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Active magnetic bearings working principle and characteristics of knowledge - bearing

by:Waxing     2020-06-03
Active magnetic bearing the working principle of magnetic bearing is a new type of high-performance bearing, in the field of magnetic levitation, is the most widely used active magnetic bearings. Figure 1 shows a simple part of the magnetic bearing and its functions. Displacement sensor to detect the rotor deviate from the reference point, as the microprocessor of the controller will detect the displacement transformation into a control signal, then the power amplifier to convert a control signal to control current, control current in performing magnet magnetic force so that to maintain its suspension rotor position unchanged. Damping and stiffness of the suspension system stability is determined by the control law. Figure 1. The working principle of active magnetic bearing stiffness and damping could be widely within the physical limits, the change can be adjusted according to the technical requirements, it can even be in the process of running change. A practical need multiple rotor magnet, as shown in figure 2, the magnets by a multivariable controller connected together, the corresponding hardware is shown in figure 3. Rotor about 0. 8 m, the quality of 12 kg, displacement and measured with a CCD sensor for microcomputer controller to generate the digital signal directly. The demonstration of the rotor of the air gap is quite big, to 10 mm. As a kind of novel is not yet widely used machine parts, magnetic bearing belongs to the mechanical and electrical products. Figure 2 supporting screenshots of the rotor in a plane figure 3 magnetic bearing rotor (left, right Intermediate driver) Active magnetic bearing rotor bearing characteristics of the following is the special performance of magnetic bearing rotor bearing, it is because it has the special performance, makes the magnetic bearing popularity in the field of application. 1, because the magnetic bearing has no contact, no lubrication and wear etc, it can be used in the vacuum technology, clean room and aseptic workshop, and the transmission of the corrosive medium or medium very pure. Bearing gap usually only tenths of a millimeter, but under special circumstances air gap can be up to 20 mm, the bearing capacity is very small. 2, allows the rotor high-speed rotation, the rotating speed is only limited by material strength. To improve the speed of the high-powered machine design with new structure provides a possibility. In fact, if use can bear a high stress, and at the same time with excellent soft magnetic properties of amorphous metals, rotational speed can be up to about 350 m/s. Because do not need lubrication and seal. And shaft neck diameter is larger, can be obtained to design has brought about many advantages, such as axial rigidity is bigger and is not sensitive to vibrations. 3, bearing of the low power consumption, is only 1/5 of the traditional bearing power, 1/20 and reduce the operation cost. 4, because there is no mechanical wear and tear, low maintenance cost and long life, not only this is current in turbomachinery continuously the main reason for the application of magnetic bearing. 5, magnetic bearing capacity per unit area ( Than the load) Depending on the ferromagnetic materials and bearing the design of the magnet, is about 20 n/cm2, also can achieve 40 n/cm2. Reference area is the cross-sectional area of the bearing, thus bearing the maximum carrying capacity mainly bearing function of the volume. 6, dynamic performance mainly depends on the magnetic levitation control law, so it is possible within the physical limits make and bearing stiffness and damping of working environment and the running state and even speed. The term 'rigidity' and 'damping' includes not only the traditional static parts play Ze and damping constant, but also related to the frequency of dynamic stiffness. This makes it possible to use magnetic glaze bearing vibration isolation, make the rotor smoothly through the critical speed, even when the system is under non conservative perturbation stability of the rotor. 7, the control precision of the rotor, such as the rotor rotation accuracy, mainly depends on control links in signal measuring precision. For example, ordinary inductance sensor resolution is about 0. 01 - 0. Between 001 mm. 8, in order to implement the control of magnetic bearing, the need to measure all or part of the rotor state variables. The measuring signal can also be used for the size of the unbalanced assessment and operation condition on-line monitoring, so as to improve the reliability of the system. 9, magnetic bearing can not only support the rotor. Damping vibration and stability of the rotor, but also can be used as a vibrator. On rotor vibration, the vibration signal and response signal can be used to identify some rotor characteristic of it is uncertain. There are, of course, must be to the disadvantage of magnetic bearings, are summarized as follows: 1, because of the magnetic bearing was still in the stage of development, not mass production, and complicated structure, which result in the price of magnetic bearing is extremely high. However, have seen the slash costs. 2, because the user is not yet. Basic knowledge of the design of magnetic bearing, so the new technology is not easy to be accepted. 3, due to the magnetic bearing is a new technology in the rapid development of F, it is difficult to a review of the application of it in the future to make clear, this kind of situation and computer in the process of application of situation is similar. 4, in some special cases, although the security, reliability, energy consumption and the optimal design obtained satisfactory results, but we still need to efforts of general system design method is studied.
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