Servo motor knowledge

1. What is a servo motor

The word "servo" is derived from the Greek word "slave". "Servo motor" can be understood as a motor that absolutely obeys the control signal: before the control signal is sent, the rotor is stationary; when the control signal is sent, the rotor immediately rotates; when the control signal disappears, the rotor can stop immediately.

Servo motor is a micro motor used as an actuator in an automatic control device. Its function is to convert an electrical signal into the angular displacement or angular velocity of the rotating shaft. Servo motor, also known as executive motor, is used as an actuator in an automatic control system to convert the received electrical signal into angular displacement or angular velocity output on the motor shaft.

2. Servo motor classification

Servo motors are divided into two categories: AC servo and DC servo.

The basic structure of an AC servo motor is similar to that of an AC induction motor (asynchronous motor). There are two excitation windings Wf and control winding WcoWf with a phase space displacement of 90° electrical angle on the stator, connected to a constant AC voltage, and using the AC voltage or phase change applied to Wc to achieve the purpose of controlling the operation of the motor. AC servo motors have the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict non-linearity indexes of mechanical characteristics and adjustment characteristics (requirements less than 10% to 15% and less than 15% to 25%, respectively).

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 armature back electromotive force, K is constant, j is magnetic flux per pole, Ua, Ia are armature voltage and armature current, Ra is Armature resistance, changing Ua or changing φ, can control the speed of the DC servo motor, but generally the method of controlling the armature voltage is adopted. 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 regulation characteristics and fast time response.

3. Advantages and disadvantages of DC servo motors

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

Disadvantages: brush commutation, speed limit, additional resistance, and wear particles (not suitable for dust-free and explosive environments).

4. Advantages and disadvantages of AC servo motors

Advantages: good speed control characteristics, smooth control in the entire speed zone, almost no oscillation, high efficiency of more than 90%, low heat generation, high-speed control, high-precision position control (depending on the encoder accuracy).

 In rated operating area Inside, it can achieve constant torque, low inertia, low noise, no brush wear, and maintenance-free (suitable for dust-free and explosive environments).

Disadvantages: The control is more complicated, the driver parameters need to be adjusted on-site to determine the PID parameters, and more connections are required.

DC servo motors are divided into brush and brushless motors.

Brushed motors have low cost, simple structure, large starting torque, wide speed range, easy control, and need maintenance, but they are easy to maintain (change carbon brushes), generate electromagnetic interference, have requirements for the use environment, and are usually cost-sensitive For general industrial and civil occasions.

The brushless motor is small in size, light in weight, large in output, fast in response, high in speed, small inertia, stable torque and smooth rotation, complex control, intelligent, flexible electronic commutation, square wave or sine wave commutation, maintenance-free motor, high efficiency and energy saving , Small electromagnetic radiation, low temperature rise and long life, suitable for various environments.

Reported by Jessica