JP2008232745A - Iron piece detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an iron piece detector for reducing an effect due to an external noise, and improving the detection sensitivity. <P>SOLUTION: In the iron piece detector 10 of the invention, two first coils 16 face one surface of a to-be-inspected object 12 and are juxtaposed and attached in the transportation direction of the to-be-inspected object 12, and two second coils 16 face the other surface of the to-be-inspected object 12 and are juxtaposed and attached so as to face the first coils 16 through the to-be-inspected object 12. The first coils 16 are separated from each other at a separation distance W. The second coils 16 are separated from each other at the separation distance W. The first and second coils are separated at a separation distance H. The separation distance H is 0.6-2.0 times as long as the separation distance W. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an iron piece detector, and more particularly, to an iron piece detector using a magnetic induction method used for detecting an iron piece (metal foreign matter).

  If metal foreign objects are mistakenly mixed during the manufacturing process of processed food products, etc., the safety of consumers will be impaired. Therefore, it is more important than ever to inspect metal foreign objects using an iron piece detector at the final stage of the processing process. ing. In addition, the iron piece detector is used for inspecting sewing products, aluminum foil products, and the like, and removes iron pieces in the inspection object. For detecting such iron pieces, an iron piece detector using a magnetic induction method is often used. The iron piece detector can detect a magnetic field generated from a magnet by using a change in magnetic flux generated when the magnetized iron piece passes through the coil.

  FIG. 5 is a diagram showing a schematic configuration of a conventional iron piece detector. FIG. 1A shows a front cross section of the iron piece detector, and the object to be inspected flows in a direction perpendicular to the paper surface. Moreover, (2) has shown the cross section of the A arrow directional view of (1). The conventional iron piece detector 1 includes a plurality of ferrite magnets 4 (for example, alnico magnets) that generate a static magnetic field on the upper surface of an opening 3 provided at the center of the frame 2 through which the object to be inspected passes along the conveyance path of the object to be inspected. They are mounted in a straight line in the intersecting direction, that is, in the width direction. Moreover, in order to detect an iron piece on the lower surface of the opening 3, two sets of inspection bodies each having an iron core 5 attached to the shaft center and a plurality of coils 6 wound thereon are attached. The opening 3 has a static magnetic field and has a magnetic field distribution as shown in (2). At this time, since the magnetic field in the normal opening is not disturbed, the voltage generated in the coil 6 is zero.

ここでμ：透磁率、Ｈ：磁界とする。 The magnetic flux density B in the opening 3 can be expressed by Equation 1.

Here, μ: permeability, H: magnetic field.

ここでＭ：磁化とする。 When an iron piece enters the opening 3, the magnetic flux density B changes (Formula 2).

Here, M is magnetization.

Due to the change in the magnetic flux density B, a voltage V is generated in the coil 6. The voltage V can be expressed as Equation 3.

  FIG. 6 shows a conventional differential connection, and FIG. 7 shows the output voltage waveforms of the coils 6A and 6B when magnetized metal passes through the coils 6A to 6B. In the differential connection, the plus of the coil 6A and the minus of the coil 6B are connected so that the output voltages of the coils changing at the same time cancel each other, and the minus of the coil 6A and the plus of the coil 6B are connected. Further, a detection signal can be generated by setting the detection threshold value Vth of the output voltage.

Such detectors using a magnetic induction method are disclosed in, for example, Patent Documents 1 to 3. In Patent Document 1, a plurality of detection units each made of a small iron core and a coil are arranged in a direction orthogonal to the passing direction of the object to be inspected, and no deformation of the coil due to external noise or vibration of the detector occurs, and the iron piece. An iron piece detector detecting section having a large detection area is disclosed. Further, Patent Document 2 is an electromagnetic induction method using a permanent magnet so that two detectors combining a permanent magnet, an iron core, and a coil are arranged so that the S pole and the N pole face each other so as to increase the voltage sensitivity. I have to. Furthermore, in Patent Document 3, the first coil and the second coil are arranged across a hollow portion through which an object to be inspected, and the change in magnetic flux due to the presence or absence of a metal piece is increased to improve detection sensitivity. Is disclosed. FIG. 8 shows a sensitivity distribution when a plurality of detection bodies and magnets each made of an iron core and a coil are arranged in the width direction of the conveyance path of the inspection object.
JP-A-10-121370 Japanese Utility Model Publication No.59-52496 JP 2006-113043 A

  However, in such a conventional iron piece detector, if the detection sensitivity is set high, there is a problem that stable inspection cannot be performed due to the influence of external noise derived from the setting environment of the apparatus.

  Moreover, the meter-reading apparatus disclosed in Patent Document 3 has a configuration in which a plurality of detectors and magnets each made of an iron core and a coil are arranged side by side in order to specify the location of a metallic foreign object in the object to be inspected. When a plurality of detectors and magnets are arranged side by side as described above, a gap is generated between the coils. Then, as shown in the sensitivity distribution described above, the flow of magnetic lines of force weakens in the gaps between the coils, and the voltage decreases. Therefore, the magnitude of the magnetic flux is generated in the inspection region, and the magnetic flux distribution is nonuniform. Therefore, there is a problem that a constant detection sensitivity cannot be obtained.

  Accordingly, in order to solve the above-described conventional problems, an object of the present invention is to provide an iron piece detector that reduces the influence of external noise and improves detection sensitivity.

  In the iron piece detector of the present invention, a plurality of first coil portions facing one side of the inspection object are arranged side by side along the conveyance direction of the inspection object, and the second coil surface facing the other side of the inspection object. A plurality of coil portions are arranged side by side so as to face the first coil portion via the object to be inspected, and the first coil portion and the second coil portion are arranged vertically and horizontally symmetrically with the object to be inspected as the center. It is characterized by.

  Moreover, the iron piece detector of the present invention has two first coil portions facing one side of the inspection object arranged side by side along the transport direction of the inspection object, and facing the other side of the inspection object. Two second coil parts are mounted side by side so as to face the first coil part through the object to be inspected, and the first coil part and the second coil part are the first coil parts or the second coil parts. The distance between the parts is a separation distance W, the separation between the first coil part and the second coil part is a separation distance H, and the separation distance H is 0.6 to 2.0 times the separation distance W. It is characterized by setting.

  In this case, the first coil portion is attached with a first magnet having the same polarity of N or S poles along the longitudinal direction, and the second coil portion is different from the first magnet along the longitudinal direction. It is good to attach the 2nd magnet of the same pole of S pole or N pole which becomes.

  The first coil part and the second coil part may include an iron core set at least as long as the length of the inspection object at the axis.

  According to the iron piece detector of the present invention having the above-described configuration, a plurality of first coil portions facing one side of the inspection object are mounted side by side along the conveyance direction of the inspection object, and face the other side of the inspection object. A plurality of second coil parts are attached to face the first coil part through the object to be inspected, and the first coil part and the second coil part are attached vertically and horizontally symmetrically about the object to be inspected. . More specifically, the first coil portions or the second coil portions are separated by a separation distance W, the first coil portion and the second coil portion are separated by a separation distance H, and the separation distance H is the separation distance W. It is set to 0.6 times to 2.0 times. For this reason, noise can be canceled by a combination of the first coil portion and the second coil portion arranged symmetrically in the vertical and horizontal directions with respect to the noise magnetic field generated from the vertical direction, the horizontal direction, and the oblique direction. For example, in the case of horizontal external noise, noise of the same output voltage acts vertically between the upper and lower coil sections. Therefore, noise can be canceled by taking the difference between the upper and lower coils. Therefore, the detection sensitivity of the iron piece can be improved without being affected by external noise.

  The 1st magnet attached to the 1st coil part is arranged so that it may become the same pole like N pole-N pole or S pole-S pole, and the 2nd magnet attached to the 2nd coil part is opposite 1st. The same pole of S pole or N pole which is different from the magnet is attached. Usually, for example, lines of magnetic force from the first coil part to the second coil part with the object to be inspected are generated. At this time, the 1st coil part or the 2nd coil part is constituted by the same poles. For this reason, for example, since a magnetic force line does not arise between the magnets of the first coil part arranged in two along the transport direction, the magnetic force line is not dispersed. Therefore, it is possible to avoid a decrease in the magnetic field lines resulting from the diffusion of the magnetic field lines, and to improve the detection sensitivity of the iron piece.

  It arrange | positions so that a to-be-inspected object may be pinched | interposed by the 1st coil part and the 2nd coil part which were equipped with the iron core set to the length of the to-be-inspected object at least as an axis. Since the iron cores of the first coil portion and the second coil portion face the entire surface of the object to be inspected, uniform lines of magnetic force flow from one coil portion to the other coil portion. Therefore, it becomes a uniform magnetic field and the detection sensitivity of the iron piece can be improved.

  The iron piece detector of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an iron piece detector. (1) is a front view of the iron piece detector, (2) is a plan view, and (3) is a side view. As shown in the figure, the iron piece detector 10 is provided with an opening 14 through which the inspection object 12 passes mainly at the center of the main body, and a coil portion 16 and a magnet 18 are disposed on the upper surface 14a and the lower surface 14b of the opening 14.

  The opening 14 is formed to be longer than the conveyor width and larger than the height of the inspection object 12 placed on the belt conveyor 20 because the inspection object 12 placed on the belt conveyor 20 passes therethrough. The size of the opening 14 is arbitrarily changed by the belt conveyor 20 of the inspection object 12.

  The coil portion 16 is attached to the upper surface 14a and the lower surface 14b of the opening 14 with the coil surface exposed or covered with a non-magnetic cover. The coil portion 16 is composed of an iron core 22 and a coil 24. The iron core 22 is attached along the width direction of the belt conveyor 20. The length of the iron core 22 is at least equal to or longer than the length of the object to be inspected 12, and is preferably set to be substantially the same as the length of the belt conveyor 20 in the width direction. The coil 24 is formed by winding a plurality of electric wires around the iron core 22. The coil part 16 of this embodiment is set as the structure which fitted the iron core 22 in the center of the bobbin as an example, and attached the coil 24 which wound the electric wire around the outer periphery of the iron core 22.

  The magnet 18 is attached to the opposite surface of the coil portion 16 facing the opening 14. The length of the magnet 18 is set to be larger than the width G of the coil portion 16 in the transport direction, and a plurality of magnets 18 are attached at predetermined intervals along the longitudinal direction of the coil portion 16. In the present embodiment, as an example, the coil portion 16 and the magnet 18 are fixed to the detector main body by fixing means such as screws.

  Moreover, the coil part 16 is attached so that it may oppose the upper surface 14a and the lower surface 14b of the opening part 14 so that the to-be-inspected object 12 may be pinched | interposed as shown in FIG. 1 (3) (16A and 16C or 16B and 16D). Two coil portions 16 are arranged on the upper surface 14a or the lower surface 14b and attached to the same plane (first coil portions 16A and 16B or second coil portions 16C and 16D). The arrangement relationship of the four coil parts 16A to 16D is such that the separation distance W between the first coil parts 16A and 16B (or the separation distance W between the second coil parts 16C and 16D) and the coil part. A separation distance H between 16A and the coil 16C (or a separation distance H between the coil portions 16B and 16D) is set at a later-described separation distance.

  At this time, the arrangement of the magnets 18 is as shown in FIG. That is, the first magnet 18a attached to the upper surface 14a of the opening 14 has the upper surface as the S pole and the lower surface as the N pole. The first magnets 18a placed on the two rows of coil portions 16A and 16B are arranged such that the upper surface is the S pole and the lower surface is the N pole.

  On the other hand, the 2nd magnet 18b attached to the lower surface 14b of the opening part 14 is arrange | positioned so that it may have a different polarity from the 1st magnet 18a attached to the upper surface 14a. That is, the upper surface of the second magnet 18b is an S pole and the lower surface is an N pole. The second magnets 18b placed on the two rows of coil portions 16C and 16D are arranged such that the upper surface is the S pole and the lower surface is the N pole.

  Thereby, the arrangement relationship of the magnets 18 is as follows. The lower surfaces of the two rows of first magnets 18a arranged on the upper surface 14a side of the opening 14 are N poles-N poles, and the upper surfaces of the two rows of second magnets 18b arranged on the lower surface 14b side are arrangements of S poles-S poles. It becomes. The four coil portions 16A to 16D are symmetrical in the vertical direction when divided by 16A and 16C, and 16B and 16D. Moreover, if it is divided into 16A and 16B and 16C and 16D, it becomes symmetrical in the horizontal direction.

Next, the operation of the iron piece detector 10 having the above configuration will be described below.
The metal detector 10 is attached so that the belt conveyor 20 passes through the opening 14 during the conveyance of the belt conveyor 20 that conveys the inspection object 12. The magnetic flux distribution between the coils attached to the upper surface 14a and the lower surface 14b of the opening 14 is shown in FIG. As illustrated, the first magnet 18a on the upper surface 14a has an N pole on the coil side, and the second magnet 18b on the lower surface 14b has an S pole on the coil side. Therefore, the magnetic field flows from the coil portions 16A and 16B on the upper surface 14a side to the coil portions 16C and 16D on the lower surface 14b side. At this time, the magnets 18 on the upper surface or the lower surface are all arranged in the same pole as the N pole-N pole or the S pole-S pole. Magnetic field lines are not generated. Accordingly, the lines of magnetic force do not disperse, and the lines of magnetic force efficiently flow from the first coil part to the second coil part, so that a large magnetic flux can be obtained.

  FIG. 3 is an explanatory diagram of sensitivity distribution of the iron piece detector of the present invention. The horizontal axis of the figure shows the position (mm) in the belt width direction, the vertical axis shows the voltage (V), and represents the sensitivity distribution on the conveyor belt surface.

ここでｋ：定数、Ｂ：磁束密度をそれぞれ表している。 In general, the reception voltage V can be expressed by Equation 4.

Here, k is a constant, and B is a magnetic flux density.

  As shown in Formula 4, the received voltage V is proportional to the magnetic flux density B, so that the received voltage V increases as the magnetic flux density B increases.

  In the iron piece detector 10 of the present invention, the iron core 22 is set to be at least the length of the object to be inspected. For this reason, when the inspection object is sandwiched between the first coil portion and the second coil portion, the entire surface of the iron core 22 faces the inspection object 12. Since the magnetic lines of force flow uniformly in the iron core, the magnetic lines of force from the upper surface 14 a to the lower surface 14 b of the opening 14 flow uniformly through the upper and lower iron cores 22. With this uniform magnetic flux, the maximum received voltage is uniformly obtained across the width direction of the belt conveyor, as shown in FIG. 3, and the iron piece detection sensitivity is increased.

  FIG. 4 is an explanatory diagram of a noise magnetic field acting on the coil portion of the present invention. In the iron piece detector 10 of the present invention, the first coil portions 16A and 16B and the second coil portions 16C and 16D are attached vertically and horizontally symmetrically with the object to be inspected as the center. As the magnetic field, a noise magnetic field a acting from the vertical direction, a noise magnetic field b acting from the horizontal direction, and a noise magnetic field c acting from the oblique direction can be considered.

  FIG. 4A shows a noise magnetic field a acting from the vertical direction. At this time, the noise magnetic field a can be canceled by the left and right combinations of the coil portions 16A, 16B or 16C, 16D. That is, for example, the same output voltage of the noise magnetic field a acts on the left and right coil portions 16A and 16B. Therefore, noise can be canceled by taking the difference between the left and right coil portions. For this reason, it is possible to improve the detection sensitivity. The same effect can be obtained regardless of whether the noise magnetic field a is from top to bottom or from bottom to top.

  FIG. 4B shows a noise magnetic field acting from the horizontal direction. At this time, the noise magnetic field b can be offset by taking the difference in the same manner as described above by the combination of the upper and lower portions of the coil portions 16A, 16C or 16B, 16D. The same effect can be obtained whether the noise magnetic field a is from left to right or right to left.

  FIG. 4 (3) shows a noise magnetic field c acting from an oblique direction. At this time, the difference between the coil portions 16A, 16D or 16B, 16C in the oblique direction can be similarly taken to cancel the noise magnetic field c. It is assumed that the noise magnetic field c acting from an oblique direction acts from the upper right. In this case, the combination of the coil portions 16 may be the coil portions 16B and 16C or 16A and 16D.

  Here, the arrangement of the coil part 16 is such that four coil parts 16A to 16D are mounted symmetrically around the object to be inspected with respect to the noise magnetic field acting from the horizontal direction, the vertical direction and the oblique direction. Is obtained, the coil portions 16 are arranged at equal intervals in the vertical and horizontal directions, or at least the first coil portions 16A and 16B or the second coil portions 16C and 16D are separated from each other by a separation distance W. It is necessary to set the separation distance H between the first coil portion and the second coil portion so that the separation distance H is 0.6 to 2.0 times the separation distance W. Thus, the noise magnetic field from any direction can be canceled by the combination of the four coil portions 16A to 16D.

  In the present embodiment, the two rows of magnets 18 arranged on the upper surface 14a side of the opening 14 are N pole-N pole, and the two rows of magnets 18 arranged on the lower surface 14b side are described by arrangement of S pole-S pole. However, the configuration in which the upper and lower sides are switched, that is, the two rows of magnets 18 arranged on the upper surface 14a side of the opening portion 14 are S-poles and the two rows of magnets 18 arranged on the lower surface 14b side are N-pole-N poles. Needless to say, similar effects can be obtained even in the arrangement.

  In the present embodiment, the arrangement in which the coil portion 16 is arranged on the upper surface 14a or the lower surface 14b of the opening 14 has been described. However, the arrangement configuration of the coil portion is not limited to this, and one side of the object to be inspected It is only necessary to place the object to be inspected between the coil part and the coil part on the opposite side across the object, and the same effect can be achieved with the arrangement on the left or right side of the opening. can do. In this case, it is particularly effective for an inspected object such as a plastic bottle.

It is a figure which shows the structure outline of the iron piece detector of this invention. It is a figure which shows magnetic flux distribution between the coils of the iron piece detector of this invention. It is explanatory drawing of the sensitivity distribution of the iron piece detector of this invention. It is explanatory drawing of the noise magnetic field which acts on the coil part of this invention. It is a figure which shows the structure outline of the conventional iron piece detector. The connection diagram of the conventional iron piece detector is shown. It is explanatory drawing of the signal waveform of the conventional iron piece detector. It is explanatory drawing of the sensitivity distribution of the conventional iron piece detector.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ......... Iron piece detector, 2 ......... Frame, 3 ......... Opening part, 4 ......... Ferrite magnet, 5 ......... Iron core, 6 ......... Coil, 10 ......... Iron piece inspection machine, 12 ......... inspection object, 14 ......... opening, 16 ......... coil part, 18 ......... magnet, 20 ......... belt conveyor, 22 ......... iron core, 24 ......... coil.

Claims (4)

A plurality of first coil portions facing one side of the inspection object are mounted side by side along the transport direction of the inspection object, and the second coil portion facing the other side of the inspection object is attached to the inspection object. A plurality of side by side facing the first coil portion,
An iron piece detector, wherein the first coil portion and the second coil portion are arranged vertically and laterally symmetrically with respect to the inspection object. Two first coil portions facing one side of the inspection object are mounted side by side along the transport direction of the inspection object, and the second coil portion facing the other side of the inspection object is attached to the inspection object. Two are mounted side by side facing the first coil part via
The first coil part and the second coil part have a separation distance W between the first coil parts or the second coil parts, and are separated from the first coil part and the second coil part. An iron piece detector, wherein the distance H is set to 0.6 to 2.0 times the separation distance W. A first magnet having the same polarity of N pole or S pole is attached to the first coil portion along the longitudinal direction,
3. The iron piece detection according to claim 1, wherein a second magnet having the same polarity as the S pole or the N pole that has a different polarity from the first magnet is attached to the second coil portion along the longitudinal direction. Machine.   The said 1st coil part and the said 2nd coil part were equipped with the iron core set to the axial center at least more than the length of the said to-be-inspected object, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. Iron piece detector.

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