Knowledge of servo motor

Servo motor is a micro special motor used as an actuator in an automatic control device. Its function is to convert electrical signals into angular displacement or angular velocity of a rotating shaft. The servo motor is also called an executive motor. It is used as an actuator in an automatic control system and converts the received electrical signals into angular displacement or angular velocity output on the motor shaft.

Classification of servo motors

The servo motor is divided into two categories: AC servo and DC servo.

The basic structure of an AC servo motor is similar to an AC induction motor (asynchronous motor). On the stator, there are two excitation windings Wf and control windings WcoWf with a phase space displacement of a 90 ° electrical angle. They are connected to a constant AC voltage and use the AC voltage or phase change applied to Wc to control the motor.

AC servo motors have the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict non-linearity indicators of mechanical characteristics and adjustment characteristics.

Advantages and disadvantages of DC servo motors

Advantages: precise speed control, hard torque speed characteristics, simple control principle, convenient use, and low price.

Disadvantages: brush commutation, speed limitation, additional resistance, and wear particles.

The basic structure of a DC servo motor is similar to that of a general DC motor. Motor speed n = E / K1j = (Ua-IaRa) / K1j, where E is the armature back electromotive force, K is a constant, j is the magnetic flux per pole, Ua, Ia are the armature voltage and armature current, and Ra is The armature resistance can change the speed of the DC servo motor by changing Ua or changing φ, but the method of controlling the armature voltage is generally used. In the permanent magnet DC servo motor, the field winding is replaced by a permanent magnet, and the magnetic flux φ is constant.  The DC servo motor has good linear adjustment characteristics and fast time response.

Advantages and disadvantages of AC servo motor

Advantages: good speed control characteristics, smooth control can be achieved in the entire speed zone, almost no oscillation, high efficiency of more than 90%, less heat generation, high-speed control, high accuracy position control, constant torque can be achieved in the rated operating area, Low inertia, low noise, no brush wear and maintenance-free. Disadvantages: the control is more complicated, the drive parameters need to be adjusted on-site to determine the PID parameters, and more wiring is required.