Linear Motors and Parallel Machines: A Model of Machine Tool Technology Innovation

In today's global financial crisis, which has not yet shaken off its complicated influence, people have in-depth reflection on the future development. What kind of posture and face will we adopt to welcome a new era? It can be imagined that after the crisis, the global economic environment will undergo tremendous and profound changes, and the development model of technology and products will no longer be repeated in the past. We will create a high-tech and innovation-based outcome to support energy conservation and environmental protection. Low-carbon economy is the dominant, green and efficient modern civilization.

The theme of this year's show is "to welcome the post-crisis era with technological innovation." So, what are the eye-catching commonalities and key technologies in today's machine tools? The reporter noticed linear motors and parallel machine tools.

Linear motor: The future is still a big bottleneck is still a few days ago, the China Machine Tool Industry Association, the relevant person told reporters: "direct drive technology is the direction of the development of the industry, but also the shortcomings of domestic machine tools, in this area, Germany and Japan took the lead. But Recently, I learned that Japan also encountered difficulties in the development of direct-drive technology, that is, it cannot solve the problem of heat dissipation during high-power, high-torque machining."

The United States Ingersoll Corporation is a well-known machine tool manufacturer, Chrysler Motor Company purchased six of its HVM600 horizontal machining centers for the production of advanced automotive engine cylinder heads. The spindle speed of the machine is 20,000 r/min, and the X/Y/Z triaxial axes are driven by GEFANUC linear motors. The six machining centers produce 300 cylinder heads per day, which is equivalent to the production of 11 non-linear motor-driven machining centers.

At present, the most well-known machine tool manufacturers in the world have introduced linear motor-driven machine tools almost without exception, covering most machine types.

Domestic applications of linear motors in machine tools have also been carried out since 1995, such as the Guangdong Institute of Technology's linear induction motor-driven GD-3 high-speed CNC machine tool feed unit, Tsinghua Research's long-stroke permanent magnet linear servo unit, Beijing The linear motor driven machining center developed by the Institute of Electrical and Mechanical Services, the cylindrical parallel motor-driven parallel mechanism-driven coordinate measuring machine and the flat permanent-magnet linear motor-driven grinder developed by Zhejiang University, and the linear motor-driven EDM developed by Beijing Machine Tool Research Institute Machine tools, non-circle cutting of pistons developed by the National University of Science and Technology of the People's Republic of China have adopted linear motor-driven cutting tools and machine tools developed by Beihang and China Southern in cooperation with relevant organizations. In addition, some enterprises such as Hangzhou Machine Tool Group, Jiangsu Duoling CNC Machine Tool Co., Ltd., Jinan Jiemai CNC Co., Ltd., Shenzhen Dazu Laser Technology Co., Ltd., and Nanjing Sikai Company also used surface grinders, laser scribing machines, and lasers, respectively. Cutting machines, engraving and milling machines, and machining centers use different linear motor technologies and achieved good results.

In recent years, the use of linear motors in CNC machine tools has become particularly hot in the world. The reason is that the driving mechanism of traditional machine tools relies on screw drive. The screw drive itself has a series of unfavorable factors, such as: length limit, mechanical clearance, friction , torque, one-cycle error, etc., while the linear motor not only does not have this defect, and the structure is simple, the precision can be 10 times or even 100 times the screw, the acceleration can be more than 20 times the traditional machine tools.

The development of linear motor technology has experienced a long history and several wave-like developments. Compared with non-linear motor drives, the new linear motor-driven device has a simple structure, no contact, and no wear. The advantages of low noise, high speed, high precision, and flexible combination are obvious, but due to the side-effects caused by the breaking of the magnetic circuit in the linear motor itself and the large air gap in the installation, it is in some straight-line motions. Whether or not a new type of linear motor is used to drive the device or system, the trade-offs between the advantages and disadvantages must be weighed, and a linear motion device or system that can take full advantage of the advantages of the linear motor should be selected for development and application. Today, with the rapid development of science and technology, in the place where some rotary servo motors or other drive devices are incompetent or barely able to cope with it, we are looking for a place where linear motors can give full play to their advantages, and seek their own in the process of satisfying human needs and improving the good wishes of mankind. The prospects for development are broad, but the choice is to be cautious.

Parallel machine tools: the concept is unique and controversial The first batch of electrical robots appeared in the world in the early 1970s and were used to replace human labor in some extremely monotonous and dangerous work areas. This kind of robot uses the serial technology. Its technical advantage is that the working terminal can move in all directions, has sufficient dynamic performance and flexibility, and can reach the required working area, but its accuracy and rigidity are poor.

For a long time, the developers of the machine tool manufacturing industry have dreamed of combining the advantages of a robot with good flexibility, a large working area, and the advantages of traditional machine tools with high precision and rigidity. In the past 20 years, people have been focusing on the development of PKM.

Since its inception, the research and development of parallel machine tools is still in the research, trial production and trial phase. The research contents of the dynamic characteristics of the parallel machine tools and the influence of their machining accuracy are still at the initial stage. At the expense of working space and flexibility, it attempts to obtain high stiffness, high load-bearing capacity, and good sports characteristics. However, the parallel machines developed at home and abroad have not reached the desired accuracy.

Wu Bulin, executive vice president of the China Machine Tool Industry Association, told the reporter: “I am not optimistic about the development of parallel machine tools. An academician holds the same point of view as me. He asked me: What kind of processing must be achieved with a parallel machine tool? ”

However, this does not hinder the impulse of companies to try. In September 2009, Weihai Huadong Numerical Control Co., Ltd. (hereinafter referred to as “East China CNC”) and Sweden EXECON (hereinafter referred to as “Axcon”) signed the “EIM-01 Manufacturing License Agreement”. East China CNC has introduced Aixinkang's complete series of parallel kinematic machine tool technology through manufacturing licenses. The company manufactures and sells series parallel motion five-axis linkage CNC machine tools. Axicon guarantees that the machine tool products produced with its technology will be accepted at the user's factory. Parallel machine tools have begun to enter the real operation stage and present a number of competitive landscapes.

Liang Xunji, honorary director of China Machine Tool Industry Association, believes that the parallel machine tool can be used as a "smart dry alternative." Due to the high flexibility of this machine tool, it is possible to carry out anthropomorphized machining of large-scale workpieces, which is equivalent to a gantry milling machine with a capacity of more than 10 million yuan per unit. Secondly, its application range has great potential.

In fact, Harbin Measuring & Cutting Tools Group (hereinafter referred to as "Harbin") first introduced the Axicon parallel motion machine tool in 2006, and it was also the operation of Liang Xunyi. As an expert, he has not only promoted the promotion of parallel machine tools on one occasion. The reason is his future grasp of this technology and his preference for this type of machine.

At the last China International Machine Tool Show (CIMT2009), as the country’s first technology importer, Harbin also exhibited a prototype of a parallel machine tool.

Liang Xunyi said that the three companies that introduce Axicon parallel machine tools in China have different product specifications. Harbin mainly produces 700mm specifications (this specification is also transferred to Korean companies at the same time); East China CNC mainly does 900mm, 1000mm, 1100mm, 1300mm specifications of the parallel machine; Long March Zigong mainly do 300mm, 500mm.