JP4145883B2 - Metal detector - Google Patents

Description

  The present invention relates to a metal detector that detects the presence or absence of a metal in a test object.

  Conventionally, as a metal detector, a determination target value that is generated based on a voltage induced in a receiving coil due to passage of an object to be inspected and is used to determine the presence or absence of metal in the object to be inspected. A threshold value larger than the determination target value when there is no metal is set, and when the determination target value is equal to or greater than the threshold value, it is determined that there is metal in the object to be inspected, and when the determination target value is less than the threshold value What determines that there is no metal in is known (for example, refer patent documents 1 and 2).

Japanese Laid-Open Patent Publication No. 3-129598 (2nd page, FIG. 6) JP-A-11-118765 (page 3-5, FIGS. 2, 5)

  However, the conventional metal detector has a problem that the metal in the inspection object cannot be detected depending on the type and size of the metal mixed in the inspection object. That is, depending on the type and size of the metal mixed in the object to be inspected, the voltage induced in the receiving coil when only the metal mixed in the object to be inspected passes, and the object to be inspected in which no metal is mixed As shown in FIG. 10 (a) and FIG. 10 (b), the voltage induced in the receiving coil when it is assumed that only the body has passed is substantially at the same level with the opposite phase, and as a result, The voltage induced in the receiving coil due to the passage of the inspection object is small as shown in FIG. 10C, and the determination target value of the inspection object mixed with metal may be smaller than the threshold value. When the determination target value is smaller than the threshold value, the metal in the inspection object cannot be detected.

  The present invention has been made to solve the conventional problems, and an object of the present invention is to provide a metal detector capable of detecting the presence or absence of a metal in an object to be inspected with higher sensitivity.

The metal detector of the present invention comprises a determination means for determining the presence or absence of the metal in the inspection object by comparing a determination target value used for determination of the presence or absence of metal in the inspection object with a predetermined threshold value. A target value generating means for generating the determination target value based on a magnetic field that changes due to the passage of the object to be inspected, and a passage detecting means for detecting the passage of the object to be inspected. A small threshold value that is smaller than a maximum value of the determination target value generated by the target value generation means based on the object to be inspected not containing the metal, and the determination means includes the passage detection A configuration for determining that the metal is present in the object to be inspected when the determination target value is equal to or less than the small threshold value within a period in which the magnetic field is changed by the passage of the object to be inspected detected by a means. is doing.

  With this configuration, the metal detector of the present invention can detect the metal in the object to be inspected that could not be detected in the past, so the presence or absence of metal in the object to be inspected is detected with higher sensitivity than in the past. be able to.

  Further, the metal detector of the present invention includes useful determination means for determining whether or not the small threshold is useful, and the useful determination means is based on the object to be inspected not containing the metal. A configuration in which the small threshold is determined to be useful when the maximum value of the determination target value generated by the target value generation unit is larger than the determination target value generated outside the period by the target value generation unit. Have.

  The present invention can provide a metal detector capable of detecting the presence or absence of a metal in a test object with higher sensitivity than in the past.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
First, the configuration of the metal detector according to the first embodiment will be described.

  As shown in FIG. 1, a metal detector 10 according to this embodiment includes a signal generator 11 that generates a sine wave signal, and an object to be inspected by being excited by a sine wave signal generated by the signal generator 11. A transmission coil 12 that generates an alternating magnetic field on a conveyance path 90 of 80 (see FIG. 2) and a position that receives substantially the same amount of the alternating magnetic field generated by the transmission coil 12 are differentially connected to each other. Two receiving coils 13, 14, an amplifier 15 that amplifies the voltage at the connection point between the receiving coils 13, 14, a phase shifter 16 that shifts the sine wave signal generated by the signal generator 11, and a phase shift A pair for generating a determination target value 30 (see FIG. 3) used for determining the presence or absence of metal in the object 80 by multiplying and detecting the output of the amplifier 15 by the sine wave signal phase-shifted by the detector 16. The presence or absence of metal in the inspected object 80 is determined by comparing the detection circuit 17 as a value generation means and the peak value of the determination target value 30 generated by the detection circuit 17 with threshold values 31 and 32 (see FIG. 3). And a determination unit 18 as determination means.

  Here, the phase shifter 16 outputs the output of the detection circuit 17 when an object to be inspected 80 (hereinafter referred to as “non-defective product”) that is not mixed with metal passes through an alternating magnetic field generated by the transmission coil 12. The output of the detection circuit 17 is increased when the object 80 to be inspected (hereinafter referred to as “defective product”) is reduced and passes through the alternating magnetic field generated by the transmission coil 12. The amount of phase shift is set.

  Further, the determination unit 18 determines that there is metal in the inspected object 80 when the peak value of the determination target value 30 generated by the detection circuit 17 is equal to or greater than the threshold value 31 as shown in FIG. When the peak value of the determination target value 30 generated by the detection circuit 17 is less than the threshold 31 and greater than the threshold 32 as shown in FIG. It is determined that there is no metal, and when the peak value of the determination target value 30 generated by the detection circuit 17 is equal to or less than the threshold value 32 as shown in FIG. It is like that.

  The threshold value 31 is set manually or automatically so as to be larger than a non-defective product value 33 (see FIG. 3) that is the maximum value of the determination target value 30 generated in advance by the detection circuit 17 based on the non-defective product. The threshold value 32 is set manually or automatically so as to be smaller than the non-defective product value 33, and constitutes a small threshold value.

  A sorting device 20 for sorting the inspected object 80 being transported on the transport path 90 is provided downstream of the transport path 90 from the metal detector 10. The sorting apparatus 20 includes a switching unit 21 that switches the traveling direction of the inspection object 80 being conveyed on the conveyance path 90, and proceeds to the inspection object 80 that is not mixed with metal in the direction indicated by the arrow 90a. The object 80 in which the metal is mixed is advanced in the direction indicated by the arrow 90b.

  Next, the operation of the metal detector 10 will be described.

  When the inspection object 80 conveyed on the conveyance path 90 passes through the alternating magnetic field generated by the transmission coil 12, the voltages induced in the two reception coils 13 and 14 change, and the detection circuit 17 A determination target value 30 is generated.

  Then, when the peak value of the determination target value 30 generated by the detection circuit 17 is greater than or equal to the threshold value 31 as illustrated in FIG. 3A, the determination unit 18 determines the object 80 passing through the alternating magnetic field. Then, it is determined that there is metal in the inspected object 80, and the peak value of the determination target value 30 generated by the detection circuit 17 is less than the threshold 31 and larger than the threshold 32 as shown in FIG. When it is determined that there is no metal in the inspection object 80, and the peak value of the determination target value 30 generated by the detection circuit 17 is equal to or less than the threshold value 32 as shown in FIG. It is determined that there is metal in 80.

  Therefore, for example, the plurality of inspected objects 80 are non-defective products, non-defective products, defective products in which metal is mixed only in position A (see FIG. 2), defective products in which metal is mixed in only position B (see FIG. 2), and position C. (Refer to FIG. 2) Defective product mixed with metal only, Defective product mixed with metal only at position D (refer to FIG. 2), Defective product mixed with metal only at position E (see FIG. 2), position A defective product in which metal is mixed only in F (see FIG. 2), a defective product in which metal is mixed only in position G (see FIG. 2), a defective product in which metal is mixed only in position H (see FIG. 2), Since the determination target value 30 generated by the detection circuit 17 is as shown in FIG. 4 when passing through the alternating magnetic field in the order of defective products mixed with metal only at the position I (see FIG. 2), the metal detection is performed. Machine 10 is a defective product in which metal is mixed only in position D, and a defect in which metal is mixed only in position E. Goods, it is possible to detect the position H only defective metal is mixed and defective products metal only in position I is mixed as a defective product. The reason why the determination target value 30 varies depending on the metal mixing position in the defective product is as follows. For example, the mutual phase relationship between the induced voltage of only the inspected object 80 excluding the metal of the defective product and the induced voltage of only the metal of the defective product differs depending on the metal mixing position in the defective product. Among the defective products, the determination target value 30 of the defective product, which is a superimposed signal of the induced voltage of only the inspected object 80 excluding the metal and the induced voltage of only the metal of the defective products, differs depending on the metal mixing position in the defective product. In addition, since the magnetic field strength distribution between the transmission coil 12 and the reception coils 13 and 14 is not necessarily uniform with respect to the conveyance direction of the object 80, the determination target value 30 of the defective product is that the metal in the defective product is It differs depending on which position between the transmission coil 12 and the reception coils 13 and 14 passes through.

  Note that the determination result by the determination unit 18 is input to the sorting device 20 at predetermined time intervals regardless of whether or not the object 80 has entered the alternating magnetic field of the metal detector 10. When the determination result of the determination unit 18 changes from the determination result that there is metal in the inspection object 80 to the determination result that there is no metal in the inspection object 80, the sorting device 20 moves the inspection object 80 with the arrow 90a. The switching unit 21 is switched at a predetermined timing so as to advance in the direction shown. Further, when the determination result of the determination unit 18 changes from the determination result that there is no metal in the inspection object 80 to the determination result that there is metal in the inspection object 80, the sorting device 20 moves the inspection object 80 to the arrow. The switching unit 21 is switched at a predetermined timing so as to advance in the direction indicated by 90b. Therefore, the inspected object 80 that has not been detected as a defective product by the metal detector 10 is conveyed in the direction indicated by the arrow 90a, but the inspected object 80 that has been detected as a defective product by the metal detector 10 is the arrow 90b. It is conveyed in the direction indicated by.

  As described above, in the metal detector 10, when the peak value of the determination target value 30 of the defective product is smaller than the threshold value 31, if the threshold value 32 or less is present, there is a metal in the inspected object 80. Is determined. In other words, the metal detector 10 has an object to be inspected 80 in which the peak value of the determination target value 30 is smaller than the non-defective product value 33 that could not be detected in the past (in the example shown in FIG. And defective metals in which metal is mixed only at position E) can be detected. Therefore, the metal detector 10 can detect the presence or absence of metal in the inspection object 80 with higher sensitivity than in the past.

  Moreover, even if the metal detector 10 is a non-defective product, when the peak value of the determination target value 30 is equal to or less than the threshold value 32, the metal detector 10 determines that there is metal in the inspection object 80. Therefore, even if the metal detector 10 is a non-defective product, it is possible to detect the inspected object 80 in which the peak value of the determination target value 30 is less than or equal to the threshold value 32 and the water amount, salt content, etc. are extremely less than the standard. . That is, the metal detector 10 can also be used for the quality check of the inspection object 80.

  The metal detector 10 is configured to determine the presence or absence of metal in the object 80 by comparing the peak value of the determination target value 30 with the threshold values 31 and 32. The presence or absence of metal in the object 80 may be determined by comparing the absolute value of the value or the peak value of the determination target value 30 with the threshold values 31 and 32.

(Second Embodiment)
First, the configuration of the metal detector according to the second embodiment will be described.

  Of the configuration of the metal detector according to the present embodiment, the same configuration as the configuration of the metal detector 10 (see FIG. 1) according to the first embodiment is the same as the configuration of the metal detector 10. The same reference numerals are assigned and detailed description is omitted.

  As shown in FIG. 5, the configuration of the metal detector 40 according to the present embodiment is configured to detect the inspection object passage sensor 41 as a passage detection unit that detects the passage of the inspection object 80 using light or the like. The configuration is the same as that of the machine 10.

  Further, the determination unit 18 determines the presence or absence of metal in the inspection object 80 within a period 50 (see FIG. 6) in which the magnetic field changes due to the passage of the inspection object 80 detected by the inspection object passage sensor 41. It is supposed to be. Here, the period 50 starts when the passage of the inspection object 80 is detected by the inspection object passage sensor 41, and is based on the length of the inspection object 80 in the conveyance direction and the conveyance speed of the inspection object 80. The period is calculated automatically or manually.

  Next, the operation of the metal detector 40 will be described.

  When the inspection object 80 conveyed on the conveyance path 90 passes through the alternating magnetic field generated by the transmission coil 12, the inspection object passage sensor 41 detects the passage of the inspection object 80, and then 2 The voltage induced in the two receiving coils 13 and 14 changes, and the determination target value 30 is generated by the detection circuit 17.

  Then, the determination unit 18 determines that the maximum value of the determination target value 30 generated by the detection circuit 17 for the inspected object 80 passing through the alternating magnetic field is greater than or equal to the threshold value 31 within the period 50 as shown in FIG. When it becomes, it determines with there being metal in the to-be-inspected object 80, and the maximum value of the determination target value 30 produced | generated by the detection circuit 17 is less than the threshold value 31 within the period 50, as shown in FIG.6 (b). If it is greater than the threshold value 32, it is determined that there is no metal in the inspection object 80, and the maximum value of the determination target value 30 generated by the detection circuit 17 is within the period 50 as shown in FIG. When the threshold value is 32 or less, it is determined that there is metal in the inspected object 80.

  The determination result by the determination unit 18 is input to the sorting device 20 every time the period 50 ends. When the determination result input from the determination unit 18 is a determination result that there is no metal in the inspection object 80, the sorting device 20 causes the switching unit 21 to advance the inspection object 80 in the direction indicated by the arrow 90a. Switch. In addition, when the determination result input from the determination unit 18 is a determination result that there is metal in the inspection object 80, the sorting device 20 switches the inspection object 80 so as to advance in the direction indicated by the arrow 90b. 21 is switched. Therefore, the inspected object 80 that has not been detected as a defective product by the metal detector 40 is conveyed in the direction indicated by the arrow 90a, but the inspected object 80 that has been detected as a defective product by the metal detector 40 is the arrow 90b. It is conveyed in the direction indicated by.

  As described above, since the metal detector 40 determines the presence or absence of metal only within the period 50, the determination unit 18 notifies the occurrence of a defective product by, for example, sounding a buzzer. When the determination result is notified by display, voice, or the like, it is possible to prevent the occurrence of a defective product from being misreported outside the period 50.

  The metal detector 40 includes the inspection object passage sensor 41 as the passage detection means. However, the metal detector 40 may include an object that detects the passage of the inspection object 80 by other methods as the passage detection means. good.

  For example, the metal detector 40 may be provided with what detects the passage of the inspected object 80 by processing the determination target value 30 generated by the detection circuit 17 as the passage detection means. Specifically, for example, as shown in FIG. 7, the metal detector 40 measures the noise level that is the determination target value 30 generated by the detection circuit 17 in a state where the inspection object 80 does not pass through. The noise level range 35 is set in advance, and when the determination target value 30 generated by the detection circuit 17 is out of the range 35, it can be detected that the object 80 is passing. When the passage of the inspection object 80 is detected when the determination target value 30 falls outside the range 35, the period 50 is started when the determination target value 30 falls outside the range 35, and the inspection object 80 is conveyed. This is a period calculated based on the length of the direction and the conveyance speed of the inspection object 80, and is set automatically or manually.

  Further, if the operation of the transport path 90 is stopped when the determination unit 18 determines that there is metal in the object 80, the user manually removes the object 80 in which the metal is mixed. Therefore, the sorting device 20 may not be provided.

  The metal detector 40 determines the presence or absence of metal in the object 80 by comparing the maximum value of the determination target value 30 with the threshold values 31 and 32. The presence / absence of metal in the inspected object 80 may be determined by comparing the maximum value with the threshold values 31 and 32.

(Third embodiment)
First, the configuration of the metal detector according to the third embodiment will be described.

  Of the configuration of the metal detector according to the present embodiment, the same configuration as the configuration of the metal detector 40 (see FIG. 5) according to the second embodiment is the same as the configuration of the metal detector 40. The same reference numerals are assigned and detailed description is omitted.

  As shown in FIG. 8, in the configuration of the metal detector 60 according to the present embodiment, the metal detector 40 includes a useful determination unit 61 as a useful determination unit that determines whether or not the threshold value 32 is useful. The configuration is the same.

  The usefulness determination unit 61 uses the threshold value 32 when the non-defective product value 33 is larger than the noise level maximum value 34 (see FIG. 9), which is the determination target value 30 generated outside the period 50 by the detection circuit 17. It comes to judge.

  Next, the operation of the metal detector 60 will be described.

  The metal detector 60 stores a non-defective value 33 corresponding to the determination target value 30 generated by the detection circuit 17 for a predetermined number (for example, 50) of non-defective products that pass through an alternating magnetic field, and stores the predetermined number (for example, When the minimum value of the 50 non-defective values 33 is larger than the maximum noise level 34, the threshold 32 is determined to be useful and the threshold 32 is automatically set.

  And the metal detector 60 performs the operation | movement similar to the metal detector 40 which concerns on 2nd Embodiment using the threshold value 32 set automatically.

  The metal detector 60 is configured to automatically set the threshold value 32. However, when the usefulness determination unit 61 determines that the threshold value 32 is useful, an indication or sound indicating that the threshold value 32 is useful is provided. For example, the threshold value 32 may be set according to an instruction from the user.

  As described above, the metal detector according to the present invention has the effect of being able to detect the presence or absence of metal in an object to be inspected with higher sensitivity than before, and is installed on a production line such as food. It is useful as a detector.

Block diagram of a metal detector and a sorting device in the first embodiment of the present invention 1 is an external perspective view of an object to be inspected in which presence or absence of metal contamination is detected by the metal detector shown in FIG. (A) The figure which shows an example of the output of the detection circuit of the metal detector shown in FIG. 1 when a defective product is conveyed on the conveyance path. (B) The metal detection shown in FIG. 1 when the non-defective product is conveyed on the conveyance path. The figure which shows an example of the output of the detector circuit of a machine (c) The example different from the example shown in FIG. 3 (a) of the output of the detector circuit of a metal detector shown in FIG. 1 when a defective article is conveyed on a conveyance path Figure showing The figure which shows an example of the output of the detection circuit of the metal detector shown in FIG. 1 when a several to-be-inspected object is conveyed on the conveyance path. Block diagram of a metal detector and a sorting device in the second embodiment of the present invention (A) The figure which shows an example of the output of the detection circuit of the metal detector shown in FIG. 5 when a defective product is conveyed on the conveyance path. (B) The metal detection shown in FIG. 5 when the non-defective product is conveyed on the conveyance path. The figure which shows an example of the output of the detector circuit of a machine (c) The example different from the example shown in FIG. 6 (a) of the output of the detector circuit of a metal detector shown in FIG. 5 when a defective article is conveyed on a conveyance path Figure showing The figure which shows the example different from the example shown in FIG. 6 of the output of the detection circuit of the metal detector shown in FIG. 5 when a to-be-inspected object is conveyed on the conveyance path. Block diagram of a metal detector and a sorting device in the third embodiment of the present invention The figure which shows an example of the output of the detection circuit of the metal detector shown in FIG. 8 when a to-be-inspected object is conveyed on the conveyance path. (A) The figure which shows an example of the voltage induced in the receiving coil of the conventional metal detector when it is assumed that only the metal mixed in to the to-be-tested object has passed. (B) Only to-be-inspected object in which the metal is not mixed. The figure which shows an example of the voltage induced in the receiving coil of the conventional metal detector when it is assumed that the metal has passed. (C) In the receiving coil of the conventional metal detector when the test object mixed with metal passes Diagram showing an example of induced voltage

Explanation of symbols

10 Metal detector 17 Detection circuit (target value generation means)
18 determination part (determination means)
30 judgment target value 31 threshold 32 threshold (small threshold)
33 Good value (maximum value)
40 Metal detector 41 Inspected object passage sensor (passage detection means)
50 period 60 metal detector 61 useful judgment part (useful judgment means)
80 Inspected object

Claims (2)

The presence / absence of the metal in the object to be inspected is determined by comparing the determination target value (30) used for determining the presence / absence of the metal in the object to be inspected (80) with a predetermined threshold (31, 32). Determination means (18), target value generation means (17) for generating the determination target value based on a magnetic field that changes due to the passage of the object to be inspected, and passage detection for detecting the passage of the object to be inspected (80) Means (41) ,
The predetermined threshold value is a small threshold value (32) which is a threshold value smaller than the maximum value (33) of the determination target value generated by the target value generation means based on the object to be inspected in which the metal is not mixed. Contains
The determination means is in the inspection object when the determination target value is equal to or less than the small threshold value within a period (50) in which the magnetic field changes due to the passage of the inspection object detected by the passage detection means. It is determined that the metal is present in the metal detector (10, 40, 60). Useful determination means (61) for determining whether or not the small threshold (32) is useful ;
The useful determination means has a maximum value (33) of the determination target value (30) generated by the target value generation means (17) based on the object to be inspected (80) in which the metal is not mixed. when greater than the period (50) the decision target values that are generated outside the target value generation means, said small threshold metal detector according to claim 1, characterized in that determined to be useful (60 ).

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