25 January 2013
Automated systems and robotics place tough demands on the dynamic cables that provide them with power and control services.Here, Giuseppe Di Lorenzo of Nexans takes a look at some of the challenges faced by the company's
Automation cables have a very different life from static cables, since they are expected to deliver high performance and total reliability across a broad spectrum of chain, bus, sensor, robotic and control applications - even under extreme dynamic loads experienced at high operating speeds.
A key challenge that faces developers of automation cables is the demand for an ever smaller bending radius to provide the high level of flexibility required by modern installations.Where a bending radius of 7 times the cable diameter was once considered normal, we are now aiming for a bending radius as small as 4 times.
The construction of the cable has a significant impact on the bending radius that can be achieved. This includes conductors, fillers, insulation and jacketing. As well as paying specific attention to the construction, a general reduction in diameter of the cable is required.
Although the design and engineering of the cable are important, the key to success is in really close attention to consistent process control to maintain the production of the cable within tightly controlled parameters.
Need for speed To achieve the desired high levels of productivity and throughput, we are now seeing automated equipment moving faster and faster. For example, robotic spot-welding machines routinely achieve repetition rates of several hundred welds per minute. To cope with this, automation cables not only need to be lighter in weight, to keep their inertia as low as possible, they must resist the high stresses due to acceleration and ensure a long fatigue life under repeated bending and stretching cycles - as well as torsional cycling in the case of 3-axis machinery.
To ensure that its automated cables meet this 'need for speed', Nexans is making ongoing investments in its Automation Application Centre, part of the Nexans Research Centre in Nuremburg. This facility enables cables to be exposed to dynamic operating loads that simulate in-service, conditions, thus ensuring that they offer the combination of bending, tension and torsional strength needed for their intended application.
As an example of how requirements are becoming more demanding, we are now carrying out acceleration testing at 50ms2, 10 times more than the previous level of 5ms2.
At the same time, we now expect cables to achieve a cycle life of 20 million cycles - double the 10 million cycles that used to be accepted as an industry standard.
Environmental considerations When you consider that automated systems may be installed anywhere in the world, then the behaviour of cables in extreme environmental conditions becomes an important consideration.We are now seeing cables specified for both high temperatures (90Â°C) as well as low temperatures (down to -40Â°C). In fact, one of the most demanding applications for automation cables is found not in the factory, but in offshore wind farms.
It is important that cable conductor and insulation materials provide the fire and heat resistance demanded for safety and performance, as well as offering resistance to attack by oils and other chemicals. Important developments in material technologies are being made in this area such as TPM (Thermoplastic Modified) insulation and flame retardant PUR Medoxprotect-S jacket material.
Hybrid cables A key trend in the automation industry is towards hybrid cables that combine power, control and data cores within a single cable.
They are well suited to meet the needs of decentralised control systems as well as making installation easier and more elegant.
Engineered solutions Nexans offers a wide scope of cable products for automation under its Motionline brand that conform to all major international safety standards, such as German (VDE), Canadian (CSA), American (ANSI), Chinese (CCC) and UL worldwide. However, the catalogue range is sometimes only a starting point, since we frequently have to design and engineer a special cable to deliver the vital combination of high-performance, reliability and long life required for a specific application. This is especially true for miniaturised installations where a cable often needs to tailor made to fit the available space envelope.