Principle of AC servo motor
The stator structure of AC servo motor is basically similar to that of capacitor split-phase single-phase asynchronous motor. The stator is equipped with two windings with a position difference of 90°, one is the excitation winding Rf, which is always connected to the AC voltage Uf; The other is the control winding L, which is connected to the control signal voltage Uc. So AC servo motor is also called two servo motors.
The rotor of the AC servo motor is usually made of squirrel cage, but in order to make the servo motor have a wide speed range, linear mechanical characteristics, no “rotation” phenomenon and fast response performance, it should have the rotor resistance and small moment of inertia compared with ordinary motors. At present, there are two types of rotor structures widely used: one is the squirrel cage rotor with high resistivity guide bar made of conductive material with high resistivity. In order to reduce the moment of inertia of the rotor, the rotor is made slender; The other is a hollow cup rotor made of aluminum alloy, the cup wall is very thin, only 0.2-0.3mm, in order to reduce the magnetic resistance of the magnetic circuit, to place a fixed internal stator in the hollow cup rotor, the moment of inertia of the hollow cup rotor is small, the reaction is rapid, and the operation is smooth, so it is widely used.
When the AC servo motor has no control voltage, only the pulsating magnetic field generated by the excitation winding is in the stator, and the rotor is stationary. When there is a control voltage, a rotating magnetic field is generated in the stator, the rotor rotates in the direction of the rotating magnetic field, in the case of constant load, the speed of the motor changes with the size of the control voltage, when the phase of the control voltage is opposite, the servo motor will reverse.