The stator structure of AC servo motor is basically similar to that of capacitive 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. 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-shaped 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-shaped rotor. Hollow cup rotor is widely used because of its small moment of inertia, rapid response and smooth operation.
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.
Permanent magnet AC servo motor
Since the 1980s, with the development of integrated circuits, power electronics technology and AC variable speed drive technology, permanent magnet AC servo drive technology has been prominent development, famous electrical manufacturers in various countries have launched their own AC servo motor and servo drive series products and continue to improve and update. Ac servo system has become the main development direction of contemporary high-performance servo system, which makes the original DC servo face the crisis of being eliminated. After the 1990s, the AC servo system that has been commercialized in all countries in the world is the sine wave motor servo drive with full digital control. The development of AC servo drive in the field of transmission is changing with each passing day.
Compared with DC servo motor, the main advantages of permanent magnet AC servo motor are:
(1) No brush and commutator, so reliable work, low maintenance and maintenance requirements.
⑵ The stator winding heat dissipation is more convenient.
(3) Small inertia, easy to improve the speed of the system.
(4) Suitable for high speed and large torque working state.
(5) Smaller volume and weight under the same power.
Comparison of servo motor and single-phase asynchronous motor