Servo couplingsDimensioning

T echnical information - definitions / det ails: •

Nominal torque of the coupling: T
KN - [ Nm ] The nominal torque of the coupling defines the max. load of the prolonged alternating-stress strength. If in normal operation T
KN is not exceeded, an infinite number of operation cycles can be carried out (see "useful life of the coupling").

•

Moment of inertia: J
-3 2 K - [ 10 kgm ] The values for the moment of inertia are defined for medium hub- bores in the given diameter range D
min /D
max . Conversion: [ kgcm
2 ] = [10
-4 kgm
2 ]

•

T orsional rigidity: C
TK - [ Nm / arc min ] The values for the specific torsional rigidity of all couplings and gear series are conversed from the existing values [103 Nm/rad] to "Newtonmeter per angular minute". This enables the constructor to determine the twisting angle failure quite easily (see "b" below) under consideration of the operating torque. 60 angular minutes (resp. arc minutes) correspond to one angular degree. This defines the conversion factor 1 rad = 57,3° = 3438 arcmin. Conversion:
^^ ^^^ [10
3 Nm/rad = 0,291 Nm/arcmin] resp. [1Nm/arcmin = 3438 Nm/rad]Example: Size KM 170: 17,5 Nm/arcmin= 60 kNm/rad

•

Max. alignment of shaf t s: [ mm ] The maximum alignment of shafts is the largest allowed misalignment between drive shaft and output shaft, which results from the calculation of the prolonged alternating-stress strength for compensating elements. If the allowed displacement values are not exceeded, an infinite number of load alternations can be carried out. In exceptional cases (e.g. during fixing) resp. at reduced numbers of load alternations, the displacement values may be considerably higher (please further consultation). - axial displacement: usually without problems (expansion due to temperature)- angular displacement: usually without problems - allowed max. value: 1 to 2 degrees - lateral or parallel displacement: If the admissible values are considerably exceeded, permanent distortion at the bellows resp. higher wear of the elastomer spider can occur. Special care during fitting must be taken!

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S pring rigidity - axial / lateral: [ N/mm ] Restoring forces of the metal bellow resp. of the elastomer spider, resulting of the misalignments.

Dimensioning of the coupling

a) according to torque: Usually the size of the coupling is chosen according to the torque. For exact determination of the necessarydriving torque, difficult calculations are neccessary (see formularies). If the size of the motor is fixed, the necessary nominal torque of the coupling can be calculated as follows: T

TKN >

_

1,25

x

TA

max
x

i

Amax = peak torque of the motori = transmission resp. reduction of the toothed belt drive resp. the spur- toothed wheel b) according to the torsional rigidity: For applications with very precise requirements (position control, transmitter), transfer errors due to high elasticdeformation can be an importand criteria of selection of the coupling. The torsional angle “ α T” is calculated asfollows:

α

T= T
A C
TK [arc minutes] with T
A = driving torque [Nm] / C
TK = torsional rigidity of the coupling [Nm/arcmin] In very few cases, metal bellow couplings can have resonance sounds (e.g. a whistling or a humming). Thencoupling types with a higher torsional rigidity or vibration reducing elastomer couplings are recommended.
Servocouplings

3

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