TKN     Rated torque of the coupling (Nm)
     Peak torque of the drive system
e.g. max. acceleration torque of drive (Nm) or max. braking torque of load (Nm)
JL     Total load inertia
(e.g. spindle + slide + workpiece + 1/2 of coupling) (kgm²)
JA     Total driving inertia
(motor [including gear ratio] + 1/2 of coupling) (kgm²)
CT     Torsional stiffness of the coupling (Nm/rad)
fe     Natural frequency of the two mass system (Hz)
fer     Excitation frequency of the drive (Hz)



     Torsional deflection (degree)


According to torque

Couplings are normally sized for the highest torque to be regularly transmitted. The peak torque of the application should not exceed the rated torque of the coupling. The following calculation provides an approximation of the minimum required coupling size, and allows for the maximum rated speed and misalignment to exist in the application:

According to acceleration torque

A more detailed calculation takes acceleration and the driving and driven moments of inertia into account. A strong inertia ratio diminishes the effect of the load factor in the sizing calculation.

According to resonant frequency

The torsional natural frequency of the coupling must be significantly higher or lower than that of the equipment. For the mechanical substitution model the two mass system applies.

In practice the following applies: fe ≥ 2⋅ fer

According to torsional deflection

To calculate transmission error as a result of torsional stress: