CA1269738A - Demagnetization apparatus for magnetic markers used with article surveillance systems - Google Patents
Demagnetization apparatus for magnetic markers used with article surveillance systemsInfo
- Publication number
- CA1269738A CA1269738A CA000541907A CA541907A CA1269738A CA 1269738 A CA1269738 A CA 1269738A CA 000541907 A CA000541907 A CA 000541907A CA 541907 A CA541907 A CA 541907A CA 1269738 A CA1269738 A CA 1269738A
- Authority
- CA
- Canada
- Prior art keywords
- working surface
- poles
- pole
- housing
- elongated section
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F13/00—Apparatus or processes for magnetising or demagnetising
- H01F13/006—Methods and devices for demagnetising of magnetic bodies, e.g. workpieces, sheet material
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Burglar Alarm Systems (AREA)
- Manufacturing Cores, Coils, And Magnets (AREA)
Abstract
ABSTRACT
A demagnetization apparatus for use with magnetically based electronic article surveillance systems having a dual status anti-theft marker containing at least one demagnetizable control element which when demagnetized allows the marker to be detected by the system when the marker is present in an interrogation zone. The apparatus includes an elongated magnetic section contained within a housing which exhibits a succession of fields of alternate polarity and a portion of which exhibits generally decreasing intensities at the working surface of the housing along that portion of the section. The peak intensity of the outermost field is controlled to have a peak intensity less than that of adjacent regions. The section and a cover plate are oriented such that the external fields near the working surface are sufficient in intensities to demagnetize the demagnetizable element of the marker positioned proximate thereto while being rapidly attenuated a short distance from the section. Accordingly, magnetically sensitive articles, such as for example, prerecorded magnetic cassettes, to which the markers are affixed, are not adversely affected.
A demagnetization apparatus for use with magnetically based electronic article surveillance systems having a dual status anti-theft marker containing at least one demagnetizable control element which when demagnetized allows the marker to be detected by the system when the marker is present in an interrogation zone. The apparatus includes an elongated magnetic section contained within a housing which exhibits a succession of fields of alternate polarity and a portion of which exhibits generally decreasing intensities at the working surface of the housing along that portion of the section. The peak intensity of the outermost field is controlled to have a peak intensity less than that of adjacent regions. The section and a cover plate are oriented such that the external fields near the working surface are sufficient in intensities to demagnetize the demagnetizable element of the marker positioned proximate thereto while being rapidly attenuated a short distance from the section. Accordingly, magnetically sensitive articles, such as for example, prerecorded magnetic cassettes, to which the markers are affixed, are not adversely affected.
Description
41287CANlA
~26~3~3 IMPROVED DEMAGNETIZATION APPARATUS FOR MAGNETIC MARKERS
USED WITH ARTICLE SURVEILLANCE SYSTEMS
. . _ _ . . .
Field of the Invention The present invention relates to electronic article surveillance ( EAS) systems of the type in which a dual status marker, affixed to articles to be protected, causes a detectable signal in response to an alternating magnetic Eield produced in an interrogation zone. Such a dual status marker may preferably comprise a piece of a high permeability, low coercive force magnetic material and at least one permanently magneti~able control element.
When the control element is demagnetized, a detectable signal corresponding to one state of the marker may be produced when the marker is in the zone, and when magnetized, a difEerent signal corresponding to another state of the marker may be produced. More particularly, the present invention relates to an apparatus for changing the state of such markers.
Back~round of the Invention _ E'AS systems of the type described above, are, for example, disclosed and claimed in U.S. Patent No. 3,665,449 ~Elder anc] Wright). With such ~ystems, a dual status marker of the type described above may be sensitized, l.e., the hiyh-coercive force control elements thereoE
demagnetized, by applyiny an alternatiny, dimini~shing amplitude magnetic Eield, or by gradually removing an alternating ield oE constant intensity such as by withdrawing a bulk magnetic eraser of the type supplied by Nortronics Company, Inc. o~ MinneapoLls, Minnesoka. As disclo~ed in the 3,665,4~9 patent, such a demaynetization operation may also be efEected throuc~h the proper selection and arrangement of a series oE perrnanent magnets in which adjacent magnets are opposikely polarized. By selectiny the magnets to be oE di~erent strengths and by arranging them in an order ranging from highest to lowest (relative ~..
, ::
.. .
' ' - :: ,
~26~3~3 IMPROVED DEMAGNETIZATION APPARATUS FOR MAGNETIC MARKERS
USED WITH ARTICLE SURVEILLANCE SYSTEMS
. . _ _ . . .
Field of the Invention The present invention relates to electronic article surveillance ( EAS) systems of the type in which a dual status marker, affixed to articles to be protected, causes a detectable signal in response to an alternating magnetic Eield produced in an interrogation zone. Such a dual status marker may preferably comprise a piece of a high permeability, low coercive force magnetic material and at least one permanently magneti~able control element.
When the control element is demagnetized, a detectable signal corresponding to one state of the marker may be produced when the marker is in the zone, and when magnetized, a difEerent signal corresponding to another state of the marker may be produced. More particularly, the present invention relates to an apparatus for changing the state of such markers.
Back~round of the Invention _ E'AS systems of the type described above, are, for example, disclosed and claimed in U.S. Patent No. 3,665,449 ~Elder anc] Wright). With such ~ystems, a dual status marker of the type described above may be sensitized, l.e., the hiyh-coercive force control elements thereoE
demagnetized, by applyiny an alternatiny, dimini~shing amplitude magnetic Eield, or by gradually removing an alternating ield oE constant intensity such as by withdrawing a bulk magnetic eraser of the type supplied by Nortronics Company, Inc. o~ MinneapoLls, Minnesoka. As disclo~ed in the 3,665,4~9 patent, such a demaynetization operation may also be efEected throuc~h the proper selection and arrangement of a series oE perrnanent magnets in which adjacent magnets are opposikely polarized. By selectiny the magnets to be oE di~erent strengths and by arranging them in an order ranging from highest to lowest (relative ~..
, ::
.. .
' ' - :: ,
-2- ~6~738 to the direction of travel), the magnetic field will appear to diminish in amplitude when passed over a control element. That patent also suggests that magnets of the same field strength may be arranged like inverted ascending steps or like an inclined plane so that the amplitude of the fleld is progressively diminished to produce the same result, and that it is not ordinarily necessary to demagnetize the control element in the strictest sense.
Rather, the magnetic influence of the control element need only be reduced to an extent permitting magnetization reversal of the marker by the applied field.
While such techniques may be useful in many areas with the markers affixed to a wide variety of articles, the magnetic fields associated therewith have been found to unacceptably interfere with magnetic states associated with certain article.s, such as prerecorded magnetic video and audio cassettes utilized in video rental businesses.
~ecause of the compact size and popularity of such prerecorded magnetic cassettes, they are ~requent targets for sho~lifters, and hence likely articles with which anti-theft markers would be used. At the same time however, such aEfixed markers would be desirably sensitized upon return of the article, and it has been found that prior art demagnetization apparatus such as those described above may unacceptably aeEect slgnals prerecorded on the magnetic tapes within the cassettes.
Summar~ of the tnvention In contrast to the demagnetization apparatus Oe the prior art acknowLeclg~d above Ln which the intensity Oe the magnetic e;eLds produced thereby extend in a virtualLy uncontrolletl Eashion, ths apparatus of the present lnventiorl provldes a succession Oe fLelds of alternating poLarity whLch rapidly decrease in intensity only a short, contr~lLed distance Erom the surEace oE the apparatu~s and thus, while being capable of demagnetizing high-coercive Eorce control elements of a marker brought close thereto, ., . ~ . .
' '`: ~ :, ., ' i. ,.
;,"',::''`' ' :' :
:: :
, . ': , .
60557~3268 would be incapable o~ appreciably inter~erlng with the magnetic signals recorded on tapes within a cassette to which the marker ls affixed.
The apparatus of the present invention is thus adapted for use with an electronic article surveillance ($AS) syste~ ~or de~ecting a sensitized dual status anti-theft marker secured to an artlale, the presence of which, within an interrogation zone is desirably known. The apparatus is particularly adapted for use with such a mar}cer affixed to the outer surface o~ prerecorded video or audio cassettes. The marker ln such a system lncludes a piece of low coercive force, hiyh-permeability ferromagnetlc material and at least one control element of a permanently magnetizable high coercive force material positioned proximate to the first material. Such an element, when demagnetized, results in the marker beiny in a ~irst state, such as, for example, a sensitized state in which the marker may be detected when it is in the interrogation zone. Conver~ely, when the control element is magnetized, the marker is in a second ~tate, such as, for example, a desensitized state ln which the marker is not detected when i~
ls in khe zone.
The apparatu~ ol the present invention comprl~es a housing having a workiny surface relative to which an artlcle may be moved, and an elonyated section o~ a permanent maynetic material associated wikh said hou~ing, ~aid elongated section having a plurality of closely spaced poles,~said poles exhibiting at the working sur~ace a succes~ion of ~ield~ of alternatlny polarity and a first portion ol which exhibits at the working ~ '' " . ' . ~
' ' '':
~26~97~
60557-32~8 surface fields of generally decreasing intensities along at least that portion of said elongated section; each pole extending across the width of said elongated sec~ion and the succession of poles extending along the length o~ said elongated section; and wherein the field intensi~y at said working surface associated with the most intense pole in said succession is approximately one and one hal f times said predetermined value oi the coercive ioree of the control element, whereby movement of sald article rela~ive to the working surface of said housing from a position adjacent the fleld associated with the most intense ~ield past each generally successively weaker ~ield of opposite polarity, will expose the marker afflxed to the article to fields of alternate polarities and generally decreasing intensities, thereby substantially demagnetizing the control element of said marker, and ~he close spacing of the alternate poles results in a rapid decrease in the intensities of the fields above the working surface so as not to adversely affect a magnetically sensltive object contained within the article.
The pole to pole spacing alony the length of the elongated section is preferably no more than 0.635 cm.
In a preferred embodiment oE the present lnvention, the elongated section also includes a second portion associated with that end of the first portion which exhibits the most intense ~ielcl at the worlcing surface oi the housing. l'his seaond portion includes a succes~ion of alternately polarized permanently magnetized reg:lons o~ approximately equal peak intensities, ancd an outermost region having a peak intenslty less than that of the .~h : ... .. .
60557-32~8 other regions. Such a preferred structure ensures that the peak inkensity at the working surface of the outermost field is not greater than that associated with the other regions.
The net field at any position along the working surface is the algebraic sum of the flux from each of the magnetized reglons of the elonyated strip positioned below the surface, with each region having a lesser effect depending upon the distance of that region from the given position. Thus, for example, the net fie].d at a position mldway alony the working surface will be in the direction dictated by the magnetized region directly therebelow, and the peak intensity will be reduced prlmarily by the opposing fields of the immediately adjacent regions of equal intensity. In contrast, if the outermost region were to provide a field of e~ual intensity with that provided by 4a ' ;; .:
5_ ~26~7~
the remaining regions, the absence o~ a yet further out field of opposite polarity would cause the intensity of the outermost field at the working surEace to be greater than that resulting from the remaining regions. Such a larger field could adversely a~fect prerecorded magnetic media positioned along the working surface. Conversely, if the initial peak field intensity is controlled to be below that at which such adverse ef~ects may occur, the subsequent even smaller ~ields associated with the rest of the second portion may not be adequate to completely demagnetize t11e control elements such that the resultant sensitivity is diminished.
Brief Description oE the Drawinys The present invention will be more fully described with reference to the accompanying drawings wherein like reEerence numerals identify corresponding components, and:
Figure 1 is a perspective view of one embodiment of the demagnetization apparatus of the present invention;
Figure 2 is an enlarged cross sectional view of Fiyure 1, taken along the lines 2-2;
Figure 3 is an enlarged Eragmentary cross sectional view of the detai.ls of the elongated magnetic section oE F'iyure 2;
Figure 4 is a graph illustrating field strength along the work:Lng surEace Eor a speciEic embodiment;
FLgure 5A i5 a Eurther enLarged frayment~ry cross-secti.ona:L view o~ the ~etails of the second portion O~ the elongate(l magnetic sect.Lon of E'igure 3;
F'igure 5~3 is a graph illu.strating the variations ln hori~onta:L Eield intensLty at the working surEace corresponcling to the structure shown in Figure SA;
Figure 6A is a similarly enlarged Eragmentary cross-sectional view oE the details of a preferred second portion o~ the elongated magnetic section accordlng to the present invention;
... ..
' . .
..
-6- ~ 26 ~ 73 8 ~ igure 6s is a c~raph illustrating the variations in horizontal Eield intensity at the working surface corresponding to the structure shown in Figure 6A; and Figures 7 and 8 are stylizecl graphs illustrating the peak field strengths along the working surface associated with second sections of the elongated m~gnetic section constructed as shown in Figures 5A and 6A, respectively.
Description of the Preferred Embodirnent As shown in Figures l and 2, the demagnetization apparatus of the present invention may be in the form of a counter top apparatus lO having a housing 12, and contained within a cavity 14 therein an elongated magnetic section 16 aæ described hereinafter. The cavity 14 is in turn covered by a non-magnetic cover plate 18 which both covers and protects the elongated magnetic section 16. In addition, the cover plate 18 provides a working sur~ace 19 over which an article 20 having a marker 22 aEfixed thereto may be passed during the use of the apparatus. For example, such a cover plate 18 may comprise a strip of non-magnetic stainless steel having a thickness in the range of 0.50 mm.
The use of a metallic cover plate 18 is further desired as such a surace resists wear from scratchirlg or chipping as rnay otherwise occur with cover plate~s having a polymeric or painted surface, and it thereby remains aesthetically acceptable even over many cycles o~ use.
While the apparatu~ 10 may be used with the workincJ surface 19 established by the cover plate 18 in a horizontal position, such that an article 20 may be moved across the horizontal ~ur~ace, the apparatu~ may also be positioned to have the workin0 surface 19 vertical.
Lhe housincJ l~ of the apparatus 10, as shown in Figure 1, includes two sides 2L. The housing is pre~erably constructed of non-magnetic materials, and may be fabricated from appropriately dimensioned and finished hardwood, or may be Eormecd from injection molded or ', ~ .
,: .
_7_ ~6~73~
machined plastic. Also, beveled faces ~not shown) may be provided on the housing 12 to carry appropria~e legends, manufacturer identification, instructions and the like~
In using the apparatus oE Figure 1, it will be recognized that the article 20 is to be moved in the direction shown by ar~ows 24~ thus causing the marker 22 af~ixed to one surface o~ the article to be moved so that the marker 22 is passed over the elongated magnetic section 16 contained within the cavity 14. Thus, for example, if the article 20 is a typically packaged video cassette, the marker 22 could be afixed to one side of the cassette, and the cassette held so as to be positioned on the cover plate 1~ and passed along the working surface 19 in the direction of arrows 24.
The marker 22 is typically constructed of a strip of a high permeability, low coercive force magnetic material such as a permalloy, certain amorphous alloys, or the like as disclosed, for example, in U.S. Patent No.
Rather, the magnetic influence of the control element need only be reduced to an extent permitting magnetization reversal of the marker by the applied field.
While such techniques may be useful in many areas with the markers affixed to a wide variety of articles, the magnetic fields associated therewith have been found to unacceptably interfere with magnetic states associated with certain article.s, such as prerecorded magnetic video and audio cassettes utilized in video rental businesses.
~ecause of the compact size and popularity of such prerecorded magnetic cassettes, they are ~requent targets for sho~lifters, and hence likely articles with which anti-theft markers would be used. At the same time however, such aEfixed markers would be desirably sensitized upon return of the article, and it has been found that prior art demagnetization apparatus such as those described above may unacceptably aeEect slgnals prerecorded on the magnetic tapes within the cassettes.
Summar~ of the tnvention In contrast to the demagnetization apparatus Oe the prior art acknowLeclg~d above Ln which the intensity Oe the magnetic e;eLds produced thereby extend in a virtualLy uncontrolletl Eashion, ths apparatus of the present lnventiorl provldes a succession Oe fLelds of alternating poLarity whLch rapidly decrease in intensity only a short, contr~lLed distance Erom the surEace oE the apparatu~s and thus, while being capable of demagnetizing high-coercive Eorce control elements of a marker brought close thereto, ., . ~ . .
' '`: ~ :, ., ' i. ,.
;,"',::''`' ' :' :
:: :
, . ': , .
60557~3268 would be incapable o~ appreciably inter~erlng with the magnetic signals recorded on tapes within a cassette to which the marker ls affixed.
The apparatus of the present invention is thus adapted for use with an electronic article surveillance ($AS) syste~ ~or de~ecting a sensitized dual status anti-theft marker secured to an artlale, the presence of which, within an interrogation zone is desirably known. The apparatus is particularly adapted for use with such a mar}cer affixed to the outer surface o~ prerecorded video or audio cassettes. The marker ln such a system lncludes a piece of low coercive force, hiyh-permeability ferromagnetlc material and at least one control element of a permanently magnetizable high coercive force material positioned proximate to the first material. Such an element, when demagnetized, results in the marker beiny in a ~irst state, such as, for example, a sensitized state in which the marker may be detected when it is in the interrogation zone. Conver~ely, when the control element is magnetized, the marker is in a second ~tate, such as, for example, a desensitized state ln which the marker is not detected when i~
ls in khe zone.
The apparatu~ ol the present invention comprl~es a housing having a workiny surface relative to which an artlcle may be moved, and an elonyated section o~ a permanent maynetic material associated wikh said hou~ing, ~aid elongated section having a plurality of closely spaced poles,~said poles exhibiting at the working sur~ace a succes~ion of ~ield~ of alternatlny polarity and a first portion ol which exhibits at the working ~ '' " . ' . ~
' ' '':
~26~97~
60557-32~8 surface fields of generally decreasing intensities along at least that portion of said elongated section; each pole extending across the width of said elongated sec~ion and the succession of poles extending along the length o~ said elongated section; and wherein the field intensi~y at said working surface associated with the most intense pole in said succession is approximately one and one hal f times said predetermined value oi the coercive ioree of the control element, whereby movement of sald article rela~ive to the working surface of said housing from a position adjacent the fleld associated with the most intense ~ield past each generally successively weaker ~ield of opposite polarity, will expose the marker afflxed to the article to fields of alternate polarities and generally decreasing intensities, thereby substantially demagnetizing the control element of said marker, and ~he close spacing of the alternate poles results in a rapid decrease in the intensities of the fields above the working surface so as not to adversely affect a magnetically sensltive object contained within the article.
The pole to pole spacing alony the length of the elongated section is preferably no more than 0.635 cm.
In a preferred embodiment oE the present lnvention, the elongated section also includes a second portion associated with that end of the first portion which exhibits the most intense ~ielcl at the worlcing surface oi the housing. l'his seaond portion includes a succes~ion of alternately polarized permanently magnetized reg:lons o~ approximately equal peak intensities, ancd an outermost region having a peak intenslty less than that of the .~h : ... .. .
60557-32~8 other regions. Such a preferred structure ensures that the peak inkensity at the working surface of the outermost field is not greater than that associated with the other regions.
The net field at any position along the working surface is the algebraic sum of the flux from each of the magnetized reglons of the elonyated strip positioned below the surface, with each region having a lesser effect depending upon the distance of that region from the given position. Thus, for example, the net fie].d at a position mldway alony the working surface will be in the direction dictated by the magnetized region directly therebelow, and the peak intensity will be reduced prlmarily by the opposing fields of the immediately adjacent regions of equal intensity. In contrast, if the outermost region were to provide a field of e~ual intensity with that provided by 4a ' ;; .:
5_ ~26~7~
the remaining regions, the absence o~ a yet further out field of opposite polarity would cause the intensity of the outermost field at the working surEace to be greater than that resulting from the remaining regions. Such a larger field could adversely a~fect prerecorded magnetic media positioned along the working surface. Conversely, if the initial peak field intensity is controlled to be below that at which such adverse ef~ects may occur, the subsequent even smaller ~ields associated with the rest of the second portion may not be adequate to completely demagnetize t11e control elements such that the resultant sensitivity is diminished.
Brief Description oE the Drawinys The present invention will be more fully described with reference to the accompanying drawings wherein like reEerence numerals identify corresponding components, and:
Figure 1 is a perspective view of one embodiment of the demagnetization apparatus of the present invention;
Figure 2 is an enlarged cross sectional view of Fiyure 1, taken along the lines 2-2;
Figure 3 is an enlarged Eragmentary cross sectional view of the detai.ls of the elongated magnetic section oE F'iyure 2;
Figure 4 is a graph illustrating field strength along the work:Lng surEace Eor a speciEic embodiment;
FLgure 5A i5 a Eurther enLarged frayment~ry cross-secti.ona:L view o~ the ~etails of the second portion O~ the elongate(l magnetic sect.Lon of E'igure 3;
F'igure 5~3 is a graph illu.strating the variations ln hori~onta:L Eield intensLty at the working surEace corresponcling to the structure shown in Figure SA;
Figure 6A is a similarly enlarged Eragmentary cross-sectional view oE the details of a preferred second portion o~ the elongated magnetic section accordlng to the present invention;
... ..
' . .
..
-6- ~ 26 ~ 73 8 ~ igure 6s is a c~raph illustrating the variations in horizontal Eield intensity at the working surface corresponding to the structure shown in Figure 6A; and Figures 7 and 8 are stylizecl graphs illustrating the peak field strengths along the working surface associated with second sections of the elongated m~gnetic section constructed as shown in Figures 5A and 6A, respectively.
Description of the Preferred Embodirnent As shown in Figures l and 2, the demagnetization apparatus of the present invention may be in the form of a counter top apparatus lO having a housing 12, and contained within a cavity 14 therein an elongated magnetic section 16 aæ described hereinafter. The cavity 14 is in turn covered by a non-magnetic cover plate 18 which both covers and protects the elongated magnetic section 16. In addition, the cover plate 18 provides a working sur~ace 19 over which an article 20 having a marker 22 aEfixed thereto may be passed during the use of the apparatus. For example, such a cover plate 18 may comprise a strip of non-magnetic stainless steel having a thickness in the range of 0.50 mm.
The use of a metallic cover plate 18 is further desired as such a surace resists wear from scratchirlg or chipping as rnay otherwise occur with cover plate~s having a polymeric or painted surface, and it thereby remains aesthetically acceptable even over many cycles o~ use.
While the apparatu~ 10 may be used with the workincJ surface 19 established by the cover plate 18 in a horizontal position, such that an article 20 may be moved across the horizontal ~ur~ace, the apparatu~ may also be positioned to have the workin0 surface 19 vertical.
Lhe housincJ l~ of the apparatus 10, as shown in Figure 1, includes two sides 2L. The housing is pre~erably constructed of non-magnetic materials, and may be fabricated from appropriately dimensioned and finished hardwood, or may be Eormecd from injection molded or ', ~ .
,: .
_7_ ~6~73~
machined plastic. Also, beveled faces ~not shown) may be provided on the housing 12 to carry appropria~e legends, manufacturer identification, instructions and the like~
In using the apparatus oE Figure 1, it will be recognized that the article 20 is to be moved in the direction shown by ar~ows 24~ thus causing the marker 22 af~ixed to one surface o~ the article to be moved so that the marker 22 is passed over the elongated magnetic section 16 contained within the cavity 14. Thus, for example, if the article 20 is a typically packaged video cassette, the marker 22 could be afixed to one side of the cassette, and the cassette held so as to be positioned on the cover plate 1~ and passed along the working surface 19 in the direction of arrows 24.
The marker 22 is typically constructed of a strip of a high permeability, low coercive force magnetic material such as a permalloy, certain amorphous alloys, or the like as disclosed, for example, in U.S. Patent No.
3,790,945 (Fearon). The marker is further provided with at least one control element 32 of a high coercive Eorce rnagnetizable material as disclosed, Eor example, in U.S.
Patent No. 3,747,086 (Peterson). The control elernent 32 is typically formed of a material such as vicalloy, mac~netic stainless steel or the like, having a predetermined value oE coercive force in the range oE 4000-19,200 ~/m. When such an element is magnetized, it prevents the marker from being detected by the system wherl the marker 22 is present in the interroyation ~one.
The (lemagnetizatLon of the contro1 eLement 32 is 3~ efecte(] upon exposure to ttle ~ieLds provlded by the eLon0ated ma~Jnetic sectlon 16 when ttle eLement 32 is brou(Jht into clo~e proxilllity wlttl the maynetic field~
associated with the section 16 at the working surface L9.
Tlle (letails oE the elongated mayrletic section L6 are shown in the cross sectional view of Figure 2. As may there be seen, the housiny 12 oE the apparatus 10 is shown to have a recess or cavity 14 within which the elongated -8- ~ 3~
magnetic section 16 may be positioned and supported by the housing within the recess, or by a frame 34 with the top oE
the recess enclosed by the cover plate 18. As an alternative, the section may be held in position within the recess 14 by the cover plate 18 (not shown).
As shown in Figure 2 and in greater detail in Figure 3, the elongated magnetic section 16 has a plurality of magnetized regions or poles 36 in a succession of closely spaced fields of alternate polarity and oE
generall~ equal intensity Erom one end of the elongated magnetic section 16 to the other. Each pole 36 extends across the width of the section 16, and the succession oE
poles extends along the length of the section 16. The elongated magnetic section 16 may be made of: ~1) an injection molded permanent magnet material, which is subsequently magnetized after molding and arranged with alternating poles; or (2) a sheet Oe permanent magnet material magnetized with uniform alternating poles. In the illustrated embodiment, the elongated magnetic section 16 was formed of a 2.3 mm thick and 76 mm wide sheet material of the type described above magnetized with 2.36 poles/cm.
The bottom of the recess 1~ on which the magnetic section 16 is positioned is inclined with respect to the working surface l9 Oe the housing 12 so that a Eir.qt portion 40 oE the section 16 exhibits magnetic fields oE
generally decreasing intensity at the working sureace Oe the housing. A second portion 50 is providecl adjacent to the most intense Eield end oE the eirst portion ~0 and planar to the working surEace 19 Oe the housing. The second portion 50 lnclude~ more than one pole and provides alternating fielcls Oe EaLrly constant peak intensltie.s at the working sureace L9 o the housing. The purpose oE the second portion 50 is to assure at least one intense field in a direction oppo~ite to the magnetizat~ion oE the control 35 element 32 in order to properly begin the demagnetization process. rhe second portion 50 also ser~es to eliminate any end effects associated with the Eirst pole 54 of the _9_ ~ 3~
first portion 40 having the most intense field associated therewith. In addition, the low ~ield end of the elongated magnetic section 16 includes a third portion 60 curved for the purpose e~plained hereinafter.
Thus, it has been found that by supporting the above ma~netic section having 2.36 poles per cm on a frame 34 as illustrated in Figures 2 and 3 having a second portion 50 of 2.54 cm, a Eirst portion 40 of 15.2 cm inclined at 2 23" to the workill~ surface 19 of the housing, and a third l~ortion 60 of 5.1 cm having a radius of 31 cm, the poles will exhibit peak fields along the working surface as illustrated in Figure 4, it beiny recognized that the alternations of magnetic polarity between each adjacent pair of poles actually results in a generally sinusoidal variation in the horizontal field along the working surface.
It is believed that the increase in field intensity at the end of the third portion 60 as shown in Figure 4, is the result of the fact that the field at the working surface 19 above the last pole is not subjected to a compensating field from an adjacent pole of opposite polarity. It is essential that this increased field be sufficiently small so as not to allow partial remagnetization oE the control element 32. Tt-us, it has been found that the third portion 60 having an arcuate curve away from the working surface provides a more rapid increase in the distance from the working surface so that a sufficiently low field will be exhibited at the working surface above the last pole to minimize any affect on the control element 32. It should be appreciated that the third portion may alternatively be inclined at a steeper angle of incline than the first portion 40. However, by utilizing an arcuate curve a smoother transition is provided between tile first portion 40 and the third portion 60.
As illustrated in Figure 4, the decrease in intensity is non-uniform. Tllis is believed to be the ~2~ 8 result of small variations in size and magnetization of different poles. However, such minor irregularities can be tolerated so long as the variations are not large enough to prevent demagnetization of the control element 32. If the fields were to decrease too slowly, the elongated section 16 would need to be impracticall~ long, and ie the fields were to decrease too rapidly, the demagnetization would not be complete, especially in view of the non-uniEormities as mentioned above. Thus, demagnetization will occur if on the average the eield intensity at the working surface 19 associated with each successive pole decreases b~ 5 to 20 percent between any two adjacent poles.
It is critical that the field associated with the most intense pole be strong enough to start the demagnetization process. This has been found to equal approximately one and one half times the predetermined value of coercive ~orce of the control elements. However, it is also critical that the Eield intensity not be strong enough to adversely affect a magnetically sensitive object 70 contained within the article 20 during demagnetization oE the control elements. Prerecorded audio cassettes are adversely a~eected by magnetic fields greater than about 100 oersteds while prerecorded video cassettes can withstand higher Eields, perhap~s as much as 16,000 ~/m. It is necessary that the fields oE the demagnetization apparatus decrease rapidly away erom the working surface 19 50 as to be suficierltly small at a distance D measured from the working surface 19 to the macJnetically sensitive object 70. ~ typical distance D is within the range oE
1.6-3.2 mm. '1'his is accomplished by keeping the pole spaciny small enough so l:hat away from the surface, difeerent poles contribute to the efective Eield, resulting ln partiaL cancelLation Erom adjacent poles oE
opposite polarity. At the sarne time, the pole spacing must not be too smalL or the Eields at the surface will not be intense enough to start the demagnetization proces~. Thus, to demagnetize the control element 32 of the affixed marker ,' ~. , .
.. . .
2~ 3~
22 without adversely affecting a prerecorded cassette, a field intensity o~ no more than 36,000 A/m pre~erably in the range of 28,000~33,600 A/m at approximately 0.76 mm above the working surface with a pole spacing of 2.36-2.76 poles/cm is preferred.
As shown in Figure 4, the ini~ial peak field resulting from the out~rmost pole of second portion 50 may be somewhat greater than that produced by the remainder of the poles in that portion. A number of field reversals along the second portion 50 are desirable in order to ensure that the magnetization states of the control elements 32 within a marker are reversed at least once before the field gradually decreases. Thus each of the successive fields of fairly constant peak intensities and successively alternating polarities along that portion must have an intensity close to the maximum allowable without adversely aEEecting prerecorded magnetic media to be positioned along the working surface. The presence oE an initial peak field Oe yet greater intensity than that along the remainder of the second portion can thus give rise to different problems. First, if the peak fields along the remainder of that portion are already close to the maximum allowable level, a first peak of still greater intensity will be much more likely to adversely afEect prerecorded media. On the other hand, if all of the intensities are reduced proportionately so that the outermost peak EieLd intensity is within the maximum allowable level, the intensities of the subsequent Etelds may be too low to initiate proper dernagnetization cycles, and the control 3~ .strips may therl not become completely demagnetized~
WhLle it is possible to control both the initial peak field so that it Ls not too hiyh, and the subsequent fields so ~hat they are not too low, normal manuEacturLng tolerances make this diEEicult. For example, if peak intensity of the outermost reyion oE the second portion is made, via appropriate selection of the magnetic strip, to have a nominal intensity of about 32,000 A/m, typical ~L~6~73~
variations due to manu~acturing tolerances will result in some peak field intensities being su~ficiently high so as to adversely affect prerecorded media~ Conversely, if the nominal intensity is decreased to about 28,~00 A/m so that the peak field experienced with typical manufacturing tolerances is below that found to adversely aEEect such recorded media, the minimum peak fields associated with the remainder oE the second portion may be too low to begin a complete magnetization reversal. The control elements of 1~ some markers may then be ultimately left in a non-completely demagnetized state and full sensitivity may not be restored.
With a construction producing Eields haviny the intensities as shown in Figure 4, (i.e., an outer~ost peak ~ield intensity of about 30,~00 A/m and an average peak intensity of about 25,600 A/m along the remainder of the second portion) markers were demagnetized satisfactorily.
When the average peak Eields were decreased by only 1600 A/m, it was observed that the sensitivity of about half of the markers after being passed along the entire working surface, was only about 95~ that observed when higher ~ields were used.
Figure 5A is a cross-sectional view of a construction in which such an undesirably high initial peak field was observed. Within the Erame 3~' was positioned a magnet strip 16' having the ~irst ~40'), second (50') and thircl portion (not shown) as previously described. Only a part of the first portion 40' ancl the second portion 50' are actually shown in Fiyure 5~. guch a strip 16' was desirably forllled of narrow, discrete sections 64, 66, 6~, 70, 72 and 7~ of Plasti~orm Brancl perrnanent magnet material. Thus, 3.2 mm thick, 3.6 mm long and 76 mm wide pieces were injection molcled usin~ appropriate Eixtures, the 3.6 mm lencJth beiny selected so that when the pieces are subsequently assembled side-by-side, a pole spacin~ of 2.76 polels/cm is obtained. After molding, the discrete pieces were exposed to a constant intensity magnetic field, ',............ .
-13- ~73~
thus producing a very uniform level of magnetization in each piece in which the tops of the pieces had a Eirst magnetic polarity and the bottoms had the opposite polarity. The pieces were then assembled, with alternate pieces positioned upside down, and a cover plate 18' added, to provide a succession of alternating ~ields at the working surface l9'. Such an assembly of discrete pieces has been ~ound to provide a more uniform succession of altern~te polarity fields of either constant or regularly decreasing intensity As shown in Figure 5A, the second portion 50' was constructed oE pieces all of which were of the same width and magnetic intensity. With such a construction, the net direction and intensity of the field at any given location along the working surface is primarily controlled by the magnetized pieces directly below that location, and will be secondarily reduced by the opposing fields of the next closest pieces. However, as the ~ield primarily associated with the outermost magnetized piece 64 is not compensated, i.e., reduced by an opposing field from a yet Eurther out magnetized piece the initial peak ~ield intensity may be yreater than that resulting from the remainder of that portion.
Such a result is shown in Figure 5B. The positive and negative peak horizontal E.ield components 76, 7~, ~0 and 82 are there shown to occur at positions above the boundar.Les of each o~ the adjacent pieces, and as each is ~ully compensated, are oE urliform intensities. In contrast, the ~irst peak 8~, belng uncompensatedr has a higher intensity.
In ~ preeerred embodiment, such hlgher initial inten9itie.g mAy be prevented by includiny a yet eurther out maynetized region o~ lower eield strength~ Such an elnbOdiment i8 shown in Figure 6Ar with the resultant ~ield inten.sities set forth in Fiyure 6B. As there shownr the second portion 50 " stil1. includes a plurality of magnetized pieces, 64', 66', 6~', 70', 72', and 74' just as ., ... ~ .
,, : ' , ''.'. ~' ' .. " ' , ' ;. :
-14- ~2~3~
described above. To such an assembly was added an outer piece ~4 which was 2.3 mm thick, and wllich wais slightly larger, i.e., 5.1 mm long in the direction of the assembled strip. This piece was then magne~ized top-to-bottom in the same manner as that of the other pieces, the resultant intrinsic ~ield intensi~y provided by that piece being about one-half that provided by each oE the other pieces.
The bottom of the piece ~4 was positioned coplanar with the remaining pieces, i.e., the top was further from the working surface 19''. The overall construction and placement were thus selected so that, as shown in Figure 6B, the initial peak field intensity 86 was not greater than that of the remaining peak intensities. With such a construction, complete demagnetization of all tested mar~ers was ~ound to result, so that 100~ Oe initial sensitivity was restored.
Figures 7 and 8 further set Eorth the peak field intensities resulting when such an additional piece with lower peak field intensity is not present (Fig. 7) and when it is present (Fig. 8). As shown in Figure 7, if the field along most of the portion 50 is selected to be about 30,400 A/m so as to appropriately condition the control elements of the markers, the initial Eield 88 may exceed 34,400 A/m and thus may advarsely aeect recorded media. Instead, as shown in Figure ~, the addition oE another, lower strength magnetized piece eliminates such an inltial peak and allows the intensities 90 along the entire portion to be optimized.
In the embodiment de~cribed above with reEerence to Figures SA! 5B, 6A, 6B, 7 and ~ the permanently magnetlzed eloncJated section having eirst, second and third portionis, 40, S0 and 60 respectively, were eormed o~
disc~ete separ~te pieces, which aEter being magnetized, were then placed side by side to Eorm the elongated sectic~n. In other embo~liments, such as those described in conjunction with Figureis 1-4, the section may be formed oE
one or more extruded pieces in which each piece is i ,.
-15- ~ ~6 ~ 7 3 8 magnetized with a succession of poles o~ alternate polarity. Accordingly, in the preferred embodiment in which the outermost pole is to provide a less field, the region or piece associated with that pole can be conEiyured to achieve that result in various ways. The region or piece itself can be smaller, it can be positioned Eurther away Erom the workiny surface, and it can be intrinsically weaker, either by being Eormed of a less strong magnetic composition, or by being magnetized to a less intense state. Similarly, the outermost net field at the working surface may be reduced by including a magnetic shim to partially shunt the Eield ~rom the magnets below the surface. Other, analogous techniques to reduce the intensity of the outermost field are likewise within the scope of the present invention.
~5 . : ..: , , ~ . ' , ~ , .
,, ~ .
Patent No. 3,747,086 (Peterson). The control elernent 32 is typically formed of a material such as vicalloy, mac~netic stainless steel or the like, having a predetermined value oE coercive force in the range oE 4000-19,200 ~/m. When such an element is magnetized, it prevents the marker from being detected by the system wherl the marker 22 is present in the interroyation ~one.
The (lemagnetizatLon of the contro1 eLement 32 is 3~ efecte(] upon exposure to ttle ~ieLds provlded by the eLon0ated ma~Jnetic sectlon 16 when ttle eLement 32 is brou(Jht into clo~e proxilllity wlttl the maynetic field~
associated with the section 16 at the working surface L9.
Tlle (letails oE the elongated mayrletic section L6 are shown in the cross sectional view of Figure 2. As may there be seen, the housiny 12 oE the apparatus 10 is shown to have a recess or cavity 14 within which the elongated -8- ~ 3~
magnetic section 16 may be positioned and supported by the housing within the recess, or by a frame 34 with the top oE
the recess enclosed by the cover plate 18. As an alternative, the section may be held in position within the recess 14 by the cover plate 18 (not shown).
As shown in Figure 2 and in greater detail in Figure 3, the elongated magnetic section 16 has a plurality of magnetized regions or poles 36 in a succession of closely spaced fields of alternate polarity and oE
generall~ equal intensity Erom one end of the elongated magnetic section 16 to the other. Each pole 36 extends across the width of the section 16, and the succession oE
poles extends along the length of the section 16. The elongated magnetic section 16 may be made of: ~1) an injection molded permanent magnet material, which is subsequently magnetized after molding and arranged with alternating poles; or (2) a sheet Oe permanent magnet material magnetized with uniform alternating poles. In the illustrated embodiment, the elongated magnetic section 16 was formed of a 2.3 mm thick and 76 mm wide sheet material of the type described above magnetized with 2.36 poles/cm.
The bottom of the recess 1~ on which the magnetic section 16 is positioned is inclined with respect to the working surface l9 Oe the housing 12 so that a Eir.qt portion 40 oE the section 16 exhibits magnetic fields oE
generally decreasing intensity at the working sureace Oe the housing. A second portion 50 is providecl adjacent to the most intense Eield end oE the eirst portion ~0 and planar to the working surEace 19 Oe the housing. The second portion 50 lnclude~ more than one pole and provides alternating fielcls Oe EaLrly constant peak intensltie.s at the working sureace L9 o the housing. The purpose oE the second portion 50 is to assure at least one intense field in a direction oppo~ite to the magnetizat~ion oE the control 35 element 32 in order to properly begin the demagnetization process. rhe second portion 50 also ser~es to eliminate any end effects associated with the Eirst pole 54 of the _9_ ~ 3~
first portion 40 having the most intense field associated therewith. In addition, the low ~ield end of the elongated magnetic section 16 includes a third portion 60 curved for the purpose e~plained hereinafter.
Thus, it has been found that by supporting the above ma~netic section having 2.36 poles per cm on a frame 34 as illustrated in Figures 2 and 3 having a second portion 50 of 2.54 cm, a Eirst portion 40 of 15.2 cm inclined at 2 23" to the workill~ surface 19 of the housing, and a third l~ortion 60 of 5.1 cm having a radius of 31 cm, the poles will exhibit peak fields along the working surface as illustrated in Figure 4, it beiny recognized that the alternations of magnetic polarity between each adjacent pair of poles actually results in a generally sinusoidal variation in the horizontal field along the working surface.
It is believed that the increase in field intensity at the end of the third portion 60 as shown in Figure 4, is the result of the fact that the field at the working surface 19 above the last pole is not subjected to a compensating field from an adjacent pole of opposite polarity. It is essential that this increased field be sufficiently small so as not to allow partial remagnetization oE the control element 32. Tt-us, it has been found that the third portion 60 having an arcuate curve away from the working surface provides a more rapid increase in the distance from the working surface so that a sufficiently low field will be exhibited at the working surface above the last pole to minimize any affect on the control element 32. It should be appreciated that the third portion may alternatively be inclined at a steeper angle of incline than the first portion 40. However, by utilizing an arcuate curve a smoother transition is provided between tile first portion 40 and the third portion 60.
As illustrated in Figure 4, the decrease in intensity is non-uniform. Tllis is believed to be the ~2~ 8 result of small variations in size and magnetization of different poles. However, such minor irregularities can be tolerated so long as the variations are not large enough to prevent demagnetization of the control element 32. If the fields were to decrease too slowly, the elongated section 16 would need to be impracticall~ long, and ie the fields were to decrease too rapidly, the demagnetization would not be complete, especially in view of the non-uniEormities as mentioned above. Thus, demagnetization will occur if on the average the eield intensity at the working surface 19 associated with each successive pole decreases b~ 5 to 20 percent between any two adjacent poles.
It is critical that the field associated with the most intense pole be strong enough to start the demagnetization process. This has been found to equal approximately one and one half times the predetermined value of coercive ~orce of the control elements. However, it is also critical that the Eield intensity not be strong enough to adversely affect a magnetically sensitive object 70 contained within the article 20 during demagnetization oE the control elements. Prerecorded audio cassettes are adversely a~eected by magnetic fields greater than about 100 oersteds while prerecorded video cassettes can withstand higher Eields, perhap~s as much as 16,000 ~/m. It is necessary that the fields oE the demagnetization apparatus decrease rapidly away erom the working surface 19 50 as to be suficierltly small at a distance D measured from the working surface 19 to the macJnetically sensitive object 70. ~ typical distance D is within the range oE
1.6-3.2 mm. '1'his is accomplished by keeping the pole spaciny small enough so l:hat away from the surface, difeerent poles contribute to the efective Eield, resulting ln partiaL cancelLation Erom adjacent poles oE
opposite polarity. At the sarne time, the pole spacing must not be too smalL or the Eields at the surface will not be intense enough to start the demagnetization proces~. Thus, to demagnetize the control element 32 of the affixed marker ,' ~. , .
.. . .
2~ 3~
22 without adversely affecting a prerecorded cassette, a field intensity o~ no more than 36,000 A/m pre~erably in the range of 28,000~33,600 A/m at approximately 0.76 mm above the working surface with a pole spacing of 2.36-2.76 poles/cm is preferred.
As shown in Figure 4, the ini~ial peak field resulting from the out~rmost pole of second portion 50 may be somewhat greater than that produced by the remainder of the poles in that portion. A number of field reversals along the second portion 50 are desirable in order to ensure that the magnetization states of the control elements 32 within a marker are reversed at least once before the field gradually decreases. Thus each of the successive fields of fairly constant peak intensities and successively alternating polarities along that portion must have an intensity close to the maximum allowable without adversely aEEecting prerecorded magnetic media to be positioned along the working surface. The presence oE an initial peak field Oe yet greater intensity than that along the remainder of the second portion can thus give rise to different problems. First, if the peak fields along the remainder of that portion are already close to the maximum allowable level, a first peak of still greater intensity will be much more likely to adversely afEect prerecorded media. On the other hand, if all of the intensities are reduced proportionately so that the outermost peak EieLd intensity is within the maximum allowable level, the intensities of the subsequent Etelds may be too low to initiate proper dernagnetization cycles, and the control 3~ .strips may therl not become completely demagnetized~
WhLle it is possible to control both the initial peak field so that it Ls not too hiyh, and the subsequent fields so ~hat they are not too low, normal manuEacturLng tolerances make this diEEicult. For example, if peak intensity of the outermost reyion oE the second portion is made, via appropriate selection of the magnetic strip, to have a nominal intensity of about 32,000 A/m, typical ~L~6~73~
variations due to manu~acturing tolerances will result in some peak field intensities being su~ficiently high so as to adversely affect prerecorded media~ Conversely, if the nominal intensity is decreased to about 28,~00 A/m so that the peak field experienced with typical manufacturing tolerances is below that found to adversely aEEect such recorded media, the minimum peak fields associated with the remainder oE the second portion may be too low to begin a complete magnetization reversal. The control elements of 1~ some markers may then be ultimately left in a non-completely demagnetized state and full sensitivity may not be restored.
With a construction producing Eields haviny the intensities as shown in Figure 4, (i.e., an outer~ost peak ~ield intensity of about 30,~00 A/m and an average peak intensity of about 25,600 A/m along the remainder of the second portion) markers were demagnetized satisfactorily.
When the average peak Eields were decreased by only 1600 A/m, it was observed that the sensitivity of about half of the markers after being passed along the entire working surface, was only about 95~ that observed when higher ~ields were used.
Figure 5A is a cross-sectional view of a construction in which such an undesirably high initial peak field was observed. Within the Erame 3~' was positioned a magnet strip 16' having the ~irst ~40'), second (50') and thircl portion (not shown) as previously described. Only a part of the first portion 40' ancl the second portion 50' are actually shown in Fiyure 5~. guch a strip 16' was desirably forllled of narrow, discrete sections 64, 66, 6~, 70, 72 and 7~ of Plasti~orm Brancl perrnanent magnet material. Thus, 3.2 mm thick, 3.6 mm long and 76 mm wide pieces were injection molcled usin~ appropriate Eixtures, the 3.6 mm lencJth beiny selected so that when the pieces are subsequently assembled side-by-side, a pole spacin~ of 2.76 polels/cm is obtained. After molding, the discrete pieces were exposed to a constant intensity magnetic field, ',............ .
-13- ~73~
thus producing a very uniform level of magnetization in each piece in which the tops of the pieces had a Eirst magnetic polarity and the bottoms had the opposite polarity. The pieces were then assembled, with alternate pieces positioned upside down, and a cover plate 18' added, to provide a succession of alternating ~ields at the working surface l9'. Such an assembly of discrete pieces has been ~ound to provide a more uniform succession of altern~te polarity fields of either constant or regularly decreasing intensity As shown in Figure 5A, the second portion 50' was constructed oE pieces all of which were of the same width and magnetic intensity. With such a construction, the net direction and intensity of the field at any given location along the working surface is primarily controlled by the magnetized pieces directly below that location, and will be secondarily reduced by the opposing fields of the next closest pieces. However, as the ~ield primarily associated with the outermost magnetized piece 64 is not compensated, i.e., reduced by an opposing field from a yet Eurther out magnetized piece the initial peak ~ield intensity may be yreater than that resulting from the remainder of that portion.
Such a result is shown in Figure 5B. The positive and negative peak horizontal E.ield components 76, 7~, ~0 and 82 are there shown to occur at positions above the boundar.Les of each o~ the adjacent pieces, and as each is ~ully compensated, are oE urliform intensities. In contrast, the ~irst peak 8~, belng uncompensatedr has a higher intensity.
In ~ preeerred embodiment, such hlgher initial inten9itie.g mAy be prevented by includiny a yet eurther out maynetized region o~ lower eield strength~ Such an elnbOdiment i8 shown in Figure 6Ar with the resultant ~ield inten.sities set forth in Fiyure 6B. As there shownr the second portion 50 " stil1. includes a plurality of magnetized pieces, 64', 66', 6~', 70', 72', and 74' just as ., ... ~ .
,, : ' , ''.'. ~' ' .. " ' , ' ;. :
-14- ~2~3~
described above. To such an assembly was added an outer piece ~4 which was 2.3 mm thick, and wllich wais slightly larger, i.e., 5.1 mm long in the direction of the assembled strip. This piece was then magne~ized top-to-bottom in the same manner as that of the other pieces, the resultant intrinsic ~ield intensi~y provided by that piece being about one-half that provided by each oE the other pieces.
The bottom of the piece ~4 was positioned coplanar with the remaining pieces, i.e., the top was further from the working surface 19''. The overall construction and placement were thus selected so that, as shown in Figure 6B, the initial peak field intensity 86 was not greater than that of the remaining peak intensities. With such a construction, complete demagnetization of all tested mar~ers was ~ound to result, so that 100~ Oe initial sensitivity was restored.
Figures 7 and 8 further set Eorth the peak field intensities resulting when such an additional piece with lower peak field intensity is not present (Fig. 7) and when it is present (Fig. 8). As shown in Figure 7, if the field along most of the portion 50 is selected to be about 30,400 A/m so as to appropriately condition the control elements of the markers, the initial Eield 88 may exceed 34,400 A/m and thus may advarsely aeect recorded media. Instead, as shown in Figure ~, the addition oE another, lower strength magnetized piece eliminates such an inltial peak and allows the intensities 90 along the entire portion to be optimized.
In the embodiment de~cribed above with reEerence to Figures SA! 5B, 6A, 6B, 7 and ~ the permanently magnetlzed eloncJated section having eirst, second and third portionis, 40, S0 and 60 respectively, were eormed o~
disc~ete separ~te pieces, which aEter being magnetized, were then placed side by side to Eorm the elongated sectic~n. In other embo~liments, such as those described in conjunction with Figureis 1-4, the section may be formed oE
one or more extruded pieces in which each piece is i ,.
-15- ~ ~6 ~ 7 3 8 magnetized with a succession of poles o~ alternate polarity. Accordingly, in the preferred embodiment in which the outermost pole is to provide a less field, the region or piece associated with that pole can be conEiyured to achieve that result in various ways. The region or piece itself can be smaller, it can be positioned Eurther away Erom the workiny surface, and it can be intrinsically weaker, either by being Eormed of a less strong magnetic composition, or by being magnetized to a less intense state. Similarly, the outermost net field at the working surface may be reduced by including a magnetic shim to partially shunt the Eield ~rom the magnets below the surface. Other, analogous techniques to reduce the intensity of the outermost field are likewise within the scope of the present invention.
~5 . : ..: , , ~ . ' , ~ , .
,, ~ .
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An apparatus which in movement relative to an article, having affixed thereto a dual status anti-theft marker including at least one remanently magnetizable control element having a coercive force of a predetermined value, demagnetizes said control element to change the status of the marker, said apparatus comprising: a housing having a working surface relative to which an article may be moved, and an elongated section of a permanent magnetic material associated with said housing, said elongated section having a plurality of closely spaced poles, said poles exhibiting at the working surface a succession of fields of alternating polarity and a first portion of which exhibits at the working surface fields of generally decreasing intensities along at least that portion of said elongated section; each pole extending across the width of said elongated section and the succession of poles extending along the length of said elongated section; and wherein the field intensity at said working surface associated with the most intense pole in said succession is approximately one and one half times said predetermined value of the coercive force of the control element, whereby movement of said article relative to the working surface of said housing from a position adjacent the field associated with the most intense field past each generally successively weaker field of opposite polarity, will expose the marker affixed to the article to fields of alternate polarities and generally decreasing intensities, thereby substantially demagnetizing the control element of said marker, and the close spacing of the alternate poles results in a rapid decrease in the intensities of the fields above the working surface so as not to adversely affect a magnetically sensitive object contained within the article.
2. The apparatus defined in claim 1, wherein the pole to pole spacing along the length of the elongated section is no more than 0.635 cm.
3. The apparatus defined in claim 1, wherein said first portion is inclined at a predetermined angle relative to said working surface of said housing to exhibit said succession of fields of alternate polarity and of decreasing intensities at said working surface.
4. The apparatus defined in claim 3, wherein said elongated section further comprises a second portion associated with that end of said first portion which exhibits the most intense field at the working surface of said housing, said second portion includes more than one pole, said poles exhibit at the surface of said housing a succession of closely spaced poles of alternating polarity and of approximately uniform intensities, and the maximum intensity of the fields at said working surface associated with said second portion is approximately one and one half times the predetermined value of coercive force of said control element.
5. The apparatus according to claim 4, wherein said second portion includes an outermost pole having a peak intensity less than that of the other regions, thereby ensuring that the peak intensity at the working surface of the outermost field is not greater than that associated with the other poles.
6. An apparatus according to claim 5, wherein said outermost pole extends approximately parallel to the working surface and at about the same height relative thereto as the remainder of the second section, and has an intrinsic field intensity approximately one-half that provided by the remainder of the poles thereof.
7. An apparatus according to claim 1, wherein said elongated section of permanent magnet material has substantially the same composition throughout and the outermost pole of said second portion thereof comprises a piece of said material of smaller dimensions than that associated with each pole in the remainder of the section.
8. An apparatus according to claim 1, wherein said elongated section comprises an assembly of discrete pieces of permanent magnetic material, each piece other than an outermost piece being magnetized to provide substantially the same intrinsic field intensity, and the outermost piece being magnetized to provide a peak intensity less than that provided by the other pieces.
9. The apparatus defined in claim 1, wherein said elongated section further comprises a third portion associated with that end of said first portion which exhibits the least intense field at the working surface of said housing, and said third portion includes a plurality of closely spaced poles, said poles exhibit at said working surface a succession of fields of alternating polarity and of generally decreasing intensities at a greater rate along said third portion than along said first portion.
10. The apparatus defined in claim 1, further comprising a thin non-magnetic plate covering the working surface of said housing to protect said elongated section while providing a durable wear surface allowing the magnetic lines of flux to extend therethrough substantially unattended.
11. The apparatus defined in claim 10, wherein said housing further comprises a recess opening onto the working surface of said housing within which said elongated section is positioned.
12. The apparatus defined in claim 1, wherein said elongated section comprises a plurality of permanent magnets.
13. The apparatus defined in claim 12, wherein said permanent magnets are injection molded.
14. The apparatus defined in claim 1, wherein said elongated section includes a permanent magnet material which has been magnetized with approximately uniform alternating poles.
15. The apparatus defined in claim 1, wherein said poles of alternate polarity are adjacent one another.
16. The apparatus defined in claim 1, wherein said poles are within the range of 3.15 to 1.6 poles/cm.
17. The apparatus defined in claim 1, wherein the average field intensity at the working surface of said housing associated with each pole of said first portion intermediate said most intense pole and said least intense pole decreases in the range of 5 to 20 percent between any two adjacent fields.
18. The apparatus defined in claim 1, wherein the field above said most intense pole is within the range of 28,000 to 33,600 A/m.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/887,721 US4689590A (en) | 1986-07-21 | 1986-07-21 | Demagnetization apparatus for magnetic markers used with electromagnetic article surveillance systems |
| US887,721 | 1986-07-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1269738A true CA1269738A (en) | 1990-05-29 |
Family
ID=25391722
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000541907A Expired - Lifetime CA1269738A (en) | 1986-07-21 | 1987-07-13 | Demagnetization apparatus for magnetic markers used with article surveillance systems |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4689590A (en) |
| EP (1) | EP0257767B1 (en) |
| JP (1) | JP2551593B2 (en) |
| AU (1) | AU589793B2 (en) |
| CA (1) | CA1269738A (en) |
| DE (1) | DE3776463D1 (en) |
Families Citing this family (20)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4811000A (en) * | 1988-03-03 | 1989-03-07 | Sensormatic Electronics Corporation | Article enclosure with magnetic marker deactivating means |
| US4967185A (en) * | 1989-08-08 | 1990-10-30 | Minnesota Mining And Manufacturing Company | Multi-directionally responsive, dual-status, magnetic article surveillance marker having continuous keeper |
| US5187462A (en) * | 1990-02-15 | 1993-02-16 | Minnesota Mining And Manufacturing Company | Multiple magnet assembly for use with electromagnetic article surveillance markers |
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| US5341125A (en) * | 1992-01-15 | 1994-08-23 | Sensormatic Electronics Corporation | Deactivating device for deactivating EAS dual status magnetic tags |
| US5285182A (en) * | 1992-09-03 | 1994-02-08 | Minnesota Mining And Manufacturing Company | Desensitizing apparatus for electromagnetic article surveillance system |
| US5432499A (en) * | 1993-05-27 | 1995-07-11 | Minnesota Mining And Manufacturing Company | Collector type article surveillance marker with continuous keeper |
| FR2709182A1 (en) * | 1993-08-20 | 1995-02-24 | Crescenzo Eric | Methods and devices for magnetizing or demagnetizing moving objects. |
| US5405702A (en) * | 1993-12-30 | 1995-04-11 | Minnesota Mining And Manufacturing Company | Method for manufacturing a thin-film EAS and marker |
| JP3683585B2 (en) * | 1994-03-10 | 2005-08-17 | ミネソタ マイニング アンド マニュファクチャリング カンパニー | Deactivators for magnetic markers in electronic article surveillance systems |
| US5625339A (en) * | 1996-01-08 | 1997-04-29 | Minnesota Mining And Manufacturing Company | Apparatus for changing the status of magnetic markers in an electronic article surveillance system |
| DE19628722A1 (en) * | 1996-07-17 | 1998-01-22 | Esselte Meto Int Gmbh | Device for deactivating a securing element for electronic article surveillance |
| US6002335A (en) * | 1998-02-18 | 1999-12-14 | 3M Innovative Properties Company | Small magnet resensitizer apparatus for use with article surveillance systems |
| US6057763A (en) * | 1998-04-10 | 2000-05-02 | 3M Innovative Properties Company | Method and apparatus for activating and deactivating electromagnetic article surveillance markers |
| AU2004201043B2 (en) * | 1998-10-13 | 2007-10-25 | Minnesota Mining And Manufacturing Company | Far field magnet resensitizer apparatus for use with article surveillance systems |
| JP2002527837A (en) * | 1998-10-13 | 2002-08-27 | ミネソタ マイニング アンド マニュファクチャリング カンパニー | A far-field magnet resensitization device for use with an article monitoring system |
| US6222453B1 (en) * | 1999-03-24 | 2001-04-24 | Nexpak | Apparatus for holding a compact disk and accepting affixation of an electronic anti-theft tag |
| US6783070B2 (en) * | 2001-01-02 | 2004-08-31 | Ronald L. Faria | Scaneze check-in-check-out library workstation |
| DE10307515A1 (en) * | 2003-02-21 | 2004-09-02 | Checkpoint Systems International Gmbh | Device and method for activating and deactivating magnetic security tags |
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|---|---|---|---|---|
| US3790945A (en) * | 1968-03-22 | 1974-02-05 | Stoplifter Int Inc | Open-strip ferromagnetic marker and method and system for using same |
| US3747086A (en) * | 1968-03-22 | 1973-07-17 | Shoplifter International Inc | Deactivatable ferromagnetic marker for detection of objects having marker secured thereto and method and system of using same |
| US3765007A (en) * | 1969-07-11 | 1973-10-09 | Minnesota Mining & Mfg | Method and apparatus for detecting at a distance the status and identity of objects |
| US3665449A (en) * | 1969-07-11 | 1972-05-23 | Minnesota Mining & Mfg | Method and apparatus for detecting at a distance the status and identity of objects |
| US3609611A (en) * | 1969-09-26 | 1971-09-28 | Robert A Parnell | Method and apparatus for stabilizing permanent magnets |
| US4271782A (en) * | 1978-06-05 | 1981-06-09 | International Business Machines Corporation | Apparatus for disorienting magnetic particles |
| US4222517A (en) * | 1978-09-18 | 1980-09-16 | Samuel Cornelious Evans | Magnetic marker |
| JPS59101408U (en) * | 1982-12-24 | 1984-07-09 | 株式会社井上ジャパックス研究所 | Demagnetizing device |
| US4499444A (en) * | 1983-05-20 | 1985-02-12 | Minnesota Mining And Manufacturing Company | Desensitizer for ferromagnetic markers used with electromagnetic article surveillance systems |
| US4665387A (en) * | 1983-07-13 | 1987-05-12 | Knogo Corporation | Method and apparatus for target deactivation and reactivation in article surveillance systems |
-
1986
- 1986-07-21 US US06/887,721 patent/US4689590A/en not_active Expired - Lifetime
-
1987
- 1987-07-13 CA CA000541907A patent/CA1269738A/en not_active Expired - Lifetime
- 1987-07-15 AU AU75694/87A patent/AU589793B2/en not_active Expired
- 1987-07-16 EP EP87306311A patent/EP0257767B1/en not_active Expired
- 1987-07-16 DE DE8787306311T patent/DE3776463D1/en not_active Expired - Fee Related
- 1987-07-20 JP JP62179268A patent/JP2551593B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JP2551593B2 (en) | 1996-11-06 |
| JPS6341009A (en) | 1988-02-22 |
| US4689590A (en) | 1987-08-25 |
| EP0257767B1 (en) | 1992-01-29 |
| DE3776463D1 (en) | 1992-03-12 |
| AU7569487A (en) | 1988-01-28 |
| EP0257767A1 (en) | 1988-03-02 |
| AU589793B2 (en) | 1989-10-19 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |