US3824513A - Position indication apparatus - Google Patents

Abstract

A position indication apparatus including a permanent magnet, a shunt for steepening the field gradient of the permanent magnet, and a device, such as a reed switch, responsive to the presence of the magnetic field. A substantially thin, substantially high coercivity permanently magnetized material occupies a portion of the surface of a circular base, such as a disc. At one edge of the magnetic material is mounted a substantially thin shunt comprised of a relatively soft magnetic material. The shunt substantially steepens the magnetic field gradient near this edge of the permanent magnet, thereby causing a substantially steeper drop-off in field intensity beyond the edge of the permanent magnet. A reed switch is positioned in parallel, spaced relation to the permanent magnet to be activated by movement of the magnet through a predetermined zone with respect to the reed switch. The zone can be substantially decreased dimensionally by the addition of the shunt, thereby greatly increasing the accuracy of the combination for use as a position indication apparatus.

Description

United States Patent [191 Webb [11] 3,824,513 July 16, 1974 POSITION INDICATION APPARATUS George Toney Webb, Austin, Tex.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

[22] Filed: Apr. 16', 1973 [21] App]. No.: 351,666

[75] Inventor:

3,497,997 3/1970 Sheckells 335/206 X 3,514,729 5/1970 Webb 335/207 3,594,669 7/1971 Yamane 335/207 Primary Examiner-R. N. Envall, Jr. Attorney, Agent, or FirmDouglas H. Lefeve 57 ABSTRACT A position indication apparatus including a permanent magnet, a shunt for steepening the field gradient of the permanent magnet, and a device, such as a reed switch, responsive to the presence of the magnetic field. A substantially thin, substantially high coercivity permanently magnetized material occupies a portion of the surface of a circular base, such as a disc. At one edge of the magnetic material is mounted a substantially thin shunt comprised of a relatively soft magnetic material. The shunt substantially steepens the magnetic field gradient near this edge of the permanent magnet, thereby causing a substantially steeper drop-off in field intensity beyond the edge of the permanent magnet. A reed switch is positioned in parallel, spaced relation to the permanent magnet to be activated by movement of the magnet through a predetermined zone with respect to the reed switch. The

zone can be substantially decreased dimensionally by the addition of the shunt, thereby greatly increasing the accuracy of the combination for use as a position indication apparatus.

9. Claims, 8 Drawing Figures 1 POSITION INDICATION APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to apparatus for indicating the position of relatively movable objects, and more specifically to the combination of a reed switch and an improved magnetic structure for repeatedly activating the reed switch when the magnetic structure is brought into a particular position with-respect to the reed switch.

2. Description of the Prior Art The utilization of a reed switch in combination with a magnetic structure for activating the reed switch is well known. Typically, a normally open reed switch and the magnetic structure are mounted in spaced relation to each other, and either the magnetic structure or the reed switch is movable along a predetermined path relative to the other. A zone exists along this path in which the reed switch is activated or deactivated depending upon whether the magnetic structure is moving closer to or farther away from the reed switch.

The combination described above may be appropriately defined as an apparatus for providing an indication of proximity and may be successfullyutilized in applications in which it is important to know that some mechanical motion of an object has occurred, but wherein it is unimportant to know with a high degree of accuracy when the object reached or passed a certain point. I

ln applications in which it is important to have a more precise indication of a movable objects arrival at or passage beyond a particular point within the above zone of activation or deactivation, US. Pat. No. 3,514,729, to George T. Webb, Ser. No. 790,954, filed Jan. 14, 1969, issued May 26, 1970, and entitled Pulse Generating Switch Device" is of interest. Disclosed therein is a magnetic structure comprising a substantially high coercivity permanently magnetized material for sequentially causing a reed switch to change from a closed state by virtue of its close proximity-to a strong magnetic field to an open state by virtue of a transition zone to another strong magnetic field of opposite polarity. The magnetic structure disclosed in that patent, however, may be used only for momentarily changing the state of the reed switch during relative movement of the structure. Further, the pulse widths produced thereby are relatively unpredictable. Also, the structure cannot be used where it is desired to produce a signal by reed switch activation which subtends a certain angular or linear distance while the switch is closed by virtue of the magnetic field and the same or anotherangular or linear distance while the switch is open because of the lack of a magnetic field.

lt is known to move a soft magnetizable material, sometimes called a shunt, relative to a magnet to decrease the magnetic field intensity that reaches a.

nearby reed switch, thereby causing the switch to change state. One example of this would be the interpolution with respect to the reed switch changing state on each interposition of the shunt at the same position of the shunt. In other .words, the zone in which the reed switch may be caused to change state becomes wider.

Another example of prior art shunting techniques is the lateral movement of a shunt into close proximity with a magnet thatis fixedly mounted with respect to a fixed reed switch. The shunt in this example essentially diverts and reduces the magnetic flux that was previously allowed to reach the reed switch.

Inboth of the aboveexamples, and in all other known devices wherein a shunt is moved relative to a magnet, the resolution of reed switch activation or deactivation is substantially lower than in the apparatus disclosed herein, wherein the shunt is fixed relative to the magnet. Very precise switch points, both on make and break of the reed switch are provided by this invention and, thus, a more accurate position indication apparatus is provided than has heretofore been achieved in the prior art.

SUMMARY OF THE INVENTlON A position indication apparatus employs a permanent magnet, a shunt for steepening the field gradient of the permanent magnet, and a device, such as a reed switch, responsive to the presence of the magnetic field. In the preferred embodiment, a substantially thin, substantially high coercivity permanently magnetized material occupies a portion of the surface of a circular base, suchas a disc. At one edge of the magnetic material is mounted a substantially thin shunt comprised of a relatively soft magnetizable material. The shunt substantially steepens the magnetic field gradient near this edge of the permanent magnet, thereby causing a substantially greater drop-off in field intensity beyond the edge of the permanent magnet. A reed switch is positioned in parallel, spaced relation to the permanent magnet to be activated by movement of the magnet through a substantially narrow predetermined zone with respect to the reed switch. The zone can be substantially decreased dimensionally by the addition of the shunt, thereby greatly increasing the accuracy of the combination for use as a position indication apparatus rather than a proximity indication apparatus.

An alternate embodiment is disclosed for indicating linear rather than angular, position. The permanent magnet and the shunt are mounted on a rectangular or square mounting base and the permanent magnet may be shutned on one end or on opposite ends for providing an accurate make" point or accurate make and break points, respectively.

Thus, a magnetic structure for reed switch activation is disclosed that may be readily mass produced at a very low cost for providing a more accurate reed switch position indicating apparatus than has heretofore been achieved in the prior art.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of a preferred embodiment of the invention depicting the combination of the permanent magnet and shunt attached to a mounting base in movable spaced relation to a reed switch.

FIG. 2 is a cross-section view of the permanent magnet shown in FIG. 1, indicating the magnetic polarity at particular regions of the magnet.

FIG. 3 shows an alternate embodiment of the invention for applications wherein linear, rather than angular position, is to be indicated.

FIG. 4 is a top plan view of the permanent magnet of FIG. 3, as positioned in FIG. 3, showing magnetic polarity at particular regions of the magnet.

FIG. 5 is a side view of the magnetic activating structure of FIG. 3 showing the relative thicknesses of the permanent magnet and the shunt.

FIG. 6 shows curves of field intensity versus magnet position of a prior art magnet structure and a magnet structure shunted in accordance with this invention.

FIG. 7 shows an apparatus for permanently magnetiz- I ing the permanent magnet of FIG. 1 in the polarity indicated by FIG. 2. I

FIG. 8 is a side view of a portion of the magnetizing apparatus shown in FIG. 7 for magnetizing the magnet of FIG. 1 after it is mounted on the mounting base of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a circular mounting base 10 is shown having a permanent magnet '11 rigidly mounted thereon. Base 10. is rigidly mounted to shaft 14 for rotation therewith. Shunts 12, also rigidly mounted to base 10, are positioned adjacent to the raeasily be aligned with the radially extending edges of magnet 11. A reed switch 20 is also shown in spaced relation to base 10 with its longitudinal axis positioned radially with respect to base 10.

The combination shown in FIG. 1, comprising reed' switch 20 and the magnetic activating structure, including magnet 11 and shunts 12 mounted on base 10, may be utilized when it is desirable toobtain an indication of a precise angular position. When a precise linear position indication is desired, the combination shown in FIG. 3 may be utilized. In FIG. 3, mounting base 30 has a permanent magnet 31 and a shunt 32 fixedly. mounted thereon. A reed switch 40 is in spaced relation to magnet 31 and shunt 32. The longitudinal axis of switch 40 is parallel to the adjacent edges of magnet 31 and shunt 32.

The field intensity of magnets 11 and 31 available for activating reed switches 20 and 40, respectively, increases as the widths of magnets 11 and 31 increase, up to the point that magnet width equals the combined length of both reed levers. The'width of magnet 11 is defined as the length of the radially extending edges thereof that are perpendicualar to center line 15. The width of magnet 31 is defined as the length of the edges thereof that are perpendicular to center line 36.

4 Magnets 11 and 31 preferably comprise a planar sheet of substantially thin and substantially high coercivity permanently magnetizable material. The thicker the magnet must be thick enough to provide enough flux to repeatedly actuate the reed switch at the distance that it is mounted away from the magnet, but should be no thicker than this.

A suitable high coercivity, permanently magnetizablematerial thatmay be formed substantially thin is barium ferrite suspended in a plastic orrubber base material. A plastic or rubber base material is preferred over a cermanic base because of the strength and also the ease of cutting a plastic or rubber material.

' Referring now to FIG. 5, it is observed that the thick ness A of magnetic 31 is slightly greater than the thickness B of shunt 32. Ideally, to achieve the greatest steepening of the field gradient of magnet 3l,shunt thickness B should be as great as magnet thickness A. If shunt thickness B were made greater than magnet thickness A, the clearance problem presented by thickness B would require that the reed switch (not shown) be mounted farther away from magnet 31 which, in turn, would decrease the field intensity of magnet 31 at the reed switch. If thicknesses A and B were nominally made the same, in mass production the situation would occasionally occur whereinthe reed switch would be necessarily mounted farther away from magnet 31 because of a clearance problem presented by shunt thickness B being greater than magnet thickness A. It has been found, however, that the field gradient steepening effect of shunt 32 is substantially the same when thickness B is percent, or more, of magnet thickness A. This is equally true for magnet 11 and shunts 12in FIG.

I. In summary, shunt thickness B can be 90 percent of magnet thickness A. The reed switch can then be positioned. very close to the magnet without the requirement of additional clearance for theshunt.

The shunt is preferrably made of a soft, magnetic maavailable at the reed switch position adjacent the surface side of the magnets.

FIG. 7 shows a perspective view of a magnetizing fixture that may be used to magnetize a magnet having the shape of a portion of an annular ring, such as magnet 11. Outer shell 51 and core 52 are made of a soft magnetic material. Copper strap 50 conducts the charging current provided by power supply 56. A heavy lead 54 connects one end of strap 50 to supply 56. Switch 57 is interposed in heavy lead 55 connecting the other end of strap 50 to supply 56. Supply 56 is capable of producing an extremely high current (approximately 20,000 amperes) for a very short time duration. Switch 57 is capable of closing the circuit and sustaining this current for this short time duration.

When using the magnetizing fixture of FIG. 7, magnet 11, before magnetization, is permanently mounted on base before shaft 14 is attached thereto. Base 10 and magnet 11 are accurately positioned on the magnetizing fixture by the cooperation of the locating pin 53 and the hole in base 10 for shaft 14. In this manner, the transition in magnetic polarity along the top and bottom surfaces of magnet 11 can be repeatedly made to occur along center line 15.

FIG. 6 shows curves comparing the field intensity versus position of a magnet of the kind disclosed herein before and after shunts are added to steepen the field gradient. No shunts were used in plotting curve 45, while a shunt was used at each end of the magnet in plotting curve 46. It is readily apparent that the addition of the shunts substantially steepens the field gradient at the magnet ends without lowering the maximum field intensity available in the center portion of the magnet.

In summary, a position indication apparatus has been disclosed which employs a reed switch and a magnetic activating structure. The magnetic activating structure includes a substantially thin, substantially high coercivity permanent magnet having mounted adjacent to an edge thereof, a soft magnetic shunt. The shunt substantially steepens the field gradient of the permanent magnet, and thus, a reliable reed switch position indication apparatus is provided having greater resolution than has heretofore been available.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that-various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, the embodiment shown in FIG. 3 for indicating linear position could employ a shunt on opposite edges of the magnet for accurately activating the reed switch as it is moved relative to these opposite edges of the magnet, as is provided in the angular position indicating apparatus in FIG. 1. Further, it will be obvious to those skilled in the art that the magnet in FIG. 1 may be constructed to subtend a different number of degrees of a circle than is shown in FIG. 1.

What is claimed is:

l. A high resolution position indication apparatus comprising, in combination:

magnetic field generating means having first and second oppositely opposed surfaces separated by a thickness, first and second oppositely polarized magnetic poles on said first surface, a magnetically neutral zone extending through said thickness and said surfaces and separating said first pole from said second pole on said'first surface, a third magnetic pole on said second surface on the same side of said neutral zone as said first pole and opposite to the polarity of said first pole, and a fourth magnetic pole on said second surface on the same side of said neutral zone as said second pole and opposite to the polarity of said second pole, whereby said first and fourth poles are of the same polarity and said second and third poles are of the same polarity, said generating means having a particular field gradient with respect to distance from an edge of said generating-means including said first, second, third, and fourth poles and through which said neutral zone extends;

indication means movable relative to said edge and I adjacent said first surface and responsive to said field for indicating the proximity of said indication means to said field; and

shunting means positioned closely adjacent to said edge of said generating means for substantially steepening said particular field gradient in a region near said edge of said generating means, thereby increasing the resolution of said indication means without substantially decreasing the maximum field intensity adjacent a center portion of said first surface.

2. The position indication apparatus as defined in claim 1 wherein said indication means comprises a reed switch having an axis substantially parallel to said surface.

3. The position indication apparatus as defined in claim 2, wherein said generating means comprises a substantially thin, substantially high coercivity, permanently magnetizable material.

4. The position indication apparatus as defined in claim 3 wherein said shunting means comprises a relatively soft magnetic material.

5. The position indication apparatus as defined in claim 4, wherein the thickness of said magnetic material included in said shunting means is at least percent of the thickness of said substantially high coercivity material.

6. The position indication apparatus as defined in claim 5, further comprising a base means to which an opposite surface of said field generating means and said shunting means are mounted, said base means including a relatively soft magnetic material, whereby said magnetic field is increased adjacent said center region of said generating means.

7. The position indication apparatus as defined in claim 6 wherein said base means is substantially circular in shape, said field generating means occupying a portion of an annular shaped area of said base means and having at least one radially extending edge, and said shunting means occupying another portion of said base means adjacent said radially extending edge.

8. The position indication apparatus as defined in claim 7, further comprising another shunting means positioned in substantially close proximity to another edge of said field generating means.

9. The position indication apparatus as defined in claim 8, wherein said substantially thin, substantially high coercivity permanently magnetized material includes barium ferrite.

Claims (9)

1. A high resolution position indication apparatus comprising, in combination: magnetic field generating means having first and second oppositely opposed surfaces separated by a thickness, first and second oppositely polarized magnetic poles on said first surface, a magnetically neutral zone extending through said thickness and said surfaces and separating said first pole from said second pole on said first surface, a third magnetic pole on said second surface on the same side of said neutral zone as said first pole and opposite to the polarity of said first pole, and a fourth magnetic pole on said second surface on the same side of said neutral zone as said second pole and opposite to the polarity of said second pole, whereby said first and fourth poles are of the same polarity and said second and third poles are of the same polarity, said generating means having a particular field gradient with respect to distance from an edge of said generating means including said first, second, third, and fourth poles and through which said neutral zone extends; indication means movable relative to said edge and adjacent said first surface and responsive to said field for indicating the proximity of said indication means to said field; and shunting means positioned closely adjacent to said edge of said generating means for substantially steepening said particular field gradient in a region near said edge of said generating means, thereby increasing the resolution of said indication means without substantially decreasing the maximum field intensity adjacent a center portion of said first surface.

2. The position indication apparatus as defined in claim 1 wherein said indication means comprises a reed switch having an axis substantially parallel to said surface.

3. The position indication apparatus as defined in claim 2, wherein said generating means comprises a substantially thin, substantially high coercivity, permanently magnetizable material.

4. The position indication apparatus as defined in claim 3 wherein said shunting means comprises a relatively soft magnetic material.

5. The position indication apparatus as defined in claim 4, wherein the thickness of said magnetic material included in said shunting means is at least 90 percent of the thickness of said substantially high coercivity material.

6. The position indication apparatus as defined in claim 5, further comprising a base means to which an opposite surface of said field generating means and said shunting means are mounted, said base means including a relatively soft magnetic material, whereby said magnetic field is increased adjacent said center region of said generating means.

7. The position indication apparatus as defined in claim 6 wherein saId base means is substantially circular in shape, said field generating means occupying a portion of an annular shaped area of said base means and having at least one radially extending edge, and said shunting means occupying another portion of said base means adjacent said radially extending edge.

8. The position indication apparatus as defined in claim 7, further comprising another shunting means positioned in substantially close proximity to another edge of said field generating means.

9. The position indication apparatus as defined in claim 8, wherein said substantially thin, substantially high coercivity permanently magnetized material includes barium ferrite.

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