01 
Characteristic of Speed Control Motor 

 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 speedcontrol,
braking, slow run, slow stop, etc.
 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 nonexcitation 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 appropriate uses.
 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.)

02 
Selection of the motor 

¨ç Selection of motor and controller
 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.
¨è Selection of gear ratio of gearhead
 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 rpm).
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.)
i = 



Use the nearest approximated value of the gearhead (gear ratio=i) 
¨é Highest number of rotations and lowest number of rotations of the motor shaft
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]
¨ê Required torque of the motor
 The required torque of the motor is found as follows.
TM : Required torque of the motor [g¡¤§¯]
TL : Torque necessary to operate actual load [g¡¤§¯]
i : Reduction ratio
¥ç : Efficiency of the gearhead
¨ë Selection of the motor
 The motor is decided by the required torque TM, rotational frequencies NL ~NH and the torquenumber of rotations curve
(hereafter, NT curve).
 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¡É,
then there are no problems with use.)
¨ì Selection of gearhead
 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.

03 
Sample Calculation for Selection (Fig. 2) 

With 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 : 10§¯
 Operating torque : 30§¸ ¡¤ §¯
 Power : Single phase 110V 60§Ô
Instantaneous braking in emergencies, but no holing power.
¨ç MOTOR and CONTROLLER
 Rotation is in one direction and there is no holding power. Therefore, the induction motor is selected.
¨è Revolutions of output shaft of gearhead
 The number of rotations of the gearhead shaft when the belt conveyor speed is 1m/minute.
Number of rotations = 

Speed of belt conveyor 
Outer diameter of drum 


= 



¡Ö 3.18 [rpm] 
 Number of rotations of the gearhead shaft when the belt conveyor speed is 2m/minute.
Number of rotations = 

Speed of belt conveyor 
Outer diameter of drum 


= 



¡Ö 6.37 [rpm] 
 Number of rotations of the gearhead shaft when the belt conveyor speed is 4m/minute.
Number of rotations = 

Speed of belt conveyor 
Outer diameter of drum 


= 



¡Ö 12.74 [rpm] 
¨é Gear ratio
The gear ratio is calculated using the higher number of rotations of the gearhead.
Number of rotations of the motor 
Number of rotations of the gearhead 


= 



¡Ö 102 
Using 102, since there is no such reduction ratio as 1/102, 1/100 is selected.
¨ê Number of rotations of motor shaft
 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.
3.18 ¡¿ 100 = 318 [rpm]
6.37 ¡¿ 100 = 637 [rpm]
12.74 ¡¿ 100 = 1274 [rpm]
¨ë Required torque of motor
 The transfer efficiency of a gearhead with gear ratio 100 is 66%, so the required torque of the motor is
Operating torque 
Gear ratio ¡¿ Efficiency 


= 



¡Ö 0.45 [kg¡¤cm] 
¨ì Selection of motor
 From the NT curve of the induction motor, it can be seen that the K8IG25NCS 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.

04 
The Principle of Speed Control 

¨ç The principle of speed control
 (Fig. 3) is the basic speed control structure of the close loop current control method.
The following are explanations of close loop speed control.
 If TachoGenerator 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 voltage".
 Comparative voltage operates the motor through the boltage amplifier and the voltage controller.
 Comparative voltage is mostly controlled by zerocrossing. 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 TachoGenerator changes, the number
of rotations immediately changes with the value.
 Accordingly, close loop speed control detects the number of rotations of the motor and controls the operating
voltage to maintain it constantly.
¨è Primary voltage control by close loop
 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 F.
 To stabilize the number of rotations, it has to make loop smaller like C¡æD¡æE¡æF by controlling the primary voltage.
 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 constant.
¨é Operation of speed controller
 The speed controller is explained in (Fig. 5).
 Number of rotations of the motor comes from the TachoGenerator 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 comparative amplifier.
 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. 6).

05 
Limit of Use 

¨ç Limit curve
 TIn the AC speed control motor NT 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¡É. Therefore, if the temperature of the winding section is less than 120¡É, 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¡É. The
difference between the winding section of the motor and the housing surface is generally between 10¡É~20¡É.
¨è The meaning of for less than 90¡É surface temperature of the motor housing
 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¡É.)
 The difference between the temperature of the surface of the motor and the winding section is about 10¡É~20¡É.
(A motor with a cooling fan has about 30¡É because the cooling fan cools the surface of the motor.)
 When the temperature of the winding section is 130¡É, the surface temperature is about 110¡É.
Therefore, 90¡É is the sufficient value.
¨é Range of use according to instantaneous braking
 Instantaneous braking uses direct current which is halfwave rectified current in the motor thus causing the
temperature of the motor to rise rapidly.
 In the NT graph, the limit curve is in the case of continuous operation, therefore, if instantaneous braking
is applied often, the range of the limit decreases.
 For instantaneous braking, temperature rises by frequent braking, thus care should be taken so that the surface
temperature of the motor does not exceed 90¡É.

