Servo System Function And Classification

- Oct 27, 2017-

Servo System Function And Classification

Now,with continuous developing technology, AC servo motor technology with its excellent cost-effective,and gradually replace the DC motor to become the dominant motor of servo system.The maturity of the AC servo system technology also makes the market present a rapid diversification development and become one of the supporting technologies of industrial automation.

Main Function

1,with low power command signal to control the high power load;

2,in the absence of mechanical connection,the input shaft control the remote located output shaft,to achieve long-range synchronous transmission;

3,make output mechanical displacement accurately track electrical signals,such as record and indicate instruments.

Main Classification

From the nature of the components of the system,there are electrical servo system,hydraulic servo system and electrical - hydraulic servo system and electrical - electrical servo system;

From physical properties of the system output,there are speed or acceleration servo system and position servo system;

From the system containing component characteristics and signal characteristics,there are analog servo system and digital

servo system;

From the structural characteristics of the system,there are single-servo system,multi-servo system and open-loop servo system,closed-loop servo system.

Servo system according to its driving components,there are stepper servo system,DC motor (referred to DC motor) servo system,

AC motor (referred to AC motor) servo system.According to the control mode,there are open-loop servo system,closed-loop servo system and semi-closed-loop servo system.In fact,CNC system is also divided into open-loop,closed-loop and semi-closed-loop three types,which is related to the three types of servo system.

1,Open-loop system

The open-loop system mainly consists of drive circuits,actuators and machine tools.Commonly used actuator is a stepper motor,usually called stepper motor as the implementation of the open-loop system for the stepper servo system.In such system,if it is high-power drive,with stepper motor as the implementation of components.The main task of the drive circuit is to convert the command pulse into the required signal to drive the actuator.

2,Closed-loop system

Closed-loop system mainly compose of actuator,detection unit,comparison links,drive circuit and machine parts..In the closed-loop system,the detection element detects the actual position of the machine moving parts and converts it into electrical signals to the comparison links.Common detection elements are rotary transformers,induction synchronizers,gratings,magnetic grids and encoder discs.The servo system consist of the detecting elements on the ball screw called the semi-closed loop system;the servo system composed of the detecting elements mounted on the table called the closed loop system.Due to the transmission error between the ball screw and the table,the accuracy of the semi-closed loop servo system is lower than the closed loop servo system.The role of the comparison link is to compare the command signal and the feedback signal,the difference between the two as the following error of servo system,the drive circuit and the control actuator drive the table to continue to move until the follow error is zero.According to the form of the comparison link signal and the feedback detection mode,the closed loop (semi closed loop) system can be divided into pulse comparison servo system,phase comparison servo system and amplitude comparison servo system.

As the comparison link output signal is relatively weak,can not drive the actuator,it is necessary to enlarge it,the drive circuit is set for this purpose.

The function of the actuator is to convert the electrical signal that represent displacement amount into a mechanical displacement based on control signal,that is,the following error signal from the comparison link.Commonly using actuators are DC wide speed motor,AC motor and so on.The actuator is an indispensable part of the servo system,and the drive circuit is different depending on the actuator.

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