伺服產品
/Servo Products
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Hardware Manual of 380V 7.5kW Servo Drive II (SPD-32C1-075)
Wiring and Signal (SPD-32C1-075)
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61
For example, if the external torque is 50% of rated torque, the speed is 2000 (rpm), and the motor rated torque is
2 (Nm), then the external torque produces a power of 0.5 * 2 * 2000 * 2
π
/ 60
≈
210 W. To be safe, that number is
usually multiplied by a safety factor of around 2 ~ 3, therefore the user needs to select a regenerative resistor of
more than 420W.
Free of External Torque Load
Assuming that the motor moves back and forth, the energy generated by the inertial force during braking will be
poured back into the drive. At this time, the capacitor of the DC bus terminal of the drive is the first buffer to absorb
and reuse the energy. However, the absorption of energy by the capacitor causes the DC bus voltage to rise, so
when the voltage rises to a certain level, the second buffered regenerative resistor is turned on to convert the
energy into heat and discharge it.
The calculation method of the regenerative energy generated by the spindle motor of the drive during braking is
provided below, and the user can calculate the required resistance according to different occasions.
E
0
in the table below is the regenerative energy required to dissipate from the rated speed to the standstill when
the motor is load-free, E
0
=J*
ω
r
2
/182, where J is the rotor inertia (kg-m
2
) and
ω
r is the rated speed of the motor
( Rpm). And Ec is the energy that the DC bus capacitor can absorb, Ec = C*(V
b,max
2
-V
b
2
)/2, where C is the capacitance
value of the DC bus terminal. V
b,max
is the maximum voltage that the DC bus can withstand, the 220V drive can
withstand 400 V, and the 380V drive can withstand 800 V. The V
b
value is the rated voltage of the DC bus, and the
value is 2 times the root of the input supply voltage.
Considering the actual application, assume that the load inertia ratio is N times the motor inertia. If the speed is
braked from the rated M times to zero speed, the regenerative resistor must consume
E
0
(N+1)*M
2
-Ec
Joule. If the
motor reciprocating cycle (Time of accelerating, being steady, to decelerating) is T sec, then the regenerative
resistor power W =
1.2
[E
0
*(N+1)*M
2
-Ec]/T, 1.2 is the safety factor.
In addition, according to the application of the spindle cover, the allowable frequency index is provided for the
user to select. The allowable frequency is defined as the continuous acceleration and deceleration of the motor. In
the case where the regenerative resistor and the motor are not overheated, the maximum number of round trips
per minute is equal to 60 seconds divided by the round trip period T, i.e. 60/T. For example, when the milling
machine is performing drilling and tapping, the spindle will frequently perform acceleration and deceleration
(single drilling involves two acceleration and deceleration actions). If it is desired that the regenerative resistor is
not prone to overheating and smoke, the number of drilling per minute must be limited to less than half of the
allowable frequency.
M3 single-axis drive-spindle motor
Drive model
Axial motor model
Rotor inertia J
(10
-4
kg-m
2
)
Rated speed
(rpm)
No-load rated speed to
static
rejuvenation energy
Eo(J)
SPD-32C1-075
S08-L11-24B4-0H0
37
5000
508
Milling machine spindle cover
(The following tables are calculated based on the load inertia ratio of 100%, and the bold indicates the
recommended power)
S08-L11-24B4-0H0
