Underground mines are among the world’s most hazardous working environments. The International Labour Organization states that, while miners make up about 1% of the global workforce, they suffer about 8% of all work-related fatal accidents. Not only that, but injuries and health conditions derived from toxic atmospheres, deafening noises and violent vibrations are endemic to the occupation.
Automation in this industry depends heavily on variable speed drives and aims to replace man with machine literally at the coal face. Indeed some of those who now run the most advanced operations, such as the Rio Tinto iron-ore mines in Western Australia, do so from control centers hundreds of miles away from the action.
But to get to the point where coal, metals and other minerals are efficiently extracted and processed entirely by unmanned machines, a number of challenges must be overcome. Mining processes must be automated in atmospheres heavy with dust, high in precipitation, subject to extremes of temperature and with naturally weak network connectivity.
Beyond the harsh operating conditions, and accepting the reality that progress happens step by step, new designs for mines must confront and resolve problems such as disparate automation technologies and less than accommodating legacy systems. By and large, the fully digital mine – an intelligently interconnected system extending from pit to port – is still the subject of aspiration, experiment and trial.
For most companies, the story begins with the introduction of pieces of autonomous and semi-autonomous machinery: loaders; haul trucks and haul trains; rock breakers and crushers; drilling and boring machines; and, in coal mining, longwall shearers, powered roof supports and conveyors.
It is a guiding principle of automation design that such an evolving arsenal of equipment should use power as efficiently as possible. What is saved in human labour should not be lost in energy expenses. In this respect variable speed drives are an indispensable aspect of the automated mine, and find application across the full range of operations.
Time and again in this environment, it is the challenging nature of the terrain that sees machinery benefit from AC drives. A surface excavator has to work its way through a layer of rock or soil of mixed composition. Some surfaces to be drilled underground are more resistant than others. Conveyor belts transport loads of varying weight. Slurry pumps suffer fluctuations in pressure caused by blockages or other natural surges and drops.
In all of these situations the variable speed drive is the precondition of accurate and responsive motor control. A robotic loader delivers a heap of coal onto a loading conveyor. Information about the load’s weight is directly acted upon by the drives which accordingly adjust the speed of the drums controlling the conveyor’s movement. Strain on the system is thus minimised, as are the chances of downtime caused by snapping belts.
It is analogous to the Best Efficiency Point automatically found by pumps and fans running on the same technology. Here the concepts of energy-efficiency and preventative maintenance amount almost to the same thing. The less energy wasted through heat, friction and stress, the less wear and tear on the equipment. In this way, soft starts, smooth acceleration and upper current and torque limits programmed into the drives’ firmware all contribute simultaneously to lower energy bills and longer machine lives.
There are, moreover, a number of specifically mining-related opportunities for the regenerative feedback of braking energy into the electrical network. These include the action of downhill conveyors, the operations of hoists and winders, and a dragline excavator’s repeated bucket lowering.
The case has been made, in the mine’s hostile environment, for dispensing with as many small and perishable mechanical parts as possible. The numerous fiddly control mechanisms used in older motor systems (their valves, dampers, fan inlet vanes, couplings, and so on) are no loss to a more streamlined operation with fewer people on site – and on standby – with replacements at the ready.
Gearless drives are symptomatic of this movement away from vulnerability in design. Where the speed at which machines operate can be synchronous with that of motor rotation, gear systems can be eliminated altogether, as they have been for certain heavy-duty conveyors and for the autogenous and semi-autogenous grinding mills that break up rocks by tumbling them around in drums.
To date, remote control and monitoring of automated machinery has been limited by the use of optical fibres or whatever Wi-Fi coverage can be made to work through the careful placement and angling of access points.
Progress in this area has been pioneered by communications innovator Ericsson, who have successfully installed a 5G wireless network in the goldmine at Kankberg run by Swedish mining company Boliden. So effective is the connectivity delivered by this network, even functioning 500 metres underground and where access points are obscured or otherwise out of the line of sight, that everything – excavation, haulage, ventilation – has now been completely automated.
Perhaps the most telling aspect of the Kankberg mine’s success is its multiplayer character. It took the arrival of a specialist in a field not traditionally associated with mining, telecommunications, to redefine that industry’s future potential. And as fruitful as the marriage was, it might not have happened without the brokerage of research and development agency Vinnova.
Automation, it seems, is as much about the collaboration of companies as it is purely the design and programming of machines. People need to come together before systems do. By all accounts, the next generation of automated mines is set to be the result of joint ventures between mining companies and the myriad industries that comprise and support the larger field of automation engineering.