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Detailed introduction

Editing of the working principle of mechanical component voltage torque motor signal voltage torque

An automatic control system in which the output controlled quantities such as the state can follow any changes of the input target (or given value). Servo mainly relies on pulses for positioning. Basically, it can be understood in this way: when a servo motor receives one pulse, it will rotate the Angle corresponding to one pulse, thereby achieving displacement. Because the servo motor itself has the function of emitting pulses, every time it rotates an Angle, it will emit the corresponding number of pulses. In this way, it forms a response with the pulses received by the servo motor. Or it can be called a closed loop. In this way, the system will know how many pulses have been sent to the servo motor and how many pulses have been received back. Thus, the rotation of the motor can be well controlled, and the positioning can reach 0.001mm. Dc servo motors are divided into brushed and brushless motors. Brushed motors have low cost, simple structure, large starting torque, wide speed regulation range, easy control, but they require maintenance (such as carbon brush replacement), generate electromagnetic interference, and have environmental requirements. It can be used in common industrial and civil occasions where cost is a concern.

Brushless motors are small in size, light in weight, have high output power, fast response, high speed, low inertia, smooth rotation and stable torque. The control is complex but easy to achieve intelligence. Its electronic commutation method is flexible and can be either square wave commutation or sine wave commutation. The motor is maintenance-free, highly efficient, operates at a low temperature, has very little electromagnetic radiation, a long service life, and can be used in various environments.

2. Ac servo motors are also brushless motors, which are divided into synchronous and asynchronous motors. Currently, synchronous motors are generally used in motion control. They have a wide power range and can achieve very high power. Large inertia, high rotational speed with low speed, and it decreases rapidly as the power increases. It is suitable for applications that operate at low speed and smoothly.

3. The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. Under the action of this magnetic field, the rotor rotates. The encoder built into the motor feeds back signals to the driver. The driver compares the feedback value with the target value and adjusts the rotation Angle of the rotor. The accuracy of a servo motor is determined by the accuracy (number of lines) of the encoder.

The functional differences between AC servo motors and brushless DC servo motors: AC servo motors are better because they are controlled by sine waves and have smaller torque ripple. Dc servo is a trapezoidal wave. But DC servo is relatively simple and cheap.

Development history of AC servo motors (Figure 2)

Ac servo motor (Figure 2)

3 Edit

Ac servo motor

The structure of the stator of an AC servo motor is basically similar to that of a capacitive phase-separated single-phase asynchronous motor. The stator is equipped with two windings whose positions are 90° apart from each other. One is the excitation winding Rf, which is always connected to the alternating voltage Uf. The other one is the control winding L, which is connected to the control signal voltage Uc. The AC servo motor is also known as a two-servo motor.

The rotor of an AC servo motor is usually made in a squirrel-cage type. However, in order to enable the servo motor to have a wide speed regulation range, linear mechanical characteristics, no "self-rotation" phenomenon and fast response performance, compared with ordinary motors, it should have the two characteristics of large rotor resistance and small moment of inertia. At present, there are two forms of rotor structures that are widely used: One is the squirrel-cage rotor with high-resistivity conductive strips made of high-resistivity conductive materials. To reduce the moment of inertia of the rotor, the rotor is made slender. Another type is a hollow cup-shaped rotor made of aluminum alloy. The cup wall is very thin, only 0.2-0.3mm. To reduce the magnetic resistance of the magnetic circuit, a fixed inner stator needs to be placed inside the hollow cup-shaped rotor. The hollow cup-shaped rotor has a very small moment of inertia, responds quickly and operates smoothly, and is widely adopted.

When there is no control voltage in an AC servo motor, only the pulsating magnetic field generated by the excitation winding exists in the stator, and the rotor remains stationary. When there is a control voltage, a rotating magnetic field is generated inside the stator. The rotor rotates along the direction of the rotating magnetic field. Under the condition of a constant load, the rotational speed of the motor varies with the magnitude of the control voltage. When the phase of the control voltage is reached, 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 made remarkable progress. Electrical manufacturers in various countries have successively launched their own series of AC servo motors and servo drivers and continuously improved and updated them. The AC servo system has become the main development direction of contemporary high-performance servo systems, putting the original DC servo at risk of being phased out. Since the 1990s, the commercialized AC servo systems have adopted all-digital controlled sinusoidal motor servo drives. The development of AC servo drive devices in the field of transmission is changing rapidly.

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

(1) It has no brushes or commutators, operates reliably, and has low requirements for maintenance and upkeep.

⑵ The stator winding is relatively convenient for heat dissipation.

⑶ It has a small inertia, which is easy to improve the rapidity of the system.

⑷ It is suitable for high-speed and high-torque working conditions.

It has a smaller volume and weight under the same power.

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Comparison between servo motors and single-phase asynchronous motors

The working principle of an AC servo motor is similar to that of a split-phase single-phase asynchronous motor, but the rotor resistance of the former is much greater than that of the latter. Compared with single-phase asynchronous motors, servo motors have three significant characteristics:

1. Large starting torque

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

2. It has a relatively wide operating range

3. No self-rotation phenomenon

A normally operating servo motor will immediately stop running as soon as the control voltage is lost. When the servo motor loses the control voltage, it operates in a single-phase state. Due to the large rotor resistance, the two torque characteristics (T1-S1 and T2-S2 curves) and the combined torque characteristic (T-S curve) generated by the interaction of the rotating magnetic fields rotating in two directions in the stator with the rotor

The output power of an AC servo motor is generally 0.1 to 100 watts. When the power supply frequency is 50Hz, the voltages are 36V, 110V, 220 and 380V. When the power supply frequency is 400Hz, there are various voltages available, such as 20V, 26V, 36V, 115V, etc.

The AC servo motor operates smoothly with low noise. However, the control characteristics are nonlinear. Moreover, due to the large rotor resistance, the loss is high and the efficiency is low. Compared with the DC servo motor of the same capacity, it is larger in volume and heavier in weight, and is only suitable for small power control systems ranging from 0.5 to 100W.