GRAVEL MINING WITH PROFINET
By Klaudija Trkaj, PROFINET Marketing Manager,
Siemens AG

Even apparently simple productions such as gravel mining become more flexible and cost effective using modular, networked automation. Thanks to the use of Component Based Automation and its interface connections to PROFIBUS, it was possible to better match work phases to one another and increase production flexibility while doing it more economically.

The Cava Fratelli Girardini gravel pit near the North Italian city of Vicenza/Venetia specializes in the mining of gravel for the building industry. The plant was automated in order to improve the entire production process. The application shows which requirements a modern automation system is expected to fulfill in order to satisfy the growing demands on the mining of materials.

The use of Component Based Automation made it possible to improve both individual process sequences and the entire production process. It also enabled better matching of the different work phases as well as enhancing production flexibility to accord with customer requirements.

A Structured Gravel Pit

The Cava Girardini gravel-processing plant is structured in accordance with the way in which the raw material is treated and the production sequences involved. First, raw material must be raised from the bottom of the lake which 'supplies' gravel, a man-made lake with a diameter of around 500 meters. A floating dredger raises the gravel from the lake bottom.

The dredger consists of a gripper which can reach an excavation depth of between several meters and 65 meters. The excavated material is transported to the surface of the lake and forwarded on conveyor belts for storage on dry land.

The second phase of the production process takes place in the water treatment plant, the heart of the production process. It is here that the water to be used for cleaning the excavated material is treated.

The cleaning process involves the removal of the sludge whirled up when the gravel was raised from the lake bottom. The gravel goes through the cleaning process several times in order to clarify the water as much as possible, ensuring the high quality of the gravel, which is later treated again with 'recycled' water.

As Alessandro Brina from Siemens, the person responsible for this project, emphasizes, the first automated plant with distributed intelligence was implemented using Component Based Automation. The first intelligent module, on which the water treatment plant depends, is controlled by a Simatic S7-300 programmable controller with CPU 314, which controls the speed of a series of pumps and converters as well as all I/O devices interfaced to the PROFIBUS DP network.

The cleansing process is followed by 'Plant 1' of the process chain in which the first treatment of the incoming excavated material is separated into two heaps (above). The second intelligent module is controlled by an S7-300 with CPU 315-2 DP, which, together with the converters interfaced to the PROFIBUS DP network, regulate the speed of the conveyor belts, sifting machines and crushers.

The conveyor belts transport the raw material to the sifting machines, where it is sorted according to size. Two rows of conveyors thus exit 'Plant 1' and transport the selected material to 'Plant 2', the last station for the final treatments. Additional sifting, crushing and other procedures process the previously selected material into different kinds of gravel or stone granulate. Following this, the finished material is stored in silos where it is available for removal and delivery to customers.

Once again, it is a CPU 315 which controls the conveyors and the loading gates for the trucks which will deliver the finished material. The trucks cover a distance of around two kilometers approximately 100 times a day to completely empty the silos or collect the material for transport to new storage facilities.

The Moby identification system, a system for the wireless acquisition and forwarding of information, is used for recording the exact position of the truck. The truck is thus capable of positioning itself precisely beneath the material output gate (right). The gate is controlled via an HMI device with diagnostic functions which, like the Moby identification system, communicates wirelessly with the controllers.

Before the system was automated, the driver was required to open the side window of the truck in all kinds of weather in order to be able to identify the relevant control signals and position the vehicle beneath the output gates, exposing himself to the dust whirling up from the gravel and the exhaust fumes from the truck. When using an automated system, on the other hand, the driver can read the positioning data on a panel inside the truck. The Moby identification system shows him the correct position, and the loading process can be started right from the comfort of the driver's seat. Communication takes place over an IE/PB Link as gateway between Ethernet and PROFIBUS and the communications processor, which enables routing on the PROFIBUS DP network and the converters and field devices.

Cost Savings Through Modularization

The various production lines which make up the plant are regarded as 'intelligent modules', that is to say, as independent units capable of controlling their part of the plant. The plant overview (top) shows five intelligent modules, which correspond to the different phases of the production process: water treatment plant, plant 1, plant 2, storage and transport by truck.

These five modules enabled the communication links between the built-in machine components to be configured graphically using the Simatic iMap engineering tool. This meant that the plant could be commissioned more quickly. It was not necessary to modify the application programs for the intelligent modules to communicate among themselves. This made it unnecessary to interrupt ongoing production even during the implementation phase of the various plants, an approach which significantly reduced the time needed for commissioning.

The use of open technology such as PROFINET guarantees the user that he will be able to upgrade his systems quickly in future. In addition, the use of IT standards simplifies the integration of production data in the company's EDP environment, enabling integrated plant management. On the cost side, water and coagulates, the latter an expensive product allowing the sediment in the water treatment plant to sink to the bottom, were reduced by 25% - a considerable savings. Moreover, the optimization of the loading and unloading procedures reduced the trips made by the trucks to empty the silos by 20%. Instead of 100 trips, only 80 trips are now required, another significant reduction in both time and costs, considering that each trip requires six minutes to complete.

Thanks to the use of PROFINET for the integration of Ethernet and PROFIBUS and the use of wireless communication, the working conditions of the truck driver have improved significantly. He no longer needs to leave his truck during loading and unloading, which means a productivity increase of 35% and a reduction in working hours. Finally, machine downtimes have been reduced by 20% because all devices can now be put to better use without 'wastefulness', which in turn reduces wear and tear on mechanical components.

It is also possible to carry out programmed maintenance in the time saved during the various work phases. Component Based Automation made it possible to improve both individual sequences and the entire production process. Better coordination between the various work phases and more flexible production were additional achievements.

Fundamental to the innovative modular concept and the successful implementation of the plant, however, was the use of the PROFINET protocol with its easy integration in the various systems.

Adapted from the Profi Interface Center Connection, Spring 2005