JP2008256718A - Metal detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal detector capable of automatically adjusting the condition setting for detecting metal under a suitable condition to influence of external electromagnetic noise and its change. <P>SOLUTION: This metal detector is provided with a measuring means 40 for measuring electromagnetic noise in an inspection area by using a magnetic field detecting part 23 on a detecting operation frequency, corresponding to its respective preset frequencies, by changing the preset frequency of a magnetic field generating means 22 in a determined frequency range, in response to article influence of an inspection object W; and frequency selection setting means 32 and 35 for setting a frequency as the preset frequency of the magnetic field generating means 22, by selecting any among of the detecting operation frequencies becoming a predetermined or less on an electromagnetic noise level measured by a measuring means 40. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal detection device for detecting a metal or a metal component in an object to be inspected, in particular, a metal or metal in an object to be inspected based on a change in a magnetic field when the object to be inspected such as food passes through an alternating magnetic field. The present invention relates to a metal detector for determining the presence or absence of a component.

  As a conventional metal detection device of this type, for example, an alternating magnetic field is generated in a product inspection region by a transmission coil so that a workpiece (inspected object) conveyed on a conveyor passes through an alternating magnetic field having a predetermined frequency, and the magnetic field is generated. The magnetic field fluctuation caused by the movement of the workpiece in the coil is detected as the fluctuation of the induced voltage to the receiving coil, and this detection signal is subjected to detection processing that synchronizes with the excitation driving signal of the transmission coil, and the output level of the detection output is It is generally known to determine the presence or absence of metal or the like by determining a threshold value.

  In addition, the influence on the magnetic field fluctuation (hereinafter referred to as the article influence) caused by the movement of the article that does not contain metal or metal component in the alternating magnetic field (hereinafter referred to as the article influence) is minimized, and the detection sensitivity for the metallic foreign object to be detected is increased. In order to increase the frequency, there is a device in which the setting of the phase angle and the alternating magnetic field frequency of the detection processing is devised (for example, see Patent Documents 1 and 2).

Further, a Lissajous figure drawn on the orthogonal coordinate plane while each inspection object passes through the alternating magnetic field is created with the output level of the two detection outputs obtained by orthogonal detection of the detection signal of the receiving coil as the orthogonal coordinate component, Based on the figure data, the ratio of the magnetic component and the non-magnetic component in each product is grasped to determine the presence or absence of metallic foreign matter in the product. The detection accuracy is improved by adjusting the relative phase between the excitation signal applied to the transmitter coil and the excitation signal applied to each synchronous detector for quadrature detection according to the change in (See, for example, Patent Document 3).
JP-A-5-232248 JP-A-5-100047 JP 2002-168834 A

  As described above, in the metal detection device that detects the fluctuation of the alternating magnetic field, the optimum frequency of the magnetic field for detecting the metal differs depending on the characteristics of the object to be inspected (moisture, salt, type of packaging material, etc.). In consideration, it is preferable to select and output one or two appropriate frequency bands to the object to be inspected from the frequency band of several kHz to several MHz which is the magnetic field frequency range.

  Further, when a plurality of metal detection devices using the same frequency band are arranged close to each other, fine adjustment is performed so that the magnetic field frequencies used by the plurality of metal detection devices are gradually changed in order to suppress mutual interference. Is good.

  However, even if the optimum magnetic field frequency is set in this way, the following unsolved problems still remain.

  That is, in the metal detection device, for example, a detection signal level N (noise) due to the influence of a representative object to be inspected without metal contamination (hereinafter referred to as a sample product) used for determining a detection condition such as a magnetic field frequency. ) Is stored in advance, and when the level ratio S / N between the detection signal level S (signal) of each object to be inspected and the stored detection signal level N is equal to or greater than a predetermined threshold (for example, 5), The test object is determined as a metal-mixed product. Therefore, in the case where a smaller metal is mixed and the detection signal level S is small, in order to correctly determine the object to be inspected as a metal mixed product, it is sufficient if the detection signal level N due to the influence of the sample product is not reduced. A high S / N ratio cannot be obtained.

  On the other hand, even when the impact of an article changes due to changes in the shape of the object to be inspected or the moisture content, stable metal detection is performed while maintaining good detection sensitivity following the change in the impact of the article. In order to do this, the detection level of the object to be inspected (non-defective product) in which no metal is mixed should be equal to or higher than the noise level of the detection signal (see Patent Document 3). Therefore, when noise exceeding the detection signal level is detected due to the influence of external electromagnetic noise from other nearby metal detectors or packaging equipment, etc., in a state where the detection signal level due to the influence of the sample article is small. In addition, the metal detection performance deteriorates because the change in the influence of the article cannot be detected, and the object to be inspected not containing metal is erroneously determined as a metal-mixed product, or conversely, metal detection that is normally detectable The product may be misjudged as a non-defective product, and the reliability of the metal detector must be greatly reduced.

  Furthermore, the influence of external electromagnetic noise is likely to change due to changes in the usage conditions of the metal detector, changes in the usage environment, and aging / aging. For this reason, the problem that the performance of the metal detection device is likely to deteriorate due to external electromagnetic noise has not been solved.

  The present invention has been made to solve the problems of the prior art, and provides a metal detection device capable of automatically adjusting the metal detection condition setting to a suitable condition with respect to the influence of external electromagnetic noise and changes thereof. The purpose is to provide.

  In order to achieve the above object, the present invention provides a magnetic field generating means for generating an alternating magnetic field of a set frequency included in a predetermined frequency range corresponding to an article influence of an object to be inspected in an inspection region of the object to be inspected, Magnetic field detecting means for detecting a change in the alternating magnetic field caused by the inspection object passing through the alternating magnetic field at a detection operating frequency corresponding to the set frequency, and based on a detection signal of the magnetic field detecting means. In a metal detection apparatus comprising a determination means for determining the presence or absence of a metal object or metal component in an inspection object, the set frequency of the magnetic field generation means is changed within the frequency range, and each of the set frequencies is handled. Measuring means for measuring electromagnetic noise in the inspection region using the magnetic field detection means for a plurality of different detection operation frequencies, and among the plurality of different detection operation frequencies Electromagnetic noise level measured by serial measurement means is provided with a frequency selecting and setting means for setting as the set frequency of the selected said magnetic field generating means any frequency equal to or less than a predetermined value.

  With this configuration, the influence of external electromagnetic noise is measured for a plurality of different detection operating frequencies, the frequency at which the influence of external electromagnetic noise is reduced is selected and the magnetic field frequency generated by the magnetic field generation means is set, and the corresponding detection The operating frequency is set.

  Further, in the metal detection device of the present invention, the measurement means measures the electromagnetic noise in the inspection region using the magnetic field detection means, thereby making the measurement means extremely easy using existing equipment. It can be realized at low cost.

  Further, the frequency selection setting means selects a frequency at which the electromagnetic noise level measured by the measurement means becomes a minimum value from the plurality of different detection operation frequencies, and sets the frequency as the setting frequency, or the frequency Preferably, the selection setting means selects a frequency at which the electromagnetic noise level measured by the measurement means is equal to or lower than a predetermined allowable noise level from among the plurality of different detection operation frequencies, and sets the selected frequency as the setting frequency.

  With this configuration, it is possible to reliably suppress a decrease in metal detection performance due to the influence of external electromagnetic noise.

  In the metal detection apparatus of the present invention, it is preferable that the magnetic field control means, the measurement means, and the frequency selection setting means are activated when the apparatus is activated or when the operation is reset. Thus, in parallel with a part of the initialization process, it is possible to measure the influence of external electromagnetic noise and to select and set a suitable generated magnetic field frequency and a corresponding detection operation frequency.

  According to the present invention, the influence of external electromagnetic noise is measured for a plurality of different detection operating frequencies, and a frequency at which the influence of external electromagnetic noise is sufficiently reduced is selected and set as the set frequency. It is possible to provide a metal detection device capable of automatically adjusting the metal detection condition setting to a suitable condition so as to reduce the influence of external electromagnetic noise regardless of the change of the noise.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First embodiment]
1-5 is a figure which shows schematic structure of the metal detection apparatus based on the 1st Embodiment of this invention.

  First, the configuration will be described.

  In FIG. 1, a workpiece W that is an object to be inspected is conveyed in a predetermined direction by a conveyor 11 that is a workpiece moving means, and the conveyance speed is set according to the conveyance speed of the production line of the workpiece W. The predetermined section in the conveyance direction of the workpiece W is an inspection area in which metal foreign matter (a foreign matter made of metal or a foreign matter containing a metal component, or a component in the case of missing parts detection) is detected. For example, an optical work detection sensor 13 for detecting the entry of the work W into the inspection area 12 is installed near the entrance of the inspection area 12. The workpiece W is an arbitrary product manufactured in plural, for example, a mass-produced food packaged individually by a packaging material or by a predetermined number of units during transportation, and is shaped like a boxed product. However, it may be an indefinite shape such as a flexible bag product enclosing a fluid or the like.

  In the vicinity of the inspection area 12 of the workpiece W, a detection unit 20 that detects a metal foreign object in the workpiece W is provided.

  The detection unit 20 includes a signal generation unit 21 that generates a transmission signal having a preset amplitude and frequency, a magnetic field generation unit 22 (magnetic field generation unit) that current-drives the transmission coil using a signal from the signal generation unit 21, And a magnetic field detector 23 composed of a differential detector or the like.

  Although not shown in detail, the signal generator 21 includes a reference signal generator that responds to the workpiece detection sensor 13, a timer for specifying a measurement period, a power amplifier, a tuning circuit, and the like. When the signal passes through 12, a transmission signal having a set frequency is generated, and the transmission coil of the magnetic field generation unit 22 is current-driven. Further, the transmission coil of the magnetic field generator 22 is arranged in the vicinity of the work conveyance path by the conveyor 11 and inspects an alternating magnetic field corresponding to the set frequency of the transmission signal when excited by current drive from the signal generator 21. It can be generated in region 12.

  The magnetic field detection unit 23 is configured to detect a metal foreign object in the workpiece W for a plurality of workpieces W (inspected objects) in cooperation with the signal generation unit 21 and the magnetic field generation unit 22. And a pair of receiving coils, a tuning circuit and an amplifier. The magnetic field detection unit 23 is adjusted so that the induced voltages of the pair of receiving coils are equally balanced only with the alternating magnetic field from the magnetic field generation unit 22 and the differential output between them is zero.

  The magnetic metal that passes through the magnetic field attracts more magnetic flux in proportion to the magnitude of the magnetic flux density, and the nonmagnetic metal that passes through the magnetic field swirls in such a direction as to cancel the change in the magnetic flux density due to the movement. An electric current is generated and Joule heat is consumed. Therefore, when the workpiece W on the conveyor 11 passes through the inspection region 12, the balanced state of the output between the receiving coils of the magnetic field detector 23 is lost.

  When the output balanced state between the two receiving coils is lost due to the movement of the workpiece W on the conveyor 11, the magnetic field detector 23 outputs a detection signal corresponding to the change in the magnetic field. This detection signal has a signal form in which a low-frequency signal component that changes due to the magnetic field passing through the workpiece W is superimposed on an AC signal component having a set frequency of the transmission signal corresponding to an alternating magnetic field from the magnetic field generation unit 22 side. .

  The detection signal of the magnetic field detection unit 23 is taken into the signal level measurement unit 24. The signal level measurement unit 24 is not shown in detail, but a pair of synchronous detectors, phase shifters, which perform quadrature detection, A band pass filter, an amplifier, an A / D converter, and the like are included.

  The pair of synchronous detectors of the signal level measuring unit 24 takes in a signal obtained by adjusting the phase of the reference signal for quadrature detection, and generates a detection output by removing a high-frequency component corresponding to a transmission signal from the detection signal. The signal level measurement unit 24 outputs a signal obtained by further applying noise removal and A / D conversion to the detection output to the metal presence / absence determination unit 26 and the detection condition control circuit 30.

  The output of the quadrature detection is, for example, a detection signal in which the influence of a non-magnetic metal causing an external magnetic field change is larger as the magnetic flux density change is larger, and a detection in which the influence of the magnetic metal causing an external magnetic field change is larger as the magnetic flux density is larger. Signal. Further, the detection signal of the low frequency component output from the signal level measuring unit 24 is a waveform of an envelope connecting instantaneous values of a predetermined phase position of the differential detection signal, and ¼ of the transmission signal period from the predetermined phase position. An envelope waveform connecting the instantaneous values whose phases are shifted by 90 degrees, that is, the phase is formed.

  On the other hand, the detection condition control circuit 30 executes arithmetic processing according to a predetermined control program based on a detection signal of the detection unit 20 and a user's operation input from an operating device (not shown), and the processing result is obtained as a signal generation unit 21. And are output to the magnetic field detector 23, respectively.

  The detection condition control circuit 30 is composed of, for example, a microcomputer including a CPU, a RAM, a ROM, and an I / O interface, and the CPU executes a control program stored in the ROM while exchanging data with the RAM. The processing described later is executed based on the signal from the signal level measurement unit 24 taken in via the I / O interface and functionally, the amplitude setting means shown in FIG. 31, a detection frequency setting unit 32, a magnetic field detection unit control unit 33, a storage unit 34, and a detection frequency selection unit 35 are realized.

  The amplitude of the signal generated by the signal generator 21 is set by the amplitude setting means 31, and the set frequency of the transmission signal of the signal generator 21 is set by the detection frequency setting means 32.

  Here, the amplitude setting means 31, together with the signal generator 21, lowers the intensity level of the generated magnetic field of the magnetic field generator 22 from the first intensity level, which is the magnetic field intensity level of the normal detection operation, and the first intensity level. It can function as a magnetic field control means for switching to any one of the second strength levels. The detection frequency setting means 32 includes a function of setting a setting frequency (generated signal frequency) of the signal generation unit 21 to define a generation magnetic field frequency of the magnetic field generation unit 22 during normal detection, and a magnetic field detection unit control unit 33. And a function of frequency selection setting means for setting the detection operating frequency of the magnetic field detection unit 23.

  The first intensity level is a magnetic field intensity level in a range generated by the magnetic field generator 22 when performing a normal metal detection operation, and the second intensity level is, for example, the first intensity level. Magnetic field strength level of 1/5 or less (corresponding to a magnetic field strength level that does not affect the metal detectors arranged close to each other). The second strength level is preferably set such that, for example, transmission signal output from the signal generation unit 21 to the magnetic field generation unit 22 is stopped and generation of the magnetic field by the magnetic field generation unit 22 is stopped, that is, the generated magnetic field strength remains normal. It is a level that can be said to be substantially zero (A / m) at about the value level.

  The magnetic field detector control means 33 supplies a detection clock signal to the detector of the magnetic field detector 23 and, based on the set frequency information from the detection frequency setting means 32, the frequency and phase of the detection clock signal (signal generator 21). (Phase difference with respect to the reference signal) can be adjusted, and the detection operation frequency of the magnetic field detection unit 23 can be defined regardless of whether the magnetic field generation unit 22 is activated (whether the magnetic field is generated).

  The storage means 34 is composed of a RAM or other rewritable memory device, and temporarily stores various setting information related to metal detection and data of measurement results in the signal level measurement unit 24, including the detection operation frequency during normal operation. Can be stored.

  The detection frequency selection unit 35 constitutes a measurement unit 40 together with the detection frequency setting unit 32, the magnetic field detection unit control unit 33, and the signal level measurement unit 24. In the measurement unit 40, the generated magnetic field of the magnetic field generation unit 22 is the above-mentioned. In the state of the second intensity level, electromagnetic noise in the inspection region 12 is measured at a plurality of different detection operation frequencies of the magnetic field detector 23 (details will be described later).

  The detection frequency selection unit 35 cooperates with the detection frequency setting unit 32 and the magnetic field detection unit control unit 33 so that the electromagnetic noise level measured by the measurement unit 40 among the plurality of different detection operation frequencies is less than a predetermined value. The frequency selection setting means for selecting one of the frequencies and setting the setting frequency of the magnetic field generation unit 22 and the detection operation frequency (detection frequency) of the magnetic field detection unit 23 corresponding thereto.

  By the way, the metal presence / absence determination unit 26 compares the detection signal amplitude level of each workpiece W conveyed to the inspection area 12 with a predetermined threshold level to determine whether or not the metal W is contained in the workpiece W, that is, the product. As a determination means for determining pass / fail as a known determination method and outputting the determination result to the display unit 27. The metal presence / absence determination unit 26 also outputs a selection command signal for separating defective products from non-defective products to a selection unit 28 provided on the downstream side of the inspection region 12 of the conveyor 11.

  Next, the operation will be described.

  When the metal detector is activated, the control system is initialized and the setting data is read by turning on the power. For example, the amplitude and the setting frequency of the transmission signal generated by the magnetic field generator 22 are determined, and the alternating operation is performed accordingly. A magnetic field is generated from the magnetic field generator 22, but at the time of activation, an operation frequency setting process as described below is executed in the present embodiment.

  FIG. 2 is a flowchart showing a schematic procedure of the operating frequency setting process.

  In the figure, first, it is checked whether the operation state of the metal detector is initially set immediately after the start button is pressed or reset after the reset button is operated (step). S1) If it is one of those cases (YES in step S1), then the type information of the workpiece W (inspected object) to be inspected after the current operating frequency setting process is set by the user or Various setting parameters and the like related to the workpiece W are read from the storage means 34 and other memory devices (step S3). Next, the magnetic field generation intensity of the magnetic field generation unit 22 is set to a second intensity level (1/5 or less of the normal operation level, for example, a level of substantially zero output) (step S4). As a result, the influence of the magnetic field from the magnetic field generator 22 on the inspection area 12 is sufficiently weak, and it becomes possible to measure the influence of external electromagnetic noise on the inspection area 12.

  Next, based on the type information of the workpiece W, a magnetic field frequency range suitable for metal detection in the workpiece W, that is, a frequency band is set, and a temporary detection operation for operating frequency setting processing within the range. A plurality of inspection frequencies which are frequencies, for example, f1 to fn (n is an integer of 1 or more) are set (step S5).

  Specifically, depending on the characteristics of the workpiece W (moisture, salt content, type of packaging material, etc.), one or more frequency bands suitable for metal detection in the workpiece W are in the range of several kHz to several MHz. Multiple selections are made. Then, in the measurement range specified by the inspection frequency band, for example, the inspection frequencies are selected in the order of preferred frequencies to be used, and the noise level of the external electromagnetic noise into the inspection region 12 is measured at the inspection frequency (step S6). ) And the measurement result is temporarily stored in the storage means 34 (step S7).

  The test frequency setting interval here is determined based on the frequency stability (for example, the accuracy and temperature characteristics of the digital direct synthesis synthesizer) in the detection unit 20, and the test frequency setting range is Q (frequency selection of the tuning circuit). Tuned characteristic value representing good quality). Specifically, if all frequency bands are a plurality of frequency bands in the range of several kHz to several MHz, and the Q value of the tuning circuit corresponding to the 1 MHz band is 100, for example, the optimum frequency search band in the 1 MHz band The width (= f / Q) is set in the form of 10 kHz, and all of a plurality of frequency bands or a specific frequency band suitable for the workpiece W is selected as the inspection frequency.

  Next, it is determined whether or not the current measurement result is equal to or lower than a predetermined electromagnetic noise level that is a threshold for determining an allowable noise level (step S8). If the magnetic field noise level is equal to or lower than a predetermined value (step S8). In the case of YES in S8, the current inspection frequency is selected as it is, and this is set as the set frequency during the subsequent operation and the corresponding detection operation frequency (in the figure, both frequencies are collectively referred to as the operation frequency). ) (Step S11).

  If the current measurement result is not a magnetic field noise level equal to or less than a predetermined value (NO in step S8), then whether the current inspection frequency was the last frequency in the predetermined measurement order, for example, frequency fn If not (step S9) and if it is not the last frequency (NO in step S9), the process returns to step S5 to set the next inspection frequency, and again enters the inspection region 12 at the inspection frequency. The noise level of the external electromagnetic noise is measured (step S6), and the measurement result is temporarily stored in the storage means 34 (step S7).

  Such a process is repeatedly executed within a predetermined number of times until the inspection frequency becomes the last frequency in the predetermined order of measurement or the measurement result is equal to or lower than a predetermined electromagnetic noise level. If the measurement result does not fall below the predetermined electromagnetic noise level (YES in step S9), the fact that the electromagnetic noise is abnormal is displayed, notified by print, voice or other output format (step S10), and then The inspection frequency with the lowest electromagnetic noise level among the set frequency and detection operation frequency set in the previous operation frequency setting process or the measurement result is set to the set frequency of the magnetic field generation unit 22 and the magnetic field detection unit 23 corresponding thereto. The detection operating frequency is set to a set value (step S11).

  After such setting of the operating frequency, the magnetic field intensity generated by the magnetic field generator 22 is then set to the first level that is the output level during the normal detection operation (step S12), and metal detection for the workpiece W is performed. Is possible. In the case of electromagnetic noise abnormality, it is possible to enter a standby state until the user inputs some operation.

  When the above setting is completed, normal metal detection is performed under detection conditions in which the influence of external noise is suppressed.

  In the present embodiment, the set frequency and the detection operating frequency are finely adjusted based on the measurement result within the preferable frequency band of the magnetic field used for the workpiece W. For example, the same frequency band is used. Even when a plurality of metal detection devices are arranged close to each other, fine adjustment can be automatically performed so that the magnetic field frequencies of the plurality of metal detection devices are gradually changed in order to suppress mutual interference.

  Furthermore, the performance degradation of the metal detection apparatus due to external electromagnetic noise can be prevented in the following points.

  3A and 3B are diagrams showing an example of detection signal output in the magnetic field detection unit 23 of the present embodiment, in which FIG. 3A shows electric noise of the magnetic field detection unit circuit, and FIG. 3B shows magnetic field fluctuation detection by the workpiece W. (C) is an output when a magnetic field fluctuation is detected when metal is mixed in the workpiece W, and (d-1) is an influence of electromagnetic noise, for example, somewhat interferes with other metal detection devices. (D-2) is output when the electromagnetic noise from other metal detection devices is interfering, and (d-3) is electromagnetic from other metal detection devices in proximity. The output when noise is strongly interfering is shown, respectively, and the Lissajous waveform obtained from the output obtained by quadrature detection of each signal is shown in association with the lower side.

  In the present embodiment, the detection operating frequency is selected and set in consideration of the influence of electromagnetic noise as shown in FIG. As shown in (b) and (c), it is possible to detect the output at the time of detecting the magnetic field fluctuation by the work W with a good S / N ratio. In the cases as shown in FIGS. 2D-2 and 3D-3, when the influence of noise cannot be suppressed only by selecting the detection operation frequency, it is possible to notify the noise abnormality.

  Each of the Lissajous waveforms shown in FIGS. 5 (a) to 5 (c) and FIGS. 5 (d-1) to (d-3) has a hatched circle due to the influence of electromagnetic noise and an elliptical shape to be inspected. This is due to magnetic field fluctuations caused by the body, and it can be said that FIGS. 5A to 5C show an ideal state. In the states shown in (b) and (d-1), the S / N ratio for the detection signal of the metallic foreign object is the same, but in the state shown in (b), the noise level is that of the object to be inspected. Whereas the influence of the article is smaller and the phase characteristic of the article can be calculated accurately and stably, the phase characteristic of the article cannot be accurately calculated due to the influence of noise in the state shown in FIG. Therefore, the metal detection lacks stability. In the state shown in (d-2) of the figure, the influence of noise is increased, and the metal detection performance is degraded. In the state shown in FIG. 6D-3, the influence of noise becomes very large, and the metal detection signal is buried under the influence of noise (in the circle), so that the metal cannot be detected.

  FIG. 4 shows an example of detection signal output of the magnetic field detection unit 23 for each detection operation frequency when the detection operation frequency is finely adjusted, and is described beside (i) to (v) in the figure. The frequency value is the frequency used as the inspection frequency, and the waveform below it is the output waveform of the measured noise detection signal. From the figure, the noise level is lowest at (ii) of 999.8 kHz. Conventionally, cases such as (i), (ii), (iv), and (v) in the figure cannot be identified. However, in this embodiment, suitable detection conditions are automatically detected by selecting the detection operation frequency based on the measurement result and setting the corresponding set frequency. Selection setting is possible.

  As described above, in the metal detection device of the present embodiment, the influence of the external electromagnetic noise is measured for a plurality of different detection operation frequencies, and the signal generation unit 21 and the magnetic field generation unit are selected by selecting a frequency at which the influence of the external electromagnetic noise is reduced. Since the set frequency is set to 22, the detection condition setting can be automatically adjusted to a suitable condition so as to suppress the influence of the external electromagnetic noise regardless of the change of the external electromagnetic noise due to a change in use environment or the like.

  In addition, it is possible to provide a dedicated magnetic field detection means, but in this embodiment, the inspection is not made using such a configuration but using the magnetic field detection unit 23 and the signal level measurement unit 24 used for normal metal detection. Since the electromagnetic noise in the region 12 is measured, the external electromagnetic noise measuring means can be easily added at a low cost and with a simple configuration.

  In addition, in the metal detection apparatus of the present embodiment, the detection frequency selection unit 35 determines a plurality of different inspection frequencies within a frequency range determined for each type of workpiece W, and thus an operation suitable for the type of workpiece W. By specifying the frequency band in advance and measuring the external electromagnetic noise in the frequency band, it becomes possible to quickly perform the operation frequency setting process at the time of startup or the like.

  Further, the detection frequency selection means 35 has the electromagnetic noise level measured by the magnetic field detection unit 23 and the signal level measurement unit 24 among a plurality of different inspection frequencies (detection operation frequencies) as the predetermined value, that is, a predetermined allowable noise level. Since the following frequency is selected and this frequency is set as the set frequency of the generated magnetic field, it is possible to surely suppress the deterioration of the metal detection performance due to the influence of external electromagnetic noise.

  In addition, since the setting condition changing process as described above is performed at the time of starting the metal detection device or resetting the operation of the metal detection device, the influence measurement of the external electromagnetic noise and the suitable operation are performed in parallel with a part of the initialization process. Various operating frequencies can be selected and set.

  Furthermore, by setting the second intensity level to an appropriate level that is 1/5 or less of the first intensity level, for example, even if the metal detectors arranged close to each other operate in the same frequency band, The optimal detection operating frequency can be selected and set without interfering and affecting each other. When the second intensity level is substantially zero, even when the metal detection devices are arranged adjacent to each other, they can be prevented from affecting each other.

[Second Embodiment]
FIG. 5 is a flowchart showing a schematic procedure of the operating frequency setting process of the metal detector according to the second embodiment of the present invention. In addition, since the structure of the metal detection apparatus of this embodiment is as substantially the same as the above-mentioned embodiment, the component and process similar to the above are demonstrated using the same code | symbol as the above.

  In FIG. 5, first, it is checked whether the operation state of the metal detector is initially set immediately after the start button is pressed or reset after the reset button is operated (step S1) If it is one of those cases (YES in step S1), then the type information of the workpiece W (inspected object) to be inspected after the current operating frequency setting process is set by the user or It is grasped and acquired from already set data (including schedule information) (step S2), and various setting parameters and the like related to the work W are read from the storage means 34 and other memory devices (step S3). Next, the magnetic field generation intensity of the magnetic field generator 22 is set to a second intensity level (1/5 or less of the normal operation level, for example, a level of zero output) (step S4). As a result, the influence of the magnetic field from the magnetic field generator 22 on the inspection area 12 is sufficiently weak, and the measurement of the influence of external electromagnetic noise on the inspection area 12 is possible.

  Next, a magnetic field frequency range suitable for metal detection in the workpiece W is set based on the type information of the workpiece W (inspection object), and a plurality of inspection frequencies, for example, f1 to fn (n) are set in the range. Is an integer greater than or equal to 1) (step S5). Then, using the frequency in the predetermined measurement order among the inspection frequencies, for example, the inspection frequencies are selected in descending order of the frequency, and the noise level of the external electromagnetic noise into the inspection region 12 is measured at the inspection frequency. (Step S6), the measurement result is temporarily stored in the storage means 34 (Step S7).

  Next, it is checked whether or not the current test frequency is the last frequency in the predetermined measurement order, for example, the frequency fn (step S9), and if not the last frequency (NO in step S9). Returning to step S5, the next inspection frequency is set, and the noise level of the external electromagnetic noise into the inspection region 12 is measured again at the inspection frequency (step S6), and the measurement result is temporarily stored in the storage means 34. (Step S7).

  Such processing is repeatedly executed a predetermined number of times until the inspection frequency reaches the last frequency in the predetermined measurement order frequency, and when it reaches the last frequency (YES in step S9), electromagnetic noise in the measurement result. The inspection frequency with the lowest level is selected, and that frequency is set as the subsequent operating frequency, that is, the set frequency of the generated magnetic field and the set value of the detected operating frequency (step S21).

  Specifically, for example, when the 1 MHz band is selected as the frequency band of one preferable inspection frequency, and the signal level measurement unit 24 outputs the detection level value using a 16-bit A / D converter, the inspection frequency 1000. The detection level is 632 at 4 kHz, the detection level is 532 at the inspection frequency of 1000.2 kHz, the detection level is 658 at the inspection frequency of 1000.0 kHz, the detection level is 587 at the inspection frequency of 999.8 kHz, and the detection level is 655 at the inspection frequency of 999.6 kHz. If the measurement result is obtained, the optimum frequency is 1000.2 kHz at which the noise detection level is the lowest, and this is the set value of the subsequent operating frequency.

  After the operation frequency is set, the magnetic field intensity generated by the magnetic field generator 22 is then set to the first intensity level that is the output level during the normal detection operation (step S12), and metal detection for the workpiece W is possible. It becomes a state.

  As described above, the metal detection apparatus of this embodiment also measures the influence of external electromagnetic noise on a plurality of different inspection frequencies (detection operation frequencies), selects a frequency at which the influence of external electromagnetic noise is reduced, and sets the generated magnetic field setting frequency. Since the setting conditions for metal detection are changed as described above, it is possible to obtain a metal detector that can obtain the same effects as those of the above-described embodiment and can reliably suppress the deterioration of the metal detection performance due to the influence of external electromagnetic noise. can do.

  Moreover, in the metal detection apparatus of the present embodiment, the detection frequency selection means 35 selects a frequency that has the lowest noise level among a plurality of different inspection frequencies and sets it as the set frequency and the detection operation frequency. The operating frequency setting process can be performed more quickly.

  Measurement result data temporarily storing the measurement result in the operation frequency setting process described above is stored in the storage unit 34, so that the change in the external electromagnetic noise can be used as information that can be compared with time, or during the detection operation. Needless to say, it can be used for switching the detection operating frequency and the generated magnetic field frequency.

  As described above, the present invention measures the influence of external electromagnetic noise on a plurality of different inspection frequencies, and selects a frequency that reduces the influence of external electromagnetic noise as the detection operation frequency. Regardless of changes in electromagnetic noise, it is possible to provide a metal detection device that can automatically adjust metal detection conditions to suitable conditions so as to reduce the influence of external electromagnetic noise. Metal detection device that detects the metal in the object to be inspected using a magnetic field, especially suitable for detecting foreign metal contamination in products that are transported or moved under its own weight, etc., and detection operating conditions that are less affected by external electromagnetic noise It is also useful for a metal detection type inspection apparatus or inspection method and program that need to be set periodically.

It is a block diagram which shows schematic structure of the metal detection apparatus which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the schematic procedure of the operating frequency setting process of the metal detection apparatus which concerns on the 1st Embodiment of this invention. It is a detection signal waveform diagram which illustrates a detection signal at the time of the magnetic field change by noise in a magnetic field detection part of a metal detection device concerning a 1st embodiment of the present invention by a work, interference between metal detectors, etc. FIG. 5 is a detection signal waveform diagram illustrating a plurality of different detection operation frequencies and noise detection signals at the frequencies in the magnetic field detection unit of the metal detection device according to the first exemplary embodiment of the present invention. It is a flowchart which shows the schematic procedure of the operating frequency setting process of the metal detection apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

12 Inspection Area 13 Work Detection Sensor 20 Detection Unit 21 Signal Generation Unit 22 Magnetic Field Generation Unit (Magnetic Field Generation Unit)
23 Magnetic field detection part (magnetic field detection means)
24 signal level measurement unit 26 metal presence / absence determination unit (determination means)
27 Display unit 28 Sorting unit 30 Detection condition control circuit 31 Amplitude setting means (magnetic field control means)
32 Detection frequency setting means (frequency selection setting means)
33 Magnetic field detector control means 34 Storage means 35 Detection frequency selection means (frequency selection setting means)
40 Measuring means

Claims (4)

Magnetic field generating means (22) for generating an alternating magnetic field of a set frequency included in a predetermined frequency range corresponding to the article influence of the object to be inspected in the inspection region (12) of the object to be inspected;
Magnetic field detection means (23) for detecting a change in the alternating magnetic field caused by the inspection object passing through the alternating magnetic field at a detection operation frequency corresponding to the set frequency;
In a metal detection apparatus comprising a determination means (26) for determining the presence or absence of a metal object or a metal component in the inspection object based on a detection signal of the magnetic field detection means,
The set frequency of the magnetic field generation means is changed within the frequency range, and electromagnetic noise in the inspection region is measured using the magnetic field detection means for a plurality of different detection operation frequencies corresponding to the set frequencies. Measuring means (40);
A frequency selection setting means (32, 32) for selecting any one of the plurality of different detection operation frequencies at which the electromagnetic noise level measured by the measurement means is a predetermined value or less and setting the selected frequency as the set frequency of the magnetic field generation means 35).   The frequency selection setting means selects a frequency at which the electromagnetic noise level measured by the measurement means becomes the lowest value from the plurality of different detection operation frequencies, and sets the selected frequency as the setting frequency of the magnetic field generation means. The metal detection device according to claim 1.   The frequency selection setting unit selects a frequency at which the electromagnetic noise level measured by the measurement unit is equal to or lower than a predetermined allowable noise level from the plurality of different detection operation frequencies, and sets the selected frequency as the setting frequency of the magnetic field generation unit. The metal detection device according to claim 1, wherein:   The metal detection apparatus according to claim 1, wherein the magnetic field control unit, the measurement unit, and the frequency selection setting unit operate when the apparatus is started or when the operation is reset.

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