Motion control without the racket

Stephan Achs
Executive Vice President
KabelSchlepp America
Milwaukee, Wis.

Edited by Kenneth Korane

Cable carriers were invented to guide and control cables and hoses feeding to the moving heads of machine tools. Initial designs were in steel and crude by today's standards, but they nevertheless performed the intended job.

During the next four decades, plastic-chain cable carriers were introduced to the market. While steel chains still have a place in harsh and difficult environments, plastic chains have taken over much of the traditional market. Cable-carrier suppliers have also found many new and diverse markets where the dynamic control of cables and hose is vital for safe and efficient machine operation.

The basic design of cable carriers has not changed since the early days of steel drag chains. Almost all cable carriers form a chain made of a series of linked plates held together by link pins. Two exceptions are Conduflex from KabelSchlepp and Stabiflex from Hennig, which use a system much like convoluted hose. While reasonably successful in limited applications, these products have not found volume acceptance by product designers. Consequently, commercially accepted plastic linked-chain assemblies, which are relatively easy to manufacture and install, have been increasingly used in industrial environments.

In operation, however, conventional cable carriers generate noise. This was once a non-issue, but in many industry sectors general background noise is becoming a problem. For instance, noise reduction is now an essential requirement of the Machinery Safety Directive. Innovative cable-carrier manufacturers are attacking this problem head-on. Here's how.

Reducing noise
Cable carriers are designed to form a prescribed radius that conforms to the recommended minimum-bend radii of cables or hose. Each chain link has a specific pitch length. Pins inserted in mating holes join the links. Manufacturers rely on various designs between pins and links to restrict the chain radius, such that the continuous chain forms a loop that does not constrict the cables or hoses.

When cable carriers move, one or more of the following can generate noise:

• Pins locking on the link radius stops (commonly referred to as stop-dogs).
• When rectangular-shape links travel around a radius, the corners of adjacent links impact and generate noise. This is termed a polygon effect.
• Moving parts contacting each other and creating a rattling noise.
• Uneven gliding surfaces on long cable carriers.

Noise levels depend on various factors, including the running-surface material, vibration effects, and operating speed. Without doubt operating speed, and the noise created by the polygon effect resonating on the running surface and within the chain itself are the biggest noise contributors. With today's equipment often requiring higher speeds and longer travels, eliminating cable-carrier noise is a vital component in quieting the overall machine.

Various companies have tried to design quiet or dampened versions of standard linked chain, which they claim reduces noise. For example, one plastic-carrier supplier recently introduced a product based on its standard chain design. The manufacturer claims that a link braking system and dampened contact points eliminate some noise caused by pins locking on the links and parts banging together.

KabelSchlepp has also adapted its standard M Series chain to incorporate softer link materials in several key locations and damping components on the chain band it-self. This significantly reduces link noise as well as that from contact between the chain and running surface.

However, both these examples only reduce generated noise to a degree, as they are still based on linked-chain designs. To create an almost silent chain, irrespective of speed, the design must:

• Eliminate fixed-pitch links.
• Eliminate pins that connect the chain links.
• Eliminate the polygon effect.
• Eliminate impact between moving parts.
• Have a smooth surface on the top and bottom of the bands to allow chains to glide over each other.

Obviously, this requires revolutionary new thinking. In 1994, KabelSchlepp patented a new type of cable carrier based on an extruded plastic band, cut and machined to form a one-piece cable carrier. In 1997 the company purchased from W. L. Gore the rights to a product known as PROfile which met all the above criteria for a silent chain. However, the product required serious redesign to eliminate operational difficulties and produce a commercially acceptable chain. Based on these efforts, KabelSchlepp recently launched a new-generation product, the Quantum.

Revolutionary design
To the untrained eye Quantum looks like a conventional plastic chain, but it fundamentally differs. Instead of linked chain forming the two side bands, two extruded, specially shaped profiles manufactured with cuts and slots allow uniform, fluid and controlled bending in a fixed radius. While the Quantum functions exactly like conventional linked chains, these extruded, shaped-plastic profiles incorporate two high-strength steel wires running the entire length. They give the bands strength and longevity.

The result is a cable carrier which can replace existing carriers, and that:

• Is half the weight of conventional linked carriers, which permits higher speeds and accelerations.
• Has no polygon effect and does not vibrate as it moves.
• Gives longer life, due to steel-wire construction and no relative moving parts.
• Is more suitable for clean rooms because there are no rubbing parts creating debris.
• The chain is manufactured in polypropylene, not polyamide as used in conventional chains. This permits use in harsh environments and exposure to coolants, lubricants, and ultra-violet radiation.
• Unique flexibility permits limited twisting and off-center mounting not permitted with linked chain.

According to Herbert Wehler, KabelSchlepp's global technical director, this development is even more fundamental than the change from steel chains to plastic over two decades ago. Compared with other carriers on the market, the new product incorporates a revolutionary design that holds many advantages for today's modern equipment designers.

At present no regulatory body has established specifications for measuring cable-carrier noise, though the likelihood of future regulation is high. In the meantime, noise-level claims by various manufacturers need clear definition as to factors such as operating speed. That is because measuring cable-carrier noise is subjective, and depends on operating conditions, speed, and even the machine on which the carrier is installed. Beware of unsubstantiated claims by any manufacturer.

Over 90% of cable carriers used in industrial applications travel less than 2 m. The best way for design engineers to establish the merits of a particular cable carrier is to obtain samples and compare them side by side on their machines. Experts recommend that engineers measure the effectiveness of various carriers to effect an intelligent design decision.