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The vibration system includes three parts: vibration source, vibration propagation path and vibration receiving structure. Vibration isolation refers to adding appropriate components in the propagation path of vibration to reduce the vibration intensity transmitted to the receiving structure. Vibration isolation technology is widely used in civil engineering, aerospace, precision manufacturing and processing fields.
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? Active vibration isolation
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Vibration isolation is the most researched and widely used vibration control technology, which can be roughly divided into passive vibration isolation, active vibration isolation and active-passive hybrid vibration isolation. Passive vibration isolation means adding passive components, such as springs, rubber and air springs. So as to reduce the vibration intensity transmitted to the receiving structure. The outstanding advantages of passive vibration isolation are simple structure, easy realization, reliable operation and no extra consumption of external energy. In view of this, passive vibration isolation has been widely used in engineering.
With the rapid development of science and technology, people put forward higher requirements for the bearing capacity and vibration control accuracy of the structure. At present, large-scale, low stiffness and flexibility are the important development trends of spacecraft structures.
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? Active vibration isolation
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These large modular space stations, solar panels, satellite antennas, optical systems and their supporting structures, space robotic arms, etc. , must ensure high running accuracy for a long time; In the future, human society will compete for the right to control space. The air force's combat airspace is in outer space, which requires high accuracy and stability of the weapon platform. In particular, the opto-electromechanical integration system such as laser platform needs to control the vibration of micron level, so the vibration control of the environment and the vibration source of the system itself is very demanding.
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In recent years, with the continuous enrichment of functions, precision instruments have become more and more large, and even devices with a total weight of more than 10 tons have been built. Due to the increasing of the device, it is very difficult to keep the natural frequency of the device at a high level, so even the low-frequency vibration that was not a problem in the past has been affected, which will bring a severe test to the traditional passive structure and vibration control method. Therefore, it is necessary to develop a device that can bear a large working load and has excellent vibration isolation performance for low-frequency vibration.
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? Active vibration isolation
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Compared with passive vibration isolation technology, active vibration isolation has obvious advantages, especially for vibration isolation in low frequency region and vibration region. In recent years, various countries with advanced technology are competing to study and begin to apply it to the vibration reduction of some large space structures. At the same time, active vibration isolation technology is especially suitable for the control of small vibration and is widely used in the vibration isolation of precision instruments.
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Active vibration isolation is to add an actuator that can meet certain requirements on the basis of passive vibration isolation, or use it as an actuator to replace some or all components of passive vibration isolation device. According to the detected vibration signal, a certain control strategy is applied to drive the actuator, so as to achieve the purpose of restraining or eliminating vibration. It is especially suitable for ultra-low frequency vibration isolation and high precision vibration isolation.
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Active vibration isolation technology has a long history, which can be traced back to18th century. It is used to adjust the speed of steam engine with centrifugal pendulum and the clock cycle with escapement mechanism. Since 1950s, three technical breakthroughs have been made in active vibration control, namely, the active damping of wing flutter has been realized, and the aircraft speed has been improved; Magnetic bearings successfully control the centrifuge rotor and create a new process of uranium isotope separation; Active vibration isolation provides an ultra-quiet environment to ensure that the inertial navigation system meets the accuracy requirements of nuclear submarines and intercontinental navigation.
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The real application of electronic technology in active vibration control began in the 1960s, so the next decade became a key breakthrough stage in the development of active vibration control. Since 1970s, people began to explore the application stages of active vibration control in various engineering fields. Since 1980s, active vibration control technology has been widely used in the vibration control of aerospace structures, the vibration control during the processing of precision equipment or precision products, the vibration control of highly flexible civil engineering structures and the semi-active vibration control of vehicles.
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? Active vibration isolation
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Active vibration isolator is mainly composed of controlled object, actuator, controller, measuring system and energy, and its development mainly depends on the development of actuator, controller and vibration isolation structure. Active vibration isolation can be divided into complete active vibration isolation and active-passive hybrid vibration isolation. Due to the complex structure and high energy consumption, the application of fully active vibration isolation is limited. Hybrid vibration isolation combines the advantages of active vibration isolation and passive vibration isolation, and has greater development space.
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Hybrid vibration isolation is a new type of vibration isolation technology, which combines passive vibration isolation and active vibration isolation technology. It is also called integrated control, hybrid control or combined control. It combines active control and passive control in structure, integrates the advantages of passive vibration isolation and active vibration isolation, and makes up for their shortcomings, so as to achieve the effect of vibration isolation in the whole frequency range. Its essential feature is to adopt active and passive control methods at the same time, and through the joint optimization design of active and passive vibration isolation systems, the transmission of vibration can be isolated to the greatest extent in a wide frequency band at a lower cost, and the stability of the system can be maintained, which can better meet the engineering needs.
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Active control and passive control of vibration can be described by mathematical models such as dynamic equation and state equation of the system. These models are different in form but unified in content, and can be transformed into each other, which provides favorable conditions for the analysis and design of hybrid vibration isolation system. Foreign countries started early in hybrid vibration isolation technology, did a lot of research, did a lot of work in developing new hybrid vibration isolation components, and applied for many patents.
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Comparatively speaking, the research on hybrid vibration isolation in China is relatively late, mainly focusing on aerospace, precision machine tools and engineering construction. The essence of hybrid vibration isolation system design is the joint optimization design of passive vibration isolation system and active control system, which will bring new and higher requirements to vibration isolation structure design.