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15. SERVO AMPLIFIERS WITH A LARGE CAPACITY
(
30k TO 55kW
)
15.8.3 Dynamic brake characteristics
POINT
Dynamic brake operates at occurrence of alarm, servo emergency stop warning
(AL.E6), and when power is turned off. Do not use dynamic brake to stop in a
normal operation as it is the function to stop in emergency.
Maximum usage time of dynamic brake for a machine operating under
recommended load inertia moment ratio is 1000 time while decelerating from
rated speed to a stop with frequency of once in 10 minutes.
Be sure to make emergency stop (EMG EM1) valid after servo motor stops
when using emergency stop (EMG
EM1) frequently in other than emergency.
(1) Dynamic brake operation
(a) Calculation of coasting distance
Fig. 15.2 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use Equation 15.1 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 (b). Please
contact your local sales office for the servo motor not indicated.)
te
Forced stop (EM1)
Machine speed
Time
OFF
ON
V
0
Dynamic brake
time constant
Fig 15.2 Dynamic Brake Operation Diagram
60
L
max
Vo
t
e
1
JM
JL
················································································································ (15.1)
L
max : Maximum coasting distance
·········································································································· [mm]
V
0 : 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
]
: Dynamic brake time
constant············································································································· [s]
t
e : Delay time of control
section·············································································································· [s]
There is delay caused by magnetic contactor built into the external dynamic brake (about 50ms) and
delay caused by the external relay.