JP2021025847A - Foreign matter inspection device - Google Patents

Abstract

To provide a foreign matter inspection device also capable of detecting foreign matters in diverse shapes by using electromagnetic waves.SOLUTION: A foreign matter inspection device (1) for detecting foreign matters (C) mixed into an inspection object (A) by using electromagnetic waves includes: an electromagnetic wave oscillator (2) for applying electromagnetic waves to the inspection object (A); an electromagnetic wave detector (6) that is illuminated by the electromagnetic wave oscillator (2) and has an electromagnetic wave detection surface (6a) on which electromagnetic waves through the inspection object (A) impinge; a cycle structure board (8) that is disposed between the inspection object (A) and the electromagnetic wave detector (6), and induces interference of electromagnetic waves through the inspection object (A); and an arithmetic processor (10) for determining presence or absence of foreign matters (C) within the inspection object (A) on the basis of electromagnetic waves detected by the electromagnetic wave detector (6).SELECTED DRAWING: Figure 1

Description

The present invention relates to a foreign matter inspection device, and more particularly to a foreign matter inspection device that detects foreign matter mixed in an inspection object by using electromagnetic waves.

It is extremely important for businesses that manufacture food products, pharmaceutical products, etc. to reliably eliminate foreign substances mixed in products. Even if it is a foreign substance that is mixed in the product to be inspected and difficult to detect visually, it is relatively easy to find a foreign substance such as metal or pebbles that has a large density difference from the object to be inspected. .. On the other hand, it is difficult to find foreign substances such as plastic pieces, insects, hair, threads, etc., which have a small density difference from the inspection object, and foreign substances having components similar to those of the inspection object.

International Publication No. 2014/132620 (Patent Document 1) describes a method and an apparatus for detecting fibrous substances such as hair. In this detection method, the inspection object is irradiated with two terahertz waves whose polarization directions are orthogonal to each other, and the fibrous form of hair or the like is based on the difference in transmittance and the difference in reflectance of the two terahertz waves. The presence or absence of contamination is detected.

International Publication No. 2014/132620

However, in the detection method described in Patent Document 1, foreign substances are detected based on the difference in absorption intensity or reflection intensity of hair for two terahertz waves whose polarization directions are orthogonal to each other. Therefore, a fibrous substance such as hair is detected. Although it is possible to detect the contamination of foreign matter, there is a problem that it is difficult to detect foreign matter having other shapes.
Therefore, an object of the present invention is to provide a foreign matter inspection device capable of detecting foreign matter having various shapes other than fibrous substances such as hair by using electromagnetic waves.

In order to solve the above-mentioned problems, the present invention is an electromagnetic wave inspection device for detecting foreign matter mixed in an inspection object by using electromagnetic waves, and an electromagnetic wave oscillator for irradiating the inspection object with electromagnetic waves. Interference between an electromagnetic wave detector equipped with an electromagnetic wave detection surface that is irradiated from this electromagnetic wave oscillator and transmits electromagnetic waves that have passed through the inspection target, and electromagnetic waves that are placed between the inspection target and the electromagnetic wave detector and have passed through the inspection target. It is characterized by having a periodic structure plate that induces the above-mentioned, and an arithmetic processor that determines the presence or absence of foreign matter in the inspection object based on the electromagnetic wave detected by the electromagnetic wave detector.

In the present invention configured as described above, the electromagnetic wave oscillator irradiates the inspection object with electromagnetic waves, and at least a part of the irradiated electromagnetic waves passes through the inspection target. The electromagnetic wave transmitted through the inspection object is incident on the periodic structure plate arranged between the inspection object and the electromagnetic wave detector, and the electromagnetic wave is transmitted by the periodic structure plate and interference is induced. The electromagnetic wave whose interference is induced by the periodic structure plate is incident on the electromagnetic wave detection surface of the electromagnetic wave detector. The arithmetic processor determines the presence or absence of foreign matter in the inspection object based on the electromagnetic wave detected by the electromagnetic wave detector.

In order to detect foreign matter mixed in an inspection object using electromagnetic waves, it is conceivable to transmit the electromagnetic wave through the inspection object and detect the transmitted electromagnetic wave with an electromagnetic wave detector to determine the presence or absence of foreign matter. .. However, the electromagnetic waves detected by the electromagnetic wave detector do not change significantly even when a foreign substance such as a minute plastic piece is mixed in the inspection object as compared with the case where the foreign substance is not mixed, and the foreign substance is not mixed. It was difficult to detect contamination with high accuracy.

As a result of diligent research by the present inventor, it was found that the presence of foreign matter is emphasized by arranging a periodic structural plate between the inspection object and the electromagnetic wave detection surface of the electromagnetic wave detector. That is, if a foreign substance is mixed in the inspection object, the electromagnetic wave transmitted through the inspection object is slightly disturbed. When the electromagnetic wave in which the turbulence is generated is incident on the periodic structure plate arranged between the inspection object and the electromagnetic wave detection surface, the electromagnetic wave interferes and the presence of foreign matter is emphasized. According to the present invention configured as described above, a periodic structure plate that transmits the electromagnetic wave transmitted through the inspection object and induces the interference of the electromagnetic wave is arranged between the inspection object and the electromagnetic wave detector. Therefore, the presence of foreign matter mixed in the inspection object can be emphasized, and the foreign matter can be detected with high accuracy.

In the present invention, preferably, the periodic structure plate is formed of a thin plate in which a large number of openings are formed at a constant pitch.
According to the present invention configured in this way, since the periodic structure plate is formed by thin plates in which a large number of openings are formed at a constant pitch, the electromagnetic waves diffracted through the openings are effective for each other. Interference can be caused, and a highly accurate periodic structure plate can be easily produced.

In the present invention, preferably, the pitch of the openings formed in the periodic structure plate has a length of 1 to 100 times the wavelength of the electromagnetic wave emitted by the electromagnetic wave oscillator.
According to the present invention configured in this way, since the opening pitch of the periodic structure plate is formed to be 1 to 100 times the wavelength of the electromagnetic wave, it is possible to effectively cause the interference of the electromagnetic wave, and the foreign matter can be introduced. The existence can be emphasized.

In the present invention, preferably, the periodic structure plate is made of a conductive material.
According to the present invention configured in this way, since the periodic structure plate is made of a conductive material, the transmittance of electromagnetic waves is lowered on the non-opening portion of the periodic structure plate, so that the opening of the periodic structure plate is increased. Interference can be effectively induced by increasing the ratio of the transmission intensity of electromagnetic waves between the portion and the non-open portion.

In the present invention, preferably, the distance between the periodic structure plate and the electromagnetic wave detection surface of the electromagnetic wave detector is four times or less the wavelength of the electromagnetic wave emitted by the electromagnetic wave oscillator.
According to the research of the present inventor, the influence of the interference induced by the periodic structure plate starts to decrease when the distance from the periodic structure plate is about four times the wavelength of the electromagnetic wave, and the effect of arranging the periodic structure plate decreases. According to the present invention configured as described above, since the distance between the periodic structure plate and the electromagnetic wave detection surface is set to 4 times or less the wavelength of the electromagnetic wave, the presence of foreign matter is emphasized by the electromagnetic wave detector. The electromagnetic waves generated can be detected, and foreign matter can be detected with high accuracy.

In the present invention, preferably, the electromagnetic wave emitted by the electromagnetic wave oscillator has a wavelength of about 0.1 mm to about 10 mm.
In the present invention configured as described above, since the electromagnetic wave oscillator irradiates an electromagnetic wave having a wavelength of about 0.1 mm to about 10 mm, when a general food product is appropriately transmitted and the inspection target is a food product, Foreign matter can be detected effectively.

According to the foreign matter inspection device of the present invention, foreign matter having various shapes can be detected by using electromagnetic waves.

It is a side view of the foreign matter inspection apparatus by embodiment of this invention. It is a top view which shows the periodic structure plate in the foreign matter inspection apparatus by embodiment of this invention partially enlarged. It is a figure which looked at the electric field intensity distribution when the electromagnetic wave was irradiated in the foreign matter inspection apparatus by embodiment seen from the side. As a comparative example, it is a figure which looked at the electric field intensity distribution from the side when the periodic structure plate was not arranged. In the foreign matter inspection device according to an embodiment of the present invention, showing an electric field intensity distribution in the L ₁ section of FIG. In the foreign matter inspection device according to an embodiment of the present invention, showing an electric field intensity distribution in the L ₂ cross-section of FIG. In the foreign matter inspection device according to an embodiment of the present invention, showing an electric field intensity distribution in the L ₃ the cross-section of FIG. As a comparative example, it shows an electric field intensity distribution in the L ₁ section of FIG. It is a graph which shows the relationship between the position of the electromagnetic wave detection surface, and the mean square error in the foreign matter inspection apparatus by embodiment of this invention. It is a graph which shows the relationship between the position of the electromagnetic wave detection surface, and the local square error in the foreign matter inspection apparatus by embodiment of this invention.

Next, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a side view of a foreign matter inspection device according to an embodiment of the present invention. FIG. 2 is a plan view showing the periodic structure plate in a partially enlarged manner.

As shown in FIG. 1, the foreign matter inspection device 1 of the present embodiment includes an electromagnetic wave oscillator 2 for irradiating the inspection object A with an electromagnetic wave, a tray 4 for placing the inspection object A, and an inspection object. An electromagnetic wave detector 6 in which an electromagnetic wave transmitted through A is incident, a periodic structure plate 8 arranged between the inspection object A and the electromagnetic wave detector 6, and an arithmetic processor for determining the presence or absence of foreign matter in the inspection object A. 10 and. The foreign matter inspection device 1 of the present embodiment can be applied to detect foreign matter mixed in any food or the like, and examples of the inspection target A include table salt, kataguri powder, umami seasoning, granulated sugar, and the like. Examples include powder products (crystals, granulated products) such as powdered soup, various raw materials such as dried parsley, spinach, and pasta sugar, confectionery, and frozen foods. Further, as the inspection object A, a liquid having a small amount of water, a substantially uniform shape, and little variation is preferable.

The electromagnetic wave oscillator 2 is configured to emit electromagnetic waves upward from the electromagnetic wave emitting surface 2a provided on the upper surface thereof. In the present embodiment, the electromagnetic wave oscillator 2 is configured to emit a coherent (interfering property) subterahertz electromagnetic wave having a wavelength λ = about 3 mm and a frequency f = about 0.1 THz. Further, in the present embodiment, the electromagnetic wave oscillator 2 is configured to emit an electromagnetic wave as a continuous wave. As the electromagnetic wave oscillator 2, an oscillator that emits an electromagnetic wave having an arbitrary wavelength can be used, but an oscillator that emits an electromagnetic wave having a wavelength of about 0.1 mm to about 10 mm is preferably used. The wavelength of the electromagnetic wave to be used is preferably set according to the permeability to the inspection object A, the thickness of the inspection object A, and the size of the foreign matter to be detected. As an example, "IMPATT Diode 100 GHz" manufactured by TERASEENSE using an impat diode can be used for the oscillator that emits the sub-terahertz electromagnetic wave. Further, the electromagnetic wave oscillator 2 is preferably configured so as to be able to emit a substantially uniform sub-terahertz electromagnetic wave with sufficient strength over the entire range in which the inspection object A is arranged.

The tray 4 is a flat plate-shaped member on which the inspection object A is placed, and is arranged above the electromagnetic wave oscillator 2 and parallel to the electromagnetic wave emitting surface 2a. _{In the present embodiment, the distance D 1} between the upper surface of the tray 4 and the electromagnetic wave emitting surface 2a is set to about 3 mm, which corresponds to the wavelength of the electromagnetic wave applied to the inspection object A. The tray 4 is preferably made of a material such as polyethylene that easily transmits the electromagnetic waves emitted from the electromagnetic wave oscillator 2, and is made of a homogeneous material and has a uniform thickness so as not to disturb the transmitted electromagnetic waves. It is preferable that it is configured in. _{Further, it is advantageous that the distance D 1} between the upper surface of the tray 4 and the electromagnetic wave emitting surface 2a is far, because it is easy to irradiate the entire inspection object A with the electromagnetic wave with a uniform intensity. The strength is reduced. _{Therefore, the distance D 1} between the upper surface of the tray 4 and the electromagnetic wave emitting surface 2a is such that an electromagnetic wave intensity of 1 μW or more, preferably 15 μW or more can be obtained over the entire range on which the inspection object A is placed. It is better to set it to. If the inspection object A can be arranged above the electromagnetic wave oscillator 2 without using the tray 4, the tray 4 can be omitted. Further, the present invention can be configured so that a belt conveyor (not shown) is provided in place of the tray 4 to continuously transfer the inspection object A.

The electromagnetic wave detector 6 is arranged above the inspection object A placed on the tray 4 and is configured to detect the electromagnetic wave transmitted through the inspection object A. Specifically, the electromagnetic wave detector 6 is arranged so that the electromagnetic wave is incident on the electromagnetic wave detection surface 6a provided on the lower surface thereof, and the electromagnetic wave detection surface 6a is the electromagnetic wave emission surface 2a of the electromagnetic wave oscillator 2 and the tray. It is arranged parallel to 4. Further, a large number of detection elements (not shown) are arranged on the electromagnetic wave detection surface 6a of the electromagnetic wave detector 6, and the electromagnetic wave detector 6 can detect the intensity distribution of the electromagnetic wave incident on the electromagnetic wave detection surface 6a. It is configured as an area sensor. _{Further, in the present embodiment, the distance D 2} between the upper surface of the tray 4 and the electromagnetic wave detection surface 6a is set to about 6 mm, which corresponds to about twice the wavelength of the electromagnetic wave irradiated to the inspection object A. There is. As an example, a terahertz detector using a Schottky barrier diode can be used as a detector for detecting electromagnetic waves. _{Further, the distance D 2} between the upper surface of the tray 4 and the electromagnetic wave detection surface 6a is preferably set to about 1 to about 8 times the wavelength of the electromagnetic wave.

The periodic structure plate 8 is arranged between the inspection object A and the electromagnetic wave detector 6 so as to transmit the electromagnetic wave transmitted through the inspection object A and induce the interference of the electromagnetic wave. Further, the periodic structure plate 8 is arranged in parallel with the electromagnetic wave detection surface 6a of the electromagnetic wave detector 6 and the tray 4. _{Further, in the present embodiment, the distance D 3} between the upper surface of the tray 4 and the lower surface of the periodic structure plate 8 is set to about 3 mm, which corresponds to about one wavelength of the electromagnetic wave radiated to the inspection object A. There is. _{Further, the distance D 4} between the lower surface of the periodic structure plate 8 and the electromagnetic wave detection surface 6a is also set to about 3 mm, which corresponds to about one wavelength of the electromagnetic wave. _{The distance D 3} between the upper surface of the tray 4 and the lower surface of the periodic structure plate 8 is set to be about 1 to 4 times the wavelength of the electromagnetic wave so that the inspection object A and the periodic structure plate 8 do not come into contact with each other. _{However, the distance D 4} between the lower surface of the periodic structure plate 8 and the electromagnetic wave detection surface 6a is preferably set to about 1 to about 4 times the wavelength of the electromagnetic wave.

In the present embodiment, the electromagnetic wave oscillator 2 is arranged on the lower side of the tray 4, and the periodic structure plate 8 and the electromagnetic wave detector 6 are arranged on the upper side of the tray 4. On the other hand, as a modification, an electromagnetic wave oscillator 2 is arranged above the tray 4 so as to emit an electromagnetic wave downward, a periodic structure plate 8 is arranged below the tray 4, and further below the tray 4. An electromagnetic wave detector 6 can also be arranged. In this case, the periodic structure plate 8 and the electromagnetic wave detector 6 can be arranged close to the lower surface of the tray 4, and the distance from the lower surface of the tray 4 is not more than 1 times the wavelength of the electromagnetic wave. A periodic structure plate 8 and / or an electromagnetic wave detector 6 can also be arranged.

As shown in FIG. 2, in the present embodiment, as the periodic structure plate 8, a thin metal plate in which a large number of openings are formed at a constant pitch is used. Specifically, the periodic structure plate 8 is composed of a thin plate member having a thickness of about 0.1 mm and a large number of square openings 8a having a side of about 5 mm formed at a constant pitch P = about 6 mm. In the present embodiment, the periodic structure plate 8 is made of nickel, and the pitch P of the opening 8a is about twice the wavelength of the electromagnetic wave. Preferably, the pitch P of the opening 8a formed in the periodic structure plate 8 is set to have a length of 1 to 100 times the wavelength of the electromagnetic wave emitted by the electromagnetic wave oscillator 2.

Further, the periodic structure plate 8 can be made of a material other than metal, but preferably, the periodic structure plate 8 is made of a conductive metal, particularly preferably nickel, gold or the like. Further, the shape of the opening provided in the thin plate can be any shape such as a rectangle or a circle as well as a square. Alternatively, the periodic structure plate 8 can be formed of a plain weave net-like member formed by knitting a wire such as metal, instead of forming a large number of openings in the thin plate. Further, in the present embodiment, the periodic structure plate 8 has a periodic structure in two directions in the vertical direction and the horizontal direction and is formed in a grid pattern, but the periodic structure may be in one direction. For example, a striped periodic structure plate can be formed by forming a large number of elongated slits at equal intervals in the metal plate. Further, when the present invention is configured to irradiate electromagnetic waves from above the inspection object A, the periodic structure plate 8 is mounted on the tray 4 for placing the inspection object A or the belt of the belt conveyor (shown in the figure). It can also be formed integrally with.

By arranging the periodic structure plate 8 between the inspection object A and the electromagnetic wave detector 6, the electromagnetic wave transmitted through the inspection object A is incident on the periodic structure plate 8. The electromagnetic waves incident on the periodic structure plate 8 pass through each of the openings 8a and are diffracted, and the diffracted electromagnetic waves cause interference with each other. That is, the ratio of the transmission intensity of the electromagnetic wave between the portion of each opening 8a on the periodic structure plate 8 and the non-opening portion becomes high, and the interference of the electromagnetic wave is effectively induced. The electromagnetic wave in which this interference is induced is incident on the electromagnetic wave detection surface 6a of the electromagnetic wave detector 6. Further, when a foreign substance is mixed in the inspection object A, the foreign substance causes a slight disturbance in the electromagnetic wave transmitted through the inspection object A. In this way, when an electromagnetic wave including turbulence is incident on the periodic structure plate 8, the influence of the turbulence caused by the foreign matter is emphasized, and the turbulence caused by the foreign matter is easily detected by the electromagnetic wave detector 6.

As shown in FIG. 1, the arithmetic processor 10 is an arithmetic unit configured to determine the presence or absence of foreign matter in the inspection object A based on the electromagnetic waves detected by the electromagnetic wave detector 6. Specifically, the arithmetic processor 10 is composed of a microprocessor that processes a detection signal input from the electromagnetic wave detector 6, a memory, an interface circuit, software that operates them, and the like. When the arithmetic processor 10 processes the signal input from the electromagnetic wave detector 6 and determines that foreign matter is mixed in the inspection object A, it displays that foreign matter is mixed and /. Alternatively, a warning sound is configured to notify that a foreign substance is mixed.

Specifically, the arithmetic processor 10 stores the intensity of the electromagnetic wave when the electromagnetic wave transmitted through the inspection object A containing no foreign matter is incident on the electromagnetic wave detector 6, and the stored electromagnetic wave is stored. The presence or absence of foreign matter is determined based on the difference between the intensity of the electromagnetic wave and the intensity of the electromagnetic wave transmitted through the inspection object A to be inspected. It is preferable that the intensity of the electromagnetic wave transmitted through the inspection object A containing no foreign matter is measured a plurality of times for the same type of inspection object A, and the average value thereof is stored in the arithmetic processor 10. The details of determining the presence or absence of foreign matter will be described later.

Next, the operation of the foreign matter inspection device 1 according to the embodiment of the present invention will be described.
First, the inspection object A to be inspected for foreign matter is placed on the tray 4 to prepare for the inspection. The inspection object A is preferably arranged substantially uniformly on the tray 4, and the thickness of the inspection object A to be arranged is preferably set to a preset default value. Next, after setting the tray 4 at a predetermined position above the electromagnetic wave oscillator 2, the electromagnetic wave oscillator 2 is operated to irradiate the inspection object A with electromagnetic waves. The electromagnetic wave transmitted through the inspection object A passes through the periodic structure plate 8 and is induced to interfere with the periodic structure plate 8 and is detected by the electromagnetic wave detector 6 arranged above the periodic structure plate 8.

_{The arithmetic processor 10 calculates the detection intensity I 1} of the electromagnetic wave detected by each detection element (not shown) on the electromagnetic wave detection surface 6a based on the detection signal input from the electromagnetic wave detector 6. On the other hand, the arithmetic processor 10 has a reference intensity of electromagnetic waves detected by each detection element (not shown) based on a detection signal detected when the inspection object A containing no foreign matter is irradiated with electromagnetic waves. I _R is remembered. The arithmetic processing device 10, the detection intensity I _1, and the mean square error by the following equation (1) based on the reference intensity _{I R (NMSE: Normalized Mean Square} Error) is calculated, and the mean square error is the predetermined threshold value When _{it is larger than E th1,} it is determined that foreign matter is mixed in the inspection object A.

That is, the denominator of Equation (1) is the square of the reference intensity I _R of each pixel of the electromagnetic wave detector 6 that constitute the area sensor (the detecting elements) is detected, is calculated by summing all the pixels. Also, the numerator of Equation (1) is the difference between the detected intensity I ₁ and the reference intensity I _R detected in the same pixel squared is calculated by summing all the pixels that value. In the present embodiment, in the mathematical formula (1), the mean square error is calculated based on the strength of all pixels, but the mean square error is calculated based on the strength of some pixels or one pixel. The present invention can also be configured to compare the value with a predetermined threshold value E _th2 to determine whether or not foreign matter is mixed in the inspection object A. Alternatively, one or a plurality of pixels having a large detection intensity I ₁ value are selected, the mean square error is calculated for the pixels, and the value _{is compared with a predetermined threshold value E th3} to allow foreign matter to enter the inspection object A. The present invention can also be configured to determine whether or not this is done.

Next, with reference to FIGS. 3 to 10, the effect of the foreign matter inspection apparatus according to the embodiment of the present invention will be described based on the simulation result by electromagnetic field analysis.
FIG. 3 is a side view of the electric field intensity distribution when an electromagnetic wave is irradiated in the foreign matter inspection device according to the embodiment of the present invention. FIG. 4 is a side view of the electric field intensity distribution when the periodic structure plate is not arranged as a comparative example.

FIG. 3 is a simulation result of the electric field intensity distribution when the electromagnetic wave is irradiated in the foreign matter inspection device 1 of the present embodiment as viewed from the side surface. The column (a) of FIG. 3 shows the simulation result when there is no foreign matter in the inspection object A, and the column (b) shows the simulation result when there is a foreign matter. Note that FIGS. 3A and 3B show simulation results when the electromagnetic wave oscillator 2 emits a continuous wave of 100 GHz from a square electromagnetic wave emitting surface 2a having a side of 40 mm. Further, the simulation was performed assuming that the electromagnetic wave oscillator 2 emits an electromagnetic wave having a Gaussian distribution having a width of 20 mm.

Further, in FIG. 3B, the foreign matter C is _{located 3 mm above the electromagnetic wave emitting surface 2a (corresponding to the distance D 1} = 3 mm to the tray 4), and the periodic structure plate 8 is 3 mm above the foreign matter (from the tray 4). The calculation was performed assuming that they are arranged at the distance D _{3 = 3 mm.} Further, as shown in FIG. 2, the periodic structure plate 8 is calculated assuming that a square opening having a side of 5 mm is formed as a metal plate having a pitch of 6 mm and a thickness of 0.1 mm. .. Further, the foreign matter C is a square having a side of 1 mm, and is calculated assuming a polystyrene resin (PS) as having a refractive index of 1.5 and a conductivity of 0.0199 (the space where electromagnetic waves are emitted has a refractive index. 1.0, conductivity 0). On the other hand, with respect to FIG. 3A, the calculation was performed under the same conditions as in FIG. 3B, except that the foreign matter C was not arranged.

Next, FIG. 4 shows, as a comparative example, a simulation result of the electric field intensity distribution when an electromagnetic wave is emitted into a space where the periodic structure plate 8 is not arranged. The calculation conditions are the same as those in FIG. 3 (b) except that the periodic structure plate 8 is not arranged.

Comparing the column (b) of FIG. 3 with the electric field intensity distribution of FIG. 4, it can be seen that when the periodic structure plate 8 is arranged in the electric field, the electric field intensity distribution becomes complicated due to the interference of electromagnetic waves. Further, comparing the electric field intensity distributions in columns (a) and (b) of FIG. 3, it can be seen that the change in the electric field due to the arrangement of the foreign matter C extends to the upper part of the periodic structure plate 8. On the other hand, in the electric field intensity distribution of FIG. 4 which is a comparative example, it can be seen that the disturbance of the electric field intensity distribution due to the arrangement of the foreign matter C remains in the vicinity of the foreign matter C and does not extend to the space above. It can be seen that by arranging the periodic structure plate 8 in this way, the disturbance of the electric field due to the presence of the foreign matter C is enhanced.

Next, the electric field intensity distribution detected at each position above the periodic structure plate 8 will be described with reference to FIGS. 5 to 8.
FIG. 5 is a diagram showing an electric field intensity distribution in _{the L 1} cross section of FIG. 3 in the foreign matter inspection device according to the embodiment of the present invention. 6, the foreign substance inspection apparatus according to an embodiment of the present invention, showing an electric field intensity distribution in the L ₂ cross-section of FIG. 7, the foreign substance inspection apparatus according to an embodiment of the present invention, showing an electric field intensity distribution in the L ₃ the cross-section of FIG. FIG. 8 is a diagram showing an electric field intensity distribution in _{the L 1} cross section of FIG. 4 as a comparative example.

The column (a) of FIG. 5 is a diagram _{showing the electric field intensity distribution in the L 1} cross section of the column (a) of FIG. 3, and the column (b) of FIG. 5 is the L ₁ cross section of the column (b) of FIG. It is a figure which shows the electric field intensity distribution in. _{The L 1} cross section of FIG. 3 corresponds to the position where the electromagnetic wave detection surface 6a of the electromagnetic wave detector 6 is arranged in the foreign matter inspection device 1 of the present embodiment, and is 6 mm above the tray 4 (the electromagnetic wave emission surface 2a). It is located 9 mm above. As shown in FIG. 5, the electric field intensity distribution in the column (b) showing the case where the foreign matter C is present has a higher electric field intensity near the center than the distribution in the column (a) where the foreign matter C is not present. , The area where the electric field strength is high is wide. Therefore, a reference intensity I _R of an electric field intensity of each point in the field shown in row (a) of FIG. 5, if the detection intensity I ₁ of an electric field intensity of each point in the electric field of the row (b), both the difference It becomes possible to detect the presence of the foreign matter C based on the above.

Next, FIG. 6 _{shows the electric field intensity distribution in the L 2} cross section of FIG. 3, the column (a) is the L ₂ cross section of the column (a) of FIG. 3, and the column (b) is the column (b) of FIG. The electric field intensity distribution in the L _{2 cross section of column) is shown. The L 2} cross section of FIG. 3 corresponds to a position 12 mm above the tray 4 (15 mm above the electromagnetic wave emitting surface 2a) in the foreign matter inspection device 1 of the present embodiment. As shown in FIG. 6, in the electric field intensity distribution in the column (b) showing the case where the foreign matter C is present, the point that the electric field intensity existing near the center is higher than the distribution in the column (a) where the foreign matter C is not present is It is slightly larger. Therefore, there is a possibility that the presence of the foreign matter C can be detected based on the difference between the electric field strength shown in the column (a) and the electric field strength in the column (b) of FIG.

Further, FIG. 7 _{shows the electric field intensity distribution in the L 3} cross section of FIG. 3, the column (a) is the L ₃ cross section of the column (a) of FIG. 3, and the column (b) is the column (b) of FIG. show respectively the electric field intensity distribution in the L ₃ cross-section of the column. _{The L 3} cross section of FIG. 3 corresponds to a position 18 mm above the tray 4 (21 mm above the electromagnetic wave emitting surface 2a) in the foreign matter inspection device 1 of the present embodiment. As shown in FIG. 7, the electric field intensity distribution in the shown row (b) if the foreign object C is present, no foreign matter C is (a) column distribution is almost the same, the electric field intensity distribution in the L ₃ section Based on this, it is difficult to detect the presence of foreign matter C.

FIG. 8 shows, as a comparative example, the electric field intensity distribution when the periodic structure plate 8 is not arranged. (B) column of Figure 8 shows an electric field intensity distribution in the L ₁ section of FIG. 4, the electric field strength in the L ₁ a cross section in the case (a) column in the simulation of FIG. 4, the foreign matter C is not disposed It shows the distribution. _{The L 1} cross section of FIG. 4 is the same as the arrangement position of the electromagnetic wave detector 6 in the foreign matter inspection device 1 of the present embodiment, and is located 6 mm above the tray 4 (9 mm above the electromagnetic wave emitting surface 2a). The electric field intensity distributions in columns (a) and (b) of FIG. 8 are almost the same, and it is difficult to detect the foreign matter C based on this electric field intensity distribution. The electric field intensity distribution when the periodic structure plate 8 is not arranged is the case where the foreign matter C is present and the case where the foreign matter C is not present even at the positions 12 mm and 18 mm above the tray 4 corresponding to FIGS. 6 and 7, respectively. It became almost the same, and it was difficult to detect the foreign matter C based on these.

Next, the relationship between the detection position of the electric field intensity distribution and the mean square error will be described with reference to FIGS. 9 and 10.
FIG. 9 is a graph showing the relationship between the position of the electromagnetic wave detection surface 6a and the mean square error calculated based on the detected electric field strength of all the pixels in the simulations shown in FIGS. 5 to 7. FIG. 10 is a graph showing the relationship between the position of the electromagnetic wave detection surface 6a and the maximum value of the local square error of the detected electric field strength in the simulations shown in FIGS. 5 to 7.

FIG. 9 is a graph in which the horizontal axis is the distance from the tray 4 and the vertical axis is the mean square error NMSE calculated by the mathematical formula (1). In FIG. 9, 6 mm on the horizontal axis _{corresponds to the L 1} cross section in FIG. 3, 12 mm corresponds to the L ₂ cross section, and 18 _{mm corresponds to the L 3} cross section, respectively. As shown in FIG. 9, the value of the mean square error becomes smaller as the position of the electromagnetic wave detection surface 6a moves away from the tray 4. That is, at a position away from the tray 4, the difference between _{the reference intensity I R measured for the inspection object A containing no foreign matter and the detection intensity I 1} measured for the inspection object A containing foreign matter. Becomes smaller, making it difficult to detect foreign matter.

From the results shown in FIG. 9, it can be read that foreign matter can be detected with sufficient accuracy if the distance from the tray 4 is about 15 mm or less, and this position is about the wavelength of the electromagnetic wave at the distance from the tray 4. The distance from the periodic structure plate 8 is 5 times, which corresponds to about 4 times the wavelength of the electromagnetic wave. Further, the closer the distance from the tray 4, the larger the value of the mean square error, and it is possible to detect foreign matter with high accuracy. However, since the inspection object A itself is thick, the electromagnetic wave detection surface 6a is trayed. There is a limit to the proximity to 4 (the lower surface of the inspection object A). Therefore, the distance from the tray 4 (the lower surface of the inspection object A) to the electromagnetic wave detection surface 6a is about twice or more the wavelength of the electromagnetic wave, and the distance from the periodic structure plate 8 to the electromagnetic wave detection surface 6a is about 1 of the wavelength of the electromagnetic wave. It is preferable to set it to twice or more. On the other hand, when the foreign matter inspection device 1 is configured so that the periodic structure plate 8 and the electromagnetic wave detector 6 are arranged under the tray or conveyor on which the inspection object A is placed, the wavelength of the electromagnetic wave is once. The periodic structure plate 8 and the electromagnetic wave detector 6 can be arranged at the following close distances.

FIG. 10 is a graph in which the horizontal axis is the distance from the tray 4 and the vertical axis is the local NMSE. In FIG. 10, 6 mm on the horizontal axis _{corresponds to the L 1} cross section in FIG. 3, 12 mm corresponds to the L ₂ cross section, and 18 _{mm corresponds to the L 3} cross section, respectively. The local NMSE maximum value in FIG. 10 is a square error for each pixel with respect to the detection intensity measured for the inspection object A containing foreign matter and the reference intensity measured for the inspection object A containing no foreign matter. Is the maximum value calculated for. That is, as shown in the following mathematical formula (2), the local NMSE maximum value is the square of the difference between the _{detection intensity I 1 at a certain point (pixel) and the reference intensity I R1} at that point (pixel). It is the maximum value among the values divided by the square of _R1.

As shown in FIG. 10, the local NMSE maximum value becomes smaller as the position of the electromagnetic wave detection surface 6a is separated from the tray 4. That is, at a position away from the tray 4, the detection intensity I _{1 measured for the inspection object A in which foreign matter is mixed and the reference strength I R1} measured for the inspection object A in which foreign matter is not mixed. Since the difference becomes small and the maximum value of the square error becomes small, it becomes difficult to detect foreign matter.

From the results shown in FIG. 10, it can be read that foreign matter can be detected with sufficient accuracy if the distance from the tray 4 is about 15 mm or less, and this position is the distance from the tray 4 and the wavelength of the electromagnetic wave. The distance from the periodic structure plate 8 is about 5 times, which corresponds to about 4 times the wavelength of the electromagnetic wave. Further, as described above, the distance from the tray 4 (the lower surface of the inspection object A) to the electromagnetic wave detection surface 6a is about twice or more the wavelength of the electromagnetic wave, and the distance from the periodic structure plate 8 to the electromagnetic wave detection surface 6a is the electromagnetic wave. It is considered preferable to set the wavelength to about 1 times or more. When the periodic structure plate 8 and the electromagnetic wave detector 6 are arranged under the tray or the conveyor, the periodic structure plate 8 and the electromagnetic wave detector 6 are arranged at a close distance of 1 times or less the wavelength of the electromagnetic wave. be able to.

According to the foreign matter inspection device 1 of the embodiment of the present invention, the periodic structure plate 8 that transmits the electromagnetic wave transmitted through the inspection object A and induces the interference of the electromagnetic wave between the inspection object A and the electromagnetic wave detector 6. Is arranged, the presence of foreign matter mixed in the inspection object A can be emphasized, and the foreign matter can be detected with high accuracy.

Further, according to the foreign matter inspection device 1 of the present embodiment, since the periodic structure plate 8 is formed by a thin plate in which a large number of openings 8a are formed at a constant pitch P (FIG. 2), electromagnetic wave interference is effective. And the periodic structure plate 8 with high accuracy can be easily produced.

Further, according to the foreign matter inspection device 1 of the present embodiment, since the pitch P of the opening 8a of the periodic structure plate 8 is formed to be about twice the wavelength of the electromagnetic wave, the interference of the electromagnetic wave can be effectively caused. , The presence of foreign matter can be emphasized.

Further, according to the foreign matter inspection device 1 of the present embodiment, since the periodic structure plate 8 is made of nickel which is a conductive material, the transmittance of electromagnetic waves on the periodic structure plate 8 becomes low, so that interference is effective. Can be triggered.

Further, according to the foreign matter inspection device 1 of the present embodiment, since the distance between the periodic structure plate 8 and the electromagnetic wave detection surface 6a is set to one wavelength of the electromagnetic wave, the presence of foreign matter is present by the electromagnetic wave detector 6. Electromagnetic waves with emphasized can be detected, and foreign matter can be detected with high accuracy.

Further, according to the foreign matter inspection device 1 of the present embodiment, since the electromagnetic wave oscillator 2 irradiates an electromagnetic wave having a wavelength of about 3 mm, when a general food product is appropriately transmitted and the inspection target A is a food product, Foreign matter can be detected effectively.

Although the preferred embodiment of the present invention has been described above, various modifications can be made to the above-described embodiment. In particular, in the above-described embodiment, the electromagnetic wave is two-dimensionally emitted from the electromagnetic wave emitting surface of the electromagnetic wave oscillator, and the electromagnetic wave transmitted through the inspection object A placed on the tray functions as an area sensor. It was detected by the detector. On the other hand, as a modification, an electromagnetic wave oscillator is configured so that electromagnetic waves are emitted linearly, and an electromagnetic wave detector that functions as a line sensor is arranged so as to face the electromagnetic wave oscillator and the electromagnetic wave detector. The present invention can also be configured such that the inspection object A mounted on a belt conveyor (not shown) passes between the spaces. According to this modification, it is possible to continuously inspect the presence or absence of foreign matter while transferring a large amount of the inspection object A by the belt conveyor.

1 Foreign matter inspection device 2 Electromagnetic wave oscillator 2a Electromagnetic wave emission surface 4 Tray 6 Electromagnetic wave detector 6a Electromagnetic wave detection surface 8 Periodic structure plate 8a Opening 10 Arithmetic processor

Claims (6)

A foreign matter inspection device that uses electromagnetic waves to detect foreign matter mixed in the inspection object.
An electromagnetic wave oscillator for irradiating an object to be inspected with electromagnetic waves,
An electromagnetic wave detector equipped with an electromagnetic wave detection surface that is irradiated from this electromagnetic wave oscillator and transmits electromagnetic waves that have passed through the inspection object.
A periodic structure plate that is placed between the inspection object and the electromagnetic wave detector to transmit the electromagnetic waves that have passed through the inspection object and induce the interference of the electromagnetic waves.
An arithmetic processor that determines the presence or absence of foreign matter in the inspection object based on the electromagnetic waves detected by the electromagnetic wave detector.
A foreign matter inspection device characterized by having. The foreign matter inspection device according to claim 1, wherein the periodic structure plate is formed of a thin plate in which a large number of openings are formed at a constant pitch. The foreign matter inspection device according to claim 2, wherein the pitch of the openings formed in the periodic structure plate has a length of 1 to 100 times the wavelength of the electromagnetic wave emitted by the electromagnetic wave oscillator. The foreign matter inspection device according to any one of claims 1 to 3, wherein the periodic structure plate is made of a conductive material. The method according to any one of claims 1 to 4, wherein the distance between the periodic structure plate and the electromagnetic wave detection surface of the electromagnetic wave detector is four times or less the wavelength of the electromagnetic wave emitted by the electromagnetic wave oscillator. Foreign matter inspection device. The foreign matter inspection device according to any one of claims 1 to 5, wherein the electromagnetic wave emitted by the electromagnetic wave oscillator has a wavelength of about 0.1 mm to about 10 mm.