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Locating trucks in warehouses

Radio frequency identification is a method to read and save data without physical or visual contact. Still (Germany) uses this technology to locate and navigate trucks, in combination with CAN.

The transponders are small but effective (Photo: Still)

TO EMLPOY RADIO FREQUENCY IDENTIFICATION (RFID), trucks read the information of so-called passive transponders, which are placed in the floor at regular intervals. With the help of the transponders, installed at distances of about 1 m, RFID technology can locate and navigate trucks, and optimize operational processes on the basis of the collected data. The transponders are embedded in the floor according to a defined structure. The unique identification number of the transponders and the storing of the respective coordinates on the central MMS computer allow the exact locating of the truck.

During operation, the RFID Locator detects the height of stacked pallets with the integrated height measuring system. This way the technology complements existing instruments such as warehouse management and truck control systems (LVS and SLS). By using the on-board CAN network, Still makes use of these means to detect the position of the truck. Information on height, load weight, speed, hydraulic movements, and other conditions of the truck will in the future be made available through a specific CAN protocol. This will affect the concrete situation in the warehouse: At crossroads, i.e. potentially dangerous spots, the speed of the truck is reduced and after the truck has passed the dangerous area, the speed limit is upped again.

RFID modules work together

The RFID Locator registers the transported goods using logical combinations of measured values (lift height, load distance, etc.) on board of the truck and the location of the truck as such. For this application, it makes sense to register the goods once (e.g. at goods receipt) by conventional means (e.g. barcode) and store that information in the central material management system.

After this, the position of the goods is permanently traced by tracking the position of the warehouse truck moving the load. RFID tags are installed everywhere in the floor of the hall, so that the truck can constantly report its position with the load to the MMS. When the load is stacked, height sensors detect the height at which the load is stored. Another sensor measuring the position of the load on the forks detects whether the load was actually taken off the forks. The MMS is fed with the information at which location the goods are stored. For retrieval processes, the system follows the same principles in reversed order.

To achieve a trouble-free procedure, the storage and retrieval processes can only be carried out by trucks equipped with RFID Locators.

The transponders are set in certain distances in the floor (Photo: Still)

The RFID Navigator module uses the location information of the Locator and connects this information to the destinations given by the control system and the stored layout of the facility to indicate the direction to the driver. This results in an optimized fleet utilization by short travel distances, guided travelling to storage/retrieval locations, short training times for temporary staff, and performance evaluation of drivers by comparing the nominal to the actual driving times.

The RFID Safety module is a driver assistance system affecting the control system of the truck when passing over certain transponders. For example, it can automatically reduce the speed of the truck at danger spots such as crossings or narrow passages. In addition, the drive direction can be controlled to monitor one-way roads or to prevent entry into sensible areas. It is also possible to control other safety features such as lighting.

The module allows triggering functions in the truck controlled by its position without any action of the driver. As an example, the maximum speed can be reduced to 10 km/h before passing a gateway. This is triggered when the truck passes over certain transponder areas. After passing the gate and when passing over the transponder areas in the opposite direction, the speed limit is lifted. In case it is needed, the RFID Safety system also switches electric consumers such as lights or horn on and off and monitors the permitted lift height as well.

The RFID Interface module is a sales name for connectivity between the truck and the central warehouse control and is included in the modules described above.

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