Single-cable solutions are increasingly gaining traction in the field of servodrive technology. In addition to the growing number of drive manufacturers offering single-cable solutions, this trend is fueled by the increasing number of manufacturers of rotary encoders that allow the implementation of such solutions in the first place. They differ not only in the protocol used, but also in technical details such as resolution and stability. Helukabel GmbH and Hengstler GmbH are two well-established companies that tackle this topic from different vantages. However, they are united in their common mission of providing customers with high-quality components that are innovative, effective and safe and that harness the tremendous potential
offered by single-cable technology.
In single-cable solutions, the cores for the encoder’s signal transmission are integrated into the servo cable,
which means that two cables are thereby combined to form a hybrid cable. This solution’s success is down
to the benefits of space and weight optimization, and in particular to the reasonable price and reduced
connection technology. In areas with limited space, this translates into additional advantages for machinery,
control cabinets and drag chains, for example.
Basic requirement for the set-up of a single-cable solution between a servomotor and a servo controller is a
digital encoder that is specifically developed for this type of communication. The encoder is permanently
connected to the servomotor. For this reason, the manufacturer of the servomotor needs to provide its
customers with an end-to-end solution: Not only the servomotor needs to be equipped with a rotary encoder,
the controller needs to be adapted to the concept of a single-cable solution as well — as communication is
always established between two units. Hengstler offers special rotary encoders in its new product range that
use the ACUROlink interface, an open protocol, creating the ideal symbiosis to meet the high requirements
of single-cable solutions. “The ACUROlink interface was specifically designed to support two- and
four-wire applications,” explains Johann Bücher, Director of Encoder Strategy at Hengstler.
Helukabel’s challenge as cable manufacturer consists in securing a sustainably stable and fail-safe data
transmission. The two-cable solution uses up to three shields to protect the signal pairs from the disruptive
influences of the power cores in the traditional set-up. In addition, it is generally recommended that the
maximum possible distance between the servo and encoder cables is considered when laying the cables.
However, the feedback cores of a hybrid cable are routed into the servo cable directly. It reduces the
physical distance almost entirely and the requirements for EMC shielding attain a new quality level.
Whether the motor rotates or not is based on the signal’s quality that arrives at the receiver. The fewer
external disruptions that penetrate the signal element, the better the data quality is that arrives at the
receiver. The shielding of the data cores accounts for the protection from EMC emissions. The longer the
shielding remains intact while in use, the longer the protection will be maintained. The service life of the shielding can be nearly “infinite” if the hybrid cable is installed in a stationary application. The service life
only starts to shorten when mechanical load is placed on the cable in a dynamic application, such as a drag
The reliability and fail-safe quality of data transmission is a product of the individual disruptions, which
means that the longer a cable, the more critical the application. Hengstler’s research and development team
tested two- and four-wire versions of their encoder using a 100-m cable in each case under load. Based on
the acquired practical experience, these tests provide adequate assurance that the cables can withstand
even future challenges arising in increasingly complex applications. It is now possible to have high-performance multi-turn control thanks to the Hengstler AD37 rotary encoder. It sets new standards with
a 10-Mbaud transfer speed and data exchange rates reaching 32 kHz, while combined with the transfer of
entire positioning data providing an extremely high electromagnetic compatibility (EMC). In addition, the data protocol of the electrical interface fulfils the requirements of SIL3 in accordance with IEC 61508 and Cat.
3PLe, in compliance with EN ISO 13489, while the AD37 rotary encoder itself and the IP core in the control
can meet all requirements from non-SIL, SIL1, SIL2 to SIL3, depending on the customer’s specific
The loads that cables are subjected to in the field are growing as the market requirements of the
manufacturers of machinery and plants increase. Machine designs are smaller than ever before, as the axes
in the field of traditional machine tools become more dynamic and faster. These developments reduce the
available space to a minimum, and the bending radii of the drag chains become tighter. Cables and wires
need to be tailored to the specific application to provide high stability in drag chain applications
while maintaining competitive prices, which means that the design team at Helukabel GmbH selects different
designs for specific requirements. They depend on parameters such as movement distance, minimum
bending radius, speed, acceleration and minimum number of cycles. In addition to the design, the choice of
materials also plays a decisive role. They primarily depend on external factors such as ambient temperatures
and/or the required durability of the materials (aggressive coolants and lubricants, for example). In addition,
there are other properties that need to be taken into consideration such as flame-resistance and
The different performance requirements of the motors translate in different cross-sections for the supply
cables. The larger the cross-section, the thicker the cable. It is necessary that the tests include different
bending radii in order to draw conclusions for all other cross-sections, as it is not enough to test one
cross-section and cable construction in a drag chain. The Helukabel Group tests cables on nine different
testing systems that can differentiate between the lengths and the acceleration and speed parameters when
testing. These tests are very intricate and require constant monitoring and supervision. However, they are
also necessary to ensure the quality and stability of data transmission.
Helukabel was the first cable manufacturer who confirmed the durability of its hybrid cables with a system
test involving more than five million cycles. In the meantime, several hundreds of kilometers of these hybrid
cables have been installed and are in use in different applications around the world.
“We are the cable manufacturer with the greatest advantage in terms of experience. We invested a great
deal of time in this solution from a very early stage and have gathered vast experience in the field to be able
to develop working, reliable solutions for drive specialists. Our Topserv Hybrid has become established as
the standard for the two-wire solution,” says Thomas Pikkemaat, Product Manager for Drive Technology at