Servo motor selection comparison

There are several different types of servo motors, each type has its own advantages and characteristics. Last time we introduced the selection process of servo motors, I believe everyone already knows about it, so today we will explain the selection comparison of servo motors. I hope it can help those friends who don’t know much about it!

The selection comparison of servo motors is as follows:

AC servo motor:

The structure of the stator of an AC servo motor is basically similar to that of a capacitive split-phase single-phase asynchronous motor. The stator is equipped with two windings whose positions are 90° different from each other. One is the excitation winding Rf, which is always directly connected to the AC voltage Uf; the other Is the control winding L, connected to the control signal voltage Uc. Therefore, the AC servo motor is also called two servo motors.

The rotor of an AC servo motor is generally made of a squirrel-cage type. However, in order for the servo motor to have a wide speed regulation range, linear mechanical characteristics, no "rotation" phenomenon and the function of rapid response, compared with ordinary motors, it should have a rotor It has the two characteristics of large resistance and small moment of inertia. There are two methods of rotor structures that are currently used: one is a squirrel cage rotor using high resistivity conductive materials made of high resistivity conductive materials. In order to reduce the rotor's moment of inertia, the rotor is made slender; the other is a squirrel cage rotor with high resistivity conductive materials. One is to use 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, a fixed inner stator is placed inside the hollow cup-shaped rotor. The hollow cup rotor has a small moment of inertia, quick response, and operates smoothly, so it is widely used.

When there is no control voltage in an AC servo motor, there is only a pulsating magnetic field generated by the excitation winding in the stator, and the rotor remains 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 turn around.

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 made remarkable progress. Electrical manufacturers from various countries have successively launched their own AC servo motor and servo drive series products. , and continue to improve and update. AC servo systems have become the main development direction of modern high-performance servo systems, leaving the original DC servo in danger of being eliminated. Since the 1990s, AC servo systems that have been commercialized in various countries around the world use fully digitally controlled sine wave motor servo drives. The development of AC servo drive equipment in the field of transmission is rapid.

Compared with DC servo motors, the main advantages of permanent magnet AC servo motors are:

(1) There are no brushes and commutators, so the operation is reliable and the maintenance requirements are low.

(2) The stator winding is more convenient for heat dissipation.

(3) The inertia is small and it is easy to improve the speed of the system.

(4) Suitable for high-speed and high-torque operation conditions.

(5) Smaller volume and weight under the same power.

Comparison between servo motor and single-phase asynchronous motor:

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

1. Large starting torque

Because the rotor resistance is large, there is a significant difference compared with the torque characteristic curve of a general asynchronous motor. It can make the critical slip S0>1, which not only makes the torque characteristics (mechanical characteristics) closer to linear, but also has a larger starting torque. Therefore, when the stator has control voltage, the rotor rotates immediately, which has the characteristics of fast starting and high sensitivity.

2. Wide operation scale

3. No rotation phenomenon

A normally operating servo motor will stop working immediately as long as the control voltage is lost. When the servo motor loses the control voltage, it is in a single-phase operating state. Due to the large rotor resistance, 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 rotor interact. ) and the component torque characteristics (T-S curve). The output power of AC servo motor is generally 0.1-100W. When the power supply frequency is 50Hz, the voltages are 36V, 110V, 220, and 380V; when the power supply frequency is 400Hz, the voltages are 20V, 26V, 36V, 115V, etc.

The AC servo motor in the servo motor runs smoothly and makes little noise. However, the control characteristics are linear, and because the rotor resistance is large, the loss is large, and the power is low, compared with the DC servo motor of the same capacity, it is larger and heavier, so it is only suitable for low-power control systems of 0.5-100W.