US3374037A

US3374037A - Magnetic bearing

Info

Publication number: US3374037A
Application number: US420024A
Authority: US
Inventors: Sanford M Weinberger
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1964-12-21
Filing date: 1964-12-21
Publication date: 1968-03-19
Anticipated expiration: 1985-03-19
Also published as: DE1489951A1; FR1460338A; NL6516625A

Description

March 19, 19 68 s, WE|NBERGER 3,374,037

MAGNETIC BEARING Filed Dec. 21, 1964 Fig 2 54 INVENTOR.

SANFORD M. WEINBERGER /7% MHZ W AGENT United States Patent 3,374,037 MAGNETIC BEARING Sanford M. Weinberger, Philadelphia, Pa., assiguor to General Electric Company, a corporation of New York Filed Dec. 21, 1964, Ser. No. 420,024 4 Claims. (Cl. 308-10) This invention pertains to the art of bearings or other supports which prevent or limit translation but permit rotation. More particularly, it pertains to the use of magnetic fields to limit or oppose displacement of a body from a central location.

In many arts it is desirable to support or center one piece with respect to another while still permitting it to move in ways such as rotation which do not impair the centering; and it is particularly desirable to do this with no or minimal static friction. It has often been proposed to employ magnetic forces to do this. In particular, the forces of magnetic attraction are desirable because they are of very considerable magnitude; for example, permanent magnets can support their own weight. Unfortunately, the inverse square law of force between magnetic poles and its more sophisticated and accurate substitutes alike indicate that it is not possible to achieve stable equilibrium by simply using magnetic attraction of permanent magnets to hold a ferromagnetic armature in a central position. If such an armature were placed in a neutral position, a slight displacement would increase the attraction of the pole approached by the armature and decrease the attraction of the pole from which the armature was moving away; this is just the opposite of the behaviour required for stability. An armature having a permeability less than that of free space, that is, a diamagnetic armature, will tend to move to a stable central position in a suitably shaped magnetic field. Unfortunately, the central forces developed by such a device are proportional to the amount by which the permeability of the diamagnetic material is less than that of free space. This quantity is very small. A bearing employing such material is the subject of application Ser. No. 367,307 entitled Diamagnetic Bearing, filed Apr. 24, -1964, by Davis and Weinberger, and assigned to the assignee of this application.

I have invented a bearing or position-seeking or centering device employing a material having a permeability greater than that of free space to produce magnetic suspension or centering. This invention may be understood by considering a symmetrical permanent magnet immersed in a fluid magnetic medium having a permeability 5 greater than that of free space. If the fluid medium is surrounded by a nonmagnetic container not much larger than the magnetic itself, the magnet will tend to orient itself so that the total energy stored in the magnetic field in the medium is a maximum. Such energy will, in general, be a maximum if the magnet is centered in the container. Since the magnetic medium is fluid, the magnet may be displaced from the central position at low speeds with no frictional resistance; but since the displacement will reduce the total magnetic energy stored in the medium, there will be a restoring force tending to return the magnet to its central position. It should be observed that linearity of the magnetic characteristics of the magnetic fluid will not impair the operativeness of my invention; it is not necessary that the fluid be subject to saturation in order for the total stored magnetic energy to be reduced by displacement of the system from its equilibrium point.

Thus, a general object of my invention is to provide a stable bearing or position-seeking device employing magnetism and a medium having permeability greater than "ice that of free space. Achievement of this general object will produce other beneficial results, such as low frictional resistance to movement, simplicity, economical design, and other objects discernible to those skilled in the art after they have knowledge of my disclosure.

For the better explanation and understanding of my invention, I have provided figures of drawing, in which:

FIG. 1 represents a simple embodiment of my invention particularly useful for exemplifying its underlying principles; and

FIG. 2 represents an embodiment of my invention applied to support a small anemometer movement suitable for measuring very slow air flow by visual counting of the revolutions.

Considering FIG. 1, there are represented two

horseshoe magnets

10 and 12 rigidly connected with each other by a tie bar 14 of non-magnetic material having a distal terminal eye 16. Magnets '10 and 12 are represented as immersed in a solution 18 of permeable magnetic fluid which may consist of'an aqueous solution grams of hydrated ferrous chloride FeCl- .4H O in 400 milliliters of water. Such a solution is known to be paramagnetic. Surrounding the

magnets

10 and 12 and containing the magnetic fluid 18 is a vessel 20, here represented in section, which may be a conventional chemical laboratory glass beaker. The eye 16 of tie bar 14 is represented as connected by a book 22 to an arm 24 which is balanced upon a knife edge bearing 26, and which carries, by means of a hook 28 a balance pan 30 represented as containing two

weights

32 and 34, respectively. The value of the

weights

32 and 34 is such as approximately to balance the immersed weight of the

magnets

10 and 12 and the weight of tie bar 14 so that gaps 36 and 3 8 exist between the poles of magnet 12 and the upper surface of fluid 18, and between the poles of magnet 10 and the lower boundary of fluid 18, respectively. Assuming

magnets

10 and 12 are alike in size, shape and magnetic characteristics, the total magnetic energy stored in fluid 18 will be a maximum when the length of the (double) gap 36 is equal to the length of the (double) gap 38. Consequently a small vertical displacement of tie bar '14 will alter the sizes of the gaps in such a way that there will be a net magnetic force tending to return the tie bar to such a position that the gap lengths will again be equal.

FIG. 2 represents a more general embodiment of my invention which is adapted not merely to resist displacement on one dimension, but in all three. Three

horseshoe magnets

40, 42 and 44 are represented mounted around the periphery of a circle, with their poles facing out. For symmetry, a fourth magnet 45 is located diametrically opposite magnet 44 and thus, in orthographic projection, is concealed by it. Horseshoe magnet 46 is located with its poles pointing upward. Similarly a lower deck of magnets comprises peripherally mounted

magnets

48, 50, 52 and 53 mounted with their poles facing out, magnet 53 being located diametrically opposite magnet 52 and thus being concealed by the latter. Magnet 54 is located with its poles pointing downward. The structure which supports the magnets in these relationships is designated generally by reference number 56; it may be of any material, preferably nonmagnetic, having suitable mechanical properties. A stub shaft 58 rises from structure 56 (conveniently, through a hole in magnet 46) and carries an anemometer 60. It is desirable to provide a float 62 to counteract in part, by its buoyancy in magnetic fluid 64, the weight of the assembly. As may be seen, the walls of container 66 (represented simply as a beaker) fit sufficiently closely around the pole faces of

magnets

40, 42, 44, 45, 48, 50, 52 and 53 so that a slight lateral displacement of the structure (or a slight rotation around a hori- Patented Mar. 19, 1968 4 zontal axis) will alter the volume of magnetic fluid lying between the pole pieces of at least some of the magnets, and will thus alter the stored magnetic energy of the system. This alteration will produce a force tending to undo the displacement.

Magnets

46 and 54 will act to check vertical displacements similarly to

magnets

12 and 14 in the embodiment represented in FIG. 1. Thus the entire assembly will tend to remain centered and upright in beaker 66. Light breezes on anemometer assembly 60 will be able to rotate it slowly, since there are no static frictional forces to require a minimum break away torque before the assembly can rotate. The anemometer is,.of course, simply a convenient example of a device which can benefit by the use of my invention.

While my examples have been of a common and readily available paramagnetic solution, any ferromagnetic fluid if it is homogeneous may be used also. Thus a colloidal suspension of finely divided ferromagnetic particles, if it is sufliciently stable as a colloid so that application of a magnetic field will not cause segregation or locking together of the magnetic particles, may be used as the magnetic fluid specified. My use of the term magnetic fluid thus implies only a permeability greater than that of free space. US. Patent 2,667,237, at column 3, lines 39 through 47 thereof, says:

Magnetiza'ble liquids, particularly a liquid of this nature in which a small quantity of iron is mixed in mercury are known. It is also known that these earlier magnetic liquids were so designed that the physical properties of the material did not change under the influence of a magnetic field; such magnetic fluids were designed solely to respond positionally to the influence of a proximate magnet.

The same patent describes a novel material of completely difierent properties with the statement: The effective viscosity of the fluid will be found to increase (with a properly constituted fluid) as the magnetic field intensity is increased. The older, conventional material may be ditferentiated by being described as having viscosity and fluidity substantially independent of any magnetic field applied to it.

In a technique so broad as the one I here disclose, there are naturally many possible variations, particularly of geometry. The basic criterion whether a given geometry will produce stable centering is that the magnetic energy stored in the device be a maximum in the desired orientation, and therefore, be reduced by any displacement.

The subdivision of the appended claims into subparagraphs is purely for ease in reading and not indicative of any necessary relation or relative importance of the elements recited.

What is claimed is:

1. A position-seeking device comprising:

a source of magnetomotive force having magnetic poles;

a magnetic fluid whose viscosity and fluidity are substantially independent of any magnetic field applied to it surrounding the said poles;

container means bounding the same fluid and generally conforming to the shape of the said source of magnetomotive force.

2. A position-seeking device comprising:

a permanent magnet having poles;

a magnetic fluid whose viscosity and fluidity are substantially independent of any magnetic field applied to it surrounding the said magnet;

a container providing a fluid boundary to form in the fluid symmetrical paths between the poles.

3. A position-seeking device comprising:

a central frame holding a plurality greater than two of horseshoe magnets symmetrically arranged at a first level with their poles facing outward,

a plurality greater than two of horseshoe magnets arranged at a second level with their poles facing outward,

a container having central internal symmetry, containing the said pluralities of horseshoe magnets with gaps between the poles of the said horseshoe magnets and the walls of the said container, and containing a magnetic fluid sufficient in volume to immerse the said pluralities of horseshoe magnets.

4. A position-seeking device as claimed in claim 3, in

which there are mounted on the said central frame a horseshoe magnet having its poles facing upward,

and

a horseshoe magnet having its poles facing downward.

References Cited UNITED STATES PATENTS 2,575,360 11/1951 Rabinow 192-21.5 2,667,237 1/1954 Rabinow 192-21.5 2,806,533 9/1957 Fleck 19221.5 2,896,931 8/1959 Didszuns 192-21.5 2,903,109 9/1959 Didszuns l9221.5 2,983,349 5/1961 Meiklejohn 192-21.5 3,250,341 5/1966 Takahaski 192-215 DAVID X. SLINEY, Primary Examiner.

J, W. GIBBS, L. L. SMITH, Assistant Examiners.

Claims

1. A POSITION-SEEKING DEVICE COMPRISING: A SOURCE OF MAGNETOMOTIVE FORCE HAVING MAGNETIC POLES; A MAGNETIC FLUID WHOSE VISCOSITY AND FLUIDITY ARE SUBSTANTIALLY INDEPENDENT OF ANY MAGNETIC FIELD APPLIED TO IT SURROUNDING THE SAID POLES; CONTAINER MEANS BOUNDING THE SAME FLUID AND GENERALLY CONFORMING TO THE SHAPE OF THE SAID SOURCE OF MAGNETOMOTIVE FORCE.