Asynchronous AC servo motors refer to AC induction motors. It is divided into three-phase and single-phase types, as well as squirrel-cage type and wire-wound type. Squirrel-cage three-phase induction motors are usually used.
Its structure is simple. Compared with a DC motor of the same capacity, its weight is 1/2 lighter, and the price is only 1/3 of the DC motor. As a result, the power factor of the power grid deteriorates. The asynchronous AC servo motor of this squirrel cage rotor is referred to as an asynchronous AC servo motor for short, denoted by IM.
Although synchronous AC servo motors are more complex than induction motors, they are simpler than DC motors. Its stator is the same as that of the induction motor. There are symmetrical three-phase windings on the stator. But the rotor is different. According to different rotor structures, it is divided into electromagnetic and non-electromagnetic types.
Non-electromagnetic type is divided into hysteresis type, permanent magnet type and reaction type. Among them, hysteresis and reaction synchronous motors have disadvantages such as low efficiency, poor power factor, and small manufacturing capacity. Permanent magnet synchronous motors are often used in CNC machine tools. Compared with the electromagnetic type, the permanent magnet type has the advantages of simple structure, reliable operation and higher efficiency.
However, the permanent magnet synchronous motor adopts rare earth magnets with high remanence induction and high coercivity, which can be about 1/2 smaller than the DC motor with 60% less mass, and the rotor inertia can be reduced to 1/5 that of the DC motor.