Mitsubishi Electric MR-J4, Instruction Manual

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18. MR-J4-03A6 SERVO AMPLIFIER
18 - 77
(1) Dynamic brake operation
(a) Calculation of coasting distance
Fig. 18.2 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use equation 18.1 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 (1) (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
OFF
ON
Machine speed
t
e
Time
EM1 (Forced stop 1)
Dynamic brake
time constant
τ
Fig. 18.2 Dynamic brake operation diagram
L
max
=
60
V
0
•
J
M
t
e
+ 1 + J L
··························································································· (18.1)
L
max
: Maximum coasting distance ······················································································ [mm]
V
0
: Machine's fast feed speed ····················································································· [mm/min]
J
M
: Moment of inertia of the servo motor ································································· [× 10
-4
kg•m
2
]
J
L
: Load moment of inertia converted into equivalent value on servo motor shaft ············· [× 10
-4
kg•m
2
]
τ : Dynamic brake time constant ···························································································· [s]
t
e
: Delay time of control section ···························································································· [s]
The processing delay time about 3.5ms.
(b) Dynamic brake time constant
The following shows necessary dynamic brake time constant τ for equation 18.1.
0
Speed [r/min]
0 1000 2000
0.0005
0.0010
0.0015
0.0020
0.0025
3000 4000 5000 6000
0236
0336
0136
Dynamic brake time
constant [ms]
HG-AK series