Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1999-08-10
2002-03-12
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
Reexamination Certificate
active
06355993
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to motors, and more specifically to high performance linear motors.
BACKGROUND
Linear motors are commonly used, for example, in micro-lithographic instruments for positioning objects such as stages, and in other precision motion devices. A linear motor uses electromagnetic force (normally called Lorentz force) to propel a moving part.
In
FIG. 1A
(reproduced from
FIG. 1
of Itagaki et al. U.S. Pat. No. 4,758,750, incorporated herein by reference in its entirety) a conventional linear motor includes magnets
2
which form one magnet pair and create a magnetic field in between. The magnetic poles N (north) and S (south) are shown. Similarly, the adjacent magnets form another magnet pair and create a magnetic field of opposite polarity. The width of two adjacent magnets plus two spaces between the magnets defines the magnetic pitch PM of the motor. The magnetic flux direction across a gap
4
is indicated by arrows
7
and
7
a
. A moving coil unit
12
has electrically conductive wires laid out in a direction perpendicular to the plane of the figure. An electric current is passed through the wires, in a direction either into the plane of the figure or out of the plane of the figure.
As those skilled in the art will recognize, a wire carrying an electric current in a magnetic field creates Lorentz force, the formula of which is:
F=NLB×I
Where F represents Lorentz force, N the number of wires, B the magnetic flux, and I the electric current. For a coil with a given length L and magnetic flux B, to maximize force F, one has to maximize the number of wires N and current I. The above formula determines both the magnitude and the direction of force F, since force F, magnetic flux B, and current I are all represented as vectors, and the symbol “×” represents vector cross product multiplication. As those skilled in the art will recognize, a task in motor design is to maximize F/{square root over (P)}, or the “motor constant” where
F/{square root over (P)}=NLBI/
(
{square root over (I
2
R
+L )})=
NLB/{square root over (R)}.
In the above expression, F is the scalar value of vector F, while P is the amount of power consumed by the motor. For each particular design configuration, the motor constant is directly related to the “copper density,” which is defined as the total wire cross sectional area as a percentage of the entire coil cross section. (The coil wires are often made of copper.)
In the configuration shown in
FIG. 1A
, the Lorentz force created by the current in coil unit
12
causes the coil to move. While traveling in the right direction of
FIG. 1A
, coil unit
12
eventually leaves the field of magnets
2
and enters the field of the adjacent magnets. Since this second magnetic field has a reversed polarity relative to that of the first magnetic field, the current in coil unit
12
must reverse in polarity so as to maintain the direction of Lorentz force. The reversal of the direction of the electric current is accomplished by a commutation circuit familiar in the art (not shown).
FIG. 1B
, reproduced from
FIG. 2
of Itagaki et al., is a cross-sectional view of the conventional linear motor of
FIG. 1A
, viewed along the line II—II in FIG.
1
A. In such a linear motor at the coil head area
12
′, the coil heads are stacked on top of each other. This arrangement requires a wide head area
12
′.
Such a conventional linear motor has several disadvantages, one of the which is the difficulty of installation and removal. As shown in
FIGS. 1A
,
1
B, a magnetic track is formed by magnets
2
and the magnetic side rails
3
. The magnetic track has a wide head area configured to match the shape and size of the wide head area
12
′ of coil assembly
12
. To remove coil assembly
12
from the magnetic track, coil assembly
12
must slide away from the magnetic track in a direction perpendicular to the surface of the paper. Since the equipment (e.g. an X-Y stage) attached to coil assembly
12
is often heavy and difficult to handle, special tools are typically required during installation and removal of coil assembly
12
.
Another disadvantage of a conventional linear motor coil is its low efficiency.
FIG. 2
shows a cross sectional view of a linear motor coil taken at a cross section perpendicular to the wire direction. Since the wire is not close packed, air gaps
50
inevitably result, substantially lowering the conductor density of the coil. As discussed above, lower conductor density often corresponds to lower motor efficiency.
It is therefore desirable to provide a linear motor having a motor coil with improved efficiency, low heat dissipation, and easy installation.
SUMMARY
A motor in accordance with the invention overcomes the above and other drawbacks of conventional linear motors. According to the invention, a linear motor comprises a motor coil in cooperation with an associated magnetic track. The motor coil includes a linear assembly of coil units, each similar to the other. Each coil unit has an electrically conductive wire wound into a closed band in a predetermined number of layers, typically a single layer. The shape of the closed band is geometric polygonal, such as diamond shaped, hexagonal, or double diamond shaped, having inner edges surrounding a void. Some embodiments comprise a row of parallelogram shaped closed bands folded into a row of double diamond shaped coil units. In some embodiments, the width of the void is an integral multiple of the width of the closed band.
The coil units are made e.g. of flex circuit material or by winding electrically conductive wires in a racetrack or folded tip fashion. In some embodiments the width of a coil unit is equal to the magnetic pitch of the associated magnetic track. In other embodiments the width of a coil unit is equal respectively to one-half or two-thirds of the magnetic pitch.
Advantageously this arrangement provides high electrical efficiency and ease of disassembly. The coil units are stacked together in a partially overlapped fashion to form a row of coil units in the motor coil so that the number of layers of wire in the useful area is substantially uniform across the entire coil. Unlike the wide end coil shape of Itagaki et al., the present shape is more planar (not flared out at the end) and so has a flat cross section that allows the coil to be easily removed from and installed in the magnetic track.
REFERENCES:
patent: 3732448 (1973-05-01), Schiethart
patent: 4736127 (1988-04-01), Jacobsen
patent: 4758750 (1988-07-01), Itagaki et al.
patent: 4760294 (1988-07-01), Hansen
patent: 4767954 (1988-08-01), Phillips
patent: 4794284 (1988-12-01), Buon
patent: 5197180 (1993-03-01), Mihalko
patent: RE34674 (1994-07-01), Beakley et al.
patent: 6040650 (2000-03-01), Rao
patent: 0 331 463 (1989-09-01), None
patent: 47-10072 (1972-05-01), None
patent: 49-88005 (1974-08-01), None
patent: 59-60885 (1984-04-01), None
patent: 64-83264 (1989-03-01), None
patent: 2-23057 (1990-01-01), None
patent: 4-150760 (1992-05-01), None
patent: 6-36336 (1994-05-01), None
Hamamatsu webpage, Photomultiplier Tubes (PMTs), Mar. 1, 2000, 1 pg.
B. F. Levine et al., “Near Room Temperature 1.3 &mgr;m Single Photon Counting With a InGaAs Avalanche Photodiode”,Electronic Letters, 5Jul. 1984, vol. 20, No. 14, pp. 596-598.
F. Zappa et al., “Solid-state single-photon detectors”,Opt. Eng. 35(4) 938-945 (Apr. 1996).
S. Takeuchi et al., “Development of a high-quantum-efficiency single-photon counting system”Applied Physics Letters, vol. 74, No. 8, Feb. 22, 1999, pp. 1063-1065.
A. Peacock et al., “Single optical photon detection with a superconducting tunnel junction”,Naturevol. 381, May 9, 1996, pp. 135-137.
S. Komiyama et al., “A single-photon detector in the far-infrared range”,Naturevol. 403, Jan. 27, 2000, pp. 405-407.
R. J. Schoelkopf et al., “A Concept for a Submillimeter-Wave Single-Photon Counter”,IEEE Transactions on Applied Superconductivity, vol. 9, No. 2, Jun. 1999, pp. 2935-2939.
Ortiz et al., “Design of the opto-electronic receiver for deep
Hazelton Andrew J.
Novak W. Thomas
Jones Judson H.
Klivans Norman R.
Nikon Corporation
Ramirez Nestor
Skjerven Morrill & MacPherson LLP
LandOfFree
Linear motor having polygonal shaped coil units does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Linear motor having polygonal shaped coil units, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Linear motor having polygonal shaped coil units will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2876305