Before a beet is turned into sugar, which is then removed from the high-bay warehouse and loaded into trucks, it has to pass through various stations. The high-bay warehouse at the Ochsenfurt plant is enormous: it has 72,000 storage spaces. There is space for up to 6,000 Euro pallets in seven aisles. Depending on the goods call-off, 10 to 25 sugar trucks leave the Ochsenfurt plant every day. When a truck docks, the warehouse logistics specialist retrieves the goods to be collected directly from the high-bay warehouse via SAP. The ordered Euro pallets arrive at the end of the intralogistics process chain via roller conveyors: a 5-lane gravity conveyor, which is fed with pallets by a cross conveyor.

Traditional security concepts are reaching their limits

In many multi-track conveyor systems, a single muting light grid or a light barrier was used in the past to simultaneously safeguard several adjacent conveyor sections. However, this type of installation is not muting as required by DIN EN IEC 62046. This is because if the protective function of the safety light grid is temporarily suppressed during active muting, people can enter the danger zone next to a pallet being conveyed out of it. Even the "Smart Process Gating" alternative for access guarding, which was developed by Leuze back in 2016, could not be used here: This technology, patented by Leuze, is based on the Leuze MLC 530 SPG safety light curtains, which make additional muting sensors superfluous. However, Leuze Safety Consultant Dr. Volker Rohbeck recognized that even this innovative process could not be used at Südzucker at this point. This is because the design of this multi-lane transportation system did not and does not allow several muting or SPG sections to be arranged next to each other.

A creative solution had to be found. The area where pallets are transferred to the gravity conveyor and the hazardous area behind it had to be protected against access by people. At the same time, the safety solution also had to release only the lane on which the pallet is ultimately discharged. This required a new safety concept that met these extended requirements. And one that offers seamless safety even in automatic processes, while at the same time ensuring an efficient material flow and high system availability. With this in mind, Dr. Volker Rohbeck and Dieter Düll, the responsible master electrician at Südzucker, subjected the plant to a complete safety check.

Multi-lane transportation system efficiently secured

Today, access guarding of the five-lane pallet retrieval system at Südzucker is carried out by two vertically aligned Leuze RSL 400 safety laser scanners. Together, they form a vertical protective field that extends across all lanes. The safety system receives information from the system control as to which lane the pallet will be output on and adjusts the protective fields of the two laser scanners accordingly shortly before the pallet passes through. If the transverse transfer carriage transfers a pallet, this is reported to the system controller and a protective field is selected. Once the pallet has passed through, the protective fields of the safety laser scanners are reset to their initial values, thereby completely "closing" the conveyor area again. The safety system does not require any additional signals such as those from muting sensors. This also means that there are no system-related design restrictions. The solution is tamper-proof and ideal for retrofitting existing systems: the two safety laser scanners are controlled by their own pre-programmed safety controller, which is part of the protection concept, and integrated into the system via two-channel safety outputs.

The article appeared in materialfluss 8-9/21.