How is a servo motor constructed? And the working principle of a servo motor

Servo motor structure

A servo motor is a DC motor that has the following 5 parts:

1. Stator winding: This type of winding is wound around the stationary part of the motor. It is also called the field winding of the motor.

2. Rotor Winding: This type of winding is wound around the rotating part of the motor. It is also called the armature winding of the motor.

3. Bearings: There are two types, font bearings and back bearings, which are used for the movement of the shaft.

4. Shaft: The iron rod to which the armature winding is coupled is called the shaft of the motor.

5. Encoder: It has an approximate sensor that determines the speed of the motor and the number of revolutions per minute of the motor.

Servo motor mechanism

It consists of three basic types:

1. Control device

2. Output sensor

3. Feedback system

The servo motor works on the phenomenon of an automatic closed-loop system. This closed-loop system requires a controller. This controller consists of a comparator and a feedback path. It has one output and two inputs. In this case, to generate an output signal, the comparator is used to compare the required reference signal, and this output signal is sensed by the sensor. The input signal to the motor is called the feedback signal. According to the feedback signal, the motor starts working. The comparator signal is called the logic signal of the motor. When the logic difference is high, the motor will turn on within the required time, and when the logic difference is low, the motor will turn off within the required time. Basically, the comparator is used to determine whether the motor is ON or OFF. The normal operation of the motor can be done with the help of a good controller.

Servo Motor Control:

Servo motors can be controlled by the PWM method, which is pulse width modulation. They send an electrical signal with inconsistent width to the motor. The width pulse varies in the range of 1 millisecond to 2 milliseconds and is transmitted to the servo motor by repeating 50 times in one second. The width of the pulse controls the angular position of the rotating shaft. Among them, three terms are used to represent the control of the servo motor, namely the maximum pulse, the minimum pulse, and the repetition rate.

For example, a servo moves with a 1 millisecond pulse to turn the motor towards 0°, while a 2 millisecond pulse turns the motor towards 180°, and the pulse widths interchange themselves between angular positions. Thus, a servo turns 5° with a pulse width of 90.1 milliseconds.

There are three wires or leads in every servo motor. Two wires use positive power and ground power, while the third wire is for the control signal.

Working Principle of Servo Motor

The servo has a position sensor, a DC motor, a gear system, a control circuit. The DC motor runs at high speed and low torque when drawing power from the battery. The speed is lower and the torque will be higher than the gear and shaft assembly connected to the DC motor. The position of the shaft is sensed by the position sensor from which it determines the position and provides information to the control circuit. The signal is decoded by the control circuit of the position sensor and the direction of rotation is processed to obtain the correct position. It requires a DC power supply of 4.8 V to 6 V.

The reduction gearbox is connected to a shaft which reduces the speed of the motor. The output shaft of the reduction gearbox is the same as the motor which is connected to an encoder or potentiometer. The output of the encoder is then connected to the control circuit. The wires of the servo motor are also connected to the control circuit. The motor is controlled by the microcontroller sending signals in the form of PWM which decodes the control circuit to rotate the motor at the desired angle and the control circuit moves the motor in the clockwise or counterclockwise direction so that the shaft also rotates in the desired direction. The encoder sends the feedback signal to the control circuit. When the motor reaches the desired angle, the control circuit stops the motor accordingly based on the signal received from the encoder.

For example, if the motor is at 30° and the microcontroller provides an angle of 60° to the motor, the control circuit rotates the motor in a clockwise direction. When the motor reaches 60°, the encoder sends a signal to the control circuit to stop the motor.