Mitsubishi Electric MR-J4, Instruction Manual

Page: 365 / 794

10. CHARACTERISTICS
10 - 8
10.3 Dynamic brake characteristics
POINT
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
(Forced stop 1) frequently in other than emergency.
Servo motors for MR-J4 may have the different coasting distance from that of
the previous model.
The electronic dynamic brake operates in the initial state for the HG series servo
motors of 600 W or smaller capacity. The time constant "
τ " for the electronic
dynamic brake will be shorter than that of normal dynamic brake. Therefore,
coasting distance will be longer than that of normal dynamic brake. For how to
set the electronic dynamic brake, refer to [Pr. PF06] and [Pr. PF12].
10.3.1 Dynamic brake operation
(1) Calculation of coasting distance
Fig. 10.3 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use equation 10.2 to calculate an approximate coasting distance to a stop. The dynamic
brake time constant
τ varies with the servo motor and machine operation speeds. (Refer to (2)(a), (b) of
this section.)
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.
V
0
OFF
ON
Machine speed
t
e
Time
EM1 (Forced stop 1)
Dynamic brake
time constant
τ
Fig. 10.3 Dynamic brake operation diagram
L
max
=
60
V
0
•
t
e
+
J
M
1 + J
L ··························································································· (10.2)
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]
For 7 kW or lower servo, there is internal relay delay time of about 10 ms. For 11 kW to 22 kW servo,
there is delay caused by magnetic contactor built into the external dynamic brake (about 50 ms) and
delay caused by the external relay.