Servochanism Explained

Servochanism, also known as servo system, is a feedback control system used to accurately follow or reproduce a process.


The servo system enables the automatic control system of the position, orientation, state, etc. of the object to be controlled to follow any change in the input target (or given value).

Its main task is to control the power, enlarge and transform the power according to the requirements of the control command, so that the torque, speed and position control of the drive device are very flexible and convenient.

In many cases, the servo system refers to a feedback control system in which the controlled amount (output of the system) is mechanical displacement or displacement velocity and acceleration.

Its function is to make the mechanical displacement (or corner) of the output accurately track the input displacement (or corner).

There is no principle difference between its structural composition and other forms of feedback control systems.

The servo system was originally used for defense military forces, such as the control of artillery, the automatic driving of ships, aircraft, and missile launches.

Later, it was gradually extended to many departments of the national economy, such as automatic machine tools and wireless tracking control.

Basic interpretation

A servo system is the use of a component (such as a lever) to bring the state of the system to or near a predetermined value.

And the desired state (required value) can be compared with the actual state, and the automatic control system of the control component is adjusted according to their difference (sometimes the rate of change of this difference).

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Main function

  1. Control the high power load with a small power command signal;
  2. In the absence of mechanical connection, the output shaft located at a remote location is controlled by the input shaft to realize remote synchronous transmission;
  3. Make the output mechanical displacement accurately track electrical signals, such as recording and indicating instruments.

Development history

Servo is a shorthand for the word ServoMechanism, from Greece.

Its meaning is slavery.

As the name implies, the system follows the external command to perform the desired motion, and the moving elements include physical quantities such as position, velocity and moment.

Review the history of the servo system, from the earliest hydraulic and pneumatic to the current electrification.

The servo system consisting of servo motor, feedback device and controller has been running for nearly 50 years.

Nowadays, with the continuous maturity of technology, AC servo motor technology has gradually replaced DC motor as the leading execution motor of servo system with its excellent cost performance.

The maturity of AC servo system technology has also made the market show rapid diversification and become one of the supporting technologies of industrial automation.

Main classification

From the nature of the components of the system, there are:

  • Electrical servo system
  • Hydraulic servo system
  • Electric-hydraulic servo system
  • Electrical-electrical servo system

From the physical properties of the system output, there are:

  • Speed or acceleration servo system
  • Position servo system

From the characteristics of the components and signal characteristics contained in the system, there are:

  • Analog servo system
  • Digital servo system

From the structural characteristics of the system, there are:

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Single return servo system

  • Multi-feed servo system
  • Open loop servo system
  • Closed loop servo system

The servo system is divided by its drive components and has:

  • Step servo system
  • DC motor servo system
  • AC motor servo system

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