GB2263848A

GB2263848A - Security tag activating/deactivating apparatus

Info

Publication number: GB2263848A
Application number: GB9300996A
Authority: GB
Inventors: Ramesh Chandra Patel
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-01-13
Filing date: 1993-01-13
Publication date: 1993-08-04
Anticipated expiration: 2013-01-13
Also published as: GB2263848B; GB9200589D0; GB9300996D0

Abstract

Apparatus for changing the magnetic state of a tag magnetisable material comprises an a.c. voltage source, a rectifier having an input derived from said a.c. voltage source and switch means having an output selectively connectable to either the a.c. voltage source or 10 the d.c. output of the rectifier. An electromagnet connected to the output of the switch means thereby selectively receives either an a.c. supply for demagnetising of the tag or a d.c. supply for magnetising (or remagnetising) of the tag.

Description

SECURITY APPARATUS DESCRIPTION This invention relates to security apparatus and in particular to apparatus for the security coding and decoding (or marking and erasing) of articles, e.g. library books.

It is known to provide in or on articles such as library books a strip or other element of magnetisable material and provide detection apparatus, e.g. adjacent the exit of the premises housing such articles, to detect whether any such articles leaving the premises have the strip in a magnetised state or in a demagnetised state. With books, the magnetisable strip may be located in the spine or binding or on a fly-leaf. Where the premises are a lending library, security marking and erasing apparatus is provided to magnetise the strips of those books being legitimately borrowed and to demagnetise the strips of the books returned to the library and newly entered into the library.

Thus all books in the library and available for borrowing can have their strips in a demagnetised state and if a book is removed from the library unlawfully, i.e. without first having its strip magnetised, this will be detected by the detection apparatus located at the libary exit and which can generate a visual and/or an audible alarm signal.

The security marking and erasing apparatus durrently used to magnetise and demagnetise the elements of magnetisable material incorporate complex electrical- and/or electronic circuits to effect, separately, strip demagnetisation on the one hand and strip magnetisation (or re-magnetisation) on the other hand. They are expensive and large items occupying considerable space.

It is accordingly considered desirable to provide security marking and erasing apparatus which can overcome or at least minimise the above-mentioned and/or other disadvantages of the prior art apparatus.

According to one aspect of the present invention there is provided security marking and erasing apparatus for changing the magnetic state of an article-associated element of magnetisable material, said apparatus comprising an a.c. voltage source, a rectifier having an input derived from said a.c.

voltage source, switch means having an output selectively connectable to either a first input from said a.c. voltage source or a second input from the d.c. output of the rectifier, and an electromagnet connected to the output of the switch means thereby selectively to receive either an a.c. supply for demagnetising of a said element or a d.c. supply for magnetising (or re-magnetising) of a said element.

Advantageously the switch means comprises a bipolar 2-way switch.

Preferably, the rectifier comprises two pairs of diodes in a bridge circuit and a capacitor across the output of the bridge.

Advantageously the a.c. voltage source comprises a transformer having a centre tap, the input to the rectifier being from across one end and the centre tap. Preferably the a.c. voltage input to the switch means is from across the two ends of the transformer.

By way of example, one embodiment of the present invention will now be described with reference to the accompanying drawings of which: Figure 1 is a schematic perspective view of security marking and erasing apparatus embodying the present invention, Figure 2A is a circuit diagram of circuit components included in the embodiment of Fig 1, and Figure 2B is a modified circuit diagram and shows optional, additional components for the Fig 1 embodiment.

The apparatus illustrated in Fig 1 comprises a generally parallelepiped housing 30 having a shallow, flat-bottomed channel 31 in its upper surface. When viewed as shown in Fig 1, the left-hand end of the channel 31 will in use be the 'entrance' end for receiving the article (having the element of magnetisable material of which the magnetic state or characteristic is to be changed), and the righthand end of the channel 31 will in use be the 'exit' end for that article. The upstandinq walls 32,33 of the channel 31 have their inwardly-facing surfaces 34,35 and their outwardly-facing surfaces 36,37 directed substantially vertically. The arris between the outwardly-facing surface of one channel wall (e.g. surface 37) and the top surface of that wall is provided with an inclined recess 40 in which a bipolar 2-way switch 18 is located.

Typically, the housing 30 may be molded of plastics material, and have dimensions of the order of approximately 22cm long x 11.5cm wide x 7.5cm high.

Within the housing 30, the apparatus comprises a transformer 10 having a centre tap 13 between its ends 11,12. A conventional rectifier 15 - comprising two pairs of diodes 14 in a bridge circuit and a capacitor 16 receives its a.c. input from across the transformer's end 11 and the centre tap 13, and supplies its d.c. output across the capacitor 16 to one pair of input poles 1,2 of the bipolar 2-way switch 18 (see Fig 2A). The other pair of input poles 3,4 of the switch 18 are a.c. supplied directly from the ends 11,12 of the transformer 10. The output poles 5,6 of switch 18 are connected directly to an electro-magnet 20 that is located towards the 'exit' end of the flat-bottomed channel 31 and closely adjacent its upper surface (see Fig 1). Typically the electromagnet 20 may be approximately 8cm in diameter.

In a preferred form, the transformer (e.g. an ALTA1 transformer, model 1783C) provides a stepped-down voltage of 60 VAC across its ends 11,12 and 30 VAC at its centre tap 13. The input to the transformer may be derived from the mains 220/240V supply either directly (as in the circuit of Fig 2A) or via the optional circuit of Fig 2B described below.

To effect magnetisation (or re-magnetisation) of a said element of magnetisable material, the position of switch 18 is selected to interconnect poles or terminals 1,5 and 2,6.

This results in a d.c. supply to electromagnet 20 from the rectifier. To effect de-magnetisation of a said element, the position of switch 18 is selected to interconnect poles or terminals 3,5 and 4,6. This results in an a.c. supply to electromagnet 20 direct from the transformer 10.

In the event that continual energisation of the electromagnet 20 may give rise to an undue heating effect, the apparatus may be modified to the circuit of Fig 2B. This provides a switching function for the power supply to the transformer 50 (replacing transformer 10 of Fig 2A). This ancillary power switching circuit is driven at a low rectified voltage derived from a mains-to-12VAC step-down transformer and rectifier section 44, and comprises a photo-emitter diode 38 and a photo-receiver diode 39 optically associated therewith.

The photo-emitter diode 38 is mounted in one of the inwardly-facing surfaces 34,35 (e.g. surface 34) of the housing 30 near the 'ehtrance' end of the channel 32, and the photo-receiver diode 39 is mounted in the other one of the inwardly-facing surfaces 34,35 (e.g. surface 35) transversely opposite the photo-emitter diode 38 and such as to receive the beam of light (or other electro-magnetic radiation) emitted therefrom. The beam is broken by the passage therethrough of the article (having the element of magnetisable material of which the magnetic state or characteristic is to be changed).

When the beam is broken, it causes the three cascadeconnected BC182L transistors 41,42 and 43 to conduct and trigger the timing device 45. This timing device causes a triac 46 to conduct and causes a red light emitting diode 48, connected in the current path to the triac 46, to be switched ON and signal this conductive condition. The triac's conductive condition, which is maintained for a predetermined time period that is pre-settable via a variable resistor 47, permits current flow to the input windings of the transformer 50. The latter provides a 100VAC output across its secondary winding terminals 11,12 to which the rectifier circuit 15 is connected. The latter provides the optional d.c. supply to electromagnet 20 (as in the circuit of Fig 2A), the a.c. supply being derived from across the secondary winding's terminals 11,12 - there being no centre tap 13 shown and the terminal 4 of two-way bipolar switch 18 being shown connected to the secondary winding's terminal 12.

The LED indicator 48 may be mounted on the top surface of housing wall 33 or in the recess 40 to indicate when the transformer 10 and electromagnet 20 are conducting.

It will be appreciated that the illustrated apparatus can be used for many other articles and is not restricted to use for books or to lending libraries.

It will also be appreciated that the apparatus may be modified either by the omission of certain features (e.g.

the indicator lamp 48 and/or the switching circuit of Fig 2B and its optically associated devices 38,39 - which are also shown in Fig 1), or to include additional features, e.g. an indicator lamp to indicate the selected position of switch 18 (for demagnetisation or for (re-)magnetisation) and/or a sensing coil to test the magnetic status of an article that has been subjected to the (re-)magnetising or demagnetising effect of the electromagnet 20.

Other modifications and embodiments of the invention will be readily apparent to those skilled in this art. All such modifications and embodiments are to be deemed within the ambit and scope of the invention, and the invention is not to be deemed limited to the particular embodiment(s) hereinbefore described which may be varied in construction and detail without departing from the scope of the patent monopoly hereby sought.

Claims

1. Security marking and erasing apparatus for changing the magnetic state of an article-associated element of magnetisable material, said apparatus comprising an a.c. voltage source, a rectifier having an input derived from said a.c.

2. Security marking and erasing apparatus according to Claim 1, wherein the switch means comprises a bipolar 2-way switch.

3. Security marking and erasing apparatus according to either preceding Claim, wherein the rectifier comprises two pairs of diodes in a bridge circuit and a capacitor across the output of the bridge.

4. Security marking and erasing apparatus according to any preceding Claim, wherein the a.c. voltage source comprises a transformer having a centre tap, the input to the rectifier being from across one end and the centre tap.

5. Security marking and erasing apparatus according to Claim 4, wherein the a.c. voltage input to the switch means is from across the two ends of the transformer.

6. Security marking and erasing apparatus according to Claim 4 or Claim 5, wherein the input to the transformer is direct from the mains supply.

7. Security marking and erasing apparatus according to Claim 4 or Claim 5, wherein the input to the transformer is derived from an electronic switching circuit operable upon interruption of a beam of light or other electromagnetic radiation.

8. Security marking and erasing apparatus according to Claim 7, wherein said switching circuit includes a timing device to maintain the input to the transformer, and hence operation of the electromagnet, for a predetermined period.

9. Security marking and erasing apparatus according to Claim 8, wherein said switching circuit includes setting means for setting the said predetermined period provided by the timing device.

10. Security marking and erasing apparatus for changing the magnetic state of an article-associated element of magnetisable material, said apparatus being substantially as herein described with reference to and/or as illustrated in Figs 1 and 2A (without the modification of Fig 2B) of the accompanying drawings.

11. Security marking and erasing apparatus for changing the magnetic state of an article-associated element of magnetisable material, said apparatus being substantially as herein described with reference to and/or as illustrated in Figs 1, 2A and 2B of the accompanying drawings.