Torque Root Mean Square

Servo Motors generally have two speed-torque curves.   One for continuous duty and one for intermittent duty.

The total torque required, at maximum velocity is needed to select a proper motor for continuous duty.

However, if the motor waits between moves, this is known as “dwell time” and can be used to calculate Root Mean Square (RMS) Torque.  This lowers the required continuous duty torque and a smaller motor can often be selected.

(TRMS)2=(T12t1+ T22t2+ T32t3+ T42t4)/(t1+t2+t3+t4)

T1=Torque required to accelerate the load from 0 to maximum speed (TF+TA)

T2=Torque required to keep the motor moving once maximum speed is attained (TF)

T3=Torque required to decelerate from maximum speed to 0 (TA-TF)

T4=Torque required while motor is sitting still

t1=time to accelerate the load

t2=time at constant speed

t3=time to decelerate the load

t4=time at rest




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