JP2008267869A - Metal detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate weight of inspected matters with utilizing detection signal due to material effect detected when the inspected matters are inspected with a metal detector. <P>SOLUTION: The detector includes: a second phase setting device 11 setting a phase so as to maximize the detection signal based on material effect of inspected matters; a second detector 9 for detecting the output signals from receiving coils 2, 3 with the phase set by the second phase setting device 11; a magnifier 16 for magnifying the output signals from the second detector 9; a filter 17 for removing noise from the output signals; an A/D convertor 14 for digitalizing the detection signals after removing noise; a CPU part 15 for computing the weight of the inspected matters based on the correlation formula or the data map with respect to the output signals, from the output signals of the A/D convertor; and a memorizing device part 19, placed to the CPU part 15, for memorizing the correlation formula or the data map. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal detector for detecting a metal or a metal component mixed in an article to be inspected, and more specifically, based on fluctuations in a magnetic field when an article to be inspected such as food passes through an alternating magnetic field. The present invention relates to a metal detector for determining the presence or absence of a metal or metal component in an inspection article.

  In general, a metal detector detects contamination of a metal to be inspected based on a change applied to an inspection magnetic field by passing the object to be inspected through a detection head portion (detection coil portion). It is configured as follows. Here, the detection head unit is composed of one excitation coil through which an alternating current flows and a pair of reception coils arranged at positions to receive magnetic lines of force generated by the alternating magnetic field from the excitation coil. The pair of receiving coils are connected to each other with opposite polarities to form a pair of receiving coils, and each receiving coil has the same size and the same three-dimensional positional relationship with respect to the exciting coil. It is arranged to be. Therefore, the magnitudes of the voltages induced in the pair of receiving coils by the alternating magnetic field are substantially equal to each other, and at the output end of the receiving coil, the induced voltages of the pair of receiving coils are canceled and no output voltage is generated. A so-called zero equilibrium state is maintained. When the metal body is moved in the space between the exciting coil and the receiving coil in this zero equilibrium state, a local change occurs in the magnetic field according to the movement of the position in the traveling direction, and the number of flux linkages of the receiving coil is increased. The amount of change appears as a detection signal of the metal body at the output end of the receiving coil. In this way, metal contamination in the article to be inspected is detected. The detection signal output to the output end of the receiving coil in this way has an amplitude and a phase that differ depending on the type of metal that is the detection target.

  By the way, in this kind of metal detector, a detection signal may be generated not only by the metal in the inspected article but also by the inspected article itself. In particular, when the article to be inspected is meat containing a large amount of electrolyte components, the magnetic flux in the search coil changes and a large detection signal is generated. This phenomenon is called a material effect (product effect) or a product effect (product effect), and is superimposed on the detection signal of the metal body as noise, which causes a decrease in detection accuracy of the metal body.

  For this reason, in this type of metal detector, there is a problem of minimizing the material effect and increasing the detection accuracy for a metal foreign object or the like as a detection target. In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. H11-260260, a technology that can automatically track a phase angle that is corrected and set so as to stably maintain a state in which a detection signal output value by a material effect is substantially zero. Has been proposed. Further, in Patent Document 2, the material effect detection signal based on the reference sample that does not include the metallic foreign matter of the article to be inspected is digitally converted and stored. There has been proposed a technique capable of detecting a phase difference.

  However, all the conventional techniques related to material effects, including the techniques disclosed in the above-mentioned patent documents, all relate to a method of removing the material effects, assuming that this material effect reduces the detection sensitivity of the metal detector. There is no disclosure of the concept of using detection signals by material effects.

Japanese Patent Laid-Open No. 5-93782 JP-A-6-160542

    The present invention has been made in view of such circumstances, and its purpose is to use the detection signal by the material effect detected when the inspection object is inspected by a metal detector, and the weight of the inspection object. Is to be able to estimate.

In order to achieve the above object, the metal detector according to the present invention comprises:
An excitation coil that generates an alternating magnetic field and a plurality of receiving coils that are arranged in the alternating magnetic field generated by the excitation coil, and detects a metal body mixed in an article to be inspected that passes through the alternating magnetic field In the metal detector that
A phase setter for setting a phase at which the detection signal based on the material effect of the article to be inspected is maximized;
A detector for detecting the detection signal output from the receiving coil at a phase set by the phase setter;
An A / D converter for digitizing the output signal of the detector;
From the output signal of the A / D converter, a controller for calculating the weight of the article to be inspected based on a correlation equation or a data map of a weight value with respect to the output signal;
And a storage unit that is attached to the controller and stores the correlation formula or data map (first invention).

  In the present invention, a sample article having a known weight is passed through the alternating magnetic field, the weight of the sample article is set by an operation setting display unit attached to the controller, and the correlation equation or data map is set by the controller. It is preferable to store the correlation equation or the data map in the storage unit (second invention).

  Further, an allowable weight range of the inspected article is set, and when the weight of the inspected article calculated by the controller is not within the allowable weight range, a weight defect signal is transmitted from the controller. Good (third invention).

Further, in the present invention, when a block article composed of a plurality of articles having a uniform weight is an article to be inspected, the number of block articles is set by the operation setting display unit attached to the controller, An operation of passing an inspection article composed of a set number of block articles through the alternating magnetic field and storing data relating to a detection signal based on a material effect in the storage device unit is performed for various numbers of operations. Perform on block goods,
During actual operation, the number of block articles is set in the operation setting display section, and a detection signal based on a material effect when the article to be inspected is passed through the alternating magnetic field is stored in the storage section. When the deviation from the data relating to the detected signal exceeds an allowable value, it is preferable that an unqualified product signal is transmitted from the controller (fourth invention).

  According to the present invention (first invention), in addition to the detection of the presence or absence of a metal body in an article to be inspected, such as food, in particular, by a metal detector, even if the article to be inspected does not contain a metal body, The weight of the article to be inspected can be estimated using a detection signal by a material effect detected when the article to be inspected is inspected. Conventionally, when inspecting a product, it is necessary to perform both an inspection of contamination by a metal detector by a metal detector and an inspection of whether or not it is within a predetermined weight range by a weight sorter. It was necessary to prepare both weight sorters. On the other hand, according to the present invention, since one metal detector can perform both functions of checking for foreign metal contamination and checking the weight, it can contribute to the purchase cost and the saving of installation space.

  Further, according to the second invention, by using a sample article having a known weight, it is possible to easily obtain a correlation equation of the weight value with respect to the detection signal based on the material effect. Further, it is also possible to pass an article to be inspected having a constant moisture and salt content but different amounts, measure the weight with another scale, and set the weight on the operation setting display unit. .

  According to the third aspect of the invention, based on the weight defect signal transmitted when the weight of the article to be inspected is not within the allowable weight range, the weight-inspected article to be inspected is reliably determined by the sorting device or the like installed in the subsequent stage. Can be eliminated.

  Further, according to the fourth invention, for example, for an article to be inspected in which a predetermined number of slice hams are vacuum-packed, data related to detection signals based on the material effect for each number of slice hams is collected and stored. In actual operation, the number of sheets to be included in the vacuum-packed slice ham to be inspected is input, the stored data is called, and this data and the article to be inspected are passed through the magnetic field. By comparing with a detection signal based on the material effect, it is possible to inspect whether or not a predetermined number of slice hams are included in the pack, and to eliminate unqualified products. In this case, the ineligible product means a “missing product” in which a predetermined number of articles are not contained in the pack and an “appropriate quantity product” in which a larger number of articles are contained in the pack. Yes.

  Next, specific embodiments of the metal detector according to the present invention will be described with reference to the drawings.

  FIG. 1 is a system configuration diagram of a metal detector according to an embodiment of the present invention.

  In the present embodiment, a detection coil unit 1 including a pair of receiving coils 2 and 3 and an excitation coil 4 is disposed in the middle of a conveyance conveyor (not shown) that conveys an article to be inspected. Here, an alternating current obtained by power amplification of the signal from the reference signal generator 5 by the amplifier 6 flows in the excitation coil 4, thereby forming an alternating magnetic field. The pair of receiving coils 2 and 3 are connected to each other with opposite polarities, and the coils 2 and 3 are arranged so as to have the same size and the same three-dimensional position relative to the exciting coil 4. Has been. Thereby, the magnitude | size of the voltage induced by a pair of receiving coils 2 and 3 by an alternating magnetic field becomes substantially equal. As a result, at the output ends of the receiving coils 2 and 3, the induced voltages of the receiving coils 2 and 3 are canceled and no output voltage is generated, so that a so-called zero equilibrium state is maintained.

  In this zero equilibrium state, when the metal body is moved in the space of the detection coil section 1 composed of the pair of receiving coils 2 and 3 and the excitation coil 4, the magnetic field to be configured is localized according to the movement of the position in the traveling direction. Change occurs, and the number of interlinkage magnetic fluxes of the receiving coils 2 and 3 changes. Therefore, only this change appears at the output end of the receiving coils 2 and 3 as a detection signal of the metal body. This detection signal is amplified by the amplifier 7 and sent to the first detector 8 and the second detector 9.

  Reference signals from a first phase setter 10 and a second phase setter 11 are input to the first detector 8 and the second detector 9, respectively. Here, a metal body such as iron, stainless steel, and aluminum mixed in the inspected article has a phase characteristic peculiar to the detection signal of the metal body, and also in an inspected article that does not include a metal foreign object. It has phase characteristics, that is, a material effect due to the influence of the electrolyte such as salt content. Considering this, the first phase setter 10 sets a phase having a high sensitivity to the metal body with a phase having little influence of the material effect. On the other hand, the second phase setter 11 sets the phase having the greatest influence of the material effect. Thus, the metal detector detection signal is detected by the first detector 8, the analog detection signal generated by the first detector 8 is amplified by the amplifier 12, noise is removed by the filter 13, and the A / D converter The signal is digitized at 14 and sent to the CPU section (controller) 15. Further, the material effect signal is detected by the second detector 11, the analog detection signal generated by the second detector 11 is amplified by the amplifier 16, noise is removed by the filter 17, and the A / D converter 14 is used. The signal is digitized and sent to the CPU unit (controller) 15.

  The CPU section 15 is provided with an operation setting display section 18 and a storage device section 19. The operation setting display unit 18 can perform various operations and settings, and can display the setting contents and inspection results. The storage unit 19 stores setting values for inspection for each of several tens of types of products (inspected articles), and the setting contents are automatically obtained by calling the inspected articles (product types). Can be changed. The CPU unit 15 performs various calculations and sets the optimum phase angle for each article to be inspected stored in the storage device unit 19 in the first phase setter 10 and the second phase setter 11. In addition, the CPU unit 15 outputs a control signal to the reference signal generator 5 and performs control to change the frequency of the reference signal generator 5 so as to obtain an optimal alternating magnetic field according to the type of metal.

  In this embodiment, focusing on the fact that a high correlation is exhibited between the output signal of the A / D converter 14 and the weight of the article when the article is passed through an alternating magnetic field, this correlation equation or data The map is stored in advance in the storage unit 19. This correlation equation or data map is obtained by passing a sample article having a known weight through the detection coil unit 1, setting the weight of the sample article on the operation setting display unit 18, and calculating on the CPU unit 15. .

  When the article to be inspected is a plurality of articles having a uniform weight (for example, sliced ham), the number of the articles is set by the operation setting display unit 18 and is composed of the set number of articles. The correlation equation or the data map is obtained by performing an operation of passing the article to be inspected through the detection coil unit 1 and storing the data related to the detection signal based on the material effect in the storage unit 19 on various numbers of articles. Can be obtained.

  Next, an experimental result when sliced ham is used as an article to be inspected is shown.

  In this experiment, sliced ham samples of 2 pieces, 4 pieces, 6 pieces, 8 pieces, 10 pieces and 12 pieces were prepared as articles to be inspected, and their weights were measured with an electronic balance. At the same time, each sample was passed through the detection coil unit 1 five times, and the detected voltage value (V) was observed. The measurement results are shown in Table 1. Moreover, the result of having calculated | required the relationship between the average voltage value of 5 times and a weight value based on this Table 1 is shown by FIG.

  From FIG. 2, the detection voltage value (V) and the weight value (g) can be approximated by a linear expression y = 0.0954x−0.1155, and the correlation coefficient is 0.9986, indicating a high correlation. I understand. From the above results, it is clear that the metal detector can be used not only for metal detection but also for weight measurement of products with a large material effect.

  As described above, the weight measurement result of the article to be inspected is displayed on the operation setting display unit 18. Further, an allowable weight range is set on the operation setting display unit 18 and the set value is stored in the storage device 19 in advance, and the weight of the article to be inspected calculated by the CPU unit 15 is the allowable weight range. When it is not within, it is preferable that a weight defect signal is transmitted from the CPU unit 15 to display “weight defect” on the operation setting display unit 18.

Further, when the article to be inspected is a plurality of articles (block articles) having a uniform weight such as sliced ham, the number of the block articles is set by the operation setting display unit 18 and the storage device unit is previously set. 19, and when the measured weight exceeds the allowable weight range, an unqualified product signal is transmitted from the CPU unit 15 and the operation setting display unit 18 is displayed as “unqualified product”. Is good.

  In the present embodiment, the first phase setter 10 sets a phase having a low effect of the material effect and a high sensitivity to the metal body, and the first detector 8 outputs a detection signal of the metal body. Although it is configured to detect, three or more phase setters and detectors are provided, and a plurality of sensitive phases are set according to the type of metal body such as iron, stainless steel, and aluminum. It can also be.

  FIG. 3 is a system configuration diagram of a metal detector according to another embodiment of the present invention.

  In the embodiment, a plurality of phase setters including a first phase setter 10 for mainly detecting a metal contamination detection signal and a second phase setter 11 for mainly detecting a product influence signal. In this embodiment, the 90 ° phase shifter 20 is used to acquire two-dimensional data in the X-axis direction and the Y-axis direction that are orthogonal to each other. In FIG. 3, parts that are the same as or correspond to those in the previous embodiment shown in FIG. 1 are assigned the same reference numerals, and detailed descriptions thereof are omitted.

  FIG. 4 is a graph of two-dimensional data of a detection signal that changes with time when a sample is passed through the detection coil unit 1. As shown in the figure, a phase change occurs in the detection signal, and the time-series data appears on the axis inclined by the angle θ counterclockwise from the X-axis direction. In this case, the signal peaks are A and A ′. The magnitude of the signal in the Y-axis direction is Asinθ.

  Here, when the coordinate axis is rotated clockwise by an angle (90 ° −θ), as shown in FIG. 5A, the new coordinate axes become X ′ and Y ′. When the coordinate conversion process is performed in the CPU unit 15, the data appears on the Y ′ axis, and the peaks of the signals are A and A ′. This state is when the signal of the material effect is maximized.

  Next, when the coordinate axis is rotated counterclockwise by the angle θ from the state shown in FIG. 4, the new coordinate axes become X ″ and Y ″ as shown in FIG. For a simple coordinate axis, the data is projected on X ″ and the signal component on the Y ″ axis is zero. This state is a state in which the material effect is minimized and the metal detection sensitivity is maximized.

  Thus, in this embodiment, a reference signal is input to the first detector 8 and the second detector 9 using the 90 ° phase shifter 20 with respect to the signal obtained from the detection coil unit 1. By performing the coordinate conversion processing in the CPU unit 15, the material effect signal and the metal detection signal can be easily maximized without using a special circuit.

The system block diagram of the metal detector which concerns on one Embodiment of this invention. Graph showing experimental results when using sliced ham as an inspection article The system block diagram of the metal detector which concerns on other embodiment of this invention. Graph showing two-dimensional data of detection signal that changes over time Graph showing two-dimensional data when the coordinate axis is rotated

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Detection coil part 2, 3 Reception coil 4 Excitation coil 5 Reference signal generator 6, 7, 12, 16 Amplifier 8 1st detector 9 2nd detector 10 1st phase setter 11 2nd phase setters 13 and 17 Filter 14 A / D converter 15 CPU unit 18 Operation setting display unit 19 Storage unit 20 90 ° phase shifter

Claims (4)

An excitation coil that generates an alternating magnetic field and a plurality of receiving coils that are arranged in the alternating magnetic field generated by the excitation coil, and detects a metal body mixed in an article to be inspected that passes through the alternating magnetic field In the metal detector that
A phase setter for setting a phase at which a detection signal based on a material effect of the article to be inspected is maximized;
A detector for detecting the detection signal output from the receiving coil at a phase set by the phase setter;
An A / D converter for digitizing the output signal of the detector;
From the output signal of the A / D converter, a controller for calculating the weight of the article to be inspected based on a correlation equation or a data map of a weight value with respect to the output signal;
A metal detector, comprising: a storage unit attached to the controller for storing the correlation formula or the data map.   A sample article having a known weight is allowed to pass through the alternating magnetic field, the weight of the sample article is set by an operation setting display unit attached to the controller, and the correlation equation or data map is calculated by the controller. The metal detector according to claim 1, wherein the correlation formula or the data map is stored in the storage unit.   The allowable weight range of the inspected article is set, and when the weight of the inspected article calculated by the controller is not within the allowable weight range, a weight defect signal is transmitted from the controller. Metal detector. When a block article composed of a plurality of articles having a uniform weight is an article to be inspected, the number of block articles is set by the operation setting display unit attached to the controller, and the set number of block articles is set. An operation to store the data related to the detection signal based on the material effect in the storage unit, and perform this operation on various numbers of block articles.
During actual operation, the number of block articles is set in the operation setting display section, and a detection signal based on a material effect when the article to be inspected is passed through the alternating magnetic field is stored in the storage section. 2. The metal detector according to claim 1, wherein when the deviation from the data relating to the detected signal exceeds an allowable value, an unqualified product signal is transmitted from the controller.

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