JP2021043176A - Metal detector - Google Patents

Abstract

To provide a metal detector that is not easily affected by noise for a long time and can maintain high inspection accuracy.SOLUTION: A metal detector 10 generates a magnetic field in an inspection area 14 at a predetermined inspection frequency, passes an inspection object 12 through the inspection area 14 to detect fluctuations in the magnetic field, and thereby inspects the inspection object 12 for foreign matters. The metal detector 10 includes a transmission signal processing unit 22 that finely adjusts the inspection frequency within a predetermined frequency range, and a range adjusting unit 38 that changes the frequency range. The metal detector measures noise at a plurality of inspection frequencies, and displays a screen for comparing the measured noise for each frequency range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a metal detector, and more particularly to a metal detector that suppresses the influence of noise.

A metal detector is known as a device for inspecting food or the like for foreign substances mixed with metal. The metal detector inspects foreign matter in an inspected object by generating a magnetic field in the inspected area, passing the inspected object through the inspected area, and detecting fluctuations in the magnetic field.

It is known that such a metal detector is easily affected by electromagnetic noise (hereinafter, simply referred to as noise) outside the device. For example, if there is an inverter device around the metal detector, a noise peak will be generated at each predetermined frequency, and if a magnetic field is generated and detected at a frequency close to that noise, the effect of noise will increase. It becomes impossible to detect small foreign substances.

Therefore, the metal detector of Patent Document 1 has a predetermined bandwidth (for example, 10 kHz) from the “predetermined frequency range corresponding to the influence of the article to be inspected” (range of several kHz to several MHz). A plurality of inspection frequencies are set with, the noise is measured at the plurality of inspection frequencies, and the inspection frequency is automatically set by selecting the inspection frequency at which the noise level is equal to or less than a predetermined value. According to this metal detector, the inspection frequency can be set to a low noise level, so that a good inspection can be performed at the beginning of the inspection.

Patent No. 4633830

However, the metal detector of Patent Document 1 has a problem that when the noise changes with time, it is immediately affected by the noise and the inspection accuracy is greatly lowered. That is, the optimization of the inspection frequency in Patent Document 1 is temporary, and there is a problem that it is immediately affected by noise. Therefore, the metal detector of Patent Document 1 has a problem that the inspection frequency must be automatically set frequently.

Further, the metal detector of Patent Document 1 has a problem that a problem occurs depending on the setting interval of the inspection frequency. For example, if the setting interval is as very large as 10 kHz, changing the inspection frequency causes a problem that a large difference appears from the detection results up to that point, and a problem that another noise peak is hit after the change. Therefore, if the inspection frequency is changed during the inspection, the inspection accuracy may deteriorate. In order to avoid such a problem, it is preferable to make the setting interval of the inspection frequency as small as possible, and finely adjust the inspection frequency to, for example, 100 Hz or less (preferably 50 Hz or less). However, when the inspection frequency is fine-tuned, there is a problem that the generated noise cannot be completely avoided or the fine adjustment must be repeated to avoid it. Therefore, changing the inspection frequency during the inspection is also necessary. Was difficult.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a metal detector that is not easily affected by noise for a long period of time and can maintain high inspection accuracy.

In the invention of claim 1, in order to achieve the above object, a magnetic field is generated in an inspection region at a predetermined inspection frequency, and an object to be inspected is passed through the inspection region to detect fluctuations in the magnetic field. In a metal detector that inspects foreign matter for an inspection object, a fine adjustment means for finely adjusting the inspection frequency within a predetermined frequency range, a range changing means for changing the frequency range for performing the fine adjustment, and a change of the frequency range. A comparative display means for measuring the magnitude of noise at a plurality of inspection frequencies and displaying a screen for comparing the magnitude of noise for each frequency range is provided by fine-tuning the inspection frequency. It is characterized by that.

According to the present invention, since the magnitude of noise is compared and displayed for each frequency range, it is possible to determine which frequency range is preferable for inspection (for example, which frequency range has no noise peaks, etc.). .. Therefore, the inspection frequency can be set in a frequency range preferable for inspection (that is, a frequency range in which the influence of noise is small), and inspection can be performed with high accuracy. Since the inspection frequency set in this way is set within the frequency range where the influence of noise is small (that is, there is no noise peak at a near frequency), the influence of noise is affected even if the frequency of noise changes over time. It is difficult to receive and can maintain high inspection accuracy.

Further, according to the present invention, when the noise frequency changes with time, the inspection frequency may be finely adjusted, and the influence of the noise can be easily avoided. At that time, since the inspection frequency does not change significantly, it is difficult for a difference in inspection results to occur before and after the adjustment, and a decrease in inspection accuracy can be suppressed.

The invention of claim 2 is characterized in that, in claim 1, the range changing means is changed so that the frequency ranges before and after the change are adjacent to each other. According to the present invention, since the frequency ranges are adjacent to each other, the inspection frequency can be set in a continuous frequency range. Therefore, it is possible to suppress a large change in the inspection frequency, and it is possible to suppress a defect associated therewith.

The invention of claim 3 is the invention of claim 1 or 2, wherein the range changing means can change the frequency range to the plus side and the minus side of the frequency, respectively. According to the present invention, the frequency range of the inspection frequency can be changed to the plus side and the minus side.

The invention of claim 4 is characterized in that, in any one of claims 1 to 3, an average value of the measured noise magnitude is obtained for each frequency range, and the average value is displayed. According to the present invention, since the average value for each frequency range is displayed, it is possible to easily determine which frequency range is optimal.

The invention of claim 5 is characterized in that, in any one of claims 1 to 4, the maximum value of the measured noise magnitude is obtained for each frequency range, and the maximum value is displayed. According to the present invention, since the maximum value for each frequency range is displayed, it is possible to determine which frequency range is optimal.

The invention of claim 6 is obtained in claim 1, wherein the fine adjustment means continuously changes the inspection frequency, and the comparison display means changes the inspection frequency within the frequency range and performs frequency analysis. It is characterized in that a screen for arranging and comparing the obtained frequency distribution maps for each frequency range is displayed. According to the present invention, since the frequency distribution maps are arranged side by side and compared, it is possible to grasp at a glance which frequency range the noise exists in.

According to the present invention, since the noise is comparatively displayed for each frequency range, the inspection frequency can be set in an appropriate frequency range, and high inspection accuracy can be maintained for a long time.

Schematic diagram showing the configuration of the metal detector of the present invention A circuit diagram for explaining the range adjustment unit of FIG. Flow diagram explaining noise detection display processing The figure which shows the display example of the noise detection result The figure which shows the display example of the noise detection result The figure which shows the display example of the noise detection result The figure which shows the display example in the metal detector of 2nd Embodiment

Hereinafter, preferred embodiments of the metal detector according to the present invention will be described with reference to the accompanying drawings. FIG. 1 schematically shows the configuration of the metal detector 10 of the present invention.

The metal detector 10 shown in the figure is a device that detects a metallic foreign matter by passing the object 12 to be inspected through the inspection region 14, a magnetic field generating unit 16 that generates a magnetic field in the inspection region 14, and a magnetic field in the inspection region 14. A magnetic field detection unit 18 for detecting fluctuations is provided. A transmission coil 17 (see FIG. 2) is provided in the magnetic field generation unit 16, and an alternating current flows through the transmission coil 17 to generate a magnetic field in the inspection region 14. A receiving coil (not shown) of the magnetic field detecting unit 18 is provided coaxially with the transmitting coil 17 of the magnetic field generating unit 16 (or at a position facing vertically), and receives that the magnetic field of the inspection region 14 has fluctuated. It can be detected as a fluctuation of the current flowing through the coil. Although the mechanism for passing the object to be inspected 12 through the inspection area 14 is omitted, a belt conveyor or the like is usually used.

The control unit 20 of the metal detector 10 is provided with a transmission signal setting unit 22, a reception signal processing unit 24, a noise detection unit 26, and a capacitor setting unit 28. The transmission signal setting unit 22 has a function of adjusting the inspection frequency of the transmission signal to the magnetic field generation unit 16 and the inspection frequency of the detection side in the reception signal processing unit 24, and finely adjusts the inspection frequency within a predetermined range. , The range can be changed significantly. For example, by setting the number of changes for a certain frequency range, the inspection frequency can be set at minute intervals, and the inspection frequency can be finely adjusted within a predetermined range. The fine adjustment interval is preferably 100 Hz or less, more preferably 50 Hz or less, and is set to, for example, 38 Hz in order to suppress the appearance of a difference in the inspection results before and after the adjustment. Further, if the interval is too narrow, the influence of noise does not change before and after the adjustment, so 10 Hz or more, preferably 30 Hz or more is preferable.

The signal whose frequency is set by the transmission signal setting unit 22 is D / A converted by the D / A converter 32, and then the output is amplified by the drive circuit 34 and the transformer circuit 36, via the capacitor adjusting unit 38 described later. It is transmitted to the transmission coil 17 of the magnetic field generation unit 16. As a result, an alternating current flows through the transmission coil 17, and an alternating magnetic field is generated in the inspection region 14.

On the other hand, the receiving coil of the magnetic field detection unit 18 is connected to the received signal processing unit 24 of the control unit 20 via the transformer circuit 46, the amplifier 44, and the A / D converter 42. The reception signal processing unit 24 performs detection processing and filter processing according to the inspection frequency generated by the frequency generation unit 22. As a result, when a metallic foreign substance is present in the object to be inspected 12, the metallic foreign substance can be detected by detecting the magnetic field fluctuation in the inspection area 14.

The noise detection unit 26 of the control unit 20 calculates the influence of noise as a numerical value using the result of the reception signal processing unit 24. Specifically, a magnetic field is generated and detected without passing the object 12 to be inspected in the inspection area 14, and the noise caused by the outside of the device is quantified and obtained from the result. The noise value is calculated, for example, by obtaining the maximum amplitude (peak to peak) of the received signal. Further, the noise detection unit 26 uses the calculated noise to generate a screen that can be compared for each frequency range, outputs the screen to the display unit 50, and displays the screen.

On the other hand, the capacitor setting unit 28 of the control unit 20 is connected to the capacitor adjustment unit 38, and by controlling the capacitor adjustment unit 38 with the capacitor setting unit 28, the transmission side when the inspection frequency range is significantly changed. Resonance is attempted.

FIG. 2 shows a circuit diagram of the capacitor adjusting unit 38. As shown in the figure, the capacitor adjusting unit 38 includes a main capacitor 62, a minus capacitor 64, and a plus capacitor 66, and these capacitors 62, 64, and 66 are the coil 37 of the transformer circuit 36 and the magnetic field generator. It is connected in parallel between the 16 transmission coils 17. Of these, the main capacitor 62 is always connected, and the resonance frequency at the normal time is set by the main capacitor 62. On the other hand, the negative capacitor 64 and the positive capacitor 66 are connected via switches 65 and 67, respectively, and the switches 65 and 67 are controlled by the above-mentioned capacitor setting 28. For example, the switch 67 of the positive capacitor 66 is normally connected, and is disconnected when the frequency range is moved to the positive side. On the contrary, the switch 65 of the negative capacitor 64 is normally disconnected and is connected when the frequency range is moved to the negative side.

Here, the normal frequency range (switch 65 is off, switch 67 is on) is set as the normal range, and the frequency range when moving to the plus side (switch 65 is off, switch 67 is off) is set as the plus range, and is minus. The frequency range when moving to the side (switch 65 is on, switch 67 is on) is set as the minus range. The capacitances of the capacitors 62, 64, and 66 are set so that the adjusted frequency ranges are adjacent to each other. That is, the plus range is set to be adjacent to the plus side with respect to the normal range, and the minus range is set to be adjacent to the minus side with respect to the normal range. For example, when the normal range has an interval of 500 Hz, it is set to move to the plus side or the minus side by the same amount as the interval of the normal range of 500 Hz.

Next, an operation method of the metal detector 10 configured as described above will be described. The metal detector 10 of the present invention is characterized by noise detection and display processing, and this noise detection and display processing is performed at the time of initial setting of the device, at the start of driving, and at the time of resetting due to a large influence of noise. Will be done.

FIG. 3 shows a flow of noise detection display processing. As shown in the figure, first, the frequency range is set (step S1). The frequency range is set by the capacitor setting unit 28 described above by switching the switches 65 and 67 of the capacitor adjustment unit 38, and is set to any of three frequency ranges (normal range, plus range, and minus range). The frequency range is set in order. For example, the normal range is set by first turning off the switch 65 and turning on the switch 67.

Next, the inspection frequency is finely adjusted (step S2). The fine adjustment of the inspection frequency is performed by the transmission signal setting unit 22 described above, and the inspection frequency is changed by several tens of Hz.

Next, the electromagnetic noise is calculated (step S3). That is, the magnetic field generation unit 16 generates a magnetic field of the inspection frequency in the inspection region 14, the magnetic field detection unit 18 detects the magnetic field fluctuation in the inspection region 14, and the noise detection unit 26 quantifies the noise. The noise obtained in this way and the inspection frequency at that time are stored in a memory (not shown).

Next, it is determined whether all the fine adjustments have been completed, that is, whether all the inspection frequencies within the frequency range have been completed (step S4), and if all the fine adjustments have not been completed, the process returns to step S2 and the inspection is performed. The frequency is finely adjusted, and the noise is calculated again (step S3). By repeating this, the noise measurement at all the inspection frequencies within the frequency range is completed.

If it is determined in step S4 that all the fine adjustments within the frequency range have been completed, the process proceeds to step S5 to determine whether or not the frequency range change has been completed, that is, whether or not the entire frequency range has been inspected. Then, when the frequency range has not been changed (when there is an unmeasured frequency range), the process returns to step S1, the frequency range is changed, and the following operation is repeated. For example, the frequency range is changed to the plus range by turning off the switch 65 and the switch 67, and steps S2 to S4 are performed. After that, the frequency range is changed to the minus range by turning on the switch 65 and the switch 67, and steps S2 to S4 are performed. This makes it possible to measure noise in the entire frequency range.

After measuring the noise in the entire frequency range, the noise detection result is displayed (step S6). As the noise detection result, for example, as shown in FIG. 4, the average value for each frequency range is displayed. That is, the average value of noise at all inspection frequencies within the normal range, the average value of noise at all inspection frequencies within the plus range, and the average value of noise at all inspection frequencies within the minus range are displayed. This allows the operator to look at the screen and determine which range is suitable for the inspection. For example, in the case of FIG. 4, only the average value in the minus range is very large, and it is assumed that there is a noise peak in this minus range. Therefore, it can be judged that the negative range is inappropriate for the inspection and the normal range or the positive range is the appropriate range for the inspection.

The operator sets the inspection frequency from the frequency range determined to be suitable for the inspection (step S7). For example, select a plus range and set the inspection frequency within that plus range. Since the inspection frequency set in this way is within the frequency range where there is little noise and there is no noise peak, the noise is unlikely to affect the inspection frequency even when the noise changes over time. Therefore, high inspection accuracy can be maintained for a long time. Further, even if the noise changes with time and slightly affects the inspection frequency, the influence of the noise can be reduced by finely adjusting the inspection frequency. At that time, since the difference in inspection results is unlikely to occur before and after the adjustment, it is possible to suppress a decrease in inspection accuracy.

As described above, according to the present embodiment, since the influence of noise is displayed in a comparable form for each frequency range, the inspection frequency can be set in the frequency range where the influence of noise is small, and the influence of noise can be set. Foreign matter inspection that is not easily affected can be performed.

Further, according to the present embodiment, by finely adjusting the inspection frequency after the setting, even if the influence of noise appears a little, the influence can be finely adjusted to reduce the influence. In that case, since the inspection frequency is not significantly changed, it is possible to suppress a large difference in the inspection results.

In the above-described embodiment, a screen for comparing the average value of noise is displayed as a noise detection result, but the present invention is not limited to this, and the influence of noise can be compared for each frequency range. It suffices to display the screen. For example, the maximum value of noise may be obtained for each frequency range and displayed. Further, as shown in FIG. 5, the maximum value and the average value of noise may be displayed at the same time. Further, as shown in FIG. 6, the value for each inspection frequency may be displayed as a graph. In this case, it is advisable to draw a line at the boundary of the frequency range so that the frequency range can be known. Further, the average value or the maximum value may be displayed, or the frequency range having the least influence of noise may be displayed in another color.

In the above-described embodiment, the number of frequency ranges is set to 3, but the number is not limited to this, and the number of frequency ranges may be set to 2 or 4 or more. In either case, the effect of the present invention can be obtained by displaying the influence of noise in a form comparable to each frequency range.

Further, in the above-described embodiment, the frequency ranges are set to be adjacent to each other, but the present invention is not limited to this, and a part of the frequency ranges may be set to overlap or be separated from each other. Further, the frequency range selection button may be displayed on the comparison display screen to easily set the frequency range.

Next, the metal detector of the second embodiment will be described. The metal detector of the second embodiment has substantially the same configuration as the metal detector of the above-described embodiment, but differs in the following points. That is, in the second embodiment, the transmission signal setting unit 22 can continuously change the inspection frequency within a predetermined frequency range and can greatly change the frequency range. Further, the noise detection unit 26 is configured to perform noise diagnosis by frequency analysis of the received signal obtained while continuously changing the inspection frequency within a predetermined frequency range. It is preferable to speed up the diagnostic process by performing the zoom FFT.

According to the second embodiment configured as described above, as a comparative display of noise, frequency analysis is performed for each frequency range to create a frequency distribution map, and the frequency distribution map for each frequency range is displayed side by side. FIG. 7 shows a display example in the second embodiment. As shown in the figure, the minus side frequency distribution diagram 70A, the normal (center) frequency distribution diagram 70B, and the plus side frequency distribution diagram 70C are displayed side by side. In the frequency distribution diagrams 70A to 70C, the frequency is displayed on the horizontal axis and the signal level (noise magnitude) is displayed on the vertical axis, so it is possible to grasp at a glance how much noise is generated at which frequency. be able to. Further, since a plurality of frequency distribution maps 70A to 70C are displayed side by side, it is possible to grasp at a glance which frequency range is suitable for foreign matter inspection. For example, in the display example of FIG. 7, it can be seen that the normal (center) noise is large and it is preferable to set it in the minus or plus range.

Reference numerals 72A to 72C in FIG. 7 are center frequencies in the respective frequency distribution diagrams 70A to 70C, and reference numerals 74A to 74C and reference numerals 76A to 76C are reference lines for each target foreign matter. Reference lines 74A to 74C indicate the signal level detected when the foreign matter to be detected is iron and has a diameter of 0.5 mm, and if noise larger than this line is generated, the noise may be mistaken for foreign matter. is there. In addition, the reference lines 76A to 76C indicate the signal level to be detected when the material of the foreign matter to be detected is stainless steel and the diameter is 1.0 mm, and when noise larger than this line is generated, the noise is regarded as the foreign matter. There is a risk of misidentification. Reference numeral 78 in FIG. 7 indicates a description of the foreign matter on the reference line, and the reference line and the description of the foreign matter are displayed in the same color.

10 ... Metal detector, 12 ... Inspected object, 14 ... Inspection area, 16 ... Magnetic field generator, 17 ... Transmission coil, 18 ... Magnetic field detection unit, 19 ... Reception coil, 20 ... Control unit, 22 ... Transmission signal setting unit , 24 ... Received signal processing unit, 26 ... Noise detection unit, 28 ... Capacitor setting unit, 32 ... D / A converter, 34 ... Drive circuit, 36 ... Transformer circuit, 38 ... Capacitor adjustment unit, 42 ... A / D conversion Instrument, 44 ... Amplifier circuit, 46 ... Transformer circuit, 50 ... Display, 62 ... Capacitor, 64 ... Minus capacitor, 65 ... Switch, 66 ... Plus capacitor, 67 ... Switch, 70A-70C ... Frequency distribution map, 72A ~ 72C ... Set frequency line, 74A to 74C ... Reference line, 76A to 76C ... Reference line, 78 ... Display of explanation of foreign matter

Claims (6)

In a metal detector that detects foreign matter in an object to be inspected passing through the inspection area by generating a magnetic field in the inspection area at the inspection frequency and detecting a change in the magnetic field in the inspection area at the inspection frequency.
A fine adjustment means for finely adjusting the inspection frequency within a predetermined frequency range, and
A range changing means for changing the frequency range and
A comparative display means for measuring the noise magnitude at a plurality of inspection frequencies by changing the frequency range and fine-tuning the inspection frequency, and displaying a screen for comparing the noise magnitude for each frequency range. When,
A metal detector characterized by being equipped with. The metal detector according to claim 1, wherein the range changing means is changed so that the frequency ranges before and after the change are adjacent to each other. The metal detector according to claim 1 or 2, wherein the range changing means can change the frequency range to a positive side and a negative side of the frequency, respectively. The metal detector according to any one of claims 1 to 3, wherein an average value of the measured noise magnitude is obtained for each frequency range, and the average value is displayed. The metal detector according to any one of claims 1 to 4, wherein a maximum value of the measured noise magnitude is obtained for each frequency range, and the maximum value is displayed. The fine adjustment means continuously changes the inspection frequency, and the fine adjustment means continuously changes the inspection frequency.
The comparative display means is characterized in that it displays a screen for arranging and comparing frequency distribution maps obtained by frequency analysis by changing the inspection frequency within the frequency range for each frequency range. Metal detector.

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