When introducing single-cable technology, the choice of the right special cables is crucial. This is shown by the example of IMA Klessmann, an internationally active manufacturer of machines and production lines for woodworking in the furniture industry. Since the beginning of 2015, the company has been using 'OCT' (One Cable Technology) single-cable technology from Beckhoff for its drilling systems and production machines for CNC processing. This includes the 'Topserv' hybrid cables for servomotors from Helukabel, which are suitable for highly dynamic drag chain applications. These cables are used, for example, in the 'Imagic' drilling systems, where they are exposed to continuous mechanical stress caused by tight bending radii and high bending cycles in the drag chains as well as abrasion caused by wood dust.

Drilling systems for woodworking from IMA place high demands on the cables in drag chains. The picture shows several drills preparing a piece of furniture for further processing.

© IMA Klessmann

IMA drilling machines are used stationary or as throughfeed machines in the furniture industry. At throughfeed speeds of around 30 m/min, several drills simultaneously drill horizontal and vertical holes in the workpieces, which are later used to assemble living room, bedroom or office furniture, for example. Up to 90 axes can be involved in such an application.

Focus on shielding

With the hybrid cable, the feedback wires are carried directly in the servo cable.

© Helukabel / Detlev Haake HZWEIA

Manufacturers of hybrid cables are now facing special challenges in order to provide machine builders with long-lasting cables. Helukabel, for example, presented a standard cable for single-cable technology in spring 2014 with the 'Topserv' servo cable series. At that time, drive manufacturers had no long-term experience with the technology in the field. However, thanks to realistic drag chain tests, Helukabel was able to confirm that the shielding of the encoder cable was still functional even after well over 5 million cycles and that encoder signals transmitted via Hiperface DSL could be read perfectly.

The quality of the signal arriving at the receiver is fundamentally relevant to the question of whether the motor turns: 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.

While 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 single-cable solution. However, this means that the power wires can more easily interfere with the transmission of data - at least if good and permanent mutual shielding of the cables is not ensured. In the worst case, a reduction in the shielding effect can lead to encoder signals becoming unreadable.

In static applications, cable shielding lasts virtually indefinitely. The situation is different in applications with moving axes and cables in drag chains, such as robots, machine tools or handling systems. Unfortunately, the choice of an unsuitable cable may only become apparent months after a machine has been commissioned. So how can permanent shielding be achieved for 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. 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. This ensures that the EMC shielding remains intact even after several million cycles. To ensure the most durable shielding possible, the braided wire should always be laid at an obtuse angle around the cores. In addition to a higher degree of coverage, this also results in better elasticity and thus a reduction in tensile forces. In addition to the braided shields, special metalized nonwovens are also used for hybrid cables.

Reduced installation effort

Overall, the installation effort for the drilling machines was reduced by around 20 to 30 % thanks to the single-cable solution, as cable assembly, installation and laying take less time. However, the space saved by the single-cable solution was less than originally expected when the number of cables was halved - this is due to the fact that the larger cable cross-sections in the drag chains also have to be taken into account.

IMA uses single-cable technology in applications up to 30 m away from the control cabinet. The first machines have been successfully in use at the customer for over a year.

Author:
Thomas Pikkemaat is Product Manager for Drive Technology at Helukabel and Commercial Operations Manager at the Windsbach plant.