The reason why the stepper motor servo motor demagnetizes when it is disassembled

The reason why the stepper motor servo motor demagnetizes when it is disassembled

"Why is my servo or stepper motor having low torque?" This is perhaps the most common question asked by "A-1" servo motor repairers, and usually the answer is simple - low magnetics.

Generally speaking, low torque is a direct result of low magnetic field strength. Servo motors and stepper motors utilize very strong permanent magnets to generate torque. If the motor's magnets are not fully magnetized, the motor will not be able to generate sufficient torque.

The so-called "permanent" magnet is, to a certain extent, misleading. For a motor to generate sufficient torque, the magnets must be saturated. Although the magnetism of a permanent magnet is "permanent", its magnetic field strength is not necessarily. In fact, there are many ways to reduce the magnetic field strength, it is only a matter of time. No matter how low the field strength is, eventually you'll notice when you spot the warning signs and you're forced to fix the problem or throw the motor away.

So how does the magnet demagnetize? The two biggest causes are overloading and dismantling the motor.

First, anytime a motor is removed, there is a high risk of demagnetizing the magnets, which will sap the motor's torque. Depending on the motor type, the reduction in the magnetic field varies and may not even be noticed. With some motors it is immediately noticeable. In fact, disassembling a stepper motor will usually reduce the magnetic field of the magnets to such an extent that the motor is useless unless the motor is properly magnetized. For some servo motors, field reduction has only a small effect, and the drive or controller will display an error when the demagnetized motor reaches full load.

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

The result of overloading the motor is excessive current flow. Excessive current will demagnetize the motor magnets. To make matters worse, it takes only a short time for the high current to demagnetize, in some cases less than a second.

Typical situation: A device goes over a limit switch and crashes to a stop, causing a momentary overcurrent that can partially demagnetize the motor. A demagnetized motor requires slightly higher current to keep running properly. The driver provides this extra current. However, more current equals more heat. Heat further degrades the magnetism. The process continues to worsen as magnets drop: more heat = less magnets = less torque = more current to keep things running = more heat, get it? This process continues until the drive hits the maximum current limit and alarms, or the motor fails to accelerate, or the motor burns out, etc. It's easy to see how long it takes for this to happen. By the time the motor "fails" completely, the original crash/overload is usually forgotten. (As long as the parameters of the stepper motor are set correctly, it will generally not be overloaded, and it will not generate a large current when it crashes, which is better than the servo motor)

So, what's the solution? First, avoid overloading the servo motor and pay special attention to your daily demands on the system. You might be able to stress your machine and increase production speed, but the high speed also comes at the cost of wear and tear on the motor. Second, watch for any potential mechanical connection problems and maintain the machine according to your manufacturer's recommended maintenance schedule. Finally, please check your drive parameters. Do not limit the maximum current too high. You will find other limiting parameters related to current, check these parameters to make sure they are suitable for your motor. In many cases, doing this will prevent the motor from being damaged and greatly extend motor life.

Once the motor is demagnetized, the only way to restore the motor is to rebuild the motor, which must include re-magnetizing the motor by an experienced and specialized repair shop.