Development Trend of Linear Motors at Home and Abroad

In recent years, the development trend of linear motors at home and abroad can be summarized into three aspects, namely: First, develop to high-speed and high-precision; second, develop to large thrust and large capacity; third, develop to logistics equipment.

1, in the high-speed, high-precision development

1.1 High-speed, high-precision modern machine tools driven by linear motors

The development of high-speed, high-precision linear motors is the first application in the modern machine tool industry. The driving mechanism of traditional machine tools relies on screw drive. The screw drive itself has a series of unfavorable factors, including: length limitation, mechanical backlash, friction, distortion, pitch error, long vibration attenuation time, and coupling with the motor. Inertia and axial compression of the screw. All of these factors limit the efficiency and accuracy of traditional drive devices. When equipment wears out, it must be constantly adjusted to ensure the required accuracy. The linear motor drive technology can ensure a fairly high level of performance and has higher efficiency and simplicity than conventional motor drives that convert rotational motion into linear motion, with the high speed and accuracy that conventional drives cannot achieve.

The advantages of linear motors for machine tool applications can be simply described as follows:

1) High responsiveness

In general, the dynamic response time of an electrical component is less than a few orders of magnitude faster than a mechanical transmission. Since the mechanical transmission components such as the lead screw with large response time are eliminated in the system, the dynamic response performance of the entire closed-loop servo system is greatly improved.

2) High accuracy

Due to the cancellation of the mechanical transmission mechanism such as the screw, the tracking error caused by the lag of the conventional system is reduced. Through the high-precision linear displacement sensor, the position detection and feedback control can greatly improve the positioning accuracy of the machine tool, and its precision error can reach 0.001 μm. 3) High transmission stiffness and smooth thrust “Direct drive” improves the rigidity of the transmission, and the layout of the linear motor can be arranged according to the machine surface shape of the guide rails and the force conditions when the table is moving, and is usually designed to be uniformly symmetrical. Make it move smoothly.

3) High transmission stiffness and smooth thrust

The linear motor feed system of the machine tool can meet the ultra-high speed cutting feed rate of 60 to 100 m/min or more. Due to its high-speed response, the acceleration and deceleration processes are greatly shortened, and the acceleration can generally reach (2 to 10) g.

4) The stroke length is not limited By the stator laying of the linear motor, the stroke length of the mover can be infinitely extended.

5) Low noise during operation The mechanical friction of the drive screw and other components is cancelled. The guide rail can be used with rolling guides or magnetic mat suspension guides (without mechanical contact), which greatly reduces the motion noise.

The United States Ingersoll Corporation is a well-known machine tool manufacturer. Chrysler Motors 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.

1.2 Development Trend of Linear Motors in the Field of Machine Tools

1) The linear motor and drive control technology applied to the machine tool are maturing

The application of linear motors and drive control technology has become more and more mature, and it has superior performance unmatched by traditional transmissions. With the improvement of motor manufacturing technology, the selection of a suitable linear motor and drive control system, coupled with a reasonable machine design, can completely produce high-performance, high-reliability machine tools. Now linear motor drive feed speed 100 m/min, acceleration 1 g ~ 2 g of the machine has been very common, the existing machine tool to achieve fast forward 240 m/min, acceleration 5 g indicator (Japan AMADA laser cutting machine). High-acceleration linear motor drives have been widely used in machining centers, CNC milling machines, lathes, grinding machines, compound machine tools, laser processing machines, and heavy-duty machine tools.

2) Linear motor-driven machine tools are still high, special, but the cost is constantly optimistic

In recent years, the cost of linear motor systems has been declining, and the proportion of machine tool costs has dropped significantly. However, the current linear motor drive is still more expensive than traditional transmissions. Therefore, the application of linear motors is still focused on high-performance machine tools, especially precision high-speed machining tools, special machining tools, large-scale machine tools, to solve the traditional transmission methods can not solve the problem.

3) The linear motor technology for machine tool applications has gradually become industrialized

The application of linear motors on machine tools is no longer a sample. According to the relevant information, in 2001, DMG Germany has adopted linear motors on 28 models, with an annual output of 1 500 sets (approximately 3,000 linear motor drive shafts), accounting for 1/3 of its total output. In 2006, JOBS LinX series products in Italy accounted for 60% of the company's total production (50 large-scale gantry machining centers and gantry milling machines annually), and became the company's main source of profit. Some experts predict that by 2010, 20% to 40% of the world's CNC machine tools will be driven by linear motor feeds. These machines are high-end machine tools, so their industrialization prospects are self-evident.

Although the application of linear motors in machine tools has good prospects, some problems still need to be solved continuously. Attention should be paid to improving the application of linear motors.

1.3 Other high-speed, high-precision equipment driven by linear motors

The development of high-speed, high-precision linear motors in addition to the field of machine tools, there are also other areas of development, such as some demanding process control systems, precision detection systems, linear servo drive systems and so on. There are dozens of companies in the United States, Japan, Germany, and the United Kingdom that produce linear servo motors for high-speed, high-precision equipment. With more and more varieties and quantities, the performance is getting better and better.

2. Development in large thrust and large capacity

In recent years, apart from the rapid development of high-speed and high-precision linear motors, the development of high-thrust and large-capacity motors is also relatively rapid. Its application areas such as: linear motor city rail transportation (subway and light rail) that began in the 1980s in Canada, Japan, the United States, Malaysia, etc., are now developing rapidly, especially in Japan and China. The advantages of applying linear motor-driven urban rail transit are mainly reflected in the following points:

1) Same capacity, lower body height, reduced tunnel area, cost reduction, land conservation;

2) Strong climbing ability, small turning radius, reduced civil construction, reduced cost, convenient line selection and transfer;

3) Non-contact traction, energy saving, low noise;

4) The train has fast acceleration and deceleration and high efficiency;

5) Low maintenance and low operating costs;

6) Compared with the traditional subway, except for the bottom of the locomotive, the overall construction mode is basically unchanged;

7) Long-term safety record. The Vancouver SkyTrain has transported 450 million passengers and operated more than 1 billion kilometers in safety in 14 years.

Japan used a linear induction motor-driven subway on Osaka Line 7 in March 1990. After a linear motor-driven subway on Tokyo Line 12 in 1991, Kobe, Yokohama, Fukuoka, Sendai, and other cities also introduced linear motors. subway. Some of the 4th, 5th, 6th and 7th lines of the Guangzhou Metro in China are already in use, and some will be used. The linear motor-driven subway car that Zhejiang University cooperates with Shanghai Nanyang Electric Group is in the process of debugging.

In addition to the applications of subways and light rails, the application of linear motors in high thrust and large capacity is also an attractive part in the application of maglev transportation. At present, some countries are still moving forward in the field of maglev transportation technology. For example, Japan, Germany, the United States, and some other countries carry out R&D and application promotion in different ways. China's Shanghai-Hangzhou Maglev line is still working.

The development of linear motors in high thrust and large capacity is also reflected in large-scale equipment such as oil field pumping units, where the oil field uses a linear motor-driven pumping unit to extract the same amount of oil in the same amount of time as a conventional pumping unit. , can save 20% ~ 40%. In addition, large-thrust, high-capacity linear motors are also used in large-scale chemical equipment, construction equipment, and other large-scale industrial and civilian equipment.

3, the development of logistics equipment

In the modern large-scale production process, logistics technology has been mentioned to an unprecedented height, and the advanced logistics equipment will directly affect the development of logistics technology. A distinctive feature of the development of modern logistics industry is the application of high technology represented by modern advanced drive technology, automation technology, and information technology. The logistics equipment of developed countries accounts for more than 20% of the total project investment, making logistics equipment continuously improve. Among them, the logistics transmission equipment driven by linear motors represents an application of modern advanced logistics transmission technology. Trends. Some developed countries (for example, the United States, Japan, Germany, France, Italy, Denmark, etc.) have basically realized in the field of logistics transmission, such as airport bag transfer, postal automated sortation, newspaper and book distribution centers, and factory assembly lines. automation. These devices generally adopt the linear motor with international advanced level as the drive system, meet the needs of multi-volume and flexible arrangement, and represent the development level of the world's logistics transmission technology.

Linear motors have unique advantages in the transmission and handling of various materials. Mainly reflected in the simple structure, reliable operation, low cost, high efficiency and intelligence. Currently in the vertical transmission, such as linear motor elevators, elevators; plane transmission, such as postal packet sorting transmission lines, various luggage sorting transmission lines, steel production transmission lines, electrical, electronic, mechanical processing production lines, food processing lines, pharmaceutical production lines, etc. All kinds of industrial processing lines and various inspection lines; there are stores, hospitals and other occasions of material transfer, handling, and the handling of three-dimensional warehouses, handling scheduling of the car garage, and so on.