Cables and wires can be found wherever moving machine and system parts are supplied with energy and information in a fail-safe manner. Cables are like umbilical cords: they supply everything that is needed for the connected systems. In addition to energy and data, this can also include media such as air or liquids. While various functional elements are integrated into round or flat cables to save space in hybrid cables, densely packed drag chains or hose packages installed on robots have established themselves as a permanent fixture for routing highly dynamic and continuously moving cables.

The stressed cables have to function in less and less space; packing density and miniaturization - with a growing range of functions - set the pace here. The cables have to withstand ever higher accelerations or speeds, abrupt movements and vibrations, and neither millions of bending cycles nor violent torsion can harm them. They often have to withstand harsh conditions, ranging from extreme temperatures to welding splashes. If high-performance power cables and sensitive data cables are laid next to each other, electromagnetic interference must also be ruled out. It would be grossly negligent to use simple standard cables here.
For a range of drag chain or robot applications, users can fall back on special cable portfolios such as the 'Kaweflex' modular system from TKD. However, the demand for individual solutions is growing rapidly.

Customized work is very popular

With customized special cables for highly dynamic applications, "all the stops are pulled out", so to speak. Using a variety of parameters - such as conductor selection, cable structure and stranding, shielding, insulation and jacket materials - designers can individually and precisely adjust the fitness of a cable. Parameters such as bending radii, flex performance, torsional strength, thermal or chemical resistance or EMC safety can be implemented in a targeted manner.
If, for example, very long travel distances (>50 m) are involved in drag chain applications, the cables are often designed with stranded bundles in order to guarantee optimum stability. Highly stranded special conductors provide the necessary flex properties and prevent wire breaks - and thus the often costly failure of the cable systems. If the permanently moving cables are also exposed to electromagnetic interference fields, precisely designed shielding solutions are used as protective measures. Factors that influence the efficiency of the selected shielding include the shield construction (e.g. as a braid or wrap), the optical coverage, the braiding angle, the number of wires and, if necessary, combinations of braiding and conductive foils.

An essential prerequisite for the longevity of motion-stressed cables is their slenderness: the lower the weight and diameter, the better the agility of the respective cable. With the right 'diet program' - such as identifying the right strand types and copper qualities or determining the optimum stranding structure - alternative designs are possible that reduce the space required by 30 to 40 % compared to conventional cables. The example of a drag chain cable from the TKD range, which has been slimmed down by a third in terms of weight and diameter compared to its predecessor model, shows how this approach works in practice. Among other things, the classic inner sheath has been replaced by a high-strength banding that is significantly thinner - but with the same performance characteristics as before. When it comes to design, it is important to take a closer look at every detail, no matter how small: Sometimes a simple measure such as omitting a filler is enough to 'slim down' the last millimeter of a cable and meet the requirements profile.

Range of special cables

Designers can precisely influence the fitness of their cables using a variety of parameters - such as conductor selection, cable structure and stranding, shielding, insulation and sheath materials. The special cables are often available as plug & play components.

© TKD

An alternative strategic approach to targeted streamlining is the design of customized hybrid cables based on the 'all-in-one' principle. Here, a large number of different supply and control cables - with appropriate shielding technology - are integrated into a single round cable to save space. With compact hybrid cables, it is important to minimize the friction of the individual components. This is achieved, for example, by the arrangement of the stranding elements and low-adhesion insulation surfaces. Additional lubricating layers can be integrated into the cable to prevent the individual structural elements - especially the cores and sheath - from snagging. Through the targeted use of fillers, individual components of different sizes can be stranded to form a harmonious round cable - all tricks to achieve the desired cable performance. The advantages of miniaturized hybrid cables are obvious: not only do they take up less space, they also reduce assembly work.

Under the 'Kaweflex' brand umbrella, TKD offers a densely populated range of special cables that are specifically designed for highly dynamic applications. The predecessors of this series were the world's first drag chain cables in which the polyester elastomer material 'Pelon' was used specifically as core insulation. This is now standard.
The Kaweflex family includes standardized special cables that are suitable for accelerations of up to 100 m/s², travel distances of up to 400 m and millions of bending cycles. The portfolio starts with robust PVC cables. TPE compounds are also in demand: TPE sheaths contain additives that form the final profile (e.g. hardness, chemical resistance, flammability and abrasion resistance). Polyurethane (PUR) is the favorite material for mechanically stressed cables, as PUR sheaths offer flexibility with great toughness - and that over a wide temperature range. PUR is also ideal for mechanical engineering due to its resistance to coolants, greases and lubricants. Possible special forms include cross-linked insulation materials that offer protection against welding spatter.

Top class robot cable

Sven Seibert is Head of Product Management at TKD Kabel in Nettetal.

© TKD

Robotic cables, which are designed for performance and durability in extreme movement sequences in three-dimensional space, are the premier class of permanently moving cables. The key requirement here is maximum torsional strength. For this segment, TKD has developed special 3D assemblies as part of the Kaweflex portfolio, which are characterized by special kinematic properties - i.e. maximum dynamics in free movements across all three axes with high bending and torsion requirements - and high agility. The area of application for the low-adhesion robot cables ranges from pick & place and handling robots to automated production systems. Torsion angles of up to +360° per meter of cable length (+180 °/m for shielded versions) are permissible for 3D assemblies. The arrangement of the individual cable elements, trimmed to minimize internal friction, and the use of sliding windings ensure agility and stability.