JP2021169980A - Metal detector - Google Patents

Abstract

To provide a metal detector that can adjust an output signal in normal time to zero in an ex-post manner.SOLUTION: A metal detector of the present invention comprises: a transmission signal output unit that outputs a transmission signal; a transmission coil that is applied with the transmission signal output from the transmission signal output unit and generates an alternating magnetic field in an inspection area Z; two reception coils that are arranged at positions where the coils can supplement a magnetic flux generated by the transmission coil and generates inductive voltages based on the alternating magnetic field in the inspection area generated by the transmission coil; a control unit 10 that determines the presence or absence of metal in the inspection area based on a difference between the inductive voltages generated in the two reception coils and outputs a determination result; an adjustment signal output unit that generates and outputs an adjustment signal based on a signal synchronized with the transmission signal output from the transmission signal output unit; and an adjustment coil that is arranged in the inspection area and applied with the adjustment signal output from the adjustment signal output unit.SELECTED DRAWING: Figure 1

Description

The present invention relates to a metal detection device that detects the presence or absence of metal in an object to be inspected, for example, food or clothing.

Conventionally, as a metal detection device of this type, for example, the one described in Patent Document 1 is known. The metal detection device described in Patent Document 1 is arranged at positions in front of and behind the conveyor, a transmission coil provided so as to surround an inspection area on the transport surface of the conveyor, and a transmission coil in the transport direction. It includes two receiving coils having the same shape.

The transmission coil generates a magnetic field in the inspection region based on the magnetic field transmission signal supplied from the waveform generation unit. The two receiving coils are arranged symmetrically with the transmitting coil in between to detect a magnetic field and generate an induced voltage. The two receiving coils are connected so that the difference between the induced voltages generated in the two is an output, and in normal times, the induced voltages generated in the two receiving coils are balanced and the received signal becomes substantially zero. On the other hand, when an object to be inspected containing metal is conveyed in the inspection region, the equilibrium of the induced voltage generated in the two receiving coils is lost, and the received signal changes. When the received signal exceeds a predetermined value in this way, it can be detected that the object to be inspected contains metal.

Japanese Patent No. 6577974

As described above, in a metal detector, ideally, when there is no metal in the inspection area, the induced voltages generated in the two receiving coils are perfectly balanced and the output signal becomes zero, but in reality Due to the imbalance of the arrangement of the two receiving coils, the output signal may have a weak fluctuation synchronized with the magnetic field transmission signal. Since such fluctuations are rate-determining with respect to the detection limit of metals, it is necessary to suppress them as much as possible. Therefore, a mechanism for inserting a metallic adjusting screw is provided in the inspection area, and when installing the metal detection device, the insertion position and insertion amount of the adjusting screw are adjusted so that the output signal in normal times is the upper limit of the predetermined allowable value. It was supposed to be as follows.

However, even if the adjustment is made at the time of installation as described above, the equilibrium of the induced voltage generated in the two receiving coils may be lost due to a change with time or the like, and the output signal in normal times may fluctuate.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a metal detection device capable of ex post-adjustment so that the output signal in normal times becomes zero.

In order to solve the above problems, the metal detection device of the present invention has a transmission signal output unit that outputs a transmission signal and a transmission coil to which a transmission signal output by the transmission signal output unit is applied to generate an alternating magnetic field in the inspection region. The difference between the two receiving coils that generate the induced voltage based on the alternating magnetic field generated by the transmitting coil and the induced voltage generated in the two receiving coils, which are arranged at positions where the magnetic flux generated by the transmitting coil can be captured. A control unit that determines the presence or absence of metal in the inspection area based on the above and outputs the determination result, and an adjustment signal output unit that generates and outputs an adjustment signal based on a reference signal synchronized with the transmission signal output by the transmission signal output unit. It includes an adjustment coil that is arranged in the inspection area and to which an adjustment signal output by an adjustment signal output unit is applied.

In the present invention, the adjustment signal output unit may output a signal in which at least one of the amplitude, phase, and waveform of the reference signal is changed as the adjustment signal. For example, the reference signal may be a signal obtained by branching the transmission signal. Then, the control unit sets at least one of the amplitude, phase, and waveform of the adjustment signal in the adjustment signal output unit so that the difference between the induced voltages generated in the two receiving coils does not exceed a predetermined allowable value. It is good to do.

In the present invention, the metal detection device further includes a transport means for transporting the object to be inspected in the transport direction so as to pass through the inspection region, and the two receiving coils are symmetrical with respect to the transport direction by the transport means with respect to the transmission coil. It should be placed in a position.

In the present invention, the metal detection device may further include a position adjusting mechanism for adjusting the physical arrangement of members in the inspection area. The position adjusting mechanism may include an adjusting screw receiver having at least one screw hole penetrating toward the inspection area, and an adjusting screw screwed into the screw hole. In this case, at least one screw hole may be provided at a position where the distances from the two receiving coils are not equal. Further, the adjusting coil may be provided on the adjusting screw.

It is a block diagram which shows the structure of a metal detection apparatus 1. It is a figure which shows the inspection area Z defined on the transport surface 61a together with the transmission coil 21 and the reception coil 22 included in the metal detection part 20. It is a figure which shows typically the circuit which comprises the signal processing part 30 and adjustment part 40. It is a figure which shows the structure of the adjustment part 40. FIG. 5A is a perspective view showing the structure of the adjusting screw 42 in a state where the adjusting coil 43 is not wound. FIG. 5B is a perspective view showing an adjusting screw 42 in a state where the adjusting coil 43 is wound.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same members are designated by the same reference numerals, and the description of the members once described will be omitted as appropriate.

[Structure of metal detector]
As shown in FIG. 1, the metal detection device 1 in the present 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 means. And. The metal detection device 1 detects the presence or absence of metal in the object W to be inspected, which is conveyed by the conveyor 60 and passes through the inspection area Z.

The object W to be inspected is, for example, a mass-produced food packaged with a packaging material, and even if it is a fixed shape such as a boxed product, it has an irregular shape such as a flexible bag containing a fluid or the like. It may be a product or a frozen product. Further, the object W to be inspected is not limited to food.

The conveyor 60 conveys the object W to be inspected under the control of the control unit 10. The conveyor 60 includes an endless annular conveyor belt 61 and transport rollers 62 and 63 as transport means for transporting the object W to be inspected in the illustrated transport direction. The conveyor belt 61 has a transport surface 61a on which the object W to be inspected is placed and transported in the transport direction.

FIG. 2 is a diagram showing an inspection region Z defined on the transport surface 61a together with a transmission coil 21 and a reception coil 22 included in the metal detection unit 20. As shown in FIG. 2, a predetermined region on the transport surface 61a of the conveyor belt 61 is the inspection region Z. Therefore, the object W to be inspected is conveyed by the conveyor 60 so as to pass through the inspection area Z.

The metal detection unit 20 includes one transmission coil 21 and two reception coils 22A and 22B (hereinafter, the two reception coils may be collectively referred to as a reception coil 22). Further, the signal processing unit 30 includes a transmission signal output unit 31, a reception signal processing unit 32, and an adjustment signal output unit 33.

The transmission coil 21 is arranged so as to surround a predetermined position in the transport direction in the inspection region Z. The number of turns of the transmission coil 21 may be, for example, about 1 to 5 turns. The transmission coil 21 is connected to the transmission signal output unit 31. The transmission signal output unit 31 outputs an AC transmission signal to the transmission coil 21 under the control of the control unit 10. The frequency, amplitude, and the like of the transmission signal output by the transmission signal output unit 31 may be set by the control unit 10. A transmission signal output by the transmission signal output unit 31 is applied to the transmission coil 21, and an alternating magnetic field is generated in the inspection region Z.

The two receiving coils 22 are arranged at positions where the magnetic flux generated by the transmitting coil 21 can be captured. Specifically, the two receiving coils 22 are formed in the same shape and surround the inspection region Z at positions symmetrical with respect to the transmitting coil 21 in the transport direction (that is, at positions equidistant from the transmitting coil 21). Each is placed. The two receiving coils 22 are connected so that the difference in induced voltage generated between them becomes an output. For example, the two receiving coils 22 may be arranged so as to be wound in opposite directions to each other and may be connected in series as shown in FIG. Then, the potential difference between both ends of the two receiving coils 22 connected in series (that is, the difference in the induced voltage between the two receiving coils) is given to the received signal processing unit 32 as the received signal which is the output of the metal detection unit 20. It is good to do. The receiving coil 22 may be provided with a post-stage amplifier that amplifies a signal or the like in a subsequent stage. In the present specification, the receiving coil 22 including the latter-stage amplifier is referred to.

By doing so, in normal times when there is no metal in the inspection region Z, ideally, due to the alternating magnetic field generated by the transmitting coil 21, the two receiving coils 22 have opposite polarities and have the same induced voltage. Occurs (ie equilibrates). Further, when metal is present in the inspection region Z, a difference in induced voltage occurs between one receiving coil 22 and the other receiving coil 22.

The received signal processing unit 32 includes a signal amplifier 32A and an AD converter 32B. The signal amplifier 32A amplifies the received signal from the metal detection unit 20 at a predetermined amplification factor according to the input voltage range of the AD converter 32B. The AD converter 32B samples the signal amplified by the signal amplifier 32A at predetermined sampling intervals, and outputs sampling data discretized to a plurality of sampling points to the control unit 10.

The control unit 10 performs processing such as comparison between the received signal and the determination threshold value based on the sampling data output from the reception signal processing unit 32, and determines the presence or absence of metal. Further, the control unit 10 may display the determination result, a signal waveform obtained by plotting the time change of the received signal, or the like on the display unit 50. The display unit 50 is, for example, a liquid crystal display device. Under the control of the control unit 10, the display unit 50 displays a determination result, a signal waveform in which the time change of the received signal is plotted, an operation interface, and the like.

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

However, in the actual metal detection device 1, the induced voltage generated in the two receiving coils 22 by the alternating magnetic field generated by the transmitting coil 21 is not completely balanced due to the influence of manufacturing error, installation environment, etc. (unbalanced). Will be) in some cases. If there is such an imbalance between the two receiving coils 22, an unnecessary variable component is generated in the received signal. When the received signal including the fluctuating component is amplified and AD-converted, it is necessary to suppress the amplification factor in order to keep the amplified signal within the input voltage range of the AD converter 32B. As a result of suppressing the amplification factor in this way, the detection sensitivity and the detection accuracy cannot be sufficiently improved.

Therefore, it is necessary to eliminate the imbalance between the two receiving coils 22 as much as possible. The adjusting unit 40 is provided in order to eliminate such an imbalance and adjust the received signal given to the received signal processing unit 32 in normal times when there is no metal in the inspection region Z so as to be less than a predetermined allowable value. Be done.

The adjusting unit 40 includes an adjusting screw receiver 41, an adjusting screw 42, and an adjusting coil 43. The adjusting screw receiver 41 and the adjusting screw 42 are examples of the position adjusting mechanism. The adjusting screw receiver 41 is a member on a flat plate provided in the vicinity of the inspection area Z over the transmission coil 21 and the two receiving coils 22A and 22B, and a plurality of screw holes 41A penetrating toward the inspection area Z. Has. In this example, as shown in FIG. 4, the screw hole 41A is on the opposite side of the receiving coil 22A from 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 receiving. A total of eight coils, two each, are provided on the opposite side of the coil 22B from the transmission coil 21. As described above, the screw holes 41A may be provided at positions where the distances from the two receiving coils 22 are not equal. Although omitted in FIG. 4, a metal plate is provided between the adjusting screw receiver 41 and the transmitting coil 21 and the receiving coil 22 to shield the inspection region Z from an external magnetic field. A hole through which the adjusting screw 42 can be inserted is provided at a position corresponding to each screw hole 41A of the metal plate.

The balance adjustment using the adjusting screw 42 is performed when the metal detection device 1 is installed. In a state where a transmission signal is applied to the transmission coil 21 to generate an alternating magnetic field, the position of the screw hole 41A into which the adjustment screw 42 is screwed and the tightening amount of the adjustment screw 42 are determined while monitoring the output voltage of the metal detection unit 20. , Adjust so that the received signal output by the metal detection unit 20 does not exceed a predetermined allowable value.

Even if the balance is adjusted by finely adjusting the physical arrangement of various members in the inspection area Z, such as tightening the adjusting screw 42, the balance may be lost after installation due to the passage of time or changes in the surrounding environment. Therefore, the metal detection device 1 of the present embodiment makes it possible to perform balance adjustment without changing the tightening amount of the adjustment screw 42 by the adjustment coil 43 and the adjustment signal output unit 33.

The adjustment signal output unit 33 supplies to the adjustment coil 43 an adjustment signal in which at least one of the amplitude, phase, and waveform of the reference signal obtained by branching the transmission signal output by the transmission signal output unit 31 is changed. Here, "changing the waveform" refers to a case where, for example, an adjustment signal of a square wave or a triangular wave is output based on a reference signal of a sine wave. The adjustment signal output unit 33 may include a variable amplifier circuit, a variable delay circuit, an arbitrary waveform generator, and the like in order to realize these adjustments. An adjustment signal supplied from 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 adjusting coil 43 causes an induced voltage in the two receiving coils 22 together with the alternating magnetic field generated by the transmitting coil 21.

The adjusting coil 43 is arranged at a position that affects each of the two receiving coils 22 differently (that is, a position that is not equidistant from the two receiving coils 22).

For example, the adjusting coil 43 may be provided while being wound around the adjusting screw 42. In this way, it is possible to adjust the balance by generating an alternating magnetic field for adjustment at the position of the adjusting screw 42 that was adjusted when the metal detection device 1 was installed. FIG. 5 shows a configuration example of the adjusting screw 42 and the adjusting coil 43, which are suitable for realizing such a configuration. FIG. 5A is a perspective view showing the structure of the adjusting screw 42 in a state where the adjusting coil 43 is not wound. FIG. 5B is a perspective view showing an adjusting screw 42 in a state where the adjusting coil 43 is wound. The adjusting screw 42 includes a screw head 42A, a screw portion 42B, a bobbin portion 42C, and a wire passage portion 42D. When the adjustment coil 43 is wound around the adjustment screw 42 as shown in FIG. 5, the screw material may be a non-magnetic metal, plastic, or the like, but a soft magnetic material such as iron may be used. It is preferable to use it. By making the adjusting screw 42 soft magnetic, the magnetic flux generated by the adjusting coil 43 can be increased.

The screw head 42A is a portion for turning the adjusting screw 42 with a predetermined tool such as a screwdriver or a wrench, and has a groove, a hole, an outer shape, or the like corresponding to the tool. The screw portion 42B is provided so as to extend from the screw head 42A. A male screw to be screwed into the female screw provided in the screw hole 41A of the adjusting screw receiver 41 is provided on the outer circumference of the screw portion 42B. The bobbin portion 42C is a portion around which the adjusting coil 43 is wound, and is provided so as to extend from the tip portion of the screw portion 42B (that is, the end portion opposite to the screw head 42A). The bobbin portion 42C is formed to be thinner than the screw portion 42B so that the outer diameter of the wound adjusting coil 43 is smaller than the inner diameter of the screw hole 41A and the valley diameter of the screw portion 42B.

The wiring portion 42D provides a space for passing the wiring 43A to the adjusting coil 43 from the screw head 42A side to the bobbin portion 42C via the screw portion 42B. The wire-passing portion 42D may be formed, for example, as a groove from the screw head 42A side through the screw portion 42B to the bobbin portion 42C. Alternatively, a part or all of the adjusting screw 42 may have a hollow structure, and the hollow portion extending from the screw head 42A side to the bobbin portion 42C may be a wire passing portion 42D. By providing such a wire passage portion 42D, an adjustment signal can be given to the adjustment coil 43 wound around the bobbin portion 42C without impairing the function of the screw.

The amplitude, phase, and waveform settings of the adjustment signal output unit 33 are adjusted by the control of the control unit 10. The control unit 10 acquires sampling data from the AD converter 32B while causing the transmission signal output unit 31 to output a transmission signal. In this state, the control unit 10 acquires sampling data while changing the amplification factor and the phase shift amount by the adjustment signal output unit 33, and the value of the received signal (voltage of the received signal converted from the sampled data) is predetermined. Identify settings that do not exceed the permissible value. Any method of changing the settings to identify the appropriate settings is optional. For example, the settings may be changed in order so as to cover the entire settable range, or the set values are sequentially determined by a binary search method or the like, which is more efficient and appropriate in a shorter time than covering the entire range. The settings may be identifiable.

The metal detection device 1 may perform the balance adjustment by the adjustment coil 43 as described above each time it is started. Further, the control unit 10 outputs an alert prompting the balance adjustment using the adjustment screw 42 to the display unit 50 or the like when the received signal cannot be contained within the predetermined allowable range even by the adjustment by the adjustment coil 43. It is good to configure.

As described above, the metal detection device 1 in the present embodiment can easily adjust the balance of the induced voltages of the two receiving coils 22 in the normal state in which no metal is present in the inspection region Z.

Although the present embodiment has been described above, the present invention is not limited to these examples. For example, in the above embodiment, two receiving coils 22 are connected in series and the voltage across the two receiving coils 22 is used as a receiving signal, but the circuit type is limited to this if the difference between the induced voltages of the two receiving coils 22 can be output. Not done. For example, the induced voltage in each of the two receiving coils 22 may be input to the differential amplifier, and the output of the differential amplifier may be used as a received signal.

Further, in the above embodiment, the transmitting coil 21 and the two receiving coils 22 are provided so as to surround the inspection area Z (that is, the object W to be conveyed by the conveyor 60 passes through the loop). However, the transmitting coil 21 and the two receiving coils 22 may be provided so as to face each other with the inspection region Z interposed therebetween. For example, the transmitting coil 21 is arranged along the upper surface of the inspection area Z, the two receiving coils 22 are arranged along the lower surface of the inspection area Z (for example, directly under the conveyor belt 61), and the two receiving coils 22 are arranged. It may be arranged so as to line up in the transport direction. Alternatively, the transmitting coil 21 is arranged on one side surface of the inspection area Z, the two receiving coils 22 are arranged along the other side surface of the inspection area Z, and the two receiving coils 22 are arranged so as to be aligned in the transport direction. You may.

Further, in the above embodiment, the object W to be inspected is conveyed by the conveyor 60 so as to pass through the inspection area Z, but the metal detection device 1 does not have to include a conveying means such as the conveyor 60. For example, the metal detection device 1 may be configured to have an input port for the object to be inspected W at the upper part and an discharge port at the lower part, and to provide an inspection area Z between the input port and the discharge port. Then, even if the metal detection is performed while the object W to be inspected dropped from the input port and passes through the inspection area Z (that is, the moving direction of the object W to be inspected is set to the vertical direction). good.

Alternatively, the inspected object W may be configured to perform metal detection on the inspected object W placed in the inspection area Z without moving the inspected object W. In this case, it is preferable that the worker or the like appropriately places the inspected object W in the inspection area Z before performing the inspection, and takes out the inspected object W from the inspection area Z after the inspection is completed.

Further, in the above embodiment, the balance of the induced voltages of the two receiving coils 22 in the normal state is adjusted by adjusting the position by tightening the adjusting screw 42, but the present invention is not limited to this, and the inspection region Z can be obtained by any method. The balance may be adjusted by finely adjusting the physical arrangement of various members (reception coil 22, transmission coil 21, adjusting screw 42, other magnetic member, etc.). For example, a mechanism capable of moving a metal bar may be provided according to the principle of leverage, and fine adjustment may be performed according to the position of the bar.

Further, in the above embodiment, the adjustment signal output unit 33 adjusts by changing at least one of the amplitude, phase, and waveform of the signal obtained by branching the transmission signal output by the transmission signal output unit 31 as a reference signal. Although the signal is generated and output, the reference signal does not have to be a branched signal as long as it is synchronized with the transmission signal. For example, a reference signal may be output from a signal source synchronized with the transmission signal, and an adjustment signal in which at least one of the amplitude, phase, and waveform is changed based on the reference signal may be generated and output. ..

In addition, those skilled in the art appropriately adding, deleting, or changing the design of each of the above-described embodiments, and those in which the features of each embodiment are appropriately combined are also provided with the gist of the present invention. As long as it is, it is included in the scope of the present invention.

1 Metal detection device 10 Control unit 20 Metal detection unit 30 Signal processing unit 40 Adjustment unit 50 Display unit 60 Conveyor W Inspected object Z Inspection area

Claims (9)

A transmission signal output unit that outputs a transmission signal and
A transmission coil to which a transmission signal output by the transmission signal output unit is applied to generate an alternating magnetic field in an inspection region, and a transmission coil.
Two receiving coils, which are arranged at positions where the magnetic flux generated by the transmitting coil can be captured and generate an induced voltage based on the alternating magnetic field generated by the transmitting coil in the inspection region,
A control unit that determines the presence or absence of metal in the inspection region based on the difference in induced voltage generated in the two receiving coils and outputs the determination result.
An adjustment signal output unit that generates and outputs an adjustment signal based on a reference signal synchronized with the transmission signal output by the transmission signal output unit.
An adjustment coil arranged in the inspection area and to which an adjustment signal output by the adjustment signal output unit is applied.
A metal detection device comprising. The metal detection device according to claim 1, wherein the adjustment signal output unit outputs a signal in which at least one of the amplitude, phase, and waveform of the reference signal is changed as an adjustment signal. The metal detection device according to claim 1 or 2, wherein the reference signal is a signal obtained by branching the transmission signal. The control unit sets at least one of the amplitude, phase, and waveform of the adjustment signal in the adjustment signal output unit so that the difference between the induced voltages generated in the two receiving coils does not exceed a predetermined allowable value. The metal detection apparatus according to claim 2 or 3. Further provided with a transport means for transporting the object to be inspected in the transport direction so as to pass through the inspection area.
The metal detection device according to any one of claims 1 to 4, wherein the two receiving coils are arranged at positions symmetrical with respect to the transmitting coil in the transport direction by the transport means. The metal detection device according to any one of claims 1 to 5, further comprising a position adjusting mechanism for adjusting the physical arrangement of members in the inspection area. The position adjusting mechanism is
An adjusting screw receiver having at least one screw hole penetrating toward the inspection area.
The metal detection device according to claim 6, further comprising an adjusting screw screwed into the screw hole. The metal detection device according to claim 7, wherein at least one screw hole is provided at a position where the distances from the two receiving coils are not equal. The metal detection device according to claim 7 or 8, wherein the adjusting coil is provided on the adjusting screw.

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