Servo motor principle
First, AC servo motor
The configuration of the AC servo motor stator is basically similar to that of a capacitive split phase single phase asynchronous motor. The stator is provided with two windings with a position difference of 90°, one is the field 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. Therefore, the AC servo motor is also called two servo motors.
The rotor of the AC servo motor is usually made into a squirrel cage type, 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 a comparison with a normal motor. Two characteristics of large rotor resistance and small moment of inertia. At present, there are two types of rotor structures that are widely used: one is a squirrel-cage rotor made of a high-resistivity conductive material made of a high-resistivity conductive material, and the rotor is made slender in order to reduce the moment of inertia of the rotor; One is a hollow cup rotor made of aluminum alloy, the cup wall is very thin, only 0.2-0.3 mm. In order to reduce the magnetic resistance of the magnetic circuit, a fixed inner stator is placed in the hollow cup rotor. The hollow cup rotor is widely used because of its small moment of inertia, rapid response, and smooth operation.
When there is no control voltage in the AC servo motor, only the pulsating magnetic field generated by the field winding is present 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 rotational speed of the motor varies with the magnitude of the control voltage. When the phase of the control voltage is opposite, the servo motor Will reverse.
The working principle of the AC servo motor is similar to that of the split-phase single-phase asynchronous motor, but the rotor resistance of the former is much larger than that of the latter, so the servo motor has three remarkable characteristics compared with the single-machine asynchronous motor:
1, the starting torque is large
Due to the large rotor resistance, the torque characteristic curve is shown by curve 1 in Fig. 3, which is significantly different from the torque characteristic curve 2 of the conventional asynchronous motor. 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 immediately rotates, that is, it has the characteristics of quick start and high sensitivity.
2, a wider range of operation
3, no rotation phenomenon
In the normal operation of the servo motor, the motor stops running as soon as the control voltage is lost. When the servo motor loses the control voltage, it is in single-phase operation. Due to the large rotor resistance, the two rotating torques in the opposite direction of the stator and the two torque characteristics generated by the rotor (T1-S1, T2-S2 curves) And synthetic torque characteristics (T-S curve)
The output power of the AC servo motor is generally 0.1-100W. When the power frequency is 50Hz, the voltage is 36V, 110V, 220, 380V; when the power frequency is 400Hz, the voltage is 20V, 26V, 36V, 115V and so on.
The AC servo motor runs smoothly and has low noise. However, the control characteristics are non-linear, and because of the large rotor resistance, large loss, and low efficiency, it is bulky and heavy compared with the same capacity DC servo motor, so it is only suitable for small power control systems of 0.5-100W.
AC servo motor principle?
The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electric motor controlled by the driver forms an electromagnetic field. The rotor rotates under the action of the magnetic field. At the same time, the encoder feedback signal from the motor is supplied to the driver. The driver according to the feedback value and target. The values ​​are compared to adjust the angle at which the rotor rotates. The accuracy of the servo motor is determined by the accuracy (number of lines) of the encoder.
The servo motor controls the engine in which the mechanical components operate in the servo system. It is a supplementary motor indirect transmission. Also known as an actuator motor, in an automatic control system, it acts as an actuator that converts the received electrical signal into an angular displacement or angular velocity output on the motor shaft. Divided into two major categories of DC and AC servo motor, its main feature is that when the signal voltage is zero, there is no rotation phenomenon, and the rotation speed decreases uniformly with the increase of torque.
Function: Servo motor, which can control the speed and position accuracy very accurately.
DC servo motors are divided into brushed and brushless motors.
The brush motor has low cost, simple structure, large starting torque, wide speed regulation range, easy control and maintenance, but convenient maintenance (replacement of carbon brushes), electromagnetic interference, and environmental requirements. It can therefore be used in cost-sensitive general industrial and residential applications.
The brushless motor is small in size, light in weight, large in output, fast in response, high in speed, small in inertia, smooth in rotation and stable in torque. The control is complex, and it is easy to realize intelligence. The electronic commutation mode is flexible, and can be square wave commutation or sine wave commutation. The motor is maintenance-free, has high efficiency, low operating temperature, low electromagnetic radiation and long life, and can be used in various environments.
AC servo motors are also brushless motors, which are divided into synchronous and asynchronous motors. At present, synchronous motors are generally used in motion control. It has a large power range and can achieve a large power. High inertia, the highest rotational speed is low, and it decreases rapidly as power increases. Therefore, it is suitable for applications with low speed and smooth operation.
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