JP7343262B2 - metal detector - Google Patents

Description

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

2. Description of the Related Art A metal detector is known as a device for testing whether metal foreign matter is mixed into food or the like. A metal detector generates a magnetic field in an inspection area, causes the object to be inspected to pass through the inspection area, and detects changes in the magnetic field to detect foreign substances in the object.

It is known that such metal detectors are susceptible to electromagnetic noise (hereinafter simply referred to as noise) external to the device. For example, if there is an inverter device around a metal detector, a mountain of noise 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 the noise will become greater. Small foreign objects cannot be detected.

Therefore, the metal detector of Patent Document 1 detects a predetermined bandwidth (for example, 10 kHz) from a "predetermined frequency range corresponding to the influence of the object to be inspected" (a range of several kHz to several MHz). The setting is automatically performed by setting a plurality of test frequencies, measuring noise at the plurality of test frequencies, and selecting a test frequency at which the noise level is equal to or less than a predetermined value. According to this metal detector, since the test frequency can be set to a low noise level, a good test can be performed at the beginning of the test.

Patent No. 4633830

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

Furthermore, the metal detector disclosed in Patent Document 1 also has a problem in that problems occur depending on the interval at which the test frequency is set. For example, if the setting interval is very large, such as 10 kHz, there will be a problem that changing the test frequency will result in a large difference from the previous detection results, or that the test will encounter another pile of noise after the change. For this reason, if the test frequency is changed during the test, there is a risk that the test accuracy will deteriorate. In order to avoid such problems, it is preferable to finely adjust the test frequency by making the test frequency setting interval as small as possible, for example, 100 Hz or less (preferably 50 Hz or less). However, when the test frequency is fine-tuned, there is a problem that the generated noise cannot be completely avoided or that fine adjustments must be made repeatedly to avoid it, and it is still necessary to change the test frequency during the test. was difficult.

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

In order to achieve the above object, the invention of claim 1 generates a magnetic field in an inspection area at a predetermined inspection frequency, and also detects fluctuations in the magnetic field by passing an object to be inspected through the inspection area. In a metal detector that performs a foreign substance inspection of an object to be inspected, a fine adjustment means for finely adjusting the inspection frequency within a predetermined frequency range, a range changing means for changing the frequency range in which the fine adjustment is performed, and a range changing means for changing the frequency range. and a comparison display means for measuring the magnitude of noise at a plurality of test frequencies by finely adjusting the test frequency and displaying a screen that compares the magnitude of noise for each frequency range , The present invention is characterized in that an average value of the measured noise magnitude is determined for each of the frequency ranges, and the average value is displayed.
In order to achieve the above-mentioned object, the invention of claim 2 generates a magnetic field in an inspection area at an inspection frequency and detects a change in the magnetic field in the inspection area at the inspection frequency. A metal detector for detecting foreign matter in an object to be inspected, comprising: fine adjustment means for finely adjusting the inspection frequency within a predetermined frequency range; range changing means for changing the frequency range; a comparison display means for measuring the magnitude of noise at a plurality of test frequencies by finely adjusting the test frequency, and displaying a screen for comparing the magnitude of the noise for each frequency range; The present invention is characterized in that the maximum value of the noise magnitude is determined for each of the frequency ranges and the maximum value is displayed.

According to the present invention, since the magnitude of noise is displayed in comparison for each frequency range, it is possible to judge which frequency range is preferable for inspection (for example, in which frequency range there are no noise peaks). . Therefore, the test frequency can be set in a frequency range preferable for testing (ie, a frequency range where the influence of noise is small), and the test can be performed with high accuracy. The test frequency set in this way is set within a frequency range where the influence of noise is small (that is, there are no noise peaks at nearby frequencies), so even if the frequency of the noise changes over time, the influence of noise can be suppressed. This makes it possible to maintain high inspection accuracy.

Further, according to the present invention, when the frequency of noise changes over time, it is only necessary to finely adjust the test frequency, and the influence of noise can be easily avoided. At this time, since the test frequency does not change significantly, a difference in test results before and after adjustment is unlikely to occur, and a decrease in test accuracy can be suppressed.
Furthermore, according to the first aspect of the invention, since the average value for each frequency range is displayed, it is possible to easily determine which frequency range is optimal. According to the second aspect of the invention, since the maximum value for each frequency range is displayed, it is possible to determine which frequency range is optimal.

The invention according to claim 3 is the invention according to claim 1 or 2, characterized in that the range changing means changes the frequency ranges before and after the change so that they are adjacent to each other. According to the present invention, since the frequency ranges are adjacent, test frequencies can be set in continuous frequency ranges. Therefore, it is possible to suppress a large change in the inspection frequency, and to suppress the problems associated with it.

The invention according to claim 4 is the invention according to claim 1 or 2, characterized in that the range changing means can change the frequency range to a plus side and a minus side of the frequency, respectively. According to the present invention, the frequency range of the test frequency can be changed to the plus side and the minus side.

The invention according to claim 5 is the invention according to claim 1 or 2, wherein the fine adjustment means continuously changes the test frequency, and the comparison display means changes the test frequency within the frequency range to adjust the frequency. The present invention is characterized by displaying a screen in which frequency distribution maps obtained by analysis are arranged and compared for each frequency range. According to the present invention, since the frequency distribution charts are compared side by side, it is possible to understand at a glance in which frequency range the noise is present.

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

Schematic diagram showing the configuration of the metal detector of the present invention Circuit diagram explaining the range adjustment section in Figure 1 Flow diagram explaining noise detection display processing Diagram showing an example of displaying noise detection results Diagram showing an example of displaying noise detection results Diagram showing an example of displaying noise detection results A diagram showing an example of display in a metal detector according to the second embodiment

Preferred embodiments of the metal detector according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 schematically shows the configuration of a metal detector 10 of the present invention.

The metal detector 10 shown in the figure is a device that detects metallic foreign objects by passing an object 12 through an inspection area 14, and includes a magnetic field generating section 16 that generates a magnetic field in the inspection area 14, and a magnetic field generating section 16 that generates a magnetic field in the inspection area 14. It includes a magnetic field detection section 18 that detects fluctuations. The magnetic field generating section 16 is provided with a transmitting coil 17 (see FIG. 2), and when an alternating current flows through the transmitting coil 17, a magnetic field is generated in the inspection area 14. A receiving coil (not shown) of the magnetic field detecting section 18 is provided coaxially with the transmitting coil 17 of the magnetic field generating section 16 (or at a position vertically opposed to the transmitting coil 17 of the magnetic field generating section 16), and receives changes in the magnetic field of the inspection area 14. It can be detected as fluctuations in the current flowing through the coil. Note that although a mechanism for passing the inspection object 12 to the inspection area 14 is omitted, a belt conveyor or the like is normally used.

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

The signal whose frequency has been set by the transmission signal setting section 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, and then sent via the capacitor adjustment section 38, which will be described later. The signal is transmitted to the transmitting coil 17 of the magnetic field generating section 16. As a result, an alternating current flows through the transmitting coil 17, and an alternating magnetic field is generated in the inspection area 14.

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

The noise detection section 26 of the control section 20 uses the results of the received signal processing section 24 to calculate the influence of noise as a numerical value. Specifically, a magnetic field is generated and detected without passing the object 12 to be inspected into the inspection area 14, and from the results, noise due to factors outside the apparatus is quantified and determined. The noise value is calculated, for example, by determining the maximum amplitude (peak-to-peak) of the received signal. Further, the noise detection unit 26 uses the calculated noise to generate a comparable screen for each frequency range, and outputs the screen to the display unit 50 for display.

On the other hand, the capacitor setting section 28 of the control section 20 is connected to the capacitor adjustment section 38, and by controlling the capacitor adjustment section 38 with the capacitor setting section 28, the transmission side can be adjusted when the test frequency range is greatly changed. Aiming for resonance.

FIG. 2 shows a circuit diagram of the capacitor adjustment section 38. As shown in the figure, the capacitor adjustment section 38 includes a main capacitor 62, a negative capacitor 64, and a positive capacitor 66, and these capacitors 62, 64, and 66 connect the coil 37 of the transformer circuit 36 and the magnetic field generating section It is connected in parallel between 16 transmitting coils 17 . Among these, the main capacitor 62 is always connected, and the resonance frequency at normal times is set by this 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 capacitor setting 28 described above. For example, the switch 67 of the positive capacitor 66 is normally connected, and is disconnected when moving the frequency range to the positive side. Conversely, the switch 65 of the negative capacitor 64 is normally disconnected, and is connected when moving the frequency range to the negative side.

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

Next, a method of operating the metal detector 10 configured as described above will be explained. 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 when resetting due to the influence of noise. It will be done.

FIG. 3 shows the flow of noise detection and display processing. As shown in the figure, first, a frequency range is set (step S1). The frequency range is set by the capacitor setting section 28 described above by switching the switches 65 and 67 of the capacitor adjustment section 38, and is set to one of three frequency ranges (normal range, plus range, minus range). Note that the frequency ranges are all set in order, and 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). Fine adjustment of the test frequency is performed by the above-mentioned transmission signal setting section 22, and the test frequency is changed by several tens of Hz.

Next, electromagnetic noise is calculated (step S3). That is, the magnetic field generator 16 generates a magnetic field at the test frequency in the test region 14, the magnetic field detector 18 detects magnetic field fluctuations in the test region 14, and the noise detector 26 converts noise into numerical values. The noise thus determined and the test frequency at that time are stored in a memory (not shown).

Next, it is determined whether all fine adjustments have been completed, that is, whether all test frequencies within the frequency range have been completed (step S4). If all fine adjustments have not been completed, the process returns to step S2 and the test is performed. The frequency is finely adjusted and the noise is calculated again (step S3). By repeating this process, noise measurements at all test frequencies within the frequency range are 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, where it is determined whether or not the change in the frequency range has been completed, that is, whether all frequency ranges have been inspected. If the change of the frequency range is not completed (if there is an unmeasured frequency range), the process returns to step S1, the frequency range is changed, and the following operations are repeated. For example, the frequency range is changed to a plus range by turning off the switch 65 and the switch 67, and steps S2 to S4 are performed. Thereafter, the frequency range is changed to the negative 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 all frequency ranges.

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

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

In this way, according to the present embodiment, the influence of noise is displayed in a form that can be compared for each frequency range, so the test frequency can be set in a frequency range where the influence of noise is small, and the influence of noise can be It is possible to perform foreign body inspections that are not easily affected.

Further, according to the present embodiment, by finely adjusting the test frequency after setting, even if the influence of noise appears a little, the influence can be reduced by fine adjustment. In that case, since the test frequency is not changed significantly, it is possible to suppress the occurrence of large differences in test results.

In the above-described embodiment, a screen for comparing the average value of noise is displayed as the noise detection result, but the screen is not limited to this, and it is possible to compare the influence of noise for each frequency range. It is fine as long as the screen is displayed. For example, the maximum value of noise may be determined for each frequency range and displayed. Furthermore, as shown in FIG. 5, the maximum value and average value of noise may be displayed simultaneously. Furthermore, as shown in FIG. 6, the values for each test frequency may be displayed graphically. In this case, it is a good idea to draw a line at the boundary of the frequency range so that you can see the frequency range. Furthermore, the average value or maximum value may be displayed, or the frequency range where the influence of noise is least may be displayed in a different color.

In addition, in the embodiment described above, the number of frequency ranges is three, but the number is not limited to this, and the number of frequency ranges may be two or four or more. In either case, the effects of the present invention can be obtained by displaying the influence of noise in a form that can be compared for each frequency range.

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

Next, a metal detector according to a second embodiment will be explained. The metal detector of the second embodiment is configured in substantially the same manner 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 section 22 is configured to continuously change the test frequency within a predetermined frequency range, and to change the frequency range significantly. Further, the noise detection unit 26 is configured to perform noise diagnosis by frequency-analyzing the received signal obtained while continuously changing the test frequency within a predetermined frequency range. Note that it is preferable to speed up the diagnostic processing by implementing 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 charts for each frequency range are displayed side by side. FIG. 7 shows a display example in the second embodiment. As shown in the figure, a minus side frequency distribution diagram 70A, a normal (center) frequency distribution diagram 70B, and a plus side frequency distribution diagram 70C are displayed side by side. In the frequency distribution charts 70A to 70C, frequency is displayed on the horizontal axis and signal level (noise level) is displayed on the vertical axis, so you can understand at a glance how much noise is occurring at which frequency. be able to. Furthermore, since a plurality of frequency distribution charts 70A to 70C are displayed side by side, it is possible to understand at a glance which frequency range is suitable for foreign object 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 negative or positive range.

Note that symbols 72A to 72C in FIG. 7 are center frequencies in the respective frequency distribution diagrams 70A to 70C, and symbols 74A to 74C and symbols 76A to 76C are reference lines for each target foreign object. The reference lines 74A to 74C indicate the signal level detected when the foreign object to be detected is iron and has a diameter of 0.5 mm, and if noise larger than this line occurs, the noise may be mistaken for a foreign object. be. In addition, the reference lines 76A to 76C indicate the signal level detected when the foreign object to be detected is made of stainless steel and has a diameter of 1.0 mm, and if noise larger than this line occurs, the noise is considered to be a foreign object. There is a risk of misunderstanding. Reference numeral 78 in FIG. 7 is a display of an explanation of the foreign object on the reference line, and the reference line and the explanation of the foreign object are displayed in the same color.

DESCRIPTION OF SYMBOLS 10... Metal detector, 12... Inspection object, 14... Inspection area, 16... Magnetic field generation part, 17... Transmission coil, 18... Magnetic field detection part, 19... Receiving coil, 20... Control part, 22... Transmission signal setting part , 24...Received signal processing section, 26...Noise detection section, 28...Capacitor setting section, 32...D/A converter, 34...Drive circuit, 36...Transformer circuit, 38...Capacitor adjustment section, 42...A/D conversion 44...Amplification circuit, 46...Transformer circuit, 50...Display unit, 62...Capacitor, 64...Minus capacitor, 65...Switch, 66...Positive capacitor, 67...Switch, 70A to 70C...Frequency distribution diagram, 72A ～72C...Setting frequency line, 74A～74C...Standard line, 76A～76C...Standard line, 78...Display of explanation of foreign matter

Claims (5)

In a metal detector that detects a foreign object 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,
Fine adjustment means for finely adjusting the test frequency within a predetermined frequency range;
Range changing means for changing the frequency range;
Comparison display means for measuring the magnitude of noise at a plurality of test frequencies by changing the frequency range and finely adjusting the test frequency, and displaying a screen that compares the magnitude of noise for each of the frequency ranges. and,
A metal detector comprising: an average value of the measured noise magnitude for each of the frequency ranges, and the average value is displayed. In a metal detector that detects a foreign object 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,
Fine adjustment means for finely adjusting the test frequency within a predetermined frequency range;
Range changing means for changing the frequency range;
Comparison display means for measuring the magnitude of noise at a plurality of test frequencies by changing the frequency range and finely adjusting the test frequency, and displaying a screen that compares the magnitude of noise for each of the frequency ranges. and,
A metal detector characterized in that the maximum value of the measured noise magnitude is determined for each of the frequency ranges and the maximum value is displayed. 3. The metal detector according to claim 1 , wherein said range changing means changes the frequency ranges before and after the change so that they are adjacent to each other. 3. The metal detector according to claim 1 , wherein said range changing means is capable of changing said frequency range to a plus side and a minus side of frequency, respectively. The fine adjustment means continuously changes the test frequency,
1 . The comparison display means displays a screen in which frequency distribution maps obtained by frequency analysis while changing the test frequency within the frequency range are arranged and compared for each frequency range. Or 2 metal detectors.

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