Servo motors are divided into two categories: 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 a phase space displacement of 90° electrical angle on the stator, which are connected to a constant AC voltage. The AC voltage or phase change applied to Wc is used to control the operation of the motor.
AC servo motors have the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict nonlinearity indicators of mechanical characteristics and adjustment characteristics (required to be less than 10%~15% and less than 15%~25% respectively)
Advantages and Disadvantages of DC Servo Motors
Advantages: precise speed control, very rigid torque-speed characteristics, simple control principle, easy to use, and cheap.
Disadvantages: brush commutation, speed limit, additional resistance, and generation of wear particles (not suitable for dust-free and explosive environments).
The basic structure of a DC servo motor is similar to that of a general DC motor. The motor speed n=E/K1j=(Ua-IaRa)/K1j, where E is the armature back electromotive force, K is a constant, j is the flux per pole, Ua and Ia are the armature voltage and armature current, and Ra is the armature resistance. Changing Ua or changing φ can control the speed of the DC servo motor, but the method of controlling the armature voltage is generally used. In permanent magnet DC servo motors, the excitation winding is replaced by a permanent magnet, and the flux φ is constant. DC servo motors have good linear regulation characteristics and fast time response.
