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Chapter 9
1326 AC Servomotors
9-2
Tc – rated torque of motor with windings at rated temperature and an
ambient of 40 C. The drive is operating in a rated ambient of 60 C.
Tp – the peak torque that can be produced by the motor/drive combination
with both at rated temperature and the motor in a 40 C ambient and the
drive in a 60 C ambient. Higher peak torques are permissible where RMS
torque is less than or equal to the rated torque (Tc). 1391-DES operation is
shown in the outer envelope and will show higher speed and 300% torque
capability.
Rated Speed – the operating speed of the drive and motor combination at
which a minimum of 70% of continuous rated torque (Tc) can be
developed. This point is defined with the motor at 25 C and drive
operating in a 60 C ambient.
Rated Operation Area – boundary of speed-torque curve where the motor
and drive combination may operate on a servo basis without exceeding the
RMS rating of either.
Duty Cycle Profile
RPM
Accelerate
(Tpa)
Total Cycle Time
2
Tpa
x t
Trms =
where:
Trms
The motors RMS or average torque over the duty cycle. (Expressed in lb.-in. or
lb.-ft. The same units must be used throughout the formula.)
Tpa
Motor peak torque to accelerate to maximum speed. (Expressed in lb.-in. or lb.-ft.
The same units must be used throughout the formula.)
Tss
Motor torque present at the motor shaft during constant speed segment.
(Expressed in lb.-in. or lb.-ft. The same units must be used throughout the
formula.)
Tpd
Motor peak torque to decelerate to zero speed. (Expressed in lb.-in. or lb.-ft. The
same units must be used throughout the formula.)
Tr
Torque when motor is at zero speed.
t
, t
, t
, t
Time for each portion of the duty cycle in seconds.
1
2
3
4
Intermittent Operation Area – Boundary of speed-torque curve where
the motor and drive combination may operate in acceleration-deceleration
mode without exceeding peak rating of either, provided that the duty cycle
RMS continuous torque limit is not exceeded.
Decelerate
(Tpd)
Steady
Speed
(Tss)
t
t
t
1
2
3
Move Cycle
2
2
2
+ Tss
x t
+ Tpd
x t
+ Tr
x t
1
2
3
4
t
+ t
+ t
+ t
1
2
3
4
Repeat
Rest
(Tr)
t
4
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