When a machine builder wanted to drive up to 50 servo axes with high dynamic forces, small bending radii and long service life requirements, it did not believe hybrid cable technology would fit the bill. In this article, Justin Leonard, the-chain director at igus, explains how service lifetime guarantees allow hybrid cables to function under these adverse conditions.
Internationally renowned machine builder, IMA Klessmann develops high-speed wood processing equipment for the fully automated production of residential, office, kitchen and bathroom furniture. These machines can operate at 60 metres per minute for example for edge processing with sawing, chamfering and/or gluing This speed, however, also prescribes the rate for the drilling stations integrated into the systems.
In the IMAGIC flex drilling system, control of each drilling spindle is separate to enable horizontal and vertical drilling, as well as dowelling. The concept of this system, which is equipped with up to 50 axes, was to keep set-up times to a minimum, even for complex drilling patterns, while at the same time operating at high speed. The designers decided to use the latest servo technology, which uses a hybrid cable for the power and encoder signalling, to allow the highly dynamic movements with high positional accuracy and extremely fast feedback.
This reduces the time and effort for commissioning, but initially it presented the designers at IMA with a challenge. However, all stakeholders at IMA agreed that it was worth pursuing this goal, not just for technical reasons. Depending on the position of the switch cabinet, which is specified by the customer, IMA can fit up to four kilometres of cables. The single-cable technology therefore saves considerable purchase cost and installation time.
There were certainly doubts on the reliability, since other leading companies in control technology had given up the idea of a one-cable concept in the past – the risks seemed too great. IMA took these concerns seriously, especially since the high dynamics of the hybrid cables was an extra factor – and the initial request to igus did not dispel their doubts. On receipt of the operational parameters and asked if the guaranteed service life was valid, the answer from igus was ‘no’.
The reason why the guarantee was invalid was the small bend radii used in the servo axes. In some instances, they were up to 50 percent smaller than that specified in the catalogue. igus has extensively tested all the chainflex hybrid cables, which are available according to the standards of more than 30 servo system manufacturers, achieving more than 25 million cycles per cable without failure. However, these values apply to the standard conditions and a defined bending radius of 10x diameter.
Keen to overcome this challenge, igus developed a tailor-made test programme for IMA, in accordance with the specification of the drive manufacturer and the Hyperface DSL bus element with over 4 million strokes at the tight bend radii. On completion of the programme, the real test data was handed over to IMA.
In the case of the bus elements in such a cable, practical testing is vital in addition to test measurements. The combined tests in the igus laboratory, which is the largest in and IMA’s series application were so successful that nothing stood in the way of a serial production launch. Both companies benefitted from the experience of working together on this project. And, ultimately, the end customer is assured by a reliability statement from IMA, since the new technology is safely tested from the very outset.
The chainflex hybrid cable range is available with both PUR and PVC jacket. What may be surprising is that IMA chose the PVC option, while the majority of the machine builders use cables with PUR jacket. This is because, in IMA’s experience, they are wear-resistant, durable and fail-safe, even in highly dynamic applications. From a purchasing standpoint, in view of the large quantity of cables, the use of cables with PVC jacket also offers significant cost savings.
