Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Code carrier, proces~ for analYzina the data o such a code
carrier as well_as coding system usinq such a code carrier fox
product identification
The invention relates to a code carrier ~c,r analyzing a code
for product identification, said code carrier is placed under a
cover layer a~d consists o~ a maynetic, magnetizable and~or
electrically conductive material, as well to as a process ~or
analyzing the data of a code carrier placed under a cover layer
oP a product, in which the code carrier consists of magnetic,
magnetizable and/or electrically conductive material and exhLbits
a geometric configuration containing the code. The invention
further relates to a coding system for product identification
wit~
a) at least one code carrier made from magnetic,
magnetlzable and/or electrically conductive material with de~ined
design, such as, e.g., recesses, opanings and/or cross section
changing over an axis of the code carrier
b) at least one field source, and
c) at least one field sensor for measuring the stray field
caused by the code carrier,
as well as the use of such a code carrier made from
magnetia, magnetizable and/or electrically con~uctive material
with defined design, such as, e.g., recesses, openings and/or
cross section changing over an axis of the code carrier for
an~lyzing he stray field ~ormlng in an electromagnetic ~ield for
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product identification by the code carrier placed under the cover
layer of the product.
Many industrial products are produced in large number of
units, and their production is and has to be monitored step-by-
step. This 18 necessary to be able to optimize the production
process and to recogniæe promptly a perhaps imminent failure of
production machines by not adhering to tolerances or other
production defects.
In this way production processes ("turn around times") can
be optimized, the downtimes of the production machines as a
result of planned lnspections are reduced and the number o~
produats not passing quality control is reduced and thus costs
are cut.
An uninterrupted monitoring of a product means that the
product as much as possible at the beginning o~ its production is
provided with a corresponding marking or coding. The marking can
then be read and logged at each production step. Thus it is
possible, for example, to record the time of the individual
production steps of each product. This makes possib~e a cost
optimizing of the production process.
Large numbers of systems for recording of products or for
monitoring production are known.
By "bar code" is understood a simple, optically readable bar
pattern. This type of coding is used today on a large saale for
identification in selling mass-produced products. But in the
production o~ products problems result in reading the bar code,
since cont~minations occur, or the bar code is covered in the
production, or else is destroyed by a processing operationO
Electronic systems for marking consist of an electronic
logic circuit in which data can be read in or read out without
contact, e.g., ~y infrared or inductively. Here, the so called
"chip cards," which are used for high security systems but al~o
for produation monitoring, are well known. In this case, the
data is in a programmable memory chip, which then can be read in
or read out by high-frequency syste~s. This is an intelligent
system, which can be used very versatilely. For this purpose,
there are reading and writing functions, which can be protected
by an appropriate protoco~. As a drawback it turns out that such
systems are too expensive for a production in large numbers.
~herefore, the chip can never be permanently integrated in the
product. In most cases the chip would not withstand the
production process as a result of thermal and mechanical
stresses. Therefore, this system ia not sturdy enough.
A magnetoresi~tive transducer for reading out of coded data
for postage meters is known from DE~Al-32 22 789. In this case,
the code is achieved by the known change o~ an electrical
resistance in a magnetic field ("magentoresistance"), and the
arrangement of magnetoresistances and so~called soft magnetic
~ocusing represents the code. In this case the shape of the code
carrier as well as its magnetizing play no role. It i9
disadvantageous in thie system that it is not suitable ~or coding
mass-produced products as a result o~ it~ arrangement as well as
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its space requirement. Moreover, the measurement of the
magnetoresistance is hardly possible in a contactless manner.
An identi~ication system for modules, whic:h are moved along
a conveyor belt, is known from DE-Al-37 29 740. In this case,
the magnetic code is achieved by an arrangement of permanent
magnets, and the code is represen~ed by the north or south pole.
The geometric shape o~ the magnets plays no role in this system.
The reading elements consist of Hall elements, which cause the
north and south pole to be recognized by the delivered voltage.
In this case, the delivered Hall voltage is very distance-
dependent and is reduced approximately with the third power of
the distance, so that a measurement only with adhering to narrow
distance tolerances produces reproducible information. Also the
magnets cannot be placed very near to one another, since
otherwise they influence one another. Such modules, which
contain permanent magnets, are neither inexpensive to produce nor
ea~y to integrate into every mass product.
A similar electronic system for acquisition of binary data
on workpieces on a transfer line is known from DE~A1-33 31 694.
In this case, the code data is written in, in a so-called EPROM
(erasable programmable read-only memory). An inductively
operating system, consisting of a special transformer, is used
both for energy supply of the EPROM and for data transfer. In
this aase, it is disadvantageous that the use of an EPROM for
ma~y mass-produced products i5 both too expensive and that
environmental conditions, existing during production, for
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example, pressure, temperature or the like, would destroy the
EPROM. Further, the use of an active component as a code memory
makss an energy source necessary in principle, which leads to
substantial limitations.
A process and a device for ac~uisition and identificatlon oP
objec 8 provided with ooded labels are known from DE-Al-27 12
016. The aim o~ this known prior art is to facilitate the
automatic sorting of packages and mail bags. In this case, the
code consists of tkin magnetic stripes or wires. The code is
achieved by subdivision of these magnetic stripes or by combining
several such magnetic stripes by groups. Another possibility is
to use materials with di~erent coercive fielcl strengths. Agaln
it i8 disadvantageous in this case that this code technically can
hardly be produced at a price so reasonable that it can be used
in mass-produced products. The known reading unit consists of an
excitation coil fed with alternating current, which in a way
known in the art can also exhibit Helmholtz geometry to produce a
homogeneous field. The code is detected by balanced detector
coils by measurement of voltage amplitudes or phase shifts, in
case of code materials with different hysteresis loops, resulting
by induction. In this system, the measured signal is dependent
on the speed of the moving object. Therefore, it is only
conditionally suitable for a product moving on a conveyor belt.
A process for representation and analysis of a digital code
applied with ~erromagnetic material to a carrier is known from
DE-A1-~4 37 547. In this case, ~he code is produced by
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ferromagnetic stripes or stripe groups meshing comblike. In this
case it is disadvantageous that the technical embodiment of this
code carrier is too complicated for mass-produced products. The
presene o~ code is detected by a ferromagnetic E-shaped core
with three coils. It is also disadvantageous in this case~that
an exact positioning of the read head i5 necessary, and furthe~
no measures were taken against "false bits" produced by
interference of extraneous voltages.
It is known ~rom AT-PS 30~ 111 to apply a ferromagnetic
carrier to a body to be identified and to code it magnetically
from the distanae to read the code with a code head. Such a
process CAn easily be disturbed because of the application of a
magnetic carrier without appropriate precautionary measures.
Some patent spaci~ications relate, for example, to coding
for skis, which corresponds to coding of a mass product. Thus it
has become known to print the suraces of skis with markings that
become visible und~r W radiation. In this case, it is
especlally disadvantageous that this marking is obliterated in
certain processing operations, such as polishing or usual
abrasion, a~ is also the case with the usual use of so-called bar
codes for product identification.
From AT-PS 390 005 it is known to code skis so that a c~de
is applied ~agnetically ~o the edges consisting of ferromagnetic
Daterial ~iron) ("magnetic areas"~. ~Again in this case it is
di~advantageous that this code can easily be disturhed
externally, espeoially demagnetized, unless special materials are
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usad~ Moreover, this code can be destroyed in any operation of
polishing the edges.
~ or many purposes an inexpensive coding system, which is and
remains permanently connected to each individual product, would
be desirable. It is also advantageous if the coding element in
the product can be covered, iOe~, not directly visible or at
least protected under a cover layer. Thus the "history" o~ the
product a~ter its æale can ~e controlled, which, e.g., can be
advantageous for guarantee purposes but also far insurance
matters, ~or example, in cases of theft.
Now the ob~ect o~ the invention is to provide a code carrier
of the initially mentloned type~ which is characterized by
sufficient mechanical stability to withstand damages during the
production operation and its application in or on the product to
be identified, as well as, further, is sufficiently protected so
that it cannot be easily destroyed in normal use. Finally, the
ob~ect o~ the invention is to configure such a code carrier with
respect to ~ts use wlth mass-produced products as economically as
possible and to be able to read it out with simple and
operationally reliable devices. In this case, it is of
substantial importance that for purposes of a use of mass-
produced products both a correspondingly simple configuration o~
~he code carrier and a simple and an operationally reliable
procedure for reading out o~ the code is~made available
Substantial attention i9 to be glven in thls case, with xespect
to the use of the code carrier fF mass-produced products, to the
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reliabl~ recognition of the code and the far-reaching
impossibility oP destroying the code by manipu]Lations or
environmental influences. To achieve this object the code
carrier according to the invention consists essentially in the
~act that the code carrier exhibits openings, recesses or a
changing cross section for the analysis of a st:ray field changing
in an axis of a plane parallel to the main axis of the code
carrier. In combination with an analysis of tha code by a simple
stray ~ield measurement in this case a correspondingly stable and
economical code carrier can be used, which is characterized by a
relatively simply geometric conPiguration and still can be
recognized with the proposed process for reading out of the data
of the code carrier or the code reliably even with inexact
guiding oP the reading device. The use of a stray field for
identification o~ the code contained in the code carrier in this
case is distance-sensitive to a substantially smaller extent and
allows the use of simple ~ield sensors for the identification of
the code. Moreover, such a simple code carrier can in an
especially simple way be integratecl during the production process
into mass-produced articles, such as, e.g., skis, tennis rackets
or the like and in view of the required choice o~ material a high
degree of stability is assured even during the production
process. Especially the analyzab1lity of such a code carrier by
measurement of a stray ~ield makes it possible to eliminate
expensive balanclng and tuning operations~ such as would be
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necessary, ~or example, in the measurement of magnetic
resistances or of a coupling field by resonance tuning.
In a particularly simple way in this case the code c~rrier
is designed as a plate or sheet, by which the incorporation in
products, especially if they are products with a multilayer
design, is especially simplified. But the code carrier can also
be formed ~rom conductive metal plastic emulsion applied to a
substratP, and, for example, such a code carrier can be applied
to the mass-produced article in a printing process in an
especially economical way in the production. To safeguard such a
conductive sheet subsec~ently ~rom mechanical destruction it is
also advantageous in this case to protect the conductive metal-
plastic emulsion or magnetic powder-plastic emulsion applied to
the substrate with a cover layer after it has dried.
For the analysis of a changing field the code carrier in a
particularly simple way can exhibit in at least two planes
paralleI to the main axis openings, recesses or changin~ cross
section, and in one plane the openings, recesses or changing
cross section ~s/are designed uniformLy. The uni~orm design in
one plane in this case offers the advantages of a clock track,
which make the analysis result independent of the speed, with
which ~he read head is moved relative to the code carrier.
To reduce the danger of will~ul destruction further it is
advantageous to make the design so that the code carrier is
placed invlsible from the outside, and advantaqeously the code
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carriar is designad as an integral component o~E the product sr of
components of the product.
The process according to the invention for analysis of data
of a code carrier placed under a cover layer of a product, in
which the code carrier consists of a magnetic, magnetizable
and/or electrically conductive material and exhibits a geometric
configuration containing the code, i5 basically characterized in
that an elec~romagnetic field i~ produaed and in that the
changing stray field basically parallel to a main axis of the
code carrier is measured and analyzed. For the productlo~ of
such an electromagnetic field either an high-frequency
alternating ~ield can be used, and the eddy currents forming in
the high-fre~uency alternating field on a conductor counteract
the field and lead to a reduction of tha lines of flux and thus a
reduction of the measured values for the field strength.
Advantageously the process according to the invention is thus
charact~rized in that the code carrier is exposed to a high-
frequency alternating field and the changes of the high-frequency
fi21d caused by the eddy currents produced in the code carrier
are detected by the characteristics of the high-frequency
resonant circuit.
In using a magnetic field advantageously a soft magnetic
material is used as code carrier and this soft magnetic material
is exposed to a magnetic field and the resulting locally
dependent magnetic stray ~ield is measured with magnetically
sensitiv~ sensors. In this case as a magnetic field there can be
produced both the field of a permanent magnet or a magnetic
steady field and, as it corresponds to a preferred embodiment of
the process according to the invention, a periodic magnetic
alternating field.
In principle, of course, also an at least partially
permansnt magnetic code carrier can deliver a locally dependent
magnetic stray field, which can be measured with magnetically
sensitive sensors. But such a permanent magnetic code carrier is
characterized by substantially less reliability, since the
magnetic stray field of such a permanent magnet can be changed ~y
a correspondingly high outside magnetic field, as a result of
which thera is a danger that the originally introduced code will
be lo~t or changed.
In a particularly advantageous way the process accordlng to
ths invention i9 performed so that the varying stray field o~ the
code carrier in the electromagnetic field is measured with at
least two sensors independent of one another and the measured
slgnals are fed to a common analysis circuit. Thus the
reliability o~ the analysis of the reading process is
substantially improved.
The invention further relates to the use of a code carr~er
made Prom magnetic, magnetizable and/or electrically conductive
material with defined design, such as, e.gO, recesses, openings
andjor cross sectlon changing over an axis of the code carrier
for analyzing the stray field forming in an electromagnetic field
for product identification by the code carrier placed under the
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cover layer o~ the product, and such a code carrier can be used
in sports equipment, especially a ski, a ball bat or the like.
Altogether by the design according to the invention a coding
system for product identi~ication is provided with
a) at least a code carrier made from magnetic, magnetizable
and/or electrically conductive material with defined design, such
as, e.g., recesses, openings and/or cross section changing over
an axis of the code carrier
b) at least one field sourae, and
c) at least one Eield sensor for measuring the stray fleld
caused by the code carrier, whose elements, considered in
themselves, are especially simply embodied and can be put into
practice and in combination guarantee a high degree o~
operational reliability, ruggedness and mechan~cal stability.
Such a coding system can, as already mentioned above,
advantageously contain a plate or sheet, and within the framework
o~ this coding system the code carrier can be formed in a
particularly simple way from a conductive metal-plastic emulsion
or magnetic powder-plastic emulsion applied to a substrate, by
which the introduction or application of the code can be further
simplified~ In such a design of the coding system, the code
carrier can ~e applied by a simple printing proc~ss or by
spraying using a stencil, which especially with mass-produced
articles leads to a further cost reduction.
The codlng system according to the invention is
advantageousIy further developed so tha~ in at least two planes
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parallal to the main axis the code carrier exhlbits openings,
recesses or changing cross section, and in one plane the
openings, recesses or changing cross section is/are designed
unifor~ly, by which a clock track is provided for the analysis,
which makes possible a measurement of the stray field
independently of the speed, with which the field source or field
sensor is moved relative to the code carrier. In this case, the
~ield source is to produce an electromagnetic field shiftable
relative to the code carrier for scanning the entire code, and in
the framework of the coding system in the way already described ..
above relative to the reading process advantageously a periodic
magnetic alternating field can be used. The field sensor
according to a preferred further development of the coding system
can be formed by a Hall probe or field plates, and advantageously
additionally at least one pickup coil can be provided for
increasing the accuracy. But a pickup coil itself can also be
u~ed as a fiQld sensor under certain conditions.
In the case of using an electric alternating field the
coding system is advantageously further developed so that a
reading device -- comprising the field source and the field
sensor - for the code of the code carrier comprises an
oscillator for an electromagnetic hf field for eneryizing eddy
currents in the code carrier, a trigger and an output stage for
Dversion of the attenuation of the hf field dependent on the
geometria shape of the code carrier into an analyzable code
signal, and with su~h a design of the:coding system the analysis
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of the code by excitation of eddy currents in the code carrier is
achieved in an especially simple way. Alternatively the design
for analysis can also be made so that a read device for the code
of the code carrier comprising the field source and the field
sensor comprises an oscillator for an electromagnetic hf field
for excitation of eddy currents in the code carrier, a detector
coil system, a difference amplifier, a comparator and
an output stage for conversion of the attenuation of the h~ field
dependent on the geometric shape o the code carrier into an
analyzable code signal.
'rhe ~nventlon is explained in greater detail below by the
embodiments diagrammatic represented in the drawing. In them,
fig. 1 to 6 show diagrammatic views of different code carriers;
Fig. 7 and 8 diagrammatically show the reading of two code
carriers and fig. 9 shows a wiring diagram of an eddy current
head: fi~. 10 to 20 show various reading processes, partially
with related signal diagrams; and fig~ 21 shows a block diagram
of an embodiment of the analysis electronics.
The code data is stored in a variation of the cross section
or more generally in a special design of the code carrier. The
change of the shape such as, e.g., of the cross section, of the
profile or the surface along at least one space axis or in an
axis of a plane parallel to the main axis of the code carrier,
determined by a simple coding instruction represents the code.
For a satisfactory recognition of the code pattern it is
additionally advantageous if, parallel to the "code track" a
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"clock track" is provided, so that in any case, independently of
the scanning speed the signals can be correctly allocated.
~ xamples for the design of the code carrier are represented
in f ig . 1 to 6 .
Fig. l shows a metal plate l, along whose space axis 2 or
axis o~ a plane parallel to the main axis a coding in the orm of
projections 3 is applied. In this case, the coding thus lies in
the spatial arrangement of projections 3 along space axis 2. A
bit pattern, deriving from it, is diagrammatically indicated.
The code carrier in this case can consist either of an
electrically conductive metal or a soft magnetic or else a hard
magnetic material. The code, which is stored in the shape
change, is always detected by spatial distortion of the
el~ctromagnetic field or stray field caused by it. In the first
aase, the presence of projections 3 is detected by the markedly
stronger attenuation of the eddy currents, in the second or third
case the projections can be detected with field sensors by their
stray fields.
According to fiy. 2, the code carrier is a body 4, whose
sur~ace exhibits fins 5 in an arrangement which means the code.
In this case again the code carrier as a function o~ the reading
process can consist of an electrically conductive metal or a soft
magnetic or else hard magnetic material.
Fig. 3 shows in cross section a metal plate 6, which
exhibits aonvexities 7 at certain intervals for coding. 1D this
case, an electrically conductive metal appears suitable as code
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carrier material. An eddy current process ~s thus suitable for
reading, if convexities 7 are located within, but plane parts of
plate 6 outside/ the detectable area o~ an eddy current sensor
(not shown) in detail.
Another advantageou~ emhodiment for such code carriers can
be formed, e.g., by a metal sheet 8, as represented in fig. 4
This metal sheet consists of a good con~uctor. The coding
result from the arrangement of holes or recesses 9 and 9'. The
holes are circular in fig. 4 but can also have any other shape,
The optimal shape of the holes i5 to match the shape and typ~ of
the sensor, which is to be used ~or reading the code data. The
presence oP the holes, for example, is detected by a commercially
available eddy current sensor. It can be pointed out that the
size of the holes and thus the achievable density bit/surface
unit is determined by the distance from which the code has to be
read. ~he greater this distance, the greater the diameter of
these hole~ has to be. Such a metal sheet with punched holes is
an especlally inexpensive code carrier easy to place. In the
embodiment shown in fig. 4 the continuous row of holes 9'
adjacent to the edge represents the clock track, which is used
for synchronization, while the data is contained in the other
hole rows 9.
Fig. 5 shows another shape of a aode carrier similar to that
of ~i~. 1. Plate 10 is provided with projections 11 on both
sldes and thus i8 coded. In this case, one side can be used as
3'code traok" and the other side as "clock track." Again in this
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case the code carrier can consist both of an electrically
conductive metal and a soft magnetic or else hard magnetic
material.
FigO 6 shows an embodiment in which the code carrier
consists of successively placed disks 12. Each disk carries
extensions 13 along its periphery, whose arrangément represents
the codeO A similar function can also be achieved by a
corresponding design of a cylindrical rod. Again in this case
the code carrier can consist both of an electrically conductive
metal and a so~t magnetic or else hard magnetic material.
Not necessarily separate, additionally incorporated
components have to be used as code carriers. It is especially
advantageous to use already existing components of the product,
which consist of a suitable material (metal or magnetic), for
receiving the code, by their being appropriately changed in their
external shape and thus ¢oded.
It is common to all these embodiment variants o~ the code
carrier that the code carrier can be integrated in the workpiece
simply and invisible from the outside or at least protected under
a cover layer. For example, at the beginning of the production
the code is fixed on~e by mechanical processin~ and cannot and is
not to be changed. The code is destroyed only by destruction of
the ele=ent itself. If that happens in any case a visible damage
of the product results so that the change of the code carrier is
al~o visible. Undesirable manipulations or those with intent to
de~raud can thus be easily detected.
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Reading of the data of the code carrier always takes place
without contact. As described a~ove, the code carrier is located
inside the product and does not lie directly on the surface.
Here, it can be pointed out that the materials used in the
product can limit the applicable reading process. Thus there are
also reading processes possible and described below which, e.g.,
allow a code on the code carrier to be detected even in the
presence oP metals or through metals.
The code of the code carrier can be detected in various
ways. The reading proces3 to be used depends among other things
on the material of the code carrier and its environment, i.e., on
the materials used in the product. Thus an electrically
conductive code carrier, such as, e.g., made ~rom copper, can be
scanned by its stray field caused by eddy currents. If the code
carrler consists of a soft magnetic material, such as iron or
permalloy, the shape variation and thus the code can be scanned
by its magnetic stray ~ield. If the code carrier consists of a
so~t magnetic metal material, magnetically inductive and eddy
current processes can be combined, which increases the reading
reliability. The magnetic processes generally bring with them
the advantage that the code can be detected even in the pr~sence
of other metals.
It should be remembered that stray fields basically can have
the following physical causes: stray fields can be causad by eddy
currents or magnetiaally. In both cases the reading process
takes pIace by saanning the stray field. In one case eddy
current~ are produced in a metal conductor by a high-frequency
alternating field. The metal conductor in this case is the code
carrier. The eddy currents produced in it cause an attenuation
of the hf oscillator. This attenuation can be obtained with
commercially available sensors, which both produce the h~ field
and measure the attenuation, are either measured by a reduction
of ~he amplitude of the oscillator or are determined as shifting
o~ the resonance ~requency o~ the oscillator. The attenuation of
the eddy currents caused in the code carrier depends in this case
relatively greatly on the transmitter-code carrier distance.
In the other case the shape-dependent stray field of the
soPt or also hard magnetic code carrier is recorded with usual
field measuring probee. It is clear that methods are related by
the Ma~well aquations, but in this case there are basic
dif~erences resulting from the physical mechanisms. These
reading processes are described below in more detail.
In the scanning o~ stray fields caused by eddy currents, any
metal is suitable as code carrier. Pre~erably, in this case it
is a good electric conductor. But tests have shown that the
magnituda o~ the electrical conductivity influences the distance
dependence of the commercially available sensors only slightly.
Analogously, the (soft) magnetic state of a metal code carrier
hardly influences the threshold value of the distance at which
the commercial eddy current sensor abruptly changes its output
1eVQ1~ 9ut commarcial eddy current sensors can be subs~antially
improved in their sensitivity, i.e., their distance dependence by
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additional d~tector coils. The arrangement of these detector
coils ha~ to be adapted to the shape of the emission lobe of the
transmitter.
A reading arrangement for stray fields caused by eddy
currents is diagrammatically represented in fig. 7. Either
reading head 14 is moved past on code carrier 16 in the direction
of arrow 15 or code carrier 16 is moved past on stationary
reading head 1~. One or more small detector coils for
improvement of the sensitivity can be placed directly at the end
of emitting oscillator head 14. The speeds usual with a conveyor
belt do not disturb the reading process. Fig. 7b is a view o~
the measuring arrangement according to ~ig. 7a. Holes in code
16, whose arrangement represents the aode, are identified by
reference 17.
Fig. 8 shows a similar arrangement as fig. 7, and the code
carrier consists of a metal plate with side projections, as
repreeented in fig. 1. It should be noted that distance x o~ the
plate ~rom the sensor necessary ~or the code recognition as well
as height h of these side projections have to be so that the
recognizability limit, which is indicated by broken line s in
fig. 8, o~ the sensor is greater than x but smaller than x ~ h.
As already mentioned, s can be enlarged to increase the
sensitivity using additional detector coils, but then the
distance of adjacent "bits," i.e., of the side projections ~lso
has to be enlarged.
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Fig. 9 shows diagrammatically the basic equipmant design for
a reading device for stray fields caused by eddy currents. The
principle of the scanning is based on contactless electronically
operating proximity sensors. Basically the reading device
consists of an oscillator 1~, a trigger 19, as well as an
amplifying logic circuit output 20. The distance of the sensor
from the code carrier i6 basically dstermined by the diameter o~
the emitting sensor surface.
Instea~ of 19, for example, a difference amplifier can also
be used, which ampli~ies the signal produced by above-mentioned
additional detector coils ~8. This signal reaches a comparator,
which compares this signal with an adjustable reference signal
and, as a functlon of the latter, emits or does not emit a signal
("bit"). The analysis than again takes place in an appropriate
logic circuit (20).
Oscillator 18 produces, with its resonant circuit an
electromagnetic hf field 21, which comes out from the active
surface of the senscr. The frequency of the alternating field
determines the depth of penetration into a metal body, as it is
represented by code carrier 22 here. Eddy currents
diagrammatically indicated by 43, which are directed so that the
primary field is shlelded, are produced in the code carrier by
the electromagnetic alternating field correspondin~ to Maxwell
~equations. The strength of these eddy currents depends on the
frec~enoy of the alternating field, on tha electrical
conductivity, as well as in the case of a magnetic material also
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on its permeability. By suitable selection oE the material of
the code carrier the sensitivity of the entire system can be
influenced in principle. But tests show that commercially
available eddy current sensors generally are too insensitive to
be able to be used in a material specific manner. Energy is
withdrawn from the oscillator by the formation of these eddy
currentsO This causes at the output of the oscillator an
amplitude change or a chanye of the resonance freque.ncy, which is
converted into a logic signal by trigger 19 and output stage 20.
Fig. 9 shows at least one additional detector coil 48.
Advantageously the syst~m consists of at least two coils, which
are wound or placed so that the induction signals produced in
them are antiparallel equal, i.e., neutralize one another. If a
metal code carrier is brought close to the oscillator, it changes
the strength and direction o~ the rotational field. As a result
the symmetry o~ the detector coil system is changed and a signal,
caused by the code carrier, results. In this way, the
sensitivity, with which, for example, a hole in a metal sheet is
detected, is significantly increased.
The strength of these eddy currents and thus the strength of
this attenuation depends basically on the sensor-metal distance.
If sensitivity limit s is placed so that parts of a geometric
shape, which represents the code, go beyond or below this limit,
the parts thus scanned can be converted as code tsee, e.g., fig.
8)~ In~this way, for example, fins or alevations can be detected
on a metal code carrier (e.g., fig.2, fig. 3, ~ig. 5 or fig. 6).
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23
Also three-dimensional cross-sectlonal changes on a metal code
carrier can thus ~e detected as code with a eddy current sensor
if the sensitivity limit goes through this cross sectio~al
variation. Another possibility is that the presence or absence
o~ a metal is recognized if the latter is located within the
sensitivity limit. In this way, e.g., holes in a metal sheet can
be detected in a metal sheet if the hole diameter corresponds
approximately to the sensor diameter. But with additional
detector coils holes with smaller diameter can also be detected,
by which altogether the data density can be increased. As a
result of the slight depth of penetration of the high-~requency
alternating field very thin metal sheets can be used, which
technically is very advantageous. It is also possible to achieve
the code by electrically conductive varnishes or metal powders,
which are suspended in plastics, and then to detect it by eddy
currents.
To be able to place as many bits as possible per surface
unit, it is advantageous to place several eddy current sensors
next to one another. Two or n holes, located next to one
another, can be detected by 2 or n eddy current sensors placed
next to one another, and the minimum di~tance of the sensors is
to correspond appro~imately to their diameter.
Eddy currents can be used for reading the code only if no
~other metals exist in the product in ths immediate vicinity of
the code carrier. If this is the case after all, the code
carrier has to be placed inside sensitivity limit s and all other
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24 ~Y~
matal compon nts have to be placed outside sensitivity limit s.
But in this case, magnetically detectable code carriers appear
especially advantageous. This means that the code of both soft
magneti¢ and hard magnetic code carriers can he detected through
other metal materials, e.g., made of aluminum, copper, etc.
With a soft magnetic material the code can be detected
outwardly by the geometry-dependent stray field of the code
carrier. There are different technical solution possib:ilities
for reading the code in a soft magnetia material. According to
the coding process achieved by the special design the code
carrier is magnetized by an exciting magnetic field produced
externally. This magnetic field can be either a steady field or
an alternating field.
Fig. 10 shows a reading arrangement for magnetically caused
stray fields with a magnetizing with a steady field, and fig. 11
shows a signal thus obtained. The steady ~ield is produced, for
example, by a permanent magnet 23. Instead of a permanent
magnet, a field coil, through which a direct current flows, can
also be used. The permanent magnet or field coil in this case
should be designed so that the magnetic field produced by it is
homogeneous over the length of the code carrier. It appears
especially advantageous if the strength of magnetic field H is
selected so that the highest value of permeability ~maxf the
material used of the code carrier is achieved. As a result a
substantial improvement oP the sensitivity o~ the system can be
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achieved. The product and with it code carrie!r 24 is moved in
the direction of arrow 25 by the magnetic ~ield. As a result of
the high permeability of the material the field lines o~ the
outside magnetic field are distorted in a way that is significant
for the special shape of the code carrier. An example of a field
line distribution in represented diagrammatically in fig. 12.
Measurement of the shape-specific field line distribution over
the length of the code carrier takes place, for example, by Hall
probes 26. Instead of Hall probes other appropriate sensors, for
example, field plates, magnetoresistance sensors, etc., can also
be used.
To detect the code in this case additionally also the
voltage can be used which is induced in additional pickup coils
(e.g., fig~ 13), if the code carrier is moved through a pickup
coil and in this way a magnetic flux change and thus a signal is
produced. A field coil is identified by 27 in ~ig. 12. Code
aarrier 28 is moved in the field coil and the formation of the
represented magnetic field lines results, which can he used for
reading the code. In this case, especlally usual, appropriately
sensitive field sensors are suitable, but the si2e of the sensor
(active surface) has to correspond approximately to the spatial
extension of the recess, elevation or cross-sectional change
representing a bit.
If an alternatlng ~ield is used as primary field, a so-
called pickup coil is suitable for reading the code. Also in
this oas- th- ~ield coil sho~ld be designed so that the magn~tic
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field produced by it is homogeneous over the :Length of the code
carrier. It appears especially advantageous if the strenyth of
magnetic field H is selected so that the highest value of
permeability ~maxf the material used of the code carrier is
achieved. The frequency of the alternating field is to be
relatively low (i.e. f less than lO kHz) to avoid shielding
effects by the eddy currents. By a skillful c;election of the
control field and its freque~cy a subs~antial improvement of the
sensitivity of the system can be achieved. Fig. 13 represents an
arrangement suitable for this and fig. l~ diagrammatically shows
the resulting reading siynal. Code carrier 30 i8 moved in the
direction of arrow 31 within primary coil 29, which procluces an
alternating ~ield. A voltage, whose amplitude is proportional to
the field line density and thus to the special shape of the code
carrier, is produced in pickup coil(s) 32~ The use of a
"compensated" pickup system is advantageous, which is
characterized in that it emits no signal in the absence of a code
carrier, i.e., the voltage is only proportional to the
magnetizing. As simplest embodiment two coils wound antiparallel
on an axis are produced, by which the "pure" field signal is
canceled. In this way, adjacent bits can be recognized with
great reliability with resolution without the use of a "track."
Special attention has to be given to the resolution of the pickup
system. The greater the average dietance between code carrier
and pickup colls, generally the poorer the resolution. A high
reso1ution can then be achieved by a Gpe~ial design o~ the pickup
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coils. ~ pickup system exhibits a high resolution if the
magnetic field "fictiously" produced by it is great at the site
of the "bit" and outside quickly goes toward zero. Another
arrangement would be the use of a dipole-compensated coaxial
system, which exhibits a higher resolution. But in this case too
the resolution can be further improved by the arrangement of the
additional coils. The length of a pickup coil again is
determined at most by the spatial extension of a cross-sectional
change representing a bit -- a shorter syste~ in any case offers
more resolution bu-t less sensitivity. The use of a periodic
alternating field is metrologically advantageous, since by the
use of a frequency- and phase-sensitive amplifier a substantial
improvement o~ the signal-to-noise ratio of the code signal can
be obtained. The amplitude of the code signal changes in unison
with the shape variation of the code carrier so that the reading
signal reproduces the code of the code carrier. Use of an
in~egrator i6 especially advantageous in the signal processing,
by which the signal voltage becomes indapendent o~ the frequency
of the exciting field but also of a movement of the object. With
the integration necessary in this case the integrator has to
exhibit two negative ~eedbacks with two different times constants
tl and t2~ Tlme constant tl has to be smaller than perlod T to
integrate the periodic alternating voltage. Time constant t2 has
to be great in comparison with tl -- it is to control the very
dlsturbing integration of offset voltage or othar parasitic
voltages, occurring over a long time, in the integrator. An
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example of a usable integrator iB a hysteresograph. The outp~t
signal is again proportional to the magnetizing and thus to the
cross section representing the code.
Instead of the pickup coils in this case, ~or example, a
Hall probe can be used, which measures the stray field varying
with the shape~
Especially advantageous is the simultaneous use o~ a pickup
system with a sensor for measuring the stray field. The
corresponding measurin~ electronics are connected to the two
measuring systems. Only if the two independent systems recognize
a "blt," ~s lt actually registered as belonging to the code. In
this way, the reliability o~ the system in regard to disturbing
influences is substantially increased.
Fig. 15, 16 show another embodiment for the reading process.
In this case a soft magnetic yoke 33, which exhibits one or more
measuring and axciting coils, is used. The code carrier can
consist of a soft magnetic or a permanent magnetic material,
which i~ provided with ~ins. The sequence of the fins represents
the code. The ~ins are identified by 34 and 35. The code
carrier is partially magnetized by moving magnetic yoke 33 if the
code carrier is soft magnetic. Conversely in case of a permanent
magnetic code carrier this code carrier magnetizes the soft
magnetic yoke.
In both cases the flux change is measured in a contactless
manner by at least one secondary coil on the same yoke. The
exciting coil can be supplied with either direct and/or
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alternating current. Which type of current is selected ~gain
depends of the sensor used, with which the stray fi~ld change
represenking the code is detected. ~'he strength of the current
in this case is determined by the material of the yoke. The
current again is to be adjusted so that the total permea~ility of
the circuît becomes maximal. ~n this case, other sensors,
sensitive to magnetic fields, can be used, such as, ~or example,
Hall probes and ~ield measuring plates. They are located in the
air gap between code carrier, which is incorporated in the
product, and the soft magnetic yoke. The read code is produced
by the measurement of the scanned resolving magnetic field or
stray field varying in this air gap, which is a result of the
variation oP the magnetic resistance caused by the fins. Thus an
output signal results, whose amplitude represents a bit seguence,
which corresponds to the code.
~ ests have shown that a code, as described above, can be
de~eated through an aluminum plate without a problemO The use of
an exciting alternating current of not too high frec~ency ~f less
than 10 kHz, but especially under 100 Hz) represents no prohlem.
Two sofk magnetic code carriers can be put and read at the
same time on the front and back side of the procluct (which
doubles the bit density to be included). If distance d of the
code carriers from one another is greatPr than distance y between
the code carrier and the soft magnetic yoke, no influence occurs
(s~e fig. 17).
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The use of ~ combined measuring system consisting of
measuring coils 44 on the limbs of soft magnetic yoke 33 and the
additional use of field sensors, e.g., Hall sensors 26, appears
especially advantageous, as represented in fig. 18. Only if the
two systems indicate the presence of a bit is it actually
registered as a code. Again as a result the reliability of the
systam in regard to undesirable parasitic voltages i.s
substantially increased. The primary coil in this case is
identified by 45 and is operated simultaneously w th direct and
alternating current. Secondary coils 44 are wound antiparallel.
The use of a permanent magnet code carrier in mass-produced
products is advisable only if the code carrier is very
inexpensive. A hard magnetic sheet would be conceivable as it is
also used on check cards.
Coding can be done in many ways:
a) A bar made from hard magnetic sheet 46 is first fully
magnetized in an axis 47. Then it is processed corresponding to
the code by punching on its edges (see ~ig. 19). The code is
recorded by measuring of the stray field on the edges
(demagnetized ~ield), and in this case the use of correspondingly
small Hall probes seems especially advantageous.
bj A bar made from a hard magnetic sheet, ~efore
incorporation into the product, i partially magnetized in
differen~ directions with the stray field of the air gap of a
soft magnetic yoke (see fig. 20). The width of the magnetized
area in this case is determined by the air yap. The stray field
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of these magnetized areas can now be recorded from the outside
with field sensors (Hall probe, pickup system, Fe yoke). Since
with the products to be recorded in this case the code has to be
detected and read at considerable distances, correspondingly
large areas on the code carrier also have to magnetized. The
width of the magnetized area corresponds approximately to the
distance at which the code can still be read. In this case, the
clock data is determined by computer from the width of a bit (~-S
bar).
c) ~lso conceivable is a comhined embodiment of a) and b~,
and then periodic recesses, for example, represent a clock track
and the presence of a north or south pole means the bit 'll'l or
"0." It would be advantageous in this embodiment that the speed
with which the code carrier (the product) is moved past the read
head is unimportant, and the data density can be increased, ~or
example, by elimination of the neutral zones.
A block diagram o~ analysis electronics of the measured
signals is represented purely diagrammatically in fig. 21.
Control 36 (hf transmitter, exciting current, Hall current)
controls at least one sensor 37 ~eddy current sensor, pickup
coil, Hall plates). The signals coming from the sensors are
amplified in amplifier 3~ (signal processing) and converted in an
analog-to-digital converter 39 to digital signals and routed to
computer 40 (code rerognition, analysis, data storage). In case
of the~r~ ording of the code with pickup coils it is better to
use a hysteresograph for recording the signal. As already
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mentioned, the simultaneous use of several measuring systems
~e.g., pickup coils and field sensors) seems particularly
favorable. Only if several measuring processes report a bit is
it routed to the computer as actually read. The code
recognition, analysis and data storage take place in the
computer. Again the actuation of sensors 36 is rsgulated by feed
control 41, optionally with insertion of position recognition 42.
Some significant aspects o~ the invention are emphasi~ed
below:
The invention serves for identification ~coding) o~
products, which are produced in large numbers of units. This
process is provided mainly for monitoring the production course
but also for safety, quality and guarantee performances. A
feature is the application of a code to a code carrier, which
can cons1st of an electrically conductive material (metal) but
also of a magnetic tsoft or permanent magnetic) or magneti~able
material. The choice of the material is decisive for the reading
process or processes but also for the legibility of the code.
The code consists of shape variation, cross-sectional changes,
changes o~ the contours, ~ins or also recesses or holes of the
code carrier or also from a pattern produced by an appropriate
metal-plastic ~mulsion, e.g., "conductive varnish," which are
detected by their stray field caused by eddy currents or also by
their geometrlcally determined magnetic stray field. The
correspondingly detected, locally dependent analogous measuring
signal, which becomes redundant by the simultaneous use of
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several independent reading processe~, can be converted into
digital data, which corresponds to the code.
The code element preferably is to be mechanically and
ther~ally rugged and invisible from the outside or covered and
thus largely insensitive to ambient influences and preferably is
to be applied in or on the product and connected as inseparably
as possible to the product.
The code carrier can exhibit any shape. The outside shape
can match the shape of the product. The great flexibility in the
design al50 marks the invention. But also parts of the product,
which con~ist of electrically conductive or magnetic material, by
changes o~ the cro~s ~ection, the contours, the surface or also
by application of recesses of any shape can be used as code
carrier.
The code carrier can also consist of permanent magnet
elements, preferably a hard magnetic sheet, plastic-magnetic
powder emulsion or metal-plastic emulsion. It is advantageous
that a magnetic code carrier be detectable even in the presence
of electrically conductive other components of the workpiece.
This applies even if they are placed immediately above or under
the code carrier.
In an arrangement for detection of the code, consisting of
one or more eddy current sensors, on which the workpiace, which
contains the cDde carrier, is moved past, eddy currents are
produced by a high-~reguency alternating field. Whether eddy
currents are actually produced or notl~greatly depands on the
34
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distance between eddy current head and metal code carri~r. The
code is now achieved in the code carrier by a special design
(cross section, thickness, holes, etc.~. As a result the
distance between eddy current head and code carrier is varied so
that a logic "0" (distance too great) or a "1" (distance small
enough) results. The properties of the high-frequency resonant
circuit chanqed as a result of the eddy currents so produced thus
are ueed as signal for detection o th~ code.
In an arrangement for the detection of a code contained in a
magnetic code carrier the code is produced in a soft magnetic
material hy a special design (cross section, surface, etc.). The
locally dependent stray field, which represents the code, is
scanne~ with se~30rs sensitive to fields.
The locally dependent stray field, which represents tha
code, can be recorded by the movement of the product with the
code carrier through a coil system with the resulting pickup
voltage.
The magnetizing magnetic field can be a periodic alternating
field. The locally dependent stray ~ield, which represents the
code, is detected with a resolving pickup coil system as periodic
alternating voltage. Advantageous in this case is the use of
frequency- and phase-sensitive amplifiers for signal processing,
which produce a better signal~noise ratio. The integration of
the signal represents another possibility, by which the freguency
of the~exciting field no longer 1nfluenoes the value of the
measurlng signal.
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The locally dependent stray field, which represents the
code, can also be detected as periodic alternating voltage with
magnet-sensitive sensors, such as, for example, Hall sensors or
field plates. The periodically occurring alternating voltage
makes the use of a frequency- and phase-sensitive ampli~ier for
signal processing especially advantageous. A better signal/noise
ratio results.
The code contained in a so~t magnetic code carrier, which is
detected by special design, can be detected with a soft magnetic
yoke. The code is detected hy the change of the magnetic
reslstance either by a monitoring oP the power input of the
primary coil or with additional special secondary coils or again
by ~i~ld-sensitive sensors, and the latter respond to the chanqe
o~ the stray field in the air gap.
If the code carrier contains permanent magnet parts, the
thus locally dependent varying stray fields, which are caused by
the permanent magnet coded by corresponding design or magnetizing
and thus represent the code, are scanned with a soft magnetic
yoke (on which induction coils are located) or else with
correspondingly small field sensors (Hall probes, etc.).
The arrangement of the detector read head is preferably such
that reading is contactless. The size of the read haads
generally corresponds approximately to the spatial extension o~
the feature desaribing a bit, as for example, a cross-sectional
change~ Otharwise the arrangement o~ the heads can match the
geometry of the code carrier, as well as that of the product, and
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36
thus can be freely selected. The ~istance is determined by the
geometric shape of a "bit" as well as its size, but also by the
basic laws of physics, for example, the distance dependence of
the stray field.
The optimal shape of the recesses or cross-sectional changes
representing the "bits" is in direct relation with the shape of
the active sur~ace of the sensor used.
The determination of the code of the code carrier can take
place by a relative movement between code carrier and
corresponding sensor basically along the main axis containing the
code, and for a corresponding resolution of the code either the
speed is known or a "clock track" is used. But with the
appropriate arrangement of several sensors the entire code
carrier can be scanned in a step, 80 that with a sensor number
corresponding to the data density the relative movement between
code carrier and sensor(s) can be eliminated and the time for
reading out the code can be shortened.
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