Metal detection device with noise suppression and high detection precision

Abstract

The invention relates to a noise-suppression high-detection-precision metal detection device. The noise-suppression high-detection-precision metal detection device comprises a probe coil and a signal processing circuit, the probe coil comprises a transmitting coil, a receiving coil and a reference coil; the signal processing circuit comprises a signal receiving demodulation circuit, a self-adaptive noise offset circuit, a self-adaptive product offset circuit and an AD acquisition circuit; a noise signal of the receiving coil is offset through the self-adaptive noise offset circuit, a product signal in the receiving coil is offset through the self-adaptive product offset circuit, and a metal foreign matter signal is obtained. According to the invention, corresponding filtering and amplification parameters are adaptively adjusted through the adaptive noise cancellation circuit according to the characteristic that noise interference in the small signal detection circuit is not related to a detected signal, interference noise is suppressed and attenuated, and the signal-to-noise ratio of the detected signal is improved. Therefore, the stability and the detection precision of the equipment are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal detection, and in particular relates to a metal detection device with noise suppression and high detection accuracy. Background Art

[0002] In the prior art, most metal detection system devices are balanced coil systems. The balanced coil system includes three coils. The middle transmitting coil is driven by a power circuit to generate a high-frequency alternating electromagnetic field in the space inside the probe. The receiving coils are evenly and equidistantly distributed on both sides of the transmitting coil, so that the signals received by the two receiving coils are the same. When disturbance or metal foreign matter passes through the probe, the two receiving coils will generate a specific voltage difference and phase difference. After that, the signal is processed by a demodulation and amplification circuit to obtain a corresponding response signal, thereby detecting metal foreign matter.

[0003] Since metal detection devices are generally used at the end of the production line, the use environment is very complex. In a complex electromagnetic environment, it is easy to generate additional interference noise that affects the detection accuracy. When detecting products, metal detectors usually encounter foods such as fresh meat, sauces, and high-salt foods. These products have a certain conductivity. Especially when the product is large in size, a large "product signal" will be generated when the product passes through the probe. This signal will seriously affect the subsequent signal processing circuit's processing of the metal foreign body signal, thereby seriously affecting the actual detection accuracy. Suppressing the size of the product signal and improving the signal-to-noise ratio of the metal foreign body signal is the key to improving the detection performance of metal detection equipment. How to suppress noise interference and suppress product signals is an important issue in the research and development of online metal detection equipment. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a metal detection device with noise suppression and high detection accuracy.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] On one hand, the present invention provides a metal detection device with noise suppression and high detection accuracy, including a probe coil, a signal processing circuit and a product to be detected;

[0007] The probe coil comprises a transmitting coil, a receiving coil and a reference coil, the receiving coil comprises a first receiving coil and a second receiving coil, the reference coil comprises a first reference coil, a second reference coil, a third reference coil and a fourth reference coil, the reference coil and the receiving coil are perpendicular to each other, the first reference coil and the second reference coil are located on the left side of the first receiving coil, the third reference coil and the fourth reference coil are located on the right side of the second receiving coil, and the first reference coil, the second reference coil, the third reference coil and the fourth reference coil are parallel to each other;

[0008] The signal processing circuit includes a signal receiving and demodulating circuit, an adaptive noise cancellation circuit, an adaptive product cancellation circuit, and an AD acquisition circuit;

[0009] The input end of the signal receiving and demodulating circuit is connected to the reference coil and the receiving coil, and is used to perform tuning, differentiation and demodulation processing on the reference coil signal and the receiving coil signal;

[0010] The input end of the adaptive noise cancellation circuit is connected to the output end of the signal receiving demodulation circuit, the input signal is the receiving coil demodulation signal, and is used to eliminate the noise signal in the receiving coil demodulation signal, and output the receiving coil noise elimination signal;

[0011] The adaptive product cancellation circuit includes five input terminals, which are respectively connected to the output terminal of the adaptive noise cancellation circuit and the output terminal of the signal receiving demodulation circuit. The input signals are the receiving coil noise elimination signal and the reference coil modulation signal, respectively, and are used to eliminate the product signal in the receiving coil noise elimination signal and output the receiving coil metal foreign body signal;

[0012] The input end of the AD acquisition circuit is connected to the output end of the adaptive product cancellation circuit, and is used to convert the metal foreign body signal of the receiving coil into a digital signal;

[0013] The product to be detected includes a metal foreign body, and the length of the product to be detected in the detection direction of the probe is N times the length of the metal foreign body in the detection direction of the probe, wherein N is an integer greater than 1.

[0014] Furthermore, the first reference coil and the second reference coil are respectively located at the upper and lower sides of the probe coil, the third reference coil and the fourth reference coil are respectively located at the upper and lower sides of the probe coil, and the probe coil is bilaterally symmetrical with the transmitting coil as the center.

[0015] Furthermore, the demodulated signal of the receiving coil includes a metal foreign body signal, a product signal, and a noise signal; the demodulated signal of the reference coil includes a metal foreign body signal and a product signal; the ratio of the product signal of the receiving coil to the metal foreign body signal is different from the ratio of the product signal of the reference coil to the metal foreign body signal at the same time; the product signal of the reference coil is basically consistent with the product signal of the receiving coil at the same time except for the amplitude.

[0016] Furthermore, the adaptive noise cancellation circuit includes a noise reference circuit, a detection signal circuit, and a second signal cancellation circuit.

[0017] Further, the input end of the noise reference circuit is connected to the output end of the signal receiving demodulation circuit, the input signal is a receiving coil demodulation signal, and the noise reference circuit includes a first amplifying and filtering circuit, a 90° phase shifting circuit, a third amplifying and filtering circuit, a fourth amplifying and filtering circuit, a first adaptive control circuit, and a first signal cancellation circuit;

[0018] The input signal of the first amplifying and filtering circuit is a demodulated signal of the receiving coil, and the output end is respectively connected to the input end of the 90° phase shifting circuit and the input end of the fourth amplifying and filtering circuit;

[0019] The output end of the 90° phase shift circuit is connected to the input end of the third amplifying and filtering circuit;

[0020] The output end of the third amplifying and filtering circuit and the output end of the fourth amplifying and filtering circuit are connected to the input end of the first signal canceling circuit;

[0021] The first adaptive control circuit is connected to the third amplifying and filtering circuit and the fourth amplifying and filtering circuit, and is used to collect the output signal of the first signal cancellation circuit, perform negative feedback regulation, and control and adjust the parameters of the third amplifying and filtering circuit and the fourth amplifying and filtering circuit;

[0022] The output end of the first signal cancellation circuit is connected to the input end of the second signal cancellation circuit, and is used to cancel the output signal of the third amplifying and filtering circuit and the output signal of the fourth amplifying and filtering circuit to obtain a noise signal.

[0023] Furthermore, the input end of the detection signal circuit is connected to the output end of the signal receiving and demodulating circuit, and the input signal is a demodulated signal of the receiving coil;

[0024] The detection signal circuit includes a second amplification and filtering circuit;

[0025] The input end of the second amplifying and filtering circuit is connected to the output end of the signal receiving and demodulating circuit, the input signal is a demodulated signal of the receiving coil, and the output end is connected to the input end of the second signal canceling circuit.

[0026] Furthermore, the second signal cancellation circuit outputs the product signal and the metal foreign body signal in the demodulated signal of the receiving coil, and is used to cancel the noise signal in the third amplification and filtering circuit according to the noise signal output by the first signal cancellation circuit, and output the product signal and the metal foreign body signal.

[0027] Furthermore, the adaptive product cancellation circuit includes a fifth amplifying and filtering circuit, a sixth amplifying and filtering circuit, a seventh amplifying and filtering circuit, an eighth amplifying and filtering circuit, a ninth amplifying and filtering circuit, a second adaptive control circuit, a third signal cancellation circuit, and a fourth signal cancellation circuit.

[0028] Further, the input end of the fifth amplifying and filtering circuit is connected to the output end of the second signal cancellation circuit, the input signal is a receiving coil noise elimination signal, the receiving coil noise elimination signal includes a product signal and a metal foreign body signal, and the output end of the fifth amplifying and filtering circuit is connected to the input end of the fourth signal cancellation circuit;

[0029] The input ends of the sixth amplifying and filtering circuit, the seventh amplifying and filtering circuit, the eighth amplifying and filtering circuit, and the ninth amplifying and filtering circuit are connected to the output end of the signal receiving and demodulating circuit, and the input signals are respectively the first reference coil demodulation signal, the second reference coil demodulation signal, the third reference coil demodulation signal, and the fourth reference coil demodulation signal, and the output ends of the sixth amplifying and filtering circuit, the seventh amplifying and filtering circuit, the eighth amplifying and filtering circuit, and the ninth amplifying and filtering circuit are connected to the input end of the third signal canceling circuit;

[0030] The output end of the third signal cancellation circuit is connected to the input end of the fourth signal cancellation circuit, and is used to cancel the metal foreign body signal in the first reference coil demodulation signal, the second reference coil demodulation signal, the third reference coil demodulation signal, and the fourth reference coil demodulation signal, and output the reference coil product signal;

[0031] The output end of the fourth signal cancellation circuit is connected to the input end of the AD acquisition circuit, and the output signal is a metal foreign body signal of the receiving coil.

[0032] Furthermore, the second adaptive control circuit is controlled and connected to the sixth amplifying and filtering circuit, the seventh amplifying and filtering circuit, the eighth amplifying and filtering circuit, and the ninth amplifying and filtering circuit, and is used to perform negative feedback regulation by collecting the output signal of the third signal cancellation circuit, and control and adjust the parameters of the sixth amplifying and filtering circuit, the seventh amplifying and filtering circuit, the eighth amplifying and filtering circuit, and the ninth amplifying and filtering circuit.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The adaptive noise cancellation circuit of the present invention utilizes the fact that the noise interference in the small signal detection circuit is unrelated to the detected signal to adaptively adjust the corresponding filtering and amplification parameters, suppress and attenuate the interference noise, and improve the signal-to-noise ratio of the detection signal, thereby improving the stability and detection accuracy of the device.

[0035] (2) The reference signal arrangement method of the present invention can better fit and generate a product signal that is the same as the balancing coil, thereby offsetting the product signal to a certain extent.

[0036] (3) The present invention sets an adaptive control circuit and updates the parameters of the adaptive control circuit in real time through negative feedback regulation, so that the circuit noise suppression effect and the product signal fitting effect are better. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A diagram showing a probe coil model of the present invention;

[0038] Figure 2 is a structural diagram of a signal processing circuit of the present invention;

[0039] Figure 3 The adaptive noise cancellation circuit diagram of the present invention;

[0040] Figure 4 The circuit diagram of the adaptive product offset of the present invention;

[0041] The reference numerals in the figure are: 1. first reference coil, 2. second reference coil, 3. third reference coil, 4. fourth reference coil, 5. first receiving coil, 6. second receiving coil, 7. first amplifying and filtering circuit, 8. second amplifying and filtering circuit, 9. third amplifying and filtering circuit, 10. fourth amplifying and filtering circuit, 11. fifth amplifying and filtering circuit, 12. sixth amplifying and filtering circuit, 13. seventh amplifying and filtering circuit, 14. eighth amplifying and filtering circuit, 15. ninth amplifying and filtering circuit, 16. first signal cancellation circuit, 17. second signal cancellation circuit, 18. third signal cancellation circuit, 19. fourth signal cancellation circuit, 20. first adaptive control circuit, 21. second adaptive control circuit. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] Embodiment 1:

[0044] This embodiment provides a metal detection device with noise suppression and high detection accuracy, including a probe coil and a signal processing circuit;

[0045] The probe coil model is as follows Figure 1 As shown, the probe coil includes a transmitting coil, a receiving coil and a reference coil, the receiving coil includes a receiving coil 1 and a receiving coil 2, the reference coil includes a reference coil 1, a reference coil 2, a reference coil 3 and a reference coil 4, the reference coil and the receiving coil are perpendicular to each other, the reference coil 1 and the reference coil 2 are located on the left side of the receiving coil 1, the reference coil 3 and the reference coil 4 are located on the right side of the receiving coil 2, and the reference coil 1, the reference coil 2, the reference coil 3 and the reference coil 4 are parallel to each other;

[0046] like Figure 2As shown, the signal processing circuit includes a signal receiving and demodulating circuit, an adaptive noise cancellation circuit, an adaptive product cancellation circuit, and an AD acquisition circuit;

[0047] The input end of the signal receiving and demodulating circuit is connected to the reference coil and the receiving coil, and is used to perform tuning, differentiation and demodulation processing on the reference coil signal and the receiving coil signal;

[0048] The input end of the adaptive noise cancellation circuit is connected to the output end of the signal receiving demodulation circuit, the input signal is the receiving coil demodulation signal, and is used to eliminate the noise signal in the receiving coil demodulation signal, and output the receiving coil noise elimination signal;

[0049] The adaptive product cancellation circuit includes five input terminals, which are respectively connected to the output terminal of the adaptive noise cancellation circuit and the output terminal of the signal receiving demodulation circuit. The input signals are the receiving coil noise cancellation signal and the reference coil modulation signal, respectively, and are used to eliminate the product signal in the receiving coil noise cancellation signal and output the receiving coil metal foreign body signal.

[0050] The input end of the AD acquisition circuit is connected to the output end of the adaptive product cancellation circuit, and is used to convert the metal foreign body signal of the receiving coil into a digital signal.

[0051] Reference coil 1 and reference coil 2 are respectively located at the upper and lower sides of the probe coil, and reference coil 3 and reference coil 4 are respectively located at the upper and lower sides of the probe coil. The probe coil is symmetrical with respect to the transmitting coil.

[0052] The demodulated signal of the receiving coil includes the metal foreign body signal, the product signal, and the noise signal, and the demodulated signal of the reference coil includes the metal foreign body signal, the product signal, and the noise signal.

[0053] like Figure 3 As shown, the adaptive noise cancellation circuit includes a noise reference circuit, a detection signal circuit, and a signal cancellation circuit 2.

[0054] The input end of the noise reference circuit is connected to the output end of the signal receiving and demodulating circuit, the input signal is the demodulated signal of the receiving coil, and the noise reference circuit includes an amplifying and filtering circuit 1, a 90° phase shifting circuit, an amplifying and filtering circuit 3, an amplifying and filtering circuit 4, an adaptive control circuit 1, and a signal canceling circuit 1;

[0055] The input signal of the amplifying and filtering circuit 1 is the demodulated signal of the receiving coil, and the output end is connected to the input end of the 90° phase shifting circuit and the input end of the amplifying and filtering circuit 4 respectively;

[0056] The output end of the 90° phase shift circuit is connected to the input end of the amplifying and filtering circuit 3;

[0057] The output end of the amplifying and filtering circuit 3 and the output end of the amplifying and filtering circuit 4 are connected to the input end of the signal canceling circuit 1;

[0058] The adaptive control circuit 1 is connected to the amplifying and filtering circuit 3 and the amplifying and filtering circuit 4, and is used to collect the output signal of the signal cancellation circuit 1, perform negative feedback regulation, and control and adjust the parameters of the amplifying and filtering circuit 3 and the amplifying and filtering circuit 4;

[0059] The output end of the signal cancellation circuit 1 is connected to the input end of the signal cancellation circuit 2, and is used to cancel the output signal of the amplifying and filtering circuit 3 and the output signal of the amplifying and filtering circuit 4 to obtain a noise signal.

[0060] The adaptive noise elimination circuit 1 collects the output signal of the signal cancellation circuit 2, performs automatic negative feedback regulation, controls and adjusts the parameters of the corresponding amplification and filtering circuit, so that the output of the noise suppression circuit reaches the minimum state, that is, the optimal state of circuit noise suppression.

[0061] The input end of the detection signal circuit is connected to the output end of the signal receiving and demodulating circuit, and the input signal is the demodulated signal of the receiving coil;

[0062] The detection signal circuit includes an amplification and filtering circuit 2;

[0063] The input end of the amplifying and filtering circuit 2 is connected to the output end of the signal receiving and demodulating circuit, the input signal is the demodulated signal of the receiving coil, and the output end is connected to the input end of the signal canceling circuit 2.

[0064] The signal cancellation circuit 2 outputs the product signal and the metal foreign body signal in the demodulated signal of the receiving coil, and is used to cancel the noise signal in the amplification and filtering circuit 3 according to the noise signal output by the signal cancellation circuit 1, and output the product signal and the metal foreign body signal.

[0065] like Figure 4 As shown, the adaptive product cancellation circuit includes an amplifying filter circuit 5, an amplifying filter circuit 6, an amplifying filter circuit 7, an amplifying filter circuit 8, an amplifying filter circuit 9, an adaptive control circuit 2, a signal cancellation circuit 3, and a signal cancellation circuit 4.

[0066] The input end of the amplifying and filtering circuit 5 is connected to the output end of the signal canceling circuit 2, the input signal is the receiving coil noise elimination signal, the receiving coil noise elimination signal includes the product signal and the metal foreign body signal, and the output end of the amplifying and filtering circuit 5 is connected to the input end of the signal canceling circuit 4;

[0067] The input ends of the amplifying filter circuit 6, the amplifying filter circuit 7, the amplifying filter circuit 8, and the amplifying filter circuit 9 are connected to the output end of the signal receiving demodulation circuit, and the input signals are respectively the demodulation signal of the reference coil 1, the demodulation signal of the reference coil 2, the demodulation signal of the reference coil 3, and the demodulation signal of the reference coil 4, and the output ends of the amplifying filter circuit 6, the amplifying filter circuit 7, the amplifying filter circuit 8, and the amplifying filter circuit 9 are connected to the input end of the signal canceling circuit 3;

[0068] The output end of the signal cancellation circuit 3 is connected to the input end of the signal cancellation circuit 4, and is used to cancel the metal foreign body signal in the demodulation signal of the reference coil 1, the demodulation signal of the reference coil 2, the demodulation signal of the reference coil 3, and the demodulation signal of the reference coil 4, and output the reference coil product signal;

[0069] The output end of the signal cancellation circuit 4 is connected to the input end of the AD acquisition circuit, and the output signal is the metal foreign body signal of the receiving coil.

[0070] The adaptive control circuit 2 is controlled and connected with the amplifying and filtering circuit 6, the amplifying and filtering circuit 7, the amplifying and filtering circuit 8, and the amplifying and filtering circuit 9, and is used to collect the output signal of the signal cancellation circuit 3, perform negative feedback regulation, and control and adjust the parameters of the amplifying and filtering circuit 6, the amplifying and filtering circuit 7, the amplifying and filtering circuit 8, and the amplifying and filtering circuit 9. The adaptive control circuit 2 collects the output signal (product signal) of the signal cancellation circuit 3, performs automatic negative feedback regulation, and controls and adjusts the parameters of the corresponding amplifying and filtering circuits so that the output of the product signal elimination circuit reaches the minimum state, that is, the minimum state where the product signal is suppressed.

[0071] Device implementation principle:

[0072] The product to be detected includes metal foreign matter, and the length of the product to be detected in the probe detection direction is several times the length of the metal foreign matter in the probe detection direction, and the length of the product to be detected in the probe detection direction is much greater than the length of the metal foreign matter in the probe detection direction.

[0073] Therefore, when the product passes through the probe, the product signal generated is also relatively large due to the generally large product size. The receiving coil 1 and the receiving coil 2 are differential structures. When the product passes through the receiving coil 1, a positive (or negative) single extreme value point signal will be generated. When passing through the receiving coil 2, a negative (or positive) single extreme value point signal will be generated (the two signals have opposite polarities). The differential signal of the two coils is a signal with two extreme points. The product signal generated by the reference coil 1 and the reference coil 2 when the product passes through the reference coil 1 and the reference coil 2 is basically the same as the product signal generated by the receiving coil 1 at the same time except for the amplitude. Similarly, the product signal generated by the reference coil 3 and the reference coil 4 is basically the same as the product signal generated by the receiving coil 2 except for the amplitude. When the product signal generated by the reference coils 1, 2, 3, and 4 is controlled by the adaptive control circuit to control the parameters of the amplification and filtering circuit to control its gain, the combined operation skill is used to fit the product signal that is basically consistent with the receiving coil. Thus, the product signal is offset.

[0074] When a metal foreign body passes through the probe at the same time, due to the very small volume of the metal foreign body, the metal signals generated by the metal in the reference small circles 1 and 2 and the receiving coil 1 at the same time have great differences in phase and amplitude. Similarly, the metal foreign body signals generated by the reference coils 3 and 4 are also very different from the metal foreign body signals generated by the receiving coil 2. Therefore, the metal signal generated in the reference coil cannot be fitted into the metal signal generated in the receiving coil, so the metal signal cannot be eliminated. The product signal generated by the reference signal can be offset by fitting the product signal consistent with the receiving coil, while the metal signal cannot be offset by the same method, thereby suppressing the product signal and improving the performance of metal signal detection. When a metal foreign body passes through the probe at the same time, due to the very small volume of the metal foreign body, the metal signals generated by the reference small circles 1 and 2 and the receiving coil 1 have great differences in phase and amplitude. Similarly, the metal foreign body signals generated by the reference coils 3 and 4 are also very different from the metal foreign body signals generated by the receiving coil 2. Therefore, the metal signal generated in the reference coil cannot be fitted into the metal signal generated in the receiving coil, so the metal signal cannot be eliminated. The product signal generated by the reference signal can be offset by fitting a product signal that is consistent with the receiving coil, while the metal signal cannot be offset by the same method, thereby suppressing the product signal and improving the performance of metal signal detection. At the same time, when a metal foreign body passes through the probe, due to the very small volume of the metal foreign body, the metal in the reference small circles 1 and 2 and the metal signal generated by the receiving coil 1 have great differences in phase and amplitude. Similarly, the metal foreign body signals generated by the reference coils 3 and 4 are also very different from the metal foreign body signals generated by the receiving coil 2. Therefore, the metal signal generated in the reference coil cannot be fitted into the metal signal generated in the receiving coil, so the metal signal cannot be eliminated. The product signal generated by the reference signal can be offset by fitting a product signal that is consistent with the receiving coil, while the metal signal cannot be offset by the same method, thereby suppressing the product signal and improving the performance of metal signal detection.

[0075] Embodiment 2:

[0076] The parts not mentioned in this embodiment are the same as those in Embodiment 1.

[0077] This embodiment includes a probe coil and a signal processing circuit;

[0078] The coil model consists of a conventional transmitting coil, receiving coils 1 and 2 equidistantly distributed next to the transmitting coil, and four reference coils equidistantly distributed at the edge of the probe. The distance between the receiving coils and the reference coils varies according to the size of the probe. Reference coils 1 and 2 are arranged outside the receiving coil 1 at the edge of the probe, respectively distributed on the upper and lower sides of the probe, and reference coil 2 is horizontally symmetrical with reference coil 1.

[0079] Reference coil 3 and reference coil 4 are arranged outside the receiving coil 2 at the edge of the probe, respectively distributed on the upper and lower sides of the probe. Reference coil 3 and reference coil 4 are horizontally symmetrical and the distance between the reference coil and the corresponding receiving coil is consistent. In actual use, the length and size of the product are much larger than the metal foreign body. The product signal induced by the receiving coil and the product signal generated by the reference signal are relatively close. The metal foreign body signal induced by the receiving coil and the metal foreign body signal generated by the reference signal have large differences in amplitude and phase. The reference coil is arranged in this way, which can better fit and generate the same product signal as the balancing coil, thereby offsetting the product signal to a certain extent.

[0080] The signal processing circuit includes a signal receiving and demodulating circuit, an adaptive noise cancellation circuit, an adaptive product cancellation circuit, and an AD acquisition circuit.

[0081] The working principle of the equipment is that the transmitting coil generates a high-frequency alternating magnetic field in the probe window, and the receiving coil and the reference coil induce corresponding induced electrical signals in the magnetic field. The signals on the receiving coil and the reference coil are processed accordingly through the signal receiving and demodulation circuit. After that, the circuit noise signal of the detection circuit is suppressed by the adaptive noise elimination circuit, and the adaptive product cancellation circuit is combined with the reference coil signal to suppress the size of the product signal to ensure the detection of the metal signal. Because the product signal in the reference coil signal is close to the product signal in the receiving coil, and the metal foreign body signal in the reference coil signal and the metal foreign body signal in the receiving coil have large differences in amplitude and phase, the reference coil signal can be used to cancel the size of the product signal in the receiving coil.

[0082] The output signal y(x) of the signal receiving and demodulating circuit is composed of the metal foreign body signal Acos(K1ω1), the product signal Bcos(K2ω2), and the noise signal S(t).

[0083] y(x)=Acos(L1ω1)+B cos(L2ω2)+S(t)

[0084] like Figure 3As shown, the noise reference circuit controls the parameters of the amplifying and filtering circuits 3 and 4 through the adaptive control circuit 1 to process the y(x) signal, so that the metal foreign body signal Acos(K1ω1) and the product signal Bcos(K2ω2) in the amplifying and filtering circuit 3 signal are offset by the metal foreign body signal Acos(L1ω1) and the product signal Bcos(K2ω2) in the amplifying and filtering circuit 4 signal, and only the noise signal S(t) is retained. Then, it is subtracted from the signal of the amplifying and filtering circuit 2 in the detection signal circuit, thereby greatly attenuating the noise component in the detection signal circuit, and only the metal foreign body signal and the product signal are retained.

[0085] like Figure 4 As shown, the parameters of the amplifying filter circuit 6, the amplifying filter circuit 7, the amplifying filter circuit 8, and the amplifying filter circuit 9 are controlled by the adaptive control circuit 2 to process the reference coil 1 signal, the reference coil 2 signal, the reference coil 3 signal, and the reference coil 4 signal, thereby offsetting the product signal Bcos (L2ω2) in the amplifying filter circuit 5 signal and retaining the metal foreign body signal Acos (L1ω1), thereby suppressing the size of the product signal, improving the signal-to-noise ratio of the metal foreign body signal, and improving the detection accuracy of the equipment.

[0086] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program code.

[0087] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A metal detection device with noise suppression and high detection accuracy, characterized in that: Including probe coil, signal processing circuit and product to be tested; The probe coil comprises a transmitting coil, a receiving coil and a reference coil, the receiving coil comprises a first receiving coil (5) and a second receiving coil (6), the reference coil comprises a first reference coil (1), a second reference coil (2), a third reference coil (3) and a fourth reference coil (4), the reference coil and the receiving coil are perpendicular to each other, the first reference coil (1) and the second reference coil (2) are located on the left side of the first receiving coil (5), the third reference coil (3) and the fourth reference coil (4) are located on the right side of the second receiving coil (6), and the first reference coil (1), the second reference coil (2), the third reference coil (3) and the fourth reference coil (4) are parallel to each other; The signal processing circuit includes a signal receiving and demodulating circuit, an adaptive noise cancellation circuit, an adaptive product cancellation circuit, and an AD acquisition circuit; The input end of the signal receiving and demodulating circuit is connected to the reference coil and the receiving coil, and is used to perform tuning, differentiation and demodulation processing on the reference coil signal and the receiving coil signal; The input end of the adaptive noise cancellation circuit is connected to the output end of the signal receiving demodulation circuit, the input signal is the receiving coil demodulation signal, and is used to eliminate the noise signal in the receiving coil demodulation signal, and output the receiving coil noise elimination signal; The adaptive product cancellation circuit includes five input terminals, which are respectively connected to the output terminal of the adaptive noise cancellation circuit and the output terminal of the signal receiving demodulation circuit. The input signals are the receiving coil noise elimination signal and the reference coil modulation signal, respectively, and are used to eliminate the product signal in the receiving coil noise elimination signal and output the receiving coil metal foreign body signal; The input end of the AD acquisition circuit is connected to the output end of the adaptive product cancellation circuit, and is used to convert the metal foreign body signal of the receiving coil into a digital signal; The product to be detected includes a metal foreign body, and the length of the product to be detected in the detection direction of the probe is N times the length of the metal foreign body in the detection direction of the probe, wherein N is an integer greater than 1.

2. A metal detection device with noise suppression and high detection accuracy according to claim 1, characterized in that: The first reference coil (1) and the second reference coil (2) are respectively located at the upper and lower sides of the probe coil, and the third reference coil (3) and the fourth reference coil (4) are respectively located at the upper and lower sides of the probe coil. The probe coil is symmetrical with respect to the transmitting coil.

3. The metal detection device with noise suppression and high detection accuracy according to claim 1, characterized in that: The receiving coil demodulation signal includes a metal foreign body signal, a product signal, and a noise signal; the reference coil demodulation signal includes a metal foreign body signal and a product signal; the ratio of the product signal to the metal foreign body signal of the receiving coil is different from the ratio of the product signal to the metal foreign body signal of the reference coil at the same time.

4. The metal detection device with noise suppression and high detection accuracy according to claim 1, characterized in that: The adaptive noise cancellation circuit comprises a noise reference circuit, a detection signal circuit, and a second signal cancellation circuit (17).

5. A metal detection device with noise suppression and high detection accuracy according to claim 4, characterized in that: The input end of the noise reference circuit is connected to the output end of the signal receiving and demodulating circuit, the input signal is a receiving coil demodulation signal, and the noise reference circuit comprises a first amplifying and filtering circuit (7), a 90° phase shifting circuit, a third amplifying and filtering circuit (9), a fourth amplifying and filtering circuit (10), a first adaptive control circuit (20), and a first signal canceling circuit (16); The input signal of the first amplifying and filtering circuit (7) is a demodulated signal of the receiving coil, and the output end is respectively connected to the input end of the 90° phase shift circuit and the input end of the fourth amplifying and filtering circuit (10); The output end of the 90° phase shift circuit is connected to the input end of the third amplifying and filtering circuit (9); The output end of the third amplifying and filtering circuit (9) and the output end of the fourth amplifying and filtering circuit (10) are connected to the input end of the first signal canceling circuit (16); The first adaptive control circuit (20) is connected to the third amplifying and filtering circuit (9) and the fourth amplifying and filtering circuit (10) and is used to collect the output signal of the first signal cancellation circuit (16), perform negative feedback regulation, and control and adjust the parameters of the third amplifying and filtering circuit (9) and the fourth amplifying and filtering circuit (10); The output end of the first signal cancellation circuit (16) is connected to the input end of the second signal cancellation circuit (17) and is used to cancel the output signal of the third amplifying and filtering circuit (9) and the output signal of the fourth amplifying and filtering circuit (10) to obtain a noise signal.

6. A metal detection device with noise suppression and high detection accuracy according to claim 4 or 5, characterized in that: The input end of the detection signal circuit is connected to the output end of the signal receiving and demodulating circuit, and the input signal is a demodulated signal of the receiving coil; The detection signal circuit comprises a second amplifying and filtering circuit (8); The input end of the second amplifying and filtering circuit (8) is connected to the output end of the signal receiving and demodulating circuit, the input signal is a demodulated signal of the receiving coil, and the output end is connected to the input end of the second signal canceling circuit (17).

7. The metal detection device with noise suppression and high detection accuracy according to claim 4, characterized in that: The second signal cancellation circuit (17) outputs the product signal and the metal foreign body signal in the demodulated signal of the receiving coil, and is used to cancel the noise signal in the third amplifying and filtering circuit (9) according to the noise signal output by the first signal cancellation circuit (16), and output the product signal and the metal foreign body signal.

8. The metal detection device with noise suppression and high detection accuracy according to claim 1, characterized in that: The adaptive product cancellation circuit comprises a fifth amplifying and filtering circuit (11), a sixth amplifying and filtering circuit (12), a seventh amplifying and filtering circuit (13), an eighth amplifying and filtering circuit (14), a ninth amplifying and filtering circuit (15), a second adaptive control circuit (21), a third signal cancellation circuit (18), and a fourth signal cancellation circuit (19).

9. The metal detection device with noise suppression and high detection accuracy according to claim 8, characterized in that: The input end of the fifth amplifying and filtering circuit (11) is connected to the output end of the second signal canceling circuit (17), the input signal is a receiving coil noise elimination signal, the receiving coil noise elimination signal includes a product signal and a metal foreign body signal, and the output end of the fifth amplifying and filtering circuit (11) is connected to the input end of the fourth signal canceling circuit (19); The input ends of the sixth amplifying and filtering circuit (12), the seventh amplifying and filtering circuit (13), the eighth amplifying and filtering circuit (14), and the ninth amplifying and filtering circuit (15) are connected to the output end of the signal receiving and demodulating circuit, and the input signals are respectively the demodulated signal of the first reference coil (1), the demodulated signal of the second reference coil (2), the demodulated signal of the third reference coil (3), and the demodulated signal of the fourth reference coil (4); the output ends of the sixth amplifying and filtering circuit (12), the seventh amplifying and filtering circuit (13), the eighth amplifying and filtering circuit (14), and the ninth amplifying and filtering circuit (15) are connected to the input end of the third signal canceling circuit (18); The output end of the third signal cancellation circuit (18) is connected to the input end of the fourth signal cancellation circuit (19), and is used to cancel the metal foreign body signal in the demodulation signal of the first reference coil (1), the demodulation signal of the second reference coil (2), the demodulation signal of the third reference coil (3), and the demodulation signal of the fourth reference coil (4), and output the reference coil product signal; The output end of the fourth signal cancellation circuit (19) is connected to the input end of the AD acquisition circuit, and the output signal is a metal foreign body signal of the receiving coil.

10. The metal detection device with noise suppression and high detection accuracy according to claim 8, characterized in that: The second adaptive control circuit (21) is connected to the sixth amplifying and filtering circuit (12), the seventh amplifying and filtering circuit (13), the eighth amplifying and filtering circuit (14), and the ninth amplifying and filtering circuit (15) to collect the output signal of the third signal canceling circuit (18), perform negative feedback regulation, and control and adjust the parameters of the sixth amplifying and filtering circuit (12), the seventh amplifying and filtering circuit (13), the eighth amplifying and filtering circuit (14), and the ninth amplifying and filtering circuit (15).

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