Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1998-10-02
2001-02-13
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C414S935000
Reexamination Certificate
active
06188147
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to magnets and more particularly to magnet arrays in electric motors.
BACKGROUND ART
Electric motors are used in a variety of electrical equipment. For example, linear electric motors produce electrical power propelling an armature in one dimension. Wafer stages utilize linear electric motors to position a wafer during photolithography and other semiconductor processing.
Electric motors are used in a variety of electrical equipment. For example, linear electric motors produce electrical power propelling an armature in one dimension. Wafer stages utilize linear electric motors to position a wafer during photolithography and other semiconductor processing.
A typical one-dimensional linear electric motor has a magnet track with pairs of opposing magnets facing each other. (U.S. Pat. No. 4,151,447, Linear Motor, issued to Johann von der Heide and Georg F. Papst on Apr. 24, 1979 discusses one-dimensional linear electric motors and is incorporated by reference herein in its entirety.) Within spaces between the pairs of opposing magnets, an armature moves. The armature has windings of a conductor which are connected to an electrical current. When the electrical current is turned on, the electrical current interacts with the magnetic fields of the magnet pairs to create force on the armature. When the armature is attached to a wafer stage, the wafer stage experiences the same force which can be used to cause movement.
In a multiphase motor, the armature has various windings grouped into phases. The phase groups are selectively pulsed with electric current to create a more efficient motor. As the armature moves within the magnet track as a first group of coils is pulsed, the first group moves out of its optimal position between the pairs of magnets. Then, it becomes more efficient to pulse a second group of windings. More phase groups are theoretically more efficient since a more even application of force and utilization of power input is maintained. However, each additional phase group complicates a timing of the pulses to the various phase groups. Presently, three-phase motors and armatures have gained favor in balancing these considerations.
Linear two-dimensional motors are also used in manufacturing. (U.S. Pat. No. 4,654,571, Single Plane Orthogonally Moveable Drive System issued to Walter E. Hinds on Mar. 31, 1987 (Hinds) and U.S. Pat. No. 4,535,278, Two-Dimensional Precise Positioning Device for Use in a Semiconductor Manufacturing Apparatus issued to Teruo Asakawa on Aug. 13, 1985 (Asakawa) discuss two-dimensional linear electric motors and are incorporated by reference herein in their entirety.) The motors are two-dimensional in that they have two-dimensional arrays of magnets and armatures instead of magnet tracks and one-dimensional armatures. However, the magnet arrays and two-dimensional armatures may move with respect to each other in more than two dimensions depending upon the design. Conventional two-dimensional linear motors typically have an array of magnets and an armature having one or more coils on one side of the array of magnets. When attached to part of a two-dimensional linear motor, a platform can be moved in two or more dimensions by the motor. For example, a wafer stage in semiconductor processing equipment may be attached to an armature or magnet array of a two-dimensional motor, and the two-dimensional motor would control positioning of the wafer stage.
A problem with conventional magnet arrays is their relatively low magnetic flux-to-mass ratio. Without a backing by a magnetically permeable material, the flux is fairly low. A magnetically permeable backing permits completed flux paths between magnets having the same polarity. Of course, the flux of the array is greater when the flux paths are completed by the magnetically permeable backing. However, magnetically permeable materials, such as iron, are relatively heavy. If the flux paths between the magnets of the same polarity could still be completed without using a heavy magnetically permeable backing, the magnetic flux-to-mass or weight ratio would be improved. For electric motors having moving magnets instead of moving coils, this reduction in mass or weight would improve the efficiency of the motors.
SUMMARY OF THE INVENTION
The invention features a magnet arrangement useable in a magnet array. The magnet arrangement includes a plurality of wedge magnets arranged in a reference plane. Each wedge magnet contains a material polarized in a first direction at a non-zero non-perpendicular angle with respect to a portion of its surface and the reference plane. The arrangement also includes a plurality of other magnets polarized in a second direction. The wedge magnets are in proximity to the other magnets, wherein the first and second directions of polarization are at an angle with respect to each other. A magnetic flux path is formed through the other magnet and the wedge magnet.
In some embodiments, a magnet arrangement has each wedge magnet with a magnetic flux polarized at the same angle with respect to a reference direction. The magnets are juxtaposed each other such that their respective magnetic fluxes combine to form a net magnetic flux in a reference direction perpendicular to the reference plane and a negligible magnetic flux along the reference plane.
The invention also features an electric motor. The electric motor has a coil array and the inventive magnet array. The magnet array includes wedge magnets. In some embodiments, an arrangement of magnets forms a concave surface. Each magnet in the arrangement has a magnetization direction at an angle with respect to a reference direction, but the arrangement's net magnetic flux is along the reference direction.
The invention's wedge magnets have an advantage that they can be appropriately arranged to form an array with a greater flux-to-mass ratio than conventional magnet arrays. In some embodiments, a magnetically permeable backing of a conventional magnet array can be replaced by magnetically impermeable material such as a ceramic. Magnetically impermeable materials such as ceramics and plastics generally have lower mass densities than magnetically permeable materials such as iron. By completing flux paths between wedge magnets via transverse magnets with the present invention instead of between conventional magnets via the magnetically permeable backing as in conventional designs, the magnetic flux is improved while the array's mass decreased. Flux-to-mass ratios of approximately 1.5 to 2 times previous flux-to-mass ratios of conventional magnet arrays of comparable size are anticipated.
In an electric motor where a magnet array moves in response to current commutation of coils, the improved flux-to-mass ratio of the inventive magnet arrays have a further advantage of improved electric motor efficiency. As measured in I
2
R dissipation, the range of flux mass ratios stated above implies an improved motor efficiency of approximately 30% to 50% compared with conventional electric motors.
These and other objects, features, and advantages of the invention will become readily apparent to those skilled the art upon a study of the following drawings and a reading of the description of the invention below.
REFERENCES:
patent: Re. 27289 (1972-02-01), Sawyer
patent: Re. 27436 (1972-07-01), Sawyer
patent: 3851196 (1974-11-01), Hinds
patent: 4151447 (1979-04-01), von der Heide et al.
patent: 4535278 (1985-08-01), Asakawa
patent: 4555650 (1985-11-01), Asakawa
patent: 4654571 (1987-03-01), Hinds
patent: 4958115 (1990-09-01), Miller
patent: 5196745 (1993-03-01), Trumper
patent: 5260580 (1993-11-01), Itoh et al.
patent: 5334892 (1994-08-01), Chitayat
patent: 5477304 (1995-12-01), Nishi
patent: 5528118 (1996-06-01), Lee
patent: 5623853 (1997-04-01), Novak et al.
patent: 5715037 (1998-02-01), Saiki et al.
patent: 5723929 (1998-03-01), Niimi
patent: 5773837 (1998-06-01), Nakasuji
patent: 07060581 (1995-07-01), None
patent: WO98/49763 (1998-11-01), None
David L. Trumper, Won-jong Kim, Mark E. W
Gery Jean-Marc
Hazelton Andrew J.
Jones Judson H.
Morrison & Foerster / LLP
Nikon Corporation
Ramirez Nestor
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