Strong / weak-field-based foreign object detection method and apparatus for metal detector, and storage medium

Abstract

A strong / weak-field-based foreign object detection method for a metal detector, the method comprising the following steps: acquiring a weak-field detection signal and a strong-field detection signal of a product to be subjected to detection (S1); on the basis of the weak-field detection signal, the strong-field detection signal, and a qualified product coefficient and a metallic foreign object coefficient that are measured in advance, calculating a metallic foreign object signal value, wherein the qualified product coefficient is different from the metallic foreign object coefficient (S2); and determining whether the metallic foreign object signal value is greater than a preset threshold value, and if the metallic foreign object signal value is greater than the preset threshold value, determining that a metallic foreign object is detected, otherwise, determining that no metallic foreign object is detected (S3). Therefore, when a small metallic foreign object cannot be detected by means of a threshold-value-based determination method, the detection precision of a metal detector is improved. The present application further relates to a strong / weak-field-based foreign object detection apparatus for a metal detector, and a storage medium.

Description

Strong and weak field foreign matter detection method and device for metal detector and storage medium TECHNICAL FIELD

[0001] The present application relates to the technical field of foreign matter detection, in particular to a strong and weak field foreign matter detection method and device for a metal detector and a storage medium. BACKGROUND

[0002] A metal detector is a device that detects foreign matter, especially metal foreign matter, based on changes in the electromagnetic field within the probe window. The electrical signal on the transmitting coil in the probe induces an electromagnetic field within the probe window, and the receiving coil in the probe detects this electromagnetic field and transmits its changes to subsequent components for processing. Products passing through the probe also have conductivity due to the moisture and salt content they contain, which significantly changes the electromagnetic field within the probe, resulting in a so-called product effect. An important task of a metal detector is to distinguish the signal of metal foreign matter from the effects caused by the product and to reject the product containing foreign matter.

[0003] The common detection method at present is the threshold judgment method. That is, the detection signal contains both the product signal and the metal foreign matter signal, and when the detection signal exceeds a certain preset threshold, it is determined that foreign matter is detected. However, as users demand higher detection accuracy, the above threshold judgment method has become increasingly difficult to meet user needs. Therefore, how to further improve detection accuracy has become a problem to be solved in the field.

[0004] SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a strong and weak field foreign matter detection method and device for a metal detector, which can improve detection accuracy when traditional threshold judgment methods cannot detect smaller metal foreign matter, thereby realizing the detection of smaller metal foreign matter.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] In a first aspect of the present application, a strong and weak field foreign matter detection method for a metal detector is provided, comprising the following steps: obtaining a weak field detection signal and a strong field detection signal of a product to be detected; based on the weak field detection signal, the strong field detection signal, and a pre-determined qualified product coefficient and metal foreign matter coefficient, calculating a metal foreign matter signal value, the qualified product coefficient being different from the metal foreign matter coefficient; determining whether the metal foreign matter signal value is greater than a preset threshold: if yes, it is considered that metal foreign matter is detected, otherwise it is considered that no metal foreign matter is detected.

[0008] As a preferred technical solution, the metal foreign matter signal value is represented as:

[0009] In the formula, m1 is a metal foreign matter signal value, a is a qualified product coefficient, b is a metal foreign matter coefficient, W1 is a weak field detection signal, and W2 is a strong field detection signal.

[0010] As a preferred technical solution, the determination process of the qualified product coefficient and the metal foreign matter coefficient specifically comprises: measuring a qualified product signal under a weak field and a qualified product signal under a strong field respectively; calculating the qualified product coefficient based on the qualified product signal under the weak field and the qualified product signal under the strong field; measuring a product signal containing a specific metal foreign matter under a weak field and a product signal containing a specific metal foreign matter under a strong field respectively; and calculating the metal foreign matter coefficient based on the product signal containing the specific metal foreign matter under the weak field and the product signal containing the specific metal foreign matter under the strong field.

[0011] As a preferred technical solution, the qualified product coefficient is represented as: a=W 1-p2 / W 1-p1

[0012] In the formula, a is a qualified product coefficient, W 1-p1 is a qualified product signal under a weak field, and W 1-p2 is a qualified product signal under a strong field.

[0013] As a preferred technical solution, the metal foreign matter coefficient is represented as: b=W 1-m2 / W 1-m1

[0014] In the formula, b is a metal foreign matter coefficient, W 1-m1 is a product signal containing a specific metal foreign matter under a weak field, and W 1-m2 is a product signal containing a specific metal foreign matter under a strong field.

[0015] As a preferred technical solution, the specific metal foreign matter comprises iron, non-ferrous metal and stainless steel.

[0016] As a preferred technical solution, the preset threshold value is 0.

[0017] As a preferred technical solution, the preset threshold value is one-tenth of the qualified product signal under a weak field in the determination process of the qualified product coefficient.

[0018] In a second aspect, the application provides a strong-weak field foreign matter detection device for a metal detector, comprising a memory, a processor, and a program stored in the memory, wherein the processor implements the method when executing the program.

[0019] In a third aspect, the application provides a storage medium having a program stored thereon, wherein the program implements the method when executed.

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. Compared with the traditional single electromagnetic field detection method, the strong and weak field foreign matter detection method provided by the present application obtains more product and foreign matter information by using strong and weak fields, and the strong and weak fields are the same frequency, so that the relationship between them basically conforms to linear superposition, so that the actual metal foreign matter signal can be easily calculated by the pre-determined product and typical metal foreign matter coefficient, even if the product signal overwhelms the metal signal, the calculation of the metal signal can still be realized, and the detection precision can be improved in the case that the traditional threshold judgment method cannot detect small metal foreign matters, so that the detection of small metal foreign matters can be realized.

[0022] 2. The present application sets the preset threshold value as one tenth of the qualified product signal in the weak field during the determination of the qualified product coefficient, and considering that test errors and metal signal fluctuations are difficult to avoid in actual testing, even if there is no metal in actual testing, the measured m1 is still a value close to 0 but not 0, and setting the threshold value to be not 0 can effectively consider the detection precision and stability in engineering. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 is a flow chart of the detection signal acquisition of the metal detector;

[0024] Fig. 2 is a flow chart of the determination of the qualified product coefficient and the metal foreign matter coefficient in the embodiment of the present application;

[0025] Fig. 3 is a flow chart of the method provided by the embodiment of the present application. DETAILED DESCRIPTION

[0026] The present application will be described in detail below in combination with the drawings and specific embodiments. The present embodiment is implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0027] EMBODIMENT

[0028] The strong and weak field foreign matter detection method for the metal detector provided by the present embodiment can improve the detection precision of the metal detector in the case that the existing threshold judgment method cannot detect small metal foreign matters, so that the detection of small metal foreign matters can be realized. The method requires that the products passing through the metal detector are independent packaging and have a certain spacing, and the weight and shape of different products should be consistent.

[0029] Generally, in a metal detector, the detection signal can be obtained in the way as shown in Fig. 1. The transmitting signal is amplified by a power amplifier circuit, and then sent into a transmitting coil through a transmitting transformer, so as to excite an electromagnetic field with a certain intensity in the probe. The receiving coil senses the change of the electromagnetic field, and its output is sent into a receiving amplifier circuit through a receiving transformer, and a balanced signal is output. The balanced signal is processed by a demodulation circuit, and then the detection signal is obtained.

[0030] By time division multiplexing or signal mixing, etc., a low-intensity electromagnetic field and a high-intensity electromagnetic field (the two signals only differ in intensity, and the frequencies are the same) can be conveniently excited in the probe window, and applied to the object passing through the probe. For simplicity of description, the low-intensity electromagnetic field is referred to as a weak field, and the high-intensity electromagnetic field is referred to as a strong field.

[0031] The transmitting signal intensity of the probe transmitting coil is denoted by H(t), the transmitting signal intensity corresponding to the weak field is denoted by H1(t), and the transmitting signal corresponding to the strong field is denoted by H2(t).

[0032] The detection signal generated by any object passing through the probe is denoted by W(t), the detection signal corresponding to the weak field is denoted by W1(t), and the detection signal corresponding to the strong field is denoted by W2(t).

[0033] The detection signal generated by a qualified product (containing no foreign matter inside) passing through the probe is denoted by p(t), the detection signal corresponding to the weak field is denoted by p1(t), and the detection signal corresponding to the strong field is denoted by p2(t).

[0034] The detection signal generated by a metal foreign matter (a certain specific metal) passing through the probe is denoted by m(t), the detection signal corresponding to the weak field is denoted by m1(t), and the detection signal corresponding to the strong field is denoted by m2(t).

[0035] The relationship of the detection signal W(t), the qualified product signal p(t), and the metal foreign matter signal m(t) is as follows: W(t) = p(t) + m(t) # (1)

[0036] Considering the case of the strong and weak fields, there are: W1(t) = p1(t) + m1(t) # (2) W2(t) = p2(t) + m2(t) # (3)

[0037] Since the difference between the strong and weak fields is only the intensity difference (for example, the weak field signal voltage is 15V, and the strong field signal voltage is 30V), the relationship of p1(t) and p2(t) can be considered as linear, that is: p2(t) = a * p1(t) # (4)

[0038] Similarly, the relationship of m1(t) and m2(t) can be considered as linear, that is: m2(t) = b * m1(t) # (5)

[0039] wherein a represents a qualified product coefficient, b represents a metal foreign matter coefficient, a and b are both unitless coefficients, the values of which are related to the intensity difference between the strong and weak fields, and are also related to the response characteristics of the product / metal in the electromagnetic field. Generally, a and b are significantly different. a and b need to be input into the device as preset values before detection begins, and the specific values can be determined through simple steps. Different metal foreign matters correspond to different values of b, for example, iron corresponds to b1, non-ferrous metal corresponds to b2, and stainless steel corresponds to b3. The determination steps of a and b are shown in FIG. 2.

[0040] In the conventional threshold judgment method, the detection signal W(t) mixed with the product signal and the metal signal is directly subjected to threshold judgment, that is, when |W(t)| is greater than a certain threshold T, it is determined that a foreign matter is detected. As shown in FIG. 3, the judgment method of the metal detection in the embodiment is as follows:

[0041] Step S1, according to the aforementioned time division multiplexing or signal aliasing method, a low-intensity electromagnetic field and a high-intensity electromagnetic field are excited in the probe window of the metal detector, and the product to be detected is passed through the probe under the low-intensity electromagnetic field and the high-intensity electromagnetic field, respectively, to obtain the weak-field detection signal W1(t) and the strong-field detection signal W2(t) of the product to be detected, which are simply denoted as W1 and W2, respectively.

[0042] Step S2, after substituting formula (4) and formula (5) into formula (2) and formula (3), the expression of the metal foreign matter signal value m1(t) can be obtained through formula transformation:

[0043] In the formula, m1(t) is simply denoted as m1.

[0044] wherein the qualified product coefficient and the metal foreign matter coefficient are determined in advance according to the flow shown in FIG. 2, and the specific steps are as follows:

[0045] 1) The selected qualified product is passed through the probe under the weak field, and the qualified product signal W 1-p1 under the weak field is measured.

[0046] 2) The qualified product is passed through the probe under the strong field, and the qualified product signal W 1-p2 under the strong field is measured.

[0047] 3) The qualified product coefficient a is calculated according to the following formula: a = W 1-p2 / W 1-p1 #(7)

[0048] 4) Taking iron as the metal foreign matter, the first product signal W

[0049] 5) Take iron as metal foreign matter, measure the first product signal under strong field by probe under strong field

[0050] 6) Calculate the first metal foreign matter coefficient b1 according to the following formula:

[0051] 7) Take non-iron as metal foreign matter, repeat the measurement and calculation process of steps 4) to 6) to obtain the second metal foreign matter coefficient b2, the non-iron refers to the metal other than iron and stainless steel (especially non-magnetic), such as copper, lead and other metals;

[0052] 8) Take stainless steel as metal foreign matter, repeat the measurement and calculation process of steps 4) to 6) to obtain the third metal foreign matter coefficient b3.

[0053] According to the weak field detection signal W1, the strong field detection signal W2 and the measured a and b1 to b3 that have been obtained, the corresponding metal foreign matter signal values are directly calculated by formula (6) respectively.

[0054] Step S3, respectively judge whether the metal foreign matter signal values corresponding to different metal foreign matters are significantly greater than 0: if yes, it is considered that the metal foreign matter is detected, otherwise it is considered that the metal foreign matter is not detected.

[0055] In actual detection, the m1 values corresponding to b1, b2 and b3 are calculated simultaneously, and the judgment is made in parallel. When the m1 value corresponding to one kind of metal foreign matter meets the judgment condition formula, it is considered that the metal foreign matter is detected.

[0056] A set of data in actual detection is as follows (the following values have been normalized) :

[0057] Table 1 measured data

[0058] Table 2 comparison of measured precision data

[0059] Table 2 shows that the diameters of the metal foreign matters that can be detected by the traditional detection method and the method provided in the embodiment under the same conditions, the smaller the value, the smaller the metal ball that can be measured, the higher the precision. From Table 2, it can be seen that the detection precision of the method is higher than that of the traditional detection method.

[0060] In the embodiment, it is considered that as long as m1>0, the foreign matter is detected. In actual use, it is a reasonable practice to take m1>0.1*W 1-p1 is a reasonable practice, where W 1-p1The reason is that, although theoretically, as long as the calculated metal signal m1 is greater than 0, it means that there is metal, due to test errors and fluctuations of product and metal signals, even if there is no metal in fact, the measured m1 is still a value close to 0 rather than 0, so the threshold is set to 0.1*W 1-p1 It is a reasonable approach in engineering to take into account the detection accuracy and stability.

[0061] It should be noted that, as can be seen from the above calculation formula, if a=b, the calculation formula cannot obtain a result. The physical meaning is that the responses of the product and the metal in the strong and weak fields are completely consistent and cannot be distinguished, so the method provided in the embodiment cannot effectively detect the case where a and b have no obvious difference.

[0062] Further, the embodiment also provides a strong and weak field foreign matter detection device for a metal detector, which comprises a memory, a processor, and a program stored in the memory. The processor implements steps S1-S3 of the foregoing method when executing the program, and the specific execution process is consistent with the foregoing, which will not be repeated here.

[0063] Further, the embodiment also provides a storage medium having a program stored thereon. The program is executed to implement steps S1-S3 of the foregoing method, and the specific execution process is consistent with the foregoing, which will not be repeated here.

[0064] The preferred embodiments of the present application are described in detail above. It should be understood that those skilled in the art can make many modifications and changes without creative labor based on the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment based on the prior art according to the concept of the present application shall be within the protection scope defined by the claims.

Claims

1. A strong-weak field foreign object detection method for a metal detection machine, characterized by, The method comprises the following steps: obtaining a weak-field detection signal and a strong-field detection signal of a product to be detected; calculating a metal foreign object signal value based on the weak-field detection signal, the strong-field detection signal, and a qualified product coefficient and a metal foreign object coefficient determined in advance, the qualified product coefficient being different from the metal foreign object coefficient; judging whether the metal foreign object signal value is greater than a preset threshold value: if yes, it is considered that a metal foreign object is detected, otherwise, it is considered that a metal foreign object is not detected.

2. The strong-weak field foreign object detection method for a metal detector according to claim 1, characterized by, The metal foreign object signal value is expressed as: wherein m1 is the metal foreign object signal value, a is the qualified product coefficient, b is the metal foreign object coefficient, W1 is the weak-field detection signal, and W2 is the strong-field detection signal.

3. The strong-weak field foreign object detection method for a metal detector according to claim 1, characterized by, The determination process of the qualified product coefficient and the metal foreign object coefficient specifically comprises: measuring a qualified product signal under a weak field and a qualified product signal under a strong field respectively; calculating the qualified product coefficient based on the qualified product signal under the weak field and the qualified product signal under the strong field; measuring a product signal containing a specific metal foreign object under a weak field and a product signal containing a specific metal foreign object under a strong field respectively; calculating the metal foreign object coefficient based on the product signal containing the specific metal foreign object under the weak field and the product signal containing the specific metal foreign object under the strong field.

4. The strong-weak field foreign object detection method for a metal detector according to claim 3, characterized by, The eligible product coefficient is expressed as: a = W 1-p2 / W 1-p1 where a is a qualified product coefficient, W 1-p1 is a qualified product signal under a weak field 1-p2 is a qualified product signal under a strong field.

5. The strong-weak field foreign object detection method for a metal detector according to claim 3, wherein, The metal foreign matter coefficient is expressed as: b = W 1-m2 / W 1-m1 where b is the metal foreign matter coefficient, W 1-m1 is the product signal containing a specific metal foreign matter under a weak field, W 1-m2 is the product signal containing a specific metal foreign matter under a strong field.

6. The strong-weak field foreign object detection method for a metal detector according to claim 3, wherein, The specific metal foreign object includes iron, non-ferrous metal, and stainless steel.

7. The strong-weak field foreign object detection method for a metal detector according to claim 1, wherein, The preset threshold value is 0.

8. The strong-weak field foreign object detection method for a metal detector according to claim 1, wherein, The preset threshold value is one-tenth of the qualified product signal under the weak field in the process of determining the qualified product coefficient.

9. A strong-weak field foreign object detection device for a metal detection machine, comprising a memory, a processor, and a program stored in the memory, wherein, The processor implements the method of any one of claims 1-8 when executing the program.

10. A storage medium having stored thereon a program, characterized by The program is executed to implement the method of any one of claims 1-8.

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