Pallet monitoring system based on a heterogeneous sensor network for transparent warehouse processes

Increased transparency of material and product flows in warehouses will necessitate real-time determination of the properties of logistical units (e.g. small bins, parcels, palletized goods, intermodal containers). The key properties of logistical units are their unique identifiers and locations at a given time. Other properties such as dimensions, weight or temperature may also be relevant, depending on the use case. This paper presents a pallet monitoring system that determines the characteristics of pallets, namely storage location, storage time, dimensions and appearance. Technically, this is done by combining the MarLO vehicle positioning system that employs passive planar markers, an RFID identification system, a dimensioning system that employs depth sensors and a load change detection system mounted on vehicles. The proposed approach was developed and evaluated in a real world test bed. This enabled us to transfer the subsystems' accuracy to our new pallet monitoring system, i.e. we achieved a pallet positioning accuracy of up to 10 cm, a pallet dimensioning accuracy of up to 5 cm in each dimension and highly accurate pallet identification. By fusing the data from these subsystems, we were able to generate the aforementioned pallet information for subsequent monitoring and control of warehouse operations in real-time.