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11. CHARACTERISTICS
11.3 Dynamic brake characteristics
11.3.1 Dynamic brake operation
(1) Calculation of coasting distance
Fig. 11.3 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use Equation 11.2 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) in this
section.)
Forced stop(EM1)
J
V
0
L
t
1
e
max
60
J
L
: Maximum coasting distance .................................................................................................[mm][in]
max
Vo
: Machine rapid feed rate ........................................................................................ [mm/min][in/min]
J
: Servo motor inertial moment................................................................................. [kg cm
M
J
: Load inertia moment converted into equivalent value on servo motor shaft
L
................................................................................................................................. [kg cm
: Brake time constant ........................................................................................................................ [s]
t
: Delay time of control section........................................................................................................... [s]
e
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 (11.2).
16
14
12
10
053
8
6
4
2
0
0
500 1000 1500 2000 2500 3000
ON
OFF
V
0
Machine speed
Fig. 11.3 Dynamic brake operation diagram
L
....................................................................................................................... (11.2)
M
23
73
43
13
Speed[r/min]
HC-KFS series
Time constant
t
e
20
18
16
14
12
10
8
6
4
2
0
500
0
11 - 5
Time
23
73
053
43
13
1000 1500 2000 2500 3000
Speed [r/min]
HC-MFS series
][oz in
]
2
2
][oz in
]
2
2
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