Torque Limiters SK
Selection of Torque Limiters
According to disengagement torque
As a rule Torque Limiters are rated according to the required disengagement torque, which must be greater than the torque that is necessary for regular machine operation.
The disengagement torque of the Torque Limiters is determined as a rule in accordance with the drive specifications.
The following calcucation has proven itself as a rule of thumb solution:
T<sub>KN</sub> = rated torque of coupling (Nm)
TAS = peak torque of motor (Nm)
or
T<sub>KN</sub> = rated torque of coupling (Nm)
PAN = drive power (kw)
n = speed of drive (min -1)
According to acceleration torque (start-up at no load)
SA = jerk or load factor
SA = 1 (uniform load)
SA = 2 (non-uniform load)
SA = 3 (jerky load)
Values for SA = 2-3 are usual for servo drives on machine-tools.
T<sub>KN</sub> = rated torque of coupling (Nm)
α = angular acceleration 
t = acceleration time (sec.)
ω = angular speed in (1/s)
n = speed of drive (min-1)
JL = moment of inertia on load side (kgm 2)
JA = moment of inertia on driving side (kgm 2)
TAS = peak torque of motor (Nm)
According to feed force
Spindle driveb
TAN T = load torque (Nm)
S = spindle pitch (mm)
FV = speed force (N)
η = spindle efficiency
Timing belt drive
TAN T = load torquet (Nm)
d0 = pinion dia. (pulley)
FV = speed force (N)
According to resonant frequency (SK 2 / 3 / 5 with bellows attachment)
Usually high resonant frequencies of the couplings are required in order to make high acceleration values possible and avoid any vibration excitation.
For the purpose of caclulation the drive is reduced to a 2 mass sytem.
CT = torsional stiffness of the coupling (Nm/rad)
JMasch. = moment of inertia of machinet (kgm2)
(spindle + slide + workpiece + half of coupling)
JMot. = moment of inertia of motor (kgm2)
(motor’s rotor + half of coupling)
fe = Resonant frequency of a two mass system (Hz)
According to torsional sitiffness (SK 2 / 3 / 5 with bellows attachment)
Transmission errors due to a torsional stress on the metal bellows:
ϕ = angle of turn (Grad)
CT = torsional stiffness of coupling (Nm/rad)
TAS T = peak torque of motor (Nm)
According to the function system
Load holding version: On SK1 / SKP models the load holding version has a double load safety margin. Ensure that models with bellows (SK2, 3 and 5) are of adequate size. The blocking load in this case should not exceed the nominal torque of the coupling.
