It is the use of position change to directly change the parameters of the excitation circuit itself to achieve stable levitation; this bearing also mainly refers to the use of permanent magnets to achieve the levitation of the rotor, it is relying on the generated repulsive force (suction can not achieve stable levitation) to change the size of the air gap, so as to change some other magnetic circuit parameters to change the size of the magnetic force to achieve the rotor “stable ” levitation.
It means that the displacement sensor detects the rotor deviating from its position, and the servo control system rapidly changes the magnetic force according to its position signal, so that the object always stays within a certain position to achieve stable levitation. Obviously to achieve accurate control, the sensor accuracy must be high, and the entire control system to make the response should be fast, or the rotor will have to touch the stator, the important point is to rely on the detection of displacement or displacement feedback to control the electromagnetic force is not very accurate.
The permanent magnet generates magnetic force to balance the gravity of the rotor, and the electromagnetic force generated by the electromagnet to balance the external load.
(1) Completely wear-free and the life of the electro-mechanical components is theoretically unlimited because the rotor has no coils.
(2) Since there is no friction between the rotor and stator, the rotor speed is limited only by the tensile strength of the material, so the rotor linear speed is higher than all other kinds of bearings. Maximum linear speed up to 200m / s.
(3) No need for lubrication and sealing, compact structure.
(4) No mechanical noise.
(5) Heat generation is very small and power consumption is very low. Compared with ordinary bearings, power consumption is reduced to 1/10~1/100.
(6) Environmental adaptability, can work in vacuum and corrosive media. While air bearings can not be used in a vacuum, liquid bearings and rolling bearings in a vacuum will produce unavoidable pollution due to the volatilization of oil molecules.
(7) Insensitive to ambient temperature, the allowable temperature range is minus 250 degrees Celsius to 450 degrees Celsius.
(8) Low machining accuracy requirement for the shaft and low manufacturing cost.
In addition to the above-mentioned advantages, the use of a control system that can adjust not only the magnitude of the magnetic force, but also the phase of the force, thus making it possible to have.
(1) Automatic balancing function. (1) Automatic balancing function, since the rotating part rotates around its own inertial spindle instead of around the geometric center, eliminating the additional dynamic pressure and thus the resulting vibration.
(2) Precise control of the rotor position, which increases the rotational accuracy to sub-micron level and enables micro-feeding of the rotor in radial and axial directions for ultra-fine machining, and compensates for tool wear errors.
(3) adjustable stiffness and damping, so that the rotor can easily pass the critical speed and achieve ultra-high speed operation.
(4) All rotary characteristics (e.g. speed, load, axis position, misalignment, kinetic frequency, etc.) can be obtained through sensors and information from the control system, thus allowing diagnosis and monitoring of the machine’s operating status, which is particularly beneficial for adaptive control of high-performance machine tools.
(5) high reliability, on the one hand, because there is no wear, no lubrication and sealing devices. The mechanical structure is simplified, thus ensuring high reliability; on the other hand, the rotating parts without winding, the stator winding is similar to the motor stator winding, the control device is made of replaceable printed circuit boards, its design, the production of rich degree technology, can obtain almost unlimited service life, so the reliability is extremely high.
With its unique advantages, magnetic bearings are widely used in various fields, from aerospace, defense and other high-tech fields to general industrial and civil facilities.