Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2~745'7
FIELD OF THE INVENTION
This invention relates to an instruction or
identification card or badge and its use in a time
recording system.
BACKGROUND TO THE INVENTION
There are many applications in which it is necessary
to confirm the identity of an individual. Such
applications include the purchase of merchandise using a
credit card, cashing che~ues at banks or validation of
cheques when used in payment for merchandise or services,
admission to locations where only authorised personnel
must be allowed accessr and the identification of users of
a time-recording system for use in monitoring the arrival
and departure of employees at a place of work.
In some of these applications it is necessary to
ensure that the holder of suc,h a card or any third party
into whose hands it may pas~; as a result of theft or
casual loss, is unable to challge the code embodied in or
on the card, and thereby gain unauthorised access or
obtain merchandise dishonestly.
A number of methods have been described for ensuring
that the codes cannot be altered without mutilatin~ a card
so drastically that it is no longer capable of heing used.
Among these methods are several in which the coding is
concealed within the structure of the card, in~isible to
the naked eye but detectable by a variety of techniques
depending on magnetic interaction, radio frequency
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12~79LS~
coupling, radioactive detection, reflection or attenuation
of infra-red radiation or other physical phenomena.
A number of techniques have been described in which
infra-red radiation is applied to one side of a composite
card and a series of infra~red detectors located on the
other side respond to the presence or absence of a
transmission path through the card at specified locations.
Some such methods have been disclosed by Scuitto and
Kramer in US Patent 3875375, by Lawrence Systems Inc., in
US Patent 406~910, by Interflex ~atensystem of Germany, in
UK Patent 2009477, by EMI Ltd, in VK Patent 1581624 and by
J.R. Scantlin of Transaction Technology Inc. in US Patents
3858032, 3819910 and 3802101.
Most of the above mentioned patents disclose
techniques in which several parallel tracks of data are
scanned by a set of several photodetectors, one such track
being used as a clock track while the corresponding data
bits in the other tracks are either translucent to
represent a binary digit ONE or opaque to represent a
binary di~it ZERO or vice ver~a. The mechanisms used to
transport the cards passed the read heads and the parallel
signal paths from the several tracks to the associated
digital electronic systems have various levels of
complexity according to the details of the intended
application.
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SUMMARY OF TE~E INVENTION
Accordingly the present invention provides a
simpler method of coding a card, in which all data is
located serially along a single track, which includes
distinct symbols for both ONEs and ZEROs and since
neither of them is represented by an opaque area,
positive clocking is inherent in the single track
without any constraint on the rate of scanning.
According to an aspect of the invention, a
combination of identification card and reading apparatus
for the card is provided. The combination comprises a
card provided with a concealed code which, while being
invisible to the naked eye when viewed in visible light,
is readable in transmission using infrared radiation.
The code is characterized by successive digits
represented by transparent windows, alternating with
regions opaque to infrared radiation. The windows and
opaque regions are arranged along a line parallel to one
edge of the card and each window represents a binary
digit of the code with one binary digit being
represented by wide rectangular windows while the other
binary digit is represented by significantly narrower
windows.
An optoelectronic reader consists of a singlP
source of infrared radiation and a single infrared
detector arranged to either sîde of a card slot to
enable the coded card to be read on passage along the
slot.
An electronic system is responsive to a signal from
the reader and has a first threshold detector arranged
to produce a clock signal each time that the reader
detects a window in the card and a second threshold
detector arranged to produce a second signal to
represent a binary ONE when a second threshold level of
output from the electronic reader is passed. The
absence of the second signal, when a clock signal is
detected~ indicates the presence of a binary ZERO where
the code windows are self-clocking and the code can be
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canned independently of the rate at which the card is
moved along the slot.
For non-binary codes, windows or more than two
discrete widths may similarly be used.
Other features of the invention will be apparent
from the appended claims to which attention is hereby
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directed,
BRIEF DESCRIPTION OF THE ~RAWINGS
_
The invention will now be described by way of
example snly with reference to the accompanying drawings,
in which:
Figure 1 is an exploded view of the several layers
of which the plastics card is constructed;
Figure 2a shows in detail typical dimensions of two
types of transparent windows representing the binary
digits ONE and ZERO respectively;
Figure 2b shows the output current from the single
phototransistor when it responds to the passage of two
types of transparent window between it and the source of
infra-red radiation;
Figure 3 illustrates a typical configuration of a
module inccrporating the infra-red sensitive components
and a card guide, al~ of which can be mounted with minimal
mechanical disturbance in an existing apparatus, and
requires only three electrical conductors to connect it
into the parent apparatus.
Figure 4 shows an arrangement in which a card is
provided with four different codes any one of which may be
presented to the code reader according to which way round
the card is presented.
Figure 5 shows a circuit diagram of an embodiment of
the electronics incorporated in the module;
Figure 6 defines the actual shape of a moulded part
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5~
two of which joined together form the basic structure
illustrated schematically in Figure 3;
Figures 7a, 7b are exploded and diagrammatic plan
views of a further embodiment of the plastics card.
A sheet of photographic film 6 may be exposed over
most of its are~ to produce a layer of silver opaque to
infra-red radiation, except in those areas which have been
covered during exposure. The exposed and developed film
has areas 10, 12 forming a series of ~ransparent windows
spaced more or less equally along a line to form a code
zone 8 resembling a conventional bar-code of the type used
in reflected light.
This code zone 8 may be located in any part of the
sheet, with its long dimension parallel to the long
dimensioll of the sheet 6, but in a preferred embodiment it
is located near one corner of the sheet 6 for reasons
which will become apparent below In another embodiment,
the sheet 6 may have smaller dimensions than shown in
Figure 1, being in fact only marginally larger in
dimensions than the code zone 8.
Two thicker sheets 2, 4 of opaque thermoplastic
material~ typically 0.2 mm thick black polyvinylchloride
are cut or moulded to a generally rectangular shape with
or without rounded corners, and of dimensions larger than
those of the coded sheet 6 to form the visible body of the
assembled card. The outer faces 3~ 5 of these sheets may
be printed or embossed with proprietary labels, the name
., ~
31 2~79LS~
of the cardholder, a registered number or the like and
then laminated with a transparent protective layer of PVC
or other similar clear plastics 9 a magnetic strip and a
space for a specimen signature, as is usual with such
cards.
~ t least one of the inner surfaces of the sheets 2,
4 may be provided with a recessed area (or areas) 7
slightly larger than the area of sheets 6, so that when
the assembly is p~t together, the two visibly opaque
layers 2 and 4 may be intimately joined to each other
round their periphery by heat sealing or by adhesive, so
as to conceal the fact that the sheet of film 6 is
enclosed between them. The sheet 6 may be held securely
between the sheets 2 and 4 by friction but is preferably
secured by adhesive either in localised spots or evenly
spread over the whole of its two surfaces~ The latter
will produce a stronger struclure which will be unlikely
to delaminate accidentally. Although sheet 6 has been
described as consisting of exposed black and white
photographic film it could alternatively be a sheet of
transparent plastics film on which the code pattern 8 is
printed in ink of a type having good attenuation of
transmitted infra-red radiation, or it could be a sheet of
opaque material such as metal foil or metal film-coated
paper or plastics, on which areas transparent to infra-red
could be produced by known printing methods such as spark
erosion etching or laser beams.
S~
The thickness of the two black plastics layers 2, 4
must be such that the card as a whole is not translucent
in normal visible light, and there is no means other than
infra-red radiation (or perhaps X-rays or Alpha-rays in
the case of a metal-based inner layer) by which the
internal coding is detectable.
Figure 2a shows an enlarged view of the strip of
coded zone 8. It will be seen that the codings take the
form of transparent rectangular areas all (typically~ 6 mm
high perpendicular to the length of the strip 8 but of at
least two different widths.
Two different window widths 10 and 12 may be used to
represent the binary digits ONE and ZERO respectively.
Preferably the wider windows ]0 will be used to represent
ONEs and the narrower windows :l2 will be used to represent
ZEROs, but the converse arrangement may e~ually be used.
In the embodiment to be described hereafter~ it is assumed
that the larger windows 10 represent ONEs.
Figure 3 shows two elevations of a code reader
module which may be used to read the codes described
above. Figure 3a shows a cross section on line A-A of
Figure 3b, and Figure 3b shows a cross-section on line B-B
of Fiyure 3a.
Two rectangular walls of rigid plastics or metal 30
are joined by spacers 31 along two of their long sides and
one short side to form a slot 32 wide enough conveniently
to receive the assembled plastic card 1 and long enough to
~26;~5~
allow it to be inserted for about three-quarters of its
length into the slot before coming up against the end wall
33.
About a third of the distance along the slot and
offset to one side when viewed from the open end (as in
Figure 3b~ apertures 20, 22 are provided in each of the
two walls of the slot 32 facing each other and of
dimensions corresponding to those of the larger windows 10
in the coded sheet 6. Above one of these apertures is
mounted an infra-red light emitting diode or solid state
laser 19, while below the other 22 is a phototransistor 23
responsive to infra-red radiation. Between them, they
define a beam of infra-red radiation of cross-sec~ion
nominally equal to the larger size window 10.
While it is desirable that the smaller dimension of
the rectanglar apertures 20~ 22 is not significantly
different from the corresponding dimension of wide windows
10, it is advantageous to make the larger dimension of
apertures 20, 22 typically 20% larger or smaller than the
corresponding dimension of the windows 10, 12. This
ensures that the output signals from the phototransistor
23 are not critically dependent on correct lateral
positioning of the card 1 in the slot 32.
The card 1 may be pushed by hand into the slot 32
against frictional resistance from the spring-loaded panel
70, the appropriate way round so that the windows 10, 12
of the coded strip 8 pass in succession between the
4~
apertures 20 and 22. Until the presentation of the card,
there will have been no obstruction in the optical path
between the l~e~dr and the phototransistor, but the first
significant change to occur when the card is presented
will be that the dark leading edge of the code 8 will be
detected. The response of the reader to ~his signal is to
increase the current supply to the l.e.d. in order to
improve the sensitivity of the reader to the code.
As the first wide window 10 shown at the left-hand
side of Figure 2a begins to allow radiation from the
l.e.d. 19 to reach the phototransistor 23, the output
signal from the phototransistor begins to depart from a
"dark" leve] 13 shown diagrammatically in Figure 2b, and
rises to a maximum level 15 when the first wide window 10
is aligned optimally with the apertures 20, 22.
As the card is moved further into the slot 32 the
signal level from phototransistor 23 falls as the
radiation reaching it decreases and returns to below
threshold level 13 when the window 10 has completely
passed the apertures 20, 22. The spacing hetween
successive windows is such as to ensure that this
condition is met after the passage of each window. The
same result occurs each time a wide window 10 passes the
apertures 20, 22.
When the third window shown in Figure 2a reaches the
apertures 20, ~2, this being a narrow one 12 assumed for
ease of illustration to be half as wide as a wide window
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10/ the quantity of radiation reaching the phototransistor
i5 only half as great as that passing a large window 10.
Assuming that the phototransistor has a linear response to
the quantity of radiation falling on it, its output signal
will reach a level 14 nominally half that produced by the
wider windows lOo If/ in practice,the response of the
phototransistor is non-linear at the levels of radia~ion
employed, the ratio of widths between wide and narrow
windows 10, 12 may be adjusted accordingly, or it may
prove convenient to work with output signals having ratios
different from two-to-one. There is clearly scope for
adjustment as known to those skilled in the art, to
optimise the discrimination between ONEs and ZEROs.
It has been found that t:he precision of the method
is adequate to allow the use of more than two discrete
window sizes. Thus it becomes possible to use a ternary
code using three sizes oE window, a quarternary code using
four si~es of window, and even a quinternary or hexa~ code
with five or six sizes of window respectively. The use of
such codes in place of binary would enable larger code
numbers to be accommodated in a given area, or allow a
given range of code numbers to be accommodated in a
smaller arear both of which are advantageous features.
~ he use of such codes would also add to the security of
the system since they could be more dîfficult to interpret
without the correct reader.
Rather than arranging always to look for the peak
~37 4~j~
signal levels produced when a window passes between the
apertures 20, 22, it iG more convenient to set threshold
levels, such as those represented in Figure 2b, 16r 17.
Whenever the signal exceeds the lowest threshold 16 this
is interpreted by the control electronics of the parent
system as the arrival of a digit, and may be used to
generate a clock signal. Whenever the highest threshold
17 is exceeded, the electronics interprets this as
representing the most significant digit value, ONE in the
case of a binary system (or ZERO if the inverse
significance has ~een chosen). ~imilarly, the attainment
of other intermediate thresholds may be interpreted as the
presence of digits of intermediate significance, when
systems other than binary are being used.
The preferred embodiments have the space 11 between
windows approximately equal to the width of the wider
windows 10~
Figure 4 shows in cross section to reveal the coded
sheet 6, a card 1 according to the invention. In this
embodiment four separate codes have been provided in four
symmetrical positions in the ca~d so that code 8 may be
selected if its end of the card is inserted into the
reader slot, and with its side under the optical reader
components, If it is desired to read code 28 ~he card
would be presented with the other end entering the slot
first, and with the same face uppermost. To select code
38 the same end would be presented as for code 8 but the
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~.20t745~7
card would be presented upside down. Likewise code 18
could be selected with the card both reversed and upside
down. It is thus possible to use one card to input four
distinct codes to a reader. This could be useful for
example in the case of a time clock when one code could be
allocated for clocking-on and a different one for
clocking-off. Alternatively the four codes could be used
to authorise four different classes of non-standard
operations, such as working overtime, arriving late with
authority and the like.
It will be obvious to those skilled in the art that
less than four codes could be accommodated, and that two
codes could be provided for if the optical components were
arranged on the centreline of the card slot and the codes
8, 18 were aligned on the centreline of the card.
It could also be arranged that only one of the four
codes was a valid one, and this would be read on
presenting the card in one of the less obvious
orientations, the other three codes being arranged to
sound an alarm alerting a supervisor to possible
unauthorised use.
Since the code which passes between the optical
reader componen~s is arranged ~o pass completely passed
the reading station and can be read "on the fly" as each
element of the code passes the read station, it can be
arranged that the code is read either as the card is
inserted into the slot, or it may be read as it is
~2~7~157
withdrawn. Preferably, the code is read t~ice, once on
insertion and again on ~ithdrawal~ ~f appropriate
arrangements are made to load the code into one register
when it is read on insertion, and into a second register
on withdrawal, the contents of the two registers may be
used to verify each other, and the code read is accepted
as valid only if the versions held in the two registers
agree.
Figure 5 shows a simple digital circuit capable of
recognising the ONEs and ZEROs and outputting these in
computer compatible form to subsequent circuits of any
digital system with which the unit may be employed.
In this circuit diagram, the light emitting diode 19
which provides the source of (preferably infra-red)
radiation is shown connected through a series resistor 42
typically of 5,000 ohms resistance which allows a dc
current of nominally 1 milliamp to flow from a 6 volt
supply through the l.e.d. 19 to produce a low intensity
level of radiation in order to conser~e power. When no
card is present between this source and the
phototransistor 23, the phototransistor will detect the
low level of radiation and output a si~nal on its emitter
which, after processing in the interface unit 50 returns a
signal to the transistor 44 to keep it switched off. When
a card 1 is inserted between the light source 19 and the
phototransistor ~3 the change in output is used to cause
transistor 44 to switch on and shunt the 5,000 ohm
1~
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resistor 42 with one of a significantly lower value, such
as 270 ohms 43. This causes the current flowing in the
l~e.d. 19 to increase to typically 20 milliamps, so
illuminating the card with a greatly increased intensity
S of infra-red radiation. At this higher level of
radiation, the phototransistor operates at a higher level
of collector current when a better signal to noise ratio
and higher frequency response are obtained as the
alternate opaque and transparent strips of the code 8 pass
between the l.e.d. 19 and the phototransistor 2~.
The capacitor 48 connected across the emitter
resistor 46 of transistor 23 is provided to smooth out any
high frequency extraneous noise which might otherwise
impair the clarity of the signal output from the emitter
of the phototransistor 23. This output may be processed
in one of several ways, interface unit 50 may therefore
take any one of several forms. Three methods are
preferred, and the choice of which is used will depend on
the details of the application and the characteristics of
the central equipment in conjunction with which the module
is to be used.
Interface unit 50 may for example be a voltage to
frequency converter of the type in which the input voltage
is used to change the capacitance of a voltage-sensitive
capacitor. This capacitance, being used as a component in
an oscillator circuit would ~hen produce an output 58 of
varying frequency dependent on the applied voltage.
~a2~7~
Alternatively, interface unit 50 may take the form
of a conventional analogue/digital converter, wherein the
variable input voltage signal is converted to a serial
binary digit stream on output terminal 58.
A third convenient embodiment of the interface unit
50 would involve the use of voltage comparators. The
output signal from the phototransistor would in this case,
be supplied simultaneously to one input of each of a set
of voltage comparators, the other inputs of which would be
set permanently at fixed fractions of the maximum voltage
prvduced by the phototransistor when responding to wide
code windows 10. When all the comparators detected
variable inputs exceeding their fixed reference voltages,
or thresholds 16, 17 as defined in Figure 2b, an output
coded to represent binary ONE would be output at 58. When
not all the comparators indicated their thresholds to have
been exceeded, the appropriate outputs would be provided
to represent these lower signal levels.
When using comparators internal to the module, each
comparator output could be associated with a digital
latch, so that once the threshold had been exceeded the
latch would remain set until the signal output fell below
a low threshold to represent zero transmission through the
coded card, at which level all latches would be reset.
In the preferred embodiment of the design, the first
coded window in every code used would be a wide window 10
and the amplitude o~ the signal output from the
16
57
phototransistor 23 when this window was scanned would be
used as the reference voltage applied to the comparator
system used in unit 50. ~hen the output from
the phototransistor is converted in unit 50 to a frequency
or absolute digital representation of the in~tantaneous
signal levels, the recognition of the maximum amplitude
corresponding to the first bit of the code, and the
comparison of subsequent amplitudes with the first one
may be carried out using a microprocessor resident in the
central equipment~
The basic construction of the card slot and its
associated assembly has been described with reference to
Figure 3~ For manufacturer it is of course preferable to
use a low-cost moulded assembly and the proposed shape of
lS one of the two identical halves of such a moulding is
illustrated in Figure 6. It should be noted that the
apertures 62 on this figure are designed to hold the
- l.e.d. 19 and the phototransistor 23 facing each other in
the opposing apertures of a pair of mouldings, and that
the square recesses 64 are intended to accommodate small
inserts of photographic film exposed to define the
rectangular apertures designated as 20 and 22 in Figure 3.
The moulded posts 66 are intended to support the printed
circuit cards 26, 28 shown in Figure 3. The three fixing
holes 68 are provided for convenient mounting of the
module on assemblies in a parent system.
The plastic panel 70 shown within the card slot in
17
~L2q:~174S7
Figure 3 is lightly spring loaded so that it offers a
small frictional resistance to the insertion of the card
into the slo~ and also presses the card intimately and
repeatably into contact with the lower face of the slot.
Advantages are claimed for the proposed apparatus in
comparison with previously known techniques, as follows:
i) With only one light emitting diode and one
phototransistor, the cost of these and the
other associated components is minimised.
ii) Since all measurements are made using the same
l.e.d. and phototransistor, and since the
output signal level is standardised on reading
the first bit of each code, no other
compensation for the different sensitivities
of several optoelectronic components is
required.
(iii) Since the only difference between coded ONEs
and ZEROs lies in the different window widths,
the tolerances on alignment of the
optoelectronic components are not critical,
nor is it necessary to use components with
narrow beam widths.
(iv~ Because there are definite representations for
both binary digits ONE and ZERO, the code
provides its own clock signals, and therefore
the speeds of insertion and withdrawal are not
critical.
18
~2~C)74~57
~v) Since the bits are closely packed along the
length of the code and the code only occupies
one line about 6 mm wide, only a small area of
the card needs to be reserved for the code.
The rest of the card may be used for eye-
readable information. The narrow width
accommodated by the code makes it easy to
accommodate it between lines of printed text
on the card, so making it particularly
unobtrusive
(vi) The ability to accommodate several codes on
one card, which can be read independently
using the same reading facilities offers
advantages not offered by other designs of
similar card.
tvii) The manner in which the code is wholly
accommodated in one line close to the
reference edge of the card and the height of
the individual code windows is greater than
that of the aperture through which the infra
red beam is passed, ensure that the effect of
any skew which may occur when a card is
presented to a reader is minimised~
The apparatus disclosed may be fitted into the
cabinet which houses a time recording or other automatic
checking system, or alternatively it may be located
remotely from the central apparatus to which its signals
19
l~Q~gL57
are transmitted.
When fitted locally, the power supply to the module
may be a conventional d.c. supply of typically 5 volts and
a local battery 54 as shown in Figure 5 would not be
necessary. When operated remotely, however, it would be
advantageous to provide a local rechargeable battery
capable of supplying the 20mA of current to energise the
l.e d. 19 as required for short periods, and which could
then be trickle charged at a low curren~ of a few
milliamps during quiescent periods over the power supply
conductor 52.
Again, where infrequent usage and long distances
from the central equipment made it advantageous, the local
battery 54 could be a replaceable one, so making the power
supply line 52 unnecessary. The remaining two conductors
56 and 58 providing an earth and signal pair could
conveniently be a normal telephone line.
The card of Figures 7a, 7b is similar to that of
Figure 1 except that the thin central layer 6 is omitted
and instead a pair of lines of code 8a are hot foil
stamped onto one of the inner faces of the ~ptically
opaque infra-red transparent sheets 2, 4. The stamping
die used had easily movable sliders to allow the codes to
be changed easily and this provides a rapid and
inexpensive way of applying the codes~ The card may be
formed with all opaque "start up" regions 8b extending
right up to its edge that permit the control system
~L2~7~S7
associated with the bade reader to detect sooner the
presence of a bad~e.
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