What is a Servomotor?
A servomotor (or servo motor) is a simple electric motor, controlled with the help of servomechanism. If the motor as a controlled device, associated with servomechanism is DC motor, then it is commonly known as a DC Servo Motor. If AC operates the controlled motor, it is known as a AC Servo Motor. A servomotor is a linear actuator or rotary actuator that allows for precise control of linear
or angular position, acceleration, and velocity. It consists of a motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.
Types of Servo Motors
On the Basis of Rotation
1. Positional Rotation Servos: Positional servos can rotate the shaft in about half of the circle. Also, it has the feature to protect the rotational sensor from over-rotating. Positional servos are mainly used in limbs, robotic arms, and in many other places.
2. Continuous Rotation Servos: Continous servos are similar in construction to the positional servo. But, it can move in both clockwise and anticlockwise directions. These types of servos are used in radar systems and robots.
3. Linear Servos: Again linear servos are also like a positional servo, but with additional gears to the adjust the output from circular to back-and-forth. These type of servos are used in high model airplanes and are rare to find on the stores.
On the Basis of Operating Signal
There are also two types of servo motors used which differ in processing information and signal.
1. Analog Servomotors Analog servos are operated over PWM (Pulse Width Modulation) signals. And, the range of the signal is 4.8V to 6V. In this type of servo, the PWM is off when the servo is at rest. The torque produced at rest time makes the starting time inactive. Also, an analog servo can be able to send 50 pulses per seconds only.
2. Digital Servomotors
Using small microprocessors Digital Servo receives signal and acts at high-frequency voltage pulses. A digital servo can be able to send 300 pulses per seconds, which is very high in comparison to an analog servo. Digital servo gives a smooth response and consistent torque, due to faster pulse. Digital servos consume more power than an analog servo.
On the Basis of Operating Power
DC Servo Motor DC Servos are used for providing fast torque response and are also known as a permanent magnet DC motor or separately excited DC motor. The reason behind providing fast torque response is because of the torque and flus are decoupled. Thus, a small variation in the armature voltage or current can produce a notable shift in the position or speed of the shaft. DC servos are most used servo motors among all the types.
AC Servo Motor There are two types of AC servo motors one is 2 phase and the second is 3 phase. Mainly two-phase squirrel cage servo motor is used for low power applications. And, three-phase squirrel cage servo is used for high power systems.
Construction of Servo Motor
The Servo motor is DC motor which has 5 following parts:-
1. Stator Winding: This type of winding wound on the stationary part of the motor. It is also known as field winding of the motor. 2. Rotor Winding: This type of winding wound on the rotating part of the motor. It is also known as an armature winding of the motor. 3. Bearing: These are of two types,i.e, font bearing and back bearing which are used for the movement of the shaft. 4. Shaft: The armature winding is coupled on the iron rod is known as the shaft of the motor. 5. Encoder: It has the approximate sensor which determines the rotational speed of motor and revolution per minute of the motor.
Mechanism of Servo Motor
It consists of three basic types:
1. Controlling Device
2. Output Sensor
3. Feedback system
The servo motor works on the phenomenon of the automatic closed-loop system. The controller is required for this closed-loop system. This controller is composed of a comparator and a feedback path. It has one output and two inputs. In this, for producing 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 for the motor is termed as a feedback signal. On the basis of the feedback signal, the motor starts working. Comparator signal is called a logic signal of the motor. The motor would be ON for the desired time when the logical difference is higher and the motor would be OFF for the desired time when the logical difference is lower. Basically, a comparator is used to decide that motor would be ON or OFF. Proper functioning of the motor can be done with the help of a good controller.
Working of Servo Motors
The servo has a position sensor, a DC motor, a gear system, a control circuit. The DC motor run at high speed and low torque when getting power from a battery. This speed is lower and torque will be higher than gear and shaft assembly connected to DC motors. The position of shaft senses by position sensor from its definite position and supply information to the control circuit. The signal is decoded by the control circuit from the position sensor and handles the direction of rotation to get the correct position. It needs a DC supply of 4.8 V to 6 V.
The reduction gearbox is connected to a shaft which decreases the RPM of the motor. The output shaft of the reduction gearbox is the same as of motor which is connected with encoder or potentiometer. The output of the encoder is then connected to the control circuit. The wires of the servomotor are also connected to the control circuit. The motor control through microcontroller by sending signals in the form of PWM which decodes the control circuit to rotate the motor in required angle the control circuit moves the motor in a clockwise or anticlockwise direction, with this the shaft also rotates in the desired direction. the encoder sends the feedback signal to the control circuit. When the motor reaches to required angle, the control circuit stops motor accordingly with the received signals from an encoder.
For example., if the motor is at 30˚and microcontroller gives angle 60˚ to the motor then 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.
Parts of Servo Motor
Servo motors are generally an assembly of four things:
1. DC motor
2 Gearing set
3. Control circuit
4. Position-sensor (usually a potentiometer).
• The position of servo motors can be controlled more precisely than those of standard DC motors, and they usually have three wires (power, ground & control). Power to servo motors is constantly applied, with the servo control circuit regulating the draw to drive the motor.
• PWM is used for the control signal of servo motors. However, unlike DC motors it's the duration of the positive pulse that determines the position, rather than speed, of the servo shaft.
The gear mechanism connected with the motor provides the feedback to the position sensor.
Applications of Servo Motors
1. Robotics : At every joint of the robot, we connect a servomotor. Thus giving the robot arm its precise angle.
2. Conveyor belts : servo motors move , stop , and start conveyor belts carrying product along to various stages , for example , in product packaging/ bottling, and labelling .
3. Camera auto focus : A highly precise servo motor build into the camera corrects a camera lens to sharpen out of focus images.
4. Solar tracking system : Servo motors adjust the angle of solar panels throughout the day and hence each panel continues to face the sun which results in harnessing maximum energy from sunup to sundown .
Servo Motor Interfacing With Arduino
Specifications
Servo Motor consists of three pins: VCC, GROUND, and PWM signal pin.
The VCC and GND is for providing power supply, the PWM input pin is used for controlling the position of the shaft by varying pulse width.
Minimum Rotational Angle : 0 degrees
Maximum Rotational Angle : 180 degrees
Operating Voltage : +5V
Torque : 2.5 kg/cm
Operating Speed : 0.1 s/60 degree
DC Supply Voltage : 4.8V to 6V
Circuit Diagram
CODE :
#include <Servo.h>
Servo servo_1; // servo controller (multiple can exist)
int servo_pin = 3; // PWM pin for servo control
int pos = 0; // servo starting position
void setup() {
servo_1.attach(servo_pin); // start servo control
Serial.begin(9600); // start serial monitor
servo_1.write(pos); // move servo to 0 degrees
Serial.println("Positioned at 0 Degrees");
Serial.println("Input Desired Angle and Press Enter");
}
void loop() {
while (Serial.available()){
String in_char = Serial.readStringUntil('\n'); // read until the newline
Serial.print("Moving to: ");
Serial.print(in_char);
Serial.println(" Degrees");
servo_1.write(in_char.toInt()); // convert angle and write servo
delay(in_char.toFloat()*(10.0/6.0)); // delay for maximum speed
}
}Result :
When we input value in the serial monitor the servo motor will rotate at the input angle and then come back to its initial position.
Operation Of Servo Motor Using Button
Circuit Diagram
CODE :
#include <Servo.h>
Servo servo_2;
void setup()
{
pinMode(13, INPUT);
servo_2.attach(2, 500, 2300); //servo.attach(pin, min, max)
//servo.attach(pin);
pinMode(7, OUTPUT);
}
void loop()
{
if (digitalRead(13) == HIGH) {
servo_2.write(175);
digitalWrite(7, HIGH);
delay(1000); // Wait for 1000 millisecond(s)
servo_2.write(20);
digitalWrite(7, LOW);
delay(1000); // Wait for 1000 millisecond(s)
}
}Result :
When we press the button then the led will blink and servo will start moving. When button is pressed and when we input particular value in serial monitor then the servo motor will rotate at that value and set the angle of motor angle at that value input from serial monitor.
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