With realistic long-term drag chain tests, Helukabel was the first cable manufacturer to prove back in spring 2014 that digital data transmission via the Hiperface DSL protocol in its hybrid cables still works perfectly even after more than five million cycles. The durability and reliability have now also been confirmed in practice many times by mechanical engineers: Several 100 kilometers of hybrid cables from Helukabel are successfully in use worldwide in various applications.

When it comes to the practical introduction of single-cable technology, the choice of suitable special cables is crucial. This is shown by the example of IMA Klessmann from Lübbecke/Westphalia, which has been using OCT (One Cable Technology) from Beckhoff Automation for its drilling systems and complex production machines for CNC machining since the beginning of 2015. IMA is an internationally active manufacturer of machines and production lines for woodworking in the furniture industry. With the Topserv hybrid cables for servomotors from Helukabel, which have been intensively tested for highly dynamic drag chain applications, the machine manufacturer was well advised to make the switch. "The cables have now proven themselves in many of our Imagic drilling systems, despite high continuous mechanical loads," says Marcel Sulewski, team leader in electrical purchasing at IMA. The drilling machines from IMA are used in the furniture industry - stationary or as throughfeed machines. At throughfeed speeds of around 30 meters per minute, several drills simultaneously drill horizontal and vertical holes in the workpieces; up to 90 axes can be involved in such an application.

Helukabel presented a standard cable for the new single-cable technology with its Topserv servo cable series at the Hannover Messe in spring 2014. At that time, drive manufacturers did not yet have any long-term experience with the technology in the field. It was therefore all the more important that Helukabel was able to confirm through realistic drag chain tests that the shielding of the encoder cable still functioned even after more than five million cycles and that encoder signals transmitted via Hiperface DSL could be read without any problems. "The quality of the signal that arrives at the receiver is relevant to the question of whether the motor is turning," explains Thomas Pikkemaat, Product Manager for Drive Technology at Helukabel and Commercial Operations Manager at the Windsbach plant. "The less external interference penetrates the signal element, the cleaner the data arrives at the receiver. The shield of the data pair is responsible for protection against EMC emissions. The longer this remains intact in use, the longer the protective function is maintained."

Several drills prepare a piece of furniture for further processing. (Image: IMA Klessmann)

Whereas servomotors were connected to the controller with separate cables for the power supply and encoder signal in the traditional two-cable solution, the encoder cable for the motor feedback is integrated into the servo cable in the one-cable solution. However, this also makes it easier for the power wires to interfere with the transmission of data, at least if good and permanent mutual shielding of the cables is not ensured. In static applications, such shielding lasts virtually indefinitely. However, the situation is different in applications with moving axes and cables in drag chains, such as robots, machine tools or handling systems. In the worst case scenario, a reduction in the shielding effect can lead to encoder signals becoming unreadable.

So what measures can be taken to achieve durable and reliable shielding for such dynamic applications? "Braided shields made of bare or tinned copper wires can break due to mechanical tensile stress in the outer radius, which can reduce the shielding effect over time," explains Pikkemaat. "To prevent this, the braiding angle and degree of coverage of the braided shields in hybrid cables must be optimally matched to the dynamics of the application and the required bending radii as well as speed and acceleration parameters." To ensure that the shielding is as durable as possible, the braided wire should always be laid at an obtuse angle around the cores. In addition to a higher degree of coverage, this results in better elasticity and thus a reduction in tensile forces.

"It was important for us that Helukabel had intensively tested the durability and reliability of its cables for the new single-cable technology," reports Sulewski. "Thanks to the single-cable solution, we were able to reduce the installation effort for our drilling machines by an estimated 20 to 30 percent. However, the space saved by the single-cable solution was less than expected when halving the number of cables, as the larger cable cross-sections in the drag chains also have to be taken into account." More important, however, is the time saved during assembly and installation. Cables can also be replaced more quickly and the stocking of spare parts is simplified. IMA uses single-cable technology in its applications up to 30 meters away from the control cabinet. The first machines have now been successfully in use at the customer's premises for more than a year. as