Development of the hottest servo system

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Development history of servo system

servo system plays an important role in electromechanical equipment. Here is a brief talk about its development history:

(1) the development of DC servo system

servo system has experienced a process from hydraulic to electrical. The electric servo system is divided into DC servo system and AC servo system according to the type of motor driven. In the 1950s, brushless motor and DC motor were commercialized and widely used in computer peripherals and mechanical equipment. The 1970s was the most widely used era of DC servo motor

(2) AC servo system

from the late 1970s to the early 1980s, with the development of microprocessor technology, high-power and high-performance semiconductor power device technology and motor permanent magnet manufacturing technology and the increasing performance price ratio, AC servo technology - AC servo motor and AC servo control system gradually became the leading products. AC servo drive technology has become one of the basic technologies to realize automation in the industrial field, and will gradually replace DC servo system

AC servo systems are divided into two main categories according to the type of driving motor they use: permanent magnet synchronous (SM) motor AC servo systems and induction asynchronous (IM) motor AC servo systems. Among them, the AC servo system of permanent magnet synchronous motor has become fully mature in technology, has very good low-speed performance, and can realize weak magnetic high-speed control, broaden the speed range of the system, and meet the requirements of high-performance servo drive. With the substantial improvement of the performance and the reduction of the price of permanent magnet materials, it will be more and more widely used in the field of industrial production automation. At present, it has become the mainstream of AC servo system. The AC servo system of induction asynchronous motor has a good display of simulation results before development, and represents the direction of servo technology in the future because of its solid structure, easy manufacturing and low price. However, due to the vector transformation control, the control of the system is more complex than that of the permanent magnet synchronous motor servo system, and there are still some technical problems to be overcome, such as low efficiency and serious heating, when the motor runs at low speed. At present, it has not been widely used

the actuator of the system is generally an ordinary three-phase squirrel cage asynchronous motor, and the power converter usually adopts the intelligent power module IPM. In order to further improve the dynamic and static performance of the system, position and speed closed-loop control can be adopted. The following control of three-phase AC current can effectively improve the current response speed of the inverter, and can limit the outflow of transient current, which is conducive to the safe operation of IPM. The speed loop and position loop can be controlled by the single chip microcomputer electro-hydraulic servo hydraulic universal material testing machine, so that the control strategy can obtain higher control performance. If the current regulator is in proportional form, the three AC current loops shall be controlled by a sufficiently large proportional regulator, and its proportional coefficient shall be as large as possible on the premise that the system does not produce oscillation, so that the amplitude, phase and frequency of the three-phase AC current of the controlled asynchronous motor change rapidly with the given value, so as to realize the fast current control of the voltage source inverter. The current is adjusted by proportion, which has many advantages, such as simple structure, good current following performance, and fast and reliable starting and braking current limitation of the motor

(3) comparison of AC and DC servo systems

the development of DC servo drive technology is limited by the defects of the motor itself. DC servo motor has the disadvantages of complex mechanical structure and heavy maintenance workload. The rotor is easy to heat during operation, which affects the accuracy of other mechanical equipment connected to it. It is difficult to be applied to high-speed and large capacity occasions. The mechanical commutator has become the bottleneck of the development of DC servo drive technology

the AC servo motor overcomes the shortcomings of the DC servo motor caused by the brush, commutator and other mechanical components, especially the overload characteristics and low inertia of the AC servo motor reflect the advantages of the AC servo system. So AC servo system has been widely used in various fields such as factory automation (FA)

from the current application of servo drive products, DC servo products are gradually decreasing, while AC servo products are increasing, and the market share is gradually expanding. In practical application, AC servo products with higher precision, faster speed and more convenient use have become mainstream products

(4) development trend of servo system

from the previous discussion, it can be seen that digital AC servo system is more and more widely used, and users have higher and higher requirements for servo drive technology. In general, the development trend of servo system can be summarized as follows:

1 AC

servo technology will continue to rapidly change from DC servo system to AC servo system. From the current situation of the international market, almost all new products are AC servo systems. In developed countries, the market share of AC servo motors has exceeded 80%. There are more and more manufacturers of AC servo motors in China, and they are gradually surpassing those of DC servo motors. It can be predicted that in the near future, AC servo motor will completely replace DC servo motor except in some micro motor fields

2. Full digitalization

the servo control unit with new high-speed microprocessor and special digital signal processor (DSP) will completely replace the servo control unit mainly composed of analog electronic devices, so as to realize a fully digitalized servo system. The realization of full digitalization turns the original hardware servo control into software servo control, which makes it possible to apply the advanced algorithms of modern control theory (such as optimal control, artificial intelligence, fuzzy control, neural network, etc.) in the servo system

3. At present, more and more new power semiconductor devices with high switching frequency are used in the output devices of servo control system, mainly including high power transistor (GTR), power MOSFET and insulated gate transistor (IGBT). The application of these advanced devices significantly reduces the power consumption of the output circuit of the servo unit, improves the response speed of the system, and reduces the running noise. In particular, the latest servo control system has begun to use a new module that integrates the control circuit functions and high-power electronic switching devices, called intelligent power modules (IPM). This device will input isolation, energy consumption braking, over temperature

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