Magnetic bearings (active and passive) - high wear resistance and high efficiency. Active magnetic bearings

Many bearing users consider magnetic bearings a kind of "black box", although they have been used in industry for quite a long time. They are usually used in transportation or preparation natural gas, in the processes of its liquefaction, and so on. Often they are used by floating gas processing complexes.

Magnetic bearings function by magnetic levitation. They work thanks to the forces generated by magnetic field. In this case, the surfaces do not contact each other, so there is no need for lubrication. This type bearings is able to function even in fairly harsh conditions, namely at cryogenic temperatures, extreme pressures, high speeds, and so on. At the same time, magnetic bearings show high reliability.

The rotor of a radial bearing, which is equipped with ferromagnetic plates, is held in position by means of magnetic fields created by electromagnets placed on the stator. The functioning of axial bearings is based on the same principles. In this case, opposite the electromagnets on the rotor, there is a disk that is installed perpendicular to the axis of rotation. The position of the rotor is monitored by inductive sensors. These sensors quickly detect all deviations from the nominal position, as a result of which they create signals that control the currents in the magnets. These manipulations allow you to keep the rotor in the desired position.

Benefits of Magnetic Bearings undeniable: they do not require lubrication, do not threaten environment, consume little energy and, due to the absence of contacting and rubbing parts, work for a long time. In addition, magnetic bearings have a low level of vibration. Today, there are models with a built-in monitoring and condition control system. On the this moment Magnetic bearings are mainly used in turbochargers and compressors for natural gas, hydrogen and air, in cryogenic technology, in refrigeration plants, in turbo expanders, in vacuum technology, in power generators, in control and measuring equipment, in high-speed polishing, milling and grinding machines.

The main disadvantage of magnetic bearings- dependence on magnetic fields. The disappearance of the field can lead to a catastrophic failure of the system, so they are often used with safety bearings. Usually they use rolling bearings that can withstand two or one failure of magnetic models, after which they require immediate replacement. Also, for magnetic bearings, bulky and complex systems control, significantly complicating the operation and repair of the bearing. For example, a special control cabinet is often installed to control these bearings. This cabinet is a controller interacting with magnetic bearings. With its help, current is supplied to the electromagnets, which regulates the position of the rotor, guaranteeing its non-contact rotation and maintaining its stable position. In addition, during the operation of magnetic bearings, there may be a problem of heating the winding of this part, which occurs due to the passage of current. Therefore, with some magnetic bearings, additional cooling systems are sometimes installed.

One of largest manufacturers magnetic bearings- S2M company, which participated in the development of a complete life cycle magnetic bearings as well as permanent magnet motors: from development to commissioning, production and practical solutions. S2M has always tried to pursue an innovative policy aimed at simplifying the design of bearings necessary to reduce costs. She tried to make magnetic models more accessible for wider use by the industrial consumer market. S2M cooperated with companies manufacturing various compressors and vacuum pumps mainly for the oil and gas industry. At one time, the network of S2M services spread all over the world. It had offices in Russia, China, Canada and Japan. In 2007, S2M was acquired by the SKF Group for fifty-five million euros. Today, magnetic bearings based on their technologies are manufactured by the manufacturing division of A&MC Magnetic Systems.

Compact and economical modular systems bearings equipped with magnetic bearings are being used more and more in the industry. Compared to usual traditional technologies they have many benefits. Miniaturized innovative motor/bearing systems have made it possible to integrate such systems into modern series products. Today they are used in high-tech industries (semiconductor production). Recent inventions and developments in the field of magnetic bearings are clearly aimed at the maximum structural simplification of this product. This is to reduce the cost of bearings, making them more accessible to a broader market of industrial users who clearly need this kind of innovation.

Everyone knows that magnets have the ability to attract metals. Also, one magnet can attract another. But the interaction between them is not limited to attraction, they can repel each other. It's about the poles of a magnet - opposite poles attract, like poles repel. This property is the basis of all electric motors, and quite powerful ones.

There is also such a thing as levitation under the influence of a magnetic field, when an object placed above a magnet (having a pole similar to it) hangs in space. This effect has been put into practice in the so-called magnetic bearing.

What is a magnetic bearing

An electromagnetic type device in which a rotating shaft (rotor) is supported in a stationary part (stator) by magnetic flux forces is called a magnetic bearing. When the mechanism is in operation, it is influenced by physical forces that tend to shift the axis. To overcome them, the magnetic bearing was equipped with a control system that monitors the load and gives a signal to control the strength of the magnetic flux. The magnets, in turn, have a stronger or weaker effect on the rotor, keeping it in a central position.

The magnetic bearing has found wide application in industry. These are basically powerful turbomachines. Due to the absence of friction and, accordingly, the need to use lubricants, the reliability of machines is many times increased. Wear of nodes is practically not observed. It also improves the quality of dynamic characteristics and increases efficiency.

Active magnetic bearings

A magnetic bearing, where the force field is created with the help of electromagnets, is called active. Positional electromagnets are located in the bearing stator, the rotor is represented by a metal shaft. The entire system that keeps the shaft in the unit is called active magnetic suspension (AMP). It has a complex structure and consists of two parts:

• bearing block;
• electronic control systems.

The main elements of the AMP

• The bearing is radial. A device that has electromagnets on the stator. They hold the rotor. There are special ferromagnet plates on the rotor. When the rotor is suspended at the midpoint, there is no contact with the stator. Inductive sensors track the slightest deviation of the rotor position in space from the nominal. Signals from them control the strength of the magnets at one point or another to restore balance in the system. The radial gap is 0.50-1.00 mm, the axial gap is 0.60-1.80 mm.

• Magnetic works in the same way as radial. A thrust disk is fixed on the rotor shaft, on both sides of which there are electromagnets mounted on the stator.
• Safety bearings are designed to hold the rotor when the device is in the off state or in emergency situations. During operation, auxiliary magnetic bearings are not involved. The gap between them and the rotor shaft is half that of a magnetic bearing. Safety elements are assembled on the basis of ball devices or
• The control electronics includes rotor shaft position sensors, transducers and amplifiers. The whole system works on the principle of adjusting the magnetic flux in each individual electromagnet module.

Passive magnetic type bearings

Magnetic bearings on permanent magnets are rotor shaft holding systems that do not use a control scheme that includes feedback. Levitation is carried out only due to the forces of high-energy permanent magnets.

The disadvantage of such a suspension is the need to use a mechanical stop, which leads to the formation of friction and a decrease in the reliability of the system. The magnetic stop in the technical sense has not yet been implemented in this scheme. Therefore, in practice, a passive bearing is used infrequently. There is a patented model, for example, a Nikolaev suspension, which has not yet been repeated.

Magnetic strip in wheel bearing

The concept of "magnetic" refers to the ASB system, which is widely used in modern cars. The ASB bearing is different in that it has a built-in wheel speed sensor inside. This sensor is an active device embedded in the bearing gasket. It is built on the basis of a magnetic ring on which alternate poles of the element that reads the change in magnetic flux.

As the bearing rotates, there is a constant change in the magnetic field created by the magnetic ring. The sensor registers this change, generating a signal. The signal is then sent to the microprocessor. Thanks to it, systems such as ABS and ESP work. Already they correct the work of the car. ESP is responsible for electronic stabilization, ABS regulates the rotation of the wheels, the level of pressure in the system is the brake. It monitors the operation of the steering system, acceleration in the lateral direction, and also corrects the operation of the transmission and engine.

The main advantage of the ASB bearing is the ability to control the speed of rotation even at very low speeds. At the same time, the weight and size indicators of the hub are improved, the installation of the bearing is simplified.

How to make a magnetic bearing

The simplest do-it-yourself magnetic bearing is easy to make. It is not suitable for practical use, but it will clearly show the possibilities of magnetic force. To do this, you need four neodymium magnets of the same diameter, two magnets of a slightly smaller diameter, a shaft, for example, a segment plastic tube, and an emphasis, for example, a half-liter glass jar. Magnets of a smaller diameter are attached to the ends of the tube with hot glue in such a way that a coil is obtained. In the middle of one of these magnets, a plastic ball is glued on the outside. Identical poles should face outward. Four magnets with the same poles up are laid out in pairs at a distance of the length of the tube segment. The rotor is placed over the lying magnets and on the side where the plastic ball is glued, it is supported plastic jar. Here is the magnetic bearing and ready.

after watching videos of individual comrades, such as

I decided and I will be noted in this thread. in my opinion, the video is rather illiterate, so it is quite possible to whistle from the stalls.

going through a bunch of schemes in my head, looking at the principle of suspension in the central part in Beletsky's video, understanding how the "levitrnon" toy works, I came to a simple scheme. it is clear that there should be two support spikes on the same axis, the spike itself is made of steel, and the rings are rigidly fixed on the axis. instead of solid rings, it is quite possible to lay not very large magnets in the form of a prism or a cylinder arranged in a circle. The principle is the same as in the well-known toy "Livitron". only instead of the geroscopic moment, which prevents the top from tipping over, we use the "spread" between the stands rigidly fixed on the axis.

Below is a video with a toy "Livitron"

and here is the scheme that I propose. in fact, this is the toy in the video above, but as I said, it needs something that would not allow the support spike to tip over. the video above uses gyro torque, I use two coasters and a spacer between them.

Let's try to justify the work of this design, as I see it:

magnets repel weakness- you need to stabilize these spikes along the axis. here I used this idea: the magnet is trying to push the spike into the area with the lowest field strength, because. the spike has a magnetization opposite to the ring and the magnet itself is annular, where in a sufficiently large area located along the axis, the intensity is less than at the periphery. those. the distribution of the magnetic field intensity in shape resembles a glass - the intensity is maximum in the wall, and minimum on the axis.

the spike should stabilize along the axis, while being pushed out of the ring magnet into the area with the lowest field strength. those. if there are two such spikes on the same axis and the ring magnets are rigidly fixed, the axis should "hang".

it turns out that it is in the zone with a lower field strength that it is most energetically favorable.

After digging around on the Internet, I found a similar design:

a zone with less tension is also formed here, it is also located along the axis between the magnets, the angle is also used. in general, the ideology is very similar, however, if we talk about a compact bearing, the option above looks better, but requires specially shaped magnets. those. the difference between the schemes is that I extrude the supporting part into the zone with less tension, and in the scheme above, the very formation of such a zone ensures the position on the axis.
For clarity of comparison, I redrawn my diagram:

they are essentially mirror images. in general, the idea is not new - they all revolve around the same thing, I even have suspicions that the author of the video above simply did not look for the proposed solutions

here it’s practically one to one, if the conical stops are made not solid, but composite - a magnetic circuit + an annular magnet, then my circuit will turn out. I would even say the initial unoptimized idea is the picture below. only the picture above works for the "attraction" of the rotor, and I originally planned to "repulse"


for the especially gifted, I want to note that this suspension does not violate Earnshaw's theorem (prohibition). the fact is that we are not talking here about a purely magnetic suspension, without a rigid fixation of the centers on the axis, i.e. one axis is rigidly fixed, nothing will work. those. it's about choosing a fulcrum and nothing more.

in fact, if you watch Beletsky's video, you can see that approximately the same configuration of fields is already used everywhere, the only thing missing is final touch. the conical magnetic circuit distributes the "repulsion" along two axes, but Earnshaw ordered the third axis to be fixed differently, I did not argue and mechanically fixed it rigidly. why Beletsky did not try this option, I do not know. in fact, he needs two "livitrons" - fix the stands on the axis, and connect them to the tops with a copper tube.

you can also notice that you can use tips from any sufficiently strong diamagnet in place of a magnet of polarity opposite to the magnetic support ring. those. replace the magnet + conical magnetic circuit bundle, just with a diamagnetic cone. fixation on the axis will be more reliable, but diamagnets do not differ in strong interaction and high field strengths and a large "volume" of this field are needed in order to apply this at least somehow. due to the fact that the field is axially uniform relative to the axis of rotation, there will be no change in the magnetic field during rotation, i.e. such a bearing does not create resistance to rotation.

logically, such a principle should also be applicable to plasma suspension - a patched "magnetic bottle" (corktron), what will we wait and see.

why am i so sure of the result? well, because it cannot but exist :) the only thing that may have to be made magnetic circuits in the form of a cone and a cup for a more "rigid" field configuration.
well, you can also find a video with a similar suspension:

here the author does not use any magnetic circuits and uses the emphasis on the needle, as is generally necessary, understanding Earnshaw's theorem. but after all, the rings are already rigidly fixed on the axis, which means you can spread the axis between them, which is easily achieved using conical magnetic cores on magnets on the axis. those. until the "bottom" of the "magnetic glass" has been pierced, it is more and more difficult to push the magnetic circuit into the ring. the magnetic permeability of air is less than that of the magnetic circuit - a decrease air gap will increase the field strength. those. one axis is rigidly fixed mechanically - then the supports on the needle will not be needed. those. see the very first picture.

P.S.
here's what I found. from the series, a bad head does not give repentance to hands - the author is still Biletsky - mother don’t cry there - the configuration of the field is quite complex, moreover, it is not uniform along the axis of rotation, i.e. during rotation, there will be a change in the magnetic induction in the axis with all sticking out ... pay attention to the ball in the ring magnet, on the other hand, the cylinder in the ring magnet. those. man stupidly screwed up the suspension principle described here.

well, or soldered the suspension in the photo, i.e. the peppers in the photo use supports on the needle, and he hung a ball in place of the needle - oh shaitan - it worked - who would have thought (I remember they proved to me that I didn’t understand Earnshaw’s theorem correctly), but apparently it’s not crazy to hang two balls and use only two rings enough. those. the number of magnets in the device on the video can be easily reduced to 4, and possibly up to 3 i.e. a configuration with a cylinder in one ring and a ball in the other can be considered experimentally proven to work, see the drawing of the original idea. there I used two symmetric stops and a cylinder + cone, although I think that the cone that part of the sphere from the pole to the diameter work the same.

therefore, the emphasis itself looks like this - this is a magnetic circuit (i.e. iron, nickel, etc.) it’s just

a magnet ring is laid. the reciprocal part is the same, just the other way around :) and two stops work in the thrust - comrade Earnshaw forbade work on one stop.

The principle of its operation is based on the use of the force acting on a current-carrying conductor placed in a magnetic field. A current-carrying conductor can be solid or liquid. In the latter case, the supports are called

magnetohydrodynamic conductive type. Depending on the type of current, conductive suspensions are divided into direct current suspensions and alternating current(magnetic field and current must be in phase).

The conductive suspension shown in Figure 1.2.5 has simple design and at the same time has a high carrying capacity.

Figure 1.2.5 - Conductive suspension

A significant disadvantage that limits the use of conductive suspensions is the need to excite currents directly on the suspended body, which leads to a significant increase in its own weight and a decrease in the effectiveness of the suspension. The need for a large current source can also be attributed to the disadvantages.

Dedicated to conduction poles a small amount of works, but they have not yet found wide application. At the moment, the conductive suspension is used in metallurgy (for smelting pure metals), transport.

Active magnetic suspensions

Active magnetic suspension? it's manageable electromagnetic device, which holds the rotating part of the machine (rotor) in a given position relative to the stationary part (stator).

Active magnetic suspensions require a special external feedback electronic unit.

To explain the principle of operation of an active magnetic suspension, consider Figure 1.2.6, which shows the simplest structural scheme suspension. It consists of a sensor that measures the displacement of the suspended body relative to the equilibrium position, a regulator that processes the measurement signal, a power amplifier powered by external source, which converts this signal into a control current in the electromagnet winding. This signal causes forces that hold and return the ferromagnetic body to a state of equilibrium.

An obvious advantage of active circuits is the ability to achieve more efficient regulation of the weighing field and, consequently, improved power characteristics. The active suspension has a high load capacity, high mechanical strength, wide range of stiffness and damping, no noise and vibration, impervious to pollution, no wear, no need for lubrication, etc. Suspension stability, as well as the necessary stiffness and damping, is achieved by choosing the control law. The disadvantages of active magnetic suspension include high cost, power consumption from an external source, the complexity of the electronic control unit, etc.

Figure 1.2.6 - Active magnetic suspension

Important areas of application of active magnetic bearings are space technology (vacuum turbomolecular pumps), medical equipment, equipment in Food Industry, high-speed ground transportation, etc.

FOREWORD

The main element of many machines is a rotor rotating in bearings. The growth of rotation speeds and capacities of rotary machines with a simultaneous trend towards a decrease in mass and overall parameters puts forward the problem of increasing the durability of bearing assemblies as a priority. Moreover, in a number of areas modern technology bearings are required that can operate reliably in extreme conditions: in vacuum, at high and low temperatures, ultrapure technologies, in aggressive environments, etc. The creation of such bearings is also an urgent technical problem.
The solution of these problems can be carried out as an improvement of traditional rolling and plain bearings. and the creation of non-traditional bearings that use other physical principles of action.
Traditional rolling and sliding bearings (liquid and gas) have now reached a high technical level. However, the nature of the processes occurring in them limits, and sometimes makes it fundamentally impossible to use these bearings to achieve the above goals. So, significant shortcomings rolling bearings are the presence of mechanical contact between moving and stationary parts and the need for lubrication of the raceways. There is no mechanical contact in plain bearings, but a lubricating system is required to create a lubricating layer and seal this layer. It is obvious that the improvement of sealing units can only reduce, but not completely eliminate the mutual penetration of the lubricant and external environment.
Bearings are free from these disadvantages, in which magnetic and electric fields. Among them, active magnetic bearings (AMPs) are of the greatest practical interest. The work of AMN is based on the well-known principle of active magnetic suspension of a ferromagnetic body: the body is stabilized in a given position by the forces of magnetic attraction acting on the body from controlled electromagnets. The currents in the windings of electromagnets are formed using the system automatic control, consisting of body movement sensors, an electronic controller and power amplifiers powered by an external source electrical energy.
First examples practical use active magnetic suspensions in measuring instruments date back to the 40s of the XX century. They are associated with the names of D. Beams and D. Hriesinger (USA) and O. G. Katsnelson and A. S. Edelstein (USSR). The first active magnetic bearing was proposed and experimentally studied in 1960 by R. Sixsmith (USA). wide practical use AMS in our country and abroad began in the early 70s of the XX century.
The absence of mechanical contact and the need for lubrication in AMPs makes them very promising in many areas of technology. These are, first of all: turbines and pumps in vacuum and cryogenic engineering; machines for ultrapure technologies and for operation in aggressive environments; machines and devices for nuclear and space installations; horoscopes; inertial energy storage devices; as well as products for general mechanical engineering and instrument making - grinding and milling high-speed spindles, textile machines. centrifuges, turbines, balancing machines, vibration stands, robots, precise measuring instruments etc.
However, despite the successes, AMJIs are being implemented much more slowly than expected from predictions made in the early 1970s. First of all, this is due to the slow perception of innovations by the industry, including AMS. Like any innovation, in order to be in demand, AMPs need to be popularized.
Unfortunately, at the time of this writing, only one book is devoted to active magnetic bearings: G. Schweitzer. H. Bleulerand A. Traxler "Active magnetic bearings", ETH Zurich, 1994, 244 p., published in English and German. Small in volume, this book is primarily aimed at the reader who is taking the first steps in understanding the problems that arise when creating an AMS. Making very modest demands on the engineering and mathematical background of the reader, the authors build the main ideas and concepts in such a well-thought-out sequence that allows a beginner to easily get up to speed and conceptually master a new area for himself. Undoubtedly, this book is a remarkable phenomenon, and its popularizing role can hardly be overestimated.
The reader may ask if it was worth writing a real monograph, and not just a translation of the book cited above. First, since 1992 I have been invited to give lectures on the AMS at Russian universities. Finland and Sweden. A book grew out of these lectures. Secondly, many of my colleagues have expressed a desire to have a book on LMP written for developers of AML machines. Thirdly, I also realized that many engineers who do not specialize in AMB at all need a book exploring such a control object as an electromagnet.
The purpose of this book is to equip engineers with the methods of mathematical modeling, synthesis, and analysis of AMPs and thereby promote interest in this new field of technology. I have no doubt that the book will also be useful to students of many technical specialties, especially in course and diploma design. When writing the book, I relied on 20 years of experience in the field of AMB as a scientific director of the research laboratory of magnetic bearings at the Pskov Polytechnic Institute of the St. technical university.
The book contains 10 chapters. Chapter 1 gives short description of all possible types of electromagnetic suspensions, the purpose of which is to broaden the reader's horizons. Chapter 2, aimed at AMB users, introduces the reader to active magnetic bearing technology - it is the history of development, design, characteristics, development problems and a few examples. practical applications. Chapters 3 and 4 provide a method for calculating bearing magnetic circuits. An electromagnet as a control object is studied in Chapter 5. In Chapter 6, the problems of controller synthesis and analysis of the dynamics of a one-stage magnetic suspension are solved. This is a chapter on how to control the gimbal and what can get in the way of getting the dynamic performance you want. The central place is occupied by Chapter 7, which considers the problems of controlling the suspension of a rigid rotor with five degrees of freedom, investigates the interaction of the suspension and the drive motor, and also touches upon the issue of creating bearingless electrical machines. The influence of elastic bending deformations of the rotor on the dynamics of the suspension is discussed in Chapter 8. Chapter 9 is devoted to digital control of the suspension. In the final chapter 10, a number of dynamic aspects related to the implementation of rotor suspensions in AMB are considered.
As for the list of references at the end of the book, I did not try to include in it all the historically significant articles on AML and I ask for forgiveness from those researchers whose contributions to this area are not mentioned.
Since the range of issues is very wide, it was not possible to maintain one system symbols throughout the book. However, each chapter uses permanent system designations.
I am grateful to my teachers, Professors David Rakhmilevich Merknin and Anatoly Saulovnch Kelzon - they greatly contributed to the appearance of this book. I would like to thank my colleagues from the laboratory of magnetic bearings and the university, in particular Fedor Georgievich Kochevin, Mikhail Vadimovich Afanasiev. Valentin Vasilyevich Andreen, Sergey Vladimirovich Smirnov, Sergey Gennadyevich Stebikhov and Igor Ivanovich Morozov, whose efforts created many machines with AMB. I also enjoyed the conversations and teamwork with Professor Kamil Shamsuddinovich Khodjaen and Associate Professors Vladimir Alexandrovich Andreev, Valery Georgievich Bogov and Vyacheslav Grigorievich Matsevich. I would also like to note the contribution of graduate students and postgraduate students who worked with me with great enthusiasm in the field of AMS - these are Grigory Mikhailovich Kraizman, Nikolai Vadimovich Khmylko, Arkady Grigoryevich Khrostitsky, Nikolai Mikhailovich Ilyin, Alexander Mikhailovich Vetlntsyn and Pavel Vasilyevich Kiselev. Special mention deserves technical assistance in preparing the manuscript for publication by Elena Vladimirovna Zhuravleva and Andrey Semenovich Leontiev.
For help in financing the publication of the book, I would like to thank the Pskov Engineering Company and the Pskov Polytechnic Institute.