Metal detection device

Abstract

The present application provides a metal detection device capable of adjusting the output signal to zero at ordinary times. The metal detection device of the present application comprises: a transmission signal output unit that outputs a transmission signal; a transmission coil that is applied with the transmission signal output by the transmission signal output unit to generate an alternating magnetic field in an inspection area; two receiving coils that are arranged at positions capable of supplementing the magnetic flux generated by the transmission coil, and generate induced voltages based on the alternating magnetic field generated by the transmission coil in the detection area; a control unit that determines whether there is metal in the inspection area based on the difference between the induced voltages generated by the two receiving coils, and outputs the determination result; an adjustment signal output unit that generates and outputs an adjustment signal based on a signal synchronized with the transmission signal output by the transmission signal output unit; and an adjustment coil that is arranged in the inspection area and is applied with the adjustment signal output by the adjustment signal output unit.

Description

Technical Field

[0001] The present invention relates to a metal detection device for detecting whether there is metal in an object to be inspected, such as food, clothing, etc. Background Art

[0002] Conventionally, a known metal detection device of this type is described in Patent Document 1, for example. The metal detection device described in Patent Document 1 includes: a conveyor for conveying an object to be inspected; a transmitting coil disposed so as to surround an inspection area on a conveying surface of the conveyor; and two receiving coils of the same shape disposed before and after the transmitting coil in the conveying direction.

[0003] The transmitting coil generates a magnetic field in the inspection area based on a magnetic field transmission signal supplied by the waveform generator. Two receiving coils, positioned symmetrically with the transmitting coils sandwiched between them, detect the magnetic field and generate an induced voltage. The two receiving coils are connected so that the difference in the induced voltage generated between them serves as the output. Normally, the induced voltages generated in the two receiving coils are balanced, and the received signal is essentially zero. However, when an object containing metal is transported through the inspection area, the induced voltages generated in the two receiving coils become unbalanced, causing the received signal to change. This allows detection of the presence of metal in the object if the received signal exceeds a specified value.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6577974 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] As mentioned above, in a metal detector, ideally, when no metal is present in the inspection area, the induced voltages generated in the two receiving coils are perfectly balanced, resulting in a zero output signal. However, in reality, due to imbalances in the configuration of the two receiving coils, the output signal may fluctuate slightly in sync with the magnetic field transmission signal. This fluctuation limits the metal detection limit, and therefore must be minimized. Therefore, a mechanism for inserting a metallic adjustment screw is provided in the inspection area. When the metal detector is installed, the insertion position and amount of the adjustment screw are adjusted so that the output signal under normal conditions is below the specified upper limit of the allowable value.

[0009] However, even if adjustments are made during installation as described above, the induced voltages generated in the two receiving coils may become unbalanced due to changes over time, and the output signal may fluctuate during normal operation.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a metal detection device that can be adjusted afterwards so that the output signal in normal times becomes zero.

[0011] Solutions for solving problems

[0012] In order to solve the above problems, the metal detection device of the present invention comprises: a transmitting signal output unit, which outputs a transmitting signal; a transmitting coil, to which the transmitting signal output by the transmitting signal output unit is applied to generate an alternating magnetic field in the inspection area; two receiving coils, the two receiving coils being arranged at a position capable of supplementing the magnetic flux generated by the transmitting coil, and generating an induced voltage based on the alternating magnetic field generated by the transmitting coil in the inspection area; a control unit, which determines whether there is metal in the inspection area based on the difference between the induced voltages generated in the two receiving coils, and outputs the determination result; an adjustment signal output unit, which generates an adjustment signal based on a reference signal synchronized with the transmitting signal output by the transmitting signal output unit and outputs the adjustment signal; and an adjustment coil, which is arranged in the inspection area and is applied with the adjustment signal output by the adjustment signal output unit.

[0013] In the present invention, the adjustment signal output unit may output, as the adjustment signal, a signal obtained by changing at least one of the amplitude, phase, and waveform of a reference signal. For example, the reference signal may be a signal obtained by branching a transmission signal. Furthermore, the control unit may adjust at least one of the amplitude, phase, and waveform of the adjustment signal set by the adjustment signal output unit so that the difference in induced voltages generated in the two receiving coils falls within a predetermined allowable range.

[0014] In the present invention, the metal detection device may further include a conveying unit that conveys the object to be inspected in a conveying direction so as to pass through the inspection area, and the two receiving coils may be arranged at positions symmetrical with the transmitting coil as the center in the conveying direction of the conveying unit.

[0015] In the present invention, the metal detection device may further include a position adjustment mechanism for adjusting the physical configuration of the component within the inspection area. The position adjustment mechanism may further include an adjustment screw seat having at least one screw hole extending through the inspection area, and an adjustment screw threaded into the screw hole. In this case, the at least one screw hole may be positioned at unequal distances from the two receiving coils. Furthermore, the adjustment coil may be attached to the adjustment screw. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 2 is a block diagram showing the structure of the metal detection device 1 .

[0017] Figure 2 This figure shows the detection area Z defined on the conveying surface 61 a together with the transmitting coil 21 and the receiving coil 22 included in the metal detector 20 .

[0018] Figure 3 Schematic diagram of a circuit including the signal processing unit 30 and the adjustment unit 40 .

[0019] Figure 4 3 is a diagram showing the configuration of the adjustment unit 40 .

[0020] Figure 5 (a) is a perspective view showing the structure of the adjustment screw 42 in a state where the adjustment coil 43 is not wound. Figure 5 (b) is a perspective view showing the adjustment screw 42 in a state where the adjustment coil 43 is wound around it.

[0021] Description of Reference Numerals

[0022] 1: Metal detection device; 10: Control unit; 20: Metal detection unit; 30: Signal processing unit; 40: Adjustment unit; 50: Display unit; 60: Conveyor; W: Object to be inspected; Z: Inspection area. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. In the following description, the same components are denoted by the same reference numerals, and description of components that have already been described once will be appropriately omitted.

[0024] [Structure of Metal Detection Device]

[0025] like Figure 1 As shown, the metal detection device 1 in this embodiment includes a control unit 10, a metal detection unit 20, a signal processing unit 30, an adjustment unit 40, a display unit 50, and a conveyor 60 as a transport unit. The metal detection device 1 detects the presence of metal in an object W transported by the conveyor 60 and passing through an inspection area Z.

[0026] The object to be inspected W is, for example, a mass-produced food packaged in packaging material. It can be a fixed-shaped product such as a boxed product, a non-fixed-shaped product such as a soft bag containing a fluid, or a frozen product. Furthermore, the object to be inspected W is not limited to food.

[0027] The conveyor 60 transports the inspection object W under the control of the control unit 10. The conveyor 60 includes an endless conveyor belt 61 as a conveying unit for conveying the inspection object W in the conveying direction shown in the figure, and conveying rollers 62 and 63. The conveyor belt 61 has a conveying surface 61a for placing the inspection object W and conveying the inspection object W in the conveying direction.

[0028] Figure 2 61a is a diagram showing the inspection area Z defined on the conveying surface 61a together with the transmitting coil 21 and the receiving coil 22 included in the metal detector 20. Figure 2 As shown in FIG, a predetermined area on the conveying surface 61 a of the conveyor belt 61 is the inspection area Z. Therefore, the inspection target object W is conveyed by the conveyor 60 so as to pass through the inspection area Z.

[0029] The metal detector 20 includes a transmitting coil 21 and two receiving coils 22A and 22B (hereinafter, the two receiving coils may be collectively referred to as receiving coils 22 ). The signal processing unit 30 includes a transmitting signal output unit 31 , a receiving signal processing unit 32 , and an adjustment signal output unit 33 .

[0030] The transmitting coil 21 is arranged to surround a predetermined position in the transport direction within the examination region Z. The number of turns of the transmitting coil 21 is preferably set to approximately 1 to 5 turns, for example. The transmitting coil 21 is connected to a transmission signal output unit 31. Under the control of the control unit 10, the transmission signal output unit 31 outputs an AC transmission signal to the transmitting coil 21. The frequency, amplitude, etc. of the transmission signal output by the transmission signal output unit 31 are preferably set by the control unit 10. The transmission signal output by the transmission signal output unit 31 is applied to the transmitting coil 21 to generate an alternating magnetic field in the examination region Z.

[0031] The two receiving coils 22 are arranged at positions where they can supplement the magnetic flux generated by the transmitting coil 21. Specifically, the two receiving coils 22 are formed into the same shape and are respectively arranged at positions symmetrical to the transmitting coil 21 in the conveying direction (i.e., positions equidistant from the transmitting coil 21) so as to surround the inspection area Z. The two receiving coils 22 are connected so that the difference in induced voltage generated therebetween becomes the output. For example, the two receiving coils 22 are preferably arranged so as to be wound in opposite directions to each other, and as shown in FIG. Figure 3 , as shown. Furthermore, the potential difference between the two ends of the two receiving coils 22 connected in series (that is, the difference in the induced voltages in the two receiving coils) is preferably provided to the received signal processing unit 32 as the output of the metal detection unit 20, namely, the received signal. Furthermore, a post-amplifier for signal amplification may be provided after the receiving coil 22. In this specification, the receiving coil 22, including this post-amplifier, is referred to as the receiving coil 22.

[0032] In this way, when there is no metal in the inspection area Z, ideally, the two receiving coils 22 generate induced voltages of opposite polarity and equal magnitude (i.e., they are balanced) due to the alternating magnetic field generated by the transmitting coil 21. However, when there is metal in the inspection area Z, a difference occurs in the induced voltage between one receiving coil 22 and the other receiving coil 22.

[0033] The received signal processing unit 32 is composed of a signal amplifier 32A and an A / D converter 32B. The signal amplifier 32A amplifies the received signal from the metal detector 20 at a predetermined amplification factor corresponding to the input voltage range of the A / D converter 32B. The A / D converter 32B samples the signal amplified by the signal amplifier 32A at predetermined sampling intervals and outputs the sampled data, which is discretized into a plurality of sampling points, to the control unit 10.

[0034] Based on the sampled data output from the received signal processing unit 32, the control unit 10 performs processing such as comparing the received signal with a determination threshold to determine the presence of metal. Furthermore, the control unit 10 preferably causes the display unit 50 to display the determination results, a signal waveform obtained by plotting the time variation of the received signal, and the like. The display unit 50 is, for example, a liquid crystal display. Under the control of the control unit 10, the display unit 50 displays the determination results, the signal waveform obtained by plotting the time variation of the received signal, an operation interface, and the like.

[0035] In the metal detection device 1 configured as described above, under normal circumstances when no metal exists in the inspection area Z, the induced voltages of the two receiving coils 22 ideally completely cancel each other out, and the received signal is zero [V].

[0036] However, in actual metal detection devices 1, the induced voltages generated in the two receiving coils 22 by the alternating magnetic field generated by the transmitting coil 21 can sometimes become completely unbalanced (imbalanced) due to manufacturing errors, installation environment, and other factors. This imbalance between the two receiving coils 22 produces unwanted fluctuations in the received signal. When amplifying and converting a received signal containing these fluctuations, the amplification factor must be suppressed so that the amplified signal falls within the input voltage range of the AD converter 32B. However, suppressing the amplification factor in this way fails to fully improve detection sensitivity and accuracy.

[0037] Therefore, it is necessary to minimize the imbalance between the two receiving coils 22. To eliminate this imbalance and adjust the received signal provided to the received signal processing unit 32 so that it is smaller than a predetermined allowable value when no metal exists in the inspection area Z, an adjustment unit 40 is provided.

[0038] The adjustment unit 40 includes an adjustment screw seat 41, an adjustment screw 42, and an adjustment coil 43. The adjustment screw seat 41 and the adjustment screw 42 are an example of a position adjustment mechanism. The adjustment screw seat 41 is a flat plate-shaped member that is arranged near the inspection area Z across the transmitting coil 21 and the two receiving coils 22A and 22B, and has a plurality of screw holes 41A that penetrate toward the inspection area Z. In this example, as shown in FIG. Figure 4As shown, two screw holes 41A are provided on the side of the receiving coil 22A opposite to the transmitting coil 21, between the receiving coil 22A and the transmitting coil 21, between the transmitting coil 21 and the receiving coil 22B, and on the side of the receiving coil 22B opposite to the transmitting coil 21, for a total of eight screw holes 41A. As such, the screw holes 41A are preferably provided at positions with unequal distances from the two receiving coils 22. Figure 4 It is omitted in the figure, but a metal plate is provided between the adjustment screw seat 41 and the transmitting coil 21 and the receiving coil 22 to shield the external magnetic field so that the inspection area Z is not affected by the external magnetic field, and holes that can be inserted by the adjustment screws 42 are provided at positions corresponding to the screw holes 41A of the metal plate.

[0039] Balance adjustment using the adjustment screw 42 is performed when the metal detector 1 is installed. While applying a transmission signal to the transmitting coil 21 to generate an alternating magnetic field, the output voltage of the metal detector 20 is monitored. The position of the screw hole 41A into which the adjustment screw 42 is inserted and the amount by which the adjustment screw 42 is tightened are adjusted so that the received signal output by the metal detector 20 falls within a predetermined allowable range.

[0040] Even if balance is adjusted by fine-tuning the physical arrangement of various components within the inspection area Z, such as by tightening the adjustment screw 42, balance may be lost after installation due to the passage of time, changes in the surrounding environment, etc. Therefore, the metal detection device 1 of this embodiment can perform balance adjustment without changing the tightening amount of the adjustment screw 42 by adjusting the coil 43 and the signal output unit 33.

[0041] The adjustment signal output unit 33 supplies an adjustment signal to the adjustment coil 43, obtained by changing at least one of the amplitude, phase, and waveform of a reference signal. This reference signal is obtained by branching the transmission signal output by the transmission signal output unit 31. Here, "changing the waveform" refers to, for example, outputting a rectangular or triangular wave adjustment signal based on a sinusoidal reference signal. To achieve these adjustments, the adjustment signal output unit 33 may include a variable amplification circuit, a variable delay circuit, an arbitrary waveform generator, and the like. The adjustment signal supplied by the adjustment signal output unit 33 is applied to the adjustment coil 43 to generate an alternating magnetic field. The alternating magnetic field generated by the adjustment coil 43, together with the alternating magnetic field generated by the transmission coil 21, induces a voltage in the two receiving coils 22.

[0042] The adjustment coil 43 is disposed at a position that has different effects on the two receiving coils 22 (ie, at a position at unequal distances from the two receiving coils 22 ).

[0043] For example, the adjustment coil 43 is preferably wound around the adjustment screw 42. In this way, the balance can be adjusted by generating an alternating magnetic field for adjustment at the position of the adjustment screw 42 where the balance adjustment was performed when the metal detector 1 was installed. Figure 5 2 shows an example of the structure of the adjustment screw 42 and the adjustment coil 43 that is suitable for realizing such a structure. Figure 5 (a) is a perspective view showing the structure of the adjustment screw 42 in a state where the adjustment coil 43 is not wound. Figure 5 (b) is a perspective view showing the adjustment screw 42 with the adjustment coil 43 wound around it. The adjustment screw 42 includes a screw head 42A, a threaded portion 42B, a bobbin portion 42C, and a wire-passing portion 42D. Figure 5 In the illustrated configuration where the adjustment coil 43 is wound around the adjustment screw 42, the screw can be made of non-magnetic metal or plastic, but preferably a soft magnetic material such as iron. Making the adjustment screw 42 soft magnetic can enhance the magnetic flux generated by the adjustment coil 43.

[0044] The screw head 42A is a portion used to rotate the adjustment screw 42 using a specified tool such as a screwdriver or a wrench, and has a groove, hole, and shape corresponding to the tool. The threaded portion 42B is provided to extend from the screw head 42A. An external thread is provided on the outer periphery of the threaded portion 42B for threaded engagement with the internal thread of the screw hole 41A provided in the adjustment screw seat 41. The bobbin portion 42C is a portion around which the adjustment coil 43 is wound, and is provided to extend from the top end of the threaded portion 42B (that is, the end on the opposite side of the screw head 42A). The bobbin portion 42C is formed to be thinner than the threaded portion 42B so that the outer diameter of the adjustment coil 43 after winding is smaller than the inner diameter of the screw hole 41A and the minor diameter of the threaded portion 42B.

[0045] The wire passage 42D provides space for the wiring 43A leading to the adjustment coil 43 to pass from the screw head 42A side through the threaded portion 42B to the bobbin portion 42C. The wire passage 42D is preferably formed as a groove that extends from the screw head 42A side through the threaded portion 42B to the bobbin portion 42C. Alternatively, a portion or all of the adjustment screw 42 may be hollow, with the hollow portion from the screw head 42A side to the bobbin portion 42C serving as the wire passage 42D. By providing such a wire passage 42D, an adjustment signal can be provided to the adjustment coil 43 wound on the bobbin portion 42C without disrupting the function of the screw.

[0046] The settings of the amplitude, phase, and waveform made by the adjustment signal output unit 33 are adjusted under the control of the control unit 10. The control unit 10 causes the transmission signal output unit 31 to output the transmission signal and obtains sampling data from the AD converter 32B. In this state, the control unit 10 obtains sampling data while changing the amplification factor and phase offset obtained by the adjustment signal output unit 33 to determine the setting for making the value of the received signal (the voltage of the received signal obtained by converting the sampling data) converge to a range that does not exceed the prescribed allowable value. The method of changing the setting in order to determine the appropriate setting is arbitrary. For example, the setting can be changed sequentially in a manner that covers the entire range that can be set, or the setting value can be determined sequentially by a binary search method, etc., which can effectively determine the appropriate setting in a shorter time than covering the entire range.

[0047] The metal detection device 1 preferably performs the balance adjustment using the adjustment coil 43 as described above each time it is started. Furthermore, the control unit 10 is preferably configured to output an alarm to the display unit 50 or the like, urging the user to perform balance adjustment using the adjustment screw 42, if the received signal cannot be brought within a predetermined allowable range even after adjustment using the adjustment coil 43.

[0048] As described above, the metal detection device 1 in this embodiment can easily adjust the balance of the induced voltages of the two receiving coils 22 in a normal state where no metal exists in the inspection area Z.

[0049] While the above describes the present embodiment, the present invention is not limited to this example. For example, in the above embodiment, two receiving coils 22 are connected in series, and the voltage across them is used as the received signal. However, the circuit form is not limited to this, as long as the difference in the induced voltages in the two receiving coils 22 can be output. For example, the induced voltages in the two receiving coils 22 can be input to a differential amplifier, and the output of the differential amplifier can be used as the received signal.

[0050] In addition, in the above-described embodiment, the transmitting coil 21 and the two receiving coils 22 are arranged so as to surround the inspection area Z (that is, so that the inspection object W conveyed by the conveyor 60 passes through the loop), but the transmitting coil 21 and the two receiving coils 22 may be arranged so as to face each other with the inspection area Z sandwiched therebetween. For example, the transmitting coil 21 may be arranged along the upper surface of the inspection area Z, and the two receiving coils 22 may be arranged along the lower surface of the inspection area Z (for example, directly below the conveyor 61), with the two receiving coils 22 arranged in the conveying direction. Alternatively, the transmitting coil 21 may be arranged on one side of the inspection area Z, and the two receiving coils 22 may be arranged along the other side of the inspection area Z, with the two receiving coils 22 arranged in the conveying direction.

[0051] In the above-described embodiment, the inspected object W is transported by the conveyor 60 through the inspection area Z. However, the metal detection device 1 may not include a transport unit such as the conveyor 60. For example, the metal detection device 1 may be configured to include an inlet for the inspected object W at the top and an outlet at the bottom, with the inspection area Z disposed between the inlet and the outlet. Furthermore, the device may be configured to perform metal detection while the inspected object W is dropped from the inlet and passes through the inspection area Z (that is, the direction of movement of the inspected object W is set to the vertical direction).

[0052] Alternatively, the metal detection may be performed on the object W placed in the inspection area Z without moving the object W. In this case, it is preferred that an operator appropriately place the object W in the inspection area Z before the inspection and remove the object W from the inspection area Z after the inspection is completed.

[0053] Furthermore, in the above-described embodiment, the balance of the induced voltages of the two receiving coils 22 in the normal state is adjusted by tightening the adjustment screw 42 to adjust the position. However, this is not limiting. Balance adjustment can also be achieved by fine-tuning the physical arrangement of various components (receiving coil 22, transmitting coil 21, adjustment screw 42, and other magnetic components) within the inspection area Z using any method. For example, a mechanism that uses a lever to move a metal rod can be provided, and fine-tuning can be achieved by adjusting the position of the rod.

[0054] Furthermore, in the above-described embodiment, the adjustment signal output unit 33 uses a signal obtained by branching the transmit signal output by the transmit signal output unit 31 as a reference signal to generate and output an adjustment signal by varying at least one of its amplitude, phase, and waveform. However, as long as the reference signal is synchronized with the transmit signal, it need not be a signal obtained by branching the transmit signal. For example, a signal generation source synchronized with the transmit signal may output a reference signal, and based on this reference signal, an adjustment signal is generated and output by varying at least one of its amplitude, phase, and waveform.

[0055] Furthermore, additions, deletions, and design changes to the above-described embodiments made by those skilled in the art are also encompassed within the scope of the present invention as long as they encompass the spirit of the present invention.

Claims

1. A metal detection device, characterized in that: have: a transmission signal output unit that outputs a transmission signal; a transmitting coil to which the transmitting signal outputted by the transmitting signal output portion is applied so as to generate an alternating magnetic field in an examination region; two receiving coils, the two receiving coils being arranged at positions capable of supplementing the magnetic flux generated by the transmitting coil and generating an induced voltage based on the alternating magnetic field generated by the transmitting coil in the examination area; a control unit that determines whether metal is present in the inspection area based on a difference in induced voltages generated in the two receiving coils and outputs a determination result; an adjustment signal output unit that generates an adjustment signal based on a reference signal synchronized with the transmission signal output by the transmission signal output unit and outputs the adjustment signal; as well as an adjustment coil, which is arranged in the inspection area and to which the adjustment signal outputted by the adjustment signal output unit is applied, The transmitting coil and the receiving coil are coaxial coils surrounding the inspection area, and the adjustment coil is a coil smaller than both the transmitting coil and the receiving coil.

2. The metal detection device according to claim 1, characterized in that The adjustment signal output unit outputs a signal obtained by changing at least one of the amplitude, phase, and waveform of the reference signal as the adjustment signal.

3. The metal detection device according to claim 1 or 2, characterized in that: The reference signal is a signal obtained by branching the transmission signal.

4. The metal detection device according to claim 2, characterized in that: The control unit adjusts at least one of the amplitude, phase, and waveform of the adjustment signal set by the adjustment signal output unit so that the difference between the induced voltages generated in the two receiving coils falls within a range that does not exceed a predetermined allowable value.

5. The metal detection device according to claim 1 or 2, characterized in that: The apparatus further comprises a conveying unit for conveying the object to be inspected in a conveying direction so as to pass through the inspection area. The two receiving coils are arranged at positions symmetrical with respect to the transmitting coil in the conveying direction of the conveying unit.

6. The metal detection device according to claim 1 or 2, characterized in that: A position adjustment mechanism is further provided for adjusting the physical arrangement of the component within the inspection area.

7. The metal detection device according to claim 6, characterized in that: The position adjustment mechanism comprises: an adjusting screw seat having at least one screw hole extending toward the inspection area; and An adjusting screw is screwed into the screw hole.

8. The metal detection device according to claim 7, characterized in that: At least one of the screw holes is arranged at positions with unequal distances from the two receiving coils.

9. The metal detection device according to claim 7 or 8, characterized in that: The adjusting coil is arranged on the adjusting screw.

10. The metal detection device according to claim 1, wherein: The loop area of ​​the adjustment coil is smaller than both the loop area of ​​the transmitting coil and the loop area of ​​the receiving coil.

11. The metal detection device according to claim 1 or 2, characterized in that: The adjusting coil has a winding shaft on which the adjusting coil is wound.

12. The metal detection device according to claim 11, characterized in that: The winding axis intersects the transmitting coil and the receiving coil near the adjustment coil.

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