CA2049934A1

CA2049934A1 - Process and device for analysing the data on a code carrier

Info

Publication number: CA2049934A1
Application number: CA 2049934
Authority: CA
Inventors: Kurt Wally; Roland Grossinger
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-01-23
Filing date: 1991-01-23
Publication date: 1991-07-24
Also published as: JPH04504479A; EP0464186A1; AT398497B; ATA14890A; WO1991011777A1

Abstract

Abstract:
Code carrier. process for analyzing the data of such a code carrier as well as coding system using such a code carrier for product identification In a code carrier (1) for analyzing a code for product identification, said code carrier is placed under a cover layer of the product to be identified and consists of a magnetic, magnetizable and/or electrically conductive material, exhibits openings, recesses or a changing cross section (3) for the analysis of a stray field changing in an axis (2) of a plane parallel to the main axis of the code carrier (fig. 1).

1/15/1991/Sil

Description

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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 3~

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 .' . ,' ~ .

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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~ 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 12 S;~d~

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 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 , \ 16 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 :: ~

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 22 ~ 3~

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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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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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 . ~ ' 26 ~ $3~

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 .

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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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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Claims

Claims:

1. Code carrier (1,4,6,8,10,12,22,24,28,30,35,46) for analyzing a cods for product identification, said code carrier is placed under a cover layer and consists of a magnetic, magnetizable and/or electrically conductive material, characterized in that the code carrier exhibits openings, recesses or a changing cross section (3,5,9,9',11,13,17,24,34) for the analysis of a stray field changing in an axis (2,15,25,31) of a plane parallel to the main axis of the code carrier.

2. Code carrier according to claim 1, wherein the code carrier is designed as a plate (4,6,10) or sheet (8,16,46).

3. Code carrier according to claim 1, wherein the code carrier is formed from conductive metal-plastic emulsion or magnetic powder-plastic emulsion applied to a substrate.

4. Code carrier according to claim 1, 2 or 3, wherein code carrier (8,10,24) exhibits in at least two planes parallel to the main axis openings, recesses or changing cross section (9,9',11) and wherein in one plane the openings, recesses or changing cross section is/are designed uniformly.

5. Code carrier according to one of claims 1 to 4, wherein code carrier (1,4,6,8,10,12,22,24,28,30,35,46) is placed invisible from the outside.

6. Code carrier according to one of claims 1 to 5, wherein code carrier (1,4,6,8,10,12,22,24,28,30,35,46) is an integral component of the product or is formed of components of the product.

7. Process for analysis of the data of a code carrier (1,4,6,8,10,12,22,24,28,30,35,46) placed under a cover layer of a product, in which the code carrier consists of magnetic, magnetizable and/or electrically conductive material and exhibits a geometric configuration containing the code, wherein an electromagnetic field is produced and wherein the changing stray field basically parallel to a main axis of the code carrier (1,4,6,8,10,12,22,24,28,30,35,46) is measured and analyzed.

8. Process according to claim 7, wherein code carrier (22) is exposed to a high-frequency alternating field (21) and the changes of the high-frequency field caused by the eddy currents produced in the code carrier are detected by the characteristics of the high-frequency resonant circuit.

9. Process according to claim 7, wherein code carrier (24,28,30,35) made of soft magnetic material is exposed to a magnetic field and the resulting locally dependent magnetic stray field is measured with magnetically sensitive sensors (26,32).

10. Process according to claim 9, wherein a periodic, magnetic alternating field is produced.

11. Process according to one of claims 7 and 10, wherein the varying stray field of the code carrier (1,4,6,8,10,12, 22,24,28,30,35,46) in the electromagnetic field is measured with at least two sensors (26,32;26,44) independent of one another and wherein the measured signals are fed to a common analysis circuit.

12. Use of a code carrier (1,4,6,8,10,12,22,24,28,30,35,46) made of magnetic, magnetizable and/or electrically conductive material with defined design, such as, e.g., recesses, openings and/or cross section (3,5,9,9',11,13,17,24,34) 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 cover layer of the product.

13. Coding system for product identification with a) at least a code carrier (1,4,6,8,10,12, 22,24,28,30,35,46) made from magnetic, magnetizable and/or electrically conductive material with defined design, such as, e.g., recesses, openings and/or cross section (3,5,9,9', 11,13,17,24,34) changing over an axis of the code carrier b) at least one field source (14,18,23,27,29,33) and c) at least one field sensor (18,26,32) for measuring the stray field caused by the code carrier.

14. Coding system according to claim 13, wherein the code carrier is designed as a plate (4,6,10) or sheet (8,16,46).

15. Coding system according to claim 13, wherein the code carrier is formed from conductive metal-plastic emulsion or magnetic powder plastic emulsion applied to a substrate.

16. Coding system according to claim 13, 14 or 15, wherein code carrier (8,10,24) exhibits in at least two planes parallel to the main axis openings, recesses or changing cross section (9,9',11) and wherein in one plane the openings, recesses or changing cross section is/are designed uniformly.

17. Coding system according to one of claims 13 to 16, wherein field source (14,18,23,27,29,33) produces an electromagnetic field shiftable relative to the code carrier.

18. Coding system according to claim 17, wherein the field source produces a periodic, magnetic alternating field (27,29,33).

19. Coding system according to one of claims 13 to 18, wherein the field sensor is formed by a Hall probe (26) or field plates.

20. Coding system according to one of claims 13 to 18, wherein the field sensor is formed by a pickup coil (32).

21. Coding system according to one of claims 13 to 17, wherein a reading device -- comprising the field source and the field sensor -- for the code of the code carrier comprises an oscillator (18) for an electromagnetic hf field (21) for energizing eddy currents in code carrier (22), a trigger (19) and an output stage (logic 20) for conversion of the attenuation of the hf field dependent on the geometric shape of code carrier (22) into an analyzable code signal.

22. Coding system according to one of claims 13 to 17, wherein a reading device for the code of the code carrier comprising the field source and the field sensor comprises an oscillator (18) for an electromagnetic hf field (21) for excitation of eddy currents in code carrier (22), a detector coil system (48), a difference amplifier, a comparator and an output stage (logic 20) for conversion of the attenuation of the hf field dependent on the geometric shape of code carrier (22) into an analyzable code signal.