As one of the key technologies for CNC machine tools, industrial robots and other industrial machinery control, servo drive technology has received widespread attention at home and abroad.
I. Overview
As one of the key technologies for CNC machine tools, industrial robots and other industrial machinery control, servo drive technology has received widespread attention at home and abroad. In the last 10 years of the 20th century, the development of microprocessors (especially digital signal processor-DSP) technology, power electronics technology, network technology, and control technology laid a good foundation for the further development of servo drive technology. If the AC servo drive technology replaced the DC servo drive technology in the 1980s, then in the 1990s, the servo drive system was fully digitalized, intelligent, and networked for 10 years. This is especially true in some industrialized countries.
Second, the status quo and development trend abroad
Unmanned and large-scale production puts high speed, high precision and high efficiency on processing equipment. AC servo system has high response, maintenance-free (no carbon brush, commutator and other wear parts), high reliability, etc. The characteristics just adapted to this demand. For example, Japan FANUC Corporation, Mitsubishi Electric Corporation, Yaskawa Electric Corporation, German Siemens Company, AEG Company, Rexroth Indramat Company, American AB Company, GE Company, etc. successively put the AC servo system into practical use before and after 1984. The domestic AC servo drive technology started late, and it was only in the late 1980s that products were available. For example, the ACS series of Huateng Company of the Ministry of Metallurgy and the Yangzhou 5308 factory introduced the 610 series of Siemens. These products use high-power transistor modules (GTR), which belong to analog servo, but fill the domestic gap technically.
In the 1990s, the perfection of microelectronics manufacturing technology, the DSP computing speed increased geometrically, achieving the high-speed real-time control of the servo loop. Some motion control chip manufacturers also have the peripheral circuits necessary for motor control ( Such as A / D converter, position / speed detection multiplier counter, PWM generator, etc. integrated with the DSP core, so that the servo control loop sampling time is less than 100?s, automatic acceleration and deceleration control by a single chip, electronic Gear synchronous control, digital compensation control of position, speed and current. Some new control algorithms such as speed feedforward, acceleration feedforward, low pass filtering, and sag filtering are implemented. On the other hand, the development of power electronics technology has increased the switching frequency of the main circuit power components of the servo system from 2 to 5 kHz to 15 to 20 kHz. 1 GBT (insulated gate bipolar transistor) and IPM (smart power module) are The product of this era, which improves the stability of the system and reduces the noise of the system. The above two aspects are not only the basis for the digitalization of the AC servo, but also make the AC servo tend to be miniaturized. At present, servo system manufacturers in some industrialized countries are basically able to provide full digital AC servo systems or can be matched with their own CNC systems, such as Japan FANUC, Mitsubishi Electric Corporation, Yaskawa Electric Corporation, Matsushita Electric Co., Ltd. , Siemens, Germany, Rexroth Indramat, Lenze, AB, Kollmorgen, Relliance, Baldor, PacificScientific, etc.
The rapid development of all-digital AC servo technology makes it more convenient for users to adjust parameters according to load conditions (such as inertia, clearance, friction, etc.), and also eliminates some unstable factors such as drift caused by analog loops, but in the early stage of development The servo interface lacks a unified standard. Each manufacturer designs its own interface circuit, and there is no interchangeability between them. User adaptation is more troublesome. This problem is particularly acute in the case of rapid development of network technology and PC-based CNC technology.
In 1987, the German Machine Tool Association and the German Power Electronics Association jointly proposed the international standard for digital drive interfaces, namely the SERCOS (SerialReal-time Communication System) interface as a closed-loop data serial real-time communication interface for high-performance motion control systems. The associations form a joint working group of major manufacturers of motors, drive systems and CNC systems. The companies that originally joined the SERCOS working group include AEC, ABB, AMK, Banmuller, Bosch, Indramat, Siemens, Pacific Scientific and several other companies. By 1994, SERCOS became an international standard for the interface between controllers and digital servo drive systems and was adopted as the IEC61491 standard. Therefore, it has been open to the public and has grown to more than 70 companies. At the same time, the corresponding ASIC chip, SERCON816, was developed with a transmission speed of 2/4/8/16 Mbit/s. SERCOS has a high effective data transmission rate compared with other serial field buses. For example, Ethement transmits at 100 Mbit/s. When data is used, the effective data transmission rate is 5 to 10 Mbit/s; when SERCOS transmits data at 16 Mbit/s, the effective data transmission rate is 11 Mbit/s. When CAN (controllerAreaNetwork) is used for motion control, it must provide additional storage buffer and signal management resources, which cost about twice as much as the SERCOS interface. Another feature is its fiber noise suppression capability and high transmission reliability. Although the SERCOS interface was originally developed for the CNC and digital servo interface, it has been widely used in the interface between the universal motion controller and the digital servo. It is now able to meet the data communication between one controller and up to 32 servo systems within 2ms. SERCOS paves the way for digital servo networking. It is foreseeable that in the near future, servo systems with SERCOS interfaces will enter the home, office, factory floor and even servo-related fields. In 1999, Rexroth Indramat took the first place in the North American servo drive market with a 10.5% share. On the one hand, it strengthened its application engineering, sales, service and customer support. Another major factor is the commitment to open. Structure - SERCOS.
Lightweight (such as copper, wood, aluminum alloy, etc.), composite materials in the automotive, home appliances, AF industry, the use of large quantities, put forward new requirements for high-speed, efficient processing. In order to meet this demand, some industrialized countries have successively introduced linear motors and high-speed spindle motors, and put them into practical use. For the linear motor, the control technology is similar to that of the conventional AC servo motor. However, since the linear motor itself has no rotor such as a rotor, the inertia is small, so it has high dynamic response, and the detecting element is directly mounted on the mechanical side. Therefore, the displacement of the table is detected, and the commutation gap existing when the rotating motor changes direction is also avoided, which satisfies the requirements of the servo drive system for high speed and high precision machining. From the IMTS2000 exhibition, some industrialized countries are at the leading level in high-speed processing technology. IBAG has supplied the industry with a series of high-speed built-in spindle systems with a range of 0.125 to 185 kW and a maximum speed of 14,000 r/min. The repeating precision is less than 1?m, the motor bearing has three kinds of hybrid ceramic bearing, hydrostatic bearing and magnetic floating bearing, which is cooled by water pipe, and built-in position sensor is used for machining center ATC. The spindle drive adopts vector frequency conversion technology and has been widely used in mold processing, high-precision electrode processing, aluminum parts processing, high-precision grinding processing, etc., and Fisher has similar products.
Third, the domestic status and development trend
In the early 1980s, China introduced, digested, and absorbed foreign advanced technology, and achieved great results in the major scientific and technological projects of servo drive technology during the "7th Five-Year Plan", "Eighth Five-Year Plan" and "Ninth Five-Year Plan" period. However, due to product reliability and other reasons, it restricts the matching and application of CNC machine tools in China, thus affecting the development of China's equipment manufacturing industry. Some machine tool manufacturers have to choose foreign servo systems, so that domestic CNC machine tools do not have advantages in terms of price, delivery time, reliability, etc., and they have no intention to develop new varieties of market demand, thus losing huge market share. According to public statistics, more than 75% of the faults in the CNC system come from the servo part.
However, in recent years, while the country continues to organize scientific and technological research, some private high-tech companies have also injected new vitality into the development of China's servo drive technology. For example, Beijing Zhongbaolun Automation Technology Co., Ltd. has developed a new product in the market-oriented situation without investing a penny. In 1994, it successfully developed the PDC series DC servo system. There are seven specifications for torque from 1Nom to 44.1Nom. The wide-speed DC servo motor adopts the latest generation of power devices in the world--IPM, PWM control, and the modulation frequency reaches 15kHz, effectively overcoming the commutation spark generated by current interruption during SCR control. Ablation can extend the life of carbon brushes by more than one time. At the end of 1997, the company developed the PAC series AC servo system, which was matched with the 94-standard brushless AC servo motor of the 1FT5 series of the German Siemens company. The speed series has 1,200r/min, 2,000r/min, 3,000r/min, 4,000r/min, 4,500r/min, 6,000r/min, torque range 0.15～90N·; in November 2000, according to market demand, development The PAC-P series digital position type AC servo system is available. After these products were introduced to the market, they achieved good social and economic benefits. They were approved by Beijing No. 1 Machine Tool Plant, Tsinghua University Precision Instrument Factory, Qinghai No. 1 Machine Tool Plant, and XA5750 ram milling machine and XA718 vertical milling machine. , XA2412/2410 gantry milling machine and XKA5032 CNC vertical milling machine, CNC profile screw milling machine, XKA8132/8140 CNC milling machine and other supporting. In addition, it is also used in composite molding machines, automotive radial tires, two-stage forming and cutting machines, satellite wind tunnel group control, electronic component material cutting, braiding and other fields. At present, nearly 200 units are used in domestic radial tire production lines, running continuously 24 hours a day. In addition to domestic applications, since 1997, some of the company's products have been exported to Germany, Canada, Australia and other countries by Beijing First Machine Tool Plant. Nearly 1,000 sets of AC/DC servo systems have been sold since 1994. No one has been repaired in the past few years. According to the company's record figures, only 8 units are due to incorrect user wiring, resulting in fuses, power circuits and interface components. Burned out. Users who use Zhongbaolun products have changed their views on the reliability of domestic servo systems. Huazhong CNC System Co., Ltd., Everest CNC Company, Aerospace CNC Company, Institute of Electrical Engineering of Chinese Academy of Sciences and other units have been able to provide the servo system required by their own CNC system to some machine tool manufacturers through the implementation of national science and technology projects. Technical transformation. Luoyang Bearing Research Institute independently developed high-speed electric spindles, which have been applied to bearing grinding machines, printed circuit board milling, drilling and so on.
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