Author: Vjekoslav Herceg, mag. ing. min.
The world mining has been developing rapidly in recent years, following the global trend of economic development. Demand for certain minerals is growing rapidly and natural, technological, law and social conditions can greatly limit capacity. Therefore, one of the biggest challenges of modern mining is to keep up with the times. To achieve this, with quality staff and social support, modern technology is certainly one of the key success factors. Current technological progress in the world is aimed at minimizing the use of fossil fuels with the aim of reducing CO2 emissions into the atmosphere. In the mining industry, the technology is largely related to mobile machines powered dominantly by internal combustion engines. Therefore, the development of technology is based on the highest possible productivity, which directly affects the reduction of energy consumption and CO2 emissions. In the processes of obtaining mineral raw materials, various machines are used, the effect of which is investigated separately.
The productivity of a hydraulic excavator (Figure 1), as one of the most commonly used machines in mining, is the main subject in this research. The operation of this machine is relatively complex and requires the simultaneous measurement of a number of parameters to test its productivity. Some of the productivity parameters can be measured directly, some are obtained indirectly through the measurement of other parameters, depending on the measurement system. The parameters measured during a detailed researches of excavator productivity are not only the time and mass or volume of excavated material but it is also necessary to know the forces that occur during excavation (Kim et al., 2013; Lee et al. 2008). To calculate the digging forces, it is necessary to measure the pressures of the hydraulic oil in the cylinders and to calculate the digging trajectory of the work tool. The movement of the working tool during the standard cycle of the excavator takes place in all three dimensions, so to calculate the trajectory it is necessary to measure the displacement of the cylinder and the angle of rotation of the excavator. For this purpose, a specific measuring system for measuring the displacements and pressures of the hydraulic system was constructed (Figure 2).
Figure 2. Measurement system connected on excavator (Klanfar et al. 2018)
The measuring system consists of a central control unit and seven sensors that are connected to it. Pressure sensors, ranging from 0 to 400 bar, measure the hydraulic oil pressure in the cylinders of the working mechanism. Cylinder displacement or extraction is measured by "Draw-wire" sensors or linear displacement sensors. The angle of rotation of the excavator around the vertical axis is measured by a gyroscopic sensor. The system automatically records and stores all measured data on the integrated card, and it is also possible to connect it wirelessly to a laptop, in real-time, to monitor the movement of measured values on graphs. The system was laboratory tested and calibrated. Trial field measurements were done and the connection procedure was improved.
With this measuring system, it is possible to continuously monitor all the above parameters. Digging energy is obtained based on simultaneous measurements of the trajectory and forces that occur. By considering the minimum spent energy of digging at a certain trajectory (Figure 3), the optimal parameters of excavator operation can be reached (Kang et al., 2014), which leads to savings in fuel consumption (Du et. Al., 2016). By comparing the optimal parameters in different types of rocks and granulation of the material, it is possible to see the possible correlations of individual properties of the material with certain parameters of the excavator. Also, with the help of these data, it is possible to check the accuracy of existing formulations for determining the effect of excavators (Chen et al., 2013; Lee et al. 2008), as well as the formation of new ones.
Figure 3. Digging trajectory (Kim et al. 2013).
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Klanfar, M., Herceg, V., Kuhinek, D. and Sekulić, K. (2018): Construction and testing of the measurement system for excavator productivity. Rudarsko-geološko-naftni zbornik. 34, 51-58.
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Vjekoslav Herceg, mag. ing. min. is an assistant at the Department of Mining and Geotechnics at the Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb. He enrolled in the doctoral study of Applied Geosciences, Mining and Petroleum Engineering in 2016 and is currently conducting a PhD research on the subject: Excavator Productivity in Mining of mineral raw materials.
Google Scholar https://scholar.google.hr/citations?user=uQIVWFwAAAAJ&hl=hr