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10. 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 10.4 to calculate an approximate coasting distance to a stop. The dynamic
brake time constant τ varies with the servo motor and machine operation speeds. (Refer to (2) 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 ·································································· [× 10
M
J
: Load moment of inertia converted into equivalent value on servo motor shaft ·············· [× 10
L
τ: Dynamic brake time constant ···························································································· [s]
t
: Delay time of control section ···························································································· [s]
e
There is internal relay delay time of about 10 ms.
EM1 (Forced stop 1)
J
1 +
L
··························································································· (10.4)
J
M
ON
OFF
V
0
Machine speed
Fig. 10.3 Dynamic brake operation diagram
10 - 6
Dynamic brake
time constant
t
e
-4
-4
Time
2
kg•m
]
2
kg•m
]
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