JP2004279035A - Metal detection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make settable a field strength at a value appropriate to an body to be inspected by a simple work. <P>SOLUTION: A signal generator 21 is constituted in such a way as to make signal output to be supplied to a transmission coil 22 changeable. A setting means 32 of a control part 30 automatically sets the strength of an alternating magnetic field E in such a way that the output of a detection part 26 when a conforming sample of the body to be inspected is passed through the alternating magnetic field E may take 1/k of a prescribed value of a maximum output B of the detecting part 26 in a normal operating state or lie within a prescribed range in its vicinity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is used in an inspection line for food or the like, and detects a foreign substance of a metal in a metal detection device that detects whether or not metal is mixed in the object to be inspected while the object is transported. The present invention relates to a technique for performing high sensitivity.
[0002]
[Prior art]
As a metal detector used for inspection lines of foods, etc., a magnetic field is generated in a transport path of an inspected object so that a mixed metal can be detected while the inspected object is being transported, and the magnetic field is applied to the inspected object. A method of detecting a change in a magnetic field due to a mixed metal is employed.
[0003]
FIG. 10 shows a configuration of a metal detection device 10 that detects a change in a magnetic field.
The metal detector 10 includes a signal generator 11 that outputs a signal D of a predetermined frequency, a transmission coil 12 that receives the signal D and generates an alternating magnetic field E of a predetermined frequency on the transport path 2 of the device 1 to be inspected, It has two receiving coils 13a and 13b that are arranged along the transport direction of the DUT 1 at positions where the alternating magnetic field E is received by equal amounts and that are differentially connected to each other. A magnetic field change detector 13 for detecting a signal corresponding to a change in the magnetic field, a detector 16 for synchronously detecting an output signal R of the magnetic field change detector 13 with a signal having the same frequency as the signal D, and an output of the detector 16 A control unit 17 for determining whether or not metal is mixed into the test object 1 based on the signal.
[0004]
In the conventional metal detection device 10 configured as described above, when the test object 1 is not present in the alternating magnetic field E, the amplitudes of the signals generated in the two receiving coils 13a and 13b are equal and the phases are inverted. Therefore, the amplitude of the signal R becomes zero and the output of the detection unit 16 becomes zero. However, when the test object 1 is present in the alternating magnetic field E, the test object 1 In addition, due to the influence of the metal mixed in the test object 1, the equilibrium state of both signals generated in the two receiving coils 13 a and 13 b is lost, and the amplitude and phase change with the movement of the test object 1. A signal R is output.
[0005]
The signal R at this time includes not only a signal component caused by the influence of the mixed metal on the alternating magnetic field E, but also a signal component caused by the effect of the test object 1 itself (including the packaging material) on the alternating magnetic field E. Therefore, the detection limit of the mixed metal is determined by the signal component of the test object 1 itself.
[0006]
The influence of the test object 1 on the alternating magnetic field varies greatly depending on the amount of moisture contained in the test object, the material of the packaging material, and the like.
[0007]
For this reason, conventionally, the phase of synchronous detection is set so that the amplitude of the output signal of the detection unit 16 is minimized when a non-defective sample of the device under test 1 is passed through the alternating magnetic field E in advance. Is set as a threshold value, an inspection is performed on the device under test 1, and when the device under test 1 passes through the alternating magnetic field E, the amplitude of the output signal of the detection unit 16 becomes threshold. When the value exceeded the value, it was determined that metal foreign matter was mixed in the test object 1.
[0008]
However, the amplitude of the output signal of the detection unit 16 depends not only on the detection phase but also on the signal input to the detection unit 16, that is, the amplitude of the unbalanced signal output from the receiving coils 13a and 13b. The amplitude of the unbalanced signal changes according to the strength of the alternating magnetic field E generated by the transmission coil 12.
[0009]
Therefore, when the alternating magnetic field E is weak with respect to the test object, the detection output of a good sample becomes lower than the noise level, and the detection phase cannot be adjusted correctly.
[0010]
If the alternating magnetic field E is too strong with respect to the test object, an unbalanced signal having an excessive amplitude is input to the detection unit 16, and a normal detection operation cannot be performed.
[0011]
For this reason, conventionally, as described in Patent Literature 1 below, the strength of the alternating magnetic field E generated by the transmission coil 12 is configured to be manually variable, and mixed into the object to be inspected prior to the inspection. The strength was adjusted to be able to detect the metal in a stable manner.
[0012]
[Patent Document 1] JP-A-5-87942
[Problems to be solved by the invention]
However, the work of manually setting the strength of the alternating magnetic field E for each type of the test object prior to the detection phase setting process is very complicated, and is not always appropriate due to the variation in the setting work of each operator. However, there is a problem that stable operation cannot be expected because the magnetic field strength is not always set to an appropriate value.
[0014]
An object of the present invention is to solve this problem and to provide a metal detection device capable of setting the strength of an alternating magnetic field suitable for an object to be inspected by a simple operation.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the metal detection device of the present invention includes:
A signal generator (21);
A transmission coil (22) that receives a signal output from the signal generator and generates an alternating magnetic field having a frequency equal to the frequency of the signal on a transport path of the device under test;
Magnetic field change detection including two receiving coils (23a, 23b) arranged along the transport path at a position receiving the alternating magnetic field and outputting a signal corresponding to a magnetic field change caused by an object passing through the alternating magnetic field Part (23),
A detector (26) for synchronously detecting an output signal of the magnetic field change detector with a signal having the same frequency as the signal output from the signal generator;
Determining means (31) for determining the presence or absence of metal mixed in the inspection object based on the output signal of the detection unit;
The signal generator is configured to be able to vary the output of a signal supplied to the transmission coil,
The signal output from the signal generator to the transmission coil is controlled so that the magnitude of the detection output when a non-defective sample of the test object passes through the alternating magnetic field is equal to or within a predetermined range. A setting means (32) for automatically setting the output is provided.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of a metal detection device 20 to which the present invention is applied.
[0017]
In FIG. 1, a signal generator 21 generates a signal having a predetermined frequency f and outputs the signal to a transmission coil 22 and a detection unit 26 described later.
[0018]
For example, as shown in FIG. 2, the signal generator 21 includes an oscillating unit 21a that oscillates and outputs a signal D having a constant amplitude, a programmable amplifier 21b that amplifies an output signal D of the oscillating unit 21a, and a programmable amplifier 21b. A power amplifier 21c for power-amplifying the output signal D 'and supplying the power to the transmission coil 22. The output of the signal supplied to the transmission coil 22 (i.e., the strength of the alternating magnetic field) is varied by varying the amplification of the programmable amplifier 21b. ) Can be changed. Note that a variable attenuator may be used instead of the programmable amplifier 21b.
[0019]
The transmission coil 22 receives the power-amplified signal D ″ and applies an alternating magnetic field E having a frequency f equal to the signal D ″ and an intensity corresponding to the amplitude of the signal D ″ to the transport path of the DUT 1 (generally, Is formed by a conveyor).
[0020]
The alternating magnetic field E generated by the transmission coil 22 is received by the two reception coils 23a and 23b of the magnetic field change detection unit 23. The magnetic field change detection unit 23 is for outputting a signal corresponding to a change in the magnetic field due to an object passing through the alternating magnetic field E, and the two receiving coils 23a and 23b are at positions where they receive the alternating magnetic field E in equal amounts. In addition, they are arranged along the transport direction of the device under test 1, are differentially connected to each other, and output an unbalanced signal appearing between the connection points. The unbalanced signal may be amplified by an amplifier (not shown) and output.
[0021]
The transmitting coil 22 and the two receiving coils 23a and 23b are fixed to a common frame (not shown) surrounding the transport path 2, for example, so that their relative positions do not change.
[0022]
In the arrangement of the transmission coil 22 and the reception coils 23a and 23b, when the transmission coil 22 and the two reception coils 23a and 23b are opposed to each other with the conveyance path 2 interposed therebetween, the coil is wound so as to surround the conveyance path 2. The case where the receiving coils 23a and 23b are arranged coaxially before and after the transmitting coil 22, respectively, and the case where the transmitting coil 22 and the two receiving coils 23a and 23b are arranged on the same plane on the upper surface or the lower surface of the transport path 2. There is.
[0023]
Since the two receiving coils 23a and 23b are differentially connected at a position receiving an equal amount of the alternating magnetic field E, the two receiving coils 23a and 23b are not affected when the test object 1 or the mixed metal does not affect the alternating magnetic field E. Since the amplitude of the signal generated at 23b is equal and the phase is inverted, the amplitude of the signal R between the connection points becomes zero.
[0024]
Here, a case where the two receiving coils 23a and 23b of the magnetic field change detecting unit 23 are differentially connected will be described. However, signals generated in the two receiving coils 23a and 23b are subtracted by an analog subtractor. The magnetic field change detection unit 23 may be configured to perform the operation. If the magnetic fields received by the two receiving coils 23a and 23b are not equal, the difference between the signals generated in the receiving coils 23a and 23b may be corrected by a variable resistor or an amplifier having a different amplification factor.
[0025]
An entry sensor 24 for detecting the timing at which the device under test 1 enters the alternating magnetic field E is provided near the transport path 2. The entrance sensor 24 includes, for example, a light emitter and a light receiver, and detects the entrance timing of the object to be inspected from a change in an output signal of the light receiver when light incident on the light receiver from the light emitter is blocked by the object 1. I can do it. The entry of the article into the magnetic field can also be detected by a change in the amplitude of output signals X and Y of the detection unit 26 described later, and in that case, the entry sensor 24 can be omitted.
[0026]
The detection unit 26 synchronously detects the output signal R of the magnetic field change detection unit 23 by a signal having a frequency equal to the frequency of the alternating magnetic field E.
[0027]
The detection unit 26 of this embodiment is of a quadrature two-phase type, and is a phase shifter 26a that shifts the output signal D of the signal generator 21, a mixer 26b that mixes the output signal L and the signal R of the phase shifter 26a, and a mixer. BPF 26c for extracting a low-frequency component corresponding to the transport speed of the device under test 1 from the output of 26b, a phase shifter 26d for shifting the phase of the signal L by 90 degrees, a signal R and an output signal L of the phase shifter 26d. And a BPF 26f that extracts a low-frequency component corresponding to the transport speed of the DUT 1 from the output of the mixer 26e.
[0028]
The signals X and Y output from the two BPFs 26c and 26f of the detection unit 26 are converted into digital values by A / D converters 28 and 29, respectively, and input to the control unit 30 having a computer configuration.
[0029]
The control unit 30 detects the entry of the DUT 1 into the alternating magnetic field E from the output signal of the entry sensor 24 (or the change in the amplitude of the output signals X and Y of the detection unit as described above), and outputs the output signal of the detection unit 26. X and Y are fetched, and based on the data of the fetched signal and a preset threshold value, it is determined whether or not metal is mixed in the test object 1 and the result of the determination is output. The apparatus includes a determination unit 31, a setting unit 32 for setting various parameters necessary for the inspection of the test object 1, and a non-volatile memory 33 for storing the parameters and data necessary for the parameter setting. ing.
[0030]
The control unit 30 is connected to the operation unit 35 and the display 36. When the setting mode is designated by the operation unit 35, the control unit 30 performs setting processing of various parameters by the setting unit 32, and the examination mode is designated by the operation unit 35. When the determination is made, the determination unit 31 performs the metal contamination inspection of the inspection object 1 and outputs the inspection result.
[0031]
The parameters required for the inspection include the length and the transport speed of the DUT 1, the frequency of the alternating magnetic field E (the frequency of the signal D output from the signal generator 21), and the intensity of the alternating magnetic field E (for the transmission coil 22). The magnitude of the supplied signal D ″), the detection phase of the detection unit 26 (the phase shift amount of the phase shifter 26a), a threshold value for determining the presence or absence of a foreign substance, and the like.
[0032]
Here, the length and the transport speed of the inspection object are parameters for determining the capture interval and capture time of the output signals X and Y of the detection unit 26, the bandwidth of the BPFs 26c and 26f of the detection unit 26, and the like.
[0033]
Further, the frequency and strength of the alternating magnetic field E and the detection phase of the detection unit 26 are parameters for determining the sensitivity to the mixed metal.
[0034]
Further, the threshold value for determination is for determining whether or not a metal is mixed in the test object 1 and is determined according to the sensitivity to the mixed metal.
[0035]
The setting means 32 is configured so that these parameters can be set manually or semi-automatically by operating the operation unit 35. Here, the strength of the alternating magnetic field E with respect to the test object is set to an optimum value, and the detection is performed. A process for setting the phase to an optimum value and setting a threshold value for determining the presence or absence of a foreign substance in the detection phase will be described.
[0036]
Although FIG. 1 shows only signal lines necessary for setting the amplification degree of the programmable amplifier 21b of the signal generator 21 and setting the detection phase, the signal generator 21 actually outputs the signal lines. The frequency of the signal D, the bandwidth of the BPFs 26c and 26f of the detection unit 26, and the like can be controlled.
[0037]
3 and 4 are flowcharts showing the processing procedure of the setting means 32 regarding the setting of the intensity of the alternating magnetic field E, the detection phase, and the threshold value. Hereinafter, the setting processing operation will be described according to this flowchart.
[0038]
For example, when these setting processes are selected, as shown in FIG. 3, the phase shift amount Δθ of the phase shifter 26a is set to a reference value (for example, 0), and the amplification degree of the programmable amplifier 21b is minimized. In the set state, an instruction is given to pass the non-defective sample Wg of the test object 1 through the magnetic field E (S1 to S3).
[0039]
In accordance with this instruction, the operator passes the non-defective sample Wg to the magnetic field E.
[0040]
The good sample Wg is usually a non-magnetic material, but the magnetic field changes due to moisture, salt, aluminum packaging material, etc. contained in the good sample, and the equilibrium state between the magnetic field and the two receiving coils 23a and 23b is lost. The unbalanced signal is output from the magnetic field change detection unit 23, and its signal amplitude changes according to the position of the non-defective sample in the alternating magnetic field E.
[0041]
For example, assuming that the non-defective sample Wg is a material that consumes the energy of the magnetic flux (converts it to heat), as shown in FIG. 5A, the leading portion of the non-defective sample Wg and the magnetic flux intersecting the receiving coil 23a. When the magnetic flux is reduced by proceeding to the crossing position, the amplitude Va of the signal generated on the receiving coil 23a side becomes smaller than the amplitude Vb of the signal generated on the receiving coil 23b side.
[0042]
As shown in FIG. 5B, when the non-defective sample further advances and reaches a position where the number of magnetic fluxes crossing the two receiving coils 23a and 23b is equal to each other, the two receiving coils 23a and 23b Since the magnetic fluxes intersecting with each other decrease by an equal amount, the amplitudes Va and Vb of the signals generated in the two receiving coils 23a and 23b become substantially equal.
[0043]
Further, as shown in FIG. 5 (c), when the non-defective sample further advances and reaches a position where the rear end crosses only the magnetic flux intersecting with the receiving coil 23b and reduces that magnetic flux, the receiving coil 23b side The amplitude Vb of the generated signal is smaller than the amplitude Va of the signal generated on the receiving coil 23a side.
[0044]
Therefore, the waveform of the signal R when the non-defective sample passes through the alternating magnetic field E is a modulated wave whose amplitude increases and decreases as shown in FIG. The waveform of the signal X obtained by performing the synchronous detection process of the detection unit 26 with respect to the signal R, assuming that the amplitude values of the signals L and L ′ of the detection unit 26 are 1, as shown in FIG. An envelope connecting the instantaneous values of each predetermined phase position of the signal R is obtained, and the waveform of the signal Y is shifted by 90 degrees from the predetermined phase position of the signal R (the position shifted by T / 4 when the period of the signal D is T). ) Is an envelope connecting the instantaneous values for each.
[0045]
After instructing the non-defective sample to pass through the magnetic field, when the entry of the article (non-defective sample) is detected from the output signal of the entry sensor 24, the control unit 30 controls the detection unit 26 to take in the output signals X and Y for a predetermined time. Then, the data Dg is stored in the predetermined area 33b of the memory 33 as non-defective sample data (S4, S5).
[0046]
When the coordinate point determined by the two signals X and Y obtained in this manner is shown on the xy coordinates, for example, as shown in FIG. 7A, a waveform of a figure eight (Lissajous waveform) substantially symmetric with respect to the origin. Hg.
[0047]
The maximum value of the data of the good sample Wg corresponds to the coordinates Xg and Yg of the position farthest from the origin in the Lissajous waveform Hg shown in FIG. The maximum amplitude value of the detection output) A is
A = (Xg ² + Yg ² ) ^1/2
It becomes.
[0048]
The amplitude value A changes in accordance with the intensity of the alternating magnetic field E generated by the transmission coil 22, and becomes smaller as the alternating magnetic field E is weaker. The amplitude of the signal input to 26 also decreases, and the detection component for the metal mixed into the test object also decreases.
[0049]
On the other hand, if the alternating magnetic field E is too strong with respect to the test object, the amplitude of the signal input to the detection unit 26 will be excessive, and a normal detection operation will not be performed.
[0050]
Therefore, first, it is determined whether or not the magnetic field E is too weak and the signals X and Y are lower than the noise level. If the signals X and Y are lower than the noise level, the amplification is increased by a predetermined value. Returning to S3, the above-described non-defective sample passing instruction, signal fetching, and the like are performed so that signal data of a noise level or higher can be obtained (S6, S7).
[0051]
Then, when data of a signal having a noise level or more is obtained, the amplitude value A of the above-mentioned non-defective sample is obtained, and the maximum outputs Xmax and Ymax in the normal state of the detection unit 26 (here, Xmax = Ymax = B). Is determined whether the ratio B / A between the amplitude value A and the amplitude value A is equal to (or within a predetermined range near the value k), and if not, the programmable amplifier required to be equal The gain G of the signal generator 21b is obtained, and the obtained gain G is set in the programmable amplifier 21b of the signal generator 21 and stored in the predetermined area 33c of the memory 33 (S8 to S11).
[0052]
This value k is set so that the detection output by the test object itself can be obtained with a relatively small amplitude and a high SN ratio even if there is a variation in the material and the like of the test object. This is a value determined in consideration of the noise figure of the detector 26, the allowable input range, and the like.
[0053]
Further, the calculation of the amplification G is based on the assumption that the detection output A is proportional to the amplification, and the amplification when the non-defective sample is first passed is represented by Ga, and the detection output A obtained at that time is represented by A1,
G = (B / k) (Ga / A1)
Can be obtained by the following calculation.
[0054]
However, when the amplification degree of the programmable amplifier 21b can be changed only in a predetermined step, the amplification degree in which the value A is closest to B / k or the amplification degree in which the value A does not exceed B / k is obtained. This is set and stored as described above.
[0055]
Then, the non-defective sample is instructed to pass through the magnetic field again. According to the instruction, the data of the detection output when the non-defective sample passes through the alternating magnetic field E is fetched in the same manner as described above, and is stored in the predetermined area 33b of the memory 33. The amplitude value A is again obtained from the data of the detection output and is confirmed, and it is confirmed that the value A is equal to the above B / k (or that the value A is within a predetermined range near B / k). Then, the process of setting the intensity of the alternating magnetic field E is completed, and the process proceeds to the process of setting the detection phase. The process for this confirmation may be omitted, and the process may proceed to the detection phase setting process after setting the amplification degree.
[0056]
In the detection phase setting process, the phase shift amount Δθ of the phase shifter 26a is maintained at a reference value (for example, 0), and the amplification degree (magnetic field strength) is maintained in the setting state as shown in FIG. It is determined whether or not the data Dm of the foreign matter sample is stored in the predetermined area 33a of the memory 33 (S12).
[0057]
If the foreign object data Dm is stored, the process proceeds to step S16 described below. If the foreign object data Dm is not stored, an instruction is given to pass a foreign object sample of the detection target metal into the alternating magnetic field ( S13).
[0058]
Upon receiving this instruction, the operator places a predetermined foreign matter sample Ms on the transport path 2 and passes it through the alternating magnetic field E.
[0059]
When the foreign matter sample Ms passes through the alternating magnetic field E, the magnetic field changes in the same manner as in the case of the non-defective sample described above, and unbalanced signals are output from the two receiving coils 23a and 23b. It is detected.
[0060]
For example, assuming that the foreign matter sample Ms is a magnetic material such as iron having an action of collecting magnetic flux, when the foreign matter sample Ms moves near the receiving coil 23a, the magnetic flux intersecting with the receiving coil 23a and the receiving coil 23b. The amplitude becomes larger than the intersecting magnetic flux, and the amplitude Va of the signal generated on the receiving coil 23a side becomes larger than the amplitude Vb of the signal generated on the receiving coil 23b side.
[0061]
Further, when the foreign matter sample Ms is located at an intermediate position between the two receiving coils 23a and 23b, since the magnetic flux intersects with both receiving coils by an equal amount, the amplitude Va of the signal generated on the receiving coil 23a side and the receiving coil 23b side And the amplitude Vb of the signal generated at the same time.
[0062]
When the foreign matter sample Ms is moving in the vicinity of the receiving coil 23b, the magnetic flux intersecting with the receiving coil 23b becomes larger than the magnetic flux intersecting with the receiving coil 23a, and the amplitude Vb of the signal generated on the receiving coil 23b side is reduced. It becomes larger than the amplitude Va of the signal generated on the 23a side.
[0063]
Therefore, the waveform of the signal R when the foreign matter sample Ms passes through the alternating magnetic field E is also a modulated wave whose amplitude increases and decreases similarly to the waveform of the good sample described above. The waveform of the signal X obtained by the detection processing is an envelope connecting the instantaneous values at each predetermined phase position of the signal R, and the waveform of the signal Y is shifted by 90 degrees from the predetermined phase position of the signal R (the period of the signal D T is an envelope connecting the instantaneous values for each (position shifted by T / 4).
[0064]
After instructing the passage of the magnetic field of the foreign matter sample Ms, the setting unit 32 captures the output signals X and Y of the detection unit 26 for a predetermined time when the entry of the article is detected from the output signal of the entry sensor 24, The data Dm is stored in the predetermined area 33a of the memory 33 (S14, S15).
[0065]
When the coordinate point determined by the two signals X and Y obtained in this way is shown on the xy coordinates, as shown in FIG. 7A, it has a different slope from the Lissajous waveform Hg of the non-defective sample, The Lissajous waveform Hn is substantially symmetric with respect to the origin.
[0066]
When only the foreign metal sample Ms is passed through the alternating magnetic field E as described above, a narrow Lissajous waveform such as the waveform Hn is obtained. The coordinates (Xm, Ym) of Q or the coordinates (r, θ) obtained by transforming the coordinates may be stored as feature point data of the foreign matter sample Ms.
[0067]
However, the distance r from the origin and the angle θ are
r = (Xm ² + Ym ² ) ^1/2
θ = tan ⁻¹ (Ym / Xm)
Is represented by
[0068]
When the data of the foreign sample is obtained in this manner, the setting means 32 uses the data of the non-defective sample stored last in the process of setting the strength of the alternating magnetic field E, and performs the detection on the detection output of the non-defective sample. Then, the phase at which the detection output ratio α of the foreign matter sample Ms becomes the maximum is obtained and stored as the optimum detection phase θi (S16).
[0069]
This process uses the data of the two Lissajous waveforms Hn and Hg shown in FIG. 7A, and corresponds to a certain detection phase θd from each coordinate (or only the point Q) of the waveform Hn of the foreign matter sample Ms. The ratio α = Ln / Lg between the maximum value Ln of the distance to the straight line C having an angle and the maximum value Lg of the distance from each coordinate of the waveform Hg of the non-defective sample to the straight line C is obtained for different detection phases θd, and FIG. (B), the phase at which the ratio α is maximum is determined as the optimum detection phase θi, and the information of the optimum detection phase θi is set in the phase shifter 26a of the detection unit 26 when inspecting the device under test 1. Is stored in a predetermined area 33c of the memory 33 as a parameter to be executed.
[0070]
Further, with respect to the Lissajous waveform Hg of the non-defective sample, a value, for example, twice the maximum value (the voltage corresponding to the distance Lg) in the direction orthogonal to the straight line C when the ratio α becomes the maximum is determined for the presence or absence of the mixed metal. Is stored in the predetermined area 33c of the memory 33 (S17).
[0071]
Through the above processing, the optimum magnetic field strength (here, the amplification degree of the programmable amplifier 21b), the detection phase, and the threshold value for the test object are obtained and stored in the predetermined area 33c of the memory 33.
[0072]
Then, when the inspection mode for the object to be inspected is designated, the setting unit 32 sets the amplification degree stored in the predetermined area 33c of the memory 33 in the programmable amplifier 21b, and transfers the information of the optimal detection phase θi. The phase is set in the phaser 26a to set the detection phase of the detection unit 26 to the optimum detection phase θi, and other parameters necessary for the inspection of the device under test 1 are set in necessary places.
[0073]
In the state where the parameters necessary for the inspection are set in this way, the inspection of the inspection object 1 by the determining means 31 is performed.
[0074]
FIG. 8 shows a processing procedure in the inspection mode. When the inspection object 1 is detected by the entry sensor 24 (S21), the determination means 31 captures the detection signals X and Y for a predetermined time (S22). ), By comparing the magnitude of the signal with the threshold value Vr stored in the memory 33, it is determined whether or not a metal foreign substance is mixed in the device under test 1 (S23). Is output (S24).
[0075]
During the inspection mode, when the test object 1 mixed with the same kind of metal as the foreign matter sample Ms passes through the magnetic field E, the Lissajous waveforms of the signals X and Y output from the detection unit 26 are as shown in FIG. Hn and Hg are rotated on the time axis by the optimum detection phase θi as shown in FIG. 9 (rotated so that the straight line C coincides with the x-axis). However, as for the signal Y along the y-axis, the signal amplitude Vg caused by the influence of the test object 1 on the magnetic field within the time when the test object 1 passes through the alternating magnetic field E is mixed. The ratio Vn / Vg of the amplitude Vn of the signal caused by the influence of the metal becomes the maximum corresponding to the distance ratio α.
[0076]
When the optimum detection phase θi is set as described above, the determination means 31 determines the presence or absence of the mixed metal by comparing the maximum amplitude Vy of the signal Y with the threshold value Vr. Then, at this time, the maximum amplitude Vy of the signal Y is equal to or greater than the threshold value when it is equal to or greater than 2 Vg (= Vr), so that the determination means 31 outputs a signal indicating that metal is mixed.
[0077]
When no metal foreign matter is mixed in the test object 1, only the signals X and Y corresponding to the Lissajous waveform Hg 'in FIG. 9 are output, and the maximum amplitude Vy of the signal Y is small. Since the threshold value is smaller than the threshold value Vr, the determination unit 31 does not output a signal indicating that metal is mixed.
[0078]
As described above, in the metal detection device 20 of the embodiment, the detection output when the non-defective sample of the test object passes through the alternating magnetic field E is equal to the predetermined output k of the maximum output B in the normal operation state of the detection unit 26. The strength of the alternating magnetic field E is automatically set so as to be within a predetermined range of 1 or its vicinity.
[0079]
For this reason, the strength of the magnetic field can be set to a value suitable for the device to be inspected by a simple operation of passing the good sample through the magnetic field.
[0080]
In the above description, the optimum magnetic field strength, detection phase, threshold value, and the like are determined based on data obtained by passing the foreign sample and the good sample once. The data may be passed through a magnetic field, the data may be averaged, and the optimum magnetic field strength, detection phase, threshold value, and the like may be determined based on the averaged data.
[0081]
In the above description, the case where the foreign substance sample data Dm is not stored in the memory 33 has been described. However, the foreign substance data is stored in the predetermined area 33a of the memory 33 in advance by the manufacturer of the metal detection device 20 or the like. You may leave.
[0082]
Further, the foreign substance data of a plurality of foreign substance samples having different materials are stored in advance in the predetermined area 33a of the memory 33 by the above-described processing, and the plurality of foreign substance data of Any one of them can be selected, and the same processing as described above can be performed on the selected foreign substance data.
[0083]
【The invention's effect】
As described above, the signal generator of the metal detection device of the present invention is configured so that the output of the signal supplied to the transmission coil can be changed, and when the non-defective sample of the test object is passed through the alternating magnetic field. A setting means is provided for automatically setting the output of the signal supplied from the signal generator to the transmission coil so that the magnitude of the detection output is equal to or within a predetermined range.
[0084]
Therefore, the strength of the alternating magnetic field can be set to an optimum strength suitable for the test object by a simple operation of passing the test object through the alternating magnetic field.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment of the present invention; FIG. 2 is a diagram showing a configuration example of a main part of the embodiment; FIG. 3 is a flowchart showing a processing procedure in a setting mode of a main part of the embodiment; 4 is a flowchart showing a processing procedure in a setting mode of a main part of the embodiment. FIG. 5 is a diagram for explaining a relationship between a position of a non-defective sample and a change in a magnetic field. FIG. 7 is a Lissajous waveform diagram of a detection output. FIG. 8 is a flowchart showing a processing procedure of a main part of the embodiment in an inspection mode. FIG. 9 is a Lissajous waveform diagram in an optimum detection phase state. FIG. Diagrams [Description of symbols]
DESCRIPTION OF SYMBOLS 1 ... Test object, 2 ... Conveyance path, 20 ... Metal detection apparatus, 21 ... Signal generator, 22 ... Transmission coil, 23 ... Magnetic field change detection part, 23a, 23b ... Receiving coil, 24 ... Ingress sensor 26... Detector 26 a and 26 d... Phase shifter 26 b and 26 e. Mixer 26 c and 26 f BPF 30 Control part 31 Judging means 32 Setting Means, 33, memory, 35, operation unit, 36, display

Claims (1)

A signal generator (21);
A transmission coil (22) that receives a signal output from the signal generator and generates an alternating magnetic field having a frequency equal to the frequency of the signal on a transport path of the device under test;
Magnetic field change detection including two receiving coils (23a, 23b) arranged along the transport path at a position receiving the alternating magnetic field and outputting a signal corresponding to a magnetic field change caused by an object passing through the alternating magnetic field Part (23),
A detector (26) for synchronously detecting an output signal of the magnetic field change detector with a signal having the same frequency as the signal output from the signal generator;
Determining means (31) for determining the presence or absence of metal mixed in the inspection object based on the output signal of the detection unit;
The signal generator is configured to be able to vary the output of a signal supplied to the transmission coil,
The signal output from the signal generator to the transmission coil is controlled such that the magnitude of the detection output when a non-defective sample of the test object passes through the alternating magnetic field is equal to or within a predetermined range. A metal detecting device provided with setting means (32) for automatically setting an output.

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