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.
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
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. Reutlingen
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.
For more details please visit: http://www.igus.in/default.asp?PAGE=EnergyChains&C=IN&L=en
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 Indiaigus® operations in India started in the year 1998 with head quarters in Bangalore. igus offers widest range of products that includes polymer , 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.