Railways – Magnetically suspended car – Including means to sense or control car position or attitude...
Reexamination Certificate
2001-11-15
2003-08-05
Morano, S. Joseph (Department: 3617)
Railways
Magnetically suspended car
Including means to sense or control car position or attitude...
Reexamination Certificate
active
06601519
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to an apparatus for transporting a carriage along a track, substantially free of mechanical friction or magnetic drag, utilizing a hybrid support arrangement. The carriage is magnetically supported in a first direction, and the position of the carriage is stabilized in a second direction by passive means.
2. Description of Related Art
Transporting carriages along a track, substantially free of mechanical friction, has long been a goal. Numerous systems to transport passengers and cargo at high speeds or to convey manufactured articles or machine components in manufacturing systems have been devised. Prior art systems may be grouped as either “contacting systems”, i.e., wherein the carriage is in mechanical contact with the track, or “non-contacting systems”, i.e., wherein there is no mechanical contact between the carriage and the track. Each group of systems typically suffers from certain disadvantages.
Contacting Systems—Conventional mechanical track systems which require mechanical contact between the carriage and the track typically employ either slide mechanisms or wheels to transport the carriage. Such systems suffer from significant mechanical friction. Slide mechanisms, which require the use of either hydrostatic or hydrodynamic lubrication, almost always leak and contaminate the equipment. Wheeled systems employ low-friction ball or roller bearings, which also typically require lubricants. Although bearings in wheeled systems may incorporate seals to contain the lubricant, the rolling contact of the wheel with the track usually generates wear particles which ultimately contaminates the equipment.
Non-contacting Systems—Conventional non-contacting transport systems include either aerostatically supported arrangements, commonly referred to by the terms “air-bearing systems” or “gas-bearings”, or magnetically supported arrangements, commonly referred to by the terms “magnetic bearings” or “magnetic levitation systems”.
Aerostatic arrangements—Aerostatic or air-bearings use a thin film of a high-pressure gas, typically air, to support a load. Since gases have very low viscosity, the gaps between elements in such bearings must be small, typically less that about 10 micrometers. In typical linear aerostatic systems, the gas is provided to the moving element or carriage. This restricts the range of motion of the carriage due to the need to supply the high-pressure gas to the carriage from a typically stationary gas source. In such linear aerostatic arrangements, one element is a pad, through which the high-pressure gas is supplied, and the other element is a slide or slideway, on which the pad is supported by the film of gas. The pad may be perforated, slotted, or made of a porous material to distribute the gas over the face of the pad. In such arrangements, the extremely small clearances require that the surface of the pad closely conform to the slideway. This is typically accomplished by making the both the pad and the slideway extremely flat. Even when the pad is articulated to permit it to follow the surface of the slideway, only very gradual curves of very large radius can be accommodated.
Magnetically Supported Arrangements—Numerous magnetic levitation arrangements using permanent magnets and electromagnets, or combinations of the two, are known. British Patent 867,045 and British Patent 1,035,764 are typical examples of such prior art arrangements.
In electromagnetic field theory, it has long been known that magnetic levitation arrangements, using only permanent magnets, cannot be simultaneously stable in three orthogonal directions. Earnshaw first published his findings in 1849 and his work is popularly known as “Earnshaw's Theorem”. The term “magnetic stability” is usually defined in mathematical terms using the convention of a Cartesian coordinate system, i.e., orthogonal x, y, and z coordinates. For a system having a magnetic restoring force F and a displacement along the y-axis, “magnetic stability” means that the derivative of the magnetic restoring force F with respect to the displacement direction shall be negative, i.e., for a displacement along the y-axis, dF
y
/dy<0. Since Earnshaw's Theorem requires that the sum of the force derivatives be equal to zero, i.e., dF
x
/d
x
+dF
y
/dy+dF
z
/dz=0, it can be seen that all three derivatives can not simultaneously be negative.
Active stabilization systems employing position sensing and feedback control have been employed to overcome the limitations imposed by Earnshaw's Theorem. A prior art system, such as that described in U.S. Pat. No. 4,142,469, is typical of an actively stabilized magnetic levitation arrangement. This patent discloses a tracked vehicle system employing a combination of permanent magnets and one or more electromagnets, the electromagnets being energized by the feedback control system. The electromagnets are employed to control the magnet flux, which controls the lifting force, and they are used to maintain lateral position control for tracking the vehicle along the desired path.
FIG. 1
shows a system
2
from which the principles underlying an actively stabilized magnetic levitation arrangement may be appreciated. Permanent magnets
3
for a carriage
4
and permanent magnets
5
for a track base
6
levitate the carriage
4
in a first direction. The position of the carriage
4
is stabilized in a second direction by the use of carriage position or gap sensors
7
and an active carriage position feedback mechanism to energize one or more electromagnets
8
. An active stabilization system, as shown in
FIG. 1
, results in increased complexity and cost of the levitation system.
Prior art magnetically levitated transport systems typically suffer from a significant amount of magnetic drag. Magnetic drag, while somewhat analogous to mechanical friction, changes in magnitude as the carriage speed changes. Additional power must therefore be supplied by the drive system to overcome the magnetic drag, as well as the aerodynamic drag which results from air resistance.
U.S. Pat. No. 5,809,897, issued on Sep. 22, 1998, discloses an electromagnetic induction ground vehicle levitation guideway for a vehicle having magnets for providing magnetic levitation of the vehicle. The vehicle is adapted to travel in a longitudinal direction along the guideway. The guideway comprises a beam support member for supporting the weight of the vehicle, and breakaway energy absorption structure mounted to the beam support member for absorbing kinetic energy from the magnetic levitation vehicle in the event of loss of magnetic levitation.
U.S. Pat. No. 5,388,527, issued on Feb. 14, 1995, discloses a multiple magnet apparatus for positioning a magnetic levitation ground vehicle that travels along a guideway at a selected position along an axis of perturbation relative to the guideway. The vehicle carries a first magnet, having its poles aligned perpendicular to the travel path of the vehicle and to the axis of perturbation, and second magnet, with its poles aligned parallel and opposite to the poles of the first magnet. The second magnet is adjacent to the first, and spaced away along the axis of perturbation. The guideway may carry conductors to interact with the vehicle magnetic fields to maintain the vehicle at the vertical position. The conductor may be a ladder, discrete coils, or a helical meander winding. The conductors may be oriented either vertically or horizontally, depending on whether the positioning device is used for suspension, or guidance.
U.S. Pat. No. 5,440,997, issued on Aug. 15, 1995, discloses a magnetic suspension transportation system for a vehicle/rail transportation system, where interacting sets of magnets are positioned on the vehicle and the rail to suspend the vehicle from the rail and permit low friction, non-contacting movement along the rail. Also, laterally facing air castors are provided for lateral support. The transportation system is stabilized in two directions by magne
Bindloss, Jr. William
Forrest, Jr. Albert White
Suna Andris
E. I. du Pont de Nemours and Company
Magee Thomas H.
McCarry, Jr. Robert J.
Morano S. Joseph
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