
4. SELECTING A MOTOR
B–65142E/04
DESCRIPTIONS FOR THE α series
54
Servo motors can be operated in the range exceeding continuous rated
torque depending on thermal time constant. Duty characteristics shows
the Duty (%) and the “ON” time in which motor can be operated under
the given overload conditions. Calculation procedure is as follows.
1 Calculate Torque percent by formula (b) below.
2 Motor can be operated at any point on and inside the curve
corresponding to the given over load conditions obtained form 1.
3 Calculate t
F
by formula (a)
t
F
+ t
R
(
100
Duty percent
–1)
TMD +
Load torque
Continuous rated torque
(a). . . . . . . . .
(b). . . . . . . . .
t
F
: “OFF” time
t
R
: “ON” time
The values of t
R
and t
F
obtained form the above mentioned procedure
shows the ones limited by motor thermal conditions.
Note that thermal protection devices such as a circuit breaker and
thermal circuit are incorporated into the drive amplifier. These devices
also impose a restriction on motor usage.
When the motor is overloaded, the software (OVC alarm) imposes an
additional restriction on motor drive duration.
4.4.3
How to Use Duty Cycle
Curves