It has been over 10 years since the launch of CC-Link in the Asian market. This open network was soon adopted throughout the region and has continued to evolve into a world-beating network. This network was built on high data throughput performance and network availability features.
Features of CC-Link
The CC-Link network can connect up to 64 stations controlling a total of 8192 I/O. Network distance is 1,2 km, which can be extended to a maximum of 13,2 km with the use of repeaters. There is a maximum network speed of 10 Mbps with a reaction time of 3,9 ms.
With the importance of network reliability, CC-Link has the capability to configure an integral standby master. This is a floating master that will take control of the network should the master fail. As the CC-Link is a deterministic network any failure of the master will take the entire network down. However, the floating master adds reliability to the integrity of the network.
An automatic on-line return function for the distributed I/O modules ensures that if an I/O module is replaced the network does not require rebooting.
Improving throughput and efficiency at Longslow Dairy
Even though the current trend from consumers is to use plastic bottles rather than glass, Longslow Dairies Group believed that in this new age environment friendliness and recycling, supplying products in glass bottles will give the consumers a sensible cost effective environmental solution to milk packaging. To this end they have installed the first totally automated milk bottle packaging plant to meet the increasing customer demands.
'Easy to use and easy to maintain' was the main criteria given to the machine builders. Based on this, they created a very simple solution that requires no manual interaction to run the system. In fact, the initial order was to automate only parts of the system, however as the system was installed Longslow was impressed with the initial results, that allowed the system to grow until the whole plant was automated.
Before the automated system was installed the dairy was running at about 60% efficiency, now with the new system it has achieved an average efficiency of 87%. Throughput has also increased by 30% due to the improved control of the plant. The increased data flow has enabled accurate identification of bottlenecks and these problems can be addressed in an efficient manner.
To precipitate a modular construction of the plant, CC-Link was chosen. This represents the latest in fieldbus technology. The uniquely easy to install and configure fieldbus, with its high immunity to noise and flexible additional station insertion system, made it the natural choice for the backbone of communication between sections of the newly automated plant.
This was the first installation of CC-Link at Longslow. The ease of adding sensors and stations to the CC-Link system made it simple to adapt to the changing customer needs that invariably happen whilst installing new equipment.
The system for this plant is divided into seven basic sections. Each section is controlled by a compact PLC, which controls all local operations and connects back to a central Master PLC using CC-Link. Utilising intelligent slaves rather than one large PLC to control the whole plant allows sections to continue operation, even if there are problems in other plant areas, ensuring high throughput and increased section efficiency.
All communications are co-ordinated by the central Master PLC. CC-Link's 10 Mega baud speed in data transfer and flexible deterministic data packaging is crucial to the success of the entire system. Using CC-Link for the distributed control permits simultaneous controlled shut- downs of even the remote sections, and makes warm starting the production process much easier.
Installation for the entire system took only six weeks with the installer working around the daily production requirements of the dairy. The use of CC-Link drastically reduced wiring installation time, which was critical as they could only install the system at night, or during shut-down periods.
The bottling line has two in-feeds, one for returned bottles and one for new. Each returned bottle is re-used up to 15 times and makes the packing process much more environmentally friendly than disposable plastics. The used bottles are fed in crates into the system, which then removes the bottles from the crates. The system can handle 600 bottles per minute.
When the bottles have been removed from the crate they move into the soaker-washer machine. This machine sprays high-pressure water into the bottles to remove debris and then the bottles enter a soak tank. The bottles remain in the tank for 10 minutes before being rinsed of all trace elements from the cleaning process.
During the soaker-washer stages the bottles are heated to a temperature of 36° in the pre-soak, and then slowly raised to 73° in the soak tank.
The temperature rise and subsequent fall must be achieved smoothly as temperature shocks can cause the bottles to fracture. When the sterilised bottles finally leave the cleansing cycle they are given a final chilled water rinse to reduce bottle temperature to an acceptable level for filling.
As the bottles leave the cleansing stage they are supplemented by new bottles to fill the production requirement by a combination conveyor system, where new and cleansed bottles combine into a single line ready for inspection.
Line sensors are used to match the speed of the single line conveyor (via a VSD) to the exact spacing requirement needed for the inspection of the empty bottles. A prism scanner scans each bottle with three separate cameras and detects any deviations in the bottles dimensions down to 0,5 mm. The scanners detect any irregularities in the bottle as well as detecting any residual water from the rinse cycle, with all reject bottles being diverted off the production line.
Glass is highly abrasive and, as the bottles pass along the stainless steel conveyors, synthetic oil lubricates the bases. The oil reduces friction on the conveying process, preventing not only wear to the bottles but to the steel conveyor as well.
Pressure, which can develop from bottles pushing along a conveyor line, is immense. In order to keep this at a tolerable level, the bottles enter a modulated variable speed conveyor when they leave the scanning section. This constantly checks the pressure the bottles are exerting and steps the speed up or down to reduce it. The introduction of the modulating conveyor has reduced the pressure from the bottles by a third, and has decreased bottle breakage in the process. This is an important factor in the increased efficiency, because the reduced breakage has concomitantly decreased the number of times operators must stop the flow to remove broken glass.
After inspection the bottles enter the filling carousel. The bottles enter the system and are filled at a constant 4° with either milk or orange juice depending on the production requirements. The bottles are then foil capped to seal the liquid in the bottle.
Using CC-Link on the filler carousel allowed the removal of control equipment from the machine. This reduced the size of the filler system, and with fewer items to clean, improved the overall cleanliness of the process and reduced the downtime taken for cleaning purposes.
As the bottles leave the filling station they enter a crating machine which takes the freshly filled bottles and places them back into crates. The crates being the same ones in which the returned bottles were delivered. These have been washed automatically at high pressure, and then sent to the re-crater to be loaded.
The control system of the crate washer is linked directly to the bottle filling process, and the system intelligently washes only the required amount of crates that are needed for the production requirements on a just-in-time basis, reducing water consumption, and saving precious energy.
Using CC-Link between the filling and re-crating ensured critical bottlenecks are avoided in the production process
The automated combination of all sections in the process allows all parts of the system to work together seamlessly. If the production is running at 100%, all sections take this into account and set speeds accordingly. The high data processing of the CC-Link communications between sections ensures that all parts of the process are realtime speed synchronised. This intelligent linking of all sections, including crate washing, harmonises production and greatly reduces energy waste, as sections run only when needed.
The last stage in the production process is the transportation of the crated product to a re-stacking machine, where five crates are stacked for easy dispatch to waiting lorries. Since space is at a premium on site the whole process is 'just in time' production, with requirements being set daily by the received orders.
Flexibility in the system is very important, and the one supplied by the machine builder can produce any type of bottled milk without any re-configuration. Using CC-Link's flexible station recognition system means that stations can be taken off-line without any errors occurring, and introduced at any time without fuss. This means that even a change of the system to the production of bottled orange juice takes only 20 minutes, including all wash downs and physical changeover of the filler carousel to that suitable for orange juice.
For more information contact Shaun Loesch, CBI-electric: low voltage, +27 (0)11 928 2000.
| Tel: | +27 11 928 2000 |
| Email: | [email protected] |
| www: | www.cbi-lowvoltage.com |
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