Application of MEMS technology in the system monitoring parameters of powered roof support’s operation

The use of innovative technologies in hard coal production directs the development of the whole industry. The pace of environmental and social changes generates the need for continuous improvement of the coal mining process. Technological solutions of other industries that are used on a large scale are often implemented in extracting hard coal. One of the critical areas requiring continuous improvement in coal production is the machine park. This area is the most essential part of the entire production process. Machines and equipment require constant monitoring to ensure production continuity. A solution that covers this issue is the measuring and recording system that monitors the geometric parameters of the powered roof support. The system uses MEMS technologies to measure changes in the inclination of the powered roof support’s elements. The measuring system allows us to define the height and inclination of the powered roof support in the mining wall. The paper presents how the MEMS technology is used in sensors and the course of bench tests of the powered roof support, which were one of the stages determining the guidelines for the system’s operation in real conditions.


Introduction
MEMS technology is a miniaturised electro-mechanical device.The application of this technology results in the development of advanced machines and equipment [1].This solution allowed the construction of micro-integrated systems and devices that combine elements of electronics and mechanics.MEMS technology is interdisciplinary, combining engineering, design and manufacturing areas [2][3][4].Initially, the technology was used in automotive safety systems.Today, the field of application has expanded significantly.MEMS technology is used in mechanical engineering, chemistry, materials engineering, electrical engineering, fluid and optical engineering, medicine, communications systems and space science.The use of this technology in various types of sensors makes it possible to measure vibration, impact, inclination, displacement and rotation.These physical properties relate to the measurement of acceleration.The measurement uses the component force of gravity (g), which affects the object on the surface.Some of MEMS properties are vibration resistance, high reliability, low energy consumption, microscopic construction and low production costs [5].The paper presents an example of the use of MEMS technology to monitor the operation of a powered roof support section in the mining production process.This process is of great importance for the efficiency, continuity and safety of this process [6].Generally, the mining support is designed to 1295 (2024) 012004 IOP Publishing doi:10.1088/1755-1315/1295/1/012004 2 protect the working environment in the mine, both against the deformation of the rock mass [7][8][9] and ensure proper ventilation conditions [10][11][12][13].
The paper presents the installation sites, and the results of the tests carried out at the workstation.The study used MEMS technology sensors to measure the geometry of the powered roof support sections.The sensors formed a measuring and recording system consisting of a computer, software and four sensors.The solution made it possible to measure the inclination angles of the powered roof support's elements and its working height at a given stage.The installation of this system involved several steps related to the designation of locations, installation, determination of the advantages and disadvantages of the application and calibration of the entire system.The constantly deteriorating mining and geological conditions in which the support works, which is the result of the increasing depth of mining and the associated intensification of various threats, leads to the search for new solutions.These solutions would enable the use of automatic control systems limiting the need for employees to stay in dangerous zones.The measurement system used should therefore enable continuous access to the operating parameters of the support without the need for employees' intervention and adjustment of these parameters to external conditions.As of today, there are no such national solutions, which justifies undertaking work to test powered roof support in terms of the construction and implementation of a system that monitors its operating parameters.The paper discusses how the system works and its practical application at the research station.

MEMS technology in monitoring sensors
Measurements of the geometric parameters of the powered roof support's sections are data to be analysed to determine its correct operation in the wall [14][15][16].Monitoring the specified phase of the powered roof support's operation allows a broader look at its cooperation with the rock mass [17].The powered roof support section is one of the elements of the wall complex, which consists of an extraction machine, a powered roof support section and a wall conveyor.The powered roof support is crucial for the wall complex, as it is responsible for securing the passage of the team and the movement of the extraction machine and the wall conveyor towards the unmined coal bed [18][19][20].The sensors (Fig. 1) based on MEMS technologies made it possible to monitor the geometric parameters of the powered roof support and were used to develop a measuring system.The sensor is made of materials adapted to difficult working conditions.The enclosure is highstrength plastic, protecting the sensor and battery from mechanical damage caused by falling roof rocks.The changing colours signal the phase of operation of the powered roof support.The enclosure is secured by a stainless steel ring, which protects the sensor from dust and uncontrolled movement of the powered roof support.The mounting plate was made when manufacturing the powered roof support and welded by the guidelines.The mounting plate levels and assembles the sensor in contact with the powered roof support's elements.Correct levelling reduces measurement error [21,22].
The sensors communicate wirelessly with each other (Fig. 2).Communication between individual sensors uses a built-in wireless access point operating in the 2.4 GHz ISM band with authorised access in the IEEE 802.15.4 standard.The sensors are powered by a spark-proof battery, produced according to the sensor manufacturer's guidelines.Replacing it directly in the zone threatened by the explosion of methane and coal dust is permissible.Thanks to battery power, the operator is not exposed to interruptions in the operation of devices in case of a power failure brought to the wall systems.The sampling frequency adopted for this system is 1 sec.The measurement system uses a low-bleed filter to filter out noise and interference.The data collected by the system is saved while the machine is moving.When there is no movement of the machine, the data is not saved, this is due to the lack of change in the measured value.The device allows visual control of the powered roof support expansion state by visual signalling relative to the specified threshold values.The solution supports the operator during the section transfer and allows them to quickly and directly assess the state of the wall's expansion in the excavation.Geometry sensors are spark-proof devices of Group I, Category M1, with a level of protection ia.These characteristics allow for the use of the device in the mining plants' excavations and some surface installations where there is a likely risk of methane and/or coal dust explosion.Geometry sensors are suitable for pneumatic and hydraulic installations of machines and industrial facilities.The locations were chosen based on the finite element analysis (MES) method and the experience of the designers.The method used made it possible at the initial stage to exclude collisions of elements of the powered roof support with built-in sensors and eliminate the places of sensor installation where the sensors would be most exposed to external forces.The guidelines were used to create a research station and for the practical use of the entire system in real conditions.The recommendations included changes to the algorithms used, the sensors' installation method and their location.The location and construction method had a key influence on the calibration of the measuring and recording system.The correct orientation of the sensor was based on the mounting brackets used.Mounting brackets have been built in such a way that the orientation of the diffuser -sensor complies with the guidelines.In addition, a manual device limiting the measurement error was used for this purpose.Obtaining the smallest measurement error was possible thanks to additional elements in the form of mounting plates that level the sensors, presented in Figure 5.

Bench tests performed by the measuring and recording system.
The test station presented in Figure 6 has been developed according to the guidelines established in the computer simulation phase.Sensors based on MEMS technology were installed on the basic elements of the powered roof support section.They constitute the prototype of the measuring and recording system.The purpose of the research was to obtain data for defining the height of the powered roof support in its phases of operation and confirm the correct operation of the measuring system.The measurements done by the system were verified with manual measurements.The tests provided measurements in the minimum and maximum range of the powered roof support's operation.The course of changes is shown in Figure 7.The graph shows the changes in the height of the powered roof support due to how it is operated during bench testing.This data is used to predict the measurement error.The determination of the measurement error was verified on the basis of a comparison of manual measurements with data obtained from the measurement system.The error range for the bench tests was 3-10 cm.In addition, how the powered roof support is operated in real conditions with the installed measuring system confirmed the absence of collisions with its essential and additional structural elements.Thus, the analysis carried out based on computer simulations was approved.

Summary
Coal production is carried out at ever greater depths, which results in deteriorating mining and geological conditions.Natural hazards and the deformation impact of the rockmass are intensified.These phenomena make using new, reliable, powered roof supports necessary, which must ensure safety in these conditions.A critical stage in the development of the proposed system was the correct identification of the characteristics that it should have.Therefore, the analysis results became the basis for further work on conducting underground tests and the possible implementation of the section's work geometry monitoring system and implementation of the powered roof support equipped with the proposed solution.The bench tests were the basis for developing the measuring and recording system guidelines.Ongoing monitoring of geometric changes in the powered roof support occurring during the mining process will allow for: -excluding inadequate roof operation, -maintaining the expected geometric parameters of the mine workings, -increasing competitiveness in the mining market, -increasing security, -reducing the risk of undesirable consequences associated with the fall of roof rocks, -improving the quality of big data storage and analysis, -increasing the effectiveness of control and supervision of employees, -early detection and prevention of failures, -determining the inclination and height of the section in a given phase of work, -increasing the efficiency of the entire wall complex.

Height [mm]
The number of measurements Monitoring of support operation parameters as well as their registration and analysis should enable, in addition to the ongoing improvement of work safety, also the development of guidelines for improving its cooperation with the rock mass and more effective operation of the entire longwall system.The aim of the stand tests of the powered roof support in terms of monitoring the parameters of their operation was to define the guidelines for the construction of the powered roof support section for the assembly and operation of the system monitoring its operation.The conducted research made it possible to determine the correct operation of the measuring system and the changes that were used to obtain a measurement that would satisfy designers and mining practitioners.The measuring recording system is one of the tools used for improving autonomous wall complexes.The powered roof support control systems can use the data provided by the measuring sensors for wall visualisation in advanced automatic wall complexes.They will allow automated control of the powered roof support's progress following the recognition and expected shape of the wall excavation.The completed stand tests are the first stage to start testing the measurement system in the longwall conditions.

Figure 3 .
Figure 3. Determination of the working height of the support, where: froof working angle, hshield working angle, b -lemniscate working angle, H 1 -height determined from the trigonometric functions of the roof, H 2 -height determined from the trigonometric functions of the shield, H 3height determined from the trigonometric functions of the lemniscates.The sum of their specified heights determined the total height (H) of the powered roof support elements.The sensors' overall height (H) and mounting locations are shown in fig.No. 4.

Figure 7 .
Figure 7. Graph of changes in the height of the support during bench tests.