Solutions to stepper motor heating, solutions to speed failure and lost steps problems

Solutions to stepper motor heating, solutions to speed failure and lost steps problems

Heating is a common phenomenon in stepper motors, but what level of heat is considered normal, and how to minimize the heat generated by stepper motors? The following is a simple analysis.

Causes of stepper motor heating

• Why do stepper motors generate heat? For various stepper motors, the interior is composed of an iron core and a winding coil. The winding has resistance, and power will cause loss. The size of the loss is proportional to the square of the resistance and the current. This current is not a standard DC or sine wave, and will also produce harmonic losses; the iron core has a hysteresis eddy current effect, which also occurs in an alternating magnetic field. There will be loss, the size of which is related to the material, current, frequency, and voltage. This is called iron loss . Both copper loss and iron loss will appear in the form of heat, thus affecting the efficiency of the motor. Stepper motors are relatively large and have high harmonic components. The frequency of current alternation also changes with the speed. Therefore, stepper motors generally generate more heat than ordinary AC motors.
• Reasonable range of stepper motor heating. The extent to which the motor is allowed to generate heat mainly depends on the internal insulation level of the motor. The internal insulation performance will not be damaged at high temperatures (130 degrees as long as the interior does not exceed 130 degrees, and the surface temperature will be below 90 degrees. It is normal for the surface temperature of the stepper motor to be 70-80 degrees. Simple temperature measurement The method can be roughly judged by using a thermometer : if you can touch it with your hand for more than 1-2 seconds, it will not exceed 60 degrees. If you can only touch it with your hand, it will be about 70-80 degrees. If you drop a few drops of water and it will vaporize quickly, it will be 90 degrees. Degree or above.
• The heating of the stepper motor is constant with the change of speed to maintain constant torque output. When the speed is high enough, the back electromotive force inside the motor increases, the current will gradually decrease, and the torque will also decrease. , related to the heat caused by copper loss. This is not always the case at static and low speeds, and the entire heating of the motor is the sum of the two. The above is just a general situation.

Solutions to the heating problem of stepper motors

• Reduce the heat generated by the motor. Reducing heat means reducing copper loss and iron loss. Reducing copper loss has two directions: reducing resistance and current. This requires that when selecting a model, try to choose a motor with a small resistance and a small rated current. For two-phase motors, if a series motor can be used, a parallel motor is not required, but this often conflicts with the requirements of torque and high speed.
• For the selected motor, the automatic half-current control function and offline function of the driver should be fully utilized. The former automatically reduces the current when the motor is in a static state, and the latter simply cuts off the current.
• In addition, the subdivided driver current waveform is close to sinusoidal, with less harmonics, and the motor will generate less heat. There are not many ways to reduce iron loss, and the voltage level is related to it. Although high-voltage driven motors will improve high-speed characteristics, they will also increase heat generation.
• An appropriate driving voltage level should be selected, taking into account high band performance, stability, heat generation, noise and other indicators.

How to solve the problem of stepper motor speed not increasing and losing steps?

• First, the parameters of the motor are changed (for example: 57 stepper motor resistance = 0.5 ohms, inductance = 0.8MH). If we want to improve high-speed performance, we can reduce the resistance and inductance of the stepper motor accordingly, which will increase the speed and high speed. moment).
• Secondly, the power supply voltage of the stepper driver can be increased , so that the effective current magnetic field during commutation increases due to the high voltage at high speed.
• If there is no isolation between the AC power supply and the stepper driver DC bus (such as a transformer), do not connect the non-isolated port of the DC bus or the ground of the non-isolated signal to the ground. This may cause equipment damage and personal injury. Because the AC public voltage is not directed to the ground, there may be a very high voltage between the DC bus ground and the ground.
• In most high-voltage stepper driver systems, all common grounds and grounds are connected together at the signal end. Ground loops generated by multiple methods of connecting to the earth are easily affected by noise and generate flows at different reference points.
• In order to keep the command reference voltage constant, connect the signal ground of the stepper driver to the signal ground of the controller. It will also be connected to the ground of the external power supply, which will affect the operation of the controller and stepper motor driver.
• It is difficult to ground the shielding layer. There are several methods. The correct grounding point for a shield is at a reference potential point within its circuit. This point depends on whether the noise source and receiver are both grounded or floating. Make sure that the shield is grounded at the same point so that ground current does not flow through the shield.