JPH0319994B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention scans the magnitude of the magnetic field density generated on the surface of an object to be detected such as a banknote by applying a magnetic field using a magnetically sensitive variable impedance means. , relates to an authenticity identification device for banknotes, etc., which identifies a detected object from a magnetic pattern obtained at that time. 2. Description of the Related Art In the following description of each figure, the same reference numerals indicate the same or corresponding parts. Recently, there has been a strong need for automatic vending machines and exchange machines to be able to handle high-value banknotes as prices have increased. However, it is not easy to have machines correctly identify these banknotes. Various methods have been proposed and put into practical use to avoid misrecognition, and one of them is a method using a magnetic sensor. Banknotes are imprinted with magnetic ink patterns. This is very convenient when it is desired to have a machine perform banknote identification. In other words, in addition to identification using optical means, banknotes are identified using magnetic patterns that are invisible to the human eye, allowing for more precise and error-free identification. A magnetic head can also be used as this magnetic sensor, but in that case, there is a method for detecting the object by first magnetizing it, and a method for detecting changes that occur when the object approaches the magnetic head in a resonant circuit that includes the windings of the magnetic head. There is a method of detection. In the former case, the leakage magnetic flux of the magnetized object is concentrated near the paper surface, so it is necessary to place the magnetic head in close contact with the object, which requires strict precision when attaching the magnetic head to the identification device. Since the signal voltage depends on the moving speed of the subject, high-speed and stable scanning is required in order to obtain a stable signal.
The latter method also has the drawbacks of not only requiring the magnetic head to be brought into close contact with the subject during sliding scanning, but also having a large amount of induced noise due to the use of alternating current signals, and a complicated signal processing circuit. On the other hand, as a magnetic sensor, there is a method of using a magnetic detector described below that uses a magnetoresistive element that is a magnetically sensitive variable impedance element. When this magnetic detector is used, it does not use the magnetic field of an air gap provided in a part of a closed magnetic path like a magnetic head, but instead uses a so-called open gap detector that uses the magnetic field created in an open space by a magnet. As shown in Fig. 1, the signal voltage and the detection sensitivity (described later) (value at 0 mm spacing) is
(expressed as a relative value) is smaller than that with a magnetic head, and extremely close contact with the subject is not required. For example, in the case of a magnetic head, it is almost impossible to detect the pattern on the back of a bill, whereas with a magnetic detector, the signal voltage drops by only a few dB, which shows that the spacing characteristics are good. Therefore, there is a large margin for mounting accuracy, and it is possible to reduce the cost of the system. Furthermore, there is less noise when sliding and scanning a bill, and the signal voltage level is several dB higher than that of a magnetic head. Furthermore, since the contact pressure between the subject and the magnetic detector can be configured to be weak, it has the advantage of less wear and longer life than magnetic heads. FIG. 2 shows the basic configuration of a detection section in a magnetic detector. That is, 1 is a magnet, 2 is an output terminal, 3 is a subject such as a banknote having a magnetic pattern such as magnetic ink, MR ₁ and MR ₂ are magnetoresistive elements that scan the subject 3, and 4 is a magnetoresistive element that scans the subject 3. These are magnetic detectors connected in series. Now, the subject 3 is moving near the magnetoresistive element in the transport direction X as indicated by the dotted line arrow.
It shall move from the MR ₂ side towards the MR ₁ side,
Further, when the subject 3 moves to the position 3a and the magnetic material in the magnetic pattern comes in front of the magnetoresistive element MR ₂ (not shown, the magnetoresistive element MR ₁
The magnetic flux density passing through the magnetoresistive elements MR ₂ and MR ₁ is B+ΔB,B respectively in the case of 1) and the other case, and the magnetic flux density of the magnetoresistive element MR ₂ is Assuming that the resistance values corresponding to the magnetoresistive element MR ₁ are R ₂ + △R ₂ and R ₂ , respectively, and R ₁ + △R ₁ and R ₁ for the magnetoresistive element MR 1, the output voltage eo appearing at the output terminal 2 (with respect to ground) is voltage) is as follows. Note that ΔB, ΔR ₂ and ΔR ₁ are the amount of change in the magnetic flux density B and the amount of change in the resistance values R ₂ and R ₁ , respectively. When the object 3 is in position 3 and is unrelated to any magnetoresistive element, the output voltage eo
is expressed by the following formula (1). eo=Ed=R ₂ /R ₁ +R ₂ ·E (1) where E is the power supply voltage (voltage to ground) given to the magnetic detector 4. Also, Ed in equation (1) is called the output voltage DC component. When the subject 3 is at position 3a, that is, when its magnetic body is in front of the magnetoresistive element _MR2 , the output voltage eo is expressed by the following equation (2). eo=Ed+es=R ₂ +△R ₂ /R ₁ +R ₂ +△R ₂・E ≒Ed+R ₁・△R ₂ /(R ₁ +R ₂ ) ²・E …(2) Therefore, from the output voltage eo, the above output Voltage DC component
The signal voltage es excluding Ed is expressed by the following formula (2)-1. es=R ₁ △R ₂ / (R ₁ + R ₂ ) ² E...(2)-1 When the magnetic material of the object 3 comes in front of the magnetoresistive element MR ₁ , the output voltage eo is expressed by the following formula (3). eo=Ed+es=R ₂ /R ₁ +R ₂ +△R ₁・E ≒Ed−R ₂・△R ₁ /(R ₁ +R ₂ ) ²・E…(3) Therefore, as in the previous section, the signal voltage es is the following formula
It is expressed as (3)-1. es= _-R2・△ _R1 /( _R1 + _R2 ) ²・E...(3)-1 Here, it is assumed that the characteristics of the two magnetoresistive elements are equal, and _R1 = _R2 =RM,△ _R1 =△R ₂ =△RM …(4) Then, the output voltage DC component Ed is Ed = 2/1・E …(5) The signal voltage es is expressed as Equations (2)-1, (3)- 1, es=+△RM/4・RM・E or −△RM/4・RM・E (6), and the alternating amplitudes of the signal voltage es become equal.
In other words, if the amplitude (magnitude) of the signal voltage es is ES, then ES = △RM/4・RM・E …(7) Therefore, in this case, the output voltage in equation (2) or (3)
Substitute the results of equations (5), (6), and (7) for eo, and get eo=Ed+es=1/2・E±ES=1/2・E±△RM/4・RM・E …(8) It is expressed as On the other hand, the relationship between the magnetic flux density B applied to the magnetoresistive element and its resistance value RM is expressed by the following equation (9) in such a weak magnetic field. RM≒RMO(1+K・B ² )...(9) Here, RMO: resistance value when magnetic flux density B is 0, K: proportionality constant. Therefore, the resistance value corresponding to the amount of change in magnetic flux density △B
The amount of change in RM △RM is expressed as △RM=2・RMO・K・B・△B...(10), so by substituting the results of equations (9) and (10) into (7), The magnitude of the signal voltage ES is the following formula (11)
become that way. ES=K・B・△B/2(1+K・B ² )・E (11) Therefore, the magnitude ES of the signal voltage output from the magnetic detector 4 is determined by the magnetic It is proportional to the power supply voltage E applied to the detector 4 and the amount of change ΔB in magnetic flux density due to the proximity of the subject 3 to the magnetoresistive element. The amount of change ΔB depends on the material, shape, etc. of the magnetic material contained in the object 3, but in the case of characters printed with magnetic ink, it depends on the sharpness of the print, that is, the surface density of the magnetic material and the magnetic ink. depends on the magnetic permeability of Characters adopted by the American Bankers Association,
MICR (Magnetic Ink Character Recognition)
In the case of commercial characters, because they are intended for mechanical processing, they are printed more clearly than characters used on banknotes, etc., and therefore have better magnetic properties.
The output voltage when detected by a magnetic detector is also large.
On the other hand, in the case of magnetic ink characters used on banknotes, etc., they are not necessarily printed for the purpose of processing by machines, and they are severely damaged during the distribution process, so their magnetic properties are inferior and the signal voltage is low.
It is about half that of MICR characters. However, in any case, the sensitivity to characters is sufficiently high compared to a magnetic head, and the ratio of the detection signal between the character part (signal part) and the part without magnetic ink (noise part), that is, the S/N ratio, is over 14 dB. This value is sufficient for identification. However, patterns other than characters made with magnetic ink do not have a sufficient S/N ratio, resulting in misidentification of counterfeit banknotes and denominations, etc., making it difficult for magnetic sensors in banknote identification devices that require high reliability.
It is the subject of identification with the worst conditions. Now, the drawback of the magnetoresistive element used in this magnetic detector is that it is subject to large temperature changes. This temperature change is calculated by the resistance temperature coefficient of the resistance value RMO in equation (9) above and the semiconductor material that is the material of the magnetoresistive element.
It can be considered separately from the one based on the temperature change of the proportionality constant K, which depends on the mobility of InSb. The former, that is, the resistance temperature coefficient of the resistance value RMO has an extremely large resistance temperature coefficient of about -2%/°C near room temperature, but this is because two magnetoresistive elements MR ₁ with the same characteristics as in the configuration shown in Fig. 2, Temperature compensation can be achieved by connecting MR ₂ in series and extracting the output voltage eo from the connection point (output terminal 2).
That is, in this case, the output voltage eo is expressed by the following formula (12) from formulas (8) and (11), eo=Ed+es=1/2E±ES =1/2・E±K・B・△B /Z2 (1+K・B ² )
・E...(12) From this equation (12), the resistance value RMO has disappeared. On the other hand, the latter can be understood as a temperature change in detection sensitivity. That is, the detection sensitivity σ is defined as the magnitude of the signal voltage per unit change in magnetic flux density and unit power supply voltage, and is expressed by the following equation (13) from the above equation (11). σ=ES/E・△B=K・B/2 (1+KB ₂ ) …(13) The temperature coefficient of this detection sensitivity σ is expressed as dσ/dT・1/σ when T is the absolute temperature (〓). However, this value is also equal to the temperature coefficient d(ES)/dT·1/(ES) of the magnitude ES of the detected voltage. By the way, the temperature coefficient of the detection sensitivity σ is also quite large at about -0.5%/〓 at room temperature (absolute temperature 300〓), and still becomes a factor of variation in the signal voltage. Note that FIG. 3 shows the change in the detection sensitivity σ due to temperature for characters printed with magnetic ink as a ratio to the detection sensitivity at room temperature (25° C.). FIG. 4 shows a conventional banknote identification circuit using such a magnetic detector 4. That is, two magnetoresistive elements MR ₁ (resistance value R ₁ ) in the magnetic detector 4,
A bridge is constituted by a series circuit of MR ₂ (resistance value R ₂ ) and a series circuit of resistors R ₁₁ , R ₁₂ and variable resistor VR ₁ , which are provided in parallel with the series circuit and divided into two groups at the output terminal 20. and the output terminal 2 of the magnetic detector 4
and output terminal 2, which is the intermediate terminal of variable resistor VR ₁ .
0 are connected to the differential amplifier 5 via resistors R ₂₁ and R ₂₂ , respectively. In this bridge, magnetoresistive element MR ₁ and
The resistance values R ₁ and R ₂ of MR ₂ and the resistance R ₁₁ on the opposite side
The values of R ₁₂ are selected so that they are almost equal, but in order to compensate for any remaining unbalance, the voltage between the output terminal 20 and the ground is changed to the output voltage DC component Ed of the above equation (1) at the output terminal 2. By adjusting the variable resistor VR ₁ to be equal to
The signal voltage es at output terminal 2 (output voltage eo
Only the alternating current (AC component) is input to the differential amplifier 55. Further, the variation in the output signal e5 (differential amplifier output signal) of the differential amplifier 5 based on the variation in the sensitivity σ in the above equation (13) is determined by a variable that varies the amplification rate of the differential amplifier 5. It is adjusted by resistor VR ₂ and placed within a predetermined width. Next, 9 is a differentiation circuit that differentiates the differential amplifier output signal e5 and outputs a differentiation circuit output signal e9;
0 is a rectifier circuit that rectifies the differential circuit output signal e9 and outputs a rectifier output signal e10, and 6 is a rectifier circuit that binarizes the rectifier circuit output signal e10 at a certain threshold value.
A binarization circuit 8 outputs a digitized signal eB, and 8 indicates information of the binarized signal eB within a predetermined scanning period of the banknote, for example, the total number of level "1"s, set values 81, 82 to 82 for each of K denominations. A set value setting circuit 7 stores the setting as 8K, compares and discriminates the binary signal eB with the set values 81 to 8K of the set value setting circuit 8, and outputs K corresponding denomination signals 171 to 17K. This is a comparison/discrimination circuit. Also, Fig. 5 shows the magnetic detector 4 and the object 3 (banknote).
A is a plan view, B is a YY sectional view in the plan view A, and FIG.
FIG. 3 is a waveform diagram of each part explaining the operation of the circuit shown in the figure. Next, the operation shown in FIG. 4 will be explained with reference to FIGS. 5 and 6. First, in FIG. 5, the subject 3 is moved in the transport direction X on the guide plate G by a belt (not shown) or the like driven by a motor (not shown), and the magnetic pattern on the subject 3 is moved. P
is the magnetic detector 4 installed in the hole of the guide G plate.
is scanned along the scanning line L by. Also, during this scanning, the front end EF of the subject 3 is detected from the photo sensor PS ₁ , which is also installed in the hole of the guide plate G.
During the scanning period _T1 during which the rear end EB of the subject 3 reaches and passes the front surface, a rectangular wave-shaped scanning section signal ePS is output as shown in FIG. Note that here, the length between the front end EF and the rear end EB is called a scanning section D, and this length is equal to the length of the scanning line L. Now, in FIG. 4, the signal voltage es corresponding to the magnetic pattern P on the scanning line L is amplified by the differential amplifier 5 to become an amplifier output signal e5. There is a large change at the boundary of each magnetic pattern, that is, the boundary (or contour) between the area containing magnetic ink and the area not containing magnetic ink, and the change is small within the area containing magnetic ink or the area not containing magnetic ink. Therefore, in order to capture this feature, the signal is input to the differentiating circuit 9 and differentiated, and a differentiating circuit output signal e9 (FIG. 6) is output. Since the differential circuit output signal e9 is an alternating current that changes between positive and negative as shown in FIG. The rectifier circuit output signal e10 (FIG. 6) is output.
In this case, since half-wave rectification is usually sufficient, a half-wave rectification circuit is used as the rectifier circuit 10. Next, the rectifier circuit output signal e10 is binarized by a constant threshold voltage ET (FIG. 6) in the binarization circuit 6 and 2
A valued signal eB (Fig. 6) is output. The number of levels "High"("1") of the binary signal eB is integrated in the comparison/discrimination circuit 7 for the scanning time T ₁ and therefore the scanning section D, and the integrated value is sent to the set value setting circuit 8. The corresponding denomination signal 171~17K is compared with the setting value 81~8K for each denomination (including counterfeit bill signal)
Either of these will be output. [Problems to be Solved by the Invention] However, in this conventional circuit, temperature changes in the detection sensitivity of the magnetic detector are not compensated. Circuit output signal e1
0 and the binary signal eB change as shown in the dotted line diagram in FIG. , the binarized signal eBa corresponding to this portion disappears, leading to erroneous identification. For this reason, countermeasures such as increasing the tolerance of the set value are taken, but this does not improve the accuracy or reliability of identification, and the identification device remains vulnerable to counterfeit bills and damage. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an apparatus for determining authenticity of banknotes, etc., in which the detection sensitivity of a magnetoresistive element is not affected by temperature changes. [Means for Solving the Problems] According to the present invention, such problems can be solved by: a magnetic detector comprising two magnetically sensitive variable impedance means connected in series and to which a DC voltage is applied; an amplifier for amplifying an output voltage taken out from a connection point of the variable impedance means; a direct current component removing means for removing a direct current component included in the output voltage; a differentiating circuit for differentiating an output signal of the amplifier; a rectifier circuit that rectifies the output signal of the object; a zone pulse generation circuit that divides the scanning section of the surface of the object into a plurality of zones and outputs a zone pulse corresponding to each zone; and an output pulse of the zone pulse generation circuit. an integrating means for outputting an integral value for each zone of the output signal of the rectifier circuit in response to the received signal; and calculating a ratio of the integral value between predetermined zones;
a ratio comparison/determination means for comparing the ratio with reference setting values of upper and lower limits for setting the permissible range and outputting an identification signal in order to identify whether or not the ratio is within a permissible range; and the integrating means. an absolute value for outputting a determination signal by comparing the integral value of the integrating means with reference set values of upper and lower limits for setting the predetermined range in order to determine whether the integral value of is within a predetermined range; The problem is solved by providing a discriminating means and performing a logical operation on the discriminating signal output from the ratio comparison discriminating means and the discriminating signal output from the absolute value discriminating means. [Operation] In the present invention, a magnetic pattern on the surface of an object to be examined, such as a banknote, is scanned by a magnetic detector, and a signal corresponding to the magnetic pattern is amplified by an amplifier. The output signal of the amplifier varies significantly at the boundaries of individual magnetic patterns (i.e. between areas with and without magnetic ink), while within areas with and without magnetic ink. Since the change within is small, it is differentiated using a differentiator circuit to capture this feature. Since this differential signal is an alternating current that changes between positive and negative, it is rectified by a rectifier circuit in order to prevent the integral values for extracting magnetic pattern information from canceling each other out. In the present invention, the scanning section of the surface of the subject is divided into a plurality of zones, and a zone pulse corresponding to each zone is output from a zone pulse generation circuit. The integrating means receives the zone pulse output from the zone pulse generating circuit and integrates the output signal of the rectifier circuit for each zone. Therefore, the integrating means outputs individual integrated values (individual zone data) for each zone. On the other hand, the individual zone data output from the integrating means is given to the ratio comparison and discrimination means,
The ratio of individual zone data between adjacent zones is calculated. These ratios are compared with, for example, standard setting values of upper and lower allowable limits for each denomination and each scanning mode in the ratio comparison/determination means. The ratio comparison and determination means outputs an identification signal indicating that the ratio between the individual zone data is within the permissible range. On the other hand, in order to remove individual zone data that is too large or too small, the individual zone data outputted from the integrating means is determined by the absolute value discriminating means, for example, based on the standards of the upper and lower limits that are allowable for each denomination and each scanning mode. Compare with set value. The absolute value determining means outputs an absolute value determining signal indicating that the individual zone data is within a predetermined range. Finally, a logical operation is performed between the identification signal output from the ratio comparison and discrimination means and the absolute value discrimination signal output from the absolute value discrimination means, and the denomination, for example, is determined based on this logical operation signal. At this time, in the present invention, even if the detection sensitivity of the magnetic detector is affected by temperature changes, its output voltage, and therefore the output voltage of the rectifier circuit, change, and as a result, the zone data changes, the ratio comparison The determining means determines the ratio between the individual zone data. This ratio is not affected by temperature changes, so
As a result, the logical operation signal formed by the logical operation of the absolute value discrimination signal and the identification signal is determined by the influence of temperature changes on the detection sensitivity of the magnetically sensitive variable impedance means (for example, a magnetoresistive element) constituting the magnetic detector. The signal will not be received. [Embodiments of the Invention] The present invention will be explained below based on FIG. 5 and FIGS. 7 to 9. FIG. 7 shows an embodiment of the circuit configuration of the present invention corresponding to FIG. 4. To explain the differences from FIG. The rectifier circuit output signal e10 is integrated for each zone, which will be described later in FIG . An integrating circuit 12 outputs the absolute value of the N individual integral values in the integral value S to each corresponding reference setting value set in the absolute value setting circuit 13, that is, each The scanning mode differs depending on the denomination and each scanning mode (i.e., the front, back, front, back, etc. orientation of the subject 3 during scanning, and this determines the number of detection patterns that one denomination has). ) is compared with the respective allowable upper and lower limits of each of the N individual integral values allowed in each detection pattern, and outputs absolute value discrimination signals e121 to e12K corresponding to each denomination and each scanning mode. A value comparison circuit 14 sequentially calculates the ratio of the individual differential and integral values between adjacent zones in the integral value S , and sends the ratio for one detection pattern ((N-1) pieces) to the ratio setting circuit 15. The value of each gold is compared with the corresponding standard setting values set, that is, the upper and lower limits of each of the (N-1) ratios allowed in each detection pattern for each denomination and each scanning mode. seed,
Identification signals e141 to e1 corresponding to each scanning mode
This is a ratio comparison/discrimination circuit that outputs 4K. Further, the gates G1 to GK are the absolute value discrimination signals e121 to
This is a NAND gate that takes the AND conditions of e12K and identification signals e141 to e14K and outputs denomination signals 171 to 17K as comprehensive identification signals. In the present invention, as shown in FIG. 5, the scanning section D of the subject 3 is equally divided into N zones _Z1 to Zn, and when the arrival of the subject 3 is detected by the photosensor _PS1 , the As an amount proportional to the amount of movement, for example, a pulse proportional to the rotation speed of the aforementioned motor of the drive source for the subject 3, or when a synchronous motor is used as the motor, a power supply frequency, etc. is counted via the zone pulse generation circuit 16. Then, a zone pulse ZP (ZP ₁ to ZPN) (FIG. 8) corresponding to each zone is output from the zone pulse generating circuit 16. As a result, even if there is a fluctuation in the scanning speed of the object 3, the zone pulse that divides the object 3 into N equal parts is applied regardless of this.
Gain ZP. The zone pulse is obtained by dividing the scanning period _T1 in FIG. 6 into N equal parts. Further, FIG. 8 is a waveform diagram of each part explaining the circuit operation of FIG. 7, and corresponds to FIG. 6 in the prior art.
Next, the operation shown in FIG. 7 will be explained with reference to FIG. In FIG. 7, the process up to the output of the rectifier circuit output signal e10 is the same as in FIG. 4. Next, the rectifier circuit output signal e10 is sent to the integrator circuit 10 in order to aggregate all the magnetic pattern information in each zone to increase accuracy and prevent the influence of local variations.
1, the integrating circuit 11 is reset at the start point of each zone in synchronization with the zone pulses ZP ₁ to ZPN, and then integrated within the zone. N individual zone data S ₁ to SN (8th
) is output (the individual zone data S ₁ to SN
A collection of one detected pattern is the zone data S
). Each of the individual zone data S ₁ to SN is set as a standard as their permissible upper and lower limits for each denomination and each scanning mode, as described above, in order to remove excessive or insufficient individual zone data. An absolute value that is compared with the reference setting value of the absolute value setting circuit 13 that outputs the value and in the absolute value comparison circuit 12, and has a value of "High" for any of the denomination-specific scanning modes, both of which are within the allowable range. Discrimination signals e121 to e12K are output from the absolute value comparison circuit 12.
Output to NAND gates G ₁ to GK. On the other hand, the ratio comparison and discrimination circuit 14 receives the individual zone data S ₁ for the one detection pattern output from the integration circuit 11.
Input the SNs sequentially and calculate the (N-1) ratios of individual zone data between adjacent zones S ₁ /S ₂ , S ₂ /S ₃ , ~S
(N-1)/SN is calculated sequentially, and these ratios and each denomination, which is output from the ratio setting circuit 15, are
By sequentially comparing each standard setting value as the allowable upper and lower limit values for each scanning mode, identification with "High" value for some of the denomination-specific scanning modes that all fall within the allowable range. Signal e141~
Output e14K to NAND gates G ₁ to GK. In this way, the gold output from the NAND gates _G1 to GK with a "Low" value is determined by the AND conditions of the absolute value discrimination signals e121 to e12K and the identification signals e141 to e14K corresponding to the denomination-specific scanning mode. The denomination is determined by one of the denomination signals 171 to 17K. Now, in the above explanation, the ratio comparison and discrimination circuit 14
In this method, the ratio of individual zone data between adjacent zones was calculated, but in this case, the calculation time is small and the amount of information obtained is also rich, but for the purpose of eliminating fluctuations in detection sensitivity, There is no need to limit the number of zones between zones, and it is also possible to take the ratio of each individual zone data to specific individual zone data, or to take the ratio of individual zone data based on any predetermined combination. Furthermore, when the zones Z ₁ to ZN are divided into equal parts as shown in FIG. 5, the circuit can be simplified, but instead of this, even if they are divided into a plurality of predetermined arbitrary widths, covered by the invention. Further, FIG. 9 is a partial circuit diagram showing another embodiment of the present invention, and the omitted parts are the same as those in FIG. 7. In other words, in Fig. 7, in order to extract the AC component signal voltage es from the output voltage eo, a bridge is used to remove the output voltage DC component Ed. Detection of magnetic patterns becomes inferior, but the 9th
Either insert a capacitor _C1 in series with the output terminal 2 of the magnetic detector 4 as shown in Figure A, or there is a risk that the output of the differential amplifier 5, including the amplification of the output voltage DC component Ed, will be saturated. If there is no such capacitor
By short-circuiting C ₁ and inserting a replacement capacitor C ₂ in series with the output terminal of the differential amplifier 5 as shown in the dotted line diagram, the output voltage DC component Ed can be cut. It's okay. Furthermore, the operation is equivalent even if the connection between the resistor R ₁₁ and the power source E in FIG. 7 is separated, and a variable voltage is generated at the output terminal 20 from another DC power source to bias the differential amplifier 5. be. Similarly, as shown in FIG. 9B, using a DC power source E ₁ with a polarity opposite to that of the DC power source E and a variable resistor VR ₃ ,
The input terminal 5a of the output voltage eo to the differential amplifier 5 may be biased by applying a current of opposite polarity. In this case, for example, if the resistance values of the resistors R ₂₁ and _{R 22 are} equal, The output voltage DC component -Ed of opposite polarity may be given as the ground voltage of the input side terminal _R22a . In this way, various conventional biasing means can be used for the differential amplifier (arithmetic amplifier). In the above description, the magnetic detector 4 is fixed and the subject 3 is moved, but instead of this, a method may be used in which the subject 3 is fixed and the magnetic detector 4 is moved. In addition, two magnetoresistive elements in the magnetic detector 4
A method may be adopted in which only one of MR ₁ and MR ₂ is used for detecting the magnetic pattern, and the other is used only for temperature compensation (compensation for fluctuations in resistance value RMO in equation (9) above). Moreover, the above two magnetoresistive elements MR ₁ and MR ₂ are
Other magnetically sensitive variable impedance elements instead of this,
For example, the present invention can be applied to something like a magnetic diode. Effects of the Invention According to the present invention, even if the detection sensitivity of the magnetic detector is affected by temperature changes and its output voltage, and therefore the output voltage of the rectifier circuit, changes, and as a result, the zone data changes, A ratio comparison/discrimination circuit calculates the ratio of individual zone data. Since this ratio is not affected by temperature changes, it is possible to identify the authenticity of banknotes without being affected by temperature changes in the detection sensitivity of the magnetoresistive element.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of the relationship between the distance to the subject (spacing) and the detection sensitivity (relative value) in the magnetic head and magnetic detector, and Figure 2 is the basic configuration of the detection section in the magnetic detector. FIG. 3 is a diagram showing an example of temperature change in detection sensitivity as a ratio, FIG. 4 is a configuration diagram of a conventional banknote identification circuit, and FIG. 5 is a diagram showing an example of arrangement of banknotes and magnetic detectors. 6 is a signal waveform diagram of each part in FIG. 4, FIG. 7 is a diagram showing an example of the configuration of the banknote identification circuit in the present invention, and FIG.
A signal waveform diagram of each part in the figure, and FIG. 9 is a partial circuit diagram showing another example of the configuration of the banknote identification circuit according to the present invention. Explanation of symbols, 1... Magnet, 2... Output terminal, 3...
...Subject, 4...Magnetic detector, MR ₁ , MR ₂ ...
Magnetoresistive element, E, E ₁ ... DC power supply, R ₁₁ , R ₁₂ ,
R ₂₁ , R ₂₂ ... Resistor, VR ₁ , VR ₃ ... Variable resistor,
C ₁ , C ₂ ... Capacitor, 5 ... Differential amplifier, 9
... Differentiation circuit, 10 ... Rectification circuit, 11 ... Integration circuit, 12 ... Absolute value comparison circuit, 13 ... Absolute value setting circuit, 14 ... Ratio comparison and discrimination circuit, 15 ...
Ratio setting circuit, 16...Zone pulse generation circuit,
PS ₁ ...Photo sensor, ZP (ZP ₁ to ZPN)...Zone pulse, _Z1 to ZN...Zone, S ...Zone data (integral value), _S1 to SN...Individual zone data (individual integrated value) , G ₁ ~ GK……NAND gate.

Claims (1)

[Claims] 1. By applying a magnetic field, the magnitude of the magnetic field density generated on the surface of an object to be examined, such as a banknote, is scanned using a magnetically sensitive variable impedance means, and the object to be examined is identified from the magnetic pattern obtained at that time. A device for identifying authenticity of banknotes, etc., comprising: a magnetic detector comprising two magnetically sensitive variable impedance means connected in series and to which a DC voltage is applied; and an output taken out from a connection point of the two magnetically sensitive variable impedance means. an amplifier that amplifies a voltage; a DC component removal means that removes a DC component included in the output voltage; a differentiator circuit that differentiates the output signal of the amplifier; a rectifier circuit that rectifies the output signal of the differentiator circuit; a zone pulse generation circuit that divides the scanning section of the surface of the object into a plurality of zones and outputs zone pulses corresponding to each zone; and a zone pulse generation circuit that outputs zone pulses corresponding to each zone; an integrating means for outputting an integral value for each zone; and calculating a ratio of the integral value between predetermined zones;
a ratio comparison/determination means for comparing the ratio with reference setting values of upper and lower limits for setting the permissible range and outputting an identification signal in order to identify whether or not the ratio is within a permissible range; and the integrating means. an absolute value for outputting a determination signal by comparing the integral value of the integrating means with reference set values of upper and lower limits for setting the predetermined range in order to determine whether the integral value of is within a predetermined range; A device for determining authenticity of banknotes, etc., comprising: a determining device; the device performs a logical operation on the identification signal output from the ratio comparison determining device and the determining signal output from the absolute value determining device and outputs the same. .