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11. CHARACTERISTICS
11.3 Dynamic brake characteristics
Fig. 11.6 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 Fig. 11.7. Please contact
us for the servo motor not indicated.)
V
0
Time constant
Forced stop(EM1)
OFF
ON
Machine speed
t
e
Time
Fig. 11.6 Dynamic brake operation diagram
L
max
60
V
0
J
L
J
M
t
e
1
....................................................................................................................... (11.2)
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]
For 7kW or less servo, there is internal relay delay time of about 30ms. For 11kW 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.
Speed[r/min]
0
14
16
2
4
8
10
6
12
0 500 1000 1500 2000 2500 3000
13
73
23
43
053
Time constant [ms]
a. HC-KFS series
Fig. 11.7 Dynamic brake time constant 1