Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1996-08-27
1998-12-01
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
310 68D, 310 68B, H02K 709
Patent
active
058443398
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE RELATED ART
The present invention relates to an active magnetic bearing with auto position-detection, comprising first and second opposing electromagnets disposed on either side of a ferromagnetic body suspended without contact between said electromagnets, the first and second electromagnets being oriented along an axis X'X and each comprising both a magnetic circuit defining a respective air gap e.sub.1, e.sub.2 with said body of mean value equal to a common predetermined value e.sub.0, and secondly an excitation winding powered by a power amplifier whose input current is servo-controlled as a function of the position of the body relative to the magnetic circuits of the first and second electromagnets.
In the most widely used active magnetic bearing systems, the position of the suspended body, which body may be a machine rotor or a disk, for example, is continuously monitored by means of position detectors associated with the electromagnets of the activating bearings which produce the forces required for holding the body suspended in a given working position.
The fact of using position detectors that are distinct from the electromagnets which support the suspended body considerably increases the cost of machines, because of the detectors proper, because of the associated connection means, and because of the electronic circuits for feeding them.
Also, such detectors can be situated only to one side of the bearing, and as a result the detection point cannot be collinear relative to the reaction point. This offsetting of the detectors relative to the actuator members can induce perverse effects concerning rotor monitoring when account needs to be taken of the deformation to which the rotor is subjected during its rotation. For example the detectors may be located at deformation nodes whereas the activating electromagnets are closer to deformation anti-nodes, or vice versa. The information provided by the detectors is no longer an accurate reflection of reality at the bearings proper.
Document Patent No. WO-A-93/23683, to Rubner et al discloses a magnetic bearing with auto detection comprising, for a given direction, coils connected in series and conveying both current for stabilizing the position of the moving body suspended by the bearing and detection current. Such a magnetic bearing system nevertheless requires premagnetization of the stator which is achieved by means of permanent magnets, and also amplifiers, each capable of providing currents that are capable of alternating between being positive and negative depending on the position of the moving body. Implementing such premagnetizing means and complex linear amplifiers of the four-quadrant type makes implementation complex and affects overall reliability.
SUMMARY OF THE INVENTION
The present invention seeks to remedy the various drawbacks mentioned above and to make it possible to provide reliable servo-control of the electromagnets of an active magnetic bearing by providing information concerning the position of the suspended member in a manner that is cheap and does not require separate position detectors, such as detectors of inductive, capacitive, or optical type.
The invention seeks more particularly to make it possible to perform position detection of the inductive type in conventional active magnetic bearings while making use, in any given direction, of only two opposing electromagnets that produce attractive forces on the moving body, without it being necessary to add detection coils to the magnetic bearing distinct from the bearing's own electromagnets, and without it being necessary to add premagnetization means.
The invention seeks to enable active magnetic bearings to be made that are relatively cheap, in particular for machines that are to be produced in large quantities, such as textile spindles, for example, machining spindles, vacuum pumps, and hard disks for computers.
According to the invention, these objects are achieved by an active magnetic bearing with auto position-detection, comprising first and second op
REFERENCES:
patent: 3508444 (1970-04-01), Sitomer
patent: 4551708 (1985-11-01), Welburn
patent: 4577159 (1986-03-01), Pace
patent: 5093754 (1992-03-01), Kawashima
patent: 5397183 (1995-03-01), Lu et al.
patent: 5469006 (1995-11-01), Pinkerton
patent: 5469007 (1995-11-01), Toyama
patent: 5471106 (1995-11-01), Curtis et al.
Brunet Maurice
Schroeder Ulrich
Dougherty Thomas M.
Societe de Mecanique Magnetique
Williams Timothy A.
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