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12. CHARACTERISTICS
12.3 Dynamic brake characteristics
Fig. 12.3 shows the pattern in which the servo motor comes to a stop when the dynamic brake is operated.
Use Equation 12.2 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 Fig. 12.4)
V
0
Time constant
Emergency stop(EMG)
OFF
ON
Machine speed
t
e
Time
Fig. 12.3 Dynamic brake operation diagram
L
max
60
V
0
J
L
J
M
t
e
1
....................................................................................................................... (12.2)
L
max
: Maximum coasting distance .................................................................................................[mm][in]
Vo : Machine rapid feedrate ......................................................................................... [mm/min][in/min]
J
M
: Servo motor inertial moment................................................................................. [kg cm
2
][oz in
2
]
J
L
: Load inertia moment converted into equivalent value on servo motor shaft.....[kg cm
2
][oz in
2
]
: Brake time constant........................................................................................................................ [s]
t
e
: Delay time of control section...........................................................................................................[s]
(There is internal relay delay time of about 30ms.)
0
14
16
2
4
8
10
6
12
0 500 1000 1500 2000 2500 3000
13
73
23
43
Speed [r/min]
Time constant [ms]
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 500 1000 1500 2000
202
102
152
52
Speed [r/min]
Time constant [s]
a. HC-KFE series b. HC-SFE series
Fig. 12.4 Dynamic brake time constant
Use the dynamic brake at the load inertia moment indicated in the following table. If the load inertia
moment is higher than this value, the built-in dynamic brake may burn. If there is a possibility that the
load inertia moment may exceed the value, contact Mitsubishi.
Servo amplifier Load inertia moment ratio [times]
MR-E-10A to MR-E-200A 30