Vacuum | deep low temperature | high temperature | radiation resistance and automation solutions
21
2022
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11
About stepper motor heating
First, about the stepper motor heating
1. Why does the stepper get hot?
All kinds of motors we usually see have iron cores and winding coils inside. The winding has resistance, and the power will produce loss, the loss is proportional to the square of the resistance and current, which is what we often say copper loss, if the current is not the standard DC or sine wave, it will also produce harmonic loss; The core has a hysteresis eddy current effect, which will also produce a loss in the alternating magnetic field, and its size is related to the material, current, frequency, and voltage, which is called iron loss. Copper loss and iron loss will be manifested in the form of heat, thus affecting the efficiency of the motor. The stepper motor generally pursues positioning accuracy and torque output, the efficiency is relatively low, the current is generally large, and the harmonic component is high, and the frequency of current alternating also changes with the speed, so the stepper motor is generally heated, and the situation is more serious than the general AC motor.
2, why high and low temperature stepper motor, servo motor heating higher than ordinary motor?
The coil material of the high and low temperature motor needs to withstand higher temperatures and have higher insulation strength, so the heat dissipation performance is worse than the coil of the general servo motor, but it will not affect the high temperature performance of the motor.
3, the heating of the stepper motor changes with speed:
When the constant current drive technology is used, the current of the stepper motor is maintained constant at static and low speed to maintain constant torque output. When the speed is high to a certain extent, the internal back potential of the motor increases, the current will gradually decrease, and the torque will also decrease. Therefore, the heat caused by copper damage is related to speed. Static and low speed heating is generally high, high speed heating is low. However, the change of iron loss (although the proportion is small) is not entirely true, and the heat of the motor is the sum of the two, so the above is just a general situation.
4, the impact of fever
Although the motor heating generally does not affect the life of the motor, most customers do not need to pay attention. However, it can bring some negative effects in severe cases. If the thermal expansion coefficient of each part of the motor is different, the change of structural stress and the small change of the internal air gap will affect the dynamic response of the motor, and the high speed will be easy to lose step. For example, some occasions do not allow excessive heat of the motor, such as medical devices and high-precision test equipment. Therefore, the heating of the motor should be controlled as necessary.
5, how to reduce the heat of the motor:
Reducing heat means reducing copper and iron losses. There are two directions to reduce copper loss, reduce resistance and current, which requires that the motor with small resistance and small rated current should be selected as far as possible in the selection of two-phase motors, which can be connected in series without parallel motors. However, this often contradicts the requirements of torque and high speed. For the motor that has been selected, it should make full use of the driver's automatic half-current control function and off-line function, the former automatically reduces the current when the motor is at static, the latter simply cuts off the current. In addition, because the current waveform of the subdivision driver is close to sine, the harmonics are less, and the motor will heat less. There are not many ways to reduce iron loss, and the voltage level is related to it. Although the high-voltage driven motor will bring the improvement of high-speed characteristics, it will also bring the increase of heat. Therefore, the appropriate driving voltage level should be selected, taking into account high-speed, stationary and heat, noise and other indicators.
Second, how to change the stepper motor rotation reverse?
After the stepper motor is installed, if the actual rotation direction is opposite to the desired rotation direction, and it is not convenient to change the rotation direction of the motor by modifying the control program, you can change the rotation direction of the motor by switching the wiring sequence of the motor lead A+, A- (or switching B+, B-) and the driver.
The three-phase stepper motor can be reversed by switching any two phases in the three phases.
Three, how to set the output current of the stepper driver?
In general, the output current of the stepper driver is set to be no greater than the phase current of the motor. There are two exceptions:
1, if the selected motor output torque is slightly less than the required torque of the load, the electric driver output current can be set to slightly greater than the phase current of the motor (for example, the rated current is 2A, can be set to 2.5A or 3A). But the greater the current, the greater the heat of the motor.
2, for low temperature environment, set the output current of the stepper motor driver is slightly higher than the rated current of the stepper motor, in order to improve the output torque of the stepper motor.
How to choose the working voltage of the stepper driver?
The higher the power supply voltage of the stepper driver, the smaller the torque attenuation at high speed. Within the voltage range allowed by the stepper driver, it is recommended to choose as high a drive voltage as possible to improve the high-speed torque output of the stepper motor. However, the higher the voltage, the greater the heat of the stepper motor, the greater the vibration noise.
Five, how much is the standard length of the lead of the stepper motor? Can you extend it? What is the effect of lead extension on motor performance? What is the maximum extension?
1, KH stepper motor standard lead length of 3 meters, KVM stepper motor standard lead length of 1 meter.
2, the stepper motor lead can be extended to 15 meters. More than 15 meters of motor leads will lead to reduced current and motor torque will be attenuated.
6. The pulse direction signal of the servo driver requires the output signal of the PLC
High innovation drivers require the PLC pulse direction signal to be NPN output
1, Delta, Panasonic, Mitsubishi and other PLC pulse direction signal is generally NPN output, can be used directly
2, Siemens PLC pulse direction signal is generally PNP output, need to use PNP to NPN signal conversion module.
Seven, the pulse direction signal of Coley servo driver requires the output signal of PLC
The Copley driver requires the PLC pulse and direction signals to be PNP output
1, Siemens PLC is the output of PNP, can be used directly
2, Delta, Panasonic, Mitsubishi and other Japanese PLC are generally NPN output, need to use signal conversion module. Similar to the image above, change the output to "NPN to PNP"
Eight, what is the longest distance between the servo motor and the drive?
The distance between the motor and the drive is generally limited to 20 meters. It is not recommended that the cable be interchanged.
1, if a longer distance is needed, it is necessary to deal with the cable shielding and adopt the necessary anti-interference measures, such as the isolation transformer, driver grounding, power cable plus magnetic ring at the main power input of the servo driver.
2, if the cable needs intermediate switching, it is necessary to deal with the shielding layer of the feedback cable to prevent electromagnetic interference.
9. The difference between absolute position feedback and incremental position feedback
1, absolute position feedback element:
It can remember the position of the moving part before the power failure, and if the moving part has been moved manually during the power failure, the absolute value feedback element can recognize the position change after the power failure.
Systems with absolute position feedback elements do not need to return to the origin after power-on.
According to the method of saving multi-turn data during power failure, the multi-turn absolute position feedback element is divided into: mechanical type and battery type. The mechanical type uses the multi-stage gear mode to remember the multi-turn data, and the battery type uses the backup battery to save the multi-turn data. Batteries need to be replaced regularly (2-3 years).
The absolute value encoder (optional) of KECM series servo motor from Kingsley Technology is a mechanical multi-turn absolute value encoder.
2, incremental position feedback element:
When the system is powered on, the position data are all 0, and the position of the moving parts before the power failure cannot be remembered. If the moving parts have been moved manually during the power failure, the incremental feedback element cannot recognize the position change after the system is powered on again.
Systems with incremental position feedback elements need to be returned to the origin after power-on to determine the initial zero position.
The position feedback element of KECM series servo motor of Kingsley Technology adopts rotary transformer (standard), which is an incremental feedback element.
Ten, about the motor insulation level
According to the ability of different insulation materials to withstand high temperature, seven maximum allowable temperatures are specified, which are Y, A, E, B, F, H and C according to the temperature size. Their allowable operating temperatures are shown in the table below.
| Insulation class code |
Y |
A |
E |
B |
F |
H |
C |
| Allowable operating temperature (℃) |
90 |
105 |
120 |
130 |
155 |
180 |
180以上 |
For example, Class B insulation indicates that the thermal temperature of the material used in the motor is 130 ° C. The user should ensure that the generator insulation material does not exceed the temperature when the motor is working to ensure the normal operation of the generator. The motor insulation grade of Kingsley Technology is:
KH series stepper motor: Class B insulation
KVM series stepper motor: Class C insulation
KECM series servo motor: H class insulation
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Chengdu Kingshili Technology Co., Ltd.
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