Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-09-05
2002-04-02
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C359S200700, C505S166000, C505S879000
Reexamination Certificate
active
06365997
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a magnetic bearing in which a first part is mounted magnetically relative to a second part and the second part has a Type II superconducting material containing an anisotropic crystal or a plurality of grains formed of this anisotropic crystal, this crystal being anisotropic in that the superconducting current is guided in current-carrying planes. The invention is further directed to a motor with a magnetic bearing of this kind and to the use of this motor as a drive for a polygon mirror.
b) Description of the Related Art
The projection of video images by means of light beams, especially laser beams, is a technically demanding task which could not previously be carried out satisfactorily in every detail. One problem consists in manufacturing the individual components more economically than was previously done.
In this technique, a parallel light bundle, a light beam or laser beam, is acted upon by the image and color information of different image points of a video image which are illuminated on a screen sequentially by means of the light bundle in a manner analogous to the conventional representation of video images with electron tubes. The deflecting speeds for the light bundles are extremely high due to the large number of image points.
A rotating polygon mirror is often used for for horizontal or line deflection; the rate of rotation of the polygon mirror multiplied by the number of polygon sides gives the quantity of image points that can be displayed per unit of time. However, given conventional television standards, this requires far more than 100,000 revolutions per minute of the polygon mirror.
At such high rates of rotation, it is beneficial when the polygon mirror is mounted so as to be free of friction as far as possible. For this purpose, gas bearings or magnetic bearings are known from the prior art.
Of special interest among the magnetic bearings are superconducting magnetic bearings in which magnetic fields can be maintained without electrical power. In particular, the anchoring of the magnetic field, namely, the suspension or hovering of a magnet over a superconductor similar to the known Meissner-Ochsenfeld effect, allows a surprisingly simple construction of magnetic bearings.
Through the development of high-temperature superconducting materials, it has become possible to operate such magnetic bearings at the temperature of liquid nitrogen, so that expenditure was substantially reduced compared to superconductors cooled by liquid helium. The term “high-temperature superconducting” is used in its shortened form “superconducting” hereinafter.
U.S. Pat No. 4,956,571 discloses a superconducting magnetic bearing with a conical stator part which is made of a superconducting material and a corresponding, likewise conical, rotor part having permanent magnets. The stator part has a liquid vessel for the liquid nitrogen that is used as coolant.
U.S. Pat No. 5,540,116 describes a superconducting bearing in which a ring, a cap or a disk serves to reduce the magnetic resistance for increasing the forces for free levitation.
The superconducting magnetic bearing in U.S. Pat No. 5,177,387 has radially distributed permanent magnets. Associated permanent magnets of a bearing point are arranged with their poles oppositely aligned and correspond with superconducting materials. The polarity of the permanent magnets is axially oriented.
A superconducting magnetic bearing whose permanent magnet poles are arranged at the ends of a rod is known from U.S. Pat No. 4,939,120. A part made of superconducting material is provided near each end of the rod. Additional magnets corresponding with stationary driving coils are used for the drive.
U.S. Pat No. 5,196,748 describes a superconducting magnetic bearing in which annular and disk-shaped permanent magnets are stacked in like polarity on a shaft. This shaft forms the rotational axis of the bearing and the permanent magnets are magnetized in axial direction. Layers of highly permeable metal, e.g., known mu metal, through which the magnetic flux lines are guided are arranged between the permanent magnets. The stiffness of the bearing is increased somewhat compared to the solutions mentioned above by means of this metal. Further, this reference also describes a bearing showing the arrangement of the permanent magnets and highly permeable layers in radial alignment.
A fundamental defect in the prior art mentioned above is the absence of any teaching for an exact arrangement of magnets individually or collectively, how this bearing should be designed so as to be suitable for controlling polygon mirrors, and which arrangements would be best for this purpose. In this case, the quantities considered for optimization are, first, the bearing capacity, that is, essentially the force for holding, e.g., a rotor in a motor over a stator made from superconducting material; second, the attainable stiffness, i.e., the magnitude of restoring forces acting on the rotor when the rotating shaft is displaced from its rest position; and, third, the bearing damping which essentially determines the restoring time when deflecting from the optimum rotationally symmetric configuration and which should be large enough to prevent swiveling about the rotating shaft when restoring.
Stiffness and bearing damping could be influenced, for example, by intermediate layers such as mu metal layers according to U.S. Pat No. 5,196,748, wherein the bearing capacity is also possibly reduced. Therefore, increasing the bearing capacity should be the most important criterion for optimizing.
For this purpose, special materials could be selected by which high bearing capacities could also be achieved in principle.
A crystalline material whose crystal orientation can be aligned based on its anisotropic behavior by a special temperature process is described, for example, in the article “YBaCuO Large Scale Melt Texturing in a Temperature Gradient”, by F. N. Werfel, U. Flögel-Delor, D. Wippich, Inst. Phys. Conf. Ser. No. 158 IOP Publishing Ltd., 1997, pages 821 to 824. This material is also anisotropic in its superconducting and cryomagnetic properties, wherein the currents flow predominantly in parallel CuO planes in the superconducting state. A magnetic bearing was built by way of experiment by means of this material but is not described more fully.
OBJECT AND SUMMARY OF THE INVENTION
It is the primary object of the invention to provide a magnetic bearing having a simple construction and a high bearing capacity which, in particular, is also large enough that stiffness and bearing damping can be optimized in a simple manner. Further, a motor supported in magnetic bearings is to be provided, which motor can be optimized in accordance with the teaching for the magnetic bearing with respect to bearing capacity, stiffness and bearing damping, specifically in such a way that polygon mirrors for scanning light bundles for the display of video images can be operated at a high rotational speed and with high stability.
This object is met in a magnetic bearing of the type mentioned in the beginning in that the first part has a configuration of magnets with which the superconducting material interacts, and the crystal individually or in the plurality of grains is/are directed toward the first part with the normal or normals on the current-carrying planes.
However, another solution to the proposed object is also achieved by a magnetic bearing in which a first part comprises a configuration of magnets and is mounted magnetically relative to a second part, the second part being a Type II superconducting material with high critical current density which can be cooled appreciably below its critical temperature by means of a connected cooling system, wherein the superconducting material contains a plurality of grains, each comprising an anisotropic crystal; in the superconducting state, the current flowing in it (“superconducting current”) flows in every grain in a current-carrying plane of the grain (a-b planes, as they
Deter Christhard
Werfel Frank
Mullins Burton S.
Smith LLP Reed
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