Servo motors are mainly divided into AC servo and DC servo.
The basic structure of AC servo motor is similar to that of AC induction motor (asynchronous motor). There are two excitation windings Wf and control windings WcoWf with phase space displacement of 90 ° on the stator, which are connected to a constant AC voltage. The purpose of controlling the motor operation is achieved by using the AC voltage or phase change applied to Wc. AC servo motor is characterized by stable operation, good controllability, fast response, high sensitivity, and strict nonlinearity index of mechanical characteristics and regulation characteristics (less than 10%~15% and less than 15%~25% respectively).
1、 Advantages and disadvantages of DC servo motor
Advantages of DC servo motor: accurate speed control, hard torque speed characteristics, simple control principle, convenient use and low price.
Disadvantages of DC servo motor: brush commutation, speed limit, additional resistance, wear particles (not suitable for dust-free and explosive environment).
The basic structure of DC servo motor is similar to that of general DC motor. Motor speed n=E/K1j=(Ua IaRa)/K1j, where E is armature back electromotive force, K is constant, j is magnetic flux per pole, Ua and Ia are armature voltage and armature current, Ra is armature resistance, change Ua or change φ， The speed of the DC servo motor can be controlled, but the armature voltage is generally controlled. In the permanent magnet DC servo motor, the excitation winding is replaced by a permanent magnet φ Constant. DC servo motor has good linear regulation characteristics and fast time response.
2、 Advantages and disadvantages of AC servo motor
Advantages of AC servo motor: good speed control characteristics, smooth control can be achieved in the entire speed zone, almost no oscillation, more than 90% high efficiency, less heat, high-speed control, high-precision position control (depending on encoder accuracy), constant torque, low inertia, low noise, no brush wear, maintenance free (applicable to dust-free and explosive environments) can be achieved in the rated operating area.
Disadvantages of AC servo motor: the control is more complex, the driver parameters need to be determined by adjusting the PID parameters on site, and more wiring is required.
DC servo motor is divided into brush motor and brushless motor.
Brushed motors have low cost, simple structure, large starting torque, wide speed range, easy control, and need maintenance, but they are easy to maintain (replace carbon brushes), generate electromagnetic interference, and have requirements for the use environment. They are usually used in general industrial and civil occasions that are cost sensitive.
Brushless motor has small volume and light weight, large output and fast response, high speed and small inertia, stable torque and smooth rotation, complex and intelligent control, flexible electronic commutation mode, square wave or sine wave commutation, maintenance free motor, high efficiency and energy saving, small electromagnetic radiation, low temperature rise and long life, and is suitable for various environments.
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. Its power range is large, the power can be large, the inertia is large, the maximum speed is low, and the speed decreases uniformly with the increase of power. It is suitable for low-speed and stable operation.
The rotor inside the servo motor is a permanent magnet. The driver controls U/V/W three-phase electricity to form an electromagnetic field, and the rotor rotates under the effect of this magnetic field. At the same time, the encoder of the motor itself transmits the feedback signal to the driver, compares the feedback value with the target value, and adjusts the rotation angle of the rotor. The accuracy of the servo motor depends on the accuracy (number of lines) of the encoder.
