EP1848896A1

EP1848896A1 - Method for stabilising a magnetically levitated object

Info

Publication number: EP1848896A1
Application number: EP06709318A
Authority: EP
Inventors: Michel Saint-Mleux
Original assignee: Levisys SAS
Current assignee: Levisys SAS
Priority date: 2005-02-15
Filing date: 2006-02-15
Publication date: 2007-10-31
Also published as: JP2008537872A; CN101115930A; IL184935A0; US20080122308A1; FR2882203B1; WO2006087463A1; CA2597560A1; FR2882203A1; RU2007133582A

Abstract

The invention relates to a method for stabilising a magnetically levitated object (2, 21, 31, 32, 52, 200) subjected to a constant magnetic field, said object being stable in at least one direction and unstable in at least one other direction. The inventive method is characterised in that it comprises a stabilisation step, which is repeated as often as required, and consists in applying an electrical current through at least one conductive element (15a to 16c, 27, 44, 62, 211) subjected to a secondary magnetic field in such a way as to generate a compensating Laplace force in the direction of instability. The invention also relates to a magnetic levitation device (1, 20, 30, 50) stabilised by the inventive method.

Description

Method of stabilizing an object in magnetic levitation

The present invention relates to a method for stabilizing an object in magnetic levitation, as well as to a magnetic levitation device.

Magnetic fields can be used to generate forces in various actuators, allowing them to move without friction and operate without noise. Such an actuating means is used when the conventional mechanical systems reach their limits and are no longer suitable. It is more particularly applications that require very high speeds of rotation and for which it is in particular necessary to minimize friction losses, and / or avoid wear, and / or for which it is impossible to use lubricants. Examples of applications for which these advantages are particularly sought are, inter alia, the flywheels which constitute devices for storing energy in the form of kinetic energy in a wheel rotating several thousand revolutions per minute. minute, and the magnetic levitation trains for which only the friction of the air remain and which can reach speeds much higher than 400 km / h.

Most magnetic actuators currently available use magnetic levitation only with one degree of freedom. This is the case of an electric motor in which only the magnetic forces for driving the rotor are used.

In the case of most of these applications, it is particularly desirable to minimize the existing friction so as to reduce the energy losses and noise pollution they generate, and it is generally necessary for this purpose to to magnetically control an object according to several degrees of freedom.

However, when one seeks to maintain an object in total sustenance by the use of magnetic fields, that is to say having the six degrees of freedom in space, its stabilization is particularly difficult. In 1839, scientist S. Eamshaw demonstrated that it was impossible to stabilize a magnetically polarized particle in a static field. As a result, it is impossible to stabilize a ferromagnetic body in suspension. magnetic using permanent magnets or ferromagnetic elements. Several solutions for circumventing Earnshaw's law have however been devised and are currently used to stabilize objects in magnetic levitation. A first solution is to use a diamagnetic material. Such a material, unlike a ferromagnetic material which has permanent magnetization, develops a magnetic field in response to an external magnetic field to which it is subjected. This induced magnetic field tends to oppose the external magnetic field while remaining always antiparallel to it and, consequently, permanently opposes the field variations caused by the object in lift when this one deviates from its balance position. There is therefore a restoring force that keeps the object stable. This is the case of magnetic levitation using superconductors. This solution is however difficult to implement because these materials must generally be cooled to a very low temperature in liquid nitrogen to reach the state of superconductivity. Therefore, this method, although satisfactory from a theoretical point of view, remains particularly difficult to put into practice and requires cryogenic means very energy-consuming. A second solution is to use electromagnets. Indeed, in the same way that a diamagnetic material permanently develops a magnetic field opposite to the external magnetic field to which it is subjected, it is possible to modify the field developed by an electromagnet so that it is opposed to a deviation of the object in lift relative to the desired equilibrium position. Earnshaw's law is therefore not violated, magnetic levitation remaining impossible if the electromagnets are traversed by constant electric currents and thus develop stable magnetic fields, but bypassed by adjusting the magnetic fields developed by the electromagnets which are therefore variable as well as the resulting directions of these fields.

A third solution is to use alternating fields generated by coils. Field variations generate induced currents, called eddy currents, in a conductive object, creating a repulsive force that may be sufficient to lift it. These second and third solutions, however, have major drawbacks because of the electrical power required to generate sufficiently intense magnetic fields using electromagnets and coils. Moreover, the need to constantly monitor the magnetic field developed by the electromagnets requires the establishment of a complex control system, also consuming electricity, which must have an extremely short response time. This constraint is difficult to achieve because of transfer functions of such a generally non-linear system. Such a mode of levitation is said to be active, as opposed to a lift using permanent magnets, which do not consume additional energy, and which is therefore called passive levitation.

It is worth mentioning a fourth solution that makes it possible to maintain an object having permanent magnetization in levitation in a field that is also permanent. This object is marketed under the trademark LEVITRON® and is in the form of a spinning top able to maintain itself in a stable magnetic field when it is rotated. Contrary to appearances, this object does not violate Earnshaw's law. Indeed, the instability inherent in any system in lift in a stable field is always present, this being however compensated by a stabilizing gyroscopic effect coming from the rotation of the top. The equilibrium thus obtained is, however, relatively unstable and the stability conditions are particularly strict. Thus, the mass of the rotor must be precisely adjusted, as well as its speed of rotation and the direction of the magnetic field with respect to the direction of gravity.

To overcome many of these disadvantages, it has been developed a fifth solution based on a mixed system using both permanent magnets and electromagnets, and which thus reduces slightly the power consumption of the system. Such sustenance is said to be partially passive. Thus, there is known a partially passive levitation comprising a cylindrical rotor levitated between two rare earth permanent magnets developing a field of 1, 1 teslas and providing only radial stability. In the absence of complementary stabilization, the system thus has a high axial instability. To do this, each permanent magnet is associated with a controlled electromagnet to ensure the axial stabilization of the rotor around a position of average equilibrium. The use of permanent magnets makes it possible, on the one hand, to have a transfer function of the linear system and, on the other hand, to ensure centering by reluctance even if the electromagnets are not powered, the latter being used only to strengthen or reduce the applied permanent field, and thus move the balance of forces applying to the rotor. The power consumption of such a system however remains relatively high and always requires the introduction of a sensor associated with a complex and fast servocontrol system.

Due to these technical and economic constraints, this technology is only used in very specific applications for which the energetic cost hardly comes into consideration.

One of the main current applications of magnetic levitation are magnetic bearings, especially for flywheels and other rotating devices. Inertia flywheels are used to store energy in kinetic form in a rotating flywheel whose axis is held by magnetic bearings, in order to restore it in case of power failure or irregular supply. When the electric output of a wind turbine, for example, is sufficient to power an electrical system, part of this current is used to drive the flywheel by means of a motor-generator and maintain its speed to several thousand Rotations per minute. In the event of a fall in electricity production by the wind turbine, the speed of the flywheel is transformed, thanks to the same engine-generator then operating in generator mode, in electricity. This ensures a constant power supply while waiting for an increase in electricity production. In order to optimize the storage of energy, to minimize friction losses, and to restore it with maximum efficiency over the longest possible time, the steering wheel lift must be very precisely controlled and must consume the less electric current possible to control this lift. As explained above, most of the current solutions do not achieve these objectives, a lift using permanent magnets, thus not consuming electrical energy, is impossible because of Earnshaw's law, while that an active levitation requires in particular a too important electrical energy. This problem can also be applied to magnetic levitation trains, where the cost of operation, in addition to an already high installation cost, is excessive compared to the expected profitability, that the lift is ensured by means of coils requiring a very large power supply, or that it uses superconductors to generally be maintained in a bath of liquid nitrogen.

The object of the present invention is to overcome the drawbacks mentioned above, and for this purpose consists in a method of stabilizing an object in magnetic levitation subjected to at least one constant magnetic field, said object being stable in at least one direction and unstable according to at least one other direction, characterized in that it comprises a stabilization step, repeated as often as necessary, of applying an electric current through at least one conductive element subjected to a secondary magnetic field so as to generate a force of Compensatory laplace in the direction of instability.

Thus, thanks to the application of a compensating Laplace force, it is possible to easily compensate the magnetic instabilities inherent in the system while minimizing its electrical consumption. Indeed, an object in a stable magnetic field has a potential energy of harmonic type, of which the Laplacian, sum of the partial derivatives second with respect to the spatial coordinates, is null. As a result, the second partial derivatives of the potential energy with respect to each of the spatial coordinates can not all be negative, as would a perfectly stable equilibrium. Therefore, there is always at least one coordinate relative to which the second partial derivative is positive, hence for which there is no stable equilibrium position. It has surprisingly been found that the application of a Laplace force, whose potential is quadratic, in the direction of instability makes it possible to confer on the system a potential energy for which there are points of stability. Therefore, it is no longer necessary to use powerful electromagnets to stabilize such a system and overall power consumption is significantly reduced.

The magnetic field allowing the levitation of the object can be generated by one or more sources of magnetic field according to the geometry of the object. Indeed, the use of at least two magnetic sources to create a magnetic field in the desired direction may be necessary to enhance the stability of the object.

Advantageously, the stabilization step aims at keeping the object between an upper bound and a lower bound around a desired mean equilibrium position. Indeed, depending on the desired degree of stability it will be necessary to exert a force of Laplace more or less important. The more precisely the balance has to be maintained, the more it is necessary to compensate for the instabilities of the system by applying larger compensating forces. Advantageously, it will be possible to take a Laplace force providing approximately 10% of the total lift required to lift the object, the remaining 90% being ensured by the permanent magnets.

Advantageously, the method according to the invention comprises a step of detecting the position of the object able to control and / or interrupt the passage of the electric current through the conductive element. Thus, the electric current is applied only when necessary to return the object to its middle equilibrium position, which further reduces consumption. By accepting a slight oscillation around a desired average balance point, it is possible to further reduce the power consumption of the system.

The present invention also relates to a magnetic levitation device comprising a levitating object subjected to at least one constant magnetic field in interaction with corresponding magnetization means of the levite object, characterized in that it comprises: on the one hand, secondary magnetic elements capable of generating a secondary magnetic field, and on the other hand, at least one conductive element subjected to the secondary magnetic field, so that a compensating Laplace force is generated on the levite object when the conductive element is traversed by an electric current. It should be noted that corresponding magnetization means any material sensitive to a surrounding magnetic field. Such materials are of course the magnets, reacting to another magnet, but also the ferromagnetic materials, not magnetic in themselves but oriented magnetically when placed in a magnetic field. It should be understood that the constant magnetic field is generated by at least one field source, the magnetic field source and the corresponding magnetization means being interchangeable in such a way that the field source is located on the object and interacts with an external corresponding magnetization means. Preferably, the magnetic field develops, with the corresponding magnetization means, an attraction force exerted on It is also possible for the magnetic field to develop, with the corresponding magnetization means, attractive forces and repulsion forces acting on the levite object.

According to an alternative embodiment, the magnetic field is generated by at least two magnetic field sources, the magnetic field sources and the corresponding magnetization means of the levite object having a parallel magnetic orientation and in the same direction. For example, in the case of a symmetry of revolution system, it will be necessary to have two concentric permanent magnet rings in interaction, one of the rings being secured to one stator while the other ring is integral with the levite object, for example a rotor.

Preferably, the conductive element is a coil. In general, a silver conductive element will be preferred, this metal being one of the best known conductors. It may also be envisaged to use carbon nanotubes. Of course, the intensity of the developed Laplace force can vary according to a shape ratio of the coil, this shape ratio being preferably defined so as to make the maximum Laplace force in the direction contributing to the stability for a minimum electric current in the coil. Advantageously, the coil is wide and thin.

Preferably also, the magnetic field sources and / or the complementary magnetization means and / or the secondary magnetic elements are permanent magnets. Advantageously, the permanent magnets are magnets based on neodymium boron iron. Advantageously, the magnets are arranged in a so-called Halbach configuration, so as to obtain both a maximum main field and minimum parasitic fields.

According to an alternative embodiment, the secondary magnetic elements interact with at least one ferromagnetic material shaped so as to allow the reorientation of the secondary magnetic field.

Preferably, the device comprises at least one sensor capable of controlling or interrupting the passage of current through the conductive element as a function of the position of the levitated object. Thus, it is not necessary to supply the conductive element permanently, which further reduces the power consumption of the system. The flow in the conductive element can also be controlled by an all-or-nothing, proportional, integral or derivative type servocontrol circuit, or any combination thereof depending on the position of the levitated object.

Advantageously, the sensor comprises a point integral with the levite object and able to come into contact with a switch to close it.

The implementation of the invention will be better understood with the aid of the detailed description which is set out below with reference to the appended drawing in which:

Figure 1 is a schematic representation in longitudinal section of a first embodiment of an axially stabilized flywheel according to the method of the invention.

Figure 2 is a schematic representation in longitudinal section of a second embodiment of a flywheel stabilized radially according to the method of the invention. Figure 3 is a schematic representation in longitudinal section of a third embodiment of an axially stabilized flywheel according to the method of the invention.

Figure 4 is a schematic representation in longitudinal section of a fourth embodiment of a stabilized flywheel according to the invention, and using soft iron to redirect the magnetic fields.

FIG. 5 is a sectional top view of the flywheel of FIG. 4.

Figures 6 and 7 show two variants of magnetic field reorientation using soft iron.

Figure 8 is a schematic representation of a first embodiment of an instability detector.

Figure 9 is a schematic representation of a second embodiment of an instability detector. FIG. 10 is a view from above of the sensor of FIG. 9.

Figure 11 is a schematic representation of an alternative application of the stabilization method according to the invention to a magnetic levitation train.

An flywheel 1, as shown in Figure 1, comprises a cylindrical flywheel 2 magnetically levitating between a lower magnetic source 3 and a higher magnetic source 4. Each source 3, 4 comprises respectively a circular magnet 5, 6 facing a corresponding circular magnet 7, 8 of the flywheel 2.

Furthermore, the flywheel 2 has a lower central cavity 9 and a central upper cavity. The lower cavity 9 houses two pairs of additional magnets 11a, 11b, 12a, 12b superimposed, the radial magnetic field developed by one of the two pairs of additional magnets 11a, 11b, 12a, 12b being opposite to the field developed by the other pair of additional magnets 12a, 12b, 11a, 11b. In the same way, the upper cavity 10 houses two pairs of additional magnets 13a, 13b, 14a, 14b superimposed. The lower cavity 9 and the upper cavity 10 are each intended to receive respectively a set of conducting wires 15a, 15b, 15c, 16a, 16b, 16c integral with the corresponding magnetic source 3, 4 and arranged perpendicularly to the axis of the flywheel 2 Each set of lead wires 15a, 15b, 15c, 16a, 16b, 16c is connected to a power supply circuit (not shown).

The orientation of the poles of the circular magnets 5 to 8 is chosen so that the circular magnets 5, 7, on the one hand, and 6, 8, on the other hand respectively develop between them a magnetic attraction force. . The powers of the circular magnets 5 to 8 are chosen so that the force of attraction tending to bring the steering wheel 2 closer to the upper source 4 is in equilibrium with the force of attraction tending to bring the steering wheel 2 closer to the lower source. 3 increased by the force exerted by the gravity (symbolized by an arrow), that is to say the weight of the steering wheel 2.

Moreover, the magnets 5, 6 exert on the flywheel 2 a significant centering force, these tending to align the magnetic axis of the corresponding magnets 7, 8 with theirs. This centering force is sufficient to stabilize the steering wheel radially.

According to Earnshaw's law, the flywheel 2 in lift between the lower source 3 and the upper source 4 can not be stable. Indeed, the centering force of magnets 5 to 8 arranged in attraction is particularly important, it gives the steering wheel 2 a radial stability and imposes axial instability. Thus, in the absence of any complementary field regulation, the flywheel 2 naturally tends to come into contact with the lower magnetic source 3 or the upper magnetic source 4. The axial stability is ensured by the interactions between each of the additional magnets 11a. at 14b and sets of lead wires 15a to 16c correspondents. Indeed, when a conductor subjected to a perpendicular magnetic field is traversed by an electric current, it undergoes a Laplace force forming, with the current and field vectors, a direct normal ortho reference. Thus, each of the sets of conducting wires 15a to 16c traversed by an electric current interact with the corresponding additional magnets 11a to 14b. In the present case, the orientation of the additional magnet pairs 11a to 14b and the direction of the electric current flowing through the conducting wires 15a to 16c are chosen so that when the flywheel 2 approaches the lower source 3, the Laplace force generated is directed axially and tends to move the flywheel 2 from the lower source 3. Respectively, when the flywheel 2 approaches the upper source 4, the generated Laplace force must be directed axially and tend to move the steering wheel 2 away. of the upper source 4. According to the arrangement of FIG. 1, when the steering wheel 2 is at equilibrium, one half of the conducting wires 15a to 16c is subjected to the radial magnetic field of the additional magnet pairs 11a, 11b, 14a, 14b, while another half of the conducting wires 15a to 16c is subjected to the radial magnetic field of the pairs of additional magnets 12a, 12b, 13a, 13b, of the same direction but in the opposite direction to the field of the pairs of pairs. additional elements 11a, 11b, 14a, 14b. The force of Laplace resulting from this double influence is therefore null. In the present case, it was considered for the example that the power of the additional magnets 11a to 14b was the same and that the conductors son 15a to 16c were traversed by the same electrical intensity. However, it is of course possible to obtain such a balance with magnet power magnets and different electrical intensities.

However, as explained, the flywheel 2 is axially unstable and tends to approach either the lower source 3 or the upper source 4. When the flywheel 2 approaches the lower source 3, the conductors son 15a to 15c are then mainly subjected to the magnetic field of the pair of additional magnets 12a, 12b, while the conductive wires 16a to 16c are mainly subjected to the magnetic field of the pair of additional magnets 13a, 13b of the same magnetic orientation as the pair of additional magnets 12a, 12b. The direction of the electric current flowing through the conductor wires 15a to 16c is chosen so that a Laplace force is exerted on the steering wheel 2 tending to move the steering wheel 2 away from the lower source 3 to the upper source 4. It should be noted that this case is also applicable to the steering wheel before it is raised, the Laplace force thus created participating in its take-off from the lower magnetic source 3.

In the same way, when the flywheel 2 approaches the upper source 4, the set of conducting wires 15a to 15c is mainly subjected to the field of the pair of additional magnets 11a, 11b while the conducting wires 16a to 16c are mainly subject to the field of the pair of additional magnets 14a, 14b of the same magnetic orientation. The magnetic orientation of the pairs 11a, 11b and 14a, 14b being opposite to that of the pairs 12a, 12b, on the one hand, and 13a, 13b, on the other hand, the resulting Laplace force therefore has an opposite direction and tends moving the flywheel 2 away from the upper source 4 to return it to its initial unstable equilibrium position.

As a result, the flywheel 2 is stabilized axially without using any sensor or control system of the electric current and oscillates on both sides of a position of average equilibrium. Experiments have shown that the intensity of the electric current needed to stabilize a flywheel 2 having a mass of 2.4 kg is only about 15 milliamps.

An flywheel 20, as shown in FIG. 2, comprises a flywheel 21 distinguished from the steering wheel 2 mainly in that it is subjected to a lower magnetic source 3a comprising a circular magnet 5a interacting with a circular magnet 7a. corresponding steering wheel 21, so as to develop between them a repulsive force opposing the fall of the steering wheel 21 by gravity (symbolized by an arrow). Unlike the flywheel 2 of the flywheel 1, the flywheel 21 is axially stable but has a radial instability, the lower magnetic source 3 tending to push the flywheel laterally 21. As a result, the flywheel 21 must be stabilized. radially thanks to the method according to the invention.

To do this, the flywheel 21 comprises a peripheral peripheral groove 22 comprising adjacent upper and lower circular and adjacent circular upper and lower magnets 23, 24, said lateral groove 22 being intended to receive a set of conducting wires 27a, 27b 27c forming turns of a coil 27 traversed by a constant electric current. The additional magnets 23 and 25 are located opposite one another and have identical magnetic orientation. The additional magnets 24 and 26 are also located opposite one another and have a magnetic orientation identical but opposite to the magnetic orientation of the additional magnets 23, 25.

As for the flywheel 1, when the flywheel 20 is in equilibrium, the coil 27 has as many turns subjected to the magnetic field of the additional magnets 23, 25 as the turns subjected to the magnetic field of the additional magnets 24, 26, and the resulting Laplace force is therefore zero. When the flywheel 21 deviates radially, the coil 27 is, in the direction in which the flywheel 21 deviates and regardless of this direction, mainly subject to the magnetic field of the additional magnets 24, 26, while in the diametrically opposite, said coil 27 is mainly subjected to the magnetic field of the additional magnets 23, 25 opposite that of the additional magnets 24, 26. The direction of the current flowing through the coil 27 in the direction in which the flywheel 21 deviates, being opposed to that of the diametrically opposed direction, the Laplace force generated on either side of the steering wheel 21 has a direction and an identical direction. The direction of the current flowing through the coil 27 and the orientation of the additional magnets 23 to 26 are chosen so that the Laplace force acting in the direction in which the flywheel 21 deviates is centripetal, thus recalling the steering wheel. 21 to its position of equilibrium, the corresponding Laplace force exerted diametrically opposite being then centrifugal.

Thus, the flywheel 21 is stabilized radially and oscillates about its axis.

Figure 3 shows a third embodiment of a stabilized flywheel according to the method of the invention. This flywheel 30 comprises a cylindrical flywheel 31 having an axis 32 and magnetically levitating between a lower magnetic source 33 and an upper magnetic source 34. Each magnetic source comprises a magnet 35, 36 annular through which the axis 32 passes, the magnets 35, 36 having an axial magnetic orientation and each interacting with a corresponding concentric magnet 37, 38 located on the axis 32 of the flywheel 31 at the same height as said magnets 35, 36.

The orientation of the magnets 35 to 38 is chosen to be identical, the magnets 35, 37, on the one hand, and 36, 38, on the other hand, developing respectively between them a magnetic force operating a centering of the axis 32. flying 31 is therefore radially stable and has an axial instability stabilized by the method according to the invention.

To do this, the flywheel 31 has an upper peripheral groove 39 housing two outer superposed superimposed magnets 40,41 and two additional inner magnets 42, 43 superimposed, said groove 39 being intended to receive a set of conducting wires 44a, 44b, 44c forming turns of a coil 44 traversed by a constant electric current. The additional magnets 40 and 42 are concentric and have the same magnetic orientation. The additional magnets 41 and 43 are also concentric and have an identical magnetic orientation but opposite to the magnetic orientation of the additional magnets 40, 42.

As for the flywheels 1 and 20, when the steering wheel 30 is in equilibrium, the coil 44 has as many turns subjected to the magnetic field of the additional magnets 40, 42 as the turns subjected to the magnetic field of the additional magnets 41, 43, and the resulting Laplace force is therefore zero. When the flywheel 30 deviates axially and approaches the lower magnetic source 33, the coil 44 is then mainly subjected to the magnetic field of the additional magnets 41, 43. The orientation of the additional magnets 41, 43 and the direction of the electric current traversing the coil 44 are chosen so that the generated Laplace force tends to move the flywheel 30 from the lower source 33 and back to its initial unstable equilibrium position. In the same way, when the flywheel 30 approaches the upper magnetic source 34, the coil 44 is then mainly subjected to the magnetic field of the additional magnets 40, 42. The orientation of the additional magnets 40, 42 being opposite to the orientation magnets 41, 43, the generated Laplace force tends to move the flywheel 30 away from the upper source 34 and back to its initial unstable equilibrium position.

Thus, the flywheel 30 is axially stabilized and oscillates around a position of average equilibrium.

Alternatively it is possible to use fewer magnets and control the orientation of the field with soft iron. A flywheel 50, as shown in Figure 4, is an exemplary embodiment.

This flywheel 50 comprises a cylindrical flywheel 52 magnetically levitating between a lower magnetic source 53 and an upper magnetic source 54. Each magnetic source 53, 54 comprises respectively a circular magnet 55, 56 facing a corresponding circular magnet 57, 58 of the flywheel 52.

Furthermore, the flywheel 52 has a central annular groove 59 whose center houses an additional magnet 60 developing an axial magnetic field, said groove 59 having walls covered with a soft iron layer 61 to redirect the magnetic field of the magnet additional 60 in a radial direction. Other arrangements of soft iron in the vicinity of additional magnets are shown in Figures 6 and 7.

The groove 59 is intended to receive a set of conductive wires 62a, 62b, 62c forming a coil 62 integral with the upper magnetic source 64, the coil 62 having an axis which coincides with the axis of the flywheel 52. The coil 62 is connected to a power supply circuit (not shown).

As for the flywheel 1, the magnetic orientation of the magnets 55 to 58 is chosen so that the magnets 55, 57, on the one hand, and 56, 58, on the other hand, respectively develop between them a magnetic force of attraction. The powers of the magnets 55 to 58 are chosen so that the force of attraction tending to bring the steering wheel 52 closer to the upper source 54 is in equilibrium with the force of attraction tending to bring the steering wheel 52 closer to the lower source 53 increased by the force exerted by the gravity (symbolized by an arrow), that is to say the weight of the steering wheel 52.

The axial stability is ensured by the interactions between the coil 62 and the magnetic field developed by the additional magnet 60 by generating a complementary Laplace force.

According to the arrangement of Figures 4 and 5, when the steering wheel 52 is in equilibrium, no Laplace force is generated and the coil 62 is not powered. When the flywheel 52 approaches the lower source 53, an electric current is applied across the coil 62 whose direction is chosen so as to generate a Laplace force directed axially and tending to move the flywheel 52 from the lower source 53 to bring it back to its original unstable equilibrium position. When the flywheel 52 approaches the upper source 54, it is necessary to generate a Laplace force tending to move the flywheel 52 from the upper source 54. To do this, the magnetic field of the additional magnet acting on the coil 62 being constant, it is necessary to reverse the direction of the current flowing through said coil 62.

In addition to this device, it is therefore necessary to provide a sensor for detecting whether the flywheel 52 approaches the lower source 53 or the upper source 54 so as to apply current in the desired direction when necessary. Unlike the previous devices, for which no sensor is necessary but in which the electrical conductors are permanently powered, the coil 62 of the flywheel 60 does not need to be powered continuously, which further reduces the power consumption of the device. On the other hand, it requires the coupling of the supply circuit to a sensor.

Examples of sensors are shown in FIGS. 8 to 10. FIG. 8 represents a mechanical sensor 100 comprising a tip 101 having an extremely fine and solid tip ending in a ball of very small diameter (less than 1 mm) made of very hard material. , said tip being intended to be fixed in the center of the flywheel 52. A switch 102 comprising two blades 103, 104 conductive, the latter being fixed and integral with the frame of the flywheel. These two blades 103, 104 are connected to the power supply. More specifically, the blade 103 is intended to be in contact with the tip 101 and comprises for this purpose an extremely hard plate 105 ruby. When, under the effect of the Laplace force, the flywheel 52 approaches the upper source 53, the tip exerts a very weak force (a few hundred milligrams) against the plate 105 and pushes the blade 103 into contact with the blade 104, which closes the electrical circuit and allows the passage of the current. This has the effect of removing the Laplace force and the flywheel 52 then descends and moves away from the upper source 54, which distances the tip 101 and reopens the electrical circuit, with the effect of restoring the Laplace force. The same applies to a second sensor for the lower source 53. This type of operation causes the flywheel 52 to oscillate on a very small amplitude on either side of the metastable equilibrium point of Eamshaw or very closely from this point, which makes it possible to limit the power of levitation to very low values, given the mass of the steering wheel 52.

Figures 9 and 10 show a sensor 110 comprising a lower magnetic loop 111 and an upper magnetic loop 112 respectively above and below the passage of two magnets 114, 115 integral with the flywheel 52 and may have a magnetic orientation opposite. It is of course possible to have at regular intervals several magnets similar to the magnets 114, 115 on the periphery of the flywheel 52, possibly alternating their magnetic orientations. When the steering wheel is rotating, the lower magnetic loops 111 and 112 are subjected to an alternating field inducing alternating electric currents in opposite phase in said loops 111, 112. These induced currents are added by a comparator 116 and the resulting current is directed to the coil 62 to feed it. It may be possible to add an operational amplifier if the induced electromotive forces are insufficient. Indeed, when the flywheel 52 approaches the upper source 54, the upper magnetic loop 112 is subjected to a stronger magnetic field than the lower magnetic loop 111, and thus generates a greater induced electromotive force, the sum of the electromotive forces induced is therefore in favor of the upper loop 112 and the coil 62 is powered by a current flowing in the corresponding direction. Conversely, when the flywheel 52 approaches the lower source 53, the upper magnetic loop 112 is subjected to a weaker magnetic field than the lower magnetic loop 111, and thus generates a less intense induced electromotive force, the sum of the forces induced electromotrices is therefore in favor of the lower loop 111 and the coil 62 is powered by a current flowing in the opposite direction of the previous one and generates an inverted Laplace force.

It should be noted that the examples cited describe coils or conductive wires integral with the upper and / or lower sources while the flywheels comprise additional magnets. It is obvious that this arrangement can be reversed, the coil or the wires being integrated in the steering wheel, while the additional magnets are integrated in the upper and / or lower sources, and that the supply of the coil or the conductive wires is performed using an internal generator at the steering wheel. However, this embodiment is more difficult to implement and the arrangements as described above will be preferred.

Figure 11 shows an alternative application of the method according to the invention to a train 200 with magnetic levitation. This train 200 is levitated between a lower rail 201 and an upper rail 202 by means of magnets 203, 204 each cooperating with a magnet 205, 206 of the train so that the magnet 203 of the lower rail 201 develops with the magnet 205 corresponding to the train 200 a repulsive force, while the magnet 204 of the upper rail 202 develops with the corresponding magnet 206 of the train 200 an attractive force. According to Earnshaw's law, the train is unstable laterally and must be stabilized using the method of the invention. To do this, the train 200 is equipped with side rails 207 of soft iron comprising an additional magnet 208 having a vertical magnetization. This rail 207 is intended to receive a fixed complementary rail 209, secured to a track 210 along which the train moves. This complementary rail 209 is traversed by conductive wires 211 supplied with electric current and subjected to the magnetic field developed by the additional magnet 208. It is therefore possible to generate a Laplace force acting on the train 200 and to correct its instabilities magnetic.

It should be noted that one of the main advantages of the method and device that is the subject of the invention lies in the fact that it does not function by modifying the magnetic lift and positioning fields and that the position of the levite object lies at the metastable equilibrium point of Eamshaw or very close to this point, which makes it possible to limit the power of levitation to extremely low values, given the importance of the mass of the levite object. Although the invention has been described in connection with particular embodiments, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims

1. Method for stabilizing an object (2, 21, 31, 32, 52, 200) in magnetic levitation subjected to at least one constant magnetic field, said object being stable in at least one direction and unstable according to at least one other direction, characterized in that it comprises a stabilization step, repeated as often as necessary, of applying an electric current through at least one conductive element (15a to 16c, 27, 44, 62, 211) subjected to a field secondary magnet so as to generate a compensatory Laplace force in the direction of instability.

2. Method according to claim 1, characterized in that the stabilization step aims at keeping the object (2, 31, 32, 52, 200) between an upper limit and a lower limit around an equilibrium position desired medium.

3. Method according to any one of claims 1 or 2, characterized in that it comprises a step of detecting the position of the object (2, 21, 31, 52, 200) adapted to control and / or interrupt passing electrical current through the conductive member (15a-16c, 27, 44, 62, 211).

4. Device (1, 20, 30, 50) with magnetic levitation comprising an object (2, 21, 31, 32, 52, 200) in levitation subjected to at least one constant magnetic field capable of interacting with magnetization means corresponding (7, 8, 7a, 37, 38, 57, 58, 205, 206) of the levite object, characterized in that it comprises, on the one hand, secondary magnetic elements (11a to 14b, 23 to 26, 40 to 43, 60 to 62, 207, 208) adapted to generate a secondary magnetic field, and secondly, at least one conductive element (15a to 16c, 27, 44, 62, 211) subjected to the magnetic field secondary, so that a compensating Laplace force is generated on the object levite, when the conductive element is crossed by an electric current.

5. Device (1, 20, 50) according to claim 4, characterized in that the magnetic field develops, with the magnetization means (7, 8, 57, 58, 206), an attraction force acting on the object (2, 21, 52, 200) levites.

6. Device (30) according to claim 4, characterized in that the magnetic field is generated by at least two sources (33, 34) of magnetic field, the magnetic field sources and the magnetization means

(37, 38) complementary to the object levite (31, 32) have a parallel magnetic orientation and the same direction.

7. Device (20, 30, 50) according to any one of the claims

4 to 6, characterized in that the conductive element is a coil.

8. Device (1, 20, 30, 50) according to any one of claims 4 to 7, characterized in that the sources (3, 4, 3a, 33, 34, 53, 54, 201, 202) field and / or the complementary magnetization means (7, 8, 7a, 37, 38, 57, 58, 205, 206) and / or the secondary magnetic elements (11a to 14b, 23 to 26, 40 to 43, 60 62, 207, 208) are permanent magnets.

9. Device (50) according to any one of claims 4 to 8, characterized in that the secondary magnetic elements (60) interact with at least one ferromagnetic material (61, 62) shaped to allow the reorientation of the magnetic field secondary.

10. Device (50) according to any one of claims 4 to 9, characterized in that it comprises at least one sensor (100, 110) adapted to control or interrupt the flow of current through the conductive element (62). , 211) according to the position of the object (52, 200) levitates.

11. Device (50) according to claim 10, characterized in that the sensor (100) comprises a tip (101) integral with the object (52) levitated and adapted to come into contact with a switch (102) for the to close.