Underground and open-cast mines are essential for supplying the economy with resources. These include iron or copper ores and rare earths such as cobalt or lithium. Mine operators are increasingly being forced to make their existing facilities not only more environmentally friendly but also more cost-efficient through the use of new technologies such as autonomous vehicles in order to remain globally competitive. In addition to these challenges, however, they also have to meet the increasing demands on extraction volumes and extraction distances.
Belt conveyor systems, as shown in Figure 1, combine the advantages of continuous conveying with comparatively low operating costs and are therefore increasingly being used. However, with mass flows of up to 40,000 tons per hour or 20 kilometers long conveyor sections, conventional systems are reaching their technical and economic limits. In the world’s largest copper-ore mine “Chuquicamata” in northern Chile, for example, belt conveyor systems with 20,000 kW of installed drive power and the world’s strongest conveyor belt with a nominal strength of 10,000 N/mm are used. A further increase in mass flow is limited by the belt’s tensile strength and therefore requires an alternative drive concept.
Driving idlers as a possible intermediate drive
For reducing the resulting belt tension in the system, locally distributed intermediate drives such as multi-drum drives or drive belts (see Figure 2) can be used. However, due to high investment costs and technical requirements, these solutions are mainly considered when designing new systems from scratch. In order to retrofit existing systems with an intermediate drive, a space-saving solution is required that can be easily installed on site.
As part of two research projects, researchers at the ITA of Leibniz University Hannover developed idlers with an internal motor, a decentralised control system for wear-optimised operation and researched the general operating behaviour in the test rig set up specifically for this purpose (see Figure 3). The standard idlers installed in a belt conveyor system can easily be replaced by the driving idlers shown in Figure 4, which minimises the conversion and installation work required for the retrofit.
Challenges for the acceptance of driving idlers
However, the test rig cannot be used to analyse the usability of driving idlers under real conditions. Accordingly, there is currently no proof of dynamic system stability, which could reduce the entrepreneurial risk and consequently demonstrates the acceptance of this technology and the associated market potential for small and medium-sized enterprises.
As part of the research project “Future Conveyor Drive”, ITA researchers are investigating the scientific question of whether the existing physical models for describing a driving idler can be transferred to a simulation environment in order to demonstrate the dynamic behaviour of a group of several ATs on the global system behaviour of belt conveyor systems. If this is successful, the knowledge gained will be summarised in design recommendations to provide system and component suppliers with guidance for new planning and retrofitting of existing systems.
Reaching the goal with use of a co-simulation
The solution envisages the development of a co-simulation with which an “intermediate drive unit” consisting of several driving idlers can be simulated. As can be seen in Figure 5, this consists of the two simulation environments SimulationX and Matlab/Simulink. The dynamic processes of a belt conveyor system with regard to the conveyor belt and the conventional drive technology are mapped by SimulationX and extended to include the mechanical-electrical behaviour of several ATs. The decentralised control system developed in previous research projects for wear-optimised operation of several ATs is finally implemented by use of Matlab/Simulink.
Afterwards the co-simulation is analysed in the controlled test environment. After successful validation, it should be possible to scale the simulation module as required and using it for simulating real belt conveyor systems. This should enable the conveyor-specific, optimised positioning and dimensioning of the intermediate drive concept of the driving idler rollers.
Initial results confirm preliminary work and illustrate potentials
With previous findings from the co-simulation, the test rig could already be simulated as a model and various stationary operating points under varying belt speeds, nominal loads and number of active ATs could be simulated in order to analyse the influence on the resulting torque on the system’s head. To compare the results, validations were carried out on the test rig under the same parameters. It was shown that the experimentally determined system behaviour can be represented well with the simulation and thus confirms the preliminary work on the power transmission of driving idlers. For greater accuracy, the model will be extended in future with additional modules in order to better represent the influence of specific movement resistances such as the indentation rolling resistance.
Initial simulation results of the use of five driving idlers in an example system have already shown reductions in local belt tensile forces of around 28 %. This makes it possible to use conveyor belts of lower strength classes while maintaining the same mass flow, resulting in considerable advantages. On the one hand, this results in cost savings and, on the other hand, the conveying lengths can be significantly increased. Alternatively, it is conceivable to increase the mass flow without making any design changes to the system. In both cases, the simulation illustrates the monetary and ecological potential of driving idlers as intermediate drives for use in belt conveyor systems.