slim, built tough
Tailor-made cables for rugged performance
Slim is in - not only at the beach or the fitness
club, but also in high-flex cables put to work in robotics and industrial
Putting cables "on diet" (reducing
their overall diameter) is one of the most common challenges to design
engineers involved in building tailor-made cables. A significant portion
of custom-built cables is specifically designed for applications in
robots, where space is extremely limited and cables often must perform in
tight cable tracks or in a confined working environment.
What's in it for the user? Tailor-made power and
signal cables with smaller diameters than conventional cabling - yet
sport identical, or even superior, electrical and mechanical properties -
means less space, less weight, more flexibility, longer life and
ultimately, improved cost performance.
To endure harsh industrial environments,
high-flex automation cables need to be capable of withstanding a wide
spectrum of stresses. The challenges range from millions of bending
cycles at high speeds in tight cable tracks, to continuous twisting and
severe mechanical stresses. Often, cables in robots have to perform in
narrow vaults or crammed housings. Space is forever at a premium. And
then, there are environmental factors to counter: the presence of high
temperatures, wet or moist conditions, chemical contaminants, humidity,
etc. The first of these brings to mind an important consideration
applicable to welding robots that are perhaps among the most ubiquitous
of robots at work in industry.
The harsh landscape and severe challenges of
industrial applications have pushed cable manufacturers to develop a host
of solutions to combat heat and high-flex stress. To easily follow the
3-D movements of industrial robots, tailor-made automation cables are
engineered for superior twisting performance, coping with ±360° torsion
stress. Besides a high resistance to bending stress, these cables can
easily handle the forces caused by high-speed acceleration in robotics,
For example, welding robots apply more than 40 spot-welds in a 90 second
Cables on welding robots must also be able to
withstand flying sparks and hot welding splatter. This imposes two major
design constraints: welding beads may not create holes in the exterior
jacketing; and the cable material, as well as the gases generated in the
welding operation, may not ignite. Special jacketing material is used to
meet these requirements.
The "diet strategy"
Every tailor-made cable is designed, manufactured and tested to match
each customer's specifications. For creating the ideal solution, our
engineers have access to an extensive array of choices: design options
for the internal architecture and subassembly of the conductors
(different stranding and layer designs), internal fillers, unique
shielding designs and a variety of jacketing materials. A major part of
the design assessment is a thorough check of miniaturization
possibilities for any given cable application. High-performance,
high-strength materials allow for optimal downsizing. The key to
designing a superior product for such applications is to slim down the
cable, which either allows for a tighter bending radius or increases the
bend radius-to-cable diameter ratio. At elocab,
we build high-flex, diameter-reduced cables that can withstand a bending
radius as small as five times the outside diameter, designed for a life
span of up to 20 million bending cycles or 20,000 operating hours.
"diet strategy" applied by elocab
consists of hybrid solutions. Three, five or more single cables are
integrated into a new hybrid cable. The advantages of compact hybrid
designs are instantly recognized. They require less space and are easier
to install than conventional cabling.
Design engineers are able to substantially reduce
the diameter of tailor-made automation cables - by 30 to 40 per cent -
compared to standard cables, while offering identical, if not better,
electrical properties. Last but not least, these slim and trim cables
come with a bending radius reduced by up to 70 per cent.
EMI-shielding a major consideration
With the appropriate EMI-shielding, hybrid cables can include a complex
set of power and control cables. To ensure that the cables are protected
against any electric or electromagnetic interference, elocab's
engineers weigh a full range of shielding options from the use of served
wire shields to foil, and braided shields. Extremely difficult problems
are solved by multi-layer designs, which may combine the same or
different shielding methods.
"Good shielding is the answer to suppressing
the development and transmission of any undesired signals," says
electrical engineer Norm Frid, head of elocab's product design department. The choice of
material, the diameter of the shielding conductor, the angle of pitch and
the number of strands are all factors that determine the density and the
specific frequency resistance of a shield. For example, highpermeability alloys (such as Mu-metal), used as a
wrapped foil shield, can absorb low-frequency magnetic fields.
Classic EMI "problem sectors", such as machine building,
measurement and control systems as well as communications and
high-frequency technologies are among the prime users of individually
shielded, hybrid cables.
Given their application-specific design, tailor-made
cables can combine "contrary" properties that usually are not
found in a single standard cable. Despite providing optimal shielding
characteristics, they can be designed to offer a high level of
flexibility and extensive durability. Perfectly shielded - and slim -
tailor-made robotics cables are a good example.
A manufacturer's experience
and downtime are just too costly in today's competitive business
environment marked by ever-increasing levels of automated production
processes. To confidently cope with these challenges, manufacturers and
users of robotic equipment rely increasingly on the dependability of
tailor-made cables in punishing work environments.
An important user of trim automation cables made
by elocab is robotics manufacturer Cloos Schweisstechnik GmbH,
a worldwide leader in welding technology, with headquarters in Germany
and production operations in North America. The company, which supplies
robots, robot controls, welding units and peripheral equipment such as
positioners and safety devices, has relied on elocab's
expertise in this area for over ten years.
Working with a high repeatability of ±0.1 mm, the
company's high-precision welding robots are widely used in production of
truck axles, harvesters, heavy-duty construction vehicles, and trains.
Operating at speeds of up to 20 ft/mm and processing a maximum of 55 lb.
of coldwelding wire per hour, the stability and
efficiency offered by Cloos' state-of- the-art
tandem-path welding systems are among the highest in the robotics
tailor-made elocab's cables are on duty for Cloos' highly successful series of 6-axes ROMAT robots
whose industrial arms are designed as rotating joints. "From the start,
it was clear that we needed cables that could withstand the severe
torsion stress caused by our new robot," explains Sieghard Thomas, the company's manager of purchasing
and quality management.
Two hybrid-round cables, each of which combined six single cables, were
installed on the ROMAT series. These tailor-made cables supply the
power and signal information for the AC servo drives controlling the
robot's precise movements. Both the power and resolver hybrid cable run
up to 130 ft, creating the "bulletproof" connection between the
switchboard cabinet and the robot. Rated for more than 25 million bending
cycles, both hybrid cables require little maintenance.
An interesting feature of the hybrid power cable
is the integration of cables with different cross-sections. Three thicker
cables powering the strong motors for axes 1-3 are combined with three
thinner power cables for the lighter manual axes 4-6. Using special
fillers, this "uneven" cable has been transformed into an
evenly balanced, round cable.
In the ROMAT base, which can handle
rotation of up to ±440°, both compact hybrid cables are split and
fed to the AC servo drives as single resolver and power cables. Here too,
in the "bowels" of the robot, the cables are designed for
miniaturization and extreme flexibility. To deal with the exceptionally
tight spacing in the housing and the traditionally critical passageways
from one robot arm to another, the wire gauges of the power cables were
slimmed down from AWG 14/AWG 16 respectively to AWG 16/AWG 18.
Using a bundled cable design ensures that all
conductors are identical in length, thus making them equally strong and
resistant to mechanical stress caused by twisting and flexing. Also, the
jacketing is tailor-made to cope with the specific operational challenges
in the ROMAT robot. Since the cables automatically make contact
with metal while being led through the robot's tight housing, an
especially tough TPE (thermo-plastic elastomer) jacketing was selected
for its proven abrasion-resistant qualities.
"Ever since we started relying on these
cables for our most rigorous applications, we have rarely experienced
failures due to cable breaks, which is a great benefit for our
customer," says Sieghard Thomas of Cloos, affirming that "slim and sinewy" has
its place in the world of automation cables as well.