Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-06-23
2002-05-07
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S103000
Reexamination Certificate
active
06384500
ABSTRACT:
BACKGROUND OF THE INVENTION
Magnetic centering of one body relative to another body with respect to a given axis can be passive or active, depending on whether the centering magnetic fluxes are generated passively by permanently magnetized means or at least in part actively by an appropriate choice of the amplitude of an excitation current applied to windings. This is known in the art.
For physical reasons, a body cannot be centered passively relative to another body with respect to three non-coplanar axes.
For a given level of centering performance, the use of permanent magnets has the advantage of minimizing the electrical energy required for centering, compared to a configuration with no magnets.
In practice, the body which is to be centered relative to a fixed body can have various degrees of freedom relative to the fixed body. For example, the moving body may be a rotor which rotates continuously or non-continuously about a rotation axis which is often coincident with one of the three centering axes. A configuration like this is of great practical importance, especially in the space field, in momentum wheels or in reaction wheels.
However, to complement such rotation, it may be necessary to control tilting about one or more axes transverse to the rotation axis. Thus in the field of satellites it is beneficial to be able to incline the rotation axis of a momentum or reaction wheel, for example to contribute to satellite attitude control.
Magnetic bearings with the facility for tilting have already been proposed. The document WO89/12178 may be cited in particular.
However, as a general rule, magnetic bearings in connection with which the facility for tilting has been mentioned are often bulky and, most importantly, rapidly lose their centering capability when the tilt exceeds angles of the order of one degree. In the case of the previously mentioned document WO89/12178, for example, tilting about axes transverse to the rotation axis is mentioned only as a form of interference that has to be compensated. Also, the globally flat configuration of the various components of the system described (which is very flat in the direction parallel to the rotation axis) does not allow a high amplitude of tilting (not more than approximately 1°).
This is because controlling tilting within a large range of movement appears to be difficult a priori since, to be able to generate high torques electromagnetically, it appears to be necessary to provide large windings (to obtain high localized forces) around a reference axis passing through the center of tilting and to locate them at a large distance from the center of tilting (so that the forces provide high torques). These two constraints make it mandatory to locate the components conjointly assuring tilt control on a large-diameter circle; if tilting is then to be controlled within a large range of angular movement, the components assuring such movement must extend a great distance in the direction parallel to the reference axis, but the problem then arises that tilting moves and inclines some of the surfaces defining the air-gaps crossed by the fluxes generated by said windings, which reduces the thickness of some of the air-gaps; if this thickness is not to be reduced to zero, the air-gaps must have a large nominal width, which means that, for a given flux in them, the size of the windings and the power applied to them must be increased. In the foregoing, it is also necessary to prevent any contact between the surfaces defining all the other air-gaps of the bearing, in particular those which center the moving body in the direction parallel to or transverse to the reference axis.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the invention is to provide a magnetic bearing (sometimes referred to as a magnetic suspension) for centering and controlling tilting of a first body, which is mobile in tilting about a tilting center, relative to a second body, which system allows relative tilting through at least 5°, which tilting is significantly greater than that allowed by prior art magnetic bearings and can in particular reach or even exceed tilting angles of plus or minus 15°, providing good performance in centering in directions parallel to and transverse to a reference axis but having only a low power consumption.
A subsidiary object of the invention is a bearing of the aforementioned type which is compact within an annular volume surrounding a central free space to facilitate installation of equipment at the center of the bearing.
To this end the invention proposes a magnetic bearing for centering and controlling tilting of a first body, which is mobile in tilting within a range of angular movement of at least plus or minus 5° about a center of tilting, relative to a second body having a reference axis passing through the center of tilting, the bearing including centering members adapted to center the first body magnetically relative to the second body at least in the direction transverse to the reference axis and:
two permanently magnetized rings carried by a first ferromagnetic armature fastened to the first body, extending around the reference axis and each having a magnetization direction which passes at all points at least approximately through the reference axis, which rings are parallel to each other and offset in the direction parallel to the reference axis and on respective opposite sides of the center of tilting and have free edges substantially forming portions of a common sphere centered on the center of tilting,
an annular plurality of (at least three) tilt windings fastened to the second body and each including two groups of circumferential strands respectively adapted to face each of the permanently magnetized rings regardless of the orientation of the hollow outer part relative to the center of tilting within the range of movement in tilting, which windings are carried by a second ferromagnetic armature defining in conjunction with the magnetized rings air-gaps whose thickness remains constant throughout the range of angular movement in tilting, and
an excitation circuit adapted to apply excitation currents to the tilt windings adapted to generate tilt forces in the air-gaps.
The fact that the surfaces defining the air-gaps for generating tilting forces have a non-zero inclination to the reference axis means that the thickness of these air-gaps can be constant, achieving constant performance in terms of tilt control, with low electrical power consumption (all that is required to choose a small value for the constant thickness).
A posterior reasoning might suggest that giving these air-gaps a non-zero inclination is obvious, but as far as the inventors are aware this has never been proposed, no doubt because of certain prejudices in the art, including the idea that inclining the surfaces defining the air-gaps is a priori incompatible with a range of movement in the direction parallel to the reference axis (within which range of movement axial centering must be achieved) and/or the idea that it is doubtless very difficult in practice to provide inclined surfaces of this kind and thereafter to locate, without contact, the various fixed and mobile components of the bearing so that all of the air-gaps contributing both to centering and to tilting really have the required geometries and dimensions. Finally, there has no doubt been the idea that providing tilt control over a wide range of movement was incompatible with magnetic centering, given that prior art magnetic centering devices are not able to provide centering in three directions (for example the direction of the reference axis and two transverse axes) unless the moving body retains approximately the same orientation relative to the fixed body (or more generally relative to which the moving body must be centered). It has nevertheless become apparent that to enable large tilting, up to plus or minus 10° or more, or even plus or minus 15°, relative to a transverse plane intersecting the reference axis at the center of tilting, whilst retaining constant air-gaps, the requir
Chassoulier Damien
Chillet Christian
Delamare Jerome
Yonnet Jean-Paul
Alcatel
Nguyen Tran
Sughrue & Mion, PLLC
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