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Figure 1: Servo motor is a core part of servo system.



With the development of information, communication and automation technology, a wide variety of automatic control devices have been used in industry production and daily life of modern world. As one of the most common devices for automatic control, servo system, constituted by servo motor and servo drive has been widely used in our daily life.

With our article here, you can get a deeper understanding where exactly can servo motor and servo drive can be used.

1. What is Servo System?

Servo system, is a feedback control system used to accurately follow or reproduce a process.

As one of the key components of a servo system and the execution part of it, servo motor changes the object's position, orientation, state and other output controlled quantity following the input (or a given value).
Its task is to amplify, transform and regulate the power according to the requirements of the control command, so that the output torque, speed and position control of the driving device is very flexible and convenient.

2. Components of Servo System

The system is mainly composed of HMI touch screen, PLC, servo drive, permanent magnet synchronous servo motor. The servo motor is the executive mechanism of the movement. It does position, speed and current control, so as to meet the user's functional requirements.



servo system’s components

Figure 2: Servo system is composed of PLC, drive, motor, reducer and interface.

3. Features, Uses and Types of Servo System

3.1 Features of Servo System

It needs accurate detection device to compose closed speed and position loop.

Various Feedback and Comparison Principles

There are a variety of feedback comparison principles and methods. According to the different principles of detection device to achieve information feedback and different methods of feedback comparison, there are pulse comparison, phase comparison and amplitude comparison in common use.

High Performance Servo Motor

In NC machine tools for efficient and complex surface processing, the servo system will often be in the process of frequent start and brake. So the ratio of the motor's output torque to the moment of inertia is required to be large enough to generate a large acceleration or braking torque. And also the servo motor is required to have large enough output torque at low speed and smooth operation, so as to minimize the intermediate link in the connection with the mechanical moving part.

Well-Performed Regulation System with Various Speed

A system with a wide range of speed regulation, namely speed servo system. From the control structure of system, position closed-loop system of CNC machine tools could be seen as a double closed-loop automatic control system which has position adjustment in outer loop and speed adjustment in inner loop.

The actual internal working process is to convert position input into the corresponding speed signal, and then the signal will drives servo motor to realize the actual displacement. The main movement of CNC machine tools requires high speed regulation performance, so the servo system is required to be a well-performed regulation system with wide speed range.

3.2 Uses of Servo System

Control high-power load with low-power instruction signal.
Controlled by the input shaft to achieve remote synchronous transmission.
Make the output mechanical displacement accurately track the electrical signal, such as recording and indicating instrument, etc.

3.3 Different Types of Servo System

Standard

Types

 

Feature of the components

* Electrical servo system

* Hydraulic servo system

* Electric-hydraulic servo system

* Electric-electric servo system

 

Physical properties of system’s output

 

* Speed or acceleration servo system

* Position servo system

 

 

Signal function characteristics

 

* Analog servo system

* Digital servo system

 

Structural characteristics

* Single loop servo system

* Open loop servo system

* Closed loop servo system

 

Drive components

* Stepper servo system

* Direct current motor (DC motor) servo system

* Alternating current motor (AC motor) servo system


Table 1: Different types of servo motor.

4. Industries Using Servo System

Laser processing field
Robotics
CNC lathe field
Office automation equipment for large-scale integrated circuit manufacturing
Radar and other high-tech fields

5. Future Trends of Servo System Application

Automatic control system not only develops rapidly in theory, but also changes rapidly in its application devices. In every 3 ~ 5 years, there are new products on the market.

The characteristic of traditional AC servo motor is soft and its output is not single value.

Stepper motor generally is open loop control and unable to locate precisely. The motor itself also has a velocity resonance region.

PWM speed control system has a poor position-tracking performance. Frequency conversion speed regulation is simple but sometimes the accuracy is not enough.

DC motor servo system, with its excellent performance, has been widely used in the position servo system. But its disadvantages, such as complicated structure, the salient contradiction in dead zone in super-low speed, And the reversing brush will bring noise and maintenance problem.

New permanent magnet AC servo motor develops rapidly, especially when it has changed controlling way from square wave to sine wave. The system performance is better, and its speed range is wide, performing superiorly in slow speed.



servo system in a robot

Figure 3: Servo motor and servo drive work in a robot.

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