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13 CHARACTERISTICS
13.3 Dynamic brake characteristics
13.3.1 Dynamic brake operation
(1) Calculation of coasting distance
Fig. 13.3 shows the pattern in which the servo motor comes to a stop when the dynamic brake is operated.
Use Equation 13.2 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) in this section.)
V
0
Time constant
Forced stop(EMG)
OFF
ON
Machine speed
t
e
Time
Fig. 13.3 Dynamic brake operation diagram
L
max
60
V
0
J
L
J
M
t
e
1
....................................................................................................................... (13.2)
L
max : Maximum coasting distance .................................................................................................... [mm][in]
Vo : Machine rapid feed rate ..............................................................................................[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]
For 7kW or less servo, there is internal relay delay time of about 30ms. For 11k to 22kW servo,
there is delay time of about 100ms caused by a delay of the external relay and a delay of the
magnetic contactor built in the external dynamic brake.
(2) Dynamic brake time constant
The following shows necessary dynamic brake time constant
for the equations (13.2).
(a) 200V class servo motor
Speed [r/min]
0
0 1000 2000
5
10
15
20
25
3000 4000 5000 6000
43
053
13
2373
Time constant [ms]
0
0 1000 2000
5
10
15
20
25
3000 4000 5000 6000
43
053
13
23
73
Speed [r/min]
Time constant [ms]
HF-MP series HF-KP series