How to distinguish whether commonly used AC servo motors are synchronous or asynchronous?

AC servo motors are mainly divided into synchronous and asynchronous motors.
In the case of a synchronous motor, the rotating magnetic field of the stator and the magnetic field of the rotor are synchronous. The rotating magnetic field is generated by the current flowing into the stator, so the stator current of a synchronous motor is usually DC. The rotor of a synchronous motor requires the use of permanent magnets or electromagnetic coils to generate a magnetic field, and the number of magnetic poles of the rotor needs to be aligned with the rotating magnetic field of the stator. For asynchronous motors, the rotating magnetic field of the stator and the magnetic field of the rotor are not synchronous.

The rotor of an asynchronous motor generates current through electromagnetic induction, so the current frequency of the rotor is the same as that of the stator. The rotor speed of an asynchronous motor and the rotating magnetic field of the stator are not synchronous, but because the speed difference between the two is very small, they can be considered synchronous.

So, it is possible to distinguish whether a motor is synchronous or asynchronous by observing its structure.
Additionally, it can be determined by measuring the current frequency and speed of the motor. Some synchronous motors can achieve synchronization by adjusting the number of rotor poles and aligning the stator rotating magnetic field.