Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C32/00—Bearings not otherwise provided for
  • F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
  • F16C32/0406—Magnetic bearings
  • F16C32/044—Active magnetic bearings
  • F16C32/0444—Details of devices to control the actuation of the electromagnets
  • F16C32/0446—Determination of the actual position of the moving member, e.g. details of sensors

Definitions

• the present invention relates to a device for detecting the movements of a rotor mounted on active magnetic bearings, comprising a reference ring made of non-magnetic material of low resistivity, mounted on the rotor, at least two fixed coils, arranged in the vicinity of the reference ring, and means for supplying the coils with alternating current.
• An active magnetic bearing is an electromagnetic device ensuring the relative positioning of a rotating assembly with respect to a fixed part.
• the active magnetic bearing comprises a rotor secured to the rotating assembly, the bearing rotor being held in position in the magnetic fields created by electromagnets placed on the fixed part (stator).
• the bearing rotor is in equilibrium without mechanical contact with the stator under the influence of electromagnetic forces.
• the position of the rotor is identified by means of detectors which continuously deliver signals representative of the possible displacements of this rotor relative to a nominal position.
• the signals delivered by the position detectors control, through an electronic servo loop, the currents in the electromagnets of the bearings, so that the magnetic attraction forces bring the rotor back to its nominal position in the event of displacement .
• the position detectors which inform the servo circuits on the position of the rotor and allow them to react to maintain the desired position, constitute an essential link which must be reliable but also reasonable cost.
• Capacitive type detectors have thus already been proposed, optical detectors, eddy current detectors, inductive detectors with coils and magnetic or ferrite sheets.
• detectors consisting of sets of small coils wound on ferromagnetic cores, the coils being able to present certain particular configurations with a view to neutralizing the geometric defects of the rotor.
• Inductive sensors such as those described in the aforementioned publications ensure good rejection of the defects of the rotor and have a good quality of detection.
• the invention aims to remedy the aforementioned drawbacks of conventional inductive detectors and to allow detectors to be produced at reduced cost, without losing the advantages of precision and manufacturing of existing detectors.
• a device for detecting the movements of a rotor mounted on active magnetic bearings comprising a reference ring made of non-magnetic material of low resistivity, mounted on the rotor, at least two fixed coils, arranged in the vicinity of the reference ring, and means for supplying the coils with alternating current, characterized in that it comprises an annular cage, made of non-conductive material, which has a thin cylindrical wall concentric with the reference ring, providing a free space therewith, first and second parallel planar wings extending in planes perpendicular to the axis of said thin cylindrical wall, on the side opposite to the reference ring and a median dividing wall parallel to the first and second planar wings, and in that said at 97/37146 PC17FR97 / 00552
• At least two fixed coils are arranged in the annular cage while being positioned by means of said central separating partition.
• the device comprises. an annular cage of non-conductive material, the middle dividing partition of which is interrupted in four zones distributed in a cross, being offset by 45 * with respect to two radial measurement directions; four coils in the form of tiles which are distributed inside the annular cage being each disposed in contact with the thin cylindrical wall, each coil in the form of tiles comprising first and second main parts located on either side of 'an uninterrupted part of the middle dividing wall and the first and second connecting secondary parts with small radius of curvature located in areas of interruption of the middle dividing wall, the four tiled coils being mounted in bridge two a of them
• the device according to the invention comprises a pair of annular coils supplied in series and arranged in parallel planes inside the annular cage in non-conductive material, on either side of the median separating partition, the reference ring comprising, on its surface facing the annular cage, a portion of different diameter which extends axially over a length substantially equal to half of the thickness of an annular coil on either side of the median separating partition
• the device according to the invention comprises an annular cage made of non-conductive material, the median dividing partition of which is interrupted in four zones distributed in cross being offset by 45 'with respect to two radial measurement directions; four coils in the form of tiles which are distributed inside the annular cage being each disposed in contact with the thin cylindrical wall, each coil in the form of tiles comprising first and second main parts located on either side of '' an uninterrupted part of
• Each of the four tile-shaped coils has main branches, the cross section of which has along the axis zz 'a dimension of the order of half the cross section dimension of each of the two annular coils along this same axis zz'.
• said portion of different diameter defines a projecting shoulder. According to another particular embodiment, said portion of different diameter defines a groove.
• the annular cage is made of molded plastic.
• the reference ring made of non-magnetic material of low resistivity is made of silver, aluminum or bronze.
• the thin cylindrical wall of the annular cage has a thickness of the same order as that of the free space defined between said thin cylindrical wall and the reference ring.
• the thin cylindrical wall of the annular cage has a thickness of the order of 0.4 to 0.7 mm.
• the reference ring has an outer diameter smaller than that of the thin cylindrical wall of the annular cage.
• the reference ring has an internal diameter greater than that of the thin cylindrical wall of the annular cage.
• FIG. 2 is a sectional view along line II-II of Figure
• Figure 3 is a side view in the direction x'x of Figure
• FIG. 4 shows the diagram of the bridge mounting of the detector coils of Figures 1 to 3;
• FIG. 5 is a sectional view along line V-V of Figure
• FIG. 6 is a sectional view along line VI-VI of Figure 5;
• FIG. 7 shows the diagram of the series connection of the detector coils of Figures 5 and 6;
• FIG. 8 shows an alternative embodiment of the detector of Figures 5 and 6;
• FIG. 9 is a sectional view along line IX— IX of Figure 10 of a combined axial and radial detector without iron according to a third embodiment of the invention.
• FIG. 10 is a sectional view along line X-X of Figure 9;
• FIG. 11 shows an alternative embodiment of the detector of Figures 9 and 10.
• a radial detector which does not contain any magnetic or ferrous material, either at the movable part 10 of this detector or at the level of the fixed part 20.
• the mobile part of the radial detector comprises a reference ring 10 which is intended to be mounted on the rotating part of a machine tool (for example a spindle for machining, grinding or milling machine, grinding wheel holder, ...), special equipment for the light industry or the space industry (X-ray tube, vacuum pump with turbomolecular effect, centrifuge, textile spindle, turbopump, ...
• the reference ring 10 of the radial detector of Figures 1 to 3 is made of non-magnetic material of low resistivity and can be for example aluminum, bronze, silver or an equivalent material.
• the radial detector comprises a fixed part arranged opposite the reference ring 10, without contact with the latter.
• This fixed part comprises four coils B1 to B4 which are supplied by an alternating current bridge assembly supplied by a power source 1 ( Figure 4).
• the coils B1 and B2 are arranged diametrically opposite with respect to the center of the reference ring 10, in a radial direction x'x.
• the coils B1 and B2 are connected in series across the power source 1 and their common point delivers a signal L x representative of the displacement of the reference ring 10 in the direction x'x.
• the coils B3 and B4 are arranged diametrically opposite with respect to the center O of the reference ring 10, in a radial direction y'y which is perpendicular to the radial direction x'x.
• the coils B3 and B4 are also mounted in series across the power source 1 and their common point delivered a signal Ly representative of the displacement of the reference ring 10 in the direction y'y.
• the signals L x and Ly are applied to the control circuits of the active magnetic bearings and make it possible to adjust the currents of the coils of the electromagnets of the radial magnetic bearings in order to maintain the rotating assembly in a predefined nominal position, or, the if necessary, to selectively cause desired modifications to this nominal position.
• the various coils B1 to B4 are supplied in such a way that the signals supplied by two coils of the same pair B1, B2, respectively B3, B4 located diametrically opposite for detecting displacements in the same direction x'x, respectively y'y are algebraically entrenched.
• the alternating carrier current delivered by the voltage source 1 can be, for example, a few tens of kilohertz.
• the radial detector of Figures 1 to 3 has a particularly simple structure which makes it easy to make and implement and allows significant savings compared to conventional inductive detectors.
• the reference ring 10 contains neither magnetic material, such as ferrite, nor stacking of thin sheets of iron, but the fixed part of the detector is also free of iron and the coils B1 to B4 have a simple configuration and are mounted in a support 20 in the form of an annular cage which is also very simple and can be manufactured economically, for example in the form of a molded plastic part.
• the annular cage 20 of non-conductive material has a thin cylindrical wall 21 concentric with the reference ring 10 and which is arranged so as to provide a small free space e between the thin cylindrical wall 21 and the reference ring 10.
• the free space e can be of the order of a few tenths of a millimeter
• the thin cylindrical wall 21 also has a reduced thickness, which can advantageously be of the same order of magnitude as the value of the free space e.
• the thin cylindrical wall 21 can have a thickness of between approximately 0.4 and 0.7 mm, typically 0.5 mm.
• the annular cage 20 also comprises plane wings 22, 23 parallel to each other which extend from the thin cylindrical wall 21 in radial planes perpendicular to the axis z'z of the thin cylindrical wall, which corresponds to the 'reference axis of the detector
• the flat wings 22, 23 in the form of a crown have their free end facing the side opposite the reference ring 10 and define, in section along an axial plane ( Figure 2), a U-shaped profile
• An annular median dividing wall 24 parallel to the planar wings 22, 23 also extends in a radial plane from the wall thin cylindrical 21 In this way, the planar wings 22, 23, the central partition 24 and the thin cylindrical wall 21 define, in section along an axial plane, an E profile.
• the central partition 24 is interrupted in four zones 25 distributed in a cross and offset by 45 * with respect to the radial measurement directions x'x and y'y.
• the four coils B1 to B4 in the form of a tile are distributed inside the annular cage 60, each being arranged in contact with the thin cylindrical wall 21.
• Figure 3 has main parts 71, 73 located on either side of an uninterrupted part of the middle separat ⁇ ce partition 24 and connecting secondary parts 72, 74 with a small radius of curvature located in zones 25 of interruption of the partition 24.
• the assembly of the four coils B1 to B4 is thus extremely simple and their positioning is precise thanks to the guide that constitutes the annular cage 20 with its cylindrical face 21, its outer wings 22, 23 and its separating partition 24 interrupted in the four zones 25.
• the coils B1 to B4 are well pressed against the cylindrical wall 21 and taking into account the small thickness of this wall 21 and the free space e, the coils B1 to B4 are are found very close to the reference ring 10 and can thus have a high measurement sensitivity without being disturbed by the parasitic currents of the windings of neighboring active magnetic bearings or of a driving motor. ement of a rotating shaft, since the annular cage 20 for supporting the coils B1 to B4 is completely non-conductive.
• a displacement detector according to the invention will now be described with reference to FIGS. 5 to 7, applied to the detection of axial displacements in a direction z'z of a rotating shaft mounted on active magnetic bearings
• the signals delivered by such a detector radial are used to control the current control of the windings of the active magnetic bearing or bearings acting in the radial direction.
• annular cage 40 of the axial detector of Figures 5 and 6 with its wings 42, 43 attached to a thin cylindrical wall 41 and its separating partition 44 can be quite similar to the annular cage 10 of Figures 1 to 3.
• the central separating partition 44 may however be continuous, without there being interruptions similar to interruptions 25 of the annular cage 20. Such interruptions would not, however, be inconvenient for the axial detector, so that, for example to standardize the manufacturing, the annular cage 40 could if necessary be identical to the cage 20.
• Annular coils B5 and B6 are arranged in radial planes perpendicular to the axis z'z, in the two housings of the annular cage 40 defined on either side of the central separating partition 44.
• the coils B5 and B6 are connected in series between the poles E + and
• the reference ring 30 cooperating with the coils B5 and B6 placed in the annular cage 40 can be made like the reference ring 10 in a non-magnetic material of low resistivity.
• the reference ring 30 must have on its face facing the annular cage 40 a portion 31 of different diameter, such as a projection defining a shoulder, which extends axially over a length substantially equal to half the length thickness of an annular coil B5, B6, on either side of the central separating partition 44
• the free space e defined between the portion 31 and the cylindrical wall 41 must not exceed a few tenths of a millimeter.
• the difference in diameter between the projecting portion 31 and the recessed portion of the ring 30 can be of the order of a few tenths of a millimeter to a few millimeters.
• the portion 32 of different diameter from the reference ring 30 is on the contrary constituted by a groove.
• it is the part of normal diameter of the reference ring 30 which defines the small free space e of the order of a few tenths of a millimeter with the cylindrical wall 41 and the groove 32 may itself have a depth of the order of a few tenths of a millimeter or a few millimeters.
• Figures 9 and 10 show a third embodiment, which corresponds to an ironless detector according to the invention which combines the detection of radial and axial movements of a rotating member.
• FIG. 9 and 10 is particularly compact insofar as it comprises a single annular cage 60 and a single reference ring.
• the annular cage 60 with its wings 62, 63 and its central separating partition 64 can be produced in an identical manner to the annular cage 20 of a radial detector, the separating partition 64 being interrupted in four zones 65 arranged crossed.
• the annular cage 60 simply has dimensions a little larger than those of the annular cage 20 insofar as the wings 62, 63 and the central separating partition 64 must be able to accommodate side by side ia times the four shaped coils of tile B1 to B4 used for radial detection and the two annular coils B5 and B6 used for axial detection.
• the coils B1 to B4 can have the same configuration as in Figures 1 to 3 and the coils B5 and B6 can have the same configuration as in Figures 5 and 6, and the electrical assemblies can be in accordance with those of Figures 4 and 7
• the coils B5 and B6 used for axial detection must have a larger dimension than that of the coils B1 to B4 in the form of a tile.
• the dimension along the axis zz 'of the section of an annular coil B5 or B6 used for the detection of axial displacements is preferably of the order of twice the dimension along the axis zz 'of the section of a coil B1, B2, B3 or B4 used for the detection of radial displacements.
• the reference ring 50 must be made like the reference ring 30, with a portion 51 of different diameter constituting a projection (as in FIGS. 9 and 10) or a groove (as was illustrated previously on Figure 8).
• the portion 51 of different diameter defining a shoulder must extend in the axial direction at least over the entire thickness of the two main parts 71, 73 of each of the coils B1 to B4.
• the portion 51 extends in the axial direction so as to cover, on either side of the separating partition 64, half the thickness of the coils B5 and B6.
• the tile coils B1 to B4 are placed as close as possible to the cylindrical wall 61, the annular coils B5 and B6, of larger section, being placed immediately next to the coils B1 to B4.
• FIGS. 1 to 3 5, 6 and 8 to 10, embodiments have been described in which the reference ring 10, 30, 50 has an outside diameter smaller than that of the thin cylindrical wall 21, 41, 61 of the corresponding annular cage 20, 40, 60, which corresponds to the case of a rotating shaft of relatively small diameter, the fixed parts of the magnetic bearings and of the detectors being outside the rotating shaft.
• the reference ring 150 has, in particular at the level of the part 151 forming a shoulder, an internal diameter which is greater than that of the thin cylindrical wall 161 of the annular cage 160, which is in all respects comparable to the annular cage 60, except for the fact that the wings 162 , 163 and the separating partition 164 have their free ends facing inwards, and not outwards, like the corresponding elements 62, 63, 64 of the annular cage 60 of FIGS. 9 and 10.
• Such an iron-free detector is insensitive to ambient magnetic fields.
• the detector has a strong surface integration effect and has a high quality of harmonic rejection, in particular for harmonics from the fifth.
• the detector has as great a sensitivity as an inductive detector with sheet metal armatures and with a multiplicity of coils arranged in notches around pole pieces.
• the detector is very cheap, the tiled coils or the annular coils being very easy to produce and the annular cage or coil support frame which can be produced by plastic molding.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Mechanical Engineering (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• Magnetic Bearings And Hydrostatic Bearings (AREA)

Applications Claiming Priority (3)

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• 1996
  • 1996-03-28 FR FR9603861A patent/FR2746870B1/fr not_active Expired - Fee Related
• 1997
  • 1997-03-27 JP JP9534980A patent/JP2000508069A/ja active Pending
  • 1997-03-27 WO PCT/FR1997/000552 patent/WO1997037146A1/fr not_active Application Discontinuation
  • 1997-03-27 EP EP97916510A patent/EP0890033A1/de not_active Withdrawn

Non-Patent Citations (1)

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