EP0257767A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Improved demagnetization apparatus for magnetic markers used with article surveillance systems
Assignee: 3M Co
•
Filing: 1987-07-16
•
Granted: —
•
Expires: 2007-07-16
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 (16) contained within a housing (12) which exhibits a succession of fields of alternate polarity and a portion (40) 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 (18) 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.
Inventors
- 👤 Eugene C C/O Minnesota Mining And Heltemes
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 02:00
CPC Classifications
H; H01; H01F; H01F13/00; H01F13/006
Claims Analysis
Total Claims: 19
Claim 1
Independent Claim
275 words
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 (12) having a working surface (19) relative to which an article may be moved, and an elongated section (16) of permanent magnetic material associated with said housing, said elongated section (16) having a succession of alternately polarized permanently magnetized regions extending along the length of the section, each of which regions extends across the width of said section, said regions exhibiting at the working surface a succession of fields of alternating polarity, wherein said section has a first portion (40) which exhibits at the working surface fields of generally decreasing intensities, and wherein the field intensity at said working surface associated with the most intense magnetized region 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 magnetized regions 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.
Claim 2
Independent Claim
275 words
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 (12) having a working surface (19) relative to which an article may be moved, and an elongated section (16) of permanent magnetic material associated with said housing, said elongated section (16) having a succession of alternately polarized permanently magnetized regions extending along the length of the section, each of which regions extends across the width of said section, said regions exhibiting at the working surface a succession of fields of alternating polarity, wherein said section has a first portion (40) which exhibits at the working surface fields of generally decreasing intensities, and wherein the field intensity at said working surface associated with the most intense magnetized region 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 magnetized regions 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.
Claim 3
Dependent Claim
30 words
The apparatus defined in claim 1, wherein the pole to pole spacing of the magnetized regions along the length of the elongated section (16) is no more than 1.27 cm.
Claim 4
Dependent Claim
42 words
The apparatus defined in claim 1, wherein said first portion (40) 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.
Claim 5
Dependent Claim
103 words
The apparatus defined in claim 3, wherein said elongated section (16) further comprises a second portion (50) 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 magnetized region, said regions exhibits 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.
Claim 6
Dependent Claim
52 words
The apparatus according to claim 4, wherein said second portion (50) includes an outermost magnetized region (84) 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 regions.
Claim 7
Dependent Claim
51 words
An apparatus according to claim 5, wherein said outermost magnetized region (84) 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 regions thereof.
Claim 8
Dependent Claim
52 words
An apparatus according to claim 1, wherein said elongated section of permanent magnet material has substantially the same composition throughout and the outermost magnetized region of said second portion thereof comprises a piece of said material of smaller dimensions than that associated with each magnetized region in the remainder of the section.
Claim 9
Dependent Claim
65 words
An apparatus according to claim 1, wherein said elongated section (16ʹʹ) comprises an assembly of discrete pieces (64, 66, 68, 70, 72, 74) of permanent magnetic material, each piece other than an outermost piece (84) being magnetized to provide substantially the same intrinsic field intensity, and the outermost piece (84) being magnetized to provide a peak intensity less than that provided by the other pieces.
Claim 10
Dependent Claim
81 words
The apparatus defined in claim 1, wherein said elongated section (16) further comprises a third portion (60) 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.
Claim 11
Dependent Claim
42 words
The apparatus defined in claim 1, further comprising a thin non-magnetic plate (18) 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.
Claim 12
Dependent Claim
29 words
The apparatus defined in claim 10, wherein said housing further comprises a recess (14) opening onto the working surface of said housing within which said elongated section is positioned.
Claim 13
Dependent Claim
16 words
The apparatus defined in claim 1, wherein said elongated section comprises a plurality of permanent magnets.
Claim 14
Dependent Claim
13 words
The apparatus defined in claim 12, wherein said permanent magnets are injection molded.
Claim 15
Dependent Claim
24 words
The apparatus defined in claim 1, wherein said elongated section includes a permanent magnet material which has been magnetized with approximately uniform alternating polarities.
Claim 16
Dependent Claim
16 words
The apparatus defined in claim 1, wherein said regions of alternate polarity are adjacent one another.
Claim 17
Dependent Claim
18 words
The apparatus defined in claim 1, wherein said regions are within the range of 3.15 to 1.6 poles/cm.
Claim 18
Dependent Claim
51 words
The apparatus defined in claim 1, wherein the average field intensity at the working surface of said housing associated with each magnetized region of said first portion intermediate said most intense region and said least intense region decreases in the range of 5 to 20 percent between any two adjacent fields.
Claim 19
Dependent Claim
24 words
The apparatus defined in claim 1, wherein the field above said most intense magnetized region is within the range of 28,000 to 33,600 A/m.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.