Structure Of AC Servo Motor

‌AC servo motor mainly consists of two parts: stator and rotor. ‌The stator part is usually made of laminated silicon steel sheets, and two-phase windings are embedded in the surface slots: excitation winding and control winding. The two phase windings are 90° electrical angles apart in space. There are two main structural forms of the rotor part: cage rotor and non-magnetic hollow cup rotor. The cage rotor is similar to the cage rotor of the ordinary three-phase asynchronous motor, but the shape is more slender to reduce the moment of inertia. It is suitable for occasions with large volume, small air gap, small excitation current and high power factor, but the rapid response performance is slightly poor. The non-magnetic hollow cup rotor has a smaller moment of inertia and a larger resistance. It is suitable for occasions with fast response and smooth operation, but the structure is complex, the air gap is large, the load current is large, and the power factor is low. ‌

The working principle of AC servo motor is to generate a rotating magnetic field by controlling the voltage, thereby driving the rotor to rotate. When there is no control voltage, there is only a pulsating magnetic field generated by the excitation winding in the air gap, and the rotor remains stationary. After the control voltage is applied, the control winding current and the excitation winding current produce a phase difference, forming a rotating magnetic field, generating electromagnetic torque, and driving the rotor to rotate. In order to meet the special requirements of servo motors, it is usually necessary to increase the rotor resistance to avoid self-rotation and ensure that the rotor can stop quickly when the control voltage disappears.

AC servo motors are widely used in occasions that require precise position and speed control, such as CNC machine tools, robots, automated production lines, etc.