Development of CNC system for large-scale ultra precision machine tools
1. Ultra precision machining technology has become one of the important symbols of a country's manufacturing technology level, an important pillar of advanced manufacturing technology, and a key to improving manufacturing technology level.
As the foundation of ultra precision machining technology, ultra precision CNC machine tools have also been widely used in the processing of national defense industry, information industry, and civil products, becoming a key processing equipment that countries prioritize for development. All countries keep the CNC technology as the core of machine tools confidential to ensure its advantageous position in the manufacturing field.
Developed countries such as the United States, the United Kingdom, Germany, and Japan have all regarded the development of ultra precision CNC machining technology as an important strategy for developing national manufacturing technology, and have achieved great success. Although China has conducted extensive research on ultra precision CNC technology and several institutions have developed ultra precision CNC machine tools, they cannot meet the needs of the aerospace industry, civil electronics industry, and other industries for ultra precision machining equipment. Many ultra precision CNC machine tools still rely on imports, especially the development of large-scale ultra precision CNC machining equipment that can process parts with dimensions of 600mm and above. Therefore, there is an urgent need to develop such ultra precision CNC machine tools and related technologies to fill the gap and improve China's technological level in the processing of large ultra precision parts.
2. The hardware composition and functions of the CNC system are represented by the machining information sent by the bookmark1 carrier, which is calculated and processed to control the machine tool to perform machining tasks.
The numerical control device uses FANUC-18I, which has the characteristics of fast response speed and high accuracy. Its CPU is 32-bit counting, and when calculated at a full stroke of 600mm, the minimum pulse equivalent can reach 1nm. Therefore, the resolution of the numerical control system mainly depends on the detection feedback system. The high-speed serial communication interface FSSB protocol is used between the numerical control device (CNC) and the servo unit to reduce the influence of external interference and minimize the connection cable; AI (Artificial Intelligence) nano contour control module has been selected, which can perform nano interpolation on straight lines and arcs without the need for any special hardware. In addition, NURBS curve interpolation module has been selected, which can obtain a smooth machining surface closer to the design shape of the part, improve interpolation accuracy, and reduce the pressure of high-speed transmission of large capacity and small program segments.
X. The servo motor for the Z-axis and the friction wheel drive motor for the C1 axis of the workbench both use the AI series motor. The servo drive adopts high-speed and high-precision HRV (HighResponse Vector) control, and has high-precision current detection ability, which can achieve high-speed, high-precision, and stable feed.
The feed axes X and Z adopt a dual feedback strategy, and the speed feedback is achieved through a photoelectric encoder installed on the servo motor. The position feedback is achieved using Heidenhain's precision grating ruler, and a frequency doubling conversion card is selected to achieve a position resolution of over 40nm, Thus, the resolution of the entire CNC servo system is better than 50nm. This system aims to provide "The ultra precision machine tool for large aspherical optical components provides a matching CNC system that meets technical requirements. The assembled machine tool layout is a double column, double crossbeam vertical gantry structure, which is linked to the X-axis and Z-axis for machining. The maximum stroke of the X-axis is 600mm, and the maximum stroke of the Z-axis is 200. The rotating worktable is driven by friction wheels. The maximum diameter of the workpiece processed by the machine tool is 01000mm, and the machining accuracy is better than 2Um. The resolution of the CNC system is required to be 50nm." To meet the requirements of industrialization and practicality of ultra precision CNC machine tools, FANUC 18I is selected as the CNC device of the CNC system. The hardware structure of the control system is shown in.
The CNC system of this ultra precision machine tool mainly consists of six parts: industrial PC, CNC device (CNC), X and Z-axis servo feed system, position feedback system, worktable feed system, and spindle feed system.
The CNC device is the core of the CNC system, and its function is to meet the requirements of reserved combination machine: bed and automation processing technology (600mm), high resolution (50mi), and can achieve artificial intelligence nano contour control and high-precision NURBS interpolation.
3. The software structure and functions of CNC systems are the key technologies of software control management in ultra precision machine tool CNC systems.
In order to achieve the openness and real-time performance of the system, a relatively complete control and management software for CNC machine tools has been developed, which has functions such as document management, CNC programming, parameter setting, CNC machining, machining simulation, and fault diagnosis.
