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By using it with the speed controller,
a wide range of speed can be controlled (50Hz :
90~1400rpm, 60Hz : 90~1700rpm). The speed can be
controlled easily with the speed controller.
Depending on the type of speed controller, it
can be combined with the motor for various purposes
such as speed-control, braking, slow run, slow stop,
Built in T.G. (Tacho Generator) to control the
feedback. Thus, even if the power frequency is changed
but the rotating numbers does not change.
When the speed control motor with an electronic
brake is used with the speed controller, instantaneous
braking and electronic braking operate simultaneously
for strong braking power.
The speed control motor with an electronic brake
also has a non-excitation run type of electronic
brake. Even if the power is off, braking is operated
to maintain braking of a load.
Speed control motors are consisted of the induction
motor the reversible motor and the speed control
motor with an electronic brake which are small AC
motor. The applicable motor should be selected for
Output range of the induction motor is 6W~90W
(unit types are 6W~180W). The reversible motor has
an output range of 6W~40W and the electronic brake
motor has an output range of 6W~40W. (However, SR
types are 6W~90W.)
- Is speed control needed only?
- Is instantaneous braking needed?
- Is maintenance of braking power needed?
- How much is the output of the applicable motor?
- Are the slow run, slow stop runctions needed?
According to the above conditions, the types of speed
control motors and speed controllers are selected.
When the number of rotations of the output shaft of
the gear requires A rpm to B rpm, the gear ratio is
calculated by using the higher number of rotations (B
For the AC speed control motor, the number of rotations
for the motor is calculated with 1300 rpm. (This is
the reason for the output torque and the range of use
are large at 1300 rpm.)
Use the nearest approximated value of the gearhead
When the highest number of rotations
is NH and the lowest number of rotations is NL,
they are as follows.
Highest number of rotations of the required motor:
NH = B x i [rpm]
Lowest number of rotations of the required motor:
NL = A x i [rpm]
The required torque of the motor is found as follows.
여기서 TM : Required torque of
the motor [g · ㎝]
TL : Torque necessary to operate
actual load [g · ㎝]
i : Reduction ratio
η : Efficiency of the gearhead
The motor is decided by the required
torque TM, rotational frequencies NL~NH and the
torque-number of rotations curve (hereafter, N-T
In the case of the AC speed control motor (Fig.
1) of the curves, the moment curve (i curve) selects
the motor below the limit curve. (Even in the area
above the limit curve, if the surface temperature
of the motor is less than 90℃, then there are no
problems with use.)
After the motor is selected in the
above manner, the gearhead is decided with consideration
of the torque size of the load. Confirm that the
torque of the load is within the torque allowable
by the gearhead.
single direction rotation of the belt conveyor, change
the speed of the item being transported to 1m/minute,
2m/minute, and 4m/minute.
Drum diameter : 10cm
Operating torque : 30㎏ · ㎝
Power : Single phase 110V 60Hz
Instantaneous braking in emergencies, but no holing power.
- Rotation is in one direction and there is no holding
power. Therefore, the induction motor is selected.
- The number of rotations of the gearhead shaft when the
belt conveyor speed is 1m/minute.
- Number of rotations of the gearhead shaft when the belt
conveyor speed is 2m/minute.
- Number of rotations of the gearhead shaft when the belt
conveyor speed is 4m/minute.
The gear ratio is calculated using the higher number of
rotations of the gearhead.
Using 102, since there is no such reduction ratio as 1/102,
1/100 is selected.
The number of rotations of the motor shaft is calculated
by the number of rotations of the gearhead shaft x reduction
ratio for each speed of the belt conveyor to get the following.
The transfer efficiency of a gearhead with gear ratio
100 is 66%, so the required torque of the motor is
From the N-T curve of the induction motor, it can be seen
that the K8IG25NC-S motor and the K8G100B gearhead can
be combined to use. However, in such a case, make sure
that the inertia load should fall within the specification
of the selected motor.
(Fig. 3) is the basic speed control
structure of the close loop current control method.
The following are explanations of close loop speed
If Tacho-Generator changes the voltage
that is proportional to the rotations, make comparison
between the number of rotations of the motor and
the voltage preset by the volume.
This difference in voltage is called "comparative
Comparative voltage operates the motor through
the boltage amplifier and the voltage controller.
Comparative voltage is mostly controlled by zero-crossing.
Number of rotations is decided by the value that
the speed controller selects.
Even when the load changes, the number of rotations
does not change. When the Tacho-Generator changes,
the number of rotations immediately changes with
Accordingly, close loop speed control detects
the number of rotations of the motor and controls
the operating voltage to maintain it constantly.
The relationship between the torque
of the induction motor and the number of rotations
is as follows (Fig. 4) when the applied voltage
(primary voltage) of the motor is changed.
The current voltage is V1, the torque
of the load is T1 and the number of rotations is
N1. That point is A. Speed is increased to B and
when the voltage is changed from V1 to V2, then
it moves to C.
At C, the torque of the load T1 is larger than
the torque of the motor, thus the number of rotations
are lower than N2.
When the number of rotations becomes N3 and the
voltage is raised to V3, then the generated torque
becomes larger than the torque of the load to move
to E, and then the speed increases again toward
To stabilize the number of rotations, it has to
make loop smaller like C→D→E→F by controlling the
During the primary voltage control by close loop,
to meet the changes according to the number of rotations
of the motor, it should have the primary voltage
controlled and maintain the number of rotations
The speed controller is explained
in (Fig. 5).
Number of rotations of the motor comes from the
Tacho-Generator through feedback voltage through
the rectifying circuit.
The difference between the selected voltage of
the speed controller which was controlled in the
VR and the feedback voltage is amplified in the
A trigger signal is generated from the sawtooth
waveform which comes from the sawtooth waveform
generator, comparator from the comparative signal
and triac from the trigger circuit.
The angle of the triac is controlled with the
trigger signal to control voltage in the motor.
This makes the number of rotations of the motor
constant, thereby controlling it. Refer to (Fig.
TIn the AC speed control motor N-T
graph (Fig. 7), the area below the limit curve is
called the continuous operation area.
The limit curve does not go beyond the highest
temperature allowed by the motor (continuous for
induction motors and 30 minutes rating for reversible
motors) and because continuous operation is possible,
it is decided by the temperature of the motor.
Our speed control motor has a class
B insulation and the permitted temperature of the
winding section is 130℃. Therefore, if the temperature
of the winding section is less than 120℃, continuous
operation is possible, but it is difficult or the
user to measure the temperature of the winding section,
continuous operation is generally possible when
the surface temperature of the motor housing is
less than 90℃. The difference between the winding
section of the motor and the housing surface is
generally between 10℃~20℃.
The highest part of the motor's rising
temperature is the winding section. Thus, the highest
allowable temperature is decided by the insulation
level of the winding section. (Our small AC motor
has a class B insulation and the highest allowable
temperature is 130℃.)
The difference between the temperature of the
surface of the motor and the winding section is
about 10℃~20℃. (A motor with a cooling fan has about
30℃ because the cooling fan cools the surface of
When the temperature of the winding section is
130℃, the surface temperature is about 110℃. Therefore,
90℃ is the sufficient value.
Instantaneous braking uses direct
current which is half-wave rectified current in
the motor thus causing the temperature of the motor
to rise rapidly.
In the N-T graph, the limit curve is in the case
of continuous operation, therefore, if instantaneous
braking is applied often, the range of the limit
For instantaneous braking, temperature rises by
frequent braking, thus care should be taken so that
the surface temperature of the motor does not exceed