Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-08-09
2004-08-10
Pham, Toan N. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572100, C340S572600, C235S493000
Reexamination Certificate
active
06774793
ABSTRACT:
TECHNICAL FIELD
This invention relates to a deactivating element for a magnetic surveillance marker, a method of manufacturing the deactivating element, and a deactivatable magnetic marker incorporating the deactivating element.
BACKGROUND ART
Magnetic type article surveillance systems are known wherein markers containing highly permeable magnetic elements are affixed to articles to be protected from theft, such that when the articles are introduced to an interrogation zone the marker causes a detectable magnetic field disturbance which is used to activate an alarm. Such markers commonly additionally include a deactivating element which renders the marker either detectable or undetectable, depending on the state of its magnetization.
Such magnetic surveillance systems monitor the removal or passage of articles from a protected area such as a site of purchase of the articles as in a store, or a site of use of the articles as in a reference library.
Exit from the protected area involves passage through the interrogation zone which detects the presence of the marker on the article if the article is being improperly removed from the protected area.
Deactivation of magnetic electromagnetic article surveillance is described in U.S. Pat. No. 3,747,086, which describes the operating principle of a deactivatable electromagnetic marker, and the general magnetic properties of the constituent magnetic elements.
Prior markers are comprised of one or more elongated pieces of highly permeable, easily saturatable magnetic material which form the “detected element” in close proximity to one or more deactivating elements of low permeability, magnetically semi-hard material which form the “deactivating element”. When the deactivating element is magnetized, it carries a remanent magnetic flux which saturates the nearby soft magnetic element, at least in some regions, in such a way as to make the soft magnetic element undetectable in the interrogation device employed in the interrogation zone.
Prior manifestations of deactivating elements may be categorized into four classes. First, and most simply, the deactivating element consists of one continuous strip of semi-hard magnetic material which is very nearly the same length as the detected element within the marker. In order to deactivate such a marker, a DC magnetic field is applied sufficient to saturate the semi-hard material of the deactivating element. The deactivation element thereafter acts like a single bar magnet where the magnetic flux generated is adequate to locally saturate or magnetically bias the detected element, making the detected element undetectable in the interrogation device.
Deactivating elements of this class are described in U.S. Pat. Nos. 3,747,086; RE32,427 (U.S. Pat. No. 4,298,862); U.S. Pat. No. RE32,428 (U.S. Pat. No. 4,484,184); U.S. Pat. Nos. 5,401,584; 4,857,891 and 5,181,021.
In a second class, the deactivating element is again a continuous strip of semi-hard magnetic material which is very nearly the same length as the detected element in the marker. In this class, however, deactivation is achieved by magnetizing the semi-hard material in such a way as to create a pattern of alternating magnetic dipoles within the material. Where like ends of these dipoles meet, magnetic flux is forced out from the material sufficiently to saturate the nearby detected element, making the detected element undetectable in the interrogation zone.
The principle problem with deactivation elements of this class is that a complex deactivating tool is required to create the necessary pattern of magnetization within the deactivating element, and the use of such a tool requires passing the marker in near contact to the tool, with a carefully controlled orientation and direction of travel. In addition, such deactivation elements tend to be costly because magnetic material of rather high magnetic coercivity and remanence is required to retain the magnetization pattern, and generate adequate deactivating flux.
Deactivating elements of this second class are described in U.S. Pat. Nos. 4,568,921; 4,665,387 and 4,684,930.
In the third class, the deactivation element contains multiple pieces of semi-hard material, each of significantly shorter length than the detected element, and distributed more-or-less uniformly along the length of the detected element. A marker using such a deactivating element is deactivated by applying a sufficiently large magnetic field to saturate the semi-hard pieces comprising the deactivating element, leaving them each magnetized.
The spaces between the separate pieces of semi-hard magnetic material play the important role of allowing the magnetic flux generated by the pieces to locally saturate the nearby detected element. These saturated regions effectively break up the magnetic continuity of the detected element and make it undetectable in the interrogation zone.
As compared to the other two classes, a cost saving is possible because less semi-hard material is required to achieve the same deactivation performance. An additional cost reduction is possible because a semi-hard material of a lower magnetic remanence may be used.
Examples of this third class of deactivating element include the use of flakes, chips and most commonly pieces of ribbon. The principle problem with manifestations of this class is that care must be taken to size and position the small flakes, chips or separate pieces of ribbon of semi-hard magnetic material along the marker, and to ensure their relatively uniform distribution. While material handling and placing solutions have been developed to address this problem, there remain limitations on the production rate and cost of such markers.
Deactivating elements of this third class are described in U.S. Pat. Nos. 5,121,106; 5,191,315; 5,246,522; RE32,427 (U.S. Pat. No. 4,298,862); U.S. Pat. No. RE32,428 (U.S. Pat. No. 4,484,184) and U.S. Pat. No. 5,146,204.
In a fourth class, the deactivating element is formed from a thin continuous strip of semihard magnetic material with length very nearly equal to the length of the detected element in the marker, the deactivating element being made of a material having magnetic properties which can be reduced by annealing. By heat treating the strip in local sections, it is possible to create regions with significantly reduced magnetic remanence. This has the effect of creating alternating magnetizable and non-magnetizable body segments within the mechanically continuous strip. In principle, this class of deactivating elements offers the handling and ease-of-application advantages of a continuous strip, and the magnetic advantages of separated magnetic pieces, allowing the magnetic flux from the magnetizable sections to more easily saturate the nearby detected element. An additional benefit is that deactivation is accomplished by simply applying a DC magnetic field of sufficient magnitude, and therefore a complex deactivating tool is not required.
In practice, these benefits have been difficult to realize for a number of reasons. First, commercially available semihard strip materials are costly, so it has been favorable to chop the strip and apply it to the detector material in spaced apart pieces, rather than bear the expense of annealed non-magnetic material separating the magnetic zones.
Also, given the importance of keeping the material of the deactivator and detector elements as close together as possible, the geometry of the strip deactivator is not well matched to a number of marker geometries, notably those where the detector material is of near circular cross section.
Furthermore, manufacturing processes proposed for strip deactivators of this class have difficulty ensuring uniform and reliable heating of localized sections of the strip. This is particularly true with electrical current heating, where the length of the annealed section must be significantly greater than the width of the strip annealed section to obtain relatively uniform current and heat distribution.
Further complications with the manufacture of strip deactivators include electrical
Brauer Stephan F.
Lebeau Thomas
Strom-Olsen John
(Ogilvy Renault)
MXT Inc.
Pham Toan N.
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