How to choose a servo motor?

Servo motor selection:

1. AC servo motor

The structure of the stator of the AC servo motor is basically similar to that of the capacitor phase-splitting single-phase asynchronous motor. The stator is equipped with two windings with a mutual difference of 90°, one is the excitation winding Rf, which is always connected to the AC voltage Uf; the other is Is the control winding L, connected to the control signal voltage Uc. So the AC servo motor is also called two servo motors.

The rotor of the AC servo motor is usually made into a squirrel cage, but in order to make the servo motor have a wide speed range, linear mechanical characteristics, no "autorotation" phenomenon and fast response performance, compared with ordinary motors, it should have The rotor resistance is large and the moment of inertia is small. There are two types of rotor structures that are widely used: one is the squirrel-cage rotor with high-resistivity guide bars made of high-resistivity conductive materials. In order to reduce the moment of inertia of the rotor, the rotor is made slender; The first 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 reluctance of the magnetic circuit, a fixed inner stator should be placed in the hollow cup-shaped rotor. The hollow cup-shaped rotor The moment of inertia is small, the response is fast, and the operation is smooth, so it is widely used.

When the AC servo motor has no control voltage, there is only the pulsating magnetic field generated by the excitation winding in the stator, and the rotor is stationary. When there is a control voltage, a rotating magnetic field is generated in the stator, and the rotor rotates in the direction of the rotating magnetic field. When the load is constant, the speed of the motor changes with the magnitude of the control voltage. When the phase of the control voltage is opposite, the servo motor will be reversed.

2. 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 achieved outstanding development, and electrical manufacturers in various countries have successively launched their own series of AC servo motors and servo drives. And constantly improve and update. AC servo system has become the main development direction of contemporary high-performance servo system, so that the original DC servo is facing the crisis of being eliminated. After the 1990s, the AC servo systems that have been commercialized in various countries in the world are driven by fully digitally controlled sine wave motors. The development of AC servo drives in the field of transmission is changing with each passing day.

Compared with DC servo motors, permanent magnet AC servo motors have the following main advantages:

⑴No brush and commutator, so it works reliably and has low requirements for maintenance and maintenance.

(2) Stator winding heat dissipation is more convenient.

⑶ Small inertia, easy to improve the rapidity of the system.

⑷Suitable for high-speed and high-torque working conditions.

⑸ Small volume and weight under the same power.

Comparison of servo motor and single-phase asynchronous motor

Although the working principle of the AC servo motor is similar to that of the split-phase single-phase asynchronous motor, the rotor resistance of the former is much larger than that of the latter. Therefore, compared with the single-machine asynchronous motor, the servo motor has three characteristics:

1. Large starting torque

Due to the large rotor resistance, it is obviously different from the torque characteristic curve of ordinary asynchronous motors. It can make the critical slip rate S0>1, which not only makes the torque characteristic (mechanical characteristic) closer to linear, but also has a larger starting torque. Therefore, when the stator has a control voltage, the rotor rotates immediately, which has the characteristics of fast starting and high sensitivity.

2. Wide operating range

3. No rotation phenomenon

For a servo motor in normal operation, as long as the control voltage is lost, the motor will stop running immediately. When the servo motor loses the control voltage, it is in a single-phase operation state. Due to the large resistance of the rotor, the two torque characteristics (T1-S1, T2-S2 curves) generated by the two rotating magnetic fields rotating in opposite directions in the stator and the action of the rotor ) and synthetic torque characteristics (T-S curve)

The output power of AC servo motor is generally 0.1-100W. When the power frequency is 50Hz, the voltages are 36V, 110V, 220, 380V; when the power frequency is 400Hz, the voltages are 20V, 26V, 36V, 115V and so on.

The AC servo motor runs smoothly with low noise. But the control characteristic is non-linear, and because the rotor resistance is large, the loss is large, and the efficiency is low, compared with the DC servo motor of the same capacity, it is bulky and heavy, so it is only suitable for small power control systems of 0.5-100W.

Wheatstone, with 20 years of production experience, focuses on the customization of special control motor system solutions. Tonghui Motor's subsidiaries mainly include explosion-proof motors, stepping, servo, brushless DC and other control motors. The products are exported to the United States, India, Brazil and other countries, and are exported to all over the world with the user's equipment. The special servo motor developed by the company for glass bottle making machinery has been well received by the industry after several years of application, and has become a major supplier in this industry.