JP3107875B2 - Metal detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal for detecting a metal body mixed in food, a chemical product, a sewn product and the like.
It relates to a detector .

[0002]

2. Description of the Related Art As a detection principle of a metal detector, the following method is generally known. FIG. 1 shows a structural principle diagram of a detection coil portion of a metal detector. The coil 2 is an exciting coil. The coil 2 has an alternating current i having an angular frequency ω.
(Ω) flows to create an alternating magnetic field Hω. The coil 3-2 and the coil 3-1 are receiving coils. The coils 3-2 and 3-1 are connected to each other with opposite polarities to form a set of receiving coils.
They are arranged so as to be equal in size and to have the same left and right spatial relationship with respect to the exciting coil 2. Therefore, the magnitudes of the voltages induced in the coils 3-2 and 3-1 by the magnetic field H (ω) are substantially equal. As a result, at the output terminals ab of the receiving coil, the respective induced voltages are canceled to generate no output voltage, and a so-called zero-equilibrium state is maintained.
Now, in this state, the exciting coil 2 and the receiving coils 3-2 and 3
When -1 inserting the metal member P in the direction of the arrow in the space which constitutes, cause local changes in the magnetic field configuration in response to movement of the position of the traveling direction, the coils 3-2 and coils 3-
Since the first flux linkage changes, only the change amount is, as a detection signal of the metal body, appear as e ₀ to the output terminal a-b of the receiving coils 3-2,3-1.

[0003] The detection signal e ₀ output according to such a principle.
Are output with different amplitudes and phases depending on the type of the metal to be detected. When this output signal is vector-displayed, the mutual relationship as shown in FIG. 2 is confirmed as an example. The problem here is that, in addition to the metal body, the detection signal is generated very often also in the material or the product itself, which is the object to be mixed with the detection metal body. In particular, meat containing a large amount of electrolyte components generates a large detection signal in response to the magnetic field in the search coil. This effect is called a material effect or a product effect, and is superimposed as a noise on the detection signal of the metal body, and thus becomes a great obstacle to the detection operation of the metal body.
FIG. 2 shows an example of generation of a meat detection signal.

[0004]

To accommodate the removal of more such materials effects [0005], configuration such as the following have been taken conventionally. That is, in FIG. 16 , the phase angle of the detection signal of the material effect is actually measured in advance at the output terminals of the search coils 2 and 3, and the correction phase angle is calculated from this, and the phase shifter 10 is manually shifted. Alternatively, after the detection signal of the material effect is decomposed into quadrature phase angle components by the detectors 5 and 7, the output signal of either the detector 5 or 7 selected by the switch 11 becomes 0 at the output side of the amplifier 12. A method of manually adjusting the phase angle shifter 10 so that However, these methods require critical manual adjustment, and the set point after adjustment is likely to fluctuate due to changes in ambient temperature and the like. It changes at each position when passing through the search coil depending on the shape, so it is extremely difficult to accurately grasp these phase angles as described later, and it is difficult to remove the material effect accurately. .

[0005] The present onset bright, in order to solve such a problem, in advance by actually measuring the phase angle of the detection signal of the material effects prior to actual operation, a detection signal from this material effect as a fixed reference phase angle Compute and correct the state where the output value is effectively zero to obtain the material, type and
Stable detection output without being affected by
To provide a metal detector. In addition, the present invention
Is the detection signal output value by the material effect described above.
To provide a metal detector capable of automatically tracking a phase angle corrected and set so as to stably maintain a state where is effectively zero . Further, the present invention provides a metal detector capable of presetting an optimum detection state for a mixed metal body, even when there are a plurality of materials, for detecting a metal body mixed in a material or a product in which a material effect does not occur. Is what you do.

[0006]

To achieve this object, a metal detector according to claim 1 of the present application is a means for detecting a metal body whose detection output is obtained by a detection coil formed by a combination of an excitation coil and a reception coil. Decomposition means for decomposing the detection signal into two-direction components along two orthogonal axes using a quadrature fixed reference phase; and calculating the phase angle of the detection signal by a complex vector operation of the decomposed two-direction components. Output means for calculating and correcting the material effect by a correction phase angle that makes the material effect substantially zero to extract a detection signal of the metal body is configured as a metal detector. The metal detector according to claim 1, further comprising an automatic tracking function for making the material effect substantially zero by adaptively updating the corrected phase angle with the measured value of the phase angle. it can. In addition, regarding the detection of a metal body mixed in a material or a product in which a material effect does not occur, the correction phase angle is arbitrarily selected without being restricted by “material effect removal”. It is possible to have a means for calculating and setting a correction phase angle that maximizes the output of the detection signal according to the type of the metal body.

[0007]

Embodiments of the present invention will be described below. FIG.
Shows an embodiment of the present invention. In FIG. 3, the detection signals e ₀ and V output from the receiving coil 3 are input to detectors 5 and 7 via a high-frequency amplifier 4. As described above, the detection signals e ₀ and V are output as detection vectors as shown in FIG. 2 according to the type of metal body, product or material. The detectors 5 and 7 are widely known as synchronous detectors.
These are shifted by ° and used as fixed quadrature reference phase angle inputs. Therefore, detectors 5 and 7
Of the output as shown in the orthogonal coordinates of Fig. 4, the e _0, V x
The output voltages e _0x , V _x ,
e _0y and V _y are obtained. The output voltages e _ox and e _oy represent output signals of a metal body, and the output voltages V _x and V _y represent output signals (material effects) generated when products and materials pass through the search coils 2 and 3. .

Here, a description will be given of a general means for removing a material effect which becomes an obstacle when detecting the above-mentioned metal body. As an example, consider a case where the material effect of meat shown in FIG. 2 is removed and a metal body of stainless steel SUS (430) mixed in the meat is detected. Now, the meat detection vector of FIG.

[Outside 1] And displaying this on the complex plane of FIG. 5, V _ef
Let θ _{a be} the phase angle of the complex vector from the R axis, and e
_Assuming that the phase angle of the complex vector of _ss is θ _b, and the magnitudes of the respective amplitudes are A and B, the complex vector of V _{ef and} the complex vector of e _ss are represented by Equation (1) .

(Equation 1) From the above equation (1), in order to remove only the complex vector of V _ef from the state where the complex vector of V _{ef and} the complex vector of e _ss are detected at the same time, in FIG. It is understood that it is only necessary to extract the value of the R-axis component of each detection signal after superimposing the complex vector of V _{ef on} the j-axis by rotating by only.

That is, when the complex vector of V _ef is rotated leftward by ∠α, the following equation (2) is obtained.
You.

(Equation 2) Be taken out only the real part of equation (2), complex vector → 0 next to the V _ef, complex vector V _ef is removed. Similarly, the complex vector of e _ss is rotated in the same direction by ∠α.
Then, the following equation (3) is obtained.

(Equation 3) If only the real part of equation (3) is extracted, equation (4) is obtained.

(Equation 4) That is, the detection signal component of the meat material effect superimposed on the detection signal of the stainless steel metal body is removed, and only the detection signal component of the metal body becomes β _sin
It can be detected by the magnitude of (θ _b −θ _a ).

The problem here is that when a material or a product as described above passes through the space of the search coil, the temporal trajectory of the detection vector actually becomes a straight line as shown in FIG. Normally, a rather complicated hysteresis as shown in FIG. 6A is drawn.

FIG. 6 (A) shows a measured value of a detection vector when a meat block of about 10 kg is inserted through the search coil from P in FIG. FIG. 6 (B) is an actual measurement diagram when approximately 100 cc of saline solution is similarly inserted, and FIG. 6 (C) is an actual measurement diagram when a 3 mmφ iron ball is inserted. Considering FIG. 6 (A), the meat block passing through the search coil has a detection vector having a phase angle change of almost 360 ° as shown in FIG. 7 between the time when the meat block enters the search coil and the time it exits. Is generated. Accordingly, in such a case, in order to remove the material effect of the meat block by the above-described method, it is necessary to unify the detection vector that changes in a complicated manner and set a representative value as shown in FIG. , Such a detection vector is the material of the material,
Since it changes variously depending on the shape and the magnitude of the amount, it is extremely difficult to uniquely set a representative value in accordance with the material inserted into the search coil one after another.

The present invention provides an effective solution to such a problem. The principle of the present invention will be described by taking the above-described meat block material effect as an example. In FIG. 7 showing the detection vector of the meat block in FIG. 7, it has been described that when the meat block is inserted into the search coil, the detection vector changes in the direction of the arrow from the origin of the orthogonal axis. . Therefore, as described above, in order to remove the detection vector due to the material effect, it is necessary to approximate a single vector as shown by pp ′ in FIG. In such a case, a method of sampling each point of the curve and regressing it to a linear line is generally considered, but it is extremely difficult to obtain a substantially satisfactory result. The present invention solves this problem as follows.

In FIG. 9, the coordinates of each point P _{1 to} P _n of the phase characteristic of the meat block are sampled, and a detection vector corresponding to P _{1 to} P _n is obtained.

[Outside 2] It is calculated as (hereinafter referred to as "complex vector V [theta] _i"). Next, the complex vectors of Vθ _i are all converted to the small angle Δα
Only by rotating obtains a real part component (x-axis component) V _i bar complex vector V [theta] _i at this time, the whole V _i
The maximum value is searched for from the bar, and this is stored as the _Vimax bar. Next, all of the complex vectors of Vθ _i are further rotated by (Δα + Δα), the real part components are obtained in the same manner, the maximum value is similarly searched for, and this is stored. This operation is successively performed, and Δα + Δα +... Δα ≧ 360
Exit when ° is reached. Then obtained in these operations, by comparing successive values of V _imax bar group selects the minimum value in the V _imax bar, the sum of Δα to reach this minimum value as the alpha _0, this It is assumed that it is substantially equivalent to "α" shown in FIG. The process of this operation is illustrated in FIG. The effective phase angle α determined in this way is not limited to meat blocks as an example, but also to other materials and products with a large material effect, such as bread raw materials in the manufacturing process and taste-rich raw materials containing a lot of salt. It has been confirmed that the method can be applied well to various types.

An embodiment of the operation described above will be described. FIG.
, When a meat block is inserted between the search coils 2 and 3, a detection signal V corresponding to the material effect is generated. V passes through the high-frequency amplifier 4 and the detectors 5,
By 7 is decomposed in each of the x-axis component V _x and y-axis component V _y as shown in FIG. 4, operation unit 9 after passing through an A / D converter 8
Is input to Calculator 9, 11 and the minimum value of V _imax bar detection signal of the operational operation performed by meat blocks along the algorithms that shown in the flow diagram of FIG. 12 are stored, at the same time the phase angle α phase at this time Set for corner correction. The above is performed as automatic setting before actual operation.
Will be

Therefore, when the actual operation is started and the metal body is not mixed in the meat block, the arithmetic unit 9
The detection signal of the magnitude of the minimum value of the V _imax bar is output to the output terminal of. Here, if a metal body is mixed into this meat block, the detection signal of the metal body is superimposed on the minimum value of the signal output V _imax bar, but since the minimum value is effectively close to 0, the metal body Is output as described above.

Next, the automatic tracking function of the present invention will be described. The above-described correction phase angle α ₀ determined by a material or a product inserted into the search coil varies depending on the size or temperature change even if the correction type is the same type. For example, in the metal detector used in the baking process, the electrical properties of the materials and products moving in the production process fluctuate little by little, and the state of removal of the initially set material effect changes. Is well known. In the present invention, in order to cope with an obstacle due to such a variation, α ₀ for correcting the phase angle described above is used.
The not fixed, depending on the variation of alpha _0, and by automatically tracking the set value alpha _0. Tracking variations are corrected phase angle alpha ₀₁ determined to correspond to the material or product to be inserted into the search coils one after another, alpha _02, alpha _03, ...... moving sum averages a ₀ Hatton of
In this method, the values are successively set as new α ₀ values. In this case, when the mixed metal body materials and products detection of the metal body has been confirmed, alpha ₀ occurring at that time is to not be included. The magnitude of the number of times of averaging of the moving sum average value can be arbitrarily selected according to the state of the production process.

Next, the arithmetic operation for averaging α ₀ will be described. FIG. 14 and FIG. 15 are flowcharts of the operation example. First, as an initial setting, as shown in FIG. 14, the allowable angle and averaging count n at the time of calculating the running sum averages a ₀ hat correction phase angle alpha _0, for alpha _0, and alpha ₀ the deviation at the moment alpha Enter _LIM . α _LIM specifies an allowable limit of deviation in order to prevent a ₀ hat from abnormally changing when an abnormal value occurs in α ₀ . Further, the metal body even when mixed, is a ₀ hat the same reasons is programmed to also remove since there is a risk that varies significantly with the object. As described above, by the operation shown in FIG. 14, even if the preset removal state of the material effect gradually changes, automatic tracking for automatically correcting this can be performed.

Next, a method of setting the maximum sensitivity of the metal detector according to the present invention will be described. Some of the materials and products inserted into the search coil have little or no material effect. When detecting a metal object mixed in such an object, an arbitrary correction phase angle can be selected without being restricted by a material effect.
Therefore, the detection signal depends on the type of metal
Automatically calculates the correction phase angle that maximizes the output of the signal
Means to mix metal objects
Even if there is any, detect the optimum detection state for the material before actual operation.
It is possible to provide a metal detector that can be automatically set .
The present invention provides a method for detecting a metal body mixed in such a material or product up to the maximum sensitivity according to the type. As shown in FIG. 2, it is known that a detection signal of a metal body has a constant phase angle according to the type of material.
Now, here, iron (Fe) and aluminum (Al) in FIG.
FIG. 13 shows the detection vector of each metal body on the complex plane as before. Here, the phase angle difference between Fe and j-axis is β ₁ , the phase angle difference between Al and j-axis is β ₂ , and their respective amplitudes are C and D. Therefore, from the above, β ₁ and β ₂ are used as the correction phase angles, and

[Outside 3] The detection vector for the ∠Beta ₁ only turn superimposed j axis in the right direction, and Al

[Outside 4] Can be easily understood that the maximum detection values C and D in each case can be obtained by extracting only the imaginary part of each detection vector after turning β _{2 to the} left in the left direction and superimposing on the j-axis.

As described above, in the case where the material or product inserted into the search coil has no material effect,
In the embodiment shown in FIG. 3, the phase angles −β ₁ and β ₂ are set in the calculator 9 for phase angle correction, and the complex vectors of all the metal object detection signals e _Fe from the search coil are detected by the detector. A / D after decomposing into x and y axis components at 5,7
The signal is input to the arithmetic unit 9 via the converter 8. In the arithmetic unit 9, as shown in Expressions (5), (6), (7), and (8) ,

(Equation 5) Complex vector of detection vector e _Fe of each metal body, e _a1
Is preset for each of the complex vectors

[Outside 5] , The absolute value is compared, and the larger value is used as the detection output signal. It can be easily understood that this value is the maximum value from which the detection signals of various metal bodies input from the search coil can be extracted. Further, in this example, the phase β for correcting the phase angle preset in the arithmetic unit 9
It is needless to say that is also effective in a plurality of three or more.

[0021]

As described in detail above, according to the present invention, it is possible to obtain a detection output by effectively setting the material effect to 0, without being affected by the type and shape of the material or product. Therefore, a practical effect is extremely large since a stable detection output can be obtained. In addition, by providing the automatic tracking function, a state where the material effect is effectively set to 0 can be stably provided, so that the stability of the detection sensitivity can be further improved. Furthermore, when detecting a metal object that is mixed in a material or product that does not cause a material effect, the maximum detection sensitivity corresponding to the type of the different metal object that is mixed is determined using the corrected phase angle of the metal object. It is possible to set in advance so that it can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structural principle of a detection coil portion of a normal metal detector.

FIG. 2 is a vector diagram for explaining a material effect that becomes an obstacle when detecting a metal object.

FIG. 3 is a block diagram showing an embodiment of the present invention.

FIG. 4 is a vector diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 5 is a vector diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 6 is a vector diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 7 is a vector diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 8 is a vector diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 9 is a vector diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 10 is a characteristic diagram for explaining the operation of the embodiment in FIG. 3;

FIG. 11 is a flowchart showing the operation of the embodiment in FIG. 3;

FIG. 12 is a flowchart showing the operation of the embodiment in FIG. 3;

FIG. 13 is a vector diagram for explaining another function of the present invention.

FIG. 14 is a flowchart for explaining the operation of the embodiment in FIG. 3;

FIG. 15 is a flowchart for explaining the operation of the embodiment in FIG. 3;

FIG. 16 is a block diagram showing an example of a conventional metal detector.

[Description of Signs] 1 Oscillator 2 Excitation coil 3, 3-1, 3-2 Receiving coil 4 High frequency amplifier 5, 7 Detector 6 90 ° shifter 8 A / D converter 9 Computer 10 Phase angle shifter 11 Switch 12 Amplifier

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01V 3/10 B07C 5/34 G01N 27/72

Claims (3)

(57) [Claims] 1. To detect a metal body in a target product,
Detecting means for detecting the metal body by which a detection signal is obtained by a detection coil formed by a combination of an excitation coil and a reception coil; and decomposing the detection signal into two components along two orthogonal axes using a quadrature fixed reference phase. Decomposition means for calculating a phase angle of the detection signal by a complex vector operation of the decomposed two-direction components, and correcting the detection signal of the metal object by correcting the material effect of the target product by a correction phase angle of substantially 0. A metal detector provided with an output unit for taking out. 2. The apparatus according to claim 1, wherein said correction phase angle is adaptively updated by a measured value of said phase angle so as to have an automatic tracking function for making said material effect substantially zero. The metal detector as described. 3. A detecting means for detecting a plurality of metal objects in a target product, wherein the detection signal is obtained by a detection coil formed by a combination of an excitation coil and a reception coil, and the detection signal is formed at a right angle. Decomposing means for decomposing into two-direction components along two orthogonal axes using a fixed reference phase of the phase, and a phase of the detection signal determined according to the type of the metal body by calculating the decomposed two-direction components Output means for calculating a correction phase angle from the angle and performing phase correction so as to obtain the maximum value of each of the plurality of detection signals corresponding to the plurality of types of metal bodies and extracting the detection signal. Machine.