the height of the powered roof support sections for the three sections in the wall excavation.

Figure 4 .
Figure 4. Courses of changes in the height of the support section no.34-36 during tests in real conditions.