Servo motors are used as micro motors for actuators in automatic control devices, also known as actuator motors. Its function is to convert the electrical signal into the angular displacement or angular velocity of the rotating shaft. Servo: The word comes from the Greek word for "slave". People want to use the "servo mechanism" as a handy tame tool, acting in accordance with the requirements of the control signal. Before the signal arrives, the rotor is stationary; after the signal arrives, the rotor rotates immediately; when the signal disappears, the rotor can immediately stop by itself. It got its name because of its "servo" properties.
Servo motors are divided into two categories: AC and DC. AC servo motors work on the same principle as AC induction motors. There are two excitation windings Wf and control windings WcoWf with a phase space displacement of 90° on the stator, which are connected to a constant AC voltage, and the purpose of controlling the operation of the motor is achieved by using the AC voltage or phase changes applied to Wc.
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 (requirements are less than 10% to 15% and less than 15% to 25%, respectively). The working principle of a DC servo motor is the same as that of a general DC motor. The motor speed n is 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; 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 the permanent magnet DC servo motor, the excitation 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.
For DC Servo Motors
Advantages: precise speed control, very hard torque speed characteristics, simple principle, easy to use, price advantage
Disadvantages: Brush commutation, speed limitation, additional drag, generation of wear particles (for clean rooms).
For AC Servo Motors
Advantages: good speed control characteristics, smooth control in the entire speed range, almost no oscillation; high efficiency, more than 90%, no heat; high-speed control; high-precision position control (depending on what kind of encoder); rated operation In the area, to achieve constant torque; low noise; no brush wear, maintenance-free; no wear particles, no sparks, suitable for dust-free, violent environments with low inertia;
Disadvantages: The control is more complicated, the drive parameters need to be adjusted on-site for PID parameter tuning, and more connections are required.
Application of DC Servo Motor
The characteristics of DC servo motors are harder than that of AC servo motors. It is usually used in systems with slightly larger power, such as position control in servo systems.
Application of AC Servo Motor
The output power of the AC servo motor is generally 0.1-100 W, and the power frequency is divided into 50Hz, 400Hz and so on. It is widely used, such as in various automatic control, automatic recording and other systems.
