How many terminals does a servo-motor contain?

DC Servomotor

A type of servomotor that uses DC electrical input to generate mechanical output like velocity, acceleration, or position is known as a DC servomotor. 

Servo motors have 3 terminals: power, ground, and signal (command pulses).

DC Servo Motor Construction

1.) Motor: The motor used in this is a typical DC motor including its field winding which is excited separately. So depending on the excitation nature further can be categorized as armature-controlled & field-controlled servo motors.

2.) Load: The load used in this is a simple fan or industrial load which is simply connected to the motor’s mechanical shaft.

3.) Gearbox: The gearbox in this construction works like a mechanical transducer to change the motor’s output like acceleration, position, or velocity depending on the application.

4.) Position sensor: Its main function is to get the feedback signal equivalent to the current position of the load. Generally, this is a potentiometer used to provide a voltage that is proportional to the motor shaft’s absolute angle through the gear mechanism.

5.) Encoder: The encoder is a sensor that notifies the driver of the speed and position of the motor. 

6.) Comparator: The comparator function is to compare the o/p of a position sensor & a reference point to produce the error signal and give it to the amplifier. If the DC motor works with precise control, then there is no error. The position sensor, gearbox & comparator will make the system a closed loop.

7.) Amplifier: The amplifier function is to amplify the error from the comparator & feed it to the DC motor. So, it performs like a proportional controller wherever the gain is strengthened for zero steady-state error.