Working principle of servo motor

The working principle of the servo motor is relatively simple, but its work is relatively efficient. The servo circuit is built into the motor unit and uses a flexible shaft usually equipped with gears. Electrical signals control the motor and also determine the amount of shaft movement. The internal setting of servo motor is simple: small DC motor, control circuit and potentiometer. The DC motor is connected to the control wheel through gears. When the motor rotates, the resistance of the potentiometer changes, and the control circuit can accurately adjust the movement and direction.

When the shaft is in the correct (ideal) position, the motor stops supplying power. If the shaft does not stop at the target position, the motor runs until it enters the correct direction. The position of the target is transmitted by signal lines using electrical pulses. Therefore, the speed of the motor is proportional to the actual and ideal position. When the motor is close to the required position, the motor starts to rotate slowly, but when the motor turns farther, the speed is fast. In other words, servomotors only need to complete the task as quickly as possible, which makes them efficient equipment.

When the AC servo motor has no control voltage, only the pulsating magnetic field generated by the excitation winding is in the air gap, and the rotor is stationary without starting torque. When there is a control voltage and the control winding current is different from the excitation winding current, a rotating magnetic field is generated in the air gap and electromagnetic torque is generated to make the rotor rotate in the direction of the rotating magnetic field. However, it is required that the servo motor can not only be started under the control voltage, but also stop running immediately after the voltage disappears. If the servo motor continues to rotate like the general single-phase asynchronous motor after the control voltage disappears, the phenomenon of runaway will occur. We call this phenomenon of self rotation due to runaway as autorotation.

The basic working principle of traditional DC servo motor is exactly the same as that of ordinary DC motor. The electromagnetic torque is generated by the action of armature current and air gap magnetic flux to make the servo motor rotate. Usually, the armature control mode is adopted, that is, the speed is adjusted by changing the armature voltage while keeping the excitation voltage unchanged. The smaller the armature voltage, the lower the speed; When the armature voltage is zero, the motor stops. Since the armature current is zero when the armature voltage is zero, the motor will not produce electromagnetic torque and will not "rotate".