FI90806B - Coding and identification process for ferromagnetic products - Google Patents

Description

90806

Method of coding and identification of ferromagnetic products

The invention relates to a method of encoding ferromagnetic products 5, in which a magnetic identification code is generated in the product by modifying the residual stresses and / or microstructural changes in the surface area of the product or in its vicinity.

The coding method can be used, for example, for coding steel products such as steel sheets or other products made of steel or other ferromagnetic material.

Today, for example, steel products such as steel sheets are coded and labeled in a number of different ways. One way is to use a bar code such as an EAN code so that the product to be identified is coded with a unique bar code which is printed on label paper and then affixed to the side of the product. The bar code is read by a reading device, on the basis of the information provided by which the marked product 20 can be identified. However, the bar code does not withstand environmental conditions, such as mechanical wear or other severe operating conditions, very well. When storing products, the products are exposed to various bumps, chemicals and other effects that result in the complete or partial destruction of the barcode. As a separate step in its work, the barcode requires attachment to the surface of the product, and therefore the use of the barcode requires additional measures. The bar code is also not suitable, for example, for marking steel plates as a raw material for tools or equipment, if it is desired that the same marking be retained in a product made of steel plate, such as said tool or equipment or part thereof.

Another known method of encoding and identifying steel products or other products made of Ferro-35 magnetic material utilizes escort memories and code carrier buttons that contain information about the product in question. For example, the reading of the code carrier buttons is usually inductive, in which case the coil contained in the reader device 5, i.e. the receiver, activates the transmitter comprising the code carrier button, whereby the information contained in the code carrier button is readable and the product can be identified.

Accompanying memories and code carrier buttons are similar in nature to bar code tags, as they also require a special tag to be affixed to the surface of the product, which can impair the wear resistance of the tag.

U.S. Pat. No. 4,660,025 discloses, for example, a detector for preventing shoplifting, i.e. a marker attached to a commercially available product which, when exposed to an external magnetic field, emits a pulse whose harmonic oscillations are detected by a receiver device. The pulse produced by the marker is the result of a large Barkhausen pulse generated in a specially made wire comprising 20 markers. This solution requires the affixing of a separate marker to the significant product and does not modify the magnetic properties of the product to be identified.

25 Barkhausen noise measurement is a known magnetic measurement method in which the voltage induced in the measuring coil by the discontinuous movement of the walls delimiting the magnetic elementary regions, i.e. the domains, caused by a changing magnetic field, which is interpreted as Barkhausen noise-30 si. The magnitude of the measured Barkhausen noise depends on e.g. the microstructure of the material and the stress state of the material. Barkhausen noise measurement has so far been applied mainly in non-destructive testing of materials, in which, for example, the condition and durability of welds are studied. In welded structures, the material is formed unevenly li 90806 3, whereby residual stresses are formed in the material, which in turn affect the properties of the material. Residual stresses can be measured using Barkhausen noise measurement. Barkhausen noise measurement is described in more detail in, for example, the publication; Material-prufung, Band 22, 1980 Nr. 5, ss. 196 - 200.

U.S. Pat. No. 4,408,160 discloses an apparatus for measuring the tension of metal products using the Barkhausen magnetoacoustic phenomenon. However, these 10 solutions do not involve product coding or identification.

U.S. Pat. No. 4,931,730 discloses a non-destructive material testing apparatus using Barkhausen noise as a measurement signal, but this solution 15 cannot be used to encode substances or products.

It is an object of the present invention to provide a new type of method for encoding ferromagnetic products which avoids the problems associated with known solutions.

This object is achieved by a method according to the invention, characterized in that the magnetic identification code is formed in such a way that, when read by Barkhausen noise measurement, it gives a predetermined identifiable result.

The method according to the invention is based on the idea that the local magnetic properties of the product to be identified are modified. Existing residual stresses and / or microstructural changes in the product are modified or new residual stresses and / or microstructural changes are applied to the product, thereby generating a magnetic code that can be read using a Barkhausen noise measurement known per se. The magnetic code is separated from normal Barkhausen noise, allowing product identification to be performed.

The method according to the invention achieves several advantages. The main advantage is the applicability of the method in severe environmental conditions, and this is due to the fact that no special identifier needs to be affixed to the surface of the product. In the method according to the invention, the code is formed on the physical structure of the product, i.e. on the surface layer of a steel plate, for example by heating, whereby the code is located at a distance of micrometers below the surface of the product. In the invention, the coding is achieved by modifying the existing structures of the product, so that there is no need to effortlessly add any other identifiers to the surface of the product, such as a bar code or a code carrier button, at least the latter of which needs an enclosure. However, it should be mentioned that the coding of the product can also be performed by the method according to the invention by attaching to the product a sensor made of ferromagnetic material, which contains a code readable by Bark-Haus noise measurement.

The invention also relates to a method for identifying ferromagnetic products, wherein the product to be identified comprises a magnetic identification code formed by modifying the residual stresses and / or microstructural changes in the surface area of the product or in its vicinity. Known identification methods are the optically readable bar code solutions described above or, for example, inductively readable escort memory solutions with the necessary readers.

The identification method according to the invention is characterized in that the magnetic identification code of the product is read using Barkhausen noise measurement by measuring the Barkhausen noise produced by the identification code.

The identification method according to the invention is very reliable even in harsh conditions and demanding operating environments.

The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 shows the coded product schematically from above, Fig. 2 shows the measured and filtered Barkhausen noise signal, Fig. 3 shows the coded product schematically from the side and a block diagram of the equipment used, Fig. 4a shows the sum signal of the netting signal and the Barkhausen noise voltage signal produced by the coding, .10 Fig. 4b shows a higher amplitude noise voltage signal produced by the code part, and Fig. 4c shows a lower amplitude noise voltage signal produced by the code part.

The ferromagnetic product 1 to be coded according to Fig. 1 may be, for example, a steel plate which is to be coded in order to monitor the movements of the steel plate, for example with a view to the needs of factory automation. According to the basic idea of the coding method according to the invention, a code 2 20 or a similar identifier is formed in the product 1, i.e. the steel plate 1 of Fig. 1, by modifying the magnetic properties of the product 1 so as to give a predetermined identifiable result when using Barkhausen noise measurement. In a preferred embodiment of the coding method according to the invention, the code 2 is generated by mechanically, physically or chemically modifying the residual stresses and / or the microstructure of the surface area 3 of the product 1 or its vicinity. In addition to or instead of modification, new residual stresses and / or microstructural changes may also be caused to the product. In Fig. 1, the code 2 30 consists of a plurality of code parts 2a-2f located on the surface or surface area 3 of the steel plate 1 side by side. The code 2 and its code parts 2a-2f can be formed on the surface 3 of the steel plate 1 in several different ways. The most useful methods are the use of surface hardening devices known per se, heating devices or devices which cause mechanical stress and tension 6. Suitable devices for this purpose are, for example, laser devices, welding devices and grinding devices with which the surface 3 of the product 1 to be treated, for example a steel plate 1, is treated. The surface 5 3 of the product 1 can also be treated with a chemical which, mainly due to its corrosive effect, modifies the magnetic properties of the surface of the product 1. Residual stresses and microstructural changes can be, for example, rearrangements of magnetic elementary regions, or domains, or changes in dislocations and impurities. In Fig. 1, the parts 2a-2f of the code 2 are formed in such a way that the first dark part of the code 2 on the left is, for example, welded or otherwise heated or otherwise treated, whereby residual stresses and / or microstructural changes occur at the steel plate surface 3. The following part 2b of the code is omitted. The next two code parts 2c and 2d are treated in the same way as the first code part 2a, the treated code parts 2c and 2d together forming a wide 20 processed area, which in Fig. 1 appears as a uniform dark area. The next part of the code 2 again contains an unprocessed item, denoted by the reference number 2e, followed by the last part of the code, again the processed item, i.e. the code part 2f.

In a preferred embodiment of the invention, the code is formed into a regular pattern, such as a row and / or a sequence or other pattern formed by successive parts of the code 2. In the product shown in Fig. 1, i.e. in the steel plate 1, the code 2 is formed as a row formed by the code parts 2a-2f 30. The line or queue code 2 is easily readable by parallel movement of the reader device. The code 2 is also easier to generate if the parts 2a-2f of the code 2 are in a clear, regular and patterned order.

In a preferred embodiment of the coding method according to the invention, the code 2 is generated by modifying the magnetic properties of the product 1 by or by means of residual stresses and / or microstructural changes such that the code 2 parts 5a to 2f of the code 2 are two Barkhausen noise or clearly divided into two orders of magnitude, in which case the lower and higher noise voltage levels can be clearly distinguished. In a preferred embodiment, the code 2 is generated by modifying the residual stresses 10 and / or microstructural changes at some points in the product 1, and leaving the other points unmodified. For example, residual stresses and / or microstructural changes can be formed such that, for example, the heated areas of the product 1, i.e. code 2 parts 2a, 2c, 2d 15 and 2f, form an order of magnitude where Barkhausen noise is higher than in the untreated areas . For parts 2b and 2e of the Barkhausen noise level, the code forms its own order of magnitude according to the lower noise level. For the sake of clarity, the code 2a-2f in Figure 1 can also be interpreted as a binary binary code 101101. However, as a pure binary code, the coding 2 only appears after the code 2 has been confirmed, filtered and compressed. The difference in noise levels is illustrated in Fig. 2, in which the upper noise level is indicated by reference numeral Bh and the lower noise level is indicated by reference numeral B ^. The code shown in Fig. 1 is six elements long, so 26 different codes can be represented in the binary system. In practice, the codes will be longer so that the resolution of the encoding 30 is sufficiently comprehensive. For example, a code of fifteen elements can already generate 32,768 different codes.

The basic idea of the method of identifying ferromagnetic products according to the invention is such that the magnetic code 2 obtained by modifying the magnetic properties of the product 1 is read by measuring the Barkhausen noise produced by the coded product 1 at least in the region of the code 2. The identification method uses equipment according to the block diagram of Fig. 3, which in general is in accordance with the prior art already used in Barkhausen noise measurements.

The apparatus according to Fig. 3 utilizes an alternating current magnet 4 with alternating current windings 4a, whereby current is supplied to said alternating current magnet 4 via a power amplifier 5 from a magnetizing generator 6. The alternating current supplied from the magnetizing generator 6 causes the alternating magnet magnet 4 to change its proximity. The variable magnetic field can also be provided by means of a permanent magnet, so that when the code 2 is read, the permanent magnet is moved over the code area 2a-2f. The magnetic elemental regions in the product 1 located in the variable magnetic field are arranged parallel to the external magnetic field. The discontinuous movement of the walls of the domains induces in the measuring coil 20 8 of the measuring device 7, for example, the Barkhausen noise voltage 11 according to Fig. 2. Each part 2a-2f of the code 2 produces part 11a to 11f of the noise voltage to be measured by the measuring coil 8. Figures 2 and 3 show a time for the length of the noise voltage 11a produced by the code part 2a, which also indicates the reading time of the code part 2a. The entire reading time of code 2, i.e. 2a-2f, is denoted by ta_f.

Code 2a-2f is read by moving the Barkhausen noise measuring device 7 in the vicinity of the code forming pattern, or by moving the coded product relative to the Barkhausen noise measuring device 30. The noise measuring device 7 with its measuring winding 8 can, for example, be fixed, in which case an encoded product 1, such as a steel plate, is transported past the measuring winding 8. When the measuring windings 8 and the excitation windings 4a are moved relative to the product 1 (or vice versa), a series I: 90806 9 is induced in the measuring windings 8.

Barkhausen noise voltage signal 11.

Figure 4a shows a low frequency (e.g. 50 Hz) sinusoidal excitation signal-like signal 10 which is adversely and undesirably induced in the measuring coil. The desired signal, i.e. the noise voltage signal 11, is also summed up in the signal 10, of which only a portion 11a corresponding to the reading time of the first code part 2, i.e. part 2a, is shown in Fig. 4a. Thus, the first part 2a of the code produces an undesired small Barkhausen noise voltage summing up to the undesired portions of the signal-10 to 10, which slightly increases the amplitude of the sinusoidal signal 10 at the points 11a marked in Fig. 4a. The signal according to Figure 4a would also be available from other modified code parts 2c, 2d and 2 2f. For the unmodified points 2b and 2e, the noise voltage would be similar to that in Fig. 4a, but the noise voltages produced by the code portion on the rising and falling portions would be lower.

Fig. 4b shows the Barkhausen noise voltage 11a produced by the code part 2a amplified and filtered, whereby the amplitude of the Barkhausen noise voltage produced by the code part 2a is considerably higher than in Fig. 4a, and furthermore the signal of Fig. 4b no longer contains an unwanted magnetization signal. in Fig. 4a, also in Fig. 4b, only the part produced by the first part 2a of the code, i.e. the time ta part, is shown in the noise voltage signal. The amplitude of the noise voltage 11a is at a higher level Uh, which would binary represent the value 1. The signal 30 according to Figure 4b would also be available from other modified parts of the code 2, i.e. parts 2c, 2d and 2f of the code.

Figure 4c shows a signal similar to Figure 4b, but the noise voltage is obtained from the unprocessed code points 2b and 2e. Compared to Figure 4b, the amplitude of the noise time-35 is at a lower level, i.e. level U1 # 10, which would binary represent 0.

The magnetizing signal may also be non-sinusoidal, for example a triangular wave.

In a preferred embodiment of the identification method according to the invention, the measured code 2a-2f, i.e. the serial noise voltage signal 11, is expressed as a bivalent binary 1/0 signal. Based on the measured binary identification information, each encoded product 1 is clearly and unambiguously identifiable. Thus, each encoded product 1 is associated with a binary code identifying the product.

The detection of the noise voltage signal 11, i.e. the separation from other signals induced in the measuring coil 8, such as the excitation signal 10, takes place by means and means known per se. With regard to the separation, it will be briefly noted with reference to block diagram 3 that the sum signal of the noise voltage 11 and, for example, the excitation signal 10 is fed to the bandpass filter 13 via the amplifier 12. The amplifier of the noise voltage signal 11 is amplified by 70-90 dB. that the filter passes signals in the frequency range from 1 kHz to 50 kHz, whereby the harmful excitation signal and possibly also the 50 Hz frequency network disturbances 25 can be filtered to get rid of the noise voltage signal 11. The filtered noise voltage signal 11 is rectified by the negative signal parts in the rectification block 14. In the next block in the threshold element, i.e. the comparator 15, the levels of the signal voltage-30 are set so that a higher voltage level (binary 1) occurs at the output Uout of the comparator, if a higher voltage or voltage Uh occurs at the input Uln of the comparator. Correspondingly, a lower voltage level (binary 0) is set at the output Uout of the comparator if a higher voltage, i.e. a voltage I, is present at the input Uln of the comparator.

90806 11 nite U1.

It is also possible to generate the code 2 by controlling the cooling of the heated ferromagnetic product 1, for example by allowing the product 1 to be cooled differently and at a different rate from the product 1 at certain points than the product 1 to control the cooling. comprises alternating openings and closed points.

Although the invention has been described above with reference to the examples according to the accompanying drawings, it is clear that the invention is not limited thereto, but can be modified in many ways within the scope of the inventive idea set forth in the appended claims.

Claims (5)

A coding process for ferromagnetic products, wherein in the product (1) a magnetic identification code (2,2a-2f) is formed by processing residual stresses and / or microstructure changes in the surface (3) of the product (1), characterized in that the magnetic identification code is made such that upon reading with Barkhausen noise measurement it gives a predetermined identifiable result. Coding method according to claim 1, characterized in that the magnetic identification code (2) is made such that the parts (2a-2f) of the identification code generate divalent Barkhausen noise (11) or are clearly divided into two classes of magnitude. 3. Identification method for ferromagnetic products, in which the product to be identified comprises a magnetic identification code (2,2a-2f) made by treating residual stresses and / or microstructural changes in the surface (3) of the product (1). or in the vicinity thereof, characterized in that the magnetic identification code (2,2a-2f) of the product is read by means of Barkhausen noise measurement by measuring the Barkhausen noise (11) generated by the identification code (2,2a-2f). 25 Method according to claim 3, characterized in that the identification code (2) is read by moving a device (7) measuring Barkhausen noise (11) in the vicinity of the identification code (2), or by moving the coded product (1) in relation to the device (7) measuring Barkhausen noise (11). Method according to claim 3 or 4, characterized in that the measured identification code (2) is indicated as an divalent binary 1/0 signal.