How to reduce the heat of the decelerated stepper motor

The holding torque of a decelerated stepper motor is similar to the "power" of a traditional motor. Of course, there are also essential differences. The physical structure of a stepper motor is completely different from that of an AC and DC motor. The output power of the motor is variable. Generally, which type of motor is selected according to the required torque (that is, the torque of the animal's body). Generally speaking, if the torsion is less than 0.8N.m, choose 20, 28, 35, 39, 42 (the diameter or square of the motor body, the unit is mm); the torsion is about 1N.m, and the 57 motor is more suitable. In the case of multiple N.M. or larger torques, stepping motors of 86, 110, and 130 specifications should be selected.

To understand why stepper motors generate heat. For various stepper motors, the interior is composed of iron cores and winding coils. Windings have resistance, energization will produce losses. The loss is proportional to the square of the resistance and the current. This is what we often call copper loss. If the current is not a standard DC or sine wave, harmonic losses will also occur; iron cores have hysteresis The eddy current effect also produces loss in an alternating magnetic field, and its magnitude is related to the material, current, frequency, and voltage, which is called iron loss. Copper loss and iron loss will show up in the form of heat, which affects the efficiency of the motor. Stepper motors generally pursue positioning accuracy and torque output, with relatively low efficiency, relatively large currents, and high harmonic components. The frequency of current alternation also changes with the speed. Therefore, stepping motors generally have heat generation, and the situation is more than normal. The AC motor is serious. Furthermore, controlling the heating of the stepping motor within a reasonable range to what extent the heating of the motor is allowed depends mainly on the internal insulation level of the motor. The internal insulation performance will only be destroyed at high temperatures (above 130 degrees). So as long as the interior does not exceed 130 degrees, the motor will not be damaged, and the surface temperature will be below 90 degrees at this time. Therefore, the surface temperature of the stepper motor is normal at 70-80 degrees.

A simple method of temperature measurement is with a point thermometer, and it can also be roughly judged: it can be touched by hand for more than 1-2 seconds, not exceeding 60 degrees; it can only be touched by hand, about 70-80 degrees; dripping a few drops of water quickly The temperature is over 90 degrees; of course, it can also be detected with a temperature measuring gun. Thirdly, when the heat of the stepper motor changes with the speed, when the constant current drive technology is used, the current of the stepper motor will remain relatively constant at static and low speed to maintain a constant torque output. When the speed is high to a certain level, the internal back EMF of the motor will increase, the current will gradually decrease, and the torque will also decrease. Therefore, the heat generated by copper loss is related to speed. The heat is generally high at static and low speeds, and low at high speeds. However, the iron loss (although it accounts for a small proportion) changes in a different situation, and the entire heat generation of the motor is the sum of the two, so the above is just a general situation. Fourth, the influence of heat generation Although the heat generation of the motor generally does not affect the life of the motor, it is unnecessary for most customers to care. However, severe fever will bring some negative effects. For example, the different thermal expansion coefficients of the internal parts of the motor lead to changes in the structural stress and small changes in the internal air gap, which will affect the dynamic response of the motor, and it will easily lose step at high speed. Another example is that in some occasions, excessive heating of the motor is not allowed, such as medical equipment and high-precision test equipment. Therefore, necessary control should be performed on the heating of the motor. Finally, reducing the heat of the motor to reduce the heat is to reduce the copper loss and iron loss. There are two ways to reduce copper loss, reducing resistance and current. This requires the selection of motors with small resistance and low rated current when selecting models. For two-phase motors, motors that can be connected in series do not need to be connected in parallel. But this often contradicts the requirements of torque and high speed. For the selected motor, you 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 a static state, and the latter simply cuts off the current. In addition, since the current waveform of the subdivision drive is close to sinusoidal, there are fewer harmonics, and the motor will generate less heat. There are not many ways to reduce iron loss. The voltage level is related to it. Although the high-voltage drive motor will bring about the improvement of high-speed characteristics, it also brings an increase in heat generation. Therefore, the appropriate drive voltage level should be selected, taking into account high speed, stability, heat generation, noise and other indicators.