The word "servo" comes from the Greek word "slave". "Servo motor" can be understood as a motor that absolutely obeys the command of the control signal: the rotor is stationary before the control signal is sent; When the control signal is sent, the rotor rotates immediately; When the control signal disappears, the rotor can stop immediately. Servo motor is a micro special motor used as actuator in automatic control device. Its function is to convert electrical signal into angular displacement or angular velocity of rotating shaft. working principle
1. Servo mechanism is an automatic control system that enables the output controlled quantities such as the position, orientation and state of the object to follow the arbitrary change of the input target (or given value). Servo is mainly positioned by pulses. Basically, it can be understood that when the servo motor receives a pulse, it will rotate the angle corresponding to one pulse to realize displacement.
Because the servo motor itself has the function of sending pulses, each angle of rotation of the servo motor will send a corresponding number of pulses. In this way, it echoes with the pulses received by the servo motor, or closed loop. In this way, the system will know how many pulses are sent to the servo motor and how many pulses are received back. In this way, It can accurately control the rotation of the motor, so as to achieve accurate positioning, which can reach 0.001mm.
DC and AC servo motors
1. DC servo motor is divided into brushless motor and brushless motor. The brush motor has the advantages of low cost, simple structure, large starting torque, wide speed regulation range, easy control and needs maintenance, but it is inconvenient to maintain (change carbon brush), resulting in electromagnetic interference and environmental requirements. Therefore, it can be used in common industrial and civil occasions sensitive to cost.
Brushless motor has the advantages of small volume, light weight, large output, fast response, high speed, small inertia, smooth rotation and stable torque. The control is complex, easy to realize intellectualization, and its electronic commutation mode is flexible, which can be square wave commutation or sine wave commutation. The motor is maintenance free, high efficiency, low operating temperature, low electromagnetic radiation and long service life. It can be used in various environments.
2. AC servo motor is also a brushless motor, which is divided into synchronous motor and asynchronous motor. At present, synchronous motor is generally used in motion control. It has a large power range and can achieve great power. Large inertia, low maximum rotational speed, and rapidly decreases with the increase of power. Therefore, it is suitable for the application of low-speed and smooth operation.
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. The rotor rotates under the action of this magnetic field. At the same time, the encoder feedback signal provided by the motor is sent to the driver. The driver compares the feedback value with the target value to adjust the rotation angle of the rotor. The accuracy of the servo motor depends on the accuracy of the encoder (number of lines).
Functional differences between AC servo motor and brushless DC servo motor: AC servo is better because it is controlled by sine wave and the torque ripple is small. DC servo is trapezoidal wave. But DC servo is relatively simple and cheap.
Permanent magnet AC servo motor
The main advantages of permanent magnet AC servo motor compared with DC servo motor are:
(1) there is no brush and commutator, so it works reliably and has low requirements for maintenance.
⑵ the heat dissipation of stator winding is convenient.
⑶ small inertia, easy to improve the rapidity of the system.
(4) it is suitable for high-speed and large torque working state.
(5) small volume and weight under the same power.