Servo Motor

The term “servo” originates from the Greek word meaning “slave”. A “servo motor” can be understood as a motor that absolutely obeys the command of the control signal: before the control signal is issued, the rotor remains stationary; when the control signal is issued, the rotor starts to rotate immediately; when the control signal disappears, the rotor stops rotating instantly. A servo motor is a micro motor used as an actuator in automatic control devices. Its function is to convert electrical signals into angular displacement or angular velocity of the rotating shaft. A servo motor is also known as an actuator motor and is used as an actuator in automatic control systems to convert the received electrical signals into angular displacement or angular velocity output on the motor shaft.

Servo motors are divided into two major 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 windings Wc on the stator, which are spatially displaced by 90° electrical angles. They are connected to a constant AC voltage. By changing the AC voltage or phase applied to Wc, the operation of the motor can be controlled. AC servo motors have the characteristics of stable operation, good controllability, fast response, high sensitivity, and strict nonlinearity indicators for mechanical and regulating characteristics (requiring 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. The motor speed n = E / K1j = (Ua – IaRa) / K1j, where E is the armature reverse electromotive force, K is a constant, j is the flux per pole, Ua and Ia are the armature voltage and current, and Ra is the armature resistance. By changing Ua or φ, the speed of the DC servo motor can be controlled. However, the common method is to control the armature voltage. In permanent magnet DC servo motors, the excitation winding is replaced by permanent magnets, and the flux φ is constant. DC servo motors have good linear regulation characteristics and rapid time response.