A magnetic bearing, like the rest of the bearing group mechanisms, serves as a support for the rotating shaft. But unlike common rolling and plain bearings, the connection to the shaft is mechanically non-contact, that is, the principle of levitation is used.

Classification and principle of operation

Using the principle of levitation, the rotating shaft literally floats in a powerful magnetic field. A complex system of sensors allows you to control the movement of the shaft and coordinate the operation of the magnetic installation, which constantly monitors the state of the system and supplies the necessary control signals, changing the force of attraction on one side or another.

Magnetic bearings are divided into two large groups - active and passive. More details about the design of each type of bearing below.

1. Active magnetic bearings.

They are also called active magnetic suspensions. As mentioned above, they consist of two parts - the bearing itself, as well as an electronic magnetic field control system.

1, 3 – power coils; 2 - shaft There are radial and thrust mechanisms (based on the type of load they perceive), but their operating principle is the same. A special rotor is used (a regular shaft will not work), modified with ferromagnetic blocks. This rotor “hangs” in a magnetic field created by electromagnetic coils that are located on the stator, that is, around the shaft 360 degrees, forming a ring.

An air gap is formed between the rotor and stator, which allows the parts to rotate with minimal friction.

The mechanism depicted is controlled by a special electronic system, which, using sensors, constantly monitors the position of the rotor relative to the coils and, at the slightest displacement, supplies control current to the corresponding coil. This allows the rotor to be kept in the same position.

The calculation of such systems can be studied in more detail in the attached documentation.

1. Passive magnetic bearings.

Active magnetic suspensions are widely used in industry, while passive systems are still under development and testing. As the name implies, the key difference is the absence of active elements, that is, permanent magnets are used. But a system of several permanent magnets is very unstable, so practical use such systems are still questionable.

The diagram below roughly shows the operating principle of passive mechanical suspensions.

The rotor is equipped with a permanent magnet in the same way as the stator, located in a ring around the rotor. The poles of the same name are located next to each other in the radial direction, which creates the effect of levitation of the shaft. You can even assemble such a system with your own hands.

Advantages

Of course, the main advantage is the absence of mechanical interaction between the rotating rotor and the stator (ring).

It follows from this that such bearings are very durable, that is, they have increased wear resistance. Also, the design of the mechanism allows it to be used in aggressive environments - high/low temperatures, aggressive air conditions. Therefore, MPs are increasingly used in the space industry.

Flaws

• Unfortunately, the system also has many disadvantages. These include:
• Difficulty controlling active gimbals. A complex, expensive electronic gimbal control system is required. Its use can be justified only in “expensive” industries - space and military.
• The need to use safety bearings. A sudden power outage or failure of a magnetic coil can lead to catastrophic consequences for the entire mechanical system. Therefore, for insurance, mechanical bearings are also used together with magnetic ones. If the main ones fail, they will be able to take on the load and avoid serious damage.

Heating of the coil windings. Due to the passage of current, which creates a magnetic field, the winding of the coils heats up, which is often an unfavorable factor. Therefore, it is necessary to use special cooling units, which further increases the cost of using the gimbal.

The ability to operate at any temperature, in conditions of vacuum and lack of lubrication allows the use of suspensions in the space industry and in machine tools of the oil refining industry. They have also found their use in gas centrifuges for uranium enrichment. Various power plants also use maglev in their generating plants.

Below are a few interesting videos on this topic.

Below we consider the design of Nikolaev’s magnetic suspension, who argued that it is possible to ensure levitation of a permanent magnet without a stop. An experiment is shown to test the operation of this circuit.

The neodymium magnets themselves are sold in this Chinese store.

Magnetic levitation without energy consumption - fantasy or reality? Is it possible to make a simple magnetic bearing? And what did Nikolaev actually show in the early 90s? Let's look at these questions. Anyone who has ever held a pair of magnets in their hands has probably wondered: “Why can’t I make one magnet float above the other without outside support? Possessing such a unique as a constant magnetic field, they are repelled by poles of the same name completely without energy consumption. This is a great basis for technical creativity! But it's not that simple.

Back in the 19th century, the British scientist Earnshaw proved that using only permanent magnets, it is impossible to stably hold a levitating object in a gravitational field. Partial levitation, or, in other words, pseudo-levitation, is possible only with mechanical support.

How to make a magnetic suspension?

A simple magnetic suspension can be made in a couple of minutes. You will need 4 magnets at the base to make a support base, and a pair of magnets attached to the levitating object itself, which can be, for example, a felt-tip pen. Thus, we got a floating structure with an unstable balance on both sides of the felt-tip pen axis. A regular mechanical stop will help stabilize the position.

The simplest magnetic suspension with an emphasis

This design can be configured in such a way that the main weight of the levitating object rests on the support magnets, and the lateral thrust force is so small that the mechanical friction there practically approaches zero.

Now it would be logical to try to replace the mechanical stop with a magnetic one in order to achieve absolute magnetic levitation. But, unfortunately, this cannot be done. Perhaps it is due to the primitiveness of the design.

Alternative design.

Let's consider more reliable system such a suspension. Ring magnets are used as a stator, through which the axis of rotation of the bearing passes. It turns out that at a certain point, ring magnets have the property of stabilizing other magnets along their magnetization axis. But the rest is the same. There is no stable equilibrium along the axis of rotation. This has to be eliminated with an adjustable stop.

Let's consider a more rigid structure.

Perhaps here it will be possible to stabilize the axis with the help of a persistent magnet. But even here it was not possible to achieve stabilization. It may be necessary to place thrust magnets on both sides of the bearing's axis of rotation. A video with Nikolaev’s magnetic bearing has been discussed on the Internet for a long time. The image quality does not allow us to examine this design in detail and it seems that he managed to achieve stable levitation solely with the help of permanent magnets. In this case, the device diagram is identical to that shown above. Only a second magnetic stop has been added.

Checking the design of Gennady Nikolaev.

First, watch the full video, which shows Nikolaev's magnetic suspension. This video forced hundreds of enthusiasts in Russia and abroad to try to make a structure that could create levitation without a stop. But, unfortunately, it is not currently created working design such a suspension. This casts doubt on Nikolaev’s model.

For testing, exactly the same design was made. In addition to all the additions, the same ferrite magnets as Nikolaev’s were supplied. They are weaker than neodymium and do not push out with such enormous power. But testing in a series of experiments brought only disappointment. Unfortunately, this scheme also turned out to be unstable.

Conclusion.

The problem is that ring magnets, no matter how strong they are, are not able to keep the bearing axis in balance with the force from the side thrust magnets that is necessary for its lateral stabilization. The axle simply slides to the side at the slightest movement. In other words, the force with which the ring magnets stabilize the axle within itself will always be less than the force required to stabilize the axle laterally.

So what did Nikolaev show? If you look at this video more carefully, you suspect that due to the poor quality of the video, the needle stop is simply not visible. Is it by chance that Nikolaev tries to demonstrate the most interesting things? The very possibility of absolute levitation on permanent magnets is not rejected; the law of conservation of energy is not violated here. Perhaps they have not yet created a form of magnet that will create the necessary potential well that reliably holds a bunch of other magnets in stable equilibrium.

Below is a diagram of the magnetic suspension

Drawing of a magnetic suspension with permanent magnets

Many bearing consumers believe 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. They are often used by floating gas processing complexes.

Magnetic bearings operate 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 are able to function even in rather harsh conditions, namely at cryogenic temperatures, extreme pressures, high speeds and so on. At the same time, magnetic bearings show high reliability.

The radial bearing rotor, which is equipped with ferromagnetic plates, is held in the desired position with the help 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 mounted perpendicular to the axis of rotation. The rotor position is monitored by induction sensors. These sensors quickly detect all deviations from the nominal position, as a result of which they create signals that control currents in the magnets. These manipulations allow you to hold the rotor in the desired position.

Advantages 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, operate for a long time. In addition, magnetic bearings have low level vibrations Today there are models with a built-in monitoring and condition control system. On this moment Magnetic bearings are mainly used in turbocompressors and compressors for natural gas, hydrogen and air, in cryogenic technology, in refrigeration units, in turboexpanders, in vacuum technology, in electric 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 catastrophic failure of the system, so they are often used with safety bearings. Typically, they are used as rolling bearings that can withstand two or one failure of magnetic models, after which their immediate replacement is required. Also for magnetic bearings, bulky and complex systems controls that significantly complicate the operation and repair of the bearing. For example, to control these bearings, they often install special cabinet management. This cabinet is a controller that interacts with magnetic bearings. With its help, a current is supplied to the electromagnets, which regulates the position of the rotor, guarantees its non-contact rotation and maintains its stable position. In addition, during the operation of magnetic bearings, the problem of heating the winding of this part may arise, which occurs due to the passage of current. Therefore, additional cooling systems are sometimes installed with some magnetic bearings.

One of the largest manufacturers of magnetic bearings- S2M company, which participated in the development of the complete life cycle magnetic bearings, as well as motors with permanent magnets: From development to commissioning, production and practical solutions. S2M has always been committed to an innovative policy aimed at simplifying bearing designs to reduce costs. She tried to make magnetic models more accessible for wider use by the industrial consumer market. Companies producing various compressors and vacuum pumps have collaborated with S2M, mainly for oil and gas industry. At one time, the network of S2M services spread throughout the world. Its offices were in Russia, China, Canada and Japan. In 2007, S2M was acquired by the SKF group for fifty-five million euros. Today, magnetic bearings using their technologies are manufactured by the manufacturing division of A&MC Magnetic Systems.

Compact and economical modular systems, equipped with magnetic bearings, are increasingly used in industry. Compared to conventional traditional technologies, they have many advantages. Thanks to miniaturized innovative motor/bearing systems, the integration of such systems into modern series products has become possible. They are used today in high-tech industries (semiconductor production). The latest inventions and developments in the field of magnetic bearings are clearly aimed at maximum structural simplification of this product. This is to reduce bearing costs, making them more accessible to the wider industrial market that clearly needs such innovation.

PREFACE

The main element of many machines is a rotor that rotates in bearings. The increase in rotation speeds and powers of rotary machines with a simultaneous tendency to reduce mass and overall dimensions puts forward the problem of increasing the durability of bearing units 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, ultra-clean technologies, in aggressive environments, etc. The creation of such bearings is also a pressing technical problem.
The solution to these problems can be achieved by improving traditional rolling and sliding bearings. and the creation of non-traditional bearings that use different physical principles of operation.
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 to lubricate the raceways. In sliding bearings there is no mechanical contact, but a system of periodic lubricant to create a lubricating layer and seal this layer. It is obvious that improving sealing units can only reduce, but not completely eliminate, the mutual penetration of lubricant and external environment.
Bearings that use magnetic and electric fields. Among them, active magnetic bearings (AMP) are of greatest practical interest. The work of the AMS is based on the well-known principle of active magnetic suspension of a ferromagnetic body: stabilization of the body in a given position is carried out by the forces of magnetic attraction acting on the body from controlled electromagnets. Currents in the windings of electromagnets are formed using a system automatic control, consisting of body movement sensors, an electronic controller and power amplifiers powered from an external source electrical energy.
First examples practical use Active magnetic suspensions in measuring instruments date back to the 40s of the 20th 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). The widespread practical use of AMS in our country and abroad began in the early 70s of the 20th century.
The absence of mechanical contact and the need for lubrication in AMPs makes them very promising in many fields of technology. These are, first of all: turbines and pumps in vacuum and cryogenic technology; machines for ultra-clean technologies and for working in aggressive environments; machines and instruments 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, precision measuring instruments etc.
However, despite these successes, AMJIs are being implemented in practice much more slowly than expected from forecasts made in the early 1970s. First of all, this is explained by the industry’s slow acceptance of innovations, including AMP. Like any innovation, in order to be in demand, AMPs need to be popularized.
Unfortunately, at the time of writing these lines, only one book is devoted to active magnetic bearings: G. Schweitzer. N. Bleulerand A. Traxler “Active magnetic bearings”, ETH Zurich, 1994, 244 p., published in English and German languages. Small in volume, this book is aimed primarily at the reader who is taking the first steps in understanding the problems that arise when creating an AMP. Making very modest demands on the reader's engineering and mathematical background, the authors arrange the main ideas and concepts in such a thoughtful sequence that allows a beginner to easily get up to speed and conceptually master a new area. Undoubtedly, this book is a notable phenomenon, and its popularizing role can hardly be overestimated.
The reader may ask whether it was worth writing a real monograph, and not limiting ourselves to a translation of either the Russian language of the book cited above. Firstly, starting in 1992, I was invited to give lectures on AMS at Russian universities. Finland and Sweden. From these lectures a book grew. Secondly, many of my colleagues expressed a desire to receive a book about LMP, written for developers of machines with AMP. Thirdly, I also realized that many engineers who do not specialize in the field of AMP need a book that explores such a control object as an electromagnet.
The purpose of this book is to equip engineers with methods for mathematical modeling, synthesis and analysis of AMPs and thereby help stimulate interest in this new field of technology. I have no doubt that the book will also be useful for students of many technical specialties, especially during coursework and diploma design. When writing the book, I relied on 20 years of experience in the field of AMP as a scientific director of the research laboratory of magnetic supports at the Pskov Polytechnic Institute of St. Petersburg State technical university.
The book contains 10 chapters. Chapter 1 gives short description everyone possible types electromagnetic suspensions, the purpose of which is to broaden the reader’s horizons. Chapter 2, aimed at users of AMPs, introduces the reader to the technology of active magnetic bearings - the history of development, designs, characteristics, development problems and several examples of practical applications. Chapters 3 and 4 provide a methodology for calculating bearing magnetic circuits. An electromagnet as a control object is studied in Chapter 5. In Chapter 6, problems of controller synthesis and analysis of the dynamics of a single-power magnetic suspension are solved. This is a chapter about how to control the gimbal and what can prevent you from achieving the required dynamic qualities. The central place is occupied by Chapter 7, which examines the problems of controlling the suspension of a rigid rotor having five degrees of freedom, examines the interaction of the suspension and the drive motor, and also touches on the issue of creating unsupported rotors. electric machines. The effect of elastic bending deformations of the rotor on the dynamics of the gimbal is discussed in Chapter 8. Chapter 9 is devoted to digital control of the gimbal. The final chapter 10 examines a number of dynamic aspects associated with the implementation of rotor hangers in AMPs.
Regarding the list of references at the end of the book, I have not attempted to include all historically notable articles on AMP, and I apologize to those researchers whose contributions to this field are not mentioned.
Since the range of issues is very wide, it turned out to be impossible to maintain one system symbols throughout the book. However, each chapter uses a consistent notation.
I am grateful to my teachers, professors David Rakhmilevich Merknn and Anatoly Saulovnch Kelzon - they greatly contributed to the appearance of this book. I would like to thank my colleagues at the laboratory of magnetic supports and the university, especially Fedor Georgievich Kochevin, Mikhail Vadimovich Afanasyev. Valentin Vasilievich Andreen, Sergei Vladimirovich Smirnov, Sergei Gennadievich Stebikhov and Igor Ivanovich Morozov, through whose efforts many machines with AMP were created. Conversations and joint work with Professor Kamil Shamsuddnovich Khodzhaen and associate professors Vladimir Aleksandrovich Andreev, Valery Georgievich Bogov and Vyacheslav Grigorievich Matsevich were also useful to me. I would also like to acknowledge the contribution of graduate students and graduate students who worked with me with great enthusiasm in the field of AMP - these are Grigory Mikhailovich Kraizman, Nikolai Vadimovich Khmylko, Arkady Grigorievich Khrostitsky, Nikolai Mikhailovich Ilyin, Alexander Mikhailovich Vetlntsyn and Pavel Vasilievich Kiselev. The technical assistance provided by Elena Vladimirovna Zhuravleva and Andrei Semenovich Leontiev in preparing the manuscript for publication deserves special mention.
I would like to thank the Pskov Engineering Company and the Pskov Polytechnic Institute for their help in financing the publication of the book.

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Active magnetic bearings

Active magnetic bearings (AMP)
(produced by S2M Société de Mécanique Magnétique SA, 2, rue des Champs, F-27950 St. Marcel, France)

The main areas of application of active magnetic bearings are as part of turbomachines. The concept of no oil in compressors and turboexpanders makes it possible to achieve the highest reliability also due to the absence of wear on machine components. Active magnetic bearings (AMBs) are increasingly used in many industries. To improve dynamic characteristics, increase reliability and efficiency, non-contact active magnetic bearings are used.

The operating principle of magnetic bearings is based on the effect of levitation in a magnetic field. The shaft in such bearings literally hangs in a powerful magnetic field. The sensor system constantly monitors the position of the shaft and sends signals to the stator position magnets, adjusting the force of attraction on one side or another.

1 . general description AMP systems

The active magnetic suspension consists of 2 separate parts:

Bearing;

Electronic control system

The magnetic suspension consists of electromagnets (power coils 1 and 3) that attract the rotor (2).

AMP components

1. Radial bearing

The radial bearing rotor, equipped with ferromagnetic plates, is held in place by magnetic fields created by electromagnets located on the stator.

The rotor is placed in a suspended state in the center, without contacting the stator. The rotor position is controlled by inductive sensors. They detect any deviation from the nominal position and provide signals that control the current in the electromagnets to return the rotor to its nominal position.

4 coils placed along the axes V and W , and shifted at an angle of 45° from the axes X and Y , keep the rotor in the center of the stator. There is no contact between the rotor and stator. Radial clearance 0.5-1mm; axial clearance 0.6-1.8 mm.

2. Thrust bearing

A thrust bearing works on the same principle. Electromagnets in the form of a permanent ring are located on both sides of the thrust disc mounted on the shaft. Electromagnets are fixed to the stator. The thrust disk is mounted on the rotor (for example, using the hot landing). Axial position sensors are usually located at the ends of the shaft.

3. Auxiliary (insurance)

bearings

Auxiliary bearings are used to support the rotor while the machine is stopped and in the event of failure of the AMS control system. During normal operation, these bearings remain stationary. The distance between the auxiliary bearings and the rotor is usually equal to half the air gap, however, if necessary, it can be reduced. Auxiliary bearings are mainly solid lubricated ball bearings, but other types of bearings such as plain bearings can also be used.

4. Electronic control system

An electronic control system controls the position of the rotor by modulating the current that passes through the electromagnets depending on the signal values ​​of the position sensors.

5. Electronic processing system signals

The signal sent by the position sensor is compared with a reference signal, which corresponds to the nominal rotor position. If the reference signal equal to zero, the nominal position corresponds to the center of the stator. When changing the reference signal, you can move the nominal position by half the air gap. The deviation signal is proportional to the difference between the nominal position and the current position of the rotor. This signal is transmitted to the processor, which in turn sends a correction signal to the power amplifier.

Ratio of output signal to deviation signaldetermined by the transfer function. The transfer function is selected to maintain the rotor with maximum accuracy in its nominal position and for its rapid and smooth return to this position in the event of disturbances. The transfer function determines the stiffness and damping of the magnetic suspension.

6. Power amplifier

This device supplies the bearing electromagnets with the current necessary to create a magnetic field that acts on the rotor. The power of the amplifiers depends on the maximum force of the electromagnet, the air gap and the response time of the automatic control system (i.e. the speed at which this force must be changed when it encounters interference). Physical Dimensions electronic systems do not have a direct connection with the weight of the rotor of the machine; they are most likely related to the ratio of the indicator between the magnitude of the interference and the weight of the rotor. Therefore, a small shell will be sufficient for a large mechanism equipped with a relatively heavy rotor subject to little disturbance. At the same time, a mechanism subject to greater interference must be equipped with a large electrical cabinet.

2. Some characteristics of AMP

Air gap

The air gap is the space between the rotor and stator. The amount of gap indicated e, depends on diameter D rotor or bearing.

As a rule, the following values ​​are usually used:

D (mm)	e(mm)
< 100	0,3 - 0,6
100 - 1 000	0,6 - 1,0

Rotational speed

The maximum rotation speed of a radial magnetic bearing depends only on the characteristics of the electromagnetic rotor plates, namely the resistance of the plates to centrifugal force. When using standard inserts, peripheral speeds of up to 200 m/s can be achieved. The rotation speed of the axial magnetic bearing is limited by the resistance of the cast steel thrust disk. A peripheral speed of 350 m/s can be achieved using standard equipment.

The AMP load depends on the ferromagnetic material used, the rotor diameter and the longitudinal length of the suspension stator. Maximum specific load of AMP made from standard material, is 0.9 N/cm². This maximum load is smaller compared to the corresponding values ​​of classical bearings, however, the high permissible peripheral speed allows the shaft diameter to be increased so as to obtain the largest possible contact surface and therefore the same load limit as for a classical bearing without the need to increase its length.

Power consumption

Active magnetic bearings have very low energy consumption. This energy consumption comes from losses due to hysteresis, eddy currents (Foucault currents) in the bearing (power taken from the shaft) and heat losses in the electronic shell. AMPs consume 10-100 times less energy than classic mechanisms of comparable sizes. Power consumption electronic system control, for which it is necessary external source current is also very low. Batteries are used to maintain the operating condition of the gimbal in the event of a network failure - in this case they turn on automatically.

Ambient conditions

AMPs can be installed directly in the operating environment, completely eliminating the need for appropriate couplings and devices, as well as barriers for thermal insulation. Today, active magnetic bearings operate in the most various conditions: vacuum, air, helium, hydrocarbon, oxygen, sea ​​water and uranium hexafluoride, as well as at temperatures from - 253° From to + 450 ° WITH.

3. Advantages of magnetic bearings

• Non-contact/liquidless
  - absence of mechanical friction
  - no oil
  - increased peripheral speed
  
• Increased reliability
  - operational reliability of the control cabinet > 52,000 hours.
  - operational reliability of EM bearings > 200,000 hours.
  - almost complete lack of preventive maintenance
  
• Smaller turbomachinery dimensions
  - lack of lubrication system
  - smaller dimensions (P = K*L*D²*N)
  - less weight
  
• Monitoring
  - bearing load
  - turbomachine load
• Adjustable Parameters
  - active magnetic bearing control system
  - rigidity (varies depending on the dynamics of the rotor)
  - damping (varies depending on the dynamics of the rotor)
  
• Sealless operation (compressor and drive in one housing)
  - bearings in process gas
  - wide operating temperature range
  - optimization of rotor dynamics by shortening it

The undeniable advantage of magnetic bearings is the complete absence of rubbing surfaces, and, consequently, wear, friction, and most importantly the absence of departure from working area particles generated during the operation of conventional bearings.

Active magnetic bearings are characterized by high load capacity and mechanical strength. They can be used at high rotation speeds, as well as in airless spaces and at different temperatures.

Materials provided by “S2M” company, France ( www.s2m.fr).