Yaskawa Large Capacity Sigma II Series - Manual (Page 295)

7.3 SERVOPACK Ratings and Specifications
7-19
7
7.3.4 Starting and Stopping Time
The motor starting time (tr) and stopping time (tf) under a constant load are calculated using
the following formulas. Motor viscous torque and friction torque are ignored.
N
M
: Rated motor speed (min
-1
)
J
M
: Motor rotor moment of inertia (kg·m
2
)
J
L
: Load converted to shaft moment of inertia (kg·m
2
)
T
PM
: Instantaneous peak motor torque when combined with a SERVOPACK (N·m)
T
L
: Load torque (N·m)
Calculate the torque from the motor current using servomotor torque constant × motor cur-
rent (effective value).
Fig.7.2 shows the motor torque and motor speed timing chart.
Fig. 7.2 Motor Torque (Current Amplitude) and Motor Speed Timing Chart
7.3.5 Load Moment of Inertia
The larger the load moment of inertia, the worse the movement response of the load. The
size of the load moment of inertia (J
L
) allowable when using a servomotor is limited to
within 5 times the moment of inertia (J
M
).
If the load moment of inertia exceeds five times the motor moment of inertia, an overvoltage
alarm may arise during deceleration. Take one of the steps below if this occurs.
• Reduce the torque limit.
• Reduce the deceleration rate.
• Reduce the maximum motor speed.
• Consult your Yaskawa representative if the alarm cannot be cleared.
Starting time:
Stopping time:
tr =
2 π x N (J +J )
60 x (T -T )
M M L
PM L
tf =
2 π x N (J +J )
60 x (T -T )
[s]
[s]
M M L
PM L
Motor torque
(current amplitude)
Motor speed
tr tf
N
M
T
PM
TL
Time
Time
T
PM