Method And Apparatus For Stabilizing Permanent Magnets

Abstract

Method and apparatus for stabilizing permanent magnets, that is, reducing the flux density of a magnet in a predetermined direction to a preselected value. The magnet first is magnetized in the desired direction to a flux density greater than the preselected value and preferably to saturation. Thereafter, the magnet is progressively magnetized in a perpendicular direction and this correspondingly reduces the flux density in the desired direction. This magnetization in the perpendicular direction continues until the flux density in the desired direction has been reduced to the preselected value.

Description

BACKGROUND OF THE INVENTION

In many commercial uses, it is important that the magnetization of a permanent magnet in the desired direction be controlled accurately at a preselected value of flux density. One way of accomplishing this is to magnetize the magnet to a flux density which is greater than the preselected value and then stabilize the magnet, that is, reduce the flux density to the preselected value.

SUMMARY OF THE INVENTION

The present invention contemplates the provision of a simple and inexpensive method for stabilizing a permanent magnet accurately to a preselected value of flux density. More particularly, according to the invention, the magnet is magnetized in the desired direction to a flux density greater than the preselected value and then the magnet is progressively magnetized in a perpendicular direction. Such magnetization in the perpendicular direction progressively reduces the flux density of the magnet in the desired direction and is continued until the flux density in the desired direction has been reduced to the preselected value. The invention also resides in the novel apparatus for stabilizing the magnet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a reed switch which is usable with a permanent magnet stabilized in accordance with the present invention.

FIG. 2 is a perspective view of the permanent magnet assembly.

FIG. 3 is a side view of the magnet assembly.

FIG. 4 is an enlarged perspective view of the permanent magnet.

FIG. 5 is a side view of the permanent magnet assembly coacting with a reed switch.

FIG. 6 is a view similar to FIG. 5 but shows the parts in a moved position.

FIG. 7 is a graph showing the hysteresis loops of the magnet shown in FIG. 4.

FIG. 8 is a perspective view of the magnet assembly for stabilizing the permanent magnet.

FIG. 9 is an enlarged fragmentary sectional view taken along the line 9--9 in FIG. 8.

FIG. 10 is a schematic side view of the magnet assembly shown in FIG. 8.

FIG. 11 is a perspective view of the magnet assembly with the addition of means for carrying the magnet to be stabilized.

FIG. 12 is an enlarged fragmentary sectional view taken along the line 12--12 in FIG. 11.

FIG. 13 is an enlarged perspective view of the carriage for supporting the magnet to be stabilized.

FIG. 14 is an enlarged fragmentary end view of the carriage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of illustration, the invention is shown in the drawings in connection with a permanent magnet 10 especially suitable for actuating a reed switch 11. As is conventional, the reed switch is normally open and comprises two contacts 12 disposed within a sealed glass tube 13 and supported on the ends of individual reeds 14. The latter project through the sealed ends of the tube and, outside the tube, the reeds form terminals 15. Herein, the magnet 10 is an elongated ceramic bar magnet which is magnetized along the N-S axis (the arrow 16 in FIG. 3) so that one-half of the magnet is a north pole and the other half is a south pole as illustrated in FIG. 3. A steel plate 17 is secured to the back of the magnet to provide a return path for the flux of the magnet.

In use, as an example, the magnet 10 initially is spaced from the reed switch 11 a distance from the axis a of the switch greater than a preselected distance such as the distance d as shown in FIG. 5 and, when the magnet is in this position, it is ineffective to close the contacts 14. When the magnet is moved laterally toward the switch until it is spaced from the axis a by the distance d (FIG. 6) the contacts close because they are sufficiently within the flux path (shown in broken lines in FIGS. 5 and 6) of the magnet so as to be drawn together.

In many commercial applications of permanent magnets, it is important that the strength, or flux density, of the magnet be at a precise, preselected value. Thus, when used with the reed switch 11, for example, the magnet 10 should close the contacts 14 when it is spaced exactly the distance d from the axis a of the switch. Closing of the contacts should not occur when the spacing is greater nor should closing be deferred until the spacing is less than the distance d.

The present invention contemplates a new and improved method of precisely magnetizing a permanent magnet to a preselected strength of flux density and is based upon a novel manner of stabilizing the magnet. Stabilizing is taking a magnet which has been magnetized along the north-south axis to a strength above the preselected value, preferably to saturation, and then reducing the strength along this axis until it has reached the preselected value. The invention utilizes the concept that the volume of material which makes up the magnet 10 is capable of producing a fixed maximum amount of magnetic energy irrespective of the direction in which the magnet is magnetized. Thus, if a magnet is magnetized in a first direction and then is gradually magnetized in a perpendicular direction, the magnetic force in the first direction will be progressively reduced. In accordance with the present invention, therefore, the magnet 10 is magnetized along the desired axis to a flux density, and preferably to saturation, which is above the desired or preselected value and then the magnet is gradually magnetized in a perpendicular direction until the flux density along the desired axis has been reduced to the preselected value.

For example, the magnet 10 in FIG. 4 is magnetized to saturation along the N-S axis. The flux density of the magnet in this direction is illustrated by the curve 18 in FIG. 7 which is the second or operating quadrant of the hysteresis loop of the magnet 10 in the N-S direction. The magnet then is gradually magnetized in a perpendicular direction, that is, along either the axis C-D or the axis G-H. This gradually reduces the flux density in the N-S direction as indicated by the diminishing size of the hysteresis loops illustrated by the broken line curves numbered 1 through 7 in FIG. 7. Thus, if the desired flux density of the magnet 10 in the N-S direction is represented by the curve 3, the magnet is magnetized in the C-D or G-H direction until this curve is reached. As will be explained later in detail, a conventional Hall probe may be used to measure the flux density in the N-S direction and to indicate when the proper value has been obtained.

In accordance with another aspect of the invention, the magnet 10 is magnetized in a perpendicular direction, that is, the C-D or G-H direction, through the use of a permanent magnet assembly 19 (FIG. 8) with pole faces 20 which define a tapered airgap 21. While the magnetic potential between the pole faces is constant throughout the length of airgap, the magnetizing force (Oersteds) of the assembly 19 progressively increases from the wide end of the gap to the narrow end. As illustrated herein, stabilizing is accomplished by magnetizing the magnet 10 in the C-D direction. Thus, the magnet first is magnetized to saturation along the N-S axis and then, as shown in solid lines in FIG. 8, it is placed at the wide end of the airgap 21 with the N-S axis perpendicular to the force lines 22 of the assembly 19 and the C-D axis parallel to these force lines (see also FIG. 10). Without changing this orientation, the magnet is moved into the airgap (see broken line position in FIG. 8). Due to the increasing magnetizing force, the magnet is progressively magnetized in the C-D direction. At the same time, the flux density in the N-S direction correspondingly decreases and is measured by a Hall probe 23 connected to a meter 24 by leads 25. When the meter indicates that the flux density has been reduced to the preselected value, the magnet is removed from the assembly 19 either sidewise or back through the wide end of the airgap.

In the present instance, the magnet assembly 19 includes a ceramic permanent magnet 26 with flat plates 27 abutting the magnetic ends of the magnet. The plates are made of magnetic material such as cold rolled steel and project beyond one side of the permanent magnet. Attached to the inner sides of the overhanging portions of the plates 27 are wedge-shaped pole pieces 28 which also are made of a magnetic material such as cold rolled steel. The pole faces 20 are formed on the pole pieces 28 which thus define the tapered airgap 21.

As illustrated in FIGS. 11 through 14, the magnet assembly 19 may include a carriage 29 to hold the magnet 10 being stabilized and to move the magnet into the airgap 21. To support the carriage 29, brackets 30 and 31 are secured to the ends of the magnet by bolts 32 which project through horizontal slots 33 in the brackets and are threaded into the magnet, the slots 33 permitting the brackets to be adjusted for purposes of alignment. The carriage 29 is slidably supported on guides or rods 34 spanning the brackets 30 and 31 and projecting through downwardly facing arcuate grooves 35 formed on the sides of the carriage (FIGS. 13 and 14). The latter is held on the rods by plates 36 which project under the rods and are fastened to the underside of the carriage by screws 37. The ends of the rods 34 project into vertical slots 38 (FIG. 11) in the brackets 30 and 31 and are held in place by setscrews 39 which are used to aline the rods 34 and center the carriage 29 relative to the airgap 21.

The carriage 29 is slid along the rods 34 into and out of the airgap 21 by a wire 40 which is secured at one end 41 (FIG. 12) to the carriage and extends parallel to the rods through a hole 42 in the bracket 30 and around a pulley 43 journaled in a housing 44 on the bracket. From the pulley, the wire extends back through a second hole 45 in the bracket 30, through a hole 46 in the carriage, through a hole 47 in the bracket 31, around a second pulley 48 and through a second hole 49 in the bracket 31, the end 50 of the wire also being secured to the carriage. The pulley 48 is fast on a shaft 51 which is journaled in a housing 52 on the bracket 31. Also fast on the shaft 51 is a worm wheel 53 which meshes with a worm 54 on the inner end of a perpendicular shaft 55 which is journaled in the housing 52. The outer end of the shaft 55 carries a knob 56 which may be turned manually to move the carriage into and out of the airgap 21.

On the upper side of the carriage 29 is a flat boss 57 (FIG. 13) formed with an elongated slot 58 of square cross section. The slot is perpendicular to the direction in which the carriage travels and is sized to receive the magnet 10 to be stabilized. Inside the boss 57 is the Hall probe 23 and the leads 25 between the probe and the meter 24 are disposed in a flexible conduit 59.

With the foregoing arrangement, the magnet 10 first is magnetized, preferably to saturation, in the N-S direction. Then, with the carriage 29 outside the airgap 21 and next to the large end thereof, the magnet is placed in the slot 58. Next, the knob 56 is turned to advance the carriage into the wide end of the airgap and toward the narrow end thereby progressively magnetizing the magnet 10 in the C-D direction and reducing the flux density in the N-S direction. When the meter 24 indicates that the flux density in the N-S direction has been reduced to the preselected value, the carriage 29 is backed out of the airgap 21 and the stabilized magnet 10 is removed.

Claims

I claim as my invention:

1. A method of magnetizing a piece of magnetic material to a preselected flux density along a predetermined direction relative to said piece, said method comprising the steps of magnetizing said piece in said predetermined direction to a flux density value above said preselected value, thereafter moving said piece into a progressively increasing magnetic field with the piece oriented relative to the field to progressively magnetize said piece in a direction perpendicular to said predetermined direction to progressively reduce the flux density in said predetermined direction, and removing said piece from said field when the flux density in said predetermined direction has been reduced to said preselected value.

2. A method of magnetizing a piece of magnet material to a preselected flux density value along a predetermined direction and using a permanent magnet having an airgap which tapers progressively from a wide end to a narrow end, said method comprising the steps of magnetizing said piece along said predetermined direction to a flux density value above said preselected value, said predetermined direction thereby becoming the axis between the north and south poles of the magnetized piece, placing said piece at the wide end of said airgap with said axis perpendicular to the flux path of said permanent magnet across the gap, progressively moving said piece into said gap without changing the orientation of the piece relative to said permanent magnet thereby to progressively magnetize said piece in a direction perpendicular to said axis and correspondingly reduce the flux density of the piece along said axis, and stopping, the movement of said piece through said gap when the flux density of said piece along said axis has been reduced to said preselected value.

3. Apparatus for reducing the flux density of a permanent magnet along its north-south axis to a preselected value, said apparatus having, in combination, a magnet having opposed pole faces defining an airgap which tapers gradually from a wide end to a narrow end, a support having a loading position alongside the wide end of said airgap and adapted to carry the permanent magnet with its north-south axis perpendicular to the flux path across said airgap, and means for moving said support progressively into said airgap until the flux density of the permanent magnet along said axis has been reduced to said preselected value.

4. Apparatus as defined by claim 3 in which the magnet forming said tapered airgap is a permanent magnet.

5. Apparatus as defined by claim 3 including a measuring device, said measuring device including a sensor mounted on said support and operable to measure the magnetization of said permanent magnet along said north-south axis.