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A compact coupling system for limited space applications

01 October 2009

It is often the case these days that electro-mechanical systems and mechanical assemblies are designed to take up the minimum amount of space. Whilst desirable, compactness creates its own headaches, not least being the limited amount of installation space available for torque transmitting couplings. Fortunately, the couplings industry has kept one step ahead.....

Designs with axially restrictive installation spaces and limited scope for shaft connection demand compact couplings that retain all the attributes of their larger cousins without compromising performance. One company that has addressed these problems is Schmidt-Kupplung (S-K). The company’s Semiflex Compact Plus (SCP) offers a combination of compactness and functionality that allows easy integration within a tight envelope.

With an exterior diameter of 70 to 120mm, these couplings can be easily assembled by means of friction locking clamp hubs or with a clamp hub in half-shell format. Depending on the type of coupling chosen, the SCP’s drive elements are contained within a compact unit that is either identical to, or up to 27% shorter relative to the exterior diameter of the relevant clutch size. And depending on the size of the coupling, the compact compensating elements will tolerate a radial misalignment of up to 3mm commensurate with the specified limited design length.

The secret, according to S-K, is in the ‘kinematics’. With these couplings, rotary motion and torque are transmitted by means of a system of two pairs of connecting rods, arranged at 90 degrees offset to each other. These link the input and output sides with the coupling’s central disc. The connecting rods can be swivelled on the pin located on the discs, and are usually mounted by means of a needle bearing. Lateral shift is equalised purely by the swivel motion of each pair of connecting rods. In this way, radial misalignment is accommodated within a small axial design length. In terms of precision, the SCP range offers a torsional rigidity of 13kNm/rad to 140kNm/rad, depending on the exterior diameter of the coupling.

An application example
Roller conveyors are usually required for transporting small goods of low weight and compact dimensions. Loads are conveyed along transport rollers arranged transversely with respect to the conveying direction, and may be driven or free-wheeling systems. Driven systems are used whenever there is a need for varying transportation rates or fixed-cycle operations. Usually, the individual rollers are driven by a servomotor and an outer central shaft with the conveyor rollers driven by individual sets of bevel gears. To achieve a complete assembly, individual modules are combined to achieve a compact system. This configuration is a space-saving one, as long as the connecting elements are compact. Moreover, the coupling system must also be able to compensate for assembly inaccuracies and misalignments of up to 1.5mm between the individual part modules - for example, those resulting from conveyor level adjustment.

For one such application, working in a fixed cycle mode, S-K supplied size C 320 SCP couplings featuring a friction-locking shaft connection in the form of a radially operated clamp hub on both sides. An option is a clamp hub in half-shell format on one side allowing easy removal and replacement. The clutch size, with an exterior diameter of 120mm, has a total design length of 88mm, ensuring a compact connection between the individual part modules. Despite this axial compactness, the C 320 coupling offers a torsional rigidity of 73kNm/rad and accommodates a radial misalignment of up to 3.0mm.

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