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25/01/2021 - 27/01/2021

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Accurate transmission of motion with no backlash

Accurate transmission of motion with no backlash

A beam coupling is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset and even axial motion of one shaft relative to the other. Because it is made from a single piece of material, the coupling provides backlash-free transmission of motion, while the flexibility is afforded by slits cut into the coupling.

Whilst in the context of a machine design they are relatively inexpensive components, it is important to give due consideration to shaft couplings. The performance of a machine is only as good as the connections of its shafts, and the shaft coupling is often a critical part of the drive system.

The Reliance range of shaft couplings has been carefully designed and tested to provide trouble-free operation over many millions of cycles. In tests performed on typical applications, the bi-directional error produced by a Reli-a-Flex coupling used to drive a 3600 line encoder was four times smaller than that produced by a four-beam spiral coupling. When used to drive a 6.35mm lead leadscrew, the bi-directional error from the Reli-a-Flex was six times less than that of the four-beam spiral.

The Reli-a-Flex coupling also offers predictable performance, having been tested for 50,000,000 cycles at its rated torque and 80% maximum offset.

Perfect alignment is not practical in applications where two shafts need to be joined and therefore some level of misalignment will always occur. This misalignment is usually the result of the support block manu-facturing tolerances and structural alignment. Unless these tolerances are very precise, use of a solid coupling will result in high shaft loading and significant bearing loads. In certain cases this misalignment is limited to angular or radial misalignments, but is more often a combination of the two. Therefore, careful shaft coupling selection is important as differing configurations of coupling are designed to perform very differently dependent upon the application, and, as a consequence, have very different benefits and drawbacks.

There are many different designs of slit beam couplings, offering different performance characteristics with relation to torque capacity, transmission error, flexibility, size or cost. In the Reli-a-Flex range, for example, Reliance offers a range of couplings designed to provide extremely accurate transfer of motion between two rotating shafts, while catering for parallel and angular misalignment.

Other one piece couplings currently on the market may outwardly resemble the Reli-a-Flex at first glance, but there is one vital difference. The patented slot design on the Reli-a-Flex maintains a constant pivot length which minimises stress variations. On the Reli-a-Flex the pivot points travel back and forward without changing the centre piece angle, resulting in uniform stress levels and accurate angular rotation. Similar looking couplings on the market can actually have a slot pattern where the pivot points move in and out, and the centre piece angle varies. This causes stress variations and less uniform rotation.

The original range includes outside diameters from 13mm to 40mm and the additional micro sizes now available are 6mm, 8mm and 10mm. These couplings retain all the advantages of Reli-a-Flex's patented design, and are ideal for the accurate, miniature motion control applications demanded by the printing, medical and scientific instrument markets.

Reliance engineers have many years of experience working with and specifying shaft couplings and are very happy to offer applications advice on coupling selection.

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