Reasons for Stepper Motor Loss of Magnetism

In principle, ordinary stepper motors can be divided into reactive stepper motors and hybrid stepper motors. The reactive stepper motor can be disassembled, but the hybrid stepper motor cannot be disassembled. The motor is scrapped. The main reason is that the hybrid stepper motor uses a strong magnetic AlNiCo material. This material is high temperature resistant and will not demagnetize at high temperatures. Charge it to saturation during production. If disassembled, the magnetic circuit will no longer be closed. The magnetic core will be weakened or demagnetized, and a special magnetizer is needed for magnetization, which ordinary people cannot solve.

How does the magnet demagnetize? The two biggest reasons are the disassembly and overload of the motor.

First of all, whenever the motor is disassembled, it is extremely possible to demagnetize the magnet, thereby weakening the torque of the motor. Depending on the type of motor, the degree of magnetic field reduction will vary and may not even attract attention. For some motors, you will notice immediately. In fact, disassembling a stepper motor usually reduces the magnetic field of the magnet to the point where the motor loses its usefulness unless the motor is properly magnetized.

If it must be disassembled, prepare a magnetic "short circuit" tool, and then prepare a "magnetic short circuit" first, that is, use a soft iron material to lay the poles of the magnet so that the magnetic flux can pass through the iron. Without reducing the material, the magnetic gap can be removed. When reinstalling, please install the magnetic gap first, and then eliminate the "magnetic short circuit". However, sometimes "magnetic short" is very difficult. For stepper motors, the inner diameter of the tool used for "electromagnetic short-circuiting" must be equal to the inner diameter of the motor stator, and only a few wires are allowed (even on a lathe, it is difficult to machine the tool). The tool is an iron cylinder with a wall thickness of at least mm, stuffed into the gap of the magnetic circuit, the end of the cylinder is placed on the stator, the cylinder and the stator are roughly concentric, and then the rotor is connected from the stator to the iron cylinder. Complete the disassembly of the rotor.

Secondly, overload can also cause demagnetization. This can be caused by many factors: excessive feed rate, crashes, mechanical connection problems, incorrect parameter settings, and many other electrical or mechanical problems.

The result of motor overload is excessive current. Excessive current will demagnetize the magnet of the motor. Large current demagnetization only takes a short time, the shortest time is less than one second!

Case: The device generates an impact and stops the impact, resulting in an instantaneous overcurrent, which will cause partial demagnetization of the motor. The demagnetization motor needs a slightly larger current to maintain normal operation. The driver provides these additional currents. However, more current means more heat. The high heat further reduces the magnetism. Due to the decline in magnetic properties, the process continues to deteriorate. Continue until the drive reaches the maximum current limit and issues an alarm, or the motor does not meet the requirements, or the motor burns out, etc.

Solution: First, avoid overloading the motor and pay special attention to the daily needs of the system. You can click on the machine to increase the production speed, but high speed also causes motor loss. Second, observe whether there are potential mechanical connection problems and maintain the machine in accordance with the maintenance schedule recommended by the manufacturer. Check the drive parameters. Do not limit the maximum current to be too high. In many cases, this will prevent damage to the motor and greatly extend the life of the motor.

After the motor is demagnetized, the only way to restore the motor is to reinstall the motor. The installation process includes the re-excitation of the motor by an experienced factory and special installation equipment.

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