Application of servo motor in automatic control

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Application of servo motor in automatic control [Copy link]

Preface

In recent years, it is obvious that people's living standards are improving day by day, and consumption is also rising. As awareness and demands for their own quality of life are constantly being put on the agenda, consumers not only put forward requirements on the quality of internal materials, but also put forward corresponding requirements on packaging. This forces manufacturers to update their production equipment to speed up production and meet people's needs with higher requirements. Therefore, automated CNC equipment has been introduced into production, and servo motors have been widely used.

According to the observations and development trends in recent years, servo motor control technology is developing in the direction of digitalization, intelligence and communication. So, as a part of CNC machine tools and also as an actuator, how can servo motors be better used in various CNC machine tools? With the continuous advancement of digital pulse width modulation technology, microelectronics technology, and current control technology, in the ever-changing process, this paper briefly discusses the technology, current status and development trend of servo motors.

Introduction to Servo Motors

At present, in production, we usually use AC servo motors. Taking AC servo motors as an example, we will analyze the composition of its structure.

The AC servo motor can be roughly divided into two parts, namely the rotor and the stator. Among them, the squirrel cage rotor and non-magnetic cup rotor that we usually use are the rotor part. What about the stator part? The commonly used stator structure is similar to the stator of the rotary transformer. They are both composed of two-phase windings placed at 90 degrees to each other in the stator core. Therefore, the servo motor can also be called a two-phase AC motor.

Of 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, while the outer stator of the non-magnetic cup rotor AC servo motor has exactly the same structure as the squirrel-cage stator, but the inner stator is different. It is made of stacked annular steel sheets. As part of the motor's magnetic circuit, the inner stator usually does not have windings, but only replaces the core of the squirrel-cage rotor.

However, according to the current market situation, squirrel cage rotor servo motors are generally widely used because the non-magnetic cup rotor has a small inertia and a small bearing friction torque. Also, because there are no tooth slots between its rotors, there is no tooth slot adhesion between the stator and the rotor. When rotating at a constant speed, the jitter phenomenon will not occur. However, under the same volume and weight, within a certain power range, the starting torque and output power generated by the cup rotor servo motor are smaller than those of the squirrel cage rotor servo motor. At the same time, the structure and manufacturing process of the cup rotor servo motor are relatively more complicated. Therefore, the cup rotor servo motor is only used in certain occasions that require very smooth operation (such as: integral circuit).

Application of servo motor in CNC

3.1 Application characteristics of servo motors in CNC systems

AC servo motor is a type of brushless motor, but it is divided into synchronous and asynchronous motors. Synchronous motors are more common in motion control because they can achieve high power, low speed at the highest rotation, and quickly decrease as the power increases, so they are suitable for low-speed and stable operation applications. Therefore, high precision, wide speed regulation range, large torque output at low speed, fast response and no overshoot are its biggest features.

3.2 What are the advantages of servo motors compared to other motors?

AC servo motors are superior to stepper motors in many aspects. Although stepper motors are often used as actuator motors in some special occasions or in some occasions with low requirements, AC servo motors are still the most popular and widely used motors. So what are the differences between AC servo motors and stepper motors?

First , the difference in control accuracy. The control accuracy of the AC servo motor is guaranteed by the rotary encoder at the rear end of the motor shaft, while the angles of the two-phase stepper motor are generally 3.6 degrees and 18 degrees, and the angles of the five-phase hybrid stepper motor are 0.72 degrees and 0.36 degrees.

Second , the low-frequency characteristics are different. Stepper motors are prone to low-frequency vibration at low speeds. The low-frequency vibration phenomenon is determined by the characteristics of the working principle of stepper motors, and this phenomenon is harmful rather than beneficial to the normal operation of the machine. However, the operation of AC servo motors is very stable, and even at very low speeds, it can maintain stability without vibration. That is because the AC servo system has the function of resonance suppression, and there is a frequency analysis function inside the system, which will make timely adjustments when the resonance point of the machine is detected.

There are also differences in torque-frequency characteristics, overload capacity, operating performance and speed response performance. In the design process of the control system, it is necessary to comprehensively consider the control requirements, cost and other factors, and select a more appropriate control motor at the right time.

Development trend of servo motor

With the process of China's transformation from a manufacturing power to a manufacturing power and the gradual improvement of the performance-price ratio of digital AC servo systems, the market of AC servo systems as high-end precision components for controlling motors is also steadily increasing. As the most important component of CNC machine tools, the servo system has always been one of the important indicators affecting the processing performance of the system.

In recent years, with the improvement of dynamic and static characteristics of servo systems, various servo drive technologies have been developed and emerged. The key factor that determines the performance of AC servo systems is still servo control technology, but because the AC servo system itself has extremely advanced control principles and low-cost, maintenance-free characteristics, not to mention that its control characteristics are also comprehensively surpassing DC servo systems, it is bound to replace most or even all DC servo systems in the future development process. According to the current operation mode, it will develop in the direction of high efficiency, high speed, high precision and high performance in the future.

Moreover, with the current widespread promotion of intelligence and the prevalence of networked modularization, modern AC servo drive equipment also has the function of parameter memory, as well as the function of self-fault diagnosis and analysis. Some servo motors even have the function of identifying parameters, and can automatically suppress vibration when it is found, and automatically measure and reset the encoder. These are the development trends of servo motors in the intelligent phase. The key development direction of networking is how to adapt to the requirements of high-performance motion control for real-time, synchronization and reliability of data transmission. The successful development of high-end CNC systems also indicates that the development of networked digital servos has become a current priority, and servo motor drivers, power supplies, regenerative braking, and communication between motors are constantly developing in the direction of modularization.

Source: chinak