JP6622462B2 - Magnetic metal foreign object detection method and detection apparatus - Google Patents

Description

  The present invention relates to a detection method and a detection apparatus for a magnetic metal foreign object, and more specifically, a detection method and detection suitable for detecting a magnetic metal foreign object contained in an inspection object that moves in one direction in a magnetic shield space. Relates to the device.

  It is well known that a magnetic metal foreign object is detected by measuring the magnetic force of a magnetic metal foreign object contained in an object to be moved intermittently or continuously in one direction by a plurality of magnetic sensors. It is also known that the magnetic sensor is installed inside a magnetic shield box that forms a magnetic shield space, and the magnetism of the magnetic metal foreign object is measured when the inspection object passes through the magnetic shield box. It is.

  For example, a signal detection device described in Japanese Patent Laid-Open No. 2005-351746 (Patent Document 1) includes a plurality of magnetic sensors that detect a magnetic field from a subject such as meat as a signal from the subject, and a plurality of magnetic sensors. Signal processing detecting means for detecting a magnetic field from the subject in accordance with the output signal of the magnetic sensor, the magnetic sensor is installed inside the magnetic shield box, and the signal processing detecting means calculates at least a pair of differences of the output signals of the plurality of magnetic sensors. Includes differential means to take. The detection apparatus also has a summation means for obtaining the sum of the output signals of the difference means, and the difference means can derive an absolute value of the difference.

  In such a signal detection device, components of external environmental noise applied to each of the magnetic sensors are removed by taking the difference between the output signal pairs of the magnetic sensors. Even if the difference is taken, the reduction of the detection signal for the subject in each magnetic sensor is suppressed, and the signal-to-noise ratio (S / N ratio) can be improved. Further, by obtaining the absolute value of the difference and adding the absolute values, the signal component can be amplified, and the detection accuracy can be improved.

JP 2005-351746 A

  In the conventional technology that calculates the difference between the output signals of the paired magnetic sensors, if the component of external environmental noise is large, the magnetic signal from the object under test is reduced when the difference is calculated, and the signal-to-noise ratio It may be difficult to improve.

  Accordingly, an object of the present invention is to provide a magnetic metal foreign object detection method and a detection apparatus that have been improved to remove or reduce components of external environmental noise.

More in order to solve the above problems, one where the present invention is applied is installed in the magnetically shielded space for the detection of magnetic metallic foreign matter contained in the object to be inspected which moves Oite the magnetically shielded space This is a detection method using a magnetic sensor.
A reference sensor that considers that the plurality of magnetic sensors detect noise in the magnetic shield space, and a magnetic signal sensor for detecting magnetism from the magnetic metal foreign object, and a signal value of the reference sensor Using the absolute value or a value that does not exceed the absolute value as the primary calculation reference value, the calculation for obtaining the following primary difference and the subsequent n-th difference from the output signal of the magnetic signal sensor is repeated, and the n-th difference is obtained. the detection method signal caused by free environment noise and detecting a magnetic signal from the magnetic metal foreign substance on the basis of the output signal at the n-th order difference when it becomes less than a predetermined value .
Primary difference = (Absolute value of output signal of magnetic signal sensor) − (Primary calculation reference value)
nth order difference = ((n−1) th order difference) − (nth order calculation reference value)
However, the nth calculation reference value = (n−1) the calculation reference value set lower than the next calculation reference value n: 2 or an integer greater than 2

  In order to solve the above-mentioned problem, another object of the present invention is a detection device for detecting a magnetic metal foreign object.

  In this detection apparatus, the present invention is characterized in that the detection method according to the present invention is used.

In the method and apparatus for detecting a magnetic metal foreign object according to the present invention, a magnetic signal sensor for detecting a magnetic signal from the magnetic metal foreign object and external environmental noise are detected in the difference calculation between the magnetic sensor output signal and the calculation reference value. Since the difference calculation is repeated using the reference sensor and the absolute value of the signal of the reference sensor or a value that does not exceed the absolute value as the calculation reference value , the external environmental noise component is removed or reduced from the magnetic signal. In addition, the reduction of the processing signal of the magnetic signal sensor can be suppressed, and the detection accuracy of the magnetic metal foreign matter is improved.

The drawings illustrate certain embodiments of the invention according to the present disclosure and include selective and preferred embodiments as well as essential configurations of the invention.
The figure which shows the internal structure of the magnetic shield box used for the detection apparatus which concerns on this invention. The II-II arrow directional view of FIG. The block diagram of an analog / digital signal. The block diagram of a control part. The figure which illustrates the signal of the external environmental noise which a magnetic sensor outputs. FIG. 6 is a view similar to FIG. 5 when an iron ball is passed through the detection device. The figure which illustrates repetition of difference calculation by (1)-(8). The block diagram of the analog / digital signal which shows an example of an embodiment.

  With reference to the attached drawings, the details of the magnetic metal foreign object detection method and the detection apparatus to which the detection method is applied according to the present invention will be described as follows.

  FIG. 1 is a side view of an inspection process in which an example of a detection apparatus 1 according to the present invention is used, and FIG. 2 is a view taken along the line II-II in FIG. However, FIG. 1 shows the internal structure of the magnetic shield box 2 used in the detection apparatus 1, not the external structure thereof. The inspection process of FIGS. 1 and 2 is for detecting magnetic metal foreign matter contained in an object 100 to be inspected such as food such as meat, beverages, and pharmaceuticals. The inspection process includes a detection device 1 and a conveying means. The belt conveyor 4 and the magnetizing means 5 are included. The detection device 1 includes a magnetic force detection unit 23 and a control unit 26 that is electrically connected to the magnetic force detection unit 23. The belt conveyor 4 is driven by the rolls 4a and 4b and travels continuously or intermittently in the machine direction MD. The belt conveyor 4 also has an upstream portion 5a and a downstream portion 5b, and a magnetic shield box 2 that forms a magnetic shield space is installed between the upstream portion 5a and the downstream portion 5b.

  In the inspection process shown in the figure, when the inspection object 100 passes through the magnetizing means 5, a magnetic metal foreign substance (not shown) mixed in the inspection object 100 becomes apparent with increased magnetic force or enhanced magnetic force. In the process in which the inspection object 100 passes through the magnetic shield box 2, a magnetic signal from the magnetic metal foreign object is detected by a plurality of postscript magnetic sensors S in the magnetic force detection unit 23 of the detection device 1.

  The magnetizing means 5 used in the inspection process has a pair of permanent magnets 19 and 20 that are opposed to each other with the belt conveyor 4 interposed therebetween, and between the N pole of the permanent magnet 19 and the S pole of the permanent magnet 20. A DC magnetic field is formed. The permanent magnets 19 and 20 can be replaced with electromagnets.

The magnetic shield box 2 having a two-layer structure illustrated in FIGS. 1 and 2 used in the magnetic force detection unit 23 is formed of a highly permeable material such as permalloy, and includes an upstream opening 60a and a downstream opening 60b. And have. The inspection object 100 enters the magnetic shield box 2 from the upstream opening 60a and exits from the downstream opening 60b. The magnetic sensor S installed inside the magnetic shield box 2 includes a magnetic sensor S ₁ -S ₈ attached to the base board 70 at a position where the magnetic sensor S is close to and can be opposed to the inspection object 100, and the ceiling. and a magnetic sensor S ₉ mounted in the part. In the process in which the inspection object 100 passes through the magnetic shield box 2, several magnetic sensors S ₁ -S ₈ arranged at almost equal intervals in the width direction of the belt conveyor 4, that is, in the crossing direction orthogonal to the machine direction MD, are covered. Magnetism from the magnetic metal foreign matter contained in the inspection object 100 is detected.

The magnetic sensor S ₉ attached to the ceiling portion of the magnetic shield box 2 is more in contact with the magnetic shield box 2 than any of the magnetic sensors S _{1 to} S ₈ that are in use in a substantial sense with respect to the inspection object 100. The shortest distance from the inspected object 100 is large. The magnetic sensor S ₉ is not used to detect the magnetism from the inspection object 100 but is used as a reference sensor for detecting the magnetic noise inside the magnetic shield box 2 due to the external environmental noise that has entered the magnetic shield box 2. Has been. However, as described later, in the detection device 1, the magnetic sensors S _{1 to} S ₈ are always used, but the magnetic sensor S ₉ is used as necessary.

In the present invention, the types of the magnetic sensors S, that is, the magnetic sensors S _{1 to} S ₈ and the magnetic sensors S ₉ are not specified, and are commonly used in the art, such as flux gate sensors and MI sensors, A SQUID magnetic sensor or the like can be used. However, among them, the fluxgate sensor is particularly excellent in terms of ease of handling.

3 and 4 are block diagrams in the case where the detection device 1 uses the magnetic sensors S _{1 to} S ₈ and does not use the magnetic sensor S ₉ . In these drawings, the control unit 26 of the detection apparatus 1 includes a signal processing unit 28, a difference calculation unit 32, and the like, and the difference calculation unit 32 includes a pass / fail determination unit 33. It is to be noted that the block diagram in the case of using a magnetic sensor S ₉ are shown in later Figure 8.

The signal processing unit 28 is an A / D converter 31 that processes the magnetic force detection signals from the magnetic sensors S _{1 to} S ₈ in the magnetic force detection unit 23 based on predetermined processing conditions, and then converts the analog signals into digital signals. processing and outputs the detection signal from the magnetic sensor S ₁ -S ₈ as a processing signal to the differential operation circuit 32. In the case of FIG. 3, the signal processing means 28 is an amplifier 29 that amplifies the magnetic force detection signal from the magnetic force detection unit 23, and an analog that processes the amplified signal with a high-pass filter (HPF) and a low-pass filter (LPF). It has a filter 30 and an A / D converter 31 for digitally converting the filtered signal, and outputs the absolute value of the converted result to the difference calculation means 32 as a processed signal.

The difference calculation means 32 may be used as a first difference calculation means or as a second difference calculation means. In the difference calculation means 32 when used as the first difference calculation means, an even number of magnetic sensors S ₁ -S ₈ are used without using the magnetic sensor S ₉ which is the reference sensor shown in FIGS. Then, a pair of magnetic sensors is made, one of the pairs is treated as a reference sensor, and a differential calculation (see FIG. 7) is performed between the pairs. In addition, the difference calculation means 32 when used as the second difference calculation means uses the magnetic sensor S ₁ -S ₈ and the magnetic sensor S _{9 as the} reference sensor, and each of the magnetic sensors S ₁ -S ₈ and the reference performing infra difference calculation (see FIG. 8) between the sensor S _9. In the difference calculation means 32 of FIG. 3 used as the first difference calculation means, a processing signal for the inspected object 100 that has been digitally converted is used in each of the pairs formed between the magnetic sensors S _{1 to} S _8. Then, the difference calculation is performed. The difference calculation means 32 also includes an absolute value conversion circuit for deriving the absolute value of the difference obtained by the difference calculation, and a sum circuit for calculating the sum of the absolute values. The pairs of magnetic sensors illustrated in FIG. 3 are S ₁ -S ₅ , S ₂ -S ₆ , S ₃ -S ₇ , and S ₄ -S ₈ .

  The pass / fail determination means 33 determines whether or not magnetic metal foreign matter is mixed in the inspection object 100, and the sum of the absolute values of the differences obtained by the difference calculation means 32 is a threshold 34 (see FIG. 4). The inspection object 100 exceeding is determined as a defective product, and the inspection object 100 exceeding is determined as a non-defective product. The level of the threshold 34 can be changed as appropriate by using setting means 36 (see FIG. 4) provided in the control unit 26.

The determination result in the pass / fail determination means 33 can be output to the display unit 35 (see FIG. 4) formed by a liquid crystal display or the like. For the inspected object 100 determined to be defective, the voltage of each signal of the magnetic sensor S, the number of defective products, the time when the defective products are detected, and the like can be displayed on the display unit 35. For the object 100 to be inspected, it is also possible to specify the presence site of the magnetic metal foreign object from the display contents of each of the magnetic sensors S _{1 to} S ₈ .

  In the inspection process of FIG. 1, when an alarm alarm device is installed and the pass / fail determination means 33 determines that the inspection object 100 is defective, the operator can be immediately notified of the result.

  In the present invention, the number and arrangement of magnetic sensors for detecting magnetism from a magnetic metal foreign material are not limited to the illustrated example, and can be determined as appropriate according to the properties of the object 100 to be inspected.

FIG. 5-7 is a diagram for illustrating how the difference calculation proceeds when the difference calculation means 32 is the first difference calculation means using the magnetic sensors S _{1 to} S ₈ of FIG.

(1) to (8) in FIG. 5 show the magnetic sensor S ₁ processed in the block diagrams of FIGS. 3 and 4 when there is 17 Hz external environmental noise in the vicinity of the upstream side in the inspection process of FIGS. -S ₈ shows an analog signal and peak voltage (mV) in ch 1 to ch ₈ for displaying each processed signal as an output. In the figure, pick up the magnetic sensor S ₄ and S ₅ of ch4 and ch5 positioned at the center of (the width direction of the magnetic shield box 2 which is perpendicular to the machine direction of the Figures 1 and 2) crossing the direction of the magnetic shield box 2 Noise signal is large, in the state that the noise signal picked up with the magnetic sensor S ₁ and S ₈ of ch1, ch8 located on both sides in the transverse direction is small.

(1) to (8) in FIG. 6 show analog signals in each of the magnetic sensors S _{1 to} S ₈ when an iron ball having a diameter of 0.5 mm passes directly under the magnetic sensor S ₆ under environmental noise of 17 Hz. Is shown. A foreign substance signal of Vp = 240 mV appears on ch6.

(1) in FIG. 7 - (8), under the external environment noise 17 Hz, the digital signal processing and difference calculation method when passed through an iron ball of 0.5mm diameter just below the magnetic sensor _{S 6} for ch6 It shows. Magnetic sensor _{S 6} for ch6 is making a magnetic sensor _{S 2} and a pair of ch2 (see FIG. 3).

In (1) in FIG. 7, the signal in the magnetic sensor _{S 6} with iron ball having a diameter of 0.5mm, which is a magnetic metal foreign object is Vp = 240 mV.

In (2) of FIG. 7, taking the absolute value of the magnetic sensor S ₂ and the magnetic sensor S _6, to obtain the graph A and graph B.

In (3) of FIG. 7, the signal magnitudes of ch2 and ch6 in (2) of FIG. 7 are compared, and the magnetic sensor of the channel with a small signal is used as a reference sensor, and noise inside the magnetic shield box 2 is reduced. It is assumed that it is detected. A magnetic sensor of a channel with a large signal is treated as a magnetic signal sensor for magnetic metal foreign matter. Therefore, in (2) in FIG. 7, the magnetic sensor _{S 2} of ch2 is a reference sensor, the magnetic sensor _{S 6} for ch6 is magnetic signal sensor. In starting the difference calculation, the value of the signal of the magnetic sensor S ₂ is smaller than the value of the signal in (2) of FIG. 7 or the peak value of 50 mV (see FIG. 5) of the signal in (2) of FIG. 40 mV is set as the noise reference value. When 40 mV is used as the noise reference value, the signal portion larger than 40 mV uses the waveform (raw waveform) of the signal in a form obtained by adding the portion to the noise reference value, and the signal portion of 40 mV or less is used. is carried out digital operations using noise reference value 40 mV, the magnetic sensor S _2, to obtain a curve C indicating the absolute value of the noise level. Graph C is a primary calculation reference value obtained from the magnetic sensor S ₂ is the reference sensor are used in later difference operation.

  In (4) of FIG. 7, a calculation for obtaining a difference (primary difference) between the graph B and the graph C (primary computation reference value) is performed, and the absolute value of the difference is obtained to obtain the graph D.

In (5) in FIG. 7, in the half of the graph C of (3) in FIG. 7, to obtain a graph E is a secondary calculation reference value for the reference sensor or the magnetic sensor S _2. The secondary calculation reference value is a value set lower than the primary calculation reference value.

  In (6) of FIG. 7, the calculation which takes the difference (secondary difference) of the graph D and the graph E (secondary calculation reference value) is performed, the absolute value of the difference is obtained, and the graph F is obtained.

  In (7) of FIG. 7, the graph C of (3) of FIG. 7 is set to 1/4, that is, the graph E of (5) of FIG. Get. The tertiary calculation reference value is a value set lower than the secondary calculation reference value.

  In (8) of FIG. 7, an operation for obtaining a difference (third-order difference) between the graph F and the graph G (third-order calculation reference value) is performed, and the absolute value of the difference is obtained to obtain a graph H.

  In the present invention, such a difference calculation is repeated, and the calculation ends when the level of the noise component in the difference becomes a predetermined value, for example, 5 mV or less. The predetermined value is set to be sufficiently smaller than the magnetic signal from the magnetic metal foreign object.

As is apparent from the graph H, according to the present invention, the difference calculation is repeated, for example, by obtaining the second order difference, the third order difference, or the nth order difference equal to or higher than the third order difference in FIG. 2 or an integer larger than 2), noise in the magnetic shield box 2, in other words, noise components caused by external environmental noise can be significantly reduced, and the signal-to-noise ratio can be improved. Even under external environmental noise, it is possible to reliably detect a weak magnetic force from a magnetic metal foreign object. However, in the repetition of the difference calculation, the calculation reference value is changed so that the nth order calculation reference value becomes smaller than the (n−1) th order calculation reference value. For example, the (n−1) th order calculation reference value is multiplied by a positive coefficient that does not exceed 1 to obtain the nth order calculation reference value. In the example of FIG. 7, the coefficient used for the (n−1) th order calculation reference value is ½ ⁿ⁻¹ , and the coefficient is sequentially reduced every time the difference calculation is repeated. The n-th order difference obtained for each pair of magnetic sensors is preferably synthesized by a sum circuit (see FIG. 3) and amplified with a signal component and compared with a threshold value 34 (see FIG. 4).

Noise reference value 40mV adopting in the example of FIG. 7 is also a value can Kotono set in consideration of the type and size of the metal in the magnetic metal foreign substance to be detected in the detection device 1. For example, in the detection of a magnetic metal foreign object, those skilled in the art will know that the foreign object signal as a magnetic metal foreign object is at least 240 mV if an iron ball having a diameter of at least 0.5 mm is to be detected. . Also, it is possible to experimentally know in advance the magnitude of the magnetic signal possessed by the smallest magnetic metal foreign object to be detected. Therefore, in order to determine a primary calculation reference value for obtaining a primary difference from a magnetic signal in which a 240 mV foreign matter signal and noise are mixed, for example, a magnetic signal of the magnetic sensor S ₆ , 1/2 of the foreign matter signal. A noise reference value of 40 mV, which is set to be small so as not to exceed the threshold value, is adopted. The signal value of the primary difference with respect to the 240 mV foreign object signal at that time is 240−40 = 200. The signal value of the secondary difference is obtained by reducing the secondary calculation reference value to be smaller than the primary calculation reference value, for example, to 1/2 of 40 mV, and becomes 200−20 = 180. The signal value of the third order difference is obtained by making the third order calculation reference value smaller than the second order calculation reference value, for example, 1/4 of 40 mV, and is 180-10 = 170. While the difference calculation is repeated in this manner while sequentially reducing the calculation reference value, the noise level is remarkably reduced, but the level of the foreign substance signal does not change significantly (see (8) in FIG. 7).

  However, if the primary calculation reference value for obtaining the primary difference is too large, the foreign object signal is excessively reduced, and the signal-to-noise ratio cannot be improved. For example, if the noise reference value and the primary calculation reference value are set to 200 mV for a foreign substance signal of 240 mV, and the calculation reference value is decreased by half each time the calculation is repeated, the signal value of the primary difference is 240. -200 = about 40. The signal value for taking the secondary difference is 40-100 = -60, and the foreign substance signal disappears when the secondary difference is taken. Therefore, in this way of taking the noise reference value and the primary calculation reference value, it is meaningless to repeat the difference calculation.

Although depending on the arrangement of the magnetic sensors S _{1 to} S ₈ , when the magnetic metal foreign object is a large one such as an iron ball having a diameter of 1 mm, for example, the magnetic sensors S ₅ adjacent to each other sometimes referred to as S ₆ detects a substantially foreign object signal of the same level. In such a case, when the magnetic sensor S ₅ and S ₆ are used in pairs, so that the foreign material signal is eliminated in the difference calculation. Therefore, when making a pair of magnetic sensors in the detection apparatus 1, it is preferable not to make a pair with an adjacent magnetic sensor.

Such a difference calculation in the difference calculation means 32 can be summarized as follows. That is, among the magnetic signals from the magnetic metal foreign matter, the minimum value of the level of the magnetic signal to be detected is converted into an absolute value, and an appropriate value that does not exceed 1/2 of the absolute value is set as the noise reference value. A primary calculation reference value is obtained. From the output signal of the magnetic sensor, for example, the magnetic sensor S ₆ , the calculation for obtaining the first order difference and the subsequent nth order difference defined below is repeated, and a signal caused by the environmental noise included in the nth order difference is predetermined. When the value becomes less than 5 mV, for example, the calculation is stopped, and the magnetic signal from the magnetic metal foreign matter is detected based on the output signal in the n-th order difference.
Primary difference = (Absolute value of magnetic sensor output signal) − (Primary calculation reference value)
nth order difference = ((n−1) th order difference) − (nth order calculation reference value)
However, the nth calculation reference value = (n−1) the calculation reference value set lower than the next calculation reference value n: 2 or an integer greater than 2

Magnetic Sansa S ₂ that the reference sensor in the example of FIG. 7, the magnetic signal detected is primarily that of environmental noise. It is considered that the absolute value of the level of the magnetic signal does not exceed 1/2 of the value when the minimum magnetic signal of the magnetic metal foreign object to be detected is converted into an absolute value.

FIG. 8 is a block diagram similar to FIG. 3 showing an example of an embodiment of the present invention. Unlike the difference calculation means 32 in FIG. 3, the difference calculation means 32 of the detection device 1 based on this block diagram is used as the second difference calculation means in the present invention. Further, as the magnetic sensor S for the second difference calculation means, the magnetic sensors S _{1 to} S ₈ and the reference sensor S ₉ illustrated in FIG. 2 are used. Processing signals from the reference sensor S ₉ is used for erasing or reducing the noise component in the processing signals from each of the magnetic sensors S ₁ -S _8. That is, in FIG. 7, a pair is formed between the magnetic sensors S _{1 to} S ₈ , and a noise reference value is determined for a processing signal of one magnetic sensor in each pair, for example, the magnetic sensor S ₂ , and the primary calculation reference although the yield value, in FIG. 8, reference sensor determines the noise reference value and the primary calculation reference value for processing signals S _9, the magnetic sensor S ₁ -S ₈ are the primary calculation reference value Use for. For example, the reference sensor _{S 9} is also the magnetic sensor _{S 2,} the reference sensor with respect to the magnetic sensor _{S 6.} Procedure for obtaining a reference sensor primary calculation reference value defining a reference noise value for processing signals S _9, and procedures for sequentially reduced operational reference value for each repeated differential operation, the magnetic sensor S ₂ in FIG. 7 Same as the case.

If detection device 1 is intended to use a reference sensor S _9, the number of magnetic signal sensor may be odd even even.

The invention relating to the magnetic metal foreign matter detection method of the present invention described so far can be summarized at least as follows.
A detection method that uses a plurality of magnetic sensors installed in the magnetic shield space to detect a magnetic metal foreign object contained in an inspection object that moves in the magnetic shield space,
A reference sensor that considers that the plurality of magnetic sensors detect noise in the magnetic shield space, and a magnetic signal sensor for detecting magnetism from the magnetic metal foreign object, and a signal value of the reference sensor Using the absolute value or a value that does not exceed the absolute value as the primary calculation reference value, the calculation for obtaining the following primary difference and the subsequent n-th difference from the output signal of the magnetic signal sensor is repeated, and the n-th difference is obtained. the detection method signal caused by free environment noise and detecting a magnetic signal from the magnetic metal foreign substance on the basis of the output signal at the n-th order difference when it becomes less than a predetermined value .
Primary difference = (Absolute value of output signal of magnetic signal sensor) − (Primary calculation reference value)
nth order difference = ((n−1) th order difference) − (nth order calculation reference value)
However, nth-order calculation reference value = (n−1) calculation reference value set lower than the next-order calculation reference value n: 2 or an integer larger than 2 In the present invention relating to the magnetic metal foreign object detection method, There are embodiments.
(1) the make multiple pairs between the magnetic sensor, and comparing the output signals between each other said magnetic sensor paired, the said magnetic sensor having a lower level of the output signal as said reference sensor use one of the absolute value and the value lower than the absolute value of the output signal at the reference sensor as the primary operational reference value.
(2) In the magnetic shield space , one of the plurality of magnetic sensors has a noise detection magnetic sensor whose distance from the object to be inspected is larger than each of the other magnetic sensors. a is, the magnetic sensor noise detected as the reference sensor, using either an absolute value and the value lower than the absolute value of the output signal of the reference sensor as the primary operational reference value.
(3) When the primary calculation reference value is lower than the absolute value of the output signal, a portion of the output signal having a value higher than the absolute value is added to the primary calculation reference value. The primary difference is obtained.
(4) The magnetic metal foreign matter is detected using a sum of absolute values of the n-th order differences obtained for the plurality of magnetic sensors .
(5) The n-th order calculation reference value is a value obtained by multiplying the (n-1) -th order calculation reference value by a positive coefficient that does not exceed 1, and each time the calculation is repeated, the coefficient Gradually decreases.
(6) The coefficient is 1/2 ^n-1 .
(7) For the magnetic signal from the magnetic metal foreign matter, the minimum value to be detected is converted into an absolute value, and a value that does not exceed 1/2 of the absolute value is replaced with the absolute value of the output signal of the reference sensor. use.
The present invention relating to a magnetic metal foreign object detection device can be summarized as follows.
A magnetic metal foreign object detection device using the magnetic metal foreign object detection method according to the present invention.
The present invention relating to a magnetic metal foreign object detection device includes the following embodiments.
(1) The detection apparatus includes a signal processing unit and a difference calculation unit. In the signal processing unit, output signals from the plurality of magnetic sensors are filtered, an A / D converter, and an absolute value circuit. And output as a processed signal to the difference calculation means, and the difference calculation means repeats the calculation in the detection method between the processing signal and the calculation reference value.
(2) The inspection object is food.

1 Detector 2 Magnetic shield space (magnetic shield box)
4 Conveying means (belt conveyor)
28 Signal processing means (signal processing unit)
32 Difference calculation means (calculation processing unit)
60a Opening (upstream opening)
60b Opening (downstream opening)
100 inspection object S ₁ -S ₈ magnetic sensor S ₂ reference sensor (magnetic sensor)
S ₉ reference sensor (magnetic sensor)

Claims (11)

A detection method that uses a plurality of magnetic sensors installed in the magnetic shield space to detect a magnetic metal foreign object contained in an inspection object that moves in the magnetic shield space,
A reference sensor that considers that the plurality of magnetic sensors detect noise in the magnetic shield space, and a magnetic signal sensor for detecting magnetism from the magnetic metal foreign object, and a signal value of the reference sensor Using the absolute value or a value that does not exceed the absolute value as the primary calculation reference value, the calculation for obtaining the following primary difference and the subsequent n-th difference from the output signal of the magnetic signal sensor is repeated, and the n-th difference is obtained. the detection method signal caused by free environment noise and detecting a magnetic signal from the magnetic metal foreign substance on the basis of the output signal at the n-th order difference when it becomes less than a predetermined value .
Primary difference = (Absolute value of output signal of magnetic signal sensor) − (Primary calculation reference value)
nth order difference = ((n−1) th order difference) − (nth order calculation reference value)
However, the nth calculation reference value = (n−1) the calculation reference value set lower than the next calculation reference value n: 2 or an integer greater than 2 Wherein creating a plurality of pairs among the magnetic sensors, compares the output signals between each other said magnetic sensor paired, in the reference sensor the magnetic sensor having a lower level of the output signal as said reference sensor detection method according to claim 1, wherein the use of either an absolute value and the value lower than the absolute value of said output signal as said primary calculation reference value. In the magnetic shield space , one of the plurality of magnetic sensors is a noise detecting magnetic sensor having a distance from the object to be inspected that is larger than the distance in each of the other magnetic sensors. the magnetic sensor noise detected as the reference sensor, detects according to claim 1, wherein using either an absolute value and the value lower than the absolute value of the output signal of the reference sensor as the primary calculation reference value Method.   When the primary calculation reference value is lower than the absolute value of the output signal, a portion of the output signal having a value higher than the absolute value is added to the primary calculation reference value to add the primary calculation reference value. The detection method according to claim 2 or 3, wherein a difference is obtained. The detection method according to claim 1, wherein the magnetic metal foreign object is detected using a sum of absolute values of the n-th order differences obtained for the plurality of magnetic sensors .   The n-th order calculation reference value is a value obtained by multiplying the (n-1) -th order calculation reference value by a positive coefficient that does not exceed 1, and each time the calculation is repeated, the coefficient decreases in order. The detection method according to claim 1. The detection method according to claim 6, wherein the coefficient is 1/2 ⁿ⁻¹ . For the magnetic signal from the magnetic metal foreign object, the minimum value to be detected is converted to an absolute value, and a value that does not exceed 1/2 of the absolute value is used instead of the absolute value of the output signal of the reference sensor. The detection method according to claim 1. Detection device of the magnetic metal foreign substance, characterized in that the method of any of claims 1 8 are used. The detection device has a signal processing means and a difference calculation means,
In the signal processing means, output signals from the plurality of magnetic sensors are processed by a filter circuit, an A / D converter, and an absolute value conversion circuit, and output as processed signals to the difference calculation means ,
The detection device according to claim 9, wherein the difference calculation unit repeats the calculation in the detection method between the processing signal and the calculation reference value. The detection method according to claim 1, wherein the inspection object is food.

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