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Servo Motor Application in Automatic Control
- Mar 14, 2018 -

1 Introduction

In recent years, what has been witnessed is that people’s living standards are increasingly improving, and consumption is constantly rising. As cognition and demands for quality of life are continuously mentioned on the agenda, consumers are not only concerned with the quality of intrinsic substances. The requirements were put forward, and corresponding requirements were also put on the packaging. This forced the manufacturers to upgrade their own production equipment to speed up production and meet the needs of people with higher requirements. Therefore, automatic numerical control equipment was introduced. Production, at the same time, servo motors have been widely used.

According to observations and development trends in recent years, servo motor control technology is being developed in the direction of digitization, intelligence, and communication. As a part of CNC machine tools and as an actuator, how servo motors are handled is Better use of the major CNC machine tools? With the development of digital pulse width modulation technology, microelectronics technology and current control technology, a brief discussion is made on the technology, status quo and development trend of servo motors in the ever-changing process.

2. Introduction to servo motor

At present, in the production, we usually use an AC servo motor to analyze the composition of the AC servo motor as an example.

AC servo motors can be roughly divided into two major parts, namely the rotor and stator parts. Among them, we generally use the squirrel-cage rotor and the non-magnetic cup row rotor as the rotor part mentioned here. What about the stator? The commonly used stator structure and the stator of the resolver are similar in that they are all composed of two-phase windings whose spaces are mutually 90 degrees in the stator core. Therefore, the servo motor can also be called a two-phase AC motor.

In the two commonly used rotor structures, the squirrel-cage rotor AC servo motor consists of a rotor core, a rotating shaft, and a rotor winding. The non-magnetic cup-shaped rotor AC servo motor has exactly the same outer stator as the squirrel-cage stator structure. There is a difference. It is a stack of circular steel plates. As part of the magnetic circuit of an electric motor, the inner stator usually does not contain windings, but only replaces the iron core of a squirrel cage rotor.

However, based on the current market situation, the squirrel-cage rotor servo motor is generally widely used because the inertia of the non-magnetic cup-shaped rotor is small and the bearing friction resistance torque is small. Also, because there are no gaps between the rotors, there is no phenomenon of cogging between the stator and the rotor. When rotating at a constant speed, the phenomenon of jitter does not occur, but at the same volume and weight, with certain Within the range of power, the cup-rotor servo motor has smaller starting torque and output power than the squirrel-cage rotor servo motor. At the same time, the configuration and manufacturing process of the cup-rotor servo motor is relatively more complicated. Therefore, the cup-shaped rotor servo motor is used only in some occasions where the operation is required to be very stable (eg, an integral circuit).

3, servo motor in the numerical control application

3.1 Application Characteristics of Servo Motor in CNC System

AC servo motor is a type of brushless motor, but it is divided into synchronous and asynchronous motors. Synchronous motor is more common in motion control, because it can do a lot of power, in the case of the highest rotation speed It is low, and quickly decreases with increasing power, so it is suitable for applications that run smoothly at low speeds. Therefore, high precision, wide speed range, large torque output at low speed, and fast response without overshoot are its greatest features.

3.2 What are the advantages of servo motors over other motors?

AC servo motor performance in many aspects is better than stepper motor, although in some special occasions or in some less demanding occasions often use stepper motor to do the motor, but AC servo motor is still the most widely used voice The motor, then the stepper motor is different from those aspects?

One is the difference in control accuracy. AC servo motor control accuracy is ensured by the rotary encoder at the rear end of the motor shaft, while the two-phase stepper motor's pitch angle is generally 3.6 degrees and 18 degrees, and the five-phase hybrid stepper motor's pitch angle is 0.72 degrees and 0.36 degrees.

Second, the difference in low-frequency characteristics. Stepper motors are prone to low frequency vibration at low speeds. Since the characteristics of the stepper motor operating principle determine the phenomenon of low-frequency vibration, this phenomenon is harmful and unprofitable for the normal operation of the machine, but the operation of the AC servo motor is very smooth, even at a very low level. At speed, it can also maintain stability without vibration. This is because the AC servo system has the function of resonance suppression, and there is a frequency analysis function inside the system. When the mechanical resonance point is detected, it will be adjusted in due course.

There are also differences in the characteristics of the clock frequency, overload, and the performance of the running and speed response. In the design process of the control system, comprehensive consideration should be given to control requirements, costs, etc., as well as many factors, and a more appropriate control of the motor should be selected in due course.

, servo motor development trend

With the gradual transition of the process of China's transition from a manufacturing nation to a manufacturing powerhouse and the increasing cost-performance ratio of digital AC servo systems, AC servo systems are used as high-grade precision components for control motors. Its market in the industry is also steadily rising. . As the most important part of CNC machine tools, simultaneous servo system has always been one of the important indicators that affect the processing performance of the system.

In recent years, the improvement of the dynamic and static characteristics of the servo system has also been developed and various servo drive technologies have emerged. The key factor that determines the performance of the AC servo system is still servo control technology. However, because the AC servo system itself has extremely advanced control principles and low-cost, maintenance-free features, not to mention its control characteristics are also comprehensive beyond DC The servo system will inevitably replace most or all of the DC servo systems in the future development process, and will analyze them in accordance with the current operation mode. The future will be more efficient, telling, high-precision, and higher-performance.

Not only that, with the current significant promotion of intelligentization and the prevalence of networked modularization, modern AC servo drive devices also have the function of parameter memory, as well as the function of diagnosis and analysis of own faults, and some servo motors even It also has the performance of identification parameters, and can automatically suppress the vibration when it is found, and automatically measure and zero the encoder. These are the development trends of the servo motor in the intelligent method phase. The key development direction of the network is how to adapt the high-performance motion control to the real-time, synchronization and reliability requirements of data transmission. The successful development of high-end numerical control systems also indicates that the development of networked digital servos has become an urgent task at hand, as well as servo motor drives, power supplies, regenerative braking, and the communication between motors and motors are all continuing to develop toward modularization.



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