Electrical generator or motor structure – Dynamoelectric – Linear
Reexamination Certificate
1999-08-23
2001-07-31
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Linear
C310S013000, C310S014000, C310S156030, C310S089000, C310S091000
Reexamination Certificate
active
06268667
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to electromagnetic apparatus for producing linear motion. One means of producing linear motion directly by electromagnetic means is the linear electric motor devised by Professor Laithwaite of Imperial College, London. This device can be considered as a conventional rotary electric motor in which the stator and armature have been split axially and unrolled. Although the device is very effective, it does have the disadvantage that considerable unbalanced attractive forces exist between the stator and moving armature, so that some means such as a track or wheeled carriage has to be used to maintain a separation between the stator and the armature.
A second form of linear motor has a cylindrical topology like a conventional electric motor but with the magnetic field-producing elements disposed transversely around the longitudinal axis so that the magnetic fields alternate in polarity along the axis of the motor.
Examples of such linear motors are shown in OLS 2,229,711; EP 0 221 228; U.S. Pat. No. 4,714,300; EP 0 280 743; EP 0 314 493 and WO 93/01646.
OLS 2,229,711 discloses a DC motor in the form of a piston with a single coil which moves in a cylinder under the action of magnetic fields which are generated by the successively energizing and de-energizing ring-shaped coils spaced axially along the inner surface of the cylinder surrounding the piston.
EP 0 221 228 discloses an arrangement in which both linear and rotary motion of a shaft are produced, the linear motion of the shaft being produced by circumferential coils and the rotary motion by axial peripheral coils.
U.S. Pat. No. 4,714,300 discloses a pressure modulator for use in anti-skid brake systems in which a plunger is made to oscillate longitudinally in a chamber under the influence ofa longitudinally-varying magnetic field pattern generated between a winding on the inside of an outer portion of the chamber and a number of magnets disposed around the periphery of the plunger, or vice versa.
EP 0 280 743 discloses a screw for an injection molding machine which is moved linearly by the interaction between magnets on a shaft forming part of the injection screw and a number of coils surrounding the shaft and to which a three-phase alternating current is applied.
EP 0 314 493 discloses another arrangement in which a shuttle is caused to oscillate in a chamber by the interaction between two magnetic fields, one generated by a winding on the shuttle and the other by a winding forming part of the chamber wall.
WO 93/01646 discloses another arrangement in which a piston is driven longitudinally in a cylinder by means of the interaction between two radial magnetic fields, one generated by a series of circumferential coils forming part of the cylinder wall and the other by a plurality of magnets forming part of the piston, or vice versa. For many purposes, the arrangements disclosed in WO 93/01646 are quite satisfactory. However, if the invention of WO 93/01646 is to be used as a combined fluid/electromagnetic actuator, the need to provide fluid-tight seals both on the piston and where the piston rod emerges through an end wall of the cylinder is a disadvantage, particularly as heavy and off-axis loads will tend to bend the piston rod out of true. Also, the solid construction of the piston and piston rod means that larger sizes of the device will become very heavy.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the prior art.
It is another object of the present invention to provide an improved electromagnetic apparatus for producing linear motion which is lighter in construction and which has increased transverse stiffness.
Briefly stated, the present invention provides sealed telescoping tubes that are electromagnetically and fluidly actuated to provide linear motion and withstand loading. One of the tubes may be connected to a pressure or vacuum source, and the other sealed to a fixture to provide variable volume load augmentation in addition to electromagnetic actuation. Alternatively, both tubes may be sealed to provide a pneumatic or hydraulic spring with electromagnetic actuation, and the sealed tubes may also be connected to a pressure or vacuum source for load augmentation. A bearing may be used in conjunction with the seal between the tubes to provide resistance to traversal loads. The electromagnetic actuation includes a helical arrangement of coils or permanent magnets to provide linear motion or resistance. The coils can be arranged to be connected to a conventional multi-phase motor drive.
According to an embodiment of the present invention there is provided an electromagnetic apparatus for producing a linearly-directed force, comprising at least two tubular members adapted to slide telescopically, one within the other, means for producing a first magnetic field, the polarity of which alternates along at least a portion of the axial length of the inner tubular member, means for producing a second magnetic field the polarity of which alternates along at least a portion of the axial length of the outer tubular member, and means for varying at least one of the magnetic fields so as to cause the magnetic fields to interact to provide an axial force tending to cause relative motion between the tubular members.
Preferably there is provided at least one seal between the inner surface of the outer tubular member and the outer surface of the inner tubular member so as to prevent the access of harmful environmental components to those parts of the device where relative motion occurs.
The outer ends of the tubular members may include flanges by means of which they can be attached to components of another structure.
The device may be so constructed that the inner tubular member carries an array of permanent magnets and the outer tubular member an assembly of coils which are selectively energized to vary one of the magnetic fields, or vice versa. Other arrangements are possible, for example, both tubular members may carry electrical coils, or the permanent magnets may be replaced by low-reluctance magnetic elements or by a conducting sleeve in which a pattern of eddy currents is induced.
According to a particular aspect of the present invention there is provided an electromagnetic apparatus for producing a linearly-directed force comprising two cup-shaped members, one fitted within the other and adapted to allow relative motion therebetween, means for producing a first magnetic field, the polarity of which alternates along at least a part of the axial length of one of the cup-shaped members, means for producing a second magnetic field the polarity of which alternates along at least a part of the axial length of the other cup-shaped member, and means for varying at least one of the magnetic fields so as to cause the magnetic fields to interact to provide an axial force tending to cause relative motion between the cup-shaped members.
Preferably, there are seals interposed between the cup-shaped members so that they form an enclosed space and one of the cup-shaped members has an opening therein so as to enable fluid to pass into and out of the enclosed space.
The device may be constructed as a moving-coil or moving-magnet device as desired, but in a preferred arrangement the outer cup-shaped member has an electromagnetic element consisting of a plurality of annular coils separated by ferromagnetic spacers which are arranged to present a constant reluctance to a radially-directed magnetic field originating from a magnetic field-generating element associated with the inner cup-shaped element. Preferably the magnetic field generating element associated with the inner cup-shaped element is a plurality of permanent magnets.
According to another embodiment of the present invention, there is provided an apparatus for producing linearly-directed force, comprising: a plurality of tubular members, at least two of the tubular members are fittable one within another and movable relative to each other in an axial direction, mean
Advanced Motion Technologies LLC
Morrison Law Firm
Mullins Burton
LandOfFree
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