Analysis of Application Prospect of Frequency Converter in Machine Tool Industry

Inverter Introduction

The frequency converter is a power control device that utilizes the on-off function of the power semiconductor device to convert the power frequency power source to another frequency. Mainly by the rectifier (AC to DC), filtering, inverter (DC to AC), brake unit, drive unit, detection unit micro-processing unit and other components. In general, the inverter must have several basic capabilities: 1. Energy saving; 2. Speed ​​regulation; 3. Protection functions can be divided into the following two categories:

(1) Corrective actions are automatically performed after detection of abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention.

(2) Block the power semiconductor device PWM control signal after detecting the abnormality, and make the motor stop automatically. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power failure protection.

Frequency Converter Application in Machine Tool Industry

Due to the wide range of machining of the machine tool, different workpieces, different processes, and different tools, the execution components of the machine tool are required to have different speeds of movement. Therefore, the main movement of the machine tool should be able to adjust the speed, and the user of the machine tool regulates the speed of the inverter. The effect is more concerned.

The spindle is an important part of the lathe composition. It plays an important role in improving the processing efficiency, expanding the range of processing materials, and improving the processing quality. The frequency converter is mainly used in spindle speed control systems. At present, the frequency converter is very cost-effective for the customer, so the use of the frequency converter on the lathe is very common.

There are two important considerations for a general-purpose inverter to be used smoothly in the machine tool industry: one is to choose a product without speed sensor vector control, and the other is to design to operate at overspeed to increase low-speed torque.

Inverter characteristics in machine tool applications

The adjustment range of frequency conversion speed regulation is very wide, general general-purpose frequency converter can realize stepless speed regulation in the range of 0-400HZ.

Consider that the machine tool requires hard mechanical properties. In line with the inverter + ordinary motor (or variable frequency motor) transmission has a hard mechanical characteristics. It is generally capable of providing 150% load torque at low frequencies.

Consider that the machine needs a strong overload at low speeds. The inverter can provide 150% overload protection (60S) to meet the requirements of the equipment.

With the use of variable frequency speed regulation, it can simplify the original complex mechanical drag mechanism such as gear transmissions, with a high degree of automation, simple operation and easy maintenance.

Inverter has voltage (DC0-5V, DC0-10V), current analog input interface, which can be well matched with the control signal of CNC system.

Inverter advantages in machine tool applications

At present, due to the high cost performance of frequency converters, frequency converters are very popular in the numerical control of economical CNC machine tools and ordinary machine tools. Its main advantages are:

First, simplify the control circuit. The use of the frequency converter is extremely convenient and can be controlled in full scale by a few terminals on its periphery. There are perfect protection measures inside the inverter. It is not necessary to design various protection circuits in its peripheral circuits. Because the inverter's forward and reverse operation is achieved through the control terminal to change the output phase of the inverter. Therefore, two large DC contactors can be used less than the original DC speed control system. With a vector-controlled frequency converter without a speed sensor, it is also possible to remove the speed sensor used as a speed feedback, which greatly simplifies the control circuit; standard asynchronous motors can be used. The adoption of cage asynchronous motor can exert its advantages of simple structure, sturdiness and durability, reliable operation, convenient maintenance and low price, avoiding the problems of regular replacement of DC motors and maintenance of brushes and commutators.

Easy to debug. The various operating parameters of the inverter are debugged through the intelligent keyboard and display. The setting is convenient, the change is flexible, and the debugging time is short. The debugging of the traditional DC speed regulation system involves the comprehensive adjustment of many parameters such as the trigger pulse phase adjustment and the speed negative feedback debugging. It is difficult to debug and takes a long time, and it is difficult to achieve the optimal control.

In addition, use the frequency changer to change the cutting speed, choose the best economic efficiency cutting speed. After the speed is selected, changing the cutting speed by changing the diameter of the pulley and/or changing the motor is economical and convenient, which is an effective method for the machining industry to improve the processing quality and reduce the processing cost.

The frequency converter can reduce the number of pairs of gears of the speed change transmission, reduce the noise, improve the accuracy of the spindle, and have a strong ability to adapt to the required spindle speed distribution when processing various products and various materials. The CNC can be conveniently realized, and its cost is much lower than that of a numerical control system composed of DC speed regulators.

Most of economical CNC lathes cannot be automatically shifted. When a speed change is required, the machine can only be stopped and then manually shifted. The main drive system of full-function CNC lathes is mostly continuously variable. At present, there are mainly two types of continuously variable transmission systems: frequency conversion spindle system and servo spindle system. DC or AC spindle motors are generally used. Drive the spindle through the belt drive, or drive the spindle through the belt drive and the reduction gear in the spindle box (for greater torque). Due to the wide speed range of the spindle motor and stepless speed regulation, the structure of the spindle box is greatly simplified. At present, due to the high cost performance of frequency converters, it is very common for customers to use them on lathes.

Inverter's overall market situation in the machine tool industry

According to a survey conducted by Luo Baihui, head of the International Die & Mould and Plastics Industry Suppliers Association, the total market for inverters in the machine tool industry is currently around 800 million yuan. The application of inverters in lathes is the largest, and Yaskawa, Delta, Fujitsu, and Mitsubishi all have large market shares. Domestic brands also have more applications in machine tools, such as Huichuan performing well in lathes. The grinders and forging industries have high performance requirements for inverter products, and there are many foreign brands. Mitsubishi, Fuji, Siemens, Delta, etc. are at an advantage, and the number of inverters required for a machine tool is also high. Up to 4-5 sets. Because Mitsubishi inverter is close to the function of the servo, its application in the machine tool is also larger; because of its close to Mitsubishi, Delta has a much cheaper price, higher cost performance, and improved after-sales service. In recent years, the market share has increased significantly.

The development trend of the inverter

At present, the development trend of machine tool inverters is as follows: First, high performance. At present, basically all the frequency converters require the vector mastering mode, and a small number of different levels of mastering structures and algorithms have emerged. It is worth noting that Speed ​​Sensorless Vector Mastering (SVC) is being developed rapidly in recent years. Because SVC can require low-interest, high-function disposal plans, it has become a dream specification and development direction in general-purpose inverters. The second is the constant improvement of the mastery. The user's demand for the inverter is gradually transformed into a field device, and a setting tool is added to the software in order to simplify the debugging process through the user's operation. The third is the gradual increase in functional modularity and intelligent demand.

(1) High performance

At present, basically all frequency converters provide vector control methods, and there are a large number of different levels of control structures and algorithms to adapt to different market positioning and needs. It is worth noting that speed sensorless vector control (SVC) has developed rapidly in recent years. Because SVC can provide low-cost, high-performance solutions, it has become the de facto standard and development direction in general-purpose inverters.

(2) Continuous improvement in usability

The frequency converter provided by many manufacturers takes into account the requirements of field installation in terms of structure, and at the same time, it adds a startup setting tool to the software to simplify the debugging process by guiding the customer.

(3) Modulation of power mechanism

Modular power structure design provides consistency for different series and power segment products, which facilitates the improvement of product reliability, facilitates factory selection, installation, commissioning and maintenance, and effectively reduces the operation and maintenance costs.

(4) Intelligent

The first is to improve the intellectualization of the inverter by providing customized drive programming capabilities to meet the customization requirements of different application sites. This is actually the integration of some functions of the PLC into the inverter.

The second is to increase the intelligence of the inverter through communication with external intelligent devices (such as PLCs). At present, well-known manufacturers of inverters have network connectivity capabilities and support multiple protocols.

(5) High power density

Due to the advances in new power devices and thermal design technologies, current inverters are becoming more and more compact, smaller and smaller, and the power density is getting higher and higher, but the key technical indicators such as temperature rise have not declined.

(6) Reduce the influence of EMI/RFI harmonics

AC reactors and chokes are now common in frequency converters and these have played an important role in reducing the effects of EMI/RFI harmonics.

Application Prospect of Frequency Converter in Machine Tools

From the machine sales data in 2008, it can be seen that the inventory of general-purpose machine tools, especially single-function lathes, is quite serious, while the composite machine tools and large-scale heavy-duty products have a better market. These machine tools have a wide range of machining, and the machine tool execution components have different speeds of movement, and have also put forward higher requirements for the performance of the inverter. The frequency converter selected by the customer's response is because its function is close to the servo, and it increases the control of the accuracy on the basis of satisfying the intensity. In addition, some customers believe that the current frequency inverter interference with other people is more serious, the need to wave close to the sine wave, a stronger force. With the development of frequency converters and machine tools, the function of the frequency converter will also be continuously improved and it will be able to better serve the machine tool. market trend

At present, the domestic production of machine tools is mainly low-end products, processing accuracy than the gap between the level of foreign countries, the level of control is very low, the use of CNC, PLC, servo, HMI, etc. is not high. However, with the influence of market demand, more and more manufacturers have increased their efforts in development and technology introduction, and many foreign brands have begun to establish production plants in China or expand their production capacity in China. According to a survey conducted by Luo Baihui, head of the International Tooling and Hardware & Plastics Industry Suppliers Association, improving the numerical control rate and improving the quality of machine tools, especially high precision or ultra-high precision products, is one of the important ways to solve the survival and development of enterprises. . The task of improving the proportion of CNC products has become imminent. Comparing domestic and foreign automation products, the company believes that the stability of the domestic CNC system is not the biggest drawback of domestic products. The foreign CNC system technology is perfect. At present, there is still a big gap between domestic products and foreign technologies. Excluding price factors, foreign products only take a long time in the delivery cycle, and there are no other defects. Domestic CNC systems still have a long way to go in the future.

Luo Baihui said that China's machine tool end-users are mainly concentrated in the vehicle manufacturing industry, including automotive and shipbuilding, professional equipment manufacturing such as textile machinery and metallurgical equipment manufacturing plants and mold industry. The aerospace, automotive, and mold industries are the mainstays of the recent domestic machine tool market demand. The demand for machine tools in the aerospace industry is mainly a high-precision, larger-sized CNC boring and milling machine. There are not many large-scale construction projects in the automobile industry in the near future, mainly technological transformation. At present, the main purpose is to transform the special machine tool production lines that are commonly used in production into flexible production lines with high flexibility and mainly high-speed machining centers, so as to increase the flexibility of the production process and adapt to the requirements of quick product change. The implementation of major science and technology projects for high-end CNC machine tools and basic manufacturing equipment will lay the foundation for the long-term sustainable development of the Chinese machine tool industry.