(c) Lateral and Axial Flexibility of
Couplings
Lateral and axial flexibility of couplings are factors frequently overlooked. The term
flexible does not mean that the Coupling gives Complete freedom of movement to coupled
shafts with no transmissible force. More properly, flexible couplings give limited freedom
of movement with transmitted force. Simply stated: Forces are needed to make a flexible
coupling flex. These forces are either lateral (at right angles to the shafts) or axial in
nature or a combination of both. Lateral forces may produce a bending moment on the shafts
and a radial toad on the support bearings. Axial force can produce undesirable thrust
loads if not considered in the original design. Universal joints and Oldham couplings
impose relatively little lateral load on bearings. The elastomeric type of couplings will
produce lateral forces in proportion to their stiffness. Small lateral force calls for
soft rubber and in turn reduces torque capacity.
(d) Torsional Flexibility
Torsional flexibilty of a coupling is the elastic deformation induced in a flexible
coupling while transmitting torque. In some applications using encoders, it may be
essential that the torsional flexibility sometimes be very low so as not to introduce
reading errors caused by angular displacements. On the other hand torsional deflection may
be desirable for reducing peak torque In driving high inertia loads.
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