Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-06-23
2002-02-26
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C074S005460, C074S005700, C074S005700
Reexamination Certificate
active
06351049
ABSTRACT:
The invention relates to a magnetic bearing for magnetically centering a moving body relative to a fixed body with respect to three axes and preferably for controlling tilting of the moving body.
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 passively centered 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 an axis of rotation which often coincides 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 W089/12178 may be cited in particular.
However, as a general rule, magnetic bearings in connection with which the facility for tilting has been mentioned rapidly lose their centering capability when the tilt exceeds angles of the order of one degree.
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 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°, without compromising centering performance with respect to three non-coplanar axes and using dedicated components of compact geometry and low power consumption implying only a moderate increase in the weight of the moving body. A subsidiary object of the invention is to provide a magnetic bearing which can also control tilting in the range of movement concerned, which is through at least 5° or even 15° or more.
To this end the invention proposes a magnetic bearing for centering a first body, which is mobile in tilting within an angular range of movement of at least 5° about a center of tilting, relative to a second body having a reference axis passing through the center of tilting, the magnetic bearing including:
a hollow outer part at least part of which is made from a ferromagnetic material which is attached to the first body and which has an inside surface whose shape is a portion of a sphere whose center is substantially coincident with the center of tilting and which extends around a mobile reference axis having an inclination which can be zero to the reference axis on either side of a transverse plane which is perpendicular to the reference axis and passes through the center of tilting,
an inner part which is attached to the second body and which includes two separate members which are disposed on respective opposite sides of the transverse plane, which are separated in the direction parallel to the reference axis by a space having a reluctance adapted to prevent the flux lines generated by the group of windings of one of the members crossing this space, which each have a group of windings including at least the specific windings of the ferromagnetic areas and which each include a plurality of (at least three) ferromagnetic areas which are offset angularly about the reference axis, which each define in conjunction with the inside surface of the hollow outer part two air-gaps offset relative to the reference axis and which are each provided with a specific winding adapted to generate magnetic flux lines closing across the two air-gaps, and
an excitation circuit for selectively applying excitation currents to the windings of the group of windings of each member to generate magnetic fields in the air-gaps adapted to center the hollow outer part relative to the inner part in directions transverse to and parallel to the reference axis.
Thus there is a very compact inner part on which a few windings are mounted, possibly with a permanent magnet inside the space between the two separate members. The overall size and weight are therefore low. Around this inner part is a hollow outer part whose inside surface is the shape of a hollow sphere (which is why the magnetic bearing of the invention can usefully be referred as a ball joint bearing), so that the air-gaps defined therewith, at a distance from the aforementioned transverse plane, are inclined relative to the reference axis and can contribute to the generation of centering forces parallel to the reference axis.
As just indicated, the space between the two separate members of the inner part can be occupied by a magnet which is permanently magnetized in a direction parallel to the reference axis. The magnet therefore generates magnetic flux lines continuously without consuming electrical energy. On the other hand, no flux lines generated by an electrical current in any of the windings pass through the magnet.
However, another situation of practical importance is that in which this space is a free space forming a large fixed air-gap, i.e. one which does not contain any solid material, with the possible exception of a non-ferromagnetic connecting member for fastening the two members together. This space is filled with vacuum or with air, depending on the environment in which the magnetic bearing is located.
In conjunction with the air-gaps and a ferromagnetic portion of the hollow outer part and the associated specific winding, each ferromagnetic area defines a magnetic actuator. The various magnetic actuators can be independent of each other. However, for ease of manufacture and efficiency, it is beneficial for the ferromagnetic areas of each member to be part of the same ferromagnetic component.
It is also clear that the magnetic bearing is easier and less costly to manufacture if the two separate members have the same geometry. Furthermore, controlling the specific windings of the magnetic bearing is easier if the areas of each member are disposed symmetrically with respect to the transverse plane crossing the space between the separate members.
With the same aim of simplicity, the number of ferromagnetic areas of each member is advantageously an even number and each ferromagnetic area is preferably disposed opposite another ferromagnetic area with respect to the reference axis. In one particularly simple arrangement each member has four ferromagnetic areas divided into two pairs of areas which are diametrally opposed with respect to the reference axis and offset by 90° about the reference axis.
The hollow outer part can have a large angular amplitude, for example plus or minus 50° relative to the transverse plane perpendicular to the reference axis.
Each ferromagnetic area of each member preferably has first and second projections directed towards the inside surface of the hollow outer part to form the air-gaps of that area with the first of the projections surrounded by the specific winding.
The first or second projections of the ferromagnetic areas of a given member advantageously have free edges whose shape is a portion of a common sphere centered on the center of tilting, which guarantee
Chassoulier Damien
Chillet Christian
Delamare Jerome
Yonnet Jean-Paul
Alcatel
Nguyen Tran
Sughrue & Mion, PLLC
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