Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
2000-02-04
2001-11-06
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
Reexamination Certificate
active
06313551
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to linear motors. More specifically, the present invention is directed to magnet arrays for a shaft-type linear motor. The magnet arrays provided herein have an improved ratio of flux density to magnet mass.
BACKGROUND
Linear motors are used in a variety of electrical devices. For example, photolithography systems and other semiconductor processing equipment utilize linear motors to precisely position a wafer stage holding a wafer. Alternately, linear motors are used in other devices, including elevators, electric razors, machine tools, metal cutting machines, inspection machines, and disk drives.
A typical shaft-type linear motor includes a magnet array and a coil array. The magnet array includes a plurality of magnets positioned side-by-side. The magnets generate a magnetic field. Each magnet is cylindrical shaped and includes a longitudinal axis and a pair of opposed sides. Typically, each magnet is axially polarized relative to the longitudinal axis. Stated another way, the opposite poles are located on the opposed sides of each of the magnets.
The coil array includes a plurality of coils that are individually supplied with an electrical current. The electric current supplied to the coils generates an electromagnetic field. The electromagnet field interacts with the magnetic field of the magnet array. This causes the coil assembly to move relative to the magnet array. When the coil array is secured to the wafer stage, the wafer stage moves in concert with the coil array.
One of the factors that influences the performance of a shaft-type linear motor is the performance of the magnet array. The performance of the magnet array can be characterized by the ratio of the flux density of the magnetic field of the magnet array to the mass of the magnet array. The ratio between the flux density and the mass shall be referred to herein as the (“flux/mass ratio”). A high flux/mass ratio indicates an efficient magnet array.
In light of the above, an object of the present invention is to provide a magnet array for a linear motor having an improved flux/mass ratio. It is another object of the present invention to provide a method for increasing flux density without significantly increasing the mass of the magnet array. Another object of the present invention is to provide a method for decreasing the mass without significantly decreasing the flux density. Yet another object of the present invention is to provide a linear motor that dissipates less power for a given force.
SUMMARY
The present invention is directed to a magnet array that interacts with a coil array of a motor. A number of embodiments of the magnet array are provided herein. Importantly, in each embodiment, the magnet array has an improved flux/mass ratio. This improves the performance of the motor.
In one embodiment, the magnet array includes one or more magnetic, transverse sections positioned along an array axis of the magnet array. Each transverse section has a polarization that is transverse or radial to the array axis of the magnet array. High energy product, rare earth magnets cannot be easily radially polarized. The present invention solves this problem by assembling a plurality of linearly polarized, individual segments to make each transverse section. More specifically, for each transverse section, the segments are positioned together so that the polarization of the transverse section is transverse or radial to the array axis of the magnet array. Because of this design, the segments and each transverse section can be made of a high energy product, rare earth, magnetic material.
The magnet array can also include one or more magnetic, axial sections positioned along the array axis. Each axial section has an axial polarization relative to the array axis. Preferably, the magnet array includes a plurality of alternating axial sections and transverse sections positioned side-by-side along the array axis. As a result of this design, the magnet array has an improved flux density, without significantly affecting the mass of the magnet array. Thus, the magnet array has an improved flux/mass ratio.
In another embodiment, the magnet array also includes a plurality of magnetic sections positioned side-by-side along the magnet array. Each section includes a first side and an opposed second side. In this embodiment, magnetic material from the magnet array that is not generating flux that interacts with the coil array is removed from each section. More specifically, as a result of the removed material, each section includes a first channel and a second channel. The first channel extends from the first side into only a portion of the section and the second channel extends from the second side into only a portion of the section. Each channel is substantially centered on the array axis. As a result of the channels in each section, the magnet array has a decreased magnet mass, with only a negligible decrease in flux density. Thus, the magnet array has an improved flux/mass ratio.
For the embodiments provided herein, each magnetic section is typically, either substantially, right cylindrical shaped or substantially tubular shaped. Further, the embodiments can be combined. For example, the axial sections and the transverse sections can each include first and second channels to reduce the mass of the magnet array.
The present invention is also directed to a number of methods for manufacturing a magnet array with an improved flux/mass ratio. One method includes the step of manufacturing a magnetic transverse section having a polarization that is substantially transverse to the array axis. Another method includes the steps of providing a magnetic plurality of sections, and creating a first channel in at least one of the sides of at least one of the sections.
Additionally, the present invention is directed to a method for making a linear motor, a method for making an exposure apparatus that forms an image from a first object onto a second object, and a method for making a device utilizing the exposure apparatus.
Importantly, the magnet arrays provided herein have an improved flux/mass ratio. In some embodiments, the magnet array has increased flux density for a given magnet mass. Alternately, in some embodiments, the magnet array has a decreased magnet mass for a given flux density. In either case, the resulting motor is more efficient and dissipates less power for a given force.
REFERENCES:
patent: 4460855 (1984-07-01), Kelly
patent: 5014032 (1991-05-01), Aubert
patent: 5019863 (1991-05-01), Quimby
patent: 5440183 (1995-08-01), Denne
patent: 6043572 (2000-03-01), Nagai et al.
patent: 0878 899 A1 (1998-11-01), None
patent: 6-038501 (1994-02-01), None
patent: 10-313566 (1998-11-01), None
patent: 11-294520 (1999-10-01), None
Translation of Abstract for Japanese Patent 6-038501 (Complete non-translated reference previously submitted and translation of summary previously submitted).
Translation of Abstract for Japanese Patent 11-294520 (Complete non-translated reference previously submitted and translation of summary previously submitted).
Translation of Summary for Japanese Patent 6-038501.
Translation of Summary for Japanese Patent 11-294520.
Publication: IEEE Translations on Magnetics. vol. 35, No. 3. May 1999. “A General Framework for the Analysis and Design of Tubular Linear Permanent Magnet Machines.” By Jiabin Wang, Geraint W. Jewell, and David Howe.
Jones Judson H.
Nikon Corporation
Ramirez Nestor
Roeder Steven G.
Rose Jim
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