What is a servo motor?

A servo motor is a variable speed drive and it is used in many industrial productions and also for process automation. These motors are mostly used for motion control applications, the servo motors are used in motion control applications because it has high accuracy positioning, quick reversing and great performance. A servo motor can be AC or DC motor with a position sensing device. Basically, a servo motor is an electromechanical device in which an electrical input will determine the position of the armature of the motor. The servo is a compact device and its output shaft is positioned in a certain way with the help of a servo-coded signal. So the servo would maintain the angular position till the coded signal exists on the input line. So if the coded signal changes then the angular position of the shaft would change. The servo motor is controlled by a signal and it can be called a pulse width modulator.

What are the features of a servo motor?

These motors are mostly designed to use in feedback control systems, the power rating of the servo motor could vary from a fraction of watts to a few hundred watts. These motors have low rotor inertia and because of that it has quick response time and these motors are smaller in diameter and longer in length. A servo motor is compact in size and efficient and it can be used in applications where precise position control is required.

  • It has good steady state stability
  • Good speed control range
  • Throughout the entire speed range, we can see the linearity of the mechanical characteristics
  • It has low mechanical and electrical inertia, and also it has a good response

What is a servomechanism?

A servo is an automatic device that uses error sensing feedback to correct the performance of a mechanism, so this device is mostly used in systems where the feedback or error-correction signals help to control the mechanical position or other parameters. A servomechanism is different from other types of control systems because this device controls a parameter by commanding the time-based derivative of that parameter.

How servo motors are constructed? What are the parts of a servo motor?

The servo box has a DC motor and it is mechanically connected to a position feedback potentiometer, gearbox, electronic feedback, control loop circuitry, and also a motor drive electronic circuit.

Servos are basically constructed by three parts they are, motor, potentiometer, and this part are connected to the output shaft and a control board. The control circuit is capable to check the current angle of the servo motor with the help of the potentiometer. So basically a servo motor is constructed by modifying the DC motor and the modification is gear reduction, a position sensor for the motor shaft, and also an electronic circuit that can control the operation of the motor.

How does a servo motor work?

The control unit and the potentiometer of the servo motor will be connected to the output shaft. The servos are controlled by using pulse, the controller of the servo motor will control the operation of the motor by sending velocity signal to the amplifier, and this would drive the servo motor. There are many feedback devices in the servo motor and these devices would provide information on the position of the motor and velocity to the controller. The controller would compare and check these actions with the given set of instructions and the controller would control or vary the signal for a better output.

What are the types of servo motor?

AC servo motor

AC servo motor can be described as a two-phase reversible induction motor that is altered for servo operation. AC servo motors are mostly used where quick response is needed. The AC servo motors have a small diameter and high resistance rotor and because of this small diameter the AC servo motor can provide low inertia for fast starts, stops, and reversals. The high resistance in this motor will provide good speed to torque characteristics for accurate servo motor control.

DC servo motor

Mostly the DC servo motors are used where starts and stops must be done accurately and quickly. The armature inductance of this motor is very low and because of this low electrical time constant and this would improve the response of the servo motor to the signals. The Dc servo motors rotor has a copper or aluminum coil and this would rotate in the magnetic field. The DC servo motors mostly have two, four, or six poles.

How to select a servo motor?     

We must select a servo motor according to the torque-speed, dimensions, weight, motor type, and bearing type. The motor type could be of three poles or five poles and the pole refers to the permanent magnets which are attached to the electromagnets. The five-pole type has better torque than the three-pole type so this must be considered while selecting the motor.

The servos are of different speeds and torque, the torque is the force that is created by the motor to drive the servo arm. The time that is required for the servo to attain a position is considered as its speed. So the servo motor must be selected according to the application.

What is the difference between a servo motor and a stepper motor?

  • The cost of the servo motor is higher than that of a stepper with the same power rating
  • Both these motors can be used for the automation process the simplicity of the stepper motor makes it suitable for smaller applications
  • In order to obtain a proper motor function in a servo motor it requires the tuning of the closed-loop variable circuit. While in a stepper motor it doesn’t need anything like this
  • Both these motors don’t need frequent maintenance, only the brushes and encoder of the servo motor needs to be replaced after a certain period of time. The only wearing part of the stepper motor is the bearing and it must be checked.
  • Both these motors can be used for low-speed applications
  • Servo motor can maintain its rated torque, while it is not possible by a stepper motor especially at maximum torque
  • Both these motors have good reliability
  • The power to weight ratio of the servo motor is better than a stepper motor
  • Servo motor has better efficiency than a stepper motor
  • The servo motor has reserve power while the stepper motor doesn’t have this capability
  • The stepper motor produces less noise while the servo motor doesn’t make any noise
  • A servo motor is mechanically complex while the stepper motor is not
  • Servo is not suitable for systems with variable loads

How is a servo motor different from an induction motor?

The major difference between a servo motor and an induction motor is that the servo motor has a detector to detect its rotation speed and position. The construction and operation of a servo motor are similar to an induction motor but the servo motors are designed to get high precision, high speed, high-frequency positioning, and speed control of the mechanical facilities.

The servo motor has better speed than an induction motor also the servo motor has better torque than an induction motor and also the servo motors are smaller in size when compared to an induction motor. The servo motor has good efficiency and less weight when compared to an induction motor. The accuracy and the ability to control a servo motor are way better than an induction motor.

What are the difference between a DC servo motor and an AC servo motor?

  • A DC servo motor is mostly used for large power while the AC servo motor is used for small power
  • The DC servo motors are used in applications such as in machine tools and robotics while the AC servo motors are used in disk drives, tape, drivers, and printers.
  • The DC servo motor has high torque to inertia ratio and because of this it has good response to control signals

What are the advantages of a servo motor?

  • A servo motor has high output power while compared to its size and weight
  • Because of the encoder, a servo motor has high accuracy and resolution
  • The servo motor has good efficiency
  • The servo motor has high torque to inertia ratio and because of this the servo motor can quickly accelerate the loads
  • The DC servo motor has a low electrical time constant
  • Servo motors are economical and have good efficiency
  • Less maintenance is required for these motors
  • The characteristics of the AC servo motors are non-linear and they are difficult to control

What are the applications of a servo motor?

  • It is used in robotics
  • Radar systems
  • Machine tools
  • Automated manufacturing systems
  • Computers
  • CNC machines
  • Tracking systems
  • Textiles
  • Printing presses


post-graduate in Electronics & communication.

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