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10. CHARACTERISTICS
10.3 Dynamic brake characteristics
10.3.1 Dynamic brake operation
(1) Calculation of coasting distance
Fig. 10.3 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use equation 10.2 to calculate an approximate coasting distance to a stop. The dynamic
brake time constant varies with the servo motor and machine operation speeds. (Refer to (2)(a), (b) of
this section.)
A working part generally has a friction force. Therefore, actual coasting distance will be shorter than a
maximum coasting distance calculated with the following equation.
V
0
t
+
L
=
•
max
e
60
L
: Maximum coasting distance ······································································································· [mm]
max
V
: Machine's fast feed speed ···································································································[mm/min]
0
J
: Moment of inertia of the servo motor·····················································································[kg•cm
M
J
: Load moment of inertia converted into equivalent value on servo motor shaft·····················[kg•cm
L
: Dynamic brake time constant ········································································································· [s]
t
: Delay time of control section··········································································································· [s]
e
For 7 kW or lower servo, there is internal relay delay time of about 10 ms.
POINT
Do not use dynamic brake to stop in a normal operation as it is the function to
stop in emergency.
For a machine operating at the recommended load to motor inertia ratio or less,
the estimated number of usage times of the dynamic brake is 1000 times while
the machine decelerates from the rated speed to a stop once in 10 minutes.
Be sure to make EM1 (Forced stop) valid after servo motor stops when using
EM1 (Forced stop) frequently in other than emergency.
Servo motors for MR-J4 may have the different coasting distance from that of
the previous model.
EM1 (Forced stop)
Fig. 10.3 Dynamic brake operation diagram
J
1 +
L
··············································································································· (10.2)
J
M
ON
OFF
V
0
Machine speed
10 - 5
Dynamic brake
time constant
t
e
Time
2
]
2
]
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