REDwire Hybrid cables are on the horizon for servo systems

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Lapp Canada Inc

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Hybrid cables for servo systems can handle both power and data.

A new digital communications interface is poised to significantly change the design of cabling for servo systems, according to a white paper recently released by Lapp Group. Entitled “Hybrid cables handle servo power and feedback”, the white paper’s author Lucas Kehl, product manager for Lapp Group, explains that the new Hiperface DSL by SICK interface enables power and signal to share a single hybrid cable.

This advancement can offer lower installation and maintenance costs, with no need for separate encoder or resolver cables. In addition, hybrid cables take up less space in cable carriers because they eliminate the requirement for distance between servo and encoder cables of different voltage classes.

Hybrid cable design

These hybrid cables typically consist of three power cores, a green-yellow protective conductor, and an optional control core pair as an electric brake. To handle the motor-feedback communications, an additional signal pair is used. The key to this design is that the position signals from a resolver or encoder are modulated to the feedback system's power supply voltage.

Requirements for hybrid cables

While conventional practice for engineering servo systems calls for separate cables to avoid problems with electrical noise and crosstalk, the Hiperface DSL standard can avoid these problems if the right kind of cable is used. 

For instance, hybrid cables require construction to very tight specifications since data is transmitted in such close proximity to the power. In addition, hybrid cables can be particularly susceptible to electromagnetic interference, so the design must include proper shielding. 

Another requirement for hybrid cables in servo systems is mechanical robustness, because these systems usually involve movement. As a result, the white paper recommends looking for hybrid cables that offer continuous flex performance. For example, when Lapp Group manufactures continuous flex hybrid cables, the company tests them with up to 10 million alternate bending cycles. 

The white paper concludes that there are still changes to be made before hybrid cables can become the standard. One hold-up is that not every motor and drive maker supports the new interface. However, as more manufacturers begin adding it to their new products, hybrid cabling is set to change the landscape of servo system design.


Lapp Canada Inc

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