JP2005017118A - Metal detector and paper-like article inspector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the detectability of a metal detector enough to detect very small metal pieces. <P>SOLUTION: The detector uses a slender magnetic core 2 with three rail-like parallel salient poles: a center pole 2a wound with a transmitting coil 3 and side poles 2b wound with a pair of receiving coils 4, 4. The output difference between the pair of receiving coils 4, 4 is taken by adjusting the balance of the zero point and the phase and amplified by an amplifying transformer 12 with a resonance circuit to output a metal detect signal when the output exceeds a specified value. Thin conductors insulated from each other are arranged without gap in the thickness direction as seen from the overlap of the conductor portions and grounded at the ends to form an electrostatic shield plate which covers the core 2 wound with the transmitting coil 3 and the receiving coils 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal detector that detects metal mixed in an article, and in particular, aims at high sensitivity and low noise to enable detection of fine metal. Furthermore, a structure optimized to accomplish this purpose in metal detection of paper-like articles is provided.
[0002]
[Prior art]
The manufactured paper-like article such as paper or film needs to be inspected for a small piece of metal and removed from the mixed defective product. In this case, it is conceivable to use a metal detector that uses a high-frequency magnetic field in order to obtain non-magnetic metal as an object of detection and to obtain high sensitivity.
[0003]
Examples of conventional metal detection devices include a metal detection sensor in a transport conveyor disclosed in Japanese Patent Application Laid-Open No. 2001-91664, a metal detection method disclosed in Japanese Patent Application Laid-Open No. 08-086773, and a metal detector disclosed in Japanese Patent Application Laid-Open No. 2003-166704.
[0004]
Even though the conventional metal detectors have the maximum sensitivity, the length of the metal pieces is limited to, for example, about 400 μm. This may miss a piece of metal that can be seen with the naked eye and does not provide the required ability.
[0005]
In the conventional metal detector, the sensitivity adjuster is attached to the detector main body or its operation panel. This is because if the wiring that separates the sensitivity adjuster from the main body is used, noise due to a high-frequency magnetic field is induced and is not practical. For this reason, there have been restrictions on the incorporation of metal detectors into mechanical devices. This means that it cannot be installed in the back of a mechanical device in which neither a hand nor a driver can enter, and it is not possible to respond to a request to adjust sensitivity at an arbitrary position on the transport line from the convenience of operation. .
[0006]
In a metal detector using a high frequency magnetic field, an electrostatic shield plate is disposed. The reason why this is necessary will be described with reference to FIGS. FIG. 29 shows a case where the detection object W is disposed opposite to the transmission coil Ls and the reception coil Lp, and a stray capacitance C is generated between each of the coils Ls, Lp and the detection object W. This stray capacitance C varies depending on the size of the detected object W, and this charge / discharge current causes a large output change in the receiving coil Lp, resulting in noise. FIG. 30 shows a case in which the detected object W, which is a dielectric, is sandwiched between the transmission coil Ls and the reception coil Lp. For example, if the dielectric constant varies greatly due to the difference in the moisture content of the dielectric, The charging / discharging current causes a large output change in the receiving coil Lp, resulting in noise.
[0007]
In order to avoid this, as shown in FIG. 31, an electrostatic shield plate S is arranged between the transmission coil Ls, the reception coil Lp, and the detected object W. The electrostatic shield plate S is intended to block an electric field but allow a magnetic field to pass therethrough. In general, a conductor plate including a resistor is used. This is because if a conductor plate having zero resistance is used, both the magnetic field and the electric field are cut off. However, this has a problem that the magnetic field used for detection attenuates and at the same time, part of the electric field is transmitted to cause noise.
[0008]
Also, in the conventional paper-like article inspection device, if there is a paper-like article mixed with foreign matters such as metal, it is stored in the stocker in the inspection device, and only good paper-like articles are sent to the next process. ing. However, in this method, since the stocker is arranged below the conveyance line of the inspection apparatus, the total length in the conveyance direction extends by a length necessary for accommodating the paper-like article, and a large installation space in the factory is required. There was a problem to do.
[Patent Document 1] Japanese Patent Laid-Open No. 2001-91664
[Patent Document 2] Japanese Patent Application Laid-Open No. 08-086773
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2003-167064
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described conventional problems, and aims to solve the following problems.
(1) The metal detector has high sensitivity and low noise, thereby improving detection capability and enabling detection of minute metal pieces. (2) In a metal detector using a high-frequency magnetic field, it is possible to adjust sensitivity at a remote location. (3) To provide an electrostatic shield plate with a small magnetic field attenuation and a large electric field blocking effect. (4) In a paper-like article inspection apparatus, a structure is provided in which defective products are removed and stored in a stocker without increasing the overall length in the transport direction.
[0010]
In addition, the present invention provides (5) a structure of a conveyance line that is optimized in order to utilize the high detection capability of the metal detector for metal detection of paper-like articles, and (6) the object to be detected by metal is high. A structure that can easily cope with different cases is also provided.
[0011]
[Means for Solving the Problems]
The metal detector of the present invention uses a magnetic core while being a high-frequency coil in order to obtain a strong magnetic field that increases sensitivity. This is an elongated magnetic core in which three parallel magnetic poles are projected in a rail shape. Then, a transmitting coil is wound around the magnetic pole at the center of the magnetic core, and a pair of receiving coils are wound around the magnetic poles on both sides thereof to constitute a detecting means. In this method, a high-frequency magnetic flux is caused to flow from the transmission coil to the pair of reception coils, an output difference between the pair of reception coils is taken out, and a metal detection output is generated when this exceeds a predetermined threshold value.
[0012]
The output difference between the pair of receiving coils is extracted through a zero adjustment circuit composed of a variable resistor and a phase adjustment circuit composed of a variable reactance connection circuit. When the metal is not approaching the receiving coil, the output voltage and the phase of the pair of receiving coils are completely matched to prevent the occurrence of noise due to imbalance.
[0013]
In this way, the differential output that has been subjected to voltage zero adjustment and phase balance adjustment is amplified by an amplifying transformer having a resonance circuit on the secondary side. This resonance frequency is matched with the frequency of the high-frequency magnetic flux generated by the transmission coil. Since high selectivity can be obtained with this method, high sensitivity and low noise can be achieved at the same time. The metal detector itself is provided with a balance monitor circuit for displaying the output voltage and phase balance level of the receiving coil. As a result, the unbalance due to the mechanical distortion generated when the metal detector is attached to the site can be immediately removed by the zero point adjustment circuit and the phase balance adjustment circuit, and high sensitivity and low noise characteristics can be secured.
[0014]
In a metal detector that uses a high-frequency magnetic field, the structure that enables sensitivity adjustment at a remote location has a DC voltage output from a sensitivity adjuster placed outside the main body, which is a shield housing, It passes through a low-pass filter in the body and is given as a sensitivity adjustment signal in the body.
[0015]
The noise reduction in the present invention is also performed on the detection means in which a transmission coil and a pair of reception coils are wound around an elongated magnetic core. In this configuration, a plurality of the detection means having a reduced length are arranged in a straight line so as to obtain a required length, and the transmitting coils of adjacent magnetic cores have opposite polarities. This prevents the magnetic flux generated by the transmission coil from reaching far away and its reflection to become noise by shortening the major axis of the transmission coil and absorbing the magnetic flux to the adjacent transmission coil. In this structure, the detection is performed by flowing the high-frequency magnetic flux generated by each transmitting coil through a pair of receiving coils on both sides, as before the division.
[0016]
In the present invention, a metal detector that can easily cope with a case where the target articles have different heights has the following structure. This consists of a transmission part formed by winding a pair of transmission coils on the ends of two magnetic poles protruding in a rail shape on both sides of the magnetic core, and two magnetic pole tips protruding in a rail shape on both sides of the magnetic core In addition, the receiving part formed by winding a pair of receiving coils is opposed so that one side of both magnetic poles is in the same positional relationship, i.e., symmetrical and equidistant, and the output difference between the pair of receiving coils has a predetermined value. Generates metal detection output when exceeded. Then, the transmission unit and the reception unit are held by a holding mechanism so that the mutual interval can be adjusted, and the maximum sensitivity is adjusted according to the height of the target article.
[0017]
In metal detectors that use high-frequency magnetic fields, the electrostatic shield plate that covers the sensing means to eliminate noise caused by stray capacitance insulates thin good conductors from each other, and there is no gap in the thickness direction as seen by the overlapping of good conductors. It has a structure in which the ends of the good conductors are grounded in a plate shape.
[0018]
This structure of the electrostatic shield plate effectively blocks the electric field while allowing the magnetic field to penetrate well. The electrostatic shield plate is fixed to the tip surface of the magnetic pole of the magnetic core, so that even when there is vibration, the distance from the magnetic core is kept constant, and fluctuations in stray capacitance can be eliminated to prevent noise.
[0019]
In order to reduce noise generated in a metal detector caused by vibration transmitted from the outside, there is the following case structure.
[0020]
That is, a box-shaped metal case that houses a circuit board and has an open bottom, a bottom plate that covers the bottom opening of the metal case, a magnetic core that is wound with a high-frequency coil and fixed on the top plate of the metal case, An electrostatic shield plate fixed to the tip surface of the magnetic core magnetic pole, and an insulating cover placed over the metal case so as to cover at least the magnetic core and the electrostatic shield plate at a predetermined distance from the electrostatic shield plate Consists of. This structure is light and highly rigid, and minimizes the occurrence of distortion due to vibration transmitted from the conveyance line or the like, thereby reducing noise.
[0021]
When the metal detector having the above case structure is used for metal detection of a paper-like article, it is preferable that the transport line has the following structure. That is, the corner of the insulating cover on the article introduction side is a tapered surface or an R surface. This is to prevent the paper-like article fed by the supply roller from being caught on the corner of the insulating cover and hindering smooth feeding. Furthermore, in this structure, an air nozzle that blows air is provided so that the paper-like article moves along the upper surface of the insulating cover that is the detection surface. As a result, the detection sensitivity can be improved by keeping the distance from the coil for high frequency to a minimum, and the detection accuracy can be secured high.
[0022]
In the metal detector of the present invention using high frequency to achieve high sensitivity, if there is a substance that reacts to a high frequency magnetic field around it, it will cause noise. For this reason, the material of the article feed roller disposed on the article introduction side and the discharge side is an insulator having a property that hardly reacts to a high-frequency magnetic field as seen by the sensitivity of the metal detector of the present invention.
[0023]
In the inspection apparatus for paper-like articles, the present invention provides the following apparatus as a structure for removing defective products and collecting them in the stocker without increasing the overall length in the transport direction.
[0024]
This paper-like article inspection device is provided with a non-defective product discharge mechanism that is provided at a terminal portion and sends a non-defective product to the next process, a defective product discharge mechanism disposed above the non-defective product discharge mechanism, and a paper-like article according to the inspection result of the inspection machine. A guide mechanism that selectively takes a horizontal posture that directs the non-defective product to the non-defective product discharge mechanism and an upward posture that directs the paper-like article to the defective product discharge mechanism. A defective product collection stocker for receiving and stocking defective products discharged from the discharge mechanism is provided. This structure does not require a dedicated space because the defective product collection stocker protrudes above the next process apparatus.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a perspective view of a detection means 1 according to an embodiment of the present invention. FIG. 2 is a plan view thereof, and FIG. 3 is a side view thereof. In these drawings, reference numeral 2 denotes an elongated magnetic core projecting three parallel magnetic poles from the base, and is configured by arranging two elongated magnetic cores having a U-shaped cross section.
[0026]
A transmission coil 3 to which a high-frequency current is passed is wound around the magnetic pole 2 a at the center of the magnetic core 2, and a pair of reception coils 4 and 4 are wound around the magnetic pole 2 b on both sides of the magnetic core 2. As shown in FIG. 3, when a high frequency magnetic flux φ is caused to flow from the transmitting coil 3 to the receiving coils 4 and 4 on both sides to form two detection spaces D and D, and a small piece of metal enters one of the detection spaces, Utilizing the fact that a difference occurs between the outputs of the receiving coils 4 and 4, a metal detection output is generated when the output difference between the pair of receiving coils exceeds a predetermined value.
[0027]
Since this detecting means 1 has a magnetic path formed by the magnetic core 2, the sensitivity of the detecting means 1 can be increased by increasing the density of the magnetic flux φ coming out of the central magnetic pole 2a and reaching the magnetic poles 2b on both sides. That is, if the magnetic flux density is large, the loss is large when a metal enters the magnetic flux density, so that the induction output of the receiving coils 4 and 4 changes greatly. In addition, the detection means 1 has an advantage that a large magnetic flux density can be obtained with a considerably small number of turns, and the detection means 1 can be manufactured in a small size, as compared with a receiving coil having no magnetic core in a conventional detection device using a high-frequency magnetic field. is there.
[0028]
The magnetic core 2 may be any one as long as it projects three parallel magnetic poles from the base, and may be an integral type. Moreover, since the detection means 1 of the present invention detects a conductor, a conductor such as carbon is also a detection target.
[0029]
Next, FIG. 4 shows and describes the overall configuration of the metal detector 5 using the detection means 1. In FIG. 4, reference numeral 6 denotes a high frequency oscillator, 7 denotes a frequency dividing circuit thereof, and 8 denotes a power amplifier thereof. For example, 2 MHz is used as this frequency. The usable frequency range is 100 kHz to 10 MHz. Reference numeral 9 denotes a zero adjustment circuit, which is composed of a variable resistor. This variable resistor is connected to the receiving coils 4 and 4 of the detecting means 1 connected in series with a polarity that can obtain a difference in output. That is, two fixed terminals are connected to both ends of the receiving coils 4 and 4, and a movable contact is connected to the connection point of the receiving coils 4 and 4 so that the zero point can be adjusted.
[0030]
A phase adjustment circuit 10 is also connected to the receiving coils 4 and 4. For example, the variable capacitor is selectively connected to one of the receiving coils 4 and 4 by the changeover switch 11. In this way, in addition to the zero point adjustment by the variable resistor 9, the phase balance is also taken, thereby eliminating the occurrence of noise due to variations in the characteristics of the receiving coils 4 and 4. As a result, the S / N is increased, so that the amplification factor can be increased and the sensitivity can be increased.
[0031]
If a reactance variable circuit capable of adjusting both capacitive and inductive is used as the phase adjustment circuit 10, it is only necessary to connect this to one of the reception coils 4 and 4, so that the changeover switch 11 becomes unnecessary.
[0032]
Reference numeral 12 denotes an amplifying transformer having a resonance circuit on the secondary side, and this resonance frequency is matched with the frequency of the high-frequency magnetic flux generated by the transmission coil 3. The differential output that has been subjected to voltage zero adjustment and phase balance adjustment by the zero adjustment circuit 9 and the phase adjustment circuit 10 is amplified by the amplification transformer 12 with high selectivity. This is an extremely effective means for high sensitivity and low noise.
[0033]
A high frequency amplifier circuit 13 further amplifies the output of the amplifying transformer 12. Reference numeral 14 denotes a voltage detection circuit. Reference numeral 15 denotes a balance monitor circuit that displays the balance state of the output voltage and phase of the receiving coils 4 and 4. For example, as shown in the output characteristics of FIG. 5, the voltage increases due to the bias toward any of the receiving coils 4 and 4. Therefore, adjustment is performed by the zero adjustment circuit 9, the phase adjustment circuit 10, and the changeover switch 11 so that this output approaches the minimum in a state where the metal is not approaching. This is a necessary work especially after the metal detector 5 is installed on the site. This is because the detection means 1 and the surrounding casing are distorted by the external force applied at the time of installation, and the outputs of the receiving coils 4 and 4 become unbalanced.
[0034]
Reference numeral 16 denotes a voltage detection circuit, and reference numeral 17 denotes a low-frequency amplifier, which extracts a detection signal for determining the presence or absence of metal.
[0035]
Reference numeral 18 denotes a sensitivity adjuster composed of a variable resistor, 19 denotes an electric wire drawn out from the metal detector body, and 20 denotes a low-pass filter attached in the metal detector. This configuration is for enabling sensitivity adjustment at a remote location in a metal detector using a high-frequency magnetic field. The DC voltage output from the sensitivity adjuster 18 arranged outside the main body, which is a shield casing, is used. Through the electric wire 19 drawn out from the main body and the low-pass filter 20 in the main body, it is given as a sensitivity adjustment signal in the main body.
This sensitivity adjustment signal is used as a voltage threshold value of the comparator 21.
[0036]
The comparator 21 determines that the metal is detected when the detection signal output from the low-frequency amplifier 17 exceeds the voltage threshold obtained through the low-pass filter 20. An output circuit 22 amplifies the determination signal of the comparator 21 and outputs it to the outside.
[0037]
6 to 8 show other embodiments of the detection means of the present invention. The detecting means 23 is a shortened length of the detecting means 1 described in FIGS. 1 to 3, and a plurality of the detecting means 23 are arranged in a straight line to obtain a necessary length. Each detection means 23 is only short in length, and the cross-sectional shape of the magnetic core 24 is the same as the magnetic core 2 of the detection means 1. The winding method of the transmission coil 25 and the reception coil 26 is the same as that of the transmission coil 3 and the reception coil 4 of the detection means 1. However, the transmitting coils 25 of the adjacent magnetic cores 24 have opposite polarities. This is done by alternately reversing the winding direction or the current application direction. The connection of the receiving coils 26 and 26 are connected in series so that the connections on the same side are added as seen by the excitation polarity of the transmitting coil 25, and the pair of receiving coils 4 of the detecting means 1, So that an output equivalent to 4 can be obtained. The output from the receiving coils 26 and 26 may be taken out by taking a difference for each pair.
[0038]
The structure of the detection means in FIGS. 6 to 8 is intended to reduce noise by preventing the magnetic flux generated by the transmission coil 25 from reaching far away and its reflection becoming noise. This will be described next.
[0039]
Since the transmission coil 3 of the detection means 1 in FIGS. 1 to 3 has a long diameter that crosses the transport line, the magnetic flux is along a plane including the long diameter and the central axis, as shown in FIG. Spread greatly. Then, the metal reaches an undetected metal in the transport line or the like, changes the induction amount of the receiving coil 4 and causes noise.
[0040]
On the other hand, since the transmission coil 25 of the detection means 23 in FIGS. 6 to 8 has a short major axis, as shown in FIG. 9 (b), the reach distance of the magnetic flux is reduced and the magnetic flux emerging in the axial direction is adjacent. It is absorbed by the transmission coils 25 having different polarities. For this reason, the magnetic flux does not reach far and the generation of noise can be reduced.
[0041]
FIGS. 10A, 10B, and 11 show the structure of a transmission type metal detector suitable for metal detection of an article having a height. 10 (a) and 10 (b), reference numeral 27 denotes a receiving unit, which uses a magnetic core 29 having two magnetic poles 28, 28 protruding in a rail shape on both sides, and a pair of receiving coils 30, 28 at the tips of the magnetic poles 28, 28. 30 rolls. Reference numeral 31 denotes a transmitter, which similarly uses a magnetic core 33 with two magnetic poles 32 and 32 protruding like rails on both sides, and a pair of transmission coils 34 and 34 wound around the tips of the magnetic poles 32 and 32. It is.
[0042]
With this structure, high-frequency magnetic flux is caused to flow from the transmission coils 34 and 34 of the transmission unit 31 to the reception coils 30 and 30 of the reception unit 27 facing each other, and the output difference between the pair of reception coils 30 and 30 exceeds a predetermined value. When generating metal detection output. The transmitter 31 and the receiver 27 are operated by the circuit described in FIG. The receiving unit 27 and the transmitting unit 31 are configured so that both magnetic cores are opposed to each other so that the magnetic poles on one side are equally spaced. The width and length of the magnetic core 33 of the part 31 may be different. If the opposing relation between the magnetic poles on one side is the same, the output difference when there is nothing in the opposing space on both sides becomes zero, and the change when metal enters the opposing space on one side can be taken out as the output difference. .
[0043]
The reason why the receiving coils 30 and 30 and the transmitting coils 34 and 34 are wound around the tips of the magnetic poles in the receiving unit 27 and the transmitting unit 31 is that the reactance of the magnetic cores 29 and 33 is very large for the high-frequency magnetic flux. It is. If these are wound around the connecting portion of two magnetic poles, it becomes difficult to supply a sufficient magnetic flux from the tip of the magnetic pole toward the detection area.
[0044]
10 (a) and 10 (b), when the transmission unit 31 and the reception unit 27 are held by a holding mechanism 35 such as a frame as shown in FIG. The mutual interval can be adjusted according to the height of the object to be detected, and the detection sensitivity can be easily optimized.
[0045]
Since this may be a simple mechanism in which a holding position is determined by replacing a positioning pin or the like on the frame body, it is easy to implement. In this method, since the output balance of the receiving coils 30 and 30 is easily lost by adjusting the mutual interval, it is essential to adjust the zero point of the voltage and the balance of the phase after the adjustment. Since the circuit of FIG. 4 incorporates the balance monitor circuit 15, this adjustment can be performed immediately and the apparatus is highly practical.
[0046]
Next, the electrostatic shield plate of the present invention will be described. This is a metal detector that uses a high frequency magnetic field to cover the detection means in order to remove the noise caused by the capacitive component, and its structure insulates thin good conductors from each other, and the thickness direction as seen by the overlapping of good conductors. The end portions of the good conductors are grounded with no gaps. This has the feature that the attenuation of the magnetic field is small and the electric field blocking effect is large.
[0047]
For example, as shown in FIG. 12, two conductive plates 36 processed into a comb shape are used, and an insulating plate 37 is sandwiched between the conductive plates 36 as shown in FIGS. Are overlapped while providing an overlap portion 38 so that the other conductive plate 36 hides the gap. And the connection parts 39 and 39 of the electrically conductive board which overlapped up and down are connected through the through-hole 40, and are earth | grounded.
[0048]
The electrostatic shield plate 41 has no gap in the conductive plate when viewed in the thickness direction due to the overlap of the grounded conductive plate 36. Further, since a good conductor such as pure copper is used as the material of the conductive plate, there is almost no potential difference in the conductive plate 36. For this reason, it becomes a substantially perfect electrostatic shield.
[0049]
Consider the permeability of magnetic flux in this structure. Increasing the magnetic flux transmittance is how to reduce the magnetic loss W = Wh + We. If pure copper is used, the hysteresis loss Wh may be set to 0, and only the eddy current loss We becomes a problem. By the way, the eddy current loss We is expressed as We = kt. ² f ² / Ρ (where k is a proportional constant, t is a plate width, f is a frequency, and ρ is a specific resistance).
[0050]
Here, the plate width t is the width of the comb-teeth portion as shown in FIG. 12. By reducing this, the loss is reduced and the magnetic flux passes efficiently. Further, the specific resistance ρ is determined by the metal material of the conductive plate, and the proportionality constant k is determined by the thickness of the conductive plate, etc., so that it is set to an appropriate thickness.
[0051]
Other structures of the electrostatic shield plate are shown in FIGS. The electrostatic shield plate 42 is formed by cutting thin insulated wires 43 such as enameled wires into a predetermined length and arranging them in two rows as shown in FIG. And is short-circuited by soldering or the like as shown in FIG. The insulated wires 43 are fixed to each other with an adhesive so that they are as close as possible. The electrostatic shield plate 42 is attached while the soldering portion 45 is screwed to a metal housing or the like and grounded.
[0052]
The electrostatic shield plate 42 can be attached and assembled on an insulating sheet 46 as shown in FIG.
[0053]
The electrostatic shield plate 42 described with reference to FIGS. 15 to 17 also has no gap in the conductive plate when viewed in the thickness direction due to the overlapping of the conductor portions of the electric wires that are grounded good conductors. For this reason, it becomes a substantially perfect electrostatic shield, and the magnetic field is well transmitted while effectively blocking the electric field.
[0054]
These electrostatic shield plates 41 and 42 are bent in a saddle shape along the folding line l shown in FIGS. 14 and 17, and are fixed on the top surface of the metal case 47 as shown in FIGS. It is attached so as to cover the detection means 1. This attachment is performed by fixing the electrostatic shield plates 41 and 42 to the magnetic pole tip surfaces of the magnetic cores 2 and 24 with an adhesive or the like. This is to prevent the mutual interval from fluctuating due to vibration and the stray capacitance C in FIG. 31 from changing to cause noise.
[0055]
The electrostatic shield plates 41 and 42 have a lattice structure in which one side is opened in order to prevent the circulating current from flowing. However, when the generation direction of the magnetic field in the detection means is seen in FIGS. The magnetic potentials of the magnetic poles on both sides are kept at 0. If this condition is met, the circulating current does not flow, so that both sides can be short-circuited.
[0056]
The structure for attaching the electrostatic shield plate to the detection means described with reference to FIGS. 18 and 19 is similarly applied to the transmission unit 31 and the reception unit 27 of the transmission type metal detector shown in FIG. is there.
[0057]
In a metal detector using high-frequency magnetic flux, the receiving coil becomes unbalanced due to distortion caused by vibration transmitted from the outside, and noise is generated. A structure for reducing this will be described with reference to FIGS.
[0058]
FIG. 20 is an exploded perspective view of the metal detector 5 according to one embodiment of the present invention. The magnetic core 2 of the detecting means 1 is fixed on the top plate of a box-shaped metal case 47 whose bottom is opened. Then, as described with reference to FIG. 19, the electrostatic shield plate 41 is fixed to the magnetic pole tip surface of the magnetic core 2 with an adhesive or the like to cover the detection means 1. Further, a resin insulating cover 48 is put on the metal case 47. This is because, as shown in FIG. 21, in order to ensure a distance that does not come in contact with vibration, a predetermined gap G is provided with respect to the electrostatic shield plate 41, and at least the detection means 1 and the electrostatic shield plate 41 are covered. Do as follows. A circuit board 49 is accommodated in the metal case 47 as shown in FIG. 22, and its bottom opening is covered with a metallic bottom plate 50 to form a shield housing.
[0059]
As shown in FIG. 23, from the assembly of the metal case 47, a covered electric wire 52 in which wiring for sensitivity adjustment, an output signal line, a balance monitor output line, a power supply line and the like are bundled is drawn out from one end face. Further, an L-shaped metal fitting 53 for mounting is screwed to both end faces.
[0060]
This structure uses a light and highly rigid box-shaped metal case 47, and the detection means 1 and the electrostatic shield plate 41 are fixed to the top plate of the metal case 47, so that distortion caused by vibrations transmitted from a conveyor or the like is minimized. Can reduce noise. In addition, since the insulating cover 48 serving as a passage for the detection object is attached to the electrostatic shield plate 41 with a predetermined gap G, vibration generated with the passage of the detection object is electrostatically connected to the detection means 1. This is not directly transmitted to the shield plate 41, and this also has the effect of reducing noise.
[0061]
Next, a paper-like article inspection apparatus incorporating the metal detector 5 of the present invention will be described.
[0062]
In the paper-like article inspection apparatus 54 shown in FIGS. 24 to 26, 55 to 59 are drive rollers for conveying the paper-like article P, and 60 is an inspection machine arranged between the drive rollers 56 and 57. A metal detector 5 is used. Reference numerals 61 and 62 denote drop rollers arranged before and after the inspection machine 60, and the paper rollers are rotated around the drive rollers 56 and 57 so that the paper-like article P is sent along the inspection machine 60. invite.
[0063]
63 is a photoelectric switch for detecting the arrival of the paper-like article P. Reference numeral 64 denotes a drop-in roller, which rotates with the drive roller 59 and feeds the paper-like article P backward. Reference numeral 65 denotes a guide mechanism. When the paper-like article P is detected by the photoelectric switch 63, the guide plate 67 is rotated by the solenoid 66 that moves according to the determination result of the inspection machine 60. Then, a horizontal posture in which the paper-like article P is directed to the non-defective product discharge mechanism 68 and an upward posture in which the paper-like article P is directed to the defective product discharge mechanism 69 are selectively taken.
[0064]
The non-defective product discharge mechanism 68 has a drop roller 71 disposed on the drive roller 70, and the paper-like article P that has passed over the guide plate 67 in the horizontal posture remains in the horizontal posture and the drive roller 70 and the drop roller 71. And is sent to the equipment 72 of the next process.
[0065]
The defective product discharge mechanism 69 includes two driven rollers 73 and 74 disposed above the non-defective product discharge mechanism 68. The uppermost driven roller 70 is rotatably attached to the tip of a lever 76 that is fixed to a rotation support shaft 75 provided above the guide mechanism 65. The lower driven roller 73 is rotated with the dropping roller 71 of the non-defective product discharge mechanism 68, and the upper driven roller 74 is rotated with the lower driven roller 73. On both sides of the defective product discharge mechanism 69, a pair of guide rods 77, 77 curved along the movement path of the paper-like article P are arranged with their base ends fixed to the rotary support shaft 75. The guide rods 77 and 77 prevent the paper-like article P from jumping upward. The guide rods 77 and 77 are fixed to the rotary support shaft 75 together with the driven roller 74 at the top, and one of the guide rod 77 and the driven roller 74 is made into a paper shape. When it is lifted away from the passage path of the article P, the other occurs. This improves the operability when the stored paper-like article P is taken out.
[0066]
Reference numeral 78 denotes a defective product collection stocker in which a locking portion 79 is bent at one end. The defective product collection stocker 78 is disposed so as to protrude in the feed direction above the terminal end of the apparatus main body, and the defective paper-like article P discharged from the defective product discharge mechanism 69. Receive and stock. The defective product collection stocker 78 is detachably attached to the holder 80, and when a certain amount of paper-like articles are collected, the defective product collection stocker 78 can be removed and transferred together to another container.
[0067]
24 to 26, the paper-like article P that is supplied one by one and inspected by the inspection machine 60 is conveyed by driving rollers 57, 58, and 59 and a dropping roller 62. When the photoelectric switch 63 detects this arrival, the guide plate 67 of the guide mechanism 65 is moved according to the determination result of the inspection device 60. Then, the non-defective product is sent to the apparatus 72 of the next process through the non-defective product discharge mechanism 68, and the defective product is sent to the defective product collection stocker 78 through the defective product discharge mechanism 69 and stored therein.
[0068]
This structure does not require a dedicated space because the defective product collection stocker 78 is provided so as to protrude above the apparatus for the next process. Therefore, even if the paper-like article which is a defective product has a certain length, it can be accommodated without increasing the total length in the transport direction.
[0069]
In the paper-like article inspection apparatus 54, a structure in which the paper-like article P can smoothly pass over the inspection surface of the inspection machine 60 and the inspection accuracy can be improved will be described.
[0070]
FIGS. 27 and 28 are enlarged views of the vicinity of the inspection machine 60 of FIG. 24, and the height of the upper surface of the inspection machine 60 is slightly lower than the feed height of the drive roller 56. With this structure, in the inspection machine 60, the corner on the inlet side and the corner on the outlet side of the article are processed into an inclined surface or an R surface. This is to eliminate the catch of the paper-like article P sent by the drive roller 56. This processing may be performed at least at the corner on the inlet side. In this embodiment, the corners on both the inlet side and the outlet side are machined into inclined surfaces or R surfaces in order to obtain the above effects even if they are attached in the opposite direction. A plurality of air nozzles 81 are arranged above the inspection machine 60.
[0071]
Clean air that has passed through an air filter is discharged from the air nozzle 81. This air flow flows downstream along the upper surface of the inspection machine 60 while drawing the air flow from the lower side. In the state shown in FIG. 27 where there is no paper-like article P, the upper surface of the inspection machine 60 is kept in a clean state free from dust. When the paper-like article P is in the state of FIG. 28, it is moved along the upper surface of the inspection machine 60 that is slightly lower than the feed height of the drive roller 56. This keeps the distance from the high frequency coil to a minimum, so that the detection sensitivity can be increased and the detection accuracy can be maintained high.
[0072]
The transmission metal detector shown in FIG. 10 can also employ the structures shown in FIGS. The arrangement of the transmission unit 31 in this case is indicated by a broken line.
[0073]
In the metal detector of the present invention using high frequency to achieve high sensitivity, if there is a substance that reacts to a high frequency magnetic field around it, it will cause noise. For this reason, the material of the article supply roller disposed on the article introduction side and the discharge side is an insulator having a property that hardly reacts to a high-frequency magnetic field. This corresponds to the supply rollers 56 and 57 and the dropping rollers 61 and 62 in the embodiment shown in FIGS. The insulating cover 48 of FIG. 20 also uses the above insulator.
[0074]
Here, “not easily reacting to a high-frequency magnetic field” means that the detection signal is not changed in the metal detector having the sensitivity of the present invention, and does not simply mean that it is a non-magnetic insulator. For example, acrylic resin is unsuitable for use because it changes the detection signal. An example of a resin that does not easily react to a high-frequency magnetic field and can be used in the present invention is polycarbonate resin. Incidentally, the metal detectors currently in general use do not have the sensitivity to detect acrylic resin.
[0075]
【The invention's effect】
According to the present invention, high sensitivity and low noise of a metal detector using a high frequency magnetic field are achieved. As a result, the detection capability is improved, and for example, a minute metal piece having a length of about 100 μm can be detected.
[0076]
The high sensitivity and low noise are described in I.I. Coil structure capable of detecting with strong magnetic field II. Coil differential output extraction system that performs phase adjustment as well as zero adjustment, III. A highly selective amplification method in which the differential output of the coil is amplified by an amplifying transformer having a resonance circuit, IV. Limiting the magnetic flux arrival distance by alternately changing the polarity of the divided transmission coils between adjacent ones; Providing an electrostatic shield plate with a small magnetic field attenuation and a large electric field blocking effect; VI. This is achieved by an assembly structure of a shield housing that hardly generates noise due to external vibration.
[0077]
Furthermore, the present invention has the effects listed below.
Since the metal detector itself is provided with a balance monitor circuit, it is possible to immediately remove the unbalance caused by mechanical distortion caused by installation on the site by adjusting the zero point and adjusting the phase balance, thereby ensuring high sensitivity and low noise characteristics.
[0078]
In the present invention, the DC voltage output from the sensitivity adjuster arranged outside the main unit is supplied as a sensitivity adjustment signal in the main unit through the electric wire and the low-pass filter in the main unit, so that sensitivity adjustment at a remote location is possible. became.
[0079]
In the present invention, the defective product after the inspection is distributed by the guide plate so as to pass through the defective product discharge mechanism disposed above the non-defective product discharge mechanism, and is disposed at the end of the apparatus so as to protrude above the apparatus of the next process. Store in the defective product collection stocker. This makes it possible to effectively use the space in the factory without requiring a dedicated space for storing defective products.
[0080]
The present invention provides a structure optimized for metal detection of paper-like articles, and can maintain high detection accuracy. This structure is provided with an air nozzle that blows air so that the corner of the metal detector on the article introduction side has a tapered surface or an R surface and the moving paper-like article is along the upper surface of the insulating cover that is the detection surface. .
[0081]
The present invention provides a structure in which the transmission unit and the reception unit are held by the holding mechanism so that the mutual interval can be adjusted as a transmission type metal detector, so that it is easy when the metal detection target articles have different heights. Yes.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a detection means of the present invention.
FIG. 2 is a plan view showing an embodiment of the detection means of the present invention.
FIG. 3 is a side view showing an embodiment of the detection means of the present invention.
FIG. 4 is a block diagram showing an overall configuration of a metal detector according to an embodiment of the present invention.
5 is a diagram showing a differential output with respect to a deviation in voltage and phase balance in a pair of receiving coils in FIG. 4; FIG.
FIG. 6 is a perspective view showing another embodiment of the detection means of the present invention.
FIG. 7 is a plan view showing another embodiment of the detection means of the present invention.
FIG. 8 is a side view showing another embodiment of the detecting means of the present invention.
9 is a diagram showing the spread of magnetic field lines in the height direction of a transmission coil in comparison with that of the detecting means (a) of FIG. 1 and that of the detecting means of FIG. 6 (b).
FIG. 10 is a perspective view (a) and a side view of a transmission unit and a reception unit in a transmission type metal detector.
11 is a perspective view showing a structure for holding a transmitter and a receiver of the metal detector of FIG.
FIG. 12 is a plan view showing a comb-shaped conductor plate constituting the electrostatic shield plate of the present invention.
FIG. 13 is a side view of the electrostatic shield plate of the present invention.
14 is a plan view of the electrostatic shield plate of FIG.
FIG. 15 is a side view showing another embodiment of the electrostatic shield plate of the present invention.
16 is a plan view of the electrostatic shield plate of FIG. 15. FIG.
17 is a plan view of the electrostatic shield plate of FIG. 15 assembled on an insulating sheet.
FIG. 18 is a plan view of an electrostatic shield plate attached so as to cover the detection means fixed on the upper surface of the metal case.
19 is a perspective view showing the structure of FIG.
FIG. 20 is an exploded perspective view of the metal detector of the present invention.
21 is a side view showing an overlapping state of each part when the metal detector of FIG. 20 is assembled.
22 is a perspective view of a metal case portion of the metal detector of FIG. 20 as viewed from the back side.
23 is a perspective view showing a state after the metal detector of FIG. 20 is assembled.
FIG. 24 is a side view of a paper-shaped article inspection apparatus.
25 is a plan view of the paper-shaped article inspection apparatus of FIG. 24. FIG.
26 is a plan view showing a defective product discharge mechanism in the inspection apparatus of FIG. 25. FIG.
FIG. 27 is an enlarged view of the peripheral portion of the metal detector in the inspection apparatus of FIG. 24, showing a state where there is no paper-like article.
FIG. 28 is an enlarged view of the peripheral portion of the metal detector in the inspection apparatus of FIG. 24, showing a state where there is a paper-like article.
FIG. 29 is a diagram for explaining stray capacitance generated in the detection means, and showing a case where a detection object is disposed opposite to a transmission coil and a reception coil.
FIG. 30 is a diagram for explaining stray capacitance generated in the detection means, showing a case where a detection object is sandwiched between a transmission coil and a reception coil.
FIG. 31 is a diagram showing a state in which an electrostatic shield plate is arranged in order to eliminate the influence of stray capacitance generated in the detection means.
[Explanation of symbols]
1,23 detection means
2,24,29,33 Magnetic core
2a Center magnetic pole
2b Magnetic poles on both sides
3, 25, 34 Transmitting coil
4, 26, 30 Receiver coil
φ High frequency magnetic flux
D Detection space
5 Metal detector
6 High frequency oscillator
7 divider circuit
8 Power amplifier
9 Zero adjustment circuit
10 Phase adjustment circuit
11 changeover switch
12 Amplification transformer
13 High frequency amplifier circuit
14 Voltage detection circuit
15 Balance monitor circuit
16 Voltage detection circuit
17 Low frequency amplifier
18 Sensitivity adjuster
19 Electric wire
20 Low-pass filter
21 Comparator
22 Output circuit
27 Receiver
28, 32 magnetic poles
31 Transmitter
36 Conductive plate
37 Insulation plate
38 Overlap part
40 Through hole
41, 42 Electrostatic shield plate
43 Insulated wire
44 Insulation coating
45 Soldering part
46 Insulation sheet
47 Metal case
48 Insulation cover
49 Wiring board
50 Bottom plate
54 Inspection Equipment for Paper-shaped Articles
55-59 Driving roller
60 Inspection machine (metal detector)
61-62, 64 Dropping roller
65 Guide mechanism
67 Guide plate
68 Good product discharge mechanism
69 Defective product discharge mechanism
78 Defective product collection stocker

Claims (15)

From an elongated magnetic core having three parallel magnetic poles protruding like a rail, a transmission coil wound around the magnetic pole in the center of the magnetic core, and a pair of receiving coils wound around the magnetic poles on both sides of the magnetic core. Comprising the detection means
A metal detector characterized by taking an output difference between a pair of receiving coils that receive a high-frequency magnetic flux generated by a transmitting coil, and generating a metal detection output when this exceeds a predetermined value. The metal detector according to claim 1, further comprising: a zero point adjustment circuit that adjusts a voltage zero point and a phase adjustment circuit that adjusts a phase balance with respect to an output difference between the pair of receiving coils. The output difference between the pair of receiving coils that have been subjected to voltage zero adjustment and phase balance adjustment is amplified by resonating with an amplifying transformer whose secondary resonance frequency is matched with the frequency of the high-frequency magnetic flux generated by the transmitting coil. The metal detector according to claim 2. The metal detector according to claim 2 or 3, further comprising a balance monitor circuit that displays a balance level between a voltage and a phase with respect to an output difference between the pair of receiving coils. In a metal detector that detects metal by flowing high-frequency magnetic flux generated by the transmission coil through the reception coil,
A metal characterized in that the DC voltage output from the sensitivity adjuster placed outside the main body, which is a shielded housing, is passed through the wire drawn from the main body and the low-pass filter in the main body, and given as a sensitivity adjustment signal in the main body Finder. From an elongated magnetic core having three parallel magnetic poles protruding like a rail, a transmission coil wound around the magnetic pole in the center of the magnetic core, and a pair of receiving coils wound around the magnetic poles on both sides of the magnetic core. A plurality of detection means are arranged in a straight line,
The transmitter coils of adjacent magnetic cores are reversed in polarity, and high-frequency magnetic flux generated by each transmitter coil is caused to flow through a pair of receiver coils on both sides, and the output difference between the pair of receiver coils is taken, and this exceeds a predetermined value. A metal detector that generates a metal detection output when A pair of transmission coils formed by winding a pair of transmission coils around the tips of two magnetic poles protruding in a rail shape on both sides of the magnetic core, and a pair of tips on the two magnetic poles protruding in a rail shape on both sides of the magnetic core The receiving part formed by winding the receiving coil is opposed so that one side of both magnetic poles is equidistant, and a metal detection output is generated when the output difference between the pair of receiving coils exceeds a predetermined value. A metal detector characterized by The metal detector according to claim 7, wherein the transmission unit and the reception unit are held by a holding mechanism so that a mutual interval can be freely adjusted. An electrostatic shield plate characterized in that thin good conductors are insulated from each other, arranged in a plate shape without gaps in the thickness direction as seen by overlapping of the good conductor portions, and the ends of the good conductors are grounded. The metal detector according to any one of claims 1, 6, and 7, wherein the electrostatic shield plate according to claim 9 is fixed to a tip surface of a magnetic pole of a magnetic core. A box-shaped metal case containing a circuit board and having an open bottom, a bottom plate covering the bottom opening of the metal case, a magnetic core wound with a high-frequency coil and fixed on the top plate of the metal case, and a magnetic core An electrostatic shield plate fixed to the tip of the magnetic pole of the magnetic shield, and an insulating cover placed on a metal case so as to cover at least the magnetic core and the electrostatic shield plate with a predetermined spacing from the electrostatic shield plate A metal detector characterized by being made. 12. The metal detector according to claim 11, wherein a corner portion on the article introduction side of the insulating cover is a tapered surface or an R surface. 13. The metal detector according to claim 12, further comprising an air nozzle that blows air so that the paper-like article moves along the upper surface of the insulating cover that is a detection surface. The metal detector according to any one of claims 1, 6, and 7, wherein an article feed roller made of an insulator having a property that hardly reacts to a high-frequency magnetic field is arranged on the article introduction side and the discharge side. In a device that transports paper-like articles, stocks by rejecting defective products based on the inspection results of an inspection machine installed in the middle, and sends only good products to the next process,
A non-defective product discharge mechanism that is provided at the end and sends non-defective products to the next process, a defective product discharge mechanism that is placed above the non-defective product discharge mechanism, and a horizontal posture that directs paper-like articles to the non-defective product discharge mechanism according to the inspection results of the inspection machine And a guide mechanism that selectively takes an upward posture to direct the paper-like article toward the defective product discharge mechanism, and a defective product discharged from the defective product discharge mechanism provided in the discharge direction above the terminal end of the apparatus main body. An inspection apparatus for paper-like articles, comprising a defective product collection stocker that receives and stocks.

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