Image
FA0914-2
Energy and signal cables up to 14 metres in
length are guided in the hoist frame by guide rollers, and move every time the
mast is raised or lowered. (source: igus GmbH)
The design-engineers for the Still EK-X vertical order picker found the
answer: they used a chainflex cable that was originally developed for use in
energy chains. Both igus and Still determined from various tests that this
cable is not only ideal for applications in energy chains, but will also
perform well with guide rollers.
Orange
is the colour of choice for many operators of logistics and distribution
centers, warehouses, and order picking plants, because they are using
forklifts, tugs, and order picking equipment made by Still. The company is
headquartered in Hamburg and is part of the Kion Group, which in turn is the
world's number two forklift manufacturer with turnover of approx. EUR 4.5
billion (2013).
The vertical order
pickers from the EK-X series are particularly impressive systems Their job is
to travel to specific pallets in the narrow aisles of a high-bay warehouse from
where the driver picks individual packages. The order pickers reach gripping
heights of up to twelve metres. The modular design principle allows them to be
adapted to the exact application. For instance, buyers can select from various
cabs, liftmasts, operator panels, and battery systems, and even custom designed
options can be implemented.
Meticulous design – down to the last detail
The Reutlingen facility of
Kion Warehouse Systems GmbH is responsible for developing and manufacturing
this equipment. The factory builds approx. 2,000 material handling machines per
year, which are designed with extreme care down to the last detail. This is
certainly the impression at igus GmbH, which is working together with Still and
Kion Warehouse Systems as a supplier to a project.
The reason for the
collaboration was to optimise the hoist frame on the EK-X series. This created
the need to reduce the overall installation space requirements for the
electrical and hydraulic line guides in the liftmast. Achim Schwarz, Product
Manager for narrow aisle vehicles at Still GmbH: "We originally equipped
the deflection points with a polygon element that formed a semi-circle with
small rollers. But the limited installation space in the new liftmast called
for a solution with a roller."
Failure mode "Corkscrew"
Still has already
used this deflection principle in smaller order picking equipment, where it
performed well. Due to the longer cable runs on the EK-X series, the lateral
guide of the roller was improved slightly – the initial testing promptly
revealed that this solution would unfortunately not work in this case. Volker
Haspel, responsible for electrical engineering design at Kion Systems:
"The cables we normally use started twisting and then looked like a
corkscrew. They failed during the test shortly thereafter."
At this point of
the development the contact to the cable experts at igus was established. They
were already able to assist customers with similar experiences approx. 25 years
before. Andreas Muckes, Product Manager chainflex: "When we developed our
first energy chains, we found that the chain worked great, but the commercially
available cables frequently did not last long. Back then, this was the kickoff
for our cable product range."
A look under hood of the cable: Braiding in layers or
bundles?
igus then
developed the chainflex product range, which differs from conventional
industrial cables in one significant detail: conventional cables are braided in
layers. This means that the cores of a cable are braided with a relatively long
pitch in several layers around the centre, and are then equipped with a jacket
extruded in the shape of a hose. When the cables move in the energy chain, the
cores along the inner radius are compressed, and the cores along the outer
radius are stretched. This exerts pronounced push-pull forces on cores. As
these forces are distributed in the cable, the braiding structure of the cores
is destroyed. This causes the cable to deform, resulting in the so-called
"corkscrew". This ultimately leads to core failures.
After having
understood this causal relationship, igus developed cables with a completely
different design principle. The cores are first braided in bundles, which are
then braided at a small pitch around a centre element. This centre element is
not only used as a filler, but also functions as a strain relief element. The
result is very similar in appearance to a wire rope. As additional support for
this high-strength braiding structure, a jacket is extruded under pressure to
additionally guide the cores in length direction. All these measures have the
result of minimising the forces created in the cable, and preserve the structure.
Are chain compatible cables also roller compatible?
This design is
more complex, and producing these cables requires greater effort. But the
expense is worthwhile for motion-controlled cables, since cores and the entire
cable are exposed uniformly to the forces generated during bending processes.
Andreas Muckes: "We have never seen a corkscrew on a cable braided in
bundles, therefore making this one of our most important design principles.
The question now
was: are chainflex cables braided in bundles not only chain compatible but also
roller compatible? The igus lab conducted appropriate preliminary tests, and
Kion also tested the cables extensively. Mechanical engineering designers were
also included in the testing. Matthias Fohrer, Design-Engineering + Mechanical
Engineering Development: "Testing this type of cable is a highly complex
task. They perform relative motions in the hoist frame, and pronounced dynamics
occur during order picker travel. One must also take into account the tensile
forces, which occur in this case in contrast to energy chain cables." The
igus staff was pleasantly surprised to learn that the Kion design-engineers
were investing this much effort into this topic. Andreas Muckes: "Very few
companies take this approach."
New standard for liftmast cables
The tests in the
labs of both companies showed: the cable design with braiding in bundles will
hold up very well on rollers. The special jacket materials and their processing
also contribute greatly toward their durability. Testing showed that the shape
of the roller has no direct influence on the service life. The decision for the
Still designers was therefore clearcut: the cable was defined as the standard
for the EK-X liftmast. The specification calls for a chainflex cable with braiding
in bundles and TPE jacket. Instead of the original blue colour, Still receives
the custom colour black, which blends well into the environment, since the
hoist frame and hydraulic lines are black.
Sophisticated design, thoroughly tested
The cables used in
the order pickers range in length between 4.50 and 16 metres. There is no doubt
that they are exposed to extreme loads. The equipment is used continuously in
most applications, with the hoist frame always in motion. The chainflex cables
in these environments move as much as they do in many thousands of energy chain
applications. Still therefore found a solution for a task that resulted from
the modified geometry of the hoist frame and the deflection rollers. The cable
specialists at igus also benefited from these findings. They now know that
their cables are not only chain compatible but will also perform well in roller
guides.
Image
FA0914-3
The chainflex cables are braided in bundles and
were specifically developed for use in energy chains. The do not develop
"corkscrews" in response to bending motions and are therefore chain
compatible without restrictions. (source: igus GmbH)
About igus India
igus® operations in India started in the year 1998 with head quarters in Bangalore.
igus offers widest range of products that includes polymer bearings, igubal® spherical
bearings, DryLin® linear bearings & guide systems enable them to serve the
whole industrial establishments in India from a small work shop to huge
industrial establishments.
