CNC machine tools take digital technology as the core

China is the world’s largest machine tool consumer and importer in the world today. In terms of market demand, the development momentum of a number of heavy-industry-based high-growth industries, such as domestic autos, steel, machinery, molds, electronics, and chemical industries, has driven the demand for efficient and high-precision automated manufacturing equipment. Enter the stage of rapid growth. On the import side, taking the first half of 2011 as an example, the total amount of Chinese imports of machine tools from Japan and Germany has exceeded 60%. From the point of view of imported models, the demand for precision production, high-efficiency and high-speed medium-to-high-end CNC machine tools has increased significantly. It has shown that the demand structure of China's machine tools has undergone major changes.

CNC machine tools are based on digital manufacturing technology as the core of the mechanical and electrical integration machine tools, usually by the control system, servo system, detection system, mechanical transmission system and other auxiliary systems, can be roughly divided into CNC lathes, CNC milling machines, machining centers, etc. 16 Large variety. In the newly promulgated national “Twelfth Five-Year Plan”, it is clearly proposed that the high-end equipment manufacturing industry will focus on the development of information, automation, and intelligence. This is obviously inseparable from the strong support of the precision machine tool industry. According to professional analysis, the compound growth rate of the Chinese machine tool industry is expected to be about 25-30% in the next five years, among which medium and high-end CNC machine tools will become the main force for growth.

From the development of the current machine tool industry in China, self-produced CNC machine tools are still far from meeting the needs of the domestic market, especially the proportion of high-end CNC machine tools is seriously low. According to the statistics of 2011, from January to August, the average production rate of China's machine tool industry was 30.94%, which was 2.9 percentage points higher than the 28.04% in the same period of 2010, and it was in line with the 70% level of CNC of machine tools in some developed countries. Than the gap is more obvious. Especially in recent years due to the impact of the international financial crisis, machine tools companies in Germany and Japan have recovered rapidly, and they have entered China with low-price and mid-range strategies. The market has responded well, which is also the development of China's medium-to-high-end CNC machine tools industry. There is tremendous competitive pressure; at the same time, mid-range machine tools from Taiwan and South Korea are also forces that cannot be ignored. According to the statistics from the China Machine Tool Industry Association, in the first three quarters of 2011, the import of metal processing machine tools was 9.91 billion U.S. dollars, a year-on-year increase of 51.4%. Due to the surge in imports, the market share of domestic metal processing machine tools and numerically-controlled machine tools showed a decline. trend.

In order to change these current conditions as quickly as possible, in December 2008, under the support of the Ministry of Science and Technology and other ministries and commissions, the Shenyang Machine Tool Group took the lead to jointly form the “CNC Machine Tool Industry Technology Innovation Alliance” with 8 companies and 6 institutes. The focus will be on the development of key functional components such as high-speed precision CNC machine tools, high-speed precision machine tool motion characteristics, high-speed precision machine tool cutting technologies, and numerical control system application technologies. According to the person in charge of the Major Special Program Office of the Ministry of Science and Technology, the CNC machine tool project officially launched in 2009 will continue into 2020. It is expected that the total investment of the central government, local finance, and enterprises will reach several hundred billion yuan, which indicates that CNC machine tools have become The key development direction of China's machine tool industry.

Servo application in CNC machine tools

The ability to control the accuracy, speed, and power is the main goal of the machine tool products. For the Chinese machine tool industry's CNC technology is still relatively backward compared to the international advanced level, the root cause, it can be said that the slow development of high-quality functional components is one of the main reasons, the direct impact of the performance of these functional components The overall technical level of the host computer is closely related to the development of the CNC machine tool industry. Among them, the core component servo system of motion control is also included. At present, in the practical application of the numerical control machine tool industry, the AC servo system has obviously occupied certain advantages; and according to different machine transmission machinery, the applied servo system is divided into feed servo and spindle servo.

In the spindle servo drive unit, due to the need to provide the cutting power required to process various types of workpieces, it is required to be able to meet the machine spindle speed range, low speed and high torque, dynamic response and other characteristics, but also with the CNC system to achieve Rigid tapping, spindle speed control, Cs axis control real-time switching and other high performance. The feed servo drive unit uses the coordinates of the numerical control machine tool as the control object to generate the cutting feed motion of the machine tool. Therefore, the accuracy and rapidity of the position and speed control are particularly emphasized, and the reliability is high.

In order to further improve the control performance of the servo drive unit in the machine tool industry, a large number of digital processing technologies have been introduced into this field. A group of manufacturers have developed all-digital AC servo drive units. This type of servo drive product adopts digital signal processor (DSP), CPLD ultra-large-scale integrated circuit chip, and optimized PID control algorithm to achieve digital control, greatly improving control accuracy and response speed; in addition, the use of intelligent power module (IPM), thus ensuring the reliability of the whole machine.

The motors used in the machine tool industry currently include stepper motors, servo motors, and hybrid stepper motors. High-precision CNC machine tools require fully enclosed motors, high-speed, high-precision optical encoders, and high performance. The drive cooperates with high-precision speed and position control, stable and reliable, low vibration and low noise.

With the rapid development of the domestic CNC machine tool industry, the era of high-speed, sub-micron finishing has come. For example, in the consumer electronics, information and optoelectronic industries such as iPone, iPad, LEDTV, due to the diversification of 3C products and rapid production As a result, the demand for precision, small, and rapid processing has increased, and the market capacity of high-speed cutting machine tools has increased dramatically. In addition, digital, networked technology is leading the CNC machine tool into a brand new stage. “Intelligent Manufacturing” is no longer just a dream. Faced with the latest technological developments in the CNC machine tool industry, the servo control system also needs to improve its performance indicators in various aspects. Among them, distributed serial servo systems, high control accuracy and stability, and reduction of motor energy consumption are the current overall The main trend of servo system in technology research and development.

Meet the needs of multi-axis, multi-point control

In the development of motion control technology today, distributed system architecture (Distributed) highlights more and more important roles and values. It has positive significance in production decisions, integrated manufacturing, human-machine interface, energy saving and environmental protection. . In response to this trend, while requiring hardware and software to be more real-time and expandable, it is also necessary to use serial servo control to satisfy multi-axis and multi-point (I/O) control. These will become future servos. One of the main directions of system development.

Most traditional servo control systems go through a closed loop to control the positioning, speed, and torque of each device in the system; however, the number of devices (number of axes, I/O points) that must be controlled in some large distributed production systems is increasing. Increases and wiring are also more complicated. In this case, the resolution, synchronization, and real-time performance are often strained, and they are susceptible to noise such as power supply. Therefore, in recent years, some leading manufacturers have adopted various industrial Ethernet protocols to transmit digital signals and control parameters through the network to meet the requirements of real-time performance. The distributed motion control system has also developed along with it. The distributed serial servo system can be modularized, and the design is more flexible. It can freely expand the number of Motion and I/O control points for multiple axes, and requires only single-wire connection and single-machine (computer) control, which greatly saves wiring cost and space. This has become the mainstream trend of future manufacturing.

Nanjing Estun Automatic Control Technology Co., Ltd. has achieved outstanding results in this field of technology research and development. In order to enable users to use the servo system more flexibly, the Pronet series servo driver developed by the company has taken the lead in increasing the extensibility as well as the flexible and open design. With the option module, various communication interfaces and various feedback interfaces can be extended. In addition to RS485 communication interface and CAN communication interface, it can also support MODBUS communication protocol, CANopen communication protocol and PROFIBUS communication protocol. For example, corresponding to the PROFIBUS-DP communication network, the servo information (position, speed, torque, input and output, alarm, etc.) of the system can be controlled and adjusted in real time, shortening the adjustment time of the servo system, and simplifying the operation. One upper controller It can realize multi-axis motion control of up to 255 stations, and can be widely used in high-end machine tools, high-speed packaging and printing machinery and other high-end applications.

In addition, taking the DAT series of AC servo drive units introduced by Guangzhou CNC as an example, based on the mature AC servo technology, combined with serial bus and absolute encoder interface technology, it supports independent research and development of GSKLink bus technology, CNC serial The bus can realize the debugging and real-time monitoring of the servo, and significantly improve the speed accuracy and position accuracy. The maximum frequency of the position pulse command is 1MHz, 0.1m instruction accuracy, and 0.1m level control accuracy. It is a CNC machine tool and automation equipment. A good choice for high-speed, high-precision motion control.

Improve control accuracy and stability

With the rise of digital manufacturing with CNC machine tools as the technology platform, intelligent manufacturing, technology integration and technology compounding have become one of the most active trends in the development of CNC machine tools. Intelligent machine tools can monitor their own status with various sensors, analyze the status of the machine, processing and information about the surrounding environment on their own, and then take countermeasures to ensure optimal processing. In addition, the new CNC machine tools also need to have active vibration suppression to reduce vibration, intelligent thermal barriers to control thermal displacement, intelligent security barriers to prevent component collisions, voice prompts and SMS notifications, and help in selecting processing requirements. Cutting parameters and so on, in short, intelligent can improve the control accuracy of the machine tool, as well as the stability and reliability of the machine.

In the servo system, the vector control technology based on the dynamic decoupling mathematical model of the permanent magnet motor is the core control method of the servo system. In order to further improve the control accuracy and stability, some manufacturers use the high speed control loop based on vector control. Digital signal processor (DSP) with automatic gain adjustment and command smoothing function Take the MR-J3 series AC servo system developed by Mitsubishi Electric as an example. In order to achieve high-precision positioning, a high-performance servo motor encoder matched with the MR-J3 series is used. Using an absolute position encoder with a resolution of 262144 pulses/rev, the frequency response of the velocity loop is increased to 900 Hz, with high-speed/high-torque characteristics, cogging torque can be reduced, and torque ripple of the servo motor can be reduced. The machine runs smoothly and smoothly at uniform speeds. At the same time, this product can achieve automatic adjustment of all gains including position gain and speed gain through advanced self-adjusting functions and advanced vibration suppression control functions, effectively suppressing vibrations below the frequency of 100 Hz that occur when the drive components stop. The servo setup software MR-configurator has precise mechanical analysis capabilities and can be used in applications such as machine tools and general industrial machinery that require high-precision position control and smooth speed control.

The recently launched ASDA-M series is a three-in-one intelligent servo. It integrates three servos on the same base and controls the three axes synchronously. There is no time delay for data exchange between axes; Linear interpolation, arc and spiral interpolation control within the driver; new gantry control architecture, precise synchronization, can be used for pure rigid connection mechanism; software with a simple circular analysis, can strengthen the system's diagnostic capabilities. In addition, ASDA-M series servos also have excellent high-speed response performance, high and low frequency vibration suppression capabilities, precise full-closed loop control, flexible internal position programming mode, real-time position recording and position comparison, and other advantages, greatly improving the machinery Terminal positioning accuracy.

Reduce motor energy consumption

As an important functional component of CNC machine tools, the performance of the motor is directly related to the performance of the overall system. Due to its advantages in cost control, stepper motors have made it the preferred product for most economical CNC machine tools, but at the same time, its disadvantages are also obvious. That is, the inertia ratio is small and the torque output ratio per unit of power is small (Nm). /kW), poor efficiency, large heat output. The servo motor is widely used in high-precision CNC machine tools and other precision machinery industries due to its advantages of fast response, precise positioning, and relatively high technical threshold. Among them, AC servo motor is characterized by sine wave control, small torque ripple; stator winding heat dissipation is more convenient; inertia is small, easy to improve the rapidity of the system; adapt to high speed and high torque working conditions; with the same power with a smaller volume and Weight; high reliability, low maintenance and maintenance requirements.

According to the latest statistics from the International Energy Agency, industrial electricity accounts for about 42% of the world's total electricity consumption, of which two-thirds are consumed by industrial motors. Therefore, at the present stage, the servo motors and built-in rotary stator fields required for the high-speed spindles of numerically-controlled machine tools all create new market opportunities by emphasizing energy-saving benefits. For example, at present, some Japanese, European and American servo motor manufacturers have mastered key materials such as NdFeB permanent magnets, and thus have certain advantages in the quality and performance of PM servo motor products. It is estimated that the efficiency of system operation using these rare earth permanent magnet coreless motors to drive general equipment can be increased by 20-40%, and the potential for saving electricity can reach 1000-200 billion kwh.

In June last year, the EU minimum energy efficiency standards regulation for low-voltage motors came into effect. The new regulation covers two-stage, four-stage, and six-stage AC motors with most powers ranging from 0.75 kW to 375 kW, 50, and 60 Hz. In phases, increase the international energy efficiency rating of these motor products involved. At the same time, countries such as China, Australia, Brazil, and Canada have already implemented similar energy efficiency laws. The United States has implemented the NEMAP premium (National Electrical Manufacturers Association High Efficiency) standard equivalent to IE3 level since the end of 2010. The introduction of these laws and regulations will further promote the promotion of energy-saving technologies in the motor industry.

In addition, for gear grinding machines and precision machine tools, direct drive technology is another development direction that deserves attention. Direct drive linear motors are also the ideal drive mode for future high-speed, high-precision CNC machine tools. Currently, they are accepted by machine tool manufacturers. General attention is paid to the rapid development of technology. Kollmorgen, the world's leading manufacturer of motion control systems and accessories, has extensive professional experience in the research and development of direct drive technology. The direct drive linear (DDL) series of motors it introduces are frameless permanent magnet three-phase brushless servo motors. Maintenance, higher accuracy, higher bandwidth, smoother motion speed, reduced noise, and a wide range of sizes and thrusts are available for a variety of straight line applications, simplifying the design of high-thrust permanent magnets, which greatly improves the The overall reliability of the machine.

Conclusion

It is worth mentioning that while the Chinese machine tool industry is moving into high-end numerical control at the same time, the “remanufacturing” of ordinary machine tools and aging CNC machine tools is also a market with great potential. After all, it is necessary to purchase new CNC machine tools. Huge investment. At present, some leading domestic manufacturers are actively exploring this market, and strive to achieve the same effect as the purchase of new machine tools. While reducing capital investment, they will improve the quality and productivity of parts processing, shorten the product manufacturing cycle, and improve the working environment. According to the calculations of relevant manufacturers, The price of a set of economical CNC remanufactured machine tools is only 1/5-1/3 of the same function of the new CNC machine tools.

The development of CNC machine tools is directly related to the transformation and upgrading of the national basic manufacturing industry. It is one of the important national strategies for strategic development at this stage. As the main supporting industry, the servo control system urgently needs to adapt quickly to the development characteristics of the current manufacturing industry, and enhance the technical level of the overall solution from both the technical and service aspects. For the specific needs of the current high-end CNC machine tools, servo control companies should continue to provide customers with innovative motion solutions and high-quality products, help customers improve the performance of CNC machine tools, make it more market competitive, and as much as possible Shorten the time to market, save the budget, improve the reliability and efficiency of the overall system, and finally achieve the goal of improving the accuracy of CNC machine tool speed, accuracy and position control.