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Chain-suitable and "roller-suitable" cables for an order picker

chainflex® for forklifts  

Still uses chainflex® cable in the lift frame of the EK-X order picker

How do you guide energy and signal cables to the cab of an order picker via the moving lift frame with multiple guide rollers? The designers of the Still EK-X vertical order picker have found the answer: they use a chainflex® cable that originally was developed for use in energy chains. In tests igus®, as well as Still, determined that this cable is not only suited for applications with energy chains, it can also function effectively in roller guides.

Orange is the colour of choice for many operators of logistics centres and goods distribution centres, warehouses and picking systems. They use Still brand forklifts, tractors, and order pickers The enterprise, headquartered in Hamburg Germany, is part of the Kion Group, which in turn with a turnover of just under €4.5 billion (2013), is the second largest forklift manufacturer worldwide.
The EK-X type series of vertical order pickers are particularly impressive devices in Still's broad product range. Their task is to drive to those pallets in the narrow aisles of a high bay warehouse, from which the driver removes individual boxes. The order pickers offer reaching heights of up to twelve meters, and thanks to the modular design principle, they are a perfect match for the specific application. For example, the purchaser can choose from different cabs, lift masts, control panels and battery systems; custom designed options are also implemented.


Real high-performance devices in the narrow-aisle warehouse: The vertical order pickers of the EK-X type series allow reaching heights of up to twelve meters. The driver also moves upward.


Careful design – even in the smallest details
The Kion Warehouse Systems GmbH plant in Reutlingen is responsible for development and production of these devices. Here each year approximately 2000 warehouse technology devices are constructed with extreme care that extends to the smallest detail. This at least is the impression of igus® GmbH, who as supplier is working together with Still, i.e. Kion Warehouse Systems, in a project.
The purpose of the collaboration was optimisation of the lift frame on the EK-X type series. It established the necessity that the guidance of the electric and hydraulic cables in the lift mast had to be dimensioned in a manner that saved more install space. Achim Schwarz, Product Manager – Very Narrow-Aisle Devices at Still GmbH: "Originally we used a polygon element on the deflection points that formed a semi circle of small rollers. However, in the new lift mast, due to the smaller install space there had to be a solution with one roller. “


The energy cables and signal cables in the lift frame, which are up to 14m in length, are guided via guide rollers and move each time that the mast is lifted or lowered.

Failure diagnosis – "corkscrew"

Still uses this deflection principle even with smaller order pickers and it has proven to be effective. For the EK-X type series the lateral guide of the roller was improved slightly due to the greater cable lengths – and then the initial tests quickly showed that unfortunately, in this case, this solution did not work. Volker Haspel, who is responsible for Electrical Engineering at Kion Systems: "The cables that we used, twisted and looked like a corkscrew." Shortly afterwards they failed in the test.
In this development stage the contact with the igus® cable experts came about: approximately 25 years ago, igus® had already been able to help customers with similar experiences. Andreas Muckes, Product Manager chainflex®: "When we developed our first energy chains, we established that the chain worked fine; however, often the standard cables on the market did not last long. This was the actual starting point for our cable product range."

chainflex® cables

The braided in bundles chainflex® cables were developed especially for use in energy chains. In bending processes they do not develop "corkscrews" and consequently they are chain-suitable without restriction.

A look inside the cable: stranding in layers or braiding in bundles?

Thereupon igus® developed the chainflex® product range that differed from standard industrial cables in an essential point: conventional cables are stranded in layers. This means that the cores of a cable are stranded with a relatively long pitch in multiple layers around a centre and fitted with a jacket that is extruded as hose. When the cables in the energy chain move the cores in the inner radius are compressed, and the cores in the outer radius are elongated. This causes extremely high tensile forces and shear forces on the cores. When these forces propagate in the cable the stranded construction of the cores is destroyed. This results in deformation of the cable, which allows the so-called "corkscrew" to occur. Ultimately this results in core breakage.

After this causal chain was recognized, igus® developed cables based on a completely different construction principle: The cores are first braided into bundles, which in turn are braided with a small pitch length around a core element. This core element is not used as a filler, rather it is designed as a strain relief element. In appearance the result is highly reminiscent of a steel rope. To additionally support this stable braiding construction a jacket is extruded under pressure to supplementally guide the wires in the longitudinal direction. All of these measures result in the fact that the forces occurring in the cable are minimized and the construction remains intact.

Are chain-suitable cables also "roller-suitable"?

This structure is more complex and the manufacturing of these cables demands more effort, but the effort pays off in moving cables. The cores and the entire cable are uniformly stressed during bending processes. Andreas Muckes: "We have never seen a braided in bundles cable with a corkscrew, consequently this has become one of our most important design principles."
The next question was, are the braided in bundles chainflex® cables not just chain-suitable, but also roller-suitable? In the igus® lab appropriate preliminary trials were executed and the cables were also tested intensively in Kion's facilities. In this process, developers from the Mechanical Engineering organization were also included. Matthias Fohrer, Design + Development, Mechanical Engineering: "Testing such cables is definitely a complex task. They execute relative motions in the lift frame and high dynamics occur when moving the order picker. Moreover, you have to take the tensile force that occurs here into account, this is different than the situation with energy chain cables." At igus® they were pleasantly surprised that the Kion designers were so intensively involved with this issue. Andreas Muckes: "There are really not many companies that would do this."

chainflex® cables

In the development phase, the developers from Kion worked closely together with igus®. Ultimately it was shown that: The chainflex® cables are not only chain-suitable, they are also a good solution for roller guides. Left to right: Andreas Muckes, igus® Product Manager – chainflex®, Achim Schwarz, Product Manager – Very Narrow-Aisle Devices (VNA) at Still GmbH, Matthias Vohrer, Design – Mechanical Engineering at Kion Warehouse Systems, igus® Sales Consultant Michael Fuchs and Volker Haspel, Design – Electrical Engineering at Kion Warehouse Systems in Reutlingen, Germany.

New standard for lift frame cable

The tests in the laboratories of both companies showed: the cable structure with cores wound in bundles works very well on the rollers. Also the special materials of the jacket and its workmanship are significant additional aids for durability. It was shown that the shape of the roller does not have a direct influence on service life. The decision was clear for the Still designers; the cable was defined as the standard for the lift frame of the EK-X. A chainflex® cable with cores wound in bundles and TPE jacket is used. Instead of the original blue colour, Still gets the special colour black, which integrates ideally in the environment - after all, the lift frame and the hydraulic hose are black.
Thoughtfully designed, extensively tested
The cables that are used in the order pickers are between 4.50 and 16m in length. There is no question that they are highly stressed. In many applications the devices are in continuous use, which means that the lift frame is always in motion. The chainflex® cables move under these conditions just like they move in many thousands of energy chain applications. With this cable Still has found a solution for a task that arose through the changed geometry of lift frame and guide roller. The cable specialists at igus have also gained an insight: now they know that their cables are not only chain-suitable, but they have also proven to be effective in roller guides.

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