CAN in Automation (CIA): Shearer loader mining vehicle

CAN Newsletter December 2006

Source: CAN. CAN in Automation (CIA): Shearer loader mining vehicle [Electronic resource] / CAN. — Access mode to article: http://www.can-cia.org/index.php?id=246&L=2

The shearer loaders by Eickhoff Bergbautechnik use modular CompactPCI hardware and the Codesys SoftPLC together with CANopen and Profibus in a single-system solution. The bundle can also be purchased as a pre-configured, application-ready platform for any control application. In addition to the timesaving hardware/software integration, customers benefit from the ability to customize the system with in-house CPU cards and I/O assemblies.

Shearer loaders have established a worldwide reputation in mining coal seams. Depending on their design, they cut coal from the longwall face laterally up to 1,1 m and at a height of up to 6 m in one pass. Depending on the worked thickness, the cutting shearers have a diameter of 1,4 m to 3,2 m and adjustable height. The loosened coal falls onto the chain conveyor below the shearer and is transported away for further processing; hydraulically controlled safety shields secure the structure of the longwall during mining. In general, only one worker is needed to control the heavy machines, which weigh up to 130 metric tons.

In 1950, the Eickhoff company built the first, hydraulically-operated, longwall shearer loader. Since then, the system structure of shearer loaders has developed enormously, and the integrated control intelligence has increased steadily. In 1976, the first longwall shearer loader was equipped with electrical winches and cutting engines on the supporting arms. Eickhoff built the first remote controlled shearer loaders in 1978, and the first high-voltage shearer loader in 1984. In 1990, the first remote micro-processors were brought on board and in 1992 the first sensor-controlled shearer loaders were tested with three-phase current winches to increase performance even further. Since 1997, winch revolutions have been controlled by frequency converters and, in 2001, the Eickhoff SL 500 achieved a cutting capacity of 2 ? 825 kW, which is equivelant to the performance of around 16 mid-sized automobiles. With their increasing complexity and performance, the control requirements for these shearer loaders have also increased. Automatic operation, data transfer to control panels, and remote intelligence for adjusting the shearer loader to suit the geological conditions of the seam are vital features of today’s system technology. For example, different cutting processes, which are used according to the geological conditions and mining planning to optimize production, must be controlled. The cutting drives and feed force must also be aligned automatically in order to avoid overloads and keep the system in balance. For all of these functions, which offer the same kind of ease of operation as the latest automobile electronics, there must be a controller. Until now, this has been based on a Motorola 68000 processor. However, this technology is reaching its performance limits, so developers were looking for a new control platform that would ideally last for many years. Because the vision for developing shearer loader technology is tending towards centralized control panel operation in order to optimize mining efficiency further, it was decided to use a system technology based on the x86 and thus in principle open in every direction. Other system requirements were based on

recognized, official standards;
high design flexibility;
high system availability;
extremely high shock and vibration resistance;
protective lacquer coating;
dedicated approval for a temperature range from 0 °C to 70 °C;
CANopen and Profibus interfaces;
VxWorks support for both the latest and older versions;
Codesys libraries ideally already available and long-term availability.

The requirements to meet official standards and to offer high design flexibility quickly eliminated a large number of robust industrial PCs from the selection process. This is because in this segment the only established standards are those from PICMG: PICMG 1.x and PICMG 2.x. Since PICMG 2.x (CompactPCI) is fundamentally more robustly designed, the choice between them was also made relatively quickly.

It was found that in principle the 3U the form factor best met the requirements of the application, based on the compactness of the machine and the consequent need to save space. However, a few critical points still needed to be tested to make a standard IPC in accordance with PICMG 2.x into a mining-capable system.

The circuit boards had to have a protective coating to meet the high protection requirements in an environment containing conductive and explosive coal dust. Testing to ensure that the system satisfied the high requirements for mechanical stability in mining had to take place at the same time.

In the DIN EN 60068-2-27 test, continuous shocks are applied to the system for twice as long as usual (30 g over 18 ms instead of 9 ms); for vibrations, the DIN EN 60068-2-6 test description requires an amplitude of 0,35 mm at 5 Hz to 60 Hz and an acceleration of 5 g over a frequency range of 60 Hz to 500 Hz, which are significantly higher requirements in both directions than is otherwise called for in industrial use. It was also necessary to ensure that the complete system guarantees an operating temperature of 0 °C to 70 °C with passive cooling.

Comprehensive VxWorks support (both older and newer versions) and the convenient integration of the fieldbuses in the SoftPLC runtime system were also important. On the hardware side, the solutions for CompactPCI could fulfill most requirements without customer-specific adaptations, because most CompactPCI products by the manufacturer were already designed for more severe industrial conditions. Furthermore, there is the Value Line for cost-sensitive projects without special requirements. The Value Line system chassis was used with the assemblies for the highest requirements. However, a few adaptations had to be made to the hardware: for one thing, the standardized CP-Pocket system chassis was reinforced so that it could meet the higher requirements for shock and vibration resistance. For another, the option of battery-buffered storage of the retained variables (storage of control variable to be retained in the event of power loss) had to be created and, at the same time, a battery on the processor board had to be avoided because of mining standards: an already existing expansion card docked on the CPU card was provided with a small “mining” designed circuit with non-volatile RAM (NVRAM). Mining here means that the RAM battery requires series resistance and that a specific electrical distance must be maintained in the circuit in order to ensure protection against explosion.

The RAM is connected to the CPU via a plugged LPC interface, which is more than sufficient, since high access speeds are not necessary. Thus, the CPU clock battery can also be banished from the CPU board as required so that it corresponds even to the world’s toughest requirements from the Australian government’s certification board TestSafe Australia. The first systems are already in use.

As a result, the hardware system specifications could be implemented relatively quickly and could also be replaced or expanded with comparable standard products from other manufacturers; this is also important for Eickhoff, because they want to be as independent as possible through the use of standards. This is an essential advantage of CompactPCI systems over any other IPC systems.

Application-ready platforms

Furthermore, the manufacturer’s offer to prepare application-ready platforms is particularly convenient for users: practically every component necessary to build an IPC-based PLC can come from one source. The crucial factor here is the additional function of the company as a system integrator, executing the integration to the finished platform and maintaining it as a product. In practice, this comprehensive support is only needed for the hardware platform, not for the integration of the SoftPLC, because the engineers at Eickhoff have a great deal of expertise in this and integrate as much as possible themselves. For any other user, however, it is very important to know that application-ready platforms are function tested and have a uniform interface for service and support. As needed, they also come bundled with pre-installed, demo control tested SoftPLC. It was also vitally important for Eickhoff that the manufacturer has supported the VxWorks realtime operating system for many years, so that even existing solutions could be equipped with new hardware without changing the software.

The solution thus recommends itself not just for mining, but for any developer of robust controls in industry. The new system is ready to use just as quickly when purchased as an application-ready platform. Since the API for the PLC programming is always the same, the control application is ported simply by being loaded on the new system. This is especially convenient, because if, for example, the controls become more complex, they can be equipped with increased performance simply by changing the processor card, which is available as a standard component from the company up to the current Intel Core Duo technology.