Numerical control systems and related automation products are mainly matched with numerically-controlled machine tools. The CNC machine tool is a mechatronic product formed by the penetration of new technology represented by the CNC system into the traditional machinery manufacturing industry: the machine tool equipped with the CNC system greatly improves the accuracy, speed and efficiency of parts processing. This kind of numerical control working machine is one of the important material foundations of national industrial modernization.
The concept of numerical control (abbreviated as “numerical control” or “NC”) is to convert the requirements of the machined parts, such as shape and size, into numerical data instruction signals and transmit them to the electronic control device, which controls and drives the tool of the machine tool. The parts are processed by movement. In traditional manual machining, these processes need to be manually manipulated by the machine. It is difficult to meet the processing requirements of complex parts, especially for parts with multiple varieties and small batches, which have low processing efficiency and poor accuracy.
In 1952, the Massachusetts Institute of Technology and Parsons Corporation invented the world’s first three-axis CNC milling machine. The control device is composed of more than 2,000 electron tubes, about the size of an ordinary laboratory. The servo mechanism uses a small servo motor to change the angle of the swash plate of the hydraulic motor to control the speed of the hydraulic motor. Its interpolation device adopts pulse multiplier. The successful development of this NC machine tool marks the creation of NC technology and the beginning of a new, numerical control era in machine manufacturing.
At the Chicago Exhibition in 1970, the CNC numerical control system composed of minicomputers was exhibited for the first time. Around the same time, Intel invented the microprocessor. In 1974, the United States, Japan and other countries successively developed CNCs with microprocessors as the core, sometimes also called MNCs. It uses the program in the computer memory to complete the functions required by the numerical control. All or part of its control functions are realized by software, including decoding, tool compensation, speed processing, interpolation, position control, etc. The use of semiconductor memory to store the part processing program can replace the punched part paper tape program for processing. This program is convenient for display, inspection, modification and editing, thus reducing the hardware configuration of the system and improving the reliability of the system. The use of software control greatly increases the flexibility of the system and reduces the manufacturing cost of the system.
The introduction of CNC standards
As NC becomes an important equipment for mechanical automation processing, there is a need for unified terminology, technical requirements, symbols and graphics between management and operation, that is, a unified standard for worldwide technical exchange and trade. The development of NC technology has formed a number of international standards: ISO International Standards Organization standards, IEC International Electrotechnical Commission standards and EIA American Electronics Industry Association standards. The earliest established standards include the coordinate axis and movement direction of NC machine tools, the code characters of NC machine tools, the program segment format of NC machine tools, preparation functions and auxiliary functions, the size of CNC paper tape, and the terminology of CNC. The establishment of these standards has regulated and promoted the development of NC technology. Based on the needs of users and the prediction of information technology in the next five years, ISO is planning to launch a new standard “Data Structure of CNC Controllers.” It focuses the content of AMT (Advanced Manufacturing Technology) on two main levels and the connections between them: the first level CAM, for the workshop and its production machinery; the second level is the upper level, for the data generation system , Consists of CAD, CAP, CAE and NC programming systems and related databases.
Servo technology development
Servo device is an important part of CNC system. In the early 1950s, the feed drive of the world’s first NC machine tool was hydraulically driven. Because the force per unit area generated by the hydraulic system is greater than the force generated by the electrical system (about 20:1), the inertia is small and the response is fast, so at that time, the feed servo of many NC systems was hydraulic. In the early 1970s, due to the oil crisis, environmental pollution caused by hydraulic pressure, heavy system, low efficiency and other reasons, the United States GETTYS company developed a DC high-inertia servo motor with large static and starting torque and good performance. FANUC soon Introduced in 1974 and applied to NC machine tools. Since then, open-loop systems have been gradually replaced by closed-loop systems, and hydraulic servo systems have gradually been replaced by electrical servo systems.
The initial stage of electric servo technology is analog control. This control method has high noise and high drift. With the adoption of microprocessors, digital control was introduced. It has the following advantages:
- No temperature drift, good stability.
- Based on numerical calculation, high precision.
- Set the system through parameters to reduce the adjustment.
- Easy to make ASIC circuit. For modern numerical control systems, the biggest breakthrough in servo technology can be attributed to: AC drive replaces DC drive, digital control replaces analog control, or software control replaces hardware control. In the 1990s, many companies developed linear motors, driven by a fully digital servo, with high rigidity and good frequency response, so high speeds can be obtained.
The adoption of automatic programming
There are two programming methods: manual programming and automatic programming. According to statistical analysis, using manual programming, the ratio of the programming time of a part to the machining of the machine tool is about 30:1 on average. In order to improve efficiency, a computer or a programming machine must be used instead of manual programming.
Automatic programming requires an automatic programming language. The APT language developed by the Massachusetts Institute of Technology is the most typical CNC language, which greatly improves the programming efficiency. The image numerical control programming technology that has appeared since the 1970s has effectively solved geometric modeling, display of part geometric shapes, interactive design, modification and tool path generation, simulation display and verification of tool movement process, etc., thus promoting the integration of CAD and CAM. The direction of development.
Introduction and development of DNC concept
The concept of DNC has changed from “direct numerical control” to “distributed numerical control”, and its connotation has also changed. “Distributed CNC” means that one computer can control multiple CNC machine tools. In this way, machining has expanded from a stand-alone automation model to flexible production lines and computer integrated manufacturing systems. From the communication function, DNC interface can be added to the CNC system to form a manufacturing communication network. The biggest feature of the network is resource sharing, which can be achieved by forming a network through DNC functions:
- Upload or download the part program.
- Read and write CNC data.
- Transmission of PLC data.
- Memory operation control.
- System status collection and remote control, etc.
The use of programmable controllers
Before the 1970s, the NC controller and machine tool heavy current sequence control mainly relied on relays. Semiconductor logic components appeared in the 1960s. In 1969, the American DEC company developed the world’s first programmable controller PLC. The PLC quickly showed its superiority: the designed graphics are similar to the relay circuit, and the image is intuitive, which can easily realize the display, editing, diagnosis, storage and transmission of the program: the PLC does not have the bad contact of the relay circuit, and the contacts are welded. , Wear, coil burnout and other shortcomings. So it was quickly applied on NC machine tools. The command execution time on the NC machine tool can reach 0.085µs/step, and the maximum number of steps is 32000 steps. Moreover, the use of PLC can also greatly reduce the space occupied by the system and improve the speed and reliability of the system.
The development of sensor technology
When an NC system is connected to the machine, the geometric accuracy it can control is not only affected by mechanical factors, but the closed-loop system also mainly depends on the sensors used, especially position and speed sensors, which can measure linear displacement and rotation. Angle linear induction synchronizer and circle induction synchronizer, linear and circular gratings, magnetic scales, sensors using magnetoresistance, etc. These sensors are composed of optics, precision machinery, and electronic components. The general resolution is 0.01 to 0.001mm, the measurement accuracy is ±0.02 to 0.002mm/m, and the speed of the machine tool table is below 20m/min. As the accuracy of machine tools continues to improve, higher requirements have been placed on the resolution and accuracy of the sensor. So there are high-resolution sensors with “subdivision” circuits. For example, the encoder developed by FANUC can achieve a resolution of 10-7r through subdivision. The high-precision numerical control system constituted by it creates conditions for ultra-precision control and processing.
The emergence of open technology
In 1987, the U.S. Air Force published the famous “NGC (Next Generation Controller)” program, and first proposed the concept of an open architecture controller. One of the important contents of this plan is to put forward the “Open System Architecture Standard Specification (SOSAS)”. The U.S. Air Force defines an open architecture as: allowing multiple manufacturers to sell modules that are interchangeable and interoperable in a competitive environment. Machine tool manufacturers can add certain hardware and software on the open system platform to form their own system. There are basically two structures of open systems currently on the market:
- CNC+PC main board: Insert a PC main board into a traditional CNC machine. The PC board mainly runs non-real-time control, and the CNC mainly runs real-time control based on coordinate axis movement.
- PC+motion control board: insert the motion control board into the standard slot of the PC for real-time control, while the PC is mainly used for non-real-time control. In order to increase the openness, mainstream CNC system manufacturers often adopt the scheme①, that is, adding a PC board without changing the basic structure of the original system, providing a keyboard so that the user can connect the PC and the CNC, greatly improving the man-machine interface Function. Typical such as FANUC company’s 150/160/180/210 system. Some manufacturers also call this kind of device a fusion system. Because of its reliable work and open interface, it has become more and more popular with machine tool manufacturers and has become one of the development trends of NC technology.
Although my country’s numerical control system has made great progress, more than 90% of the numerical control systems supporting high-end CNC machine tools in our country are foreign products, especially for the high-end CNC machine tools urgently needed by the defense industry. The high-end CNC system determines the performance and function of the machine tool equipment. , Reliability and cost are the key factors, and foreign countries still impose restrictions on my country so far, which has become a bottleneck restricting the development of high-end CNC machine tools in my country. In order to accelerate the development of the CNC technology industry, the state has issued a series of policies, including the State Council’s approval of the implementation of the “Equipment Manufacturing Industry Adjustment and Revitalization Plan” and the “High-end CNC Machine Tool and Basic Manufacturing Equipment” National Science and Technology Major Special Program, creating a In order to improve the external environment, the “Plan for the Adjustment and Revitalization of Equipment Manufacturing Industry” clearly stated: “Insist on the integration of equipment autonomy and key construction projects, adhere to the combination of independent development and introduction, digestion and absorption, and adhere to the development of complete equipment and improve the level of basic supporting facilities. “The basic principle of integration” and increasing the market share of basic accessories such as CNC systems are an important part of the implementation of equipment autonomy. The National Science and Technology Major Project “High-end CNC Machine Tools and Basic Manufacturing Equipment” also proposed that by 2020, the market share of domestic high-end CNC machine tools should be increased to a greater extent.
At present, my country is in the mid-stage of industrialization, that is, gradually transforming from solving shortages to building an economic power. A number of high-growth industries based on heavy industries, such as coal, automobiles, steel, real estate, building materials, machinery, electronics, and chemicals, are developing strongly. It constitutes a huge demand for the machine tool market, especially CNC machine tools. my country’s consumption of machine tools has ranked first in the world for eight consecutive years since 2002. In 2009, China’s consumption of machine tools was greater than the sum of consumption of Japan, which ranked second in the world, and Germany, which ranked third. According to Zhang Guobao, deputy director of the National Development and Reform Commission, in the “Speech at the CNC System Industry Development Symposium”, in the next few years, the market demand for CNC machine tools in my country will continue to grow at an average annual rate of 10-15%, and the market potential is huge. . With the upgrading of China’s manufacturing industry, China’s existing ordinary machine tools also urgently need to be upgraded and upgraded. Therefore, the CNC system industry has a vast market space and great potential for further development.
During the “Twelfth Five-Year Plan” period, with the rapid development of the national economy, industries such as automobiles, ships, construction machinery, aerospace and aviation will provide huge demand for my country’s machine tool industry. It is expected that my country’s various CNC machine tools and digital machinery will be required by 2015 The demand for numerical control systems will reach more than 250,000 sets (not including the numerical control systems supporting imported machine tools), and the product structure will gradually shift to medium and high-end. Among them, the proportion of high-end numerical control systems will increase to about 10%. The proportion increased to about 50%. According to the requirements of one of the major national science and technology projects “High-end CNC Machine Tools and Basic Manufacturing Equipment”, by 2020, the domestic CNC system market share for medium and high-end CNC machine tools will reach more than 60%; the domestic mid-to-high-end CNC system market will have 12 The space for replacement of 10,000 units is huge in the future.