Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates to code identification apparatus
of the type in which an instrument such as a key or card
having a code recorded on it is submitted to a reader which
reads the recorded code. Apparatus of this type may be used
in locking systems and various accounting and credit control
facilities. In the case of a locking system the reader would
control the condition of a lock and the coded instrument would
normally be in the form of a key which is inserted into the
reader. In the case of credit control systems the instrument
would usually be in the form of a coded card.
The invention has particular, but not exclusive
application to apparatus in which the instrument is magnetically
coded, for example by the inclusion of small magnets at selected
locations within a magnetic body of the instrument. U.S.
patent no. 3,953,712 discloses an apparatus of this type in
which a magnetically coded instrument is inserted into a guide-
way of a reader which includes a number of sensing coils dis-
posed adjacent the guideway such that electromotive forces are
generated in the sensing coils by movement of the magnetised
portions of the instrument across them as the instrument approaches
the end of its forward travel along the guideway. The electro-
motive forces generated in the sensing coils are amplified and
influence the condition of an output circuit so as to cause
generation of an output signal. U.S. patent 4,112,292 also
discloses an apparatus in which a magnetically coded
instrument is inserted into a guideway of a reader which
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reads its code. In that case the magnetized portions of
the instrument are detected by a series of Hall Effect
devices disposed within the reader adjacent the guideway.
In both of the above described arrangements the number
of sensing elements incorporated in the reader is equal to
the number of coding locations on the instrument and the
code is read virtually instantaneously when the instrument
approaches or reaches the end of its forward travel. The
present invention provides an alternative arrangement which
permits the number of sensing elements to be reduced.
SUMMARY OF THE INVENTION
According to the invention there is provided code
identification apparatus comprising a coded instrument having
a set of code locations arranged in a line along said
instrument and a code reader to which to apply said instrument,
said reader comprising:
a body defining an instrument guideway along which to
move said instrument with said line of code locations aligned
with the direction of movement of the instrument;
code sensor means including a code sensor element mounted
on said body such that said code locations of the instrument
successively pass said sensor element as said instrument is
moved along said guideway, which sensor means provides output
signals indicative of code information at said code locations
as said locations pass the sensor elemer.t;
signal storage means to store signals provided by said
sensor means, said signal storage means comprising a plurality
of signal storage units at least equal in number
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to the number of code locations in said set;
means to extract stored signals from said storage
units; and
control means responsive to progress of said instrument
along said guideway to code said storage units in succession
to the code sensor elements as said code locations of said
instrument successively pass said code sensor element, said
control means comprising a series of instrument position
sensors spaced along said guideway at the same spacing as
said line of code locations of said instrument and each
associated with one of said storage units, which instrument
position sensors provide in response to progress of said
instrument along said guideway a succession of signals each
causing connection of the associated storage unit to said :
code sensor element;
wherein said instrument position sensors are also
connected to a sequencing logic device which produces an
output signal conditional upon generation of signals by all
of said instrument position sensors in a correct sequence
and operation of the means to extract the storedsignals from
said storage units is conditional upon generation of said
output signal from the sequencing logic device.
Preferably, the apparatus further comprises an
additional sensor adjacent the entrance to the guideway to
respond to entry of the instrument into the guideway to
activate a timer which produces a timing signal of fixed
,
duration and wherein the outputs of the timer and
said sequencing logic device are connected to said means
to extract said stored signals from said storage units
via an AND gate, whereby said instrument position sensors
must all produce signals in proper sequence within said
predetermined time interval for operation of said means
to extract said stored signals from said storage units.
Preferably further, said means to extract the stored
signals from said storage units is responsive to said
additional sensor such that extraction of said stored
signals from said storage units is initiated by said
additional sensor on withdrawal of said instrument from
said guideway.
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BRIEF DESCRIPTION OF DRAWINGS
In order that the invention may be more fully explained
one particular embodiment will be described with reference to
the accompanying drawings in which:-
Figure 1 is a perspective view of a reader to read
magnetically coded keys;
Figure 2 is a vertical cross-section through the
reader of Figure l;
Figure 3 is a cross-section on the line 3-3 in
Figure 2;
Figure 4 is a cross-section on the line 4-4 in Figure
2;
Figure 5 is a cross-section on the line 5-5 in Figure
2;
Figure 6 is an enlarged cross-section of part of the
reader shown during insertion of a magnetically coded key;
Figure 7 is a perspective view of part of the key;
Figure 8 is a diagrammatic representation of a ~all
Effect device;
Figure 9 is a block diagram of the electrical circuit
of the reader;
Figure 10 is a circuit diagram showing part of the
circuit of the reader; and
Figures llA, llB and llC join at the lines A-A and B-B
to form a composite Figure 11 illustrating the remainder of the
electric circuit of the reader.
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DESCRIPTION OF PREFERRED EMBODIMENT
The illustrated apparatus is generally similar in
layout to those described in U.S. patent no. 3,953,712 and
in U.S. patent 4,112,292.
The system makes use of an instrument 11 in the
shape of a key which is fitted with a number of magnets at
selected positions in a matrix of possible positions. There
may, as illustrated, be sixteen possible positions disposed
in a 4 x 4 matrix. The key is inserted into a reader 12
fitted with a number of sensor elements in which signals are
generated by the presence of magnets. These signals may
be used to initiate various functions depending on the
particular application of the system.
As seen in Figures 6 and 7 instrument 11 is comprised
of a pair of body portions 13, 14 which fit together at a flat
interface 16 to form a key shaped body having a head 15 and a
rectangular flat plate part 20. The two body portions are
identical. They are moulded from tough non-magnetic plastics
material such as glass fibre reinforced nylon and have inter-
engaging pegs 17 and holes 18 at the interface 16. At this
interface they are also each provided with sixteen recesses
19 arranged in a 4 x 4 matrix so that when the two body portions
are fitted together sixteen closed pockets 25 are formed within
the key and the key is coded by the inclusion of small permanent
magnets 21 within selected pockets of the matrix. Magnets 21
may be formed as small discs or cylinders of permanently mag-
netized metal, i.e. they may be unisOtropic magnets. It would,
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however, be possible to install isotropic magnets which would
lose their magnetism after a set period so enabling the issue
of keys which would be effective for a limited period only.
The key is coded according to the number and disposition of
magnets 21 in the matrix of sixteen pockets. It will be
appreciated that with the sixteen positions available for
installation of magnets and the fact that the polarity of the
magnets may be reversed simply by physical inversion of the
number of possible code combinations is very large indeed.
Reader 12 comprises a body defining a base plate 26
and an escutcheon plate 27 which has a slot 28 through which
to insert the magnetically coded front plate part 20 of key 11
lnto reader unit 12.
The reader unit 12 comprises a lower printed circuit
board 31 which is mounted above base plate 26 and is hel~
spaced from the base plate by two spacer strips 32 disposed
one to each side of the reader unit. An upper printed circuit
board 33 is mounted above the lower printed circuit board and
the two printed circuit boards are held spaced apart by two
other spacers 34 which are also disposed one to each side of
the reader unit. The printed circuit boards and the spacers
32, 34 are held together by means of long studs 35 which extend
upwardly through them on each side of the reader unit.
The inner edges of spacers 34 are provided with slots
36 which are at the same height above base plate 26 as slot 28
in escutcheon plate 27. The coded front plate part 20 of key 11
can be lnserted through slot 28 into the cavity defined betw2en
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spacers 34 and the upper and lower printed circuit boards
and the two side edges of the key then engage slots 36
which serve as a guideway for movement of the key.
A yoke member 37 mounted on base plate 26 immediately
S behind escutcheon plate 27 provides a slideway for vertical
sliding movement of a guideway barrier member or gate 38.
Gate 38 is normally biased upwardly by biasing springs 39
so as to block the key guideway entrance. Its upper edge
is chamfered so that on insertion of the key it is wedged
downwardly and does not impede entry of the key into the
guideway but it does provide an effective seal against entry
of dust or other foreign material when the key is withdrawn.
Reader unit 12 may be held on base plate 26 by means
of heat shrunk plastic tubing (not shown).
Lower printed circuit board 31 carries five light
emitting diodes LDl, LD2, LD3, LD4 and LD5 which are
arranged in a straight line concentrically of the guideway.
The circuit board also carries appropriate circuitry to
activate these light emitting diodes as will be described
below. Four Hall Effect devices HEDl,HED2,HED3 and HED4
are arranged generally in a row transverse to the guideway
and near to the guideway entrance. Devices HED2 and HED4
are mounted on the lower circuit board and devices HEDl and
HBD3 on the upper board. The spacing of these devices is
such that when the key is inserted into the guideway the
four columns of magnets pass one across each of the Hall
Effect devices.
Upper circuit board 33 also carries five photo-
transistors Ql - Q5 which are vertically aligned with the
light emitting diodes LDl - LD5.
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The basic principles of operation of a Hall Effect
device is shown diagrammatically in Figure 8. As shown in
this Figure a Hall Effect device generally comprises a semi-
conductor layer 20l fitted with a pair of control current
electrodes 202, through which to pass a control current through
the layer in one direction and a second pair of electrodes 203
to detec~ a potential difference between locations on the
- semi--conductor layer which are spaced apart in a direction
transverse to the direction of the control current. When a
control current i is passed via electrodes 202 through the
semi-conductor layer 201 whilst a magnetic field of flux
density B is perpendicular to the plane of the semi-conductor
a potential difference (open circuit Hall voltage V) is
developed between electrodes 203, in accordance with equation
V = Rh .i.B where ~ is a constant (Hall constant) of the
semi-conductor material and d is the thickness of the semi-
conductor layer.
Hall Effect devices which operate in tne manner
indicated in Figure 8 can be obtained commercially. Generally
the semi-cor.ductor layer is formed either as a wafer produced
~rom semi-conductor bars by cutting, grinding and etching; as
a layer which is vapour deposited on a chip; or as GaAs iayer
grown epitaxially from the gas phase on semi-insulating GaAs.
It has been found that Hall Effect devises known as
HONEYWELL TYPE 63SS2C are particularly suitable for use in .he
illus~rated apparatus. These devices have sensors and amplifiers
integrated into the same sensing chips so as to provide an
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amplified output signal. They are, in fact, capable of
providing two amplified outputs one being a "true" output
and the other a "compliment" of the first output. Only one
of these outputs need be used in the illustrated apparatus.
The device has an output of - 0.9mV/Gauss over a sensitivity
range of - 400 Gauss with a constant supply voltage of 5vDC
5% and'at a temperature of'24 - 2C.
- The potential difference generated by each Hall Effect
' device is of the order of only 40~0 millivolts. This presents
10 ' a signal having a polarity dependent upon the direction of
the magnetic field applied to the Hall Effect device, i.e. a
key magnet which registers with the Hall Effect device with
its north pole facing that device will generate a Hall Ef~ect
potential difference on one polarity, whereas a key magnet
which registers with its south pole facing the Hall Effect
device will generate a potential difference of opposite
polarity.
Before describing the electrical circuitry of the
reader in detail the general operating principles of the
apparatus will be described with reference to Figure 9.
Before the key is inserted into the reader, light
emitting diode LDl is'operative to produce a light beam which
. i6 detected by photo-transistor Ql on the upper circuit board.
,However, the other four light emitting diodes LD2 - LD5 are
then inactive. As the key is insert~d into the guideway it
pushes gate 38 downwardly and interrupts the light beam produced
by diode LDl. The resulting signal at photo-transistor Ul
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triggers a timing circuit, indicated in block form as 101 in
Figure 9, which applies a timing signal to one side of an AND
gate G3. This timing signal continues for a fixed time
determined by the timer circuitry.
The signal from photo-transistor ~l is also applied
to a "sequencing logic" 102 ~s wil]. be described more fully
below sequencing logic 102 is an integrated circuit ~uinary
counter which can be switched progressively thrGugh five
successive conditions Q0~ Ql' Q2'.Q3 4 5
is to activate light emitting diodes LD2 - LD4 successively
as the light beam produced by the immediately preceding light
emitting diode is cut by the key and, when all of the lisht
beams have been cut in proper sequence, to apply an output
signal to AND gate G3.
When the signal from photo-transistor Ql produced by
cutting of the first light beam.is applied to sequencing logic
102, that logic is switched from its Q0 condition to its ~l
condition which causes light emitting diode LD2 to be activated
to produce a light beam which is detected by photo-transistor Q2
As the key progresses further along the guideway the
first row of key magnet locations passes over Hall Effect
devices HEDl - HED4. When a magnet passes over one of '~he
Hall Effect devices the output voltage of that device increases
or decreases according to whether the north pole or south poie
of the magnet is facing the device. Thus it is ~ossible by
checking the voltage outputs of the Hall Effect de~ices as the
first row of magnet locations passes over them to determine
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the presence or absence of magnets and, if present,
to determine the respective magnetic polarities.
The second light beam produced by light emitting
diode LD2 is positioned so that it is cut by the leading
edge of the key at the instant the first row of magnet
locations is over the Hall Effect device and the resulting
signal produced by photo-transistor Q2 causes the signals
indicating the positions and polarities of the magnets in
that row to be stored in a first storage unit SRl. The
interruption of the second light beam also switches
sequencing logic 102 to its Q2 state which activates the
third light emitting diode LD3 to produce a light beam
detected by photo-transistor Q3.
As the key progresses further along the guideway
it successively cuts each light beam which has been produced
by interruption of the immediately preceding beam and the
signals representing the positions and polar1ties of magnets
in the second, third and fourth rows of the key are stored
at the appropriate times in three further storage units SR2,
SR3 and SR4.
When the last light beam is cut sequencing logic
102 transmits a signal to AND gate G3 and if this signal is
produced within the fixed time interval determined by entry
timer 101 AND gate G3 produces a "data ready" signal which
is transmitted via output line 100 to a central processing
unit located remotely from the reader. Sequencing logic 102
ensures that the key is inserted in one movement and
within the time interval determined by entry timer 101.
It is therefore not possible to operate the reader by
~r~ ~ 30 jiggling a key or other
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- magnetic device back and forth within the guideway.
When the key is withdrawn to remake the Light beam
produced by diode LDl the resulting signal at photo-transistor
Ql activates a "wait timer" circuit 103. The wait timer sends
a signal to the central processing unit causing that unit to
send 32 clock pulses to store units SRl - SR4 via an input line
104 to transfer the data stored in those units to the central
processing unit via,an output line 105. After a fixed wait
interval the wait timer also produces a further signal' which is
transmitted to sequencing logic 102 to reset the sequencing
logic back to its initial Q0 to enable the whole sequence to
be repeated.
The electri~ circuit will now be described in more detail
with reference to Figures 10 and 11 which are detailed circuit
diagrams. As indicated in these figures the four storage
units SRl, SR2, SR3 and SR4 may be standard type 4021 shift
registers.
Entry timer 101 is a mono-stable multivibrator which pro-
duces a pulse of a fixed time duration, for example 1/3 of
a second, and wait timer 103 is a similar mono-stable multi-
vibrator.
Schmitt triggers,'Schmitt 1 and Schmitt 2 are incor-
porated in the circuit to sharpen up the slow moving wave
forms produced by interruption of th~ light beams by the
relatively slow movement of the key within the guideway.
Hall Effect devices HEDl - HED4 are connected into
sensor circuits which include eight comparators COMPl - COMP8,
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four capacitors C8 - Cll, and gates TGl - TG4. The reason
for this. circuitry is that the outputs of the Hall Effect
devices tend to drift with time due to temperature effects.
Each Hall E.ffect device may have a standard output voltage of
approximately 3 to 4 volts.. The key magnets may produce a
signal of only about - 0.75 volts in this output but the
drift in output voltage over long time iAtervals may be
greater than this signal variation. The illustrated circuitry
overcomes this problem by effectively taking snap readings
. of the Hall Effect output voltages at the time the first.light
beam is cut, holding these as reference values by means of
capacitors C8 - Cll and deriving data signals by consequently
comparing these reference values with the instananeous output
values at the times that the successive light beams are cut.
15 Each Hall Efect device is connected to two of the comparators,
one to read if the signal goes higher than the reference and
the other to read whether it goes lower.
. The sensor circuit incorporating Hall ~ffeot device
. HEDl will be described in detail and it will be seen from
Figure 11 that the circuits with the other Hall Effect devices
are the same..
The standing output voltage of the Hall Ef~ect device,
which is in the region of 3 to 4 volts is applied to the three
series resistors R14, R15 and R16. The centre point of R14 and
R15 is taken to a capacitor C8 via a transmission gate TGl. In
the normal condition, i.e. no key in the reader, the transmission
gate is at low resistance and therefore the-voltage on the
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capacitor follows the voltage at the junction of Rl4 and RlS
which changes due to temperature effects in the Hall device.
This voltage is applied to the non-inverting input of voltage
- comparator COMP~ and the inverting input of COMP2. The
inverting input of COMPl is taken to the more positive end of
Rl4 and therefore its output is low. The non-inverting input
of COMP2 is taken to the more negative end of RlS and there-
fore its output is also low.
When the key is inserted in the reader the transmission
gate is switched o~f i.e., becomes very high resistance and CB
"remembers" the voltage at the resistor junction prior to key
being inserted. If a magnet in the key hasj say, its north
polé facing upwards, the voltage at the HEDl input rises and
the junction of Rl5, R16 rises above the voltage stored on C8
and the coMoe2 output goes high. If the magnet faces the-other
way, the voltage at the HEDl input falls and the inverting in- -
put of COMP 1 falls below the value of that stored on C8 and
the output of COMPl goes high. If no masnet is present both
outputs remain low. Because the outputs of the comparators
are only clocked into the shift registers at the correct
instant, it can be said that the 2 bit code for any one magnet
is as follows:-
COMP 1 COMP 2
NO MAGNET Low Low
MAGNET N. ~ Low High
M~GNET S. High Low
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Detailed operation of the circuit will now be
described with reference to Figures 10 and 11.
In the quiescent state i.e. with no key in the
reader, only the first light beam is operative and the reader
Ql collector is low, forcing the output of schmitt 1 high.
As LD2 - LD5 are not active the collectors of Q2 - Q5 are
high, forcing the output of schmitt 2 low.
As the key enters, breaking the first light beam,
schmitt 1 changes state, firing the entr~ timer multi-vibrator
101, via buffer Bl, and at the same time switching off trans-
mission gates TGl - TG4, and pulsing logic counter 102, to
its:Ql state via capacitor C4 and OR gate G4. The entry timer
Q output going high, enables one input of AND gate G3 whose
output does not go low due to the other input being held low
by Q5 of the counter.
Ql of the counter going high, energises the second
light emitting diode LD2, causing the input of schmitt 2 to go
low, and forcing the output high. The key then breaks this
light beam and the input of schmitt 2 goes high, fGrcing its
outputs low and pulses the clock input of the counter 102 via
capacitor C3 and gate Gl. The counter advances to its Q2 state
and the Ql output going low, clocks the parallel information
from the magnet comparators COMPl - C0MP8, into shift register
SR2. SR2 now contains the magnet information of the first row
of magnets in the key.
Q2 of the counter energises the third light beam, and
as this is cut the counter advances to its Q3 state in a
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-- similar manner to that already described, and the Q2 output,
going low clGcks the second magnet row data into SR4. Similarly,
the key entering further cuts beams 4 and S, clocking rows 3
- and 4 magnets data into SRl and SR3 respectively.
As the last beam is cut the counter is clocked to
its Q5 state, and Q5 going high stops the counter by taking CE
high and enables the other input of gate G3, whose input is
already enabled by the Q outputs of the entry timer 101. The
output of gate G3 therefore goes low, setting the flip flop
formed by gates G4 and GS, and the "data ready" line 100 goes
high, driven from the flip flop via Tl and T2.
As the key is withdrawn, the first light beam is
remade, putting a low signal on the input of schmitt 1 and so
forcing its output high, which re-opens the transmission gates
TGl - TG4, enables one input of gate G2 and fires the wait timer
multivibrator 103. The output of the multivibrator 103 then
goes low and inhibits the entry timer multivibrator 101 on lts
CD input, and also resets flip rlop G4, G5 and the 'Idata ready"
output goes low, requesting the central processing unit to
send 32 clock pulses to move the stored data in SRl - SR4 out
to the central processing unit via the buffer transistors T3,T4.
At the end of the wait period, provided a key has
not been re-inserted, the rising edge of the output signal of th~
wait timer multivibrator 103 pulses the reset input of the
logic counter 102 which reverts to its Q0 state. At the same
time the CD input is enabled on the entry timer multivibrator
101 allowing the sequence to be repeated.
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If a key is inserted during the wait period gate G2 is
inhibited and prevents the counter resetting at the end of the
wait period. If the key is inserted and withdrawn within the
wait period, the wait period recommences due to the retrigger-
able nature of the mono-stable multivibrator 103.
In the illustrated apparatus only four sensor devices
are required to read a code spread over 16 coding locations as
compared with prior art devices in which it is necessary to
provide as many sensors as there are code locat~`ons. More-
1~ over the key must be inserted so as to cut the light beams inproper sequence and to complete its movement within a given
time interval. Data stored in the store units is only trans-
ferred to the central processing unit on withdrawal of the
key there is no output from the reader until the key is
lS withdrawn There is therefore no danger that a key will be
allowed ta remain in the reader inadvertently. Moreover, the
use of comparators in the sensor circuitry enables the use of
Hall Effect devices which might otherwise give problems due
to drift in their output voltages. However, the illustrated
apparatus has been advanced by way of example only and it could
be altered considerably without changing the general principles
of operation. For example, it is not essential to use Hall
~ffect devices as the sensor elements and other means for
sensing the code could be used. It would be possible to use
sensor coils to produce signals consequent to movement of the
key magnets across them, to produce signals by blocking a
magnetic field with discs fitted to the key or to f't tne key
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with segments of different electrical conductivity to be
read by wipers in the reader.
It would also be possible to provide other means to
switch the light beams in proper sequence. For example,
it would be feasible to use simple micro-switches or a
mechanical device operated by teeth at the edge of the key.
It is accordingly to be understood that the invention
is in no way limited to the details of the illustrated -
apparatus and that many modifications and variations will
.
fall within the scope of the appended claims.
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