58
7 CHARACTERISTICS
7.3 Dynamic brake characteristics
7.3
Dynamic brake characteristics
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 EM1 (Forced stop 1) after servo motor stops when using EM1 frequently in other than
emergency.
Calculation of coasting distance
The following figure shows the pattern in which the servo motor comes to a stop when the dynamic brake is operated.
Use the following equation to calculate an approximate coasting distance to a stop.
The dynamic brake time constant
τ
varies with the servo motor and machine operation speeds.
Page 59 Dynamic brake time constant
A working part generally has a friction force. Therefore, actual coasting distance will be shorter than a maximum coasting
distance calculated with the following equation.Page 59 Dynamic brake time constant
CAUTION
• The coasting distance is a theoretically calculated value which ignores the running load such as friction. The calculated value will be longer than the actual
distance. If an enough braking distance is not provided, a moving part may crash into the stroke end, which is very dangerous. Install the anti-crash
mechanism such as an air brake or an electric/mechanical stopper such as a shock absorber to reduce the shock of moving parts.
L
max
:
Maximum coasting distance [mm]
V
0
:
Machine's fast feed speed [mm/min]
J
M
:
Moment of inertia of the servo motor [× 10
-4
kg•m
2
]
J
L
:
Load moment of inertia converted into equivalent value on servo motor shaft [× 10
-4
kg•m
2
]
τ
:
Dynamic brake time constant [s]
t
e
:
Delay time of control section [s]
There are delays caused by multiple drive units being in the process of stopping the servo motor with the dynamic brake, by a magnetic contactor built
into the external dynamic brake (about 100 ms in total), and by external relays.
Dynamic brake
time constant
τ
Time
t
e
V
0
ON
OFF
EM1 (Forced stop 1)
Machine speed
60
V
0
J
M
t
e
+
τ
1 +
J
L
L
max
=
•
Summary of Contents for Melservo-J4 MR-J4-DU*B4-RJ100 Series
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Page 75: ...9 USING STO FUNCTION 73 9 MEMO ...
Page 81: ...11 APPENDIX 11 1 Analog monitor 79 11 MEMO ...
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