Flexible shaft couplings
Connect and transmit power from a driving shaft to a driven shaft
Manage to compensate for totally 4 shaft misalignments:
Combination (angular + offset)
These shaft deviations are unavoidable, since machines are unloaded during alignment.
During operation the resulting forces are causing the shafts to bend. Other causes can for instance be thermal expansion, worn bearings, installation (human) errors.