Torque Root Mean Square RMS

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.

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

T₁=Torque required to accelerate the load from 0 to maximum speed (T_F+T_A)

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

T₃=Torque required to decelerate from maximum speed to 0 (T_A-T_F)

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