Until now, servomotors and inverters have always been connected with two cables: one cable for the power supply and one for the encoder signal, which provides information about the speed and position of the motor, for example. However, more and more drive manufacturers are offering servomotors with single-cable solutions. With so-called hybrid cables, the power supply and data transmission run via a single cable by integrating the encoder cable into the servo cable. This eliminates the need for cabling with a separate measuring system cable for the encoder.

Another advantage of hybrid cables is the simple and shorter assembly time compared to a two-cable solution. Machines can be installed and commissioned more quickly. In addition, the installation space in the energy chain is reduced so that a smaller and more cost-effective model can be used. Last but not least, the connection to the controller or motor is also more compact, meaning that the customer only needs one plug for the entire system.

Secure data transmission

The 'Chainflex' hybrid cables are equipped with an integrated bus element. They were developed for highly dynamic applications, for example in processing machines and machine tools.

© Igus

When combining the servo and encoder cables into a hybrid cable, it is important to realize the necessary data transmission properties and to ensure the interference-free function of the cable for many millions of double strokes. Reliable transmission of the bus signals over the maximum cable length with many movement cycles places special demands on the insulation materials used for the bus cores. On the one hand, the material must meet the high mechanical demands of the movement, and on the other hand, the electrical properties required for data transmission must be maintained 100%. In this segment, Igus can draw on the material experience gained from many tests. In addition, elements with shielding also come into play here. The shield protects the data pair from internal and external interference, which is extremely important for an extremely compressed cable.

In the case of hybrid cables from Igus, for example, the braided shielding ensures a long service life. The company uses a particularly narrow shield. As the braiding runs at a flat angle with high optical coverage, the forces acting on the shield wires are not too great and durability is increased. The shield structure is specially adapted depending on the type of cable. The fixed design gives the entire cable construction the necessary freedom of movement. The short lay length of the stranding provides additional safety for all 'Chainflex' cables. Particularly important here is the additional support of the stranding system by so-called gusset-filling extruded inner and outer sheaths, which completely fill the spaces between the cores with the sheath material. This prevents the stranding from untwisting.

Hybrid cables in the energy chain

In static applications, the shielding can withstand almost unlimited forces. However, if the cable is set in motion within an energy chain, for example in machine tools or handling systems, the cable is subjected to new stresses. Igus tests the complete range of cables in its in-house test laboratory in motion under real conditions. In addition to the mechanical tests in the energy chain, the transmission properties of the bus systems are analyzed here. The bus systems are measured separately and checked to ensure that data transmission is maintained over the entire test period, which lasts several million double strokes.

In the practical test

The fact that the hybrid cables from Igus work, reduce assembly time and save costs is demonstrated by their use at IMA Klessmann: up to 50 servo axes in a confined space, high dynamics, high expectations in terms of service life and small bending radii were the requirements that the hybrid cables had to meet in a new automatic drilling machine. The 'Chainflex' single-cable technology combines the power and feedback system in the servo cable. This significantly reduced the amount of material and commissioning required, but it presented those responsible at IMA Klessmann with a real challenge in the first step. Depending on the position of the control cabinet - which is specified by the customer - the company installs up to 4 km of cables. A tailor-made test program ensured that the single-cable technology used would function reliably: Here, the hybrid cables were tested and inspected with over four million strokes in the IMA-specific bending radii.

Author:
Andreas Muckes is Head of Product Management 'Chainflex' cables at Igus in Cologne.