Servo drive technology of NC machine tool

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As one of the key technologies of CNC machine tools, industrial robots and other industrial machinery control, servo drive technology has attracted widespread attention at home and abroad. In the last decade of the 20th century, the development of microprocessor (especially digital signal processor - DSP) technology, power electronics technology, network technology and control technology has laid a good foundation for the further development of servo drive technology. It is used to measure the deformation of the sample in the experimental process. If the AC servo drive technology replaced the DC servo drive technology in the 1980s, the 1990s was the decade when the servo drive system realized full digitization, intelligence and networking. This is particularly evident in some industrialized countries

II. Current situation and development trend abroad

unmanned and large-scale production puts forward the requirements of high speed, high precision and high efficiency for processing equipment. The AC servo system has the characteristics of high response, maintenance free (no carbon brush, commutator and other wear components), high reliability and so on, which just meets this demand. For example, FANUC company, Mitsubishi Electric Company, Yaskawa electric company, Siemens company, AEG company, Rexroth indramat company, A.B company and GE company in Japan put the AC servo system into practice around 1984. Domestic AC servo drive technology started late, and products came out only in the late 1980s. For example, the ACS series of Huateng company of the Automation Research Institute of the Ministry of metallurgy and the 610 series of Siemens company introduced by Yangzhou 5308 plant adopt high-power transistor module (GTR), which belongs to analog servo, but technically fill the domestic gap

in the 1990s, with the improvement of microelectronic manufacturing technology, the operation speed of DSP has increased geometrically, which meets the requirements of high-speed real-time control of servo loop. Some motion control chip manufacturers also integrate the peripheral circuits necessary for motor control (such as a/D converter, position/speed detection frequency doubling counter, PWM generator, etc.) with DSP core, so that the sampling time of servo control loop can reach less than 100 s, Automatic acceleration and deceleration control, electronic gear synchronous control and digital compensation control of position, speed and current are realized by a single chip. Some new control algorithms such as velocity feedforward, acceleration feedforward, low-pass filter and sag filter can be realized. On the other hand, with the development of power electronics technology, the switching frequency of the power components of the main circuit of the servo system is increased from 2 ~ 5KHz to 15 ~ 20kHz. 1GBT (insulated gate bipolar transistor) and IPM (intelligent power module) are the products 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 of AC servo digitization, but also make AC servo tend to miniaturization. At present, servo system manufacturers in some industrial developed countries are basically able to provide all digital AC servo systems or can be matched with their own CNC systems, such as FANUC company in Japan, Mitsubishi Electric Company, Yaskawa electric company, Panasonic company, yamayo electric company, Siemens company in Germany, Rexroth indramat company, Lenze company, A.B company in the United States, Kollmorgen company, reliance company, Baldor company Pacific scientific, etc

with the rapid development of all digital AC servo technology, it is more convenient for users to adjust parameters according to load conditions (such as inertia, clearance, friction, etc.), and it also saves some unstable factors such as drift caused by analog circuits. However, in the early stage of development, there is no unified standard for servo interface, and each manufacturer designs its own interface circuit, which is not interchangeable with each other, so user adaptation is more troublesome. With the rapid development of network technology and PC based CNC technology, this problem is particularly prominent

in 1987, the German machine tool association and the German Power Electronics Association jointly proposed the international standard of digital drive interface, that is, SERCOS (serial real-time communication system) interface as the closed-loop data serial real-time communication interface of high-performance motion control system. The two associations formed a joint working group with the main manufacturers of motor, drive system and CNC system. AEC, abb, AMK, banmuller, Bosch, indramat, Siemens, Pacific Scientific and other companies initially joined SERCOS working group. In 1994, SERCOS became the international standard for the interface between controller and digital servo drive system, and was adopted as iec61491 standard. Therefore, it is open. So far, its membership has increased to more than 70 companies. At the same time, the corresponding ASIC chip and sercon816 are developed, and the transmission speed is 2/4/8/16 Mbit/s. compared with other serial fieldbuses, SERCOS has a high effective data transmission rate. For example, when ethement transmits data at the speed of 100mbit/s, the effective data transmission rate is 5 ~ 10mbit/S; When SERCOS transmits data at the speed of 16mbit/s, the effective data transmission rate is 11mbit/s. When can (controller area network) is used for motion control, it must provide additional storage buffer and signal management resources. Its cost is about twice that of SERCOS interface. Another feature is its strong optical fiber noise suppression ability and high transmission reliability. Although the SERCOS interface was originally developed for CNC and digital servo through the expert identification interface of the dynamic force calibration device for fatigue experiment independently developed by the Chinese Academy of metrology, it has been widely used in the interface between general motion controller and digital servo. At present, it can realize data communication between one controller and up to 32 servo systems within 2ms. SERCOS paves a wide avenue for digital servo networking. It can be predicted that in the near future, servo systems with SERCOS interface will enter homes, offices, factory workshops and even various fields related to servo applications. Rexroth indramat company occupied 10.5% of the servo drive market in North America and ranked first in 1999. On the one hand, the company strengthened its application engineering, sales, service and user support, and on the other hand, it committed to an open structure - SERCOS

the extensive use of lightweight (such as copper, wood, aluminum alloy, etc.) and composite materials in automobile, household appliances and AF industry puts forward new requirements for high-speed and efficient processing. In order to meet this demand, some industrial developed countries have launched linear motor and high-speed spindle motor, and put them into practice. For the linear motor, its control technology is not much different from the traditional AC servo motor, but because the linear motor itself has no rotor and other rotating body, so its inertia is small, so it has high dynamic response, and the detection element is directly installed on one side of the machine, so as to detect the displacement of the workbench, avoid the commutation gap of the rotating motor when the direction changes, and meet the requirements of high speed High precision machining requires servo drive system. From IMTS'2000 exhibition, some industrial developed countries are at the leading level in high-speed machining technology. Ibag has provided the industry with a series of high-speed built-in spindle systems with a maximum speed of 14000r/min and a maximum speed of 0.125 ~ 185KW. The radial and axial repetition accuracy is less than 1m. There are three kinds of electric mechanical bearings: hybrid ceramic bearing, hydrostatic bearing and magnetic bearing, which are cooled by water pipe, The built-in position sensor is used for ATC of machining center. The spindle drive adopts vector frequency conversion technology, which has been widely used in mold processing, high-precision electrode processing, aluminum parts processing, high-precision grinding and other fields. Fisher also has similar products

III. domestic current situation and development trend

in the early 1980s, China introduced, digested and absorbed foreign advanced technology, and carried out major scientific and technological projects on servo drive technology during the national "Seventh Five Year Plan", "Eighth Five Year Plan" and "Ninth Five year plan", and achieved great results. 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 equipment manufacturing industry in China. Some machine tool manufacturers also have to choose foreign servo systems, so that domestic CNC machine tools do not have an advantage in price, delivery date and reliability, and have no intention to develop new varieties required by the market, thus losing a huge market share. From the public statistics, more than 75% of the faults in the CNC system come from the servo part

however, in recent years, while the state has continuously organized scientific and technological research, some private high-tech companies have also injected new vitality into the development of servo drive technology in China. For example, Beijing zhongbaolun Automation Technology Co., Ltd. has continuously developed new products under the guidance of the market without any national investment. In 1994, it successfully developed PDC series DC servo system. There are seven specifications of wide speed regulation DC servo motors with torque ranging from 1nm to 44.1nm. It adopts the latest generation of power devices in the world - IPM and PWM control, and the modulation frequency reaches 15KHz, It effectively overcomes the ablation of the commutator by the commutation spark generated by the intermittent current during the previous SCR control, and can prolong the service life of the carbon brush by more than one time. At the end of 1997, the company successfully developed PAC series AC servo system, which is matched with 94 specifications of brushless AC servo motors of 1ft5 series introduced by Lanzhou electric machinery factory from German Siemens company. The speed series includes 1200R/min, 2000r/min, 3000r/min, 4000R/min, 4500r/min and 6000r/min, and the torque range is 0.15 ~ 90N ·; In November 2000, according to the market demand, pac-p series digital position AC servo system was developed. After these products are put into the market, they have achieved good social and economic benefits, which have been recognized by Beijing No. 1 machine tool factory, Tsinghua University precision instrument factory, Qinghai No. 1 machine tool factory and other manufacturers. They are matched with xa5750 ram milling machine, xa718 vertical milling machine, xa2412/2410 gantry milling machine, xka5032 CNC vertical Jinan assay closed mechanical milling machine, CNC special-shaped screw milling machine, xka8132/8140 CNC milling machine and so on. In addition, it is also used in the fields of composite material forming machinery, automobile radial tire one-stage and two-stage forming and cutting machinery, satellite wind tunnel group control, electronic component material cutting, tape braiding and so on. At present, nearly 200 sets are used in major domestic automobile radial tire production lines, running continuously 24 hours a day. In addition to its domestic application, since 1997, some products of the company have been exported to Germany, Canada, Australia and other countries by Beijing No. 1 machine tool factory. Nearly 1000 sets of AC/DC servo systems have been sold since 1994, and none has been repaired in recent years. According to the recorded figures of the company, only 8 sets have been burned out due to the wrong wiring of users. Users who use zhongbaolun products have changed their views on the poor reliability of domestic servo systems. Through the implementation of national science and technology projects, Huazhong CNC System Co., Ltd., Everest CNC company, aerospace CNC company, Institute of electrical engineering, Chinese Academy of Sciences and other units have been able to provide each machine tool manufacturer with the servo system required by its own CNC system, and also applied to the technical transformation of some old equipment. Luoyang Bearing Research Institute independently developed high-speed motorized spindle, which has been applied to bearing grinder, printed circuit board milling, drilling and other aspects. (end)

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