JP4087362B2 - Metal detector - Google Patents

Description

  The present invention relates to a metal detection device for detecting a foreign substance containing metal or a metal component (hereinafter, simply referred to as a metallic foreign substance) mixed in an object to be inspected, particularly when an object to be inspected such as food is passed through an alternating magnetic field. The present invention relates to a metal detection device that detects foreign matter from a change in a magnetic field.

  Recently, there has been an increasing demand for improving the quality of distribution products to protect consumers. For example, the strengthening of food hygiene management systems conforming to HACCP (Hazard Analysis Critical Control Point) is highly advanced. It is requested. Under such circumstances, metal detectors for detecting metal foreign matters mixed in products in product production lines such as foods and daily necessities have been widely used.

  As a conventional metal detection device of this type, for example, a magnetic field is generated so that a product conveyed on a conveyor passes through an alternating magnetic field of a predetermined frequency, and the degree and state of change in magnetic field caused by product movement in the magnetic field. There is one that detects the presence or absence of a metallic foreign object from (see, for example, Patent Document 1).

  As shown in FIG. 6, this metal detector converts the pulse signal from the reference signal generator 1 into a sine wave by the filter 2, amplifies it by the power amplifier 3, and supplies it to the transmission coil 4 as an excitation current. An alternating magnetic field is generated in the transmission coil 4, while an alternating magnetic field from the transmission coil 4 is applied to a pair of reception coils 5a and 5b arranged opposite to the transmission coil 4 or coaxially with the transmission coil 4. Yes. The receiving coils 5a and 5b are formed so as to be equally affected by the alternating magnetic field generated from the transmitting coil 4, and are connected to each other in opposite polarities (differential connection), and only the generated magnetic field of the transmitting coil 4 is used. On the other hand, the induced voltage outputs of the receiving coils 5a and 5b are balanced with each other and the output becomes zero. When the workpiece W moves in the alternating magnetic field, the balanced state of the receiving coils 5a and 5b is lost, and the unbalanced output signal is amplified by the differential amplifier 6 and taken into the detection circuit 7. The detection circuit 7 uses the phase shift reference signal obtained by shifting (shifting) the output pulse signal of the reference signal generator 1 by a predetermined amount in the phase shift circuit 13, from the unbalanced output signal at the shifted phase. A signal that changes according to the movement of the workpiece W is output except for a high-frequency signal component that changes according to the frequency of the alternating magnetic field. This detection output is subjected to removal of high frequency noise components by the low-pass filter 8 and conversion from an analog signal to a digital signal by the A / D converter 9, and is input to the determination circuit 11 and the waveform display storage device 12.

  The determination circuit 11 performs threshold determination using the signal amplitude of the input signal as a threshold value for a predetermined voltage value or a predetermined magnification value with respect to the signal amplitude at the time of non-defective product inspection, and the amplitude of the detection signal exceeds the threshold value. If it is determined that a metal foreign object is mixed, a signal indicating the determination result is output.

  By the way, in the above-described metal detection apparatus that performs magnetic field detection, when a new product is to be inspected, detection phase adjustment is performed using a sample product that does not contain a metal foreign object prior to the inspection.

In general, the phase adjustment is performed by changing the phase shift amount of the phase shift circuit by a small step angle so that the unbalanced output of the receiving coil is minimized, so that the detection phase becomes a phase that minimizes the influence of the sample product. Thus, during actual inspection, the detection signal level of a component including a metal object or a metal component is high, and the output signal level due to the influence of other items is low (for example, patents). (Refer to paragraphs [0013] to [0014] in Document 2).
JP-A-6-160542 JP-A-11-258355

  However, the conventional metal detection device has the following problems.

  With a magnetic field frequency and detection phase at which the level of a detection signal is minimum for a sample article that does not contain metal, it is not always possible to detect metal foreign matter mixed in the object to be inspected with the highest sensitivity.

  In other words, when the magnetic field frequency and the detection phase are set so that the detection signal of the object to be inspected is minimized, the detection signal for the metal foreign object to be detected may also become small. As a result, the metal to be detected There was a problem that the detection sensitivity of the foreign matter was lowered.

  In addition, the user may have set their own detection sensitivity standard, and when the sensitivity standard is set with a material, size, shape, etc. different from steel balls and stainless steel balls that are generally used as sensitivity standards, Or, when sensitivity standards are defined for metals that are easy to mix in a production line, it is not easy to grasp those standards in advance or make settings corresponding to changes in those standards .

  An object of the present invention is to provide a metal detection device capable of solving such problems and capable of detecting metal with higher sensitivity.

In order to achieve the above object, the metal detection device of the present invention detects a change in magnetic field due to a magnetic field generating means for generating an alternating magnetic field corresponding to a reference signal and a test object passing through the alternating magnetic field. Based on magnetic field detection means for outputting a detection signal corresponding to a change in the magnetic field, detection means for synchronously detecting the detection signal output from the magnetic field detection means by a signal corresponding to the reference signal, and detection output of the detection means A metal detector including a determination unit for determining presence or absence of a metal foreign object mixed in the object to be inspected , including a metal foreign object in a detection signal of the magnetic field detection unit for a plurality of different frequencies of the reference signal. for not the phase setting means the degree of an article the influence of the test subject to set each phase with the smallest, the plurality of different frequencies, set of by the phase setting means It was under phase detection signal and the foreign matter samples wherein the magnetic field comprising a metal foreign object to be detected of the magnetic field detection means when the inspection object containing no metal foreign object through the magnetic field generated by the said magnetic field generating means has passed The detection signal of the magnetic field detection means when passing through the magnetic field generated by the generation means, and the detection signal ratio of the foreign matter sample to the detection signal of the object to be inspected that does not include metal foreign matter among the plurality of different frequencies Is provided with a frequency setting means for selecting a frequency that maximizes the frequency of the reference signal and setting the frequency of the reference signal.

  With this configuration, the frequency of the reference signal is variably set based on the detection signal of the inspection object and the detection signal of the foreign material sample, and the detection signal level of the metal foreign material is higher than the output level of the normal non-defective product detection signal. Set to standard. Therefore, by selecting and setting the reference frequency, it is possible to select a mode suitable for foreign object detection of the object to be inspected from a plurality of detection sensitivity modes corresponding to a plurality of reference frequencies, and a user-specific determination criterion is defined. Even in such a case, suitable detection conditions can be easily set, and highly sensitive metal detection becomes possible.

Further, the metal detection device of the present invention is the magnetic field detection means when the object to be inspected that does not include a metal foreign object passes through the magnetic field generated by the magnetic field generation means under the phase set by the phase setting means. And the detection signal of the magnetic field detection means when the foreign material sample passes through the magnetic field generated by the magnetic field generation means, and for the determination by the determination means based on the acquired signal information It is preferable to provide a threshold calculation means for calculating the threshold.

  With this configuration, it is possible to grasp the detection signal level in the state where the metal foreign object is mixed in the object to be inspected and the state where the foreign object is not mixed, and set a threshold value suitable for the required condition between both detection signal levels Thus, metal detection with higher sensitivity becomes possible.

  According to the present invention, the detection signal of the inspection object and the metal foreign object to be detected at the detection phase at which the detection signal level of the inspection object is minimized corresponding to a plurality of different frequencies of the reference signal defining the magnetic field frequency. Since the detection signal of the foreign material sample included is acquired and the magnetic field frequency that maximizes the level ratio is selected, a metal detection device capable of easily setting a suitable magnetic field frequency can be provided. .

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

  1-5 is a figure which shows schematic structure of the metal detection apparatus based on one embodiment of this invention.

  First, the configuration will be described.

  In FIG. 1, a work W that is an object to be inspected is transported in a predetermined direction by a conveyor B, and the transport speed is set according to the transport speed of the production line of the work W. A predetermined section in the conveyance direction of the workpiece W is an inspection area for detecting metal foreign matter (a foreign matter made of metal or a foreign matter containing a metal component) in the workpiece W. For example, an optical workpiece detection sensor 35 for detecting the entry of W into the inspection area is installed. 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 inspection area of the workpiece W, a detection unit 20 that detects a metal foreign object in the workpiece W, and a calculation according to a predetermined control program based on a detection signal of the detection unit 20 and a user operation input from the operation input unit 36 A control unit 30 that executes processing and outputs the processing result to the output unit 37 is provided.

  The detection unit 20 includes a transmission signal generation circuit 21, a transmission coil 22, a differential detector 23 (magnetic field detection unit), a quadrature detection unit 24 (detection processing unit), bandpass filters 27a and 27b, amplifiers 28a and 28b, and A / The D converter 29 is configured.

  The transmission signal generation circuit 21 includes a reference signal generator 21a and a power amplifier 21b, generates a transmission signal having a predetermined frequency, and current-drives the transmission coil 22. The transmission coil 22 is disposed in the vicinity of the work conveyance path by the conveyor B, and when excited by current drive from the transmission signal generation circuit 21, an alternating magnetic field corresponding to the frequency of the reference signal from the reference signal generator 21a. Is a magnetic field generating means for generating in the inspection area.

  The differential detector 23 cooperates with the transmission signal generation circuit 21 and the transmission coil 22 to detect a metal object or a component of a metal component in the workpiece W with respect to the plurality of workpieces W (inspection object). The differential detector 23 includes receiving coils 23a and 23b, a tuning circuit 23c, and an amplifier 23d. The reception coils 23a and 23b are composed of a pair of coils arranged so as to be linked to the magnetic flux generated from the transmission coil 22 and connected to each other with opposite polarities. Only the alternating magnetic field from the transmission coil 22 is received by these reception coils 23a. , 23b are equally balanced and adjusted so that the output of the differential detector 23, which is the difference between the two, becomes 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 B includes some metallic foreign matter and passes through the magnetic field generated by the transmitting coil 22, the magnitude relationship of the induced voltages of the receiving coils 23a and 23b changes according to the movement of the workpiece containing the metallic foreign matter. As a result, the balanced state of the output between the receiving coils 23a and 23b is greatly lost. Further, even when only a workpiece that is mainly a non-magnetic material passes through the magnetic field generated by the transmission coil 22, the reception coil 23a is not as noticeable as when it contains metallic foreign substances due to its contained components, moisture, and the like. , 23b, the equilibrium state of the output is lost.

When the output balance between the receiving coils 23a and 23b is lost due to the movement of the workpiece W on the conveyor B in this way, the receiving coils 23a and 23b detect the differential detection signal Sd (magnetic field) corresponding to the change in the magnetic field. Detection signal of the detection means) . The differential detection signal Sd has a signal form in which a low-frequency signal component that changes due to movement of the workpiece W in the magnetic field is superimposed on an AC signal component having the frequency of the transmission signal corresponding to an alternating magnetic field from the transmission coil 22 side. For example, it can be represented by a signal waveform as shown in FIG.

  The generation frequency of the reference signal generator 21a that determines the magnetic field frequency from the transmission coil 22 can be set to any one of a plurality of frequencies by a control unit 30 and a frequency setting unit 33 (frequency setting means) described later. The motion detector 23 has a required detection sensitivity for an alternating magnetic field having an arbitrary frequency selected from a plurality of different frequencies.

  The differential detection signal Sd is taken into the quadrature detection unit 24 through the tuning circuit 23c and the amplifier 23d.

  The quadrature detection unit 24 includes a pair of synchronous detectors 25a and 25b, a phase setter 26a, and a phase shifter 26b. The differential detection signal Sd from the differential detector 23 is a pair of synchronous detectors. The signals are input to the devices 25a and 25b in parallel. The synchronous detector 25a receives a signal (a signal corresponding to the reference signal) whose phase is adjusted for synchronous detection of the transmission signal via the phase setter 26a, and the synchronous detector 25b receives the signal phase from the phase setter 26a. Is shifted by 90 ° by the phase shifter 26b (a signal corresponding to the reference signal).

  The synchronous detector 25a synchronously detects the differential detection signal Sd of the differential detector 23 based on the AC signal from the phase setter 26a, and outputs the detection output from which the high-frequency component corresponding to the transmission signal has been removed to the bandpass filter 27a. Supply. Similarly, the synchronous detector 25b outputs a detection output obtained by removing a high-frequency component corresponding to a transmission signal from the differential detection signal Sd of the differential detector 23 to the band pass filter 27b based on the AC signal from the phase shifter 26b. Supply.

  The detection output by the synchronous detectors 25a and 25b here also differs depending on the phase setting value of the phase setter 26a. For example, the change in the magnetic flux density occurs at the moment (phase 0 degree) where the change in the magnetic flux density is maximum. On the side of the detection signal where the influence of the non-magnetic metal that causes Joule heat to be consumed and the external magnetic field change is larger, and the magnetic flux density is almost maximum (the moment when the amplitude of the magnetic field waveform is maximum; phase 90 °) The higher the magnetic flux density is, the more the magnetic flux is attracted and a detection signal having a greater influence of the magnetic metal causing the external magnetic field change.

  The bandpass filters 27a and 27b have filter characteristics that remove high frequency noise components from the detection signals detected by the synchronous detectors 25a and 25b. The low-frequency component detection signals (detection outputs) output from the bandpass filters 27a and 27b include an envelope waveform connecting instantaneous values of a predetermined phase position of the differential detection signal Sd, and a transmission signal period from the predetermined phase position. An envelope waveform (for example, waveforms X and Y shown in FIG. 4) connecting the instantaneous values whose phases are shifted by ¼ of τ, that is, by 90 °, is formed.

  The outputs of both band-pass filters 27 a and 27 b are amplified by amplifiers 28 a and 28 b, respectively, converted from analog to digital detection signals by A / D converter 29, and taken into control unit 30.

  As shown in FIG. 1, the control unit 30 includes a control / arithmetic unit 31 and a storage device 32. The control / arithmetic unit 31 has a microcomputer configuration including a CPU, a RAM, a ROM, and an I / O interface. The control program stored in the ROM is executed by the CPU while exchanging data with the RAM. The detection signal and the like captured via the I / O interface are processed. The storage device 32 includes an auxiliary storage device that can exchange data with the control / arithmetic unit 31 or an external database that is further connected by communication.

  The storage device 32 is used for various parameters relating to the setting of the metal detection device, a non-defective sample of the workpiece W (hereinafter simply referred to as a non-defective sample) that does not include metallic foreign matter, and a sample of metallic foreign matter on the workpiece W, for example, a test for metallic foreign matter. It is possible to store and hold detection signal data of a foreign object sample (hereinafter, simply referred to as a foreign object sample) containing a metal object or a metal component, that is, a foreign object to be detected, in a piece or a component of another specification that can be mixed. The foreign matter sample is not limited to the foreign matter to be detected in the object to be inspected, but may be a sample form of a single foreign substance or a sample form of a part of the subject to be inspected.

  When setting up the metal detector, prepare one or more foreign material samples corresponding to one or more foreign material contamination types that are likely to occur in the product to be inspected, and prepare non-defective samples for the product to be inspected. After collecting the inspection data for these samples, the control unit 30 (threshold calculation unit 31d described later) performs threshold setting for pass / fail determination. At this time, sample inspection data, operation inputs related thereto, calculation value data, and the like are temporarily stored and stored in the storage device 32.

The control / arithmetic unit 31 includes a phase control unit 31b that functions as a phase setting unit together with the phase setter 26a. When the above-described non-defective sample and foreign matter sample are inspected, the non-defective sample that does not include a metallic foreign matter is included. The phase setting unit 26a is used to set the phase that minimizes the influence of the article, and the detection sensitivity of the detection unit 20 for the metallic foreign matter mixed in the workpiece W is preliminarily increased. Here, the phase at which the article influence of the non-defective sample is minimum is, for example, the output level of the synchronous detectors 25a and 25b when the phase of the phase setter 26a (the phase difference of the detection phase with respect to the reference signal) is changed. It is set as the minimum dip point φd (see FIG. ₃ φd _{1 to} φd ₃ ). Note that the dip point φd is based on the difference between the non-defective sample and the foreign sample because the non-defective sample has a small effect on the product even if the foreign sample is in the form of a single foreign object that does not include the effect of the product. This is because it is possible to reliably capture

  The control / arithmetic unit 31 also determines the size (for example, length) and conveyance speed of the workpiece W, the generated signal frequency of the reference signal generator 21a, the set detection phase (phase difference with respect to the reference signal) of the phase setter 26a, the band pass Various setting parameters relating to the operation of the metal detection device, such as the filter bands of the filters 27a and 27b, are partly manually input from the operation input unit 36 and have a function of setting means for automatically setting the others. . The length of the work W and the conveyance speed are conditions for determining the time for capturing the detection signals X and Y, the interval thereof, the filtering bands of the bandpass filters 27a and 27b, and the like. As can be seen from the fact that the detection signal X is specified by an instantaneous value at a predetermined phase position corresponding to the phase shift amount (phase difference with respect to the reference signal) of the phase setter 26a, the waveform amplitudes of the detection signals X and Y are phase setters. It differs depending on the set phase of 26a. Therefore, the set phase of the phase setter 26a is one of the parameters that determine the sensitivity of detection of the metal object or metal component contained in the workpiece W.

  The generated signal frequency of the reference signal generator 21a is variably set by the frequency setting unit 33, and corresponds to the material and size of the metal foreign object to be detected for foreign objects among a plurality of different preset frequencies. Thus, the frequency at which the ratio α (described later) of the detection signal of the foreign material sample to the detection signal of the non-defective sample W is maximized is selected and set from a plurality of different frequencies. That is, the frequency setting unit 33 is configured to set the frequency of the reference signal based on the detection signals of the non-defective sample W and the foreign material sample, and the control / calculation unit 31 functions as a frequency setting unit together with the frequency setting unit 33. It has a functioning frequency control unit 31c. The reference signal frequency selected and set by the frequency setting unit 33 is also one of the parameters that determine the sensitivity of detection of the metal object or metal component included in the workpiece W.

  Next, a calculation process of the ratio α of the detection signal of the foreign material sample to the detection signal of the non-defective sample (inspected object) W in the control / calculation unit 31 will be described.

  When the workpiece W is detected by the workpiece detection sensor 35, the control / calculation unit 31 samples the data of the detection signals X and Y every predetermined time for a certain period of time under the set capture condition, and the sampled detection Based on the instantaneous values x and y of the signals X and Y, a coordinate point (x, y) having the instantaneous values x and y as coordinate components in the X-axis direction and the Y-axis direction while the workpiece W is passing through the magnetic field is X Data of Lissajous's figures drawn on the -Y plane is created and stored in the internal memory or in a predetermined storage area of the storage device 32.

  As shown in FIG. 4A, the Lissajous figure here is substantially symmetric with respect to the origin O and has a vertex at a coordinate farthest from the origin O. For example, the Lissajous figure Hn in FIG. It can be characterized by the coordinates (Xm, Ym) of the vertex Qn. Alternatively, the coordinate data of the vertex Qn may be converted into polar coordinates and characterized by coordinates (r, θ). Here, r is the distance from the origin O of the vertex Qn, and θ is the angle (tan θ = Ym / Xm) formed by the line segment QO and the X axis.

  When a non-defective sample of the workpiece W is inserted and passed in an alternating magnetic field, the Lissajous figure drawn by the coordinate point (x, y) becomes, for example, an approximately 8 character shape as indicated by Hg in FIG. When a foreign matter sample including a metallic foreign matter test piece is passed, the Lissajous figure drawn by the coordinate point (x, y) is different in the major axis direction from the Lissajous figure Hg, for example, as shown in FIG. It becomes a long and narrow figure of 8 as indicated by Hn. As described above, the Lissajous figure obtained based on the detection signals X and Y has an inclination (major axis) of the Lissajous figure depending on whether a metal object or a metal component (hereinafter also referred to as a metal object) is included in the detection target. Direction) is greatly different. Further, the Lissajous figures obtained for the same kind of metal objects having different sizes tend to have similar shapes in which the slope of the Lissajous figure is almost the same and the distance from the origin of the apex differs depending on the size of the metal objects etc. is there.

  In the present embodiment, at the time of setting, candidate values for a plurality of different angles θd are set based on the data of the Lissajous figures Hn and Hg when first inspected using a foreign material sample and a non-defective sample. For the angle θd, the point on the Lissajous figure that has the maximum distance from the straight line A that intersects the origin O is identified, and the ratio α = Ln / Lg of the maximum distances Ln and Lg is the maximum. A sample sensitivity setting process is performed in which the angle θd of the value is adopted as the optimum set value θi (see FIG. 4B). The control / arithmetic unit 31 also calculates the ratio α = Ln / Lg as described above for each of the cases where the plurality of different frequencies are the generated signal frequencies of the reference signal generator 21a. A reference frequency that maximizes α is selected and set. In addition, when there are a plurality of types of metal foreign objects that are highly likely to be mixed, the setting process may be performed by collecting data of inspection results for a plurality of foreign samples having different mixing modes.

  The control / arithmetic unit 31 also functions as a determination unit 31a (determination unit) that determines that the workpiece W does not contain a metallic foreign object, and passes (OK), and if the metallic foreign object contains a foreign object, it rejects (NG). With this function, the pass / fail of each workpiece W to be inspected, that is, the presence / absence of metal foreign matter is determined. The threshold for this determination is the calculated value of the detection signal ratio α for the non-defective sample and the foreign material sample stored in the storage device 32 by the function as the threshold calculation unit 31d (threshold calculation means) of the control / calculation unit 31. Based on this, a specific level value between the detection signal amplitude level of the foreign material sample and the detection signal amplitude level of the non-defective sample is calculated and set so as to become the threshold level. Here, the detection signal ratio α and the threshold value are rotated by the optimum angle θi so that the A axis in FIG. 4B is the X axis, as shown in FIG. The maximum distances Ln and Lg are obtained as peak outputs Vn and Vg of the Y-axis component, respectively, and these ratios are grasped in the form of Vn / Vg.

  Based on this threshold value, the determination unit 31a of the control / calculation unit 31 compares the detection signal amplitude level of each workpiece W manufactured on the actual manufacturing line and transported to the inspection area with the threshold level, and a metal is contained in the workpiece W. It is judged whether or not foreign matter is included, that is, whether or not the product is acceptable, or further, the type of foreign matter mixed in is estimated from the inspection data. The data is output to the output unit 37.

  Next, the operation will be described.

FIG. 5 is a flowchart showing a schematic procedure of the setting process of the metal detection device of the present embodiment.
[Setting mode]
When setting the metal detector, if the user presses a menu key (not shown), a menu screen (details not shown) with selection items such as auto setting, detection sensitivity (level) change, and statistics menu is displayed. However, for example, by selecting the auto setting and executing the inspection measurement of the non-defective sample and foreign material sample of the workpiece W, the initial setting process necessary for the operation is performed.

  In this setting process, first, the reference value of the phase angle φ for setting the detection phase of the synchronous detectors 25a and 25b with respect to the generated signal (reference signal) from the reference signal generator 21a is read from the storage device 32 or the like. At the same time (step S1), values (reference values) of a plurality of different frequencies f1 to fn as generated by the reference signal generator 21a are read from the storage device 32 or the like (step S2).

  Next, after setting input such as the type of workpiece W and conveyance conditions is input and the data is read into the control / calculation unit 31 (step S3), the inspection is performed when the non-defective sample is flowed to the inspection area as the workpiece W and inspected. Output data is collected (step S4), and a phase (dip point θd in FIG. 4, step S5) that minimizes the influence of the non-defective sample is set.

  Next, inspection output data when the foreign material sample is flowed to the inspection area and inspected is collected (step S6). Inspection output data when the foreign material sample is inspected and inspection output data when the non-defective sample is inspected first. Based on the above, the ratio α (output ratio α in FIG. 5) of these detection signals is obtained (step S7).

  When the inspection of the sample and the calculation of the detection signal ratio α are completed, the generated signal frequency of the reference signal generator 21a used for the current inspection is a predetermined switching order (for example, f1, f2, It is checked whether or not it is the last frequency fn (for example, the highest frequency) in the order of f3... fn (step S8). If it is not the last frequency fn (NO in step S8), step S4 is performed. Returning to step S4, the inspection from step S4 to step S7 and the calculation process of the detection signal ratio α are executed using the next reference frequency. Here, the frequency f is an arbitrary frequency such that n is 4 to 6 between several Hz and several MHz.

  When the inspection / measurement for the last frequency fn among a plurality of different frequencies is completed (YES in step S8), the frequency at which the calculated value of the detection signal ratio α is maximized is the generated signal frequency of the reference signal generator 21a. Is selected and set (step S9), and the current setting process is terminated.

[Operation mode]
After the setting as described above is completed and the metal detection device is ready for operation, when an operation key (not shown) is pressed, normal operation is started, and an operation screen is displayed on the output unit 37, indicating that the product is a product. Inspection on a production line of a large number of workpieces W is performed.

  When the contamination of the metal foreign matter is detected, for example, in addition to the NG display indicating the occurrence of the foreign matter contaminated product, the product number, the product name, or the type of the detected metallic foreign matter is displayed on the output unit 37, for example. Is done.

[Product switching mode]
Further, when the production of the planned number of workpieces W is completed and switching to another type is performed, a type switching key (not shown) of the operation input unit 36 is operated. At this time, if switching to a new product type, the setting process described above is executed again, and if the product is already switched to a sample-tested product type, various setting parameters are set based on the stored data for the selected product type. Such inspection conditions are automatically switched to new conditions.

  As described above, in the present embodiment, the reference signal of the reference signal generator 21a that defines the magnetic field frequency is changed to a plurality of different frequencies, and the work W passes through the generated magnetic field of the transmission coil 22 for each frequency. And the detection signal of the differential detector 23 when the foreign material sample passes through the magnetic field generated by the transmission coil 22 and the non-defective sample of the plurality of frequencies is obtained. The frequency at which the ratio α of the detection signal of the foreign substance sample to the detection signal is maximized is selected, and the frequency of the reference signal is variably set. Further, when setting the reference signal frequency, the control / calculation unit 31 and the frequency setting unit 33 as the phase setting means set the phase that minimizes the degree of the influence of the article of the work W in the detection signal of the differential detector 23. Therefore, the metal foreign matter detection signal level is set to a higher level than the normal non-defective product detection signal output level. As a result, a mode suitable for foreign object detection can be easily selected from a plurality of detection sensitivity modes corresponding to a plurality of reference frequencies, and the influence of articles of each type of inspection object is small, and the foreign object detection sensitivity is high. This makes it possible to perform stable foreign object detection, and facilitates sensitivity setting work even for user-specific sensitivity standards and unknown foreign substances of different materials and sizes, etc. Suitable detection conditions can be set, and phase setting work and the like can be reduced.

  In addition, when the control / calculation unit 31 as the determination unit moves the foreign sample by the conveyor B (when the foreign sample passes through the generated magnetic field), the detection signal of the differential detector 23 and the non-defective sample are transferred to the conveyor. The detection signal of the differential detector 23 when it is moved by B (when the non-defective sample passes through the generated magnetic field) is acquired, and based on the acquired signal information, metal foreign matter is mixed into the workpiece W. Since the threshold value for determining whether or not there is a metal foreign matter is mixed in the workpiece W, the detection signal levels in the state where the metal foreign matter is mixed and the state where the workpiece W is not mixed are reliably grasped. In the meantime, a threshold value that suits the required conditions can be set, and highly sensitive metal detection can be performed. For example, when the difference between both detection signal levels is small, a threshold is set in the middle of both detection signal levels, and when there is a large difference between both detection signal levels, in order to eliminate false detection due to variations in the influence of non-defective products. Alternatively, a signal level of about 70% of the detection signal level of the foreign material sample may be set as the threshold value.

  As described above, the present invention detects the detection signal of the inspection object at the detection phase at which the detection signal level of the inspection object is minimized corresponding to a plurality of different frequencies of the reference signal that defines the magnetic field frequency. The detection signal of the foreign material sample including the metallic foreign material to be acquired is acquired, and the magnetic field frequency at which the ratio α of the detection signal levels is maximized is selected and set. It has an effect that metal detection can be performed, and is suitable for a metal detection device for detecting metal in an object to be inspected, particularly suitable for detecting contamination of metal foreign matter in a product conveyed on a conveyor. Therefore, it is useful for a metal detection device or a metal detection type inspection device in which detection sensitivity needs to be set or changed easily under favorable conditions according to the foreign substance contamination type.

It is a block diagram which shows the structure of the detection part of the metal detection apparatus which concerns on one embodiment of this invention, and a control part. It is a wave form diagram which illustrates the waveform of the differential detection signal of the metal detection apparatus concerning one embodiment of the present invention. The graph which shows the relationship between the detection signal output level and detection phase of the metal detection apparatus which concerns on one embodiment of this invention, The solid line in the graph shows the output level of the detection signal about the good sample of the workpiece | work W, and a broken line is The output level of the detection signal about the foreign material sample which put the metal foreign material piece in the workpiece | work is each shown. Explanatory drawing (b) of setting of Lissajous figure (a) calculated | required from the detection signal of the good quality sample and foreign material sample of the metal detection apparatus based on one embodiment of this invention, and the optimal workpiece | work phase angle (theta) i based on the figure data And (c) of a rotational deformation process for setting detection sensitivity based on the graphic data. It is a flowchart which shows the schematic procedure of the setting process of the metal detection apparatus which concerns on one embodiment of this invention. It is a block diagram which shows the structure of the metal detection apparatus of a prior art example.

Explanation of symbols

20 detector 21 transmission signal generation circuit (magnetic field generation means)
21a Reference signal generator 21b Power amplifier 22 Transmitting coil 23 Differential detector (magnetic field detecting means)
23a, 23b Reception coil 23c Tuning circuit 23d Amplifier 24 Quadrature detection unit (detection processing means)
25a, 25b Synchronous detector 26a Phase setter (phase setting means)
26b Phase shifters 27a, 27b Bandpass filters 28a, 28a Amplifier 29 A / D converter 30 Control unit 31 Control / calculation unit 31a Determination unit (determination means)
31b Phase control unit (phase setting means)
31c Frequency control unit (frequency setting means)
31d Threshold calculation unit (threshold calculation means)
32 storage device 33 frequency setting unit (frequency setting means)
35 Work detection sensor 36 Operation input unit 37 Output unit
W Workpiece (inspected object)

Claims (2)

Magnetic field generating means (21) for generating an alternating magnetic field corresponding to the reference signal;
Magnetic field detection means (23) for detecting a change in the magnetic field due to the inspected object (W) passing through the AC magnetic field and outputting a detection signal corresponding to the change in the magnetic field;
Detection means (24) for synchronously detecting a detection signal output from the magnetic field detection means (23) with a signal corresponding to the reference signal;
In a metal detection apparatus comprising: determination means (31a) for determining the presence or absence of metal foreign matter mixed in the object to be inspected (W) based on the detection output of the detection means (24).
Phase setting means for setting, for a plurality of different frequencies of the reference signal, phases for minimizing the degree of influence of the article (W) on the inspection object (W) that does not include metal foreign matter in the detection signal of the magnetic field detection means (23). (26a, 31b),
With respect to the plurality of different frequencies, the object to be inspected (W) that does not include a metal foreign substance in the magnetic field generated by the magnetic field generating means (21) under the phase set by the phase setting means (26a, 31b). The detection signal of the magnetic field detection means (23) when passing and the foreign matter sample containing the metallic foreign matter to be detected of the magnetic field detection means (23) when passing through the magnetic field generated by the magnetic field generation means (21). Obtaining a detection signal, and selecting a frequency at which a detection signal ratio (α) of the foreign object sample to a detection signal of the object to be inspected (W) that does not include a metal foreign object is a maximum among the plurality of different frequencies, A metal detection apparatus comprising frequency setting means (31c, 33) for setting the frequency of the reference signal. Under the phase set by the phase setting means, the magnetic field detection means (23) when the object to be inspected (W) that does not include a metallic foreign object passes through the magnetic field generated by the magnetic field generation means (21). A detection signal and a detection signal of the magnetic field detection means (23) when the foreign material sample passes through the magnetic field generated by the magnetic field generation means (21) are acquired, and the determination is performed based on the acquired signal information The metal detection apparatus according to claim 1, further comprising a threshold value calculation means (31d) for calculating a threshold value for determination by the means (31a).

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