GB2201126A - Security documents - Google Patents

Abstract

A card or badge carries data in binary form by providing windows of high and low transmissivity to infra-red radiation. The high transmissivity windows are transparent whereas the low transmissivity windows are partially obscured by two groups of spaced opaque areas each extending partially across the window. The areas are printed on a surface which will be in the interior of the finished card by means for example of a thermal dot printer. One group of areas is printed by energising a first group of dot printing elements and the other group of areas is printed by energising a second group of elements, the arrangement of the areas being such that the two groups of printing elements have approximately equal duty cycles. <IMAGE>

Description

CARD OR BADGE FOR CARRYING DATA This invention relates to cards or badges for carrying data and in particular to such cards and badges in which the data is carried in a concealed manner and can be read from the card or badge by a reading device.

Such cards or badges have many applications. One example of such an application is for use in relation to locations for which access is restricted to authorised persons only.

Access to the location is controlled by an electronically operated lock which is responsive to data carried by a card. The card may carry merely sufficient data to operate the lock or when it#is desired to maintain a record of those entering the location, the data carried by the card may identify the card holder. Another application is for controlling access to a computer system such as through terminals of a banking or credit card computer system where only authorised users may gain access. In this application the data carried by the card identifies the holder of the card for accounting purposes. Cards may also be used in time recording systems for monitoring the times of arrival and departure of employees at a place of work, the cards carrying identification data for the employees.

In those applications where the card is used as a security measure, it is essential to ensure that the data carried by the card cannot be changed whereby unauthorised use of the card could be facilitated. In addition it is often desirable that the data is recorded on the card in such a manner that it is not readily discernable by a user of the card or any third party into whose hands the card may fall inadvertently or by theft.

Various methods have been proposed and are used for recording data in cards and badges. A commonly used method is to provide, on a face of the card, a stripe of magnetic material on which data can be recorded and subsequently read by means of magnetic transducing heads. Another method is to use a laminated card in which an inner layer carries data recorded as a series of areas of differing opacity to infra-red radiation. The data is usually recorded in binary form with transparent regions or windows representing binary digits of one value and partially transparent or opaque regions or windows representing binary digits of the other value. The outer layers of the card are bonded to the inner layer and are transparent to infra-red radiation but are opaque to radiation in the visible spectrum.Thus the data can be read from the card by means of a photocell sensitive to infra-red radiation passing through the card from a source of infra-red radiation but cannot be read by visual inspection of the card.

The reading device for the cards may be of simple construction and hence the manufacturing costs may be kept low if the card is fed manually through a reading position.

As a result of this manual feeding of the card, the speed at which the card is moved will be indeterminate and is likely to be non-uniform. In order to allow for~varying speeds of movement of the card the card needs to carry means to provide an indication of the position of recording of each binary digit along a track on the card. A convenient method of providing such indications is to record the data in a self clocking form. The binary digits of a string of data may be recorded along a track as a series of regions separated by opaque stripes extending across the track, the regions being differentiated to represent the two different binary digits. In one proposal differentiation of the regions is effected by forming the regions to have two different transmissivities to infra-red radiation.This is accomplished by the provision of shading bars extending in the lengthways direction of the track across the regions required to be of lower transmissivity.

A convenient method of manufacturing cards for reading by infra-red radiation is to form the opaque stripes-and other opaque portions by a printing process on a sheet which is of plastics material and then to bond the printed sheet between outer sheets. The printing is conveniently effected by using a thermal dot printer in which the dots are selectively heated to-cause ink on a transfer ribbon to be transferred to the surface of the plastic sheet as the sheet passes the printing head. However a problem has been found to arise with the use of thermal printing due to thermal inertia in the printing head. When an opaque strip is to be printed all the elements of the head are heated for a period, dependent upon the speed of feeding the sheet past the printing head, such that the desired length of strip ( measured in the direction of feed of the sheet) is printed on the sheet.However when shading bars are=printed to extend across selected areas t6 represent the other binary value, certain of the elements corresponding to the widths of these bars are maintained in the heated state for the duration of the passage of these areas past the printing head. As a consequence these elemen-ts tend to retain more heat than the other elements so that when the next -opaque -stripe is printed the boundary of the stripe tends to be poorly defined.

According to one aspect of t-he present invention a card or badge carrying digital data for reading by a reading device wherein the digital data is recorded along a track on the card extending substantially parallel to an edge of the card, successive digits of the data being represented by regions of substantially similar dimensions spaced along the track and separated by opaque regions, digits of a first value being represented by regions having a first transmissivity and digits of a second value being represented by regions having a second transmissivity lower than said first transmissivity the lower transmissivity of the second regions is effected by the provision of a first group of opaque areas spaced tranversely of said track and extending from one edge of the region only partially across the region toward an opposite edge thereof and by the provision of a second group of opaque areas spaced transversely of said track aligned with the spaces between the opaque areas of the first group and extending from said opposite edge of the region only partially acros-s the region toward said one edge thereof.

Preferably the digital data carried by the card is concealed from inspection by visible radiation but is readable by transmission of infra-red radiation through the card or badge.

Usually the digital data would be recorded in binary for-m.

Preferably the opaque areas have substantially similar dimensions and may be rectangular.

The opaque areas may have other forms such as tapering or part circular.

According to another aspect of the invention a data reading system includes a card or badge as hereinbefore defined and a reading device having a scanning aperture for scanning along the track on the card to read the digital data carried by said card or badge, the dimension of the scanning aperture in a direction transverse to the track is less than the transverse width of the track and the pitch in a direction transverse to the track of the opaque regions is a sub-multiple of said dimension of the scanning aperture.

According to a further aspect of the invention a method of printing a representation of digital data along a track on a surface by means of -a thermal printer having printing elements selectively energisable to transfer ink-from a transfer ribbon to said surface comprises the steps of causing relative movement between the surface and the printing elements such that the print elements are positioned successively along the length of the-track; energising a group df printing elements at successive intervals to print a series of opaque stripes extending transversely of said track and substantially equally spaced along the length of said track to define digit recording regions between said stripes; and to record digits bf one value in one or more selected regions by energisation of a first sub-group of said group of elements during passage of only a first part of the region or regions relative- to the print elements and by energisation of a second sub-group of said group of elements during passage of only a second part of the region or regions relative to the print elements, element 3 in one sub-group being excluded from the other sub-group.

An- embodiment of the invention will now be described by way of-example with reference to the drawings in which: Figure 1 is an exploded view of a card and Figure 2 shows an inner surface of the card bearing a data tracks in accordance with the invention.

Referring to the drawings, a card shown in Figure 1 includes a sheet of synthetic pl-astics material 10 carrying on one surface one or more data tracks 11 extending substantially parallel to one edge of the card. The sheet 10 is transparent to infra-red radiation and the data is recorded on the sheet by means of markings which are opaque to infra-red radiation as will be explained in more detail hereinafter. In order to prevent erasure of, or changes to, the recorded data the sheet 10 is bonded between outer sheets 12. The outer sheets 12 are transparent to infra-red radiation but are sufficiently opaque to radiation in the visible spectrum to prevent visual inspection of the data carried by the card.

The data is recorded in binary form as a string of binary digits along the track or tracks 11. The positions of recording the binary digits are bounded by means of a series of opaque stripes 13 extending across the width of the track and equally spaced along the length of the track 12. Opaque start and end markers 14 are provided at the ends of the tracks 11. These markers 14 have an extent greater than that occupied by recording positions for the data in order to provide to a reading device unique signals indicating-that the entire data track has been read.

The positions at which digits of data are recorded along the track can be considered as transparent windows which permit infra-red radiation to pass through the card and the opaque stripes. In order to record binary digits which can have one of two values the windows are made to have a high or low tranmissivity of infra-red radiation. Windows which are to have high transmissivity representing one binary value are transparent regions 16 bounded by the stripes 13.

Windows which are to have low transmissivity representing the other binary value are regions 17 bounded by the stripes 13 and partially obscured by opaque areas 15. The opaque areas 15 extend partially across the window in a direction lengthwise of the track and consist of one group of areas extending from one edge of the window and another group of areas extending from the other edge of the window.

The areas in the two groups are interspaced so that, looked at in a lengthwise direction of the track within a window, an opaque area 15 is followed or preceded by a transparent area. In a preferred form the opaque areas are of rectangular form and extend approximately half way across the windows. In order to provide the desired differentiation between the opaque stripes 13, the windows of high transmissivity and the windows of low transmissivity it is preferred that the opaque areas 15 are of such extent as to reduce the transmissivity of the windows to approximately half that of the unobscured windows.

A preferred method of recording the data on the sheet 10 makes use of a thermal dot printer to transfer ink from a transfer ribbon to the plastic sheet. The thermal dot printer has a print head consisting of a plurality of selectably heatable print elements arranged in a line. The sheet 10 is fed past the print head in the direction of the length of the data track to be printed and with the print head orientated such that the line of elements extends perpendicular to the direction of feed.The print elements are energised at equal intervals for a period of time sufficient to print the ,tripes 13 and, where it is desired to record a binary value to be represented by a partially obscured wind-ow, selected ones of the print elements corresponding to the required opaque areas of one group are maintained in an energised state for a period corresponding to approximately half the length of the window and then are de-energised. Following this different ones of the printing elements are selected to print the other group of opaque areas.Thus it will be seen that printing elements used for printing the opaque areas to form partially obscured windows of low transmissivity are energised for only approximately ha-lf the time of passage of the length of the window past the printing head-and as a consequence most or all of the printing elements have substantially equal duty cycles. As a result the residual heat in the printing -elements is approximately uniformly spread between the printing elements so that the stripes 13 are printed with a well defined substantially straight trailing edge regardless of whether or not the stripe follows a window of high or low transmissivity.

It will be appreciated that the opaque areas 15 may be of other shape than rectangular as described hereinbefore. For example the areas may be of tapered form with the widest part abutting the stripes 13 in which case the printing elements are progressively de-energised and energised and the areas may extend more than half way across the windows.

Other forms which the opaque areas may have are approximately semi-elliptical or semi-circular.

The dimensions of the windows are typically 6 to 8 mm.

transverse to the length of the track and 0.5 mm. along the track. In order to allow high tolerance in manual feeding of the card through a reading device, the reading device has a scanning aperture considerably smaller than the width of the track and may have for example a dimension of 2 mm.

across the track and 0.4 mm. along the track. The stripes 13 have a dimension lengthwise of the track which is slightly less than that of the scanning aperture of the reading device. Because the scanning aperture has a dimension transverse to the track considerably smaller than that of the windows and, due to possible misalignment of the card, it may be aligned with any part of the width of the track the opaque areas 15 of the windows of low transmissivity need to be substantially uniformly distributed across the width of the track in such a manner that the infra-red radiation transmitted by a window of low transmissivity is substantially unaffected by misalignment of the card. Accordingly the dimensions of width and pitch, transversely of the track, of the opaque areas 15 are arranged to be sub-multiples of the transverse dimension.

While the description hereinbefore relates to cards or badges intended to be read by means of infra-red radiation it should be understood that the representation of and method of recording digital data described hereinbefore are not limited to cards intended to be read by infra-red radiation and may be used for other purposes where it is desired to provide regions of different transmissivity to radiation.

Claims (12)

1. A card or badge carrying digital data for reading by a reading device wherein the digital data is recorded along a track on the card extending substantially parallel to an edge of the card, successive digits of the data being represented by regions of substantially similar dimensions spaced along the track and separated by opaque regions, digits of a first value being represented by regions having a first transmissivity and digits of a second value being represented by regions having a second transmissivity lower than said first transmissivity and wherein the lower transmissivity of the second regions is effected by the provision of a first group of opaque areas spaced tranversely of said track and extending from one edge of the region only partially across the region toward an opposite edge thereof and by the provision of a second group of opaque areas spaced transversely of said track aligned with the spaces between the opaque areas of the first group and extending from said opposite edge of the region only partially across the region toward said one edge thereof.

2. A card o-r badge as claimed in claim 1 wherein the digital data carried by the card is concealed from inspection by visible radiation.

3. A card or badge as claimed in claim 1 or 2 wherein the data is readable by transmission of infra-red radiation through the card or badge.

4. A card or badge as claimed in any preceding claim wherein the digital data is recorded in binary form.

5. A card or badge as claimed in any preceding claim wherein the opaque areas have substantially similar dimensions.

6. A card or badge as claimed in any preceding claim wherein the opaque areas are rectangular.

7. A card or badge as claimed in any one of claims 1 to 5 wherein the opaque areas taper in a direction lengthwise of the track.

8. A card or badge as claimed in any one of claims 1 to 5 wherein the opaque areas are part circular.

9. A data reading system including a card or badge as claimed in any preceding claim and a reading device having a scanning aperture for scanning along the track on the card to read the digital data carried by said card or badge wherein the dimension of the scanning aperture in a direction transverse to the track is less than the transverse width of the track and the pitch in a direction transverse to the track of the opaque regions is a submultiple of said dimension of the scanning aperture.

10. A method of printing a representation of digital data along a track on a surface by means of a thermal printer having printing elements selectively energisable to transfer ink from a transfer ribbon to said surface comprising the- steps of causing relative movement between the surface and the printing elements such that the print elements are positioned successively along the length of the track; energising a group of printing elements at successive intervals to print a series of opaque stripes extending transversely of said track and substantially equally spaced along the length of said track to define digit recording regions between said stripes; and to record digits of one value in one or more selected regions by energisation of a first sub-group of said group of elements during passage of only a first part of the region or regions relative to the print elements and by energisation of a second sub-group of said group of elements during passage of only a second part of the region or regions relative to the print elements, elements in one sub-group being excluded from the other sub-group.

11. A card or badge carrying digital data constructed as hereinbefore described with reference to the drawings.

12. A method of of printing a representation of digital data along a track on a surface as hereinbefore described with reference to the drawings.