Taking sorting to a whole new level
"It almost looks like an oversized model railroad," says Support Automation Manager Andreas Hädinger, standing in the control room overlooking the labyrinth of chutes and conveyors. Below him, packages of all sizes race past at 2.5 meters per second on the tray sorter. From there they are brought to a tilt tray, and a chute guides them to their destination: the loading container for their postal code.
Important step: Switching to POWERLINK
To say the distribution center is larger than a model railroad is quite an understatement. In the 21,000-square-meter facilities, 450 workers operate 123 docking stations, 26 automated address readers, 272 chutes, 4 tracks and 2 portal cranes with a capacity of up to 16 tons – sorting around 26,000 packages per hour and more than 500,000 on a busy day. The Swiss Post operates two other nearly identical distribution centers in Härkingen and Daillens. To achieve such an impressive sorting performance, they must be kept up to date with state-of-the-art technology. A significant upgrade came in 2012 with the implementation of new controllers and the switch to POWERLINK. "The X20 controllers from B&R give us a substantial boost in processing performance, and switching to POWERLINK made us considerably faster," says Hädinger.
800 new drives installed
The performance enhancements didn't end there, however. On the heels of the switch to POWERLINK began the planning phase of another expansion that would once again rely on components from B&R. To improve sorting efficiency, the plans called for a new line that would divert incorrectly sorted packages to an additional loop, from which they could then be resorted. This expansion pushed the hourly throughput from 20,000 to 25,000 packages.
This substantial increase in efficiency was achieved without any structural changes to the hall, despite the installation of 670 new conveyor belts covering an additional 2,100 meters. A cross-sorter was also added to join the new and existing systems. 800 new drives were installed to handle the infeed and outfeed lines of the cross-sorter, which was erected on a 370-ton iron structure 6 meters above the hall floor.
Pushing the limits
Achieving this level of precision logistics had the developers pushing the limits of what is possible. Recalling the early stages of the project – when the architecture was being developed for the cross-sorter and the additional 800 drives – Hädinger explains: "We wanted to use the X20 controller to run 90 drives with response times of 2.5 milliseconds. That means there are 16 levels between the first and last drive. That was an unbelievable challenge."
B&R finds optimal solutions
"Customer requirements can be staggering at times," says Daniel Christen, who is responsible for application development, training and support at B&R, "but those are the challenges that are the most rewarding once you arrive at the optimal solution." In this case it was not only the requirements for the drives, but the safety technology as well, that put B&R to the test.
There were two particularly tough nuts to crack: "We wanted controllers with two safety modules each, which wasn't yet common at the time. That was because we wanted to process as many as 170 modules and each safety controller is limited to 100. We therefore had to split the program and have two safety controllers in the master."
The right mix of virtual and hardware-based safety
The other challenge was making the architecture work with the safety circuits of the existing hardware, whereas the new SafeLOGIC safety controllers from B&R offer an extensive range of functionality: safe I/O, motion control, line integration, machine options and integrated diagnostics. The safety application is programmed in B&R's Automation Studio development environment.
"Traditional hardwired safety technology responds to safety events by abruptly shutting down the machine – often making work more difficult for service personnel. B&R safety technology, on the other hand, allows production to continue at a safely reduced speed even when a safety door is open or an operator reaches into a protected area. In most cases it is possible to avoid stopping the machine," says Christen, pointing out the advantages of the new safety solution.
Safety circuits simplified
Hädinger now has some tips for anyone planning the safety technology for a large facility: "It's easiest if you first clarify exactly where systems interact. When you have conveyor belts spanning multiple levels, you have to carefully consider what's going to happen at the top when someone at the bottom hits the stop button," he says. "Our adaptations to the hardware architecture helped simplify the safety circuits and minimized the number of belts affected when we have a stoppage."
High system availability
With the scale of the project and the challenging nature of the requirements, B&R knew they would need to have engineers on site at the distribution center in Frauenfeld to provide assistance through critical phases. This was something that Hädinger greatly appreciated, particularly one instance when B&R support technicians even traveled from Austria to Switzerland over the weekend. "By Monday morning, everything was up and running smoothly."
System availability is 100% ensured. "The system has been unbelievably stable since switching to POWERLINK – virtually the only time we have a problem is when there is a package jam," reports Hädinger, standing in the window of the control room surveying the hall below, where a steady stream of packages flows to and from the cross-sorter. "Using openSAFETY over POWERLINK has also saved us several kilometers of cable," says Christen.
- Daniel ChristenDevelopment, Training and Support, B&R"Traditional hardwired safety technology responds to safety events by abruptly shutting down the machine – often making work more difficult for service personnel. B&R safety technology, on the other hand, allows production to continue at a safely reduced speed even when a safety door is open or an operator reaches into a protected area. In most cases, a full production stop can be avoided."