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

Profile

• What was needed: Plastic bearing made of iglidur J
• Requirements: The automation company was looking for components with a drastic reduction in the moving structural non-motorised masses and for a bearing and guidance technology that would enable accelerations of up to approx. 250m/s² (25g).
• Industry: Packaging technology
• Success for the customer: Endurance tests carried out in-house 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.

Problem

In packaging and filling machines and in conveyor technology, product ejectors are required that can reliably separate and eject individual faulty products 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 cycle rates of approx. 500 - 1,000 cycles per minute, top speeds of up to 5m/s and accelerations of up to 150m/s². 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 remained almost the same. This results in a drastically increased acceleration capacity for these new linear motors.
From a technical point of view, this high motor dynamics cannot be utilised with conventional guides, which are manufactured using roller bearing technology and from 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, which 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 would enable accelerations of up to approx. 250m/s2 (25g).

Solution

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 CFK front plate. By using these materials, the constructive moving masses could be reduced from 263 grams to 45 grams compared to the conventionally (steel) designed HighDynamic linear motor module. An increase in acceleration values is only possible through a radical reduction in mass.
With regard to the selection of a suitable bearing for guiding the CFK tube, the decision was made in favour of iglidur J bearings, whereby a total of four bearing bushes were installed in two bearing blocks (see picture below).
With these components, the newly designed actuator can, for example, implement a stroke of 160mm in just 60ms travel time, controlled by the path curve. During such a movement, 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 already completed after a travel distance of 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 lifting cycles and a running distance of several thousand kilometres, no significant abrasion and wear could be detected on the CFK tubes and on the iglidur J bearings. Due to the positive results of the tests, the product was presented to the public at MOTEK 2015 at the end of testing.