Mitsubishi Electric MR-J4-100A(-RJ), Instruction Manual

Page: 657 / 908

16. USING A DIRECT DRIVE MOTOR
16 - 18
16.5.3 Dynamic brake characteristics
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.
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 the direct drive motor stops when
using EM1 (Forced stop 1) frequently in other than emergency.
(1) Dynamic brake operation
(a) Calculation of coasting distance
Fig. 16.3 shows the pattern in which the servo motor comes to a stop when the dynamic brake is
operated. Use equation 16.1 to calculate an approximate coasting distance to a stop. The dynamic
brake time constant
τ varies with the direct drive motor and machine operation speeds. (Refer to (1)
(b) in this section.)
Dynamic brake
time constant
τ
Time
t
e
V
0
ON
OFF
EM1 (Forced stop 1)
Machine
speed
Fig. 16.3 Dynamic brake operation diagram
L
max
=
60
V
0
•
J
M
t
e
+ 1 + J L
······················································································ (16.1)
L
max
: Maximum coasting distance [mm]
V
0
: Machine's fast feed speed [mm/min]
J
M
: Moment of inertia of direct drive motor [kg•cm
2
]
J
L
: Load moment of inertia converted into equivalent value on direct drive motor rotor [kg•cm
2
]
τ : Dynamic brake time constant [s]
t
e
: Delay time of control section
There is internal relay delay time of about 10 ms.
[s]