When companies from the automation industry place an order with Murrelektronik, one cog in the logistics center in Oppenweiler meshes with another. The ordered products are transported via conveyor belts to the picking and packing stations, and just a short time later they are neatly packaged and sent to their destination. To ensure that all logistics processes run at full speed, all picking and packing stations are normally occupied; if an employee takes a break, a colleague ("jumper") immediately takes over his or her tasks. If there is a shortage of packaging material, an "internal logistician" takes care of the situation so that no bottlenecks occur. In the past, there was an overview of who was currently working where on a board installed in the logistics center; individual signal towers served as status displays for individual areas.

A team led by Oliver Behnke, head of the Murrelektronik logistics center, set out to simplify this. The decision was made to install a whole series of Modlight70 signal towers in a clearly visible position. Since then, employees in the operational area and colleagues in the logistics center's control room can see at a glance whether all processes are running according to plan. The employees at the picking and packing stations operate the lights from their workstation using radio buttons. If the green LED element lights up, everything is in order. The yellow element symbolizes that an employee is taking a break, in which case a "jumper" can set off. Blue stands for a packaging bottleneck, red indicates a malfunction. This is a clear symbolism - nothing has to happen "on call" any more.

The spatial extent of the logistics center proved to be a challenge - this became clear at an early stage of planning. Trusting that the radio signals would be transmitted over long distances or even through walls without interference seemed impractical to Oliver Behnke and his team. For this reason, they decided to transmit the radio signals digitally via cables using a decentralized installation solution based on the Cube field bus system. For this purpose, the radio receivers were positioned in control cabinets at several locations within the logistics center. These radio receivers control the inputs of the IP20 fieldbus module Cube20. These input modules communicate with the PLC controller, which processes the signals and transfers them to the Cube67 field bus system located in the field, which controls the Modlight70 signal tower.

The Cube Cable modules are equipped with 1.5 meter long connecting cables. (Image: Murr)

The packing density is remarkable. "In this specific case, we only had to install one module per control cabinet," reports Oliver Behnke. In practice, the individual channel diagnostics directly on the module proved to be advantageous. "If there is a fault somewhere in the wiring, the LED at the affected slot lights up and we can rectify the fault in a short space of time without having to search for it."

Practical modules with a direct Modlight signal connection are used to integrate the actuators into the Cube67 system. These "Cube Cable modules" are equipped with a 1.5 meter long connection cable, the eight-pin M12 connection is attached directly to the signal tower. The individual connection modules are in turn connected to a system cable, which is used to transmit both the signal and the power. "This means we don't need a separate power supply. This makes installation quick and easy."

The Modlight70 signal towers can be assembled modularly from a connection element and several colored LED modules with a diameter of 70 millimetres using a bayonet lock. "We have assigned the colors to specific functions throughout the logistics center, which is why we use the signal towers in identical configurations," explains Oliver Behnke. The energy-saving LED technology, the long service life and the fact that the modules are maintenance-free are important to him. pb