Mitsubishi Electric Melservo-J3 Series MR-J3-B, Instruction Manual

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13 - 6
13. CHARACTERISTICS
13.3 Dynamic brake characteristics
POINT
The dynamic brake operates when an alarm or servo forced stop warning
(AE6) occurs, or when the power is turned off. Do not use dynamic brake to
stop in a normal operation as it is the function to stop in emergency.
For a machine operating at the recommended load to motor inertia ratio or less,
the estimated number of usage times of the dynamic brake is 1000 times while
the machine decelerates from the rated speed to a stop once in 10 minutes.
Be sure to enable forced stop (EMG) after servo motor stops when using forced
stop (EMG) frequently in other than emergency.
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.)
Dynamic brake
time constant
Forced stop(EMG)
OFF
ON
Machine speed
Time
V
0
t
e
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 ............................................................................................. [×10 -4 kg·m
2
]
J
L
: Load inertia moment converted into equivalent value on servo motor shaft .................... [×10 -4 kg·m
2
]
: Dynamic brake time constant ........................................................................................................... [s]
t
e
: Delay time of control section ............................................................................................................. [s]
For 7kW or lower servo amplifiers, there is internal relay delay time of about 10ms. For 11k to 22
kW servo amplifiers, there is delay caused by magnetic contactor built into the external dynamic
brake (about 50ms) and delay caused by the external relay.