As the inner parts of cables become more and more complex and application-specific, making them becomes increasingly sophisticated as well. It is therefore no wonder that cable manufacturers want to keep up with these new requirements and update their production machinery accordingly.

Circling at high speed

Communication cables are manufactured with braiding machines. A braiding machine consists of a coil carrier and a rotor. Circling the coil carrier at high speed, the rotor pulls single wires off a number of creels and thus allows the braiding machine to twist (or “braid”) single wires into the final product.

To produce high quality cables you have to register and control these movement patterns accurately. The standard solution for control tasks involving rotating parts is well known and has been used for braiding machines too: slip rings transferring signals from rotary encoders and proximity sensors to the control unit. The downside of this solution is susceptibility to failure, especially when the machines are in continuous operation.

Two-step upgrade

To avoid this, Kabel Sterner GmbH decided to start upgrading its braiding machines to achieve reliable communications. Kabel Sterner chose a two-step approach: replacing slip ring technology with wireless communication between two radio modules, and switching from classic analog control technology to Profibus. These two steps are closely related, as the wireless connection is part of the communication path to the control unit and thus has to deliver absolutely fail-safe and error-free Profibus transmission.

Confined space

Some interesting challenges had to be overcome, to successfully switch from the existing solution to wireless data communication. As a start, the radio modules had to be fitted into a confined space, and possible disturbances due to the metallic surroundings had to be considered as well. Furthermore, the two radio modules including antennas would be circling each other with more than 400 RPM, and with a constant fluctuation of the radio path from 0.3 m to 1.5 m. So, in essence this application is about building a Profibus radio path rotating at high speed in an extremely confined space.

Two years without problems

To achieve this, they deployed two Profibus-enabled radio modules from the DATAEAGLE 3715 (Schildknecht AG) series, fitted with omnidirectional antennas and Bluetooth radio technology. It proved to be the right decision. More than two years of trouble-free operation of the braiding machine proves the exceptionally stable performance of Profibus together with the reliability of the DATAEAGLE radio modules – not least because of their built-in filtering procedures for reliable transmission of Profibus signals, patented by Schildknecht.

Machine operator convinced

Wireless PROFIBUS has proven its worth and has convinced the machine operator: “To begin with we were quite skeptical about the idea of switching from slip ring to radio technology, because of the unique requirements. But the promise of higher operational reliability eventually persuaded us to take this decision, and we have not been disappointed,” says the responsible expert from the Kabel Sterner GmbH technical maintenance team, evaluating the project in retrospect.

Thomas Schildknecht