As a digital execution element, stepper motor is widely used in motion control system. Many users and friends in the use of stepper motors, feel that the motor works with a large heat, the heart is skeptical, do not know whether this phenomenon is normal. In fact, heat is a common phenomenon of stepper motors, but what degree of heat is considered normal, and how to minimize the stepper motor heat?
一、to understand why the stepper motor will heat up.
For all kinds of stepper motors, the internal is composed of iron core and winding coil. Winding resistance, power will produce loss, loss size and resistance and current is proportional to the square, this is what we often call copper loss, if the current is not standard DC or sine wave, will also produce harmonic loss; core hysteresis eddy current effect, in the alternating magnetic field will also produce loss, the size of the material, current, frequency, voltage related, which is called iron loss. Copper loss and iron loss will be manifested in the form of heat generation, thus affecting the efficiency of the motor.
Stepping motor generally pursue positioning accuracy and torque output, efficiency is relatively low, the current is generally large, and high harmonic components, the frequency of current alternating with the speed and change, so stepping motors generally have a heat situation, and the situation is more serious than the general AC motor.
二、 the stepper motor heat control within a reasonable range.
Motor heat allowed to what extent, mainly depends on the motor internal insulation level. Internal insulation is not destroyed until it is at a high temperature (above 130 degrees). So as long as the internal does not exceed 130 degrees, the motor will not be damaged, and then the surface temperature will be below 90 degrees. Therefore, a stepper motor surface temperature of 70-80 degrees is normal. Simple temperature measurement method with a thermometer, you can also roughly judge: with the hand can touch more than 1-2 seconds, not more than 60 degrees; with the hand can only be touched, about 70-80 degrees; a few drops of water quickly vaporized, it is more than 90 degrees; of course, you can also use the temperature gun to detect.
三、 the stepper motor heating with the speed change.
When using constant current drive technology, the stepper motor in the static and low speed, the current will maintain a relatively constant to maintain a constant torque output.
When the speed is high to a certain degree, the reverse potential inside the motor rises, the current will gradually decrease, and the torque will also decrease. Therefore, the heat generation due to copper loss is related to the speed.
Heat generation is generally high at static and low speeds and low at high speeds. But the iron loss (although a small proportion) change is not the case, and the whole motor heat is the sum of the two, so the above is just a general situation.
四、 the impact of heat
Motor heat, although generally does not affect the life of the motor, most customers do not need to pay attention to. However, serious heat will bring some negative effects.
Such as the internal parts of the motor thermal expansion coefficient of different structural stresses caused by changes in the internal air gap and the small changes will affect the dynamic response of the motor, high-speed will be easy to lose step.
Another example is that some occasions do not allow excessive heating of the motor, such as medical equipment and high-precision test equipment. Therefore, the motor heat should be necessary control.
五、 reduce the motor heat.
Reduce the heat, is to reduce the copper loss and iron loss. Reduce copper losses have two directions, reduce resistance and current, which requires the selection of small resistance and rated current as much as possible in the selection of small motors, two-phase motors, can be used in series motors do not have to parallel motor.
But this often contradicts the requirements of torque and high speed.
For the motor has been selected, it should make full use of the drive's automatic half-current control function and offline function, the former automatically reduces the current when the motor is in static state, the latter simply cut off the current.
In addition, finely divided drive due to the current waveform close to sinusoidal, less harmonics, motor heating will be less. Not many ways to reduce iron losses, the voltage level is related to the motor of the high-voltage drive, although it will bring the high-speed characteristics of the enhancement, but also bring an increase in heat.
Therefore, we should choose the appropriate drive voltage level, taking into account the high speed, smoothness and heat, noise and other indicators.
Post time: Sep-13-2024