Mitsubishi Electric FR-A700 Technical Manual page 456

1) Calculate the brake torque required to decelerate
the motor in the determined deceleration pattern:
J (N -N )
T 1 2
T
- T
B =
9.55 t
2) Calculate the required brake torque coefficient β
as following formula
T
B
β =
TM: rated motor torque to be used
T
M
3) From the technical note No.30 (data part), select
the brake unit which satisfies the brake torque
coefficient β.
4) Using the following formula, find the power
W returned from the load, and using the
MECH
data manual, make sure that the intersection of
the deceleration time of t and the permissible
brake unit power W
RS
brake unit used (refer to Technical note No.30
(data part)). (The motor-compensated power is
ignored. For further details, refer to the Technical
note No.31 (selection part).
W = 0.1047 T
MECH
5) When using the brake unit frequently (more than
10 times/hour as a guideline), ensure that the
value calculated by the following formula is within
the permissible continuous power W
Technical note No.30 (data part)).
Brake operation time
W = W
MECH
[Example 3] Calculated in the conventional unit system
To decelerate a 3.7kW 4P motor from 1750 to 0 r/min in two
seconds with FR-F720-3.7K.
Assuming that:
Load torque (TL) (reflected to the motor shaft)
1.96 [N m]
: 10% of 3.7kW 4P
Load JL (reflected to the motor shaft)
: 10 times greater than 3.7kW 4P
Rated motor torque (T ) : 19.6 [N m] on 3.7kW 4P
M
The brake torque is calculated as follows:
(0.016 + 0.16) (1750 - 0)
TB =
9.55 2
T
Brake torque coefficient =
T
Since the brake torque coefficient ( ) must be 0.72 or higher,
select the brake unit combination, in which the brake torque
coefficient ( ) = 1.2, from the Technical Note No. 30 (Data Part).
Hence, the brake unit used in this case is the BU-3700.
W = 0.1047 14.2 (1750 + 0)/2 = 1300[W]
MECH
Since the energy of 2200 [W] is consumed in two seconds, the
BU-3700 brake unit can be used according to the Technical note.
(1300 [W] < 2200 [W])
2s
min [N m]
L
is below the curve of the
(N +N )/2[W]
B 1 2
(refer to
RC
[W]
1 cycle time
2
0.16 [kg m ]
- 1.96 = 14.2[N m]
14.2
B
= = 0.72
19.6
M
BU-3700
2200W
[Exercise 4]
It is desired to repeat the start and stop of the load used in
Exercise 3 at intervals of 15 seconds.
1300
W =
15
The BU-3700 can be used because its permissible continuous
power is 300W according to the data in the manual. In addition
to this calculation, it is also necessary to examine whether the
motor may be used repeatedly.
(5) Continuous use of the brake unit
When the motor is used in the brake region, select a
brake unit which satisfies the condition that the brake
resistor power consumed continuously is not more
than the permissible continuous power of the brake
unit.
When a negative load is operated repeatedly as
shown below, find the power returned from the load in
the whole region where the negative load is applied
during other than deceleration and check that it is
within the permissible continuous power W
data part of Technical note.
Operation pattern of the continuous regenerative duty
(6) Combination of the brake unit and inverter
common
A larger brake unit may be required when the
repeated use of the brake unit is frequent or a
negative load is driven. When a larger brake unit is
used, the inverter capacity must also be increased.
When higher brake capability is required, select the
FR-CV (power
converter).
490
SELECTION
2
= 173[W]
Rise
Fall
T
load
supply regeneration
common
in the
RC
common