In this forum, Motion System Design editors speak with industry experts about the latest trends in cable design and cable carrier systems for today's motion-centric automation environment.
HOW DO CABLE AND CARRIERS TRANSLATE TO PRODUCTIVITY?
Rick • Lapp: Nobody wants downtime. So performance is extremely important and with ever-evolving automation technology, smaller is usually better. Advancements in electronic components mean less copper in confined areas, which translates to smaller bend radiuses. Speed can be an issue as well, since machines are now producing goods faster and more efficiently. This all leads to smaller cables, being able to flex faster and in tighter cable tracks.
Brian • Gore: Selecting the wrong cables or deciding not to follow the track manufacturer's design criteria could be disastrous. Cables that fail in the field cause expensive downtime when they need to be replaced. Even worse, failing cables can cause sporadic manufacturing problems from intermittent signals.
Don • igus: Selecting cables and carriers should be considered two separate tasks, but keep in mind that one component directly affects the other. Cable carriers are one of many options to choose from when deciding how to control and manage cables. Carriers are an essential line of defense against cable damage and in most cases can extend the service life of cables and hoses.
Andy • SAB: Today's cables are the nerve tracts in highly developed automation systems. Cables and their corresponding tracks can only function as a successful system if they're carefully chosen. Factors like conductors made of extra fine ETP copper wires, TPE insulation, special shielding, and PUR sheathing increase service life as much as 100 times compared with standard materials.
Ned • C&M: Selecting the correct cable for installation in a cable carrier can directly affect the success of the entire system. The right cable can aid in the flawless operation of an automated system and help achieve a full schedule of uninterrupted operating runs between maintenance cycles. Using an incorrect cable can lead to direct as well as indirect system performance problems.
Mark • A&A: Cable and hose carriers with their clean and fairly simple designs often make them a superior choice over alternatives like festoons, reels, or pantographs, especially in applications with multiple conduits and high velocities and duty cycles. When selecting a carrier, it's critical to consider cost, specialized and overall performance parameters, and delivery requirements up front.
Howard • Cicoil: To maximize productivity, cabling must squeeze into ever smaller spaces, while shedding weight and the associated inertia that otherwise bogs down everything trying to move. Automated equipment is expected to achieve 100% accuracy and uptime, and cabling is often the key to success.
Larry • KabelSchlepp: Cables used in motion applications are subject to many more stresses than cables used in static applications. It's imperative that cables and cable carriers are properly selected to accommodate variables such as minimum cable bending radius, speed and acceleration, operational size limitations, and resistance to environmental conditions.
WHAT ARE SOME CHALLENGES WHEN SPECIFYING CABLE AND CABLE CARRIERS?
Rick • Lapp: Typically, cable is one of the last products specified, but it could be one of the most important. A machine that is not running due to a cable failure is eating away at profits. Knowing the difference between a continuous flexing cable and a flexible cable is a good starting point. A cable that feels very flexible and “noodle like” is not necessarily a continuous flex cable. Design issues such as lay length of the conductors, finer copper stranding, slipping agents so conductors can move freely, and jacketing processes must also be considered.
Brian • Gore: Demanding space constraints, strict cost targets, and changing electrical requirements drive designers in multiple directions. The best approach is to design systems with large bend radii with ample space available in cable tracks for future cable requirements. Unfortunately, system designers are often unable to add to the height or length of a machine once a demanding footprint has been established. We have frequent discussions with designers who are given a cable budget based on less demanding mechanical requirements, driving their program managers to choose between reliability and design concept.
Don • igus: Specifying cables and cable carriers begins with a complete understanding of the application. Some crucial questions that need to be answered include: How many cycles will the machine need to perform per day? What are the space requirements for the cables and cable management? What is the cost and risk of failure from either component? How long do cables and carriers need to perform without failure? Also, proper installation should be considered just as important as the selection process.
Andy • SAB: One of the main challenges in choosing the right cable type and corresponding track is matching the cable construction with the demands of the application. In extreme applications, it's absolutely necessary for an onsite inspection. Will the cables be exposed to high temperatures or chemicals? What are the electrical requirements? Will the application include continuous bending stress for multi-shift operation? Often there are special requirements and only a special construction will provide the best solution.
Ned • C&M: Specifying the correct cable for a dynamic cable track installation is often one of the most challenging portions of system design. When you take into account everything that must be considered for a superior cable track installation, such as application environment, bend radius, cycle speed, number of cycles, material availability, and electrical performance, it becomes apparent that there's more to it than “open the catalog and choose.” Often, the best approach is to consult a custom cable manufacturer that specializes in high performance cable products.
Mark • A&A: Carriers need to be selected to perform specific, often demanding functions, yet also handle basic application requirements. These requirements for specialty operation make stock carriers a poor choice. On the other hand, custom carriers designed for specific applications can be expensive and require longer lead times. Sometimes specialty carriers, well suited for certain aspects of an application, such as quiet operation, fail or under perform because they can't handle overall requirements.
Howard • Cicoil: The first challenge comes from the fact that most cabling is made up of round wire, and the engineer is usually forced to choose standard catalog cables, as custom cables have long lead times and are often too expensive. A second challenge comes from the high speed, repetitive motion required in most automation equipment. Most cables are not rated for flex cycles, or bend radius, so engineers are left to their own devices to specify cabling. The result is often premature cable failures and high warranty costs. Selecting cable that will last through dynamic motion cycles is a critical challenge for automation engineers. Flexible flat cables take up less space than round cables, operate with smaller bend radiuses, and are rated for millions of flexing cycles.
Larry • KabelSchlepp: When specifying high-flex cables and cable carrier systems, an engineer must consider many factors, such as weight, speed, acceleration, and the environment. Will the carrier system be able to support the load of cables placed inside it? Will it be able to hold up to extreme accelerations and high speeds? What environmental elements will be present? Solutions include enclosed tube carriers for protection, steel carriers for resistance to heat, cold, and UV, and stainless steel and polymer carriers for corrosion.
DESCRIBE THE IMPACT NEW MATERIALS ARE LIKELY TO HAVE.
Rick • Lapp: Rather than struggling to meet a new footprint with old technology, new materials combine to make smaller OD cables, with shield, that fit in tighter areas and flex faster in keeping with today's automation needs.
Brian • Gore: One area where new materials will drive change is in flat cables. The number of standard components employing flat cable continues to grow. As a result, designers have more options than ever with excellent EMI protection and lifetime exceeding 20 million cycles on a 50 mm bend radius. They also have one less constraint to worry about because flat cable maximizes the number of conductors that fit in a cable track without overfilling it.
Andy • SAB: New materials that are better shielded protect cables from external interference while reducing the risk of signal disturbances transmitted to the outside. Both tasks are important because signal errors may damage machines just as easily as external equipment. High-tech developments like carbon or special copper shields, used with foils and non-woven tapes, provide the added benefit of support.
Ned • C&M: The trend in cable manufacturing is toward smaller, lighter, faster, longer life, and lower cost. By achieving tighter bends, for example, cable will fit in smaller cable tracks, reducing the size and weight of the entire system.
Howard • Cicoil: Extruded silicone flat cables can be used without cable carriers in many applications, saving space, cost, and weight. This gives designers the opportunity to design servo axes that are more responsive and dynamic, as there is less inertia added from cable carriers. Custom silicone flat cables can be designed with individually shielded conductors, reducing EMI, crosstalk noise, and interference, optimizing electrical performance.
Larry • KabelSchlepp: The availability of stronger yet lighter weight materials that function in a wider range of environments has resulted in several new generation cable and hose carrier systems that far outperform systems based on older technology. Carriers made from new polymers, for instance, resist extreme temperatures and hot chips, exhibit less friction and wear in gliding applications, and self-support over greater distances.
HOW WILL CABLE AND CABLE CARRIERS LOOK IN THE FUTURE?
Rick • Lapp: On the cable side, we will most likely see more composite construction, combining fiber with power or fiber with control or all three together. The direction is toward products that flex faster, longer, and tighter, and last for 20 million or more cycles.
Don • igus: Construction materials will certainly change, influenced in part by the growing shift towards environmentally friendly products. In the future, perhaps cable and cable carriers will be completely made of recyclable and reusable materials that are as strong and cost effective as current materials. The future also promises more reliable wireless solutions for power and data transmission.
Andy • SAB: Systems consisting of cable track and cable require the combined know-how of two manufacturers. When a defect or failure occurs, the question often arises: Who is responsible? The future will address this with something called “direct cable entry” - a system based on axially movable cables. This arrangement offers freedom of motion in all directions and is suitable for short and quick linear movements. It also reduces noise, operating silently, and is suitable for clean room environments.
Ned • C&M: It's conceivable that the cable track and flex cable combination of the future bares no resemblance to what is in use today. Considering the current research in nanotechnology, superconductors, and polymeric composites, one might visualize a sort of self supported, laminated or layer deposited ribbon, subject to no flex fatigue, and capable of carrying high current in a tiny package.
Mark • A&A: Increasing demands for productivity will further increase demands for carriers that achieve higher speeds and longer travels. While most of today's long travel carrier systems are plastic and designed to glide in a guide trough, extreme tow forces and the wear inherent to this kind of operation will make this solution less feasible. Systems that eliminate troughs, in favor of rails or lightweight moving carriage systems, thereby reducing tow force and motor requirements, will continue to evolve and take their place.
Howard • Cicoil: In the future, cables will become an integral part of the machines in which they are employed, in much the same way that nerves and blood vessels are part of the human body. They will seamlessly attach to fixed and moving structural components, carrying electrical signals, light signals, pneumatics, and fluids exactly where they are needed.
Larry • KabelSchlepp: As materials and manufacturing technologies improve, you'll see an increase in new and exotic products that solve very specific design challenges. More efficient tools, such as cheaper yet more capable rapid prototyping devices like 3D printers, will produce high-tolerance “usable” parts that can be installed in low-volume applications. Preproduction testing using solid modeling and finite element analysis tools will also contribute to better designs.
Meet the experts
KabelSchlepp America Inc.
SAB North America
W.L. Gore & Associates Inc.