Good Neighbors

With the construction of a distribution center for COOP in Norway, Turck and Witron demonstrate that UHF-RFID can also be used for short distances

The distribution process

The new distribution center of the grocery retailer COOP Norge Handel AS near Oslo, is the size of approximately seven soccer pitches. Goods arrive at the goods-in bays of the “COOP-Logistikksenter” on pallets. The pallets are unloaded here and temporarily stored in the pallet store. The unmixed pallets are then depalletized fully or semi-automatically and transferred to trays or containers. Besides the trays and containers, the Norwegians use two different types of pallets in the distribution center: Plastic pallets fitted with UHF tags, and wooden pallets that are provided in the distribution center with a combined barcode-UHF label. The barcode is used to identify the carrier as a wooden pallet. The trays and containers are likewise identified by their barcode.

Combined barcode-RFID identification

One requirement of COOP was for particularly thorough testing. The customer wanted to use the UHF tag already integrated by the manufacturer in the plastic pallets for the identification. This saves the installation of labeling systems that would otherwise have to provide all pallets with barcodes.

During the planning phase the specialists at Witron closely examined the possibility of implementing UHF identification. The system required a UHF read/write head at each incoming goods area as well as each crossing point in the pallet conveying system – 250 in all.

RS485 interface and controllable antenna required

Besides the need for the RS485 interface, another requirement eliminated the possibility of using a large number of different UHF read/write heads for the application: “The controllability of the antenna was a very important selection criterion for us because we had to implement a great deal of near field communication in the plant. Apart from a few other suppliers, this feature was primarily offered by Turck,” explained Christian Fuhrmann, who is responsible for the control technology development.

RSSI filter prevents crosstalk

During Tests Witron found out that crosstalk occurs if an antenna energizes a tag that it is not at all meant to read. This tag can then also be energized by a read/write head in close proximity and thus achieves a range that exceeds its actual maximum range. This means that read/write heads receive data from very distant tags which their antenna output power should not allow them to see. “In this case we were able to prevent this by setting different parameters on the read/write head. RSSI filters can be used or you can restrict the number of read operations that the read/write head performs,” Fuhrmann explains. The RSSI value specifies the strength of a signal. It is used to estimate the distance of a target. By setting filters, objects at a particular distance can be excluded from read operations.