WO2015109894A1

WO2015109894A1 - Method and device for testing paper money thickness via electrical eddy current

Info

Publication number: WO2015109894A1
Application number: PCT/CN2014/093255
Authority: WO
Inventors: 黎明
Original assignee: 广州中智融通金融科技有限公司
Priority date: 2014-01-22
Filing date: 2014-12-08
Publication date: 2015-07-30
Also published as: CN103743333B; CN103743333A

Abstract

A method for testing paper money thickness via electrical eddy current, the method comprising: inserting paper money (306) between a reference shaft (301) and a floating wheel (302), the position of the reference shaft (301) being fixed; a metal sheet (303) fixed to the floating wheel (302) has a displacement in a vertical direction; a PCB circuit (305) detects, via an electrical eddy current coil (304) on the PCB circuit (305), the voltage variation caused by the displacement; and the PCB circuit (305) calculates and obtains the thickness of the paper money (306) according to the voltage variation. Also provided is a device for testing the paper money thickness via the electrical eddy current. The method and the device improve the stability and accuracy of paper money thickness measurement.

Description

Method and device for detecting eddy current thickness by eddy current

The present application claims priority to Chinese Patent Application No. 201410030052.3, entitled "Method and Apparatus for Detecting Thickness of Banknotes by Eddy Currents" on January 22, 2014, the entire contents of which are incorporated herein by reference. In the application.

Technical field

The present invention relates to the field of eddy currents, and more particularly to a method and apparatus for eddy current detection of banknote thickness.

Background technique

In the ATM machine and the banknote sorting machine, the thickness detection of the banknote is an essential function, and the thickness of the banknote can be used to identify the tape and the folding tape attached to the banknote, thereby eliminating the unqualified banknote. Since the tape may be stuck anywhere on the banknote, the thickness detection must cover the entire banknote range. It is necessary to provide a closely arranged multi-way thickness sensor. Each thickness sensor has the same structure and the same detection principle. The signal detected by the multi-channel independent thickness sensor is spliced into the thickness characteristics of the entire banknote to identify whether the banknote is abnormal.

At present, the banknote test can only measure the thickness of about 0.03mm, which is equivalent to the thickness after attaching a layer of tape on the banknote, which seriously affects the accuracy of the banknote thickness detection.

Summary of the invention

Embodiments of the present invention provide a method and apparatus for detecting the thickness of a banknote by eddy current, which can improve the stability and accuracy of the thickness measurement of the banknote.

A method for detecting the thickness of a banknote by an eddy current, comprising:

Inserting a banknote between a reference axis and a floating wheel, the position of the reference axis being fixed;

Displacement of the metal piece fixed to the floating wheel in a vertical direction;

The PCB circuit detects the amount of voltage change caused by the displacement through an eddy current coil on the PCB circuit;

The PCB circuit calculates the thickness of the banknote based on the amount of voltage change.

Optionally, before the inserting the banknote between the reference axis and the floating wheel, the method further includes:

Let the reference axis and the floating wheel idle;

The PCB circuit passes through the distance between the eddy current coil and the metal piece on the floating wheel To zero voltage.

Optionally, detecting, by the eddy current coil on the PCB circuit, the amount of voltage change caused by the displacement, specifically includes:

The PCB circuit obtains a current voltage by a distance between the eddy current coil and a metal piece on the floating wheel;

The PCB circuit obtains a voltage change amount according to the current voltage and the zero-value voltage.

Optionally, calculating, by the PCB circuit, the thickness of the banknote according to the amount of voltage change specifically includes:

The PCB circuit calculates the thickness of the banknote according to the voltage change amount and the K value, and the K value is a voltage change value corresponding to the thickness of the 100 um banknote.

The K value corresponding to the voltage range of the plurality of current voltages is measured by a nonlinear correction method to obtain a K value mapping table.

Optionally, before the PCB circuit calculates the thickness of the banknote according to the voltage change amount and the K value, the method further includes:

The PCB circuit queries the K value mapping table according to the current voltage to obtain a K value.

A device for detecting the thickness of a banknote by an eddy current, comprising:

a reference shaft fixed to the device for pushing the banknote with the floating wheel when the banknote is inserted;

The floating wheel, at least two floating wheels are mounted on the device for pushing the banknote with the reference axis when the banknote is inserted, and correspondingly shifting in a vertical direction;

a metal piece fixed on the corresponding floating wheel, and corresponding displacement in the vertical direction is generated as the displacement of the floating wheel is used to generate an eddy current effect with the corresponding eddy current coil;

The eddy current coil, at least two eddy current coils are mounted on a PCB circuit board for generating an eddy current effect with a corresponding metal piece;

A PCB circuit board is fixed on the device for detecting a voltage variation caused by a corresponding displacement by an eddy current coil on the PCB circuit, and calculating a thickness of the banknote according to the voltage variation amount.

Optionally, it includes:

When the reference axis and the floating wheel are idling, the PCB circuit board passes through the eddy current coil The distance from the metal piece on the floating wheel is zero voltage;

When the banknote is inserted between the reference axis and the floating wheel, the PCB circuit board obtains the current voltage through the distance between the eddy current coil and the metal piece on the floating wheel;

The PCB circuit board obtains a voltage change amount according to the current voltage and the zero-value voltage.

Optionally, the PCB circuit board specifically includes:

a crystal oscillator using an active crystal oscillator for providing a stable frequency to the eddy current coil as an excitation source for inputting an oscillating signal to the CPLD;

The CPLD is configured to receive the oscillating signal, and divide the oscillating signal to output signals of two different frequencies to a driving circuit;

The driving circuit receives signals of two different frequencies of the CPLD frequency-divided output, and drives the eddy current coil to operate according to the signal;

a detection circuit for detecting an envelope of the high frequency signal output by the eddy current coil and obtaining an analog signal;

a comparison amplifier for amplifying an output signal obtained by the detection circuit to increase the intensity of the analog signal;

An A/D converter receives the analog signal from the comparison amplifier for converting the analog signal into a digital signal, and transmitting the digital signal to a CPU;

The CPU is configured to analyze and process the digital signal, calculate the zero-value voltage, the current voltage, and the voltage change amount, and calculate the thickness of the banknote according to the voltage change amount.

Optionally, the PCB circuit board further includes:

The reference voltage module is connected to the CPU through an IIC interface, such that the CPU adjusts an output of the reference voltage through the IIC interface for providing a reference voltage for the comparison amplifier.

It can be seen from the above technical solutions that the embodiments of the present invention have the following advantages:

In the embodiment of the present invention, the banknote is inserted between the reference shaft and the floating wheel, the position of the reference shaft is fixed, and the metal piece fixed to the floating wheel is displaced in the vertical direction, and the PCB circuit passes through the PCB. The eddy current coil on the circuit detects the amount of voltage change caused by the displacement, and the PCB circuit calculates the thickness of the banknote based on the amount of voltage change. In the embodiment of the present invention, the PCB circuit calculates the thickness of the banknote according to the eddy current effect measurement voltage variation, and the voltage variation can be accurately and stably measured by the eddy current effect, and therefore, according to the voltage variation amount, The thickness of the banknote is accurate and stable, which improves the accuracy of the banknote thickness detection.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work.

1 is a flow chart of an embodiment of a method for detecting the thickness of a banknote by an eddy current flow according to an embodiment of the present invention;

2 is a flow chart showing another embodiment of a method for detecting the thickness of a banknote by an eddy current flow according to an embodiment of the present invention;

3 is a schematic structural view of an embodiment of an apparatus for detecting the thickness of a banknote by an eddy current flow according to an embodiment of the present invention;

4 is a schematic structural view of an embodiment of a PCB circuit board in an apparatus for detecting the thickness of a banknote by an eddy current flow according to an embodiment of the present invention;

Figure 5 is a plan view of Figure 3;

6 is a schematic diagram of input and output voltages of a comparison amplifier in an apparatus for detecting the thickness of a banknote by an eddy current flow according to an embodiment of the present invention;

Figure 7 is a graph showing the relationship between the output Vs of the detector circuit and the distance D from the metal piece to the eddy current coil in the embodiment of the present invention.

detailed description

Embodiments of the present invention provide a method and apparatus for eddy current detection of banknote thickness for improving the stability and accuracy of thickness measurement of banknotes.

In order to make the object, the features and the advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only a part of the embodiments of the invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

Referring to FIG. 1, an embodiment of a method for detecting the thickness of a banknote by eddy current in an embodiment of the present invention include:

101. Insert a banknote between the reference axis and the floating wheel;

When the eddy current is used to detect the thickness of the banknote, the banknote is first inserted between the reference axis and the floating wheel, and the position of the reference axis is fixed.

102. The metal piece fixed to the floating wheel is displaced in a vertical direction;

As the banknote is inserted between the reference axis and the floating wheel, the floating wheel is displaced in the vertical direction, and the metal piece fixed to the floating wheel is also displaced in the vertical direction.

103. The PCB circuit detects a voltage variation caused by the displacement by using an eddy current coil on the PCB circuit;

After the metal piece is displaced in the vertical direction, the PCB circuit detects the amount of voltage change caused by the displacement through the eddy current coil on the PCB circuit.

104. The PCB circuit calculates the thickness of the banknote according to the voltage change amount.

After the PCB circuit obtains the voltage change amount, the thickness of the banknote is calculated according to the voltage change amount.

In this embodiment, the banknote is inserted between the reference shaft and the floating wheel, the position of the reference shaft is fixed, the metal piece fixed to the floating wheel is displaced in the vertical direction, and the PCB circuit passes the electricity on the PCB circuit. The eddy current coil detects the amount of voltage change caused by the displacement, and the PCB circuit calculates the thickness of the banknote based on the voltage change amount. In this embodiment, the PCB circuit calculates the thickness of the banknote according to the eddy current effect measurement voltage, and since the voltage variation can be accurately and stably measured by the eddy current effect, the banknote obtained according to the voltage variation amount is The thickness is accurate and stable, which improves the accuracy of banknote thickness detection.

For ease of understanding, the method for detecting the thickness of the banknote by the eddy current in the embodiment of the present invention is described in detail below. Referring to FIG. 2, another embodiment of the method for detecting the thickness of the banknote by the eddy current in the embodiment of the present invention includes:

201, let the reference axis and the floating wheel idle;

Before detecting the thickness of the banknote, the reference axis and the floating wheel need to be idling, that is, the reference shaft and the floating wheel are rotated without inserting the banknote.

202. The PCB circuit obtains a zero-value voltage by a distance between the eddy current coil and a metal piece on the floating wheel;

When the reference shaft and the floating wheel are idling, since the metal piece is fixedly mounted on the floating wheel, The metal piece has a fixed distance from the eddy current coil, and the PCB circuit can obtain a zero voltage through a fixed distance between the eddy current coil and the metal piece on the floating wheel. It can be understood that the zero-value voltage is also fixed because there is a fixed distance between the eddy current coil and the metal piece on the floating wheel during idling.

203. Insert the banknote between the reference axis and the floating wheel;

204. The metal piece fixed to the floating wheel is displaced in a vertical direction;

205. The PCB circuit obtains a current voltage by a distance between the eddy current coil and a metal piece on the floating wheel.

Since the metal piece is displaced in the vertical direction, the distance between the eddy current coil and the metal piece on the floating wheel is changed. At this time, the PCB circuit can pass through the eddy current coil and the floating wheel. The distance between the metal sheets gives the current voltage. It will be appreciated that since the displacement of the metal sheet is due to the insertion of the banknote, the value of the displacement may be equal to the thickness of the banknote.

206. The PCB circuit obtains a voltage change amount according to the current voltage and the zero value voltage;

After obtaining the current voltage and the zero-value voltage, the PCB circuit can obtain a voltage change amount according to the current voltage and the zero-value voltage. It can be known that the voltage variation can be an absolute value of the difference between the current voltage and the zero voltage.

207. The PCB circuit calculates the thickness of the banknote according to the voltage change amount and the K value.

After the PCB circuit obtains the voltage variation, the PCB circuit can calculate the thickness of the banknote based on the voltage variation and the K value. It can be understood that the K value is a voltage change value corresponding to the thickness of the 100 um banknote, and the K value can be pre-stored in the PCB circuit.

It should be noted that the K value can be obtained by inserting the standard banknote, and the PCB circuit obtains the corresponding voltage variation V0. Since the thickness of the standard banknote is known, the thickness of the standard banknote is assumed to be D0, so that K=V0/ is obtained. D0*100um, the obtained K value can be pre-stored in the PCB circuit.

It should be noted that due to the influence of equipment vibration and mechanical wear in actual use, The distance between the metal piece and the eddy current coil is slightly changed, and the linear relationship between the distance and the voltage change amount is broken, that is, the K value may be changed, so in order to compensate for the change of the K value, The K value corresponding to the voltage range of the current voltage is measured by using a nonlinear correction method, and a K value mapping table is obtained. Before the PCB circuit calculates the thickness of the banknote according to the voltage variation amount and the K value, the PCB circuit according to the The current voltage queries the K value mapping table to obtain a K value. It can be understood that the K value obtained by querying the PCB circuit from the K value mapping table has been nonlinearly corrected, and the PCB circuit can calculate the thickness of the banknote according to the linear relationship between the K value and the voltage variation.

In this embodiment, the reference shaft and the floating wheel are idling, and the PCB circuit obtains a zero voltage through the distance between the eddy current coil and the metal piece on the floating wheel, and inserts the banknote between the reference axis and the floating wheel. The position of the reference shaft is fixed, the metal piece fixed to the floating wheel is displaced in the vertical direction, and the PCB circuit obtains the current voltage through the distance between the eddy current coil and the metal piece on the floating wheel, and the PCB circuit is based on The current voltage and the zero-value voltage obtain a voltage change amount, and the PCB circuit calculates the thickness of the banknote according to the voltage change amount and the K value. In this embodiment, the PCB circuit calculates the thickness of the banknote according to the eddy current effect measurement voltage, and since the voltage variation can be accurately and stably measured by the eddy current effect, the banknote obtained according to the voltage variation amount is The thickness is accurate and stable, which improves the accuracy of banknote thickness detection. Further, since the K value can be correspondingly compensated by the nonlinear correction method, the PCB circuit can calculate the thickness of the banknote according to the voltage variation amount and the K value without being affected by equipment vibration and mechanical wear, further ensuring The stability and accuracy of banknote thickness detection.

For ease of understanding, according to the embodiment described in FIG. 2, the method for detecting the thickness of the banknote by the eddy current flow in the embodiment of the present invention is described below in a practical application scenario:

Before the operator detects the thickness of the banknote, the reference shaft and the floating wheel are idling, and the PCB circuit obtains a zero-value voltage through the distance between the eddy current coil and the metal piece on the floating wheel, assuming that the zero-value voltage is V1.

The operator inserts the banknote between the reference axis and the floating wheel. As the banknote is inserted, the floating wheel is displaced in the vertical direction, and the metal piece fixed on the floating wheel is also displaced in the vertical direction. The circuit obtains the current voltage by the distance between the eddy current coil and the metal piece on the floating wheel, assuming that the current voltage is V2.

Then the PCB circuit calculates the voltage variation amount V3=|V2-V1|, assuming that it is obtained in this embodiment. V3 = 600 mV.

The PCB circuit obtains the K value from the memory. Assuming that the K value is 500 mV, the banknote thickness D1 = V3 / K * 100 = 600 / 500 * 100 = 120 um.

It should be noted that, assuming that the K value is nonlinearly corrected, the PCB circuit queries the K value K1 corresponding to the current voltage V2 from the K value map of the memory.

The method for detecting the thickness of the banknote by the eddy current is described above. The following describes the device for detecting the thickness of the banknote by the eddy current. Referring to FIG. 3 to FIG. 5, an embodiment of the device for detecting the thickness of the banknote by the eddy current in the embodiment of the present invention includes:

a reference shaft 301, fixed to the device for pushing the banknote 306 with the floating wheel 302 when the banknote 306 is inserted;

The floating wheel 302, at least two floating wheels 302 are mounted on the device for pushing the banknote 306 with the reference shaft 301 when the banknote 306 is inserted, and correspondingly displaced in the vertical direction;

The metal piece 303 is fixed on the corresponding floating wheel 302, and generates a corresponding vertical displacement as the displacement of the floating wheel 302 is generated for generating an eddy current effect with the corresponding eddy current coil 304;

The eddy current coil 304, at least two eddy current coils 304 are mounted on the PCB circuit board 305 for generating an eddy current effect with the corresponding metal piece 303;

The PCB circuit board 305 is fixed to the device for detecting the amount of voltage change caused by the corresponding displacement through the eddy current coil 304 on the PCB circuit board 305, and calculating the thickness of the banknote 306 based on the voltage change amount.

It should be noted that the floating wheel 302 is fixed to the device by the floating wheel shaft 307.

It should be noted that when the reference shaft 301 and the floating wheel 302 are idling, the PCB circuit board 305 obtains a zero voltage through the distance between the eddy current coil 304 and the metal piece 303 on the floating wheel 302; when the banknote 306 Inserted between the reference axis 301 and the floating wheel 302, the PCB circuit board 305 obtains the current voltage through the distance between the eddy current coil 304 and the metal piece 303 on the floating wheel 302; the PCB circuit board 305 according to the current voltage and the zero The value voltage gives a voltage change amount.

Referring to FIG. 4, the PCB circuit board 305 in this embodiment specifically includes:

The crystal oscillator 401 adopts an active crystal oscillator for providing a stable frequency to the eddy current coil 304 as an excitation source, and inputs an oscillation signal for the CPLD 402;

The CPLD 402 is configured to receive the oscillating signal, and divide the oscillating signal to output signals of two different frequencies to the driving circuit 403;

The driving circuit 403 receives signals of two different frequencies output by the CPLD 402, and drives the eddy current coil 304 to operate according to the signal;

The detection circuit 404 is configured to detect an envelope of the high frequency signal output by the eddy current coil 304 and obtain an analog signal;

The comparison amplifier 405 is configured to amplify and output the analog signal obtained by the detection circuit 404 to increase the intensity of the analog signal;

The A/D converter 406 receives the analog signal from the comparison amplifier 405 for converting the analog signal into a digital signal, and sends the digital signal to the CPU 407;

The CPU 407 is configured to analyze and process the digital signal, calculate the zero-value voltage, the current voltage, and the voltage change amount, and calculate the thickness of the banknote 306 according to the voltage change amount.

In this embodiment, the PCB circuit board 305 further includes:

The reference voltage module 408 is connected to the CPU 407 through an IIC interface such that the CPU 407 adjusts the output of the reference voltage through the IIC interface for providing a reference voltage to the comparison amplifier 405.

It should be noted that the oscillating signal generated by the crystal oscillator 401 is input to the CPLD 402, and after being divided by the CPLD 402, the two signals of different frequencies can be output to the 12-way eddy current coil 304 via the driving circuit 403, respectively. A1 to A6, B1 to B6, wherein A1 to A6 and B1 to B6 are alternately arranged on the PCB circuit board 305 to prevent mutual interference.

The following is a detailed description of the non-linear correction of the K value in the embodiment of the present invention. Referring to FIG. 6 and FIG. 7 , an embodiment of the method for nonlinearly correcting the K value in the embodiment of the present invention specifically includes:

First, the relationship between the voltage Vs output from the detector circuit and the distance D from the metal piece to the eddy current coil is obtained by measurement. It is assumed that the adjustment range of the reference voltage is Vbmin to Vbmax, the variation range of Vo is Vomin to Vomax, and Vo=(Vs-Vb)*G, G is the amplification factor of the comparison amplifier 405, and D is adjusted so that Vs is at Vbmin+Vomax/ Change from 2/G to Vbmax+Vomax/2/G to get the relationship between Vs and D. The relationship curve is as follows:

Before the actual measurement, the PCB circuit board obtains the corresponding voltage variation V ₀₁ by inserting the standard banknote. Since the thickness of the standard banknote is known, the thickness of the standard banknote is assumed to be D ₀₁ , so K=V ₀₁ / D ₀₁ *100um, that is, the K value Kw of the current working point is obtained. Then, according to the current reference voltage Vb and the value of the comparative amplified output Vo, the CPU can calculate the current Vs value Vsw=Vo/G+Vb, and the CPU calculates the slope Bw of the Vsw point by looking up the internally stored relationship curve, assuming that Vsw is at Between Vs1 and Vs2, then Bw = (Vs2-Vs1) / (D2-D1).

In the actual measurement, the current Vs value Vsv can also be obtained from the reference voltage Vb and the value of the comparative amplified output Vo. The lookup table calculates the slope Bv of the Vsv point, then the current K value Kv = Bv * Kw / Bw. That is, the nonlinear correction of the K value is achieved.

The method for non-linear correction of the K value in this embodiment is one of the methods for correcting or compensating the K value, which is not limited herein.

A person skilled in the art can clearly understand that for the convenience and brevity of the description, the specific working process of the system, the device and the unit described above can refer to the corresponding process in the foregoing method embodiment, and details are not described herein again.

In the several embodiments provided by the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the device embodiments described above are merely illustrative. For example, the division of the unit is only a logical function division. In actual implementation, there may be another division manner, for example, multiple units or components may be combined or Can be integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interface, device or unit, and may be in an electrical, mechanical or other form.

The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

The integrated unit is implemented in the form of a software functional unit and sold as a separate product When sold or used, it can be stored on a computer readable storage medium. Based on such understanding, the technical solution of the present invention, which is essential or contributes to the prior art, or all or part of the technical solution, may be embodied in the form of a software product stored in a storage medium. A number of instructions are included to cause a computer device (which may be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like. .

The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to be limiting; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that The technical solutions described in the embodiments are modified, or the equivalents of the technical features are replaced by the equivalents of the technical solutions of the embodiments of the present invention.

Claims

A method for detecting the thickness of a banknote by an eddy current, comprising:

Inserting a banknote between a reference axis and a floating wheel, the position of the reference axis being fixed;

Displacement of the metal piece fixed to the floating wheel in a vertical direction;

The PCB circuit detects the amount of voltage change caused by the displacement through an eddy current coil on the PCB circuit;

The PCB circuit calculates the thickness of the banknote based on the amount of voltage change.
The method of claim 1 wherein said inserting said banknote between said reference axis and said floating wheel further comprises:

Let the reference axis and the floating wheel idle;

The PCB circuit obtains a zero voltage by the distance between the eddy current coil and the metal piece on the floating wheel.
The method according to claim 2, wherein the detecting, by the eddy current coil on the PCB circuit, the amount of voltage change caused by the displacement comprises:

The PCB circuit obtains a current voltage by a distance between the eddy current coil and a metal piece on the floating wheel;

The PCB circuit obtains a voltage change amount according to the current voltage and the zero-value voltage.
The method according to claim 3, wherein the calculating, by the PCB circuit, the thickness of the banknote according to the amount of voltage change comprises:

The PCB circuit calculates the thickness of the banknote according to the voltage change amount and the K value, and the K value is a voltage change value corresponding to the thickness of the 100 um banknote.
The method of claim 4, wherein the inserting the banknote between the reference axis and the floating wheel further comprises:

The K value corresponding to the voltage range of the plurality of current voltages is measured by a nonlinear correction method to obtain a K value mapping table.
The method according to claim 5, wherein the PCB circuit further comprises: calculating the thickness of the banknote according to the voltage change amount and the K value:

The PCB circuit queries the K value mapping table according to the current voltage to obtain a K value.
An apparatus for detecting the thickness of a banknote by an eddy current, comprising:

a reference shaft fixed to the device for pushing the banknote with the floating wheel when the banknote is inserted;

The floating wheel, at least two floating wheels are mounted on the device for pushing the banknote with the reference axis when the banknote is inserted, and correspondingly shifting in a vertical direction;

a metal piece fixed on the corresponding floating wheel, and corresponding displacement in the vertical direction is generated as the displacement of the floating wheel is used to generate an eddy current effect with the corresponding eddy current coil;

The eddy current coil, at least two eddy current coils are mounted on a PCB circuit board for generating an eddy current effect with a corresponding metal piece;

A PCB circuit board is fixed on the device for detecting a voltage variation caused by a corresponding displacement by an eddy current coil on the PCB circuit, and calculating a thickness of the banknote according to the voltage variation amount.
The device according to claim 7, comprising:

When the reference axis and the floating wheel are idling, the PCB circuit board obtains a zero-value voltage through a distance between the eddy current coil and a metal piece on the floating wheel;

When the banknote is inserted between the reference axis and the floating wheel, the PCB circuit board obtains the current voltage through the distance between the eddy current coil and the metal piece on the floating wheel;

The PCB circuit board obtains a voltage change amount according to the current voltage and the zero-value voltage.
The device according to claim 7, wherein the PCB circuit board comprises:

a crystal oscillator using an active crystal oscillator for providing a stable frequency to the eddy current coil as an excitation source for inputting an oscillating signal to the CPLD;

The CPLD is configured to receive the oscillating signal, and divide the oscillating signal to output signals of two different frequencies to a driving circuit;

The driving circuit receives signals of two different frequencies of the CPLD frequency-divided output, and drives the eddy current coil to operate according to the signal;

a detection circuit for detecting an envelope of the high frequency signal output by the eddy current coil and obtaining an analog signal;

a comparison amplifier for amplifying an output signal obtained by the detection circuit to increase the intensity of the analog signal;

An A/D converter receives the analog signal from the comparison amplifier for converting the analog signal into a digital signal, and transmitting the digital signal to a CPU;

The CPU is configured to analyze and process the digital signal, calculate the zero-value voltage, the current voltage, and the voltage change amount, and calculate the thickness of the banknote according to the voltage change amount.
The device according to claim 9, wherein the PCB circuit board further comprises:

The reference voltage module is connected to the CPU through an IIC interface, such that the CPU adjusts an output of the reference voltage through the IIC interface for providing a reference voltage for the comparison amplifier.