Virtually wear-free plain bearings for high accelerations in product ejectors

In packaging and filling machines and in conveyor technology, product ejectors are required that can reliably separate and eject faulty products individually from the product flow at very high output rates. In the past, pneumatic cylinders were used for this purpose, but these do not work reliably in modern high-speed machines.
Jung Antriebstechnik und Automation GmbH therefore supplies linear motor modules such as the UltraDynamikTM, which are equipped with standard steel guide rails and guide carriages in which ball chains run. These systems achieve top speeds of up to 5m/s and accelerations of up to 150m/s2 at cycle rates of approx. 500 - 1,000 cycles per minute. They are used by customers in continuous operation.
The peak forces of this linear motor technology have been continuously increased through improved magnetic materials with the same motor size. However, the moving motor masses have remained almost the same. This results in a drastically increased acceleration capacity for these new linear motors.
Technically, this high motor dynamics cannot be utilised with conventional guidance, which is manufactured using roller bearing technology and steel materials. The reasons for this are the relatively large moving non-motorised masses of the steel structural elements and, above all, the high accelerations that make it impossible for the bearing elements to 'roll' as intended.
The automation company was therefore looking for components with a drastic reduction in the moving non-motorised structural masses and for a bearing and guide technology that enables accelerations of up to approx. 250m/s2 (25g).

The new design of the actuator focussed on a radical reduction of the moving masses. For this reason, two 10mm CFK tubes were selected as guide elements and a front plate made of CFK. By using these materials, the structural moving masses could be reduced from 263 grams to 45 grams compared to the conventionally (steel) designed HighDynamic linear motor module. Only by radically reducing the mass it is possible to increase the acceleration values.
With regard to the selection of a suitable bearing for the guidance of the CFK tube, the decision was made in favour of iglidur J plain bearings, whereby a total of four bearings were installed in two lead screw support blocks (see image below).
With these components, the newly designed actuator can, for example, realise a stroke of 160mm in only 60ms travel time, controlled by the path curve. During such a movement process, speeds of 4m/s and accelerations of 200m/s2 (20g) are achieved even on this short stroke. The pure acceleration or the braking process is completed after a travelling distance of just 40mm.
In order to be able to make a statement about the long-term practical suitability of this solution, an endurance test series was started at Jung Antriebstechnik, in which the new actuator was tested under very real conditions. This showed that even after several million stroke cycles and a running distance of several thousand kilometres, no significant abrasion or wear could be detected on the CFK tubes and the iglidur J plain bearings. Due to the pleasing results of the tests, the product was presented to the public at MOTEK 2015 after the end of testing.