JP2020038221A - Foreign matter detection device and foreign matter detection method - Google Patents

Abstract

To provide a foreign matter detection device capable of accurately detecting foreign matter according to the type of an object to be inspected or foreign matter.SOLUTION: A foreign matter detection device 20 has: a plurality of photon detection type X-ray sensors 31to 31that outputs a pulse signal of a peak value corresponding to the energy of a photon each time an X-ray photon is input; and transmission image data generation means 40 that determines whether the peak value of each pulse signal falls in any of a plurality of areas obtained by dividing a predetermined range in advance, and using data generated from a result of accumulating the number of pulse signal inputs for each area, and generates a plurality of transmission image data that is a combination of regions optimal for detection of foreign matter with respect to an object to be inspected W.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for detecting foreign matter in an inspection object using X-rays.

  In factories that manufacture foods and the like, a foreign substance detection device checks whether or not foreign substances such as metal and plastic are mixed in the product.

  Conventionally, as this foreign matter detecting device, a sensor (a plurality of X-ray sensors) emits X-rays into a passage of an inspection object conveyed in a predetermined direction by a conveyor or the like and transmits the X-rays through the inspection object. Is detected by a line sensor integrated in a direction perpendicular to the passing direction), and the detection signal is locally changed due to the presence of a foreign substance.

  However, as described above, in the method of detecting the intensity of X-rays transmitted through the inspection object using a sensor, foreign substances are accurately detected due to differences in transmittance due to articles whose thickness or material changes in the X-ray transmission direction. In some cases, it was not possible.

  As a technique for solving this, for example, Patent Document 1 performs a process such as subtraction (difference processing of image data) on two pieces of transmitted X-ray data obtained by changing the energy of X-rays transmitted through an inspection object. Thus, it has been proposed to improve the detection accuracy of foreign matter.

JP-A-10-318943

  However, in the above-mentioned Patent Document 1, X-rays output from a single X-ray source and transmitted through the inspection object are arranged side by side in the transport direction of the inspection object, and two detections having different energy sensitivities to the X-ray are performed. Two transmission X-ray data are obtained by detecting with a detector (line sensor).

  For this reason, the path through which the X-rays incident on one detector necessarily pass through the object to be inspected and the path through which the X-rays incident on the other detector pass through the object to be inspected do not coincide with each other. Due to the influence, it is conceivable that foreign substances in the inspection object cannot be correctly recognized. It is also conceivable that accurate foreign object detection cannot be performed due to the characteristic difference between the sensor elements of the two detectors.

  In addition, Patent Document 1 discloses that two X-ray sources having different X-ray energies are used. In this case, an X-ray source and two corresponding X-ray sources are arranged so that the two X-rays do not interfere with each other. The distance between the detectors (line sensors) must be widened, which increases the size of the entire apparatus, changes the posture of the test object being transported during that time, and uses two detectors as described above. Therefore, there is a possibility that the detection accuracy of the foreign matter may be reduced.

As a method of solving this, attention is paid to the fact that the energy of X-ray photons generated from an X-ray tube or the like varies, and a pulse signal of a peak value corresponding to the energy is generated each time an X-ray photon is incident. The pulse signal output from the X-ray sensor within a certain time is classified into a plurality of regions according to the difference of the peak value, and the number of pulse signals for each region is accumulated. By doing so, it is conceivable to obtain transmission image data when the X-ray energies are different. According to this method, a plurality of X-ray sensors may be arranged in a line in a direction intersecting with the passing direction of the inspection object, and the above problem can be solved.

  However, in the related art as disclosed in Patent Document 1, since two detectors having different energy sensitivities are used, the energy regions of the two transmission X-ray data used for the subtraction processing are necessarily fixed.

  The present invention solves the above-described problems, and performs subtraction processing by creating a plurality of transmission image data in an optimal energy region according to the type of an inspection object or a foreign substance while using a photon detection type X-ray sensor. Therefore, it is an object of the present invention to provide a foreign substance detection device and a foreign substance detection method capable of performing foreign substance detection with high accuracy.

In order to achieve the above object, a foreign matter detection device according to claim 1 of the present invention is provided.
An X-ray generator (22) that emits X-rays into a passage through which the inspection object passes;
At a position for receiving X-rays emitted from the X-ray generator to the passage and transmitted through the inspection object, the X-ray generation units are arranged so as to be arranged in a direction intersecting with the passing direction of the inspection object, and receive X-rays, respectively. A plurality of X-ray sensors (311-31N) for converting into electric signals;
While the inspection object is passing between the X-ray generating unit and the plurality of X-ray sensors, a signal output from each of the plurality of X-ray sensors is divided for a predetermined period to perform predetermined signal processing. A two-dimensional position information determined by a passing direction of the inspection object and a direction in which the X-ray sensors are arranged, and transmission image data generating means for generating transmission image data of the inspection object based on a signal processing result for each position; (40)
A foreign matter detection device having a determination means (50) for determining the presence or absence of a foreign matter in the inspection object based on the transmission image data generated by the transmission image data generation means;
The X-ray sensor is a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the photon every time a photon of the X-ray is input,
The transmission image data generating means,
For each of the X-ray sensors, it is determined whether the peak value of the pulse signal output from the X-ray sensor within the predetermined period falls into any of a plurality of regions in which the predetermined range is divided in advance. Is configured to accumulate the number of input pulse signals for each of the regions, and to generate a plurality of transmission image data that is a combination of regions optimal for detecting foreign matter with respect to the inspection object using the accumulation result for each of the regions. And
The determining means includes:
By performing predetermined image processing including subtraction processing on a plurality of transmission image data obtained by the transmission image data generating means, it is configured to determine the presence or absence of foreign matter in the inspection object. Features.

According to a second aspect of the present invention, there is provided a foreign matter detection device according to the first aspect.
The number of regions into which a predetermined range is previously divided into a plurality of regions is three or more.

According to a third aspect of the present invention, there is provided a foreign matter detection device according to the first or second aspect,
The transmission image data generation unit is configured to generate transmission image data for each of the plurality of areas divided in advance in the predetermined range, and to find a combination of transmission image data that is optimal for detecting a foreign substance with respect to the inspection object. It is characterized by having been done.

  According to a fourth aspect of the present invention, in the foreign object detection device according to the third aspect, the transmission image data generating unit is configured to transmit the transmission image data for each area in which the predetermined range is divided into a plurality of areas in advance. Is generated, and a part of the plurality of generated transmission image data is combined to create new transmission image data.

  According to a fifth aspect of the present invention, there is provided a foreign matter detection apparatus according to the first or second aspect, wherein the transmission image data generating means is configured to transmit the transmission image data optimal for the foreign matter detection with respect to the inspection object. When the combination of the combinations is known, only the transmission image data for the region according to the combination is generated.

  According to a sixth aspect of the present invention, in the foreign object detection device according to the fifth aspect, the transmission image data generating means adds a cumulative number of area identification signals of a plurality of areas to generate a new transmission image. It is characterized in that image data is created.

Also, the foreign matter detection method according to claim 7 of the present invention,
Emitting X-rays from the X-ray generator (22) to a passage through which the inspection object passes;
X-rays emitted to the passage and transmitted through the inspection object are received by a plurality of X-ray sensors (311 to 31N) arranged in a direction intersecting with the passing direction of the inspection object and converted into electric signals. ,
While the inspection object is passing between the X-ray generating unit and the plurality of X-ray sensors, a signal output from each of the plurality of X-ray sensors is divided for a predetermined period to perform predetermined signal processing. Generating two-dimensional position information determined by a passing direction of the inspection object and a direction in which the X-ray sensors are arranged, and transmitting image data of the inspection object including a signal processing result for each position;
Based on the generated transmission image data, determining the presence or absence of a foreign substance in the inspection object,
Each time an X-ray photon is input, a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the photon is used as the X-ray sensor,
In the step of generating the transmission image data,
For each of the X-ray sensors, it is determined whether the peak value of the pulse signal output from the X-ray sensor within the predetermined period falls into any of a plurality of regions in which the predetermined range is divided in advance. The number of pulse signal inputs is accumulated for each region, and using the accumulation result for each region, a plurality of transmission image data that is a combination of regions optimal for detecting a foreign substance with respect to the inspection object is generated.
In the step of determining the presence or absence of foreign matter in the inspection object,
By performing predetermined image processing including subtraction processing on the plurality of generated transmission image data, the presence or absence of a foreign substance in the inspection object is determined.

  The present invention uses a photon detection type, which outputs a pulse signal of a peak value corresponding to the energy of an X-ray photon as an X-ray photon is input, to generate a plurality of energy regions that have been generated. By using the transmitted image data described above, a plurality of transmitted image data is created by combining the optimum energy regions according to the type of the inspection object and the foreign matter, and the subtraction processing is performed, so that the foreign matter can be detected with high accuracy.

FIG. 2 is a configuration diagram of an embodiment of the present invention. FIG. 4 is a diagram illustrating a relationship between a pulse signal output from an X-ray sensor and a region. It is a figure showing an example of three kinds of transmission image data obtained for every field of a peak value. FIG. 3 is a diagram illustrating a relationship between a tube current (a dose of X-rays) and a thickness of an inspection object. It is a figure showing a waveform when a pulse signal outputted from an X-ray sensor overlaps.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the overall configuration of a foreign matter detection device 20 to which the present invention is applied.

The foreign matter detection device 20 includes a transport device 21, an X-ray generation unit 22, a plurality of X-ray sensors 31 _{1 to} 31 _N , a transmission image data generation unit 40, a determination unit 50, a thickness detection unit 60, and an X-ray dose variable. It has means 70.

  The transport device 21 is for transporting the inspection object W in a predetermined direction (in the drawing, a direction orthogonal to the paper surface, hereinafter, referred to as a passing direction or a transport direction), and is generally inspected like a conveyor. A device that horizontally transports the object W at a constant speed is used, but it is not always necessary to use a transport device having a power source, and a method of sliding on a slope using the weight of the inspected object or from above. A method of dropping may be used.

  The X-ray generation unit 22 emits X-rays to a passage through which the inspection object W conveyed in a predetermined direction by the conveyance device 21 passes. In this embodiment, the X-rays that spread in the width direction of the transport path are emitted from above the inspection object W transported by the transport device 21. However, the emission direction of the X-rays is not limited to this, and the X-rays are emitted. The light may be emitted from the side of the object W to the side.

  The X-ray source of the X-ray generation unit 22 includes a hot cathode X-ray tube that accelerates electrons emitted from a superheated filament and collides with an anode target to emit X-rays, and a grid control type hot cathode X-ray. A tube is used, and additionally contains the power required to drive the X-ray tube.

  The dose of X-rays (sum of energy per unit time) emitted by the X-ray generation unit 22 depends on the number of electrons (tube current) and the tube voltage reaching the anode target from the filament of the X-ray tube per unit time. Correspondingly, the tube current depends on the filament current that determines the amount of emitted electrons, the grid voltage that controls the flow of electrons, and the like. The X-ray dose emitted by the X-ray generation unit 22 is varied by the X-ray dose varying unit 70, which will be described later.

Each of the plurality of N X-ray sensors 31 _{1 to} 31 _N receives an X-ray and converts the X-ray into an electric signal. X transmitted through
At the position where the line is received, they are arranged in a line with almost no gap in a direction intersecting (in this example, orthogonal) with the passing direction of the inspected objects W (the direction orthogonal to the paper surface).

As an actual device, the plurality of N X-ray sensors 31 _{1 to} 31 _N are each configured by a single line sensor 30 integrally connected thereto, and are arranged on the lower surface side of the transport path of the transport device 21. I have. Here, for example, if the width of the X-ray sensor is 1 mm, the gap between the X-ray sensors is so small as to be negligible with respect to the width, and the width of the transport path for transporting the inspection object W is 200 mm, approximately 200 A line sensor having an X-ray sensor may be used.

An X-ray sensor used in a conventional foreign matter detection device is a scintillator-type photosensor that generally generates visible light by incident X-rays, receives the visible light by a photosensor, and converts the light into an electric signal. The X-ray sensors 31 _{1 to} 31 _N used by the foreign matter detection device 20 receive the X-ray photons transmitted through the inspection object W each time the X-ray photons are input. It is a photon detection type (CdTe sensor) that outputs a pulse signal of a peak value corresponding to energy, and the number of pulses output per unit time indicates the density of a transmitted image.

The transmission image data generation unit 40 outputs signals output from the X-ray sensors 31 _{1 to} 31 _N while the inspection object W passes between the X-ray generation unit 22 and the X-ray sensors 31 _{1 to} 31 _N. Are subjected to predetermined signal processing by dividing the scan time by scan time, a two-dimensional position information determined by a passing direction of the inspected object W and an arrangement direction of the X-ray sensors, and an inspected object composed of a signal processing result for each position. Is generated.

As described above, the X-ray sensors 31 _{1 to} 31 _N of the photon detection type output one pulse signal of a peak value corresponding to the energy of one photon in response to the input of one photon. Since the energy of the X-ray photons emitted from the unit 22 varies even when the tube current is constant, the pulse signal P output from each X-ray sensor is accordingly adjusted as shown in FIG. The peak values H ₁ , H ₂ , H ₃ ,... Of ₁ , P ₂ , P ₃ ,.

In other words, X-rays having different energies are mixed, and the peak values H ₁ , H ₂ , H ₃ ,... Of the pulse signal output from one X-ray sensor during the scan time are previously set to the peak values. if the entire output range to determine enters one the regions R ₁ to R _M divided into a plurality M (in FIG. 2 M = 4), the cumulative number of the pulse signal input within the scanning time for each region, It is possible to generate a plurality of transmission image data having different X-ray transmission energy ranges for a portion corresponding to the scan time.

In order to generate a plurality of transmission image data having different ranges of the X-ray transmission energy, the transmission image data generation unit 40 converts the output signals of the X-ray sensors 31 _{1 to} 31 _N into A / D converters 41 ₁ respectively. into digital data sequence by to 41 _N, it is input to the peak value detection unit ₄₂ 1 through 42 _N.

Each of the peak value detecting means 42 _{1 to} 42 _N is for detecting the peak value of the pulse signal from the input data sequence, and performs, for example, a differentiation process on the input data sequence to obtain a differential value (signal slope) detects a zero-cross timing when switched to a negative value of the predetermined or less from the positive value equal to or greater than a predetermined, detecting the data value at that zero-cross timing as the crest value of the pulse signals, respectively region determining means 43 ₁ To 43 _N.

Region determining means ₄₃ 1 ~ 43 _N includes a boundary value region _{L 1 ~L M-1} for dividing the output range of the above-mentioned peak value in the region _R 1 to R _M of the plurality M, the peak value detecting means ₄₂ 1-42 comparing the peak value detected in _N, its peak value to determine enters one region, and outputs the region identification signal representative of a region where the peak value enters an area cumulative means 44 ₁ ~ 44 _N.

Accumulating means 44 ₁ ~ 44 _N each region receives an area identification signal output from the region judging means 43 ₁ ~ 43 _N within the scan time, and the cumulative number of inputs of a region identification signal indicating the same area, respectively , The cumulative number for each area within the scan time is obtained and sequentially output.

The cumulative number of the region identification signals is the cumulative number of the pulse signals in which the peak value is included in the pulse signals output from one X-ray sensor within the scan time, and the cumulative value of each region is calculated. _By storing the cumulative number of area identification signals output from _{1 to} 44 _{N for} each scan time in the transmission image data memory 45 in parallel and in time series, the X-ray transmission image for the inspection object for each area is stored. Data is obtained.

As a simple example, the scan time is 3 units, the number of X-ray sensors N is 3, the number of peak value areas M is 3, and the cumulative number of pulse signals is A (order of peak value areas, order of scan time, sensor expressed in sequence order) of in the first scan time T1, of the first X-ray pulse signal sensor ₃₁₁ has output, the cumulative number of those whose peak value enters the area R ₁ a (1, 1 , 1), a (2,1,1 cumulative number of those entering the area R _2), the cumulative number of those entering the area R ₃ and a (3,1,1).

Further, in the same scan time within T1, of the second X-ray sensor ₃₁₂ is a pulse signal output, the cumulative number of those whose peak value enters the area R ₁ A (1,1,2), the area R ₂ a (2, 1, 2) the cumulative number of those entering, the cumulative number of those entering the area R ₃ and a (3,1,2).

Further, in the same scan time within T1, 3-th of the pulse signal X-ray sensor ₃₁₃ is output, A (1,1,3) the cumulative number of those whose peak value enters the area R _1, region R ₂ a (2, l, 3) the cumulative number of those entering, the cumulative number of those entering the area R ₃ and a (3,1,3).

Similarly, in the next scan time T2, among the pulse signals output by the _first X-ray sensor 311, the cumulative number of the pulse signals whose peak values fall in the region R ₁ is A (1,2,1), the cumulative number of those entering the R ₂ a (2,2,1), the cumulative number of those entering the area R ₃ and a (3,2,1), the second X-ray sensor ₃₁₂ is a pulse signal output among them, the cumulative number of those whose peak value enters the area _{R 1 a (1,2,2), a} (2,2,2) the cumulative number of those entering the area R _2, the cumulative number of those entering the area R ₃ was the a (3,2,2), 3 th of pulse signals X-ray sensor ₃₁₃ has output, the cumulative number of those whose peak value enters the area R ₁ a (1,2,3), region the cumulative number of those entering the R ₂ a (2,2,3), the cumulative number of those entering the area R ₃ and a (3,2,3).

Further, within the next scan time T3, among the pulse signals output by the _first X-ray sensor 311, the cumulative number of the pulse signals whose peak values fall in the region R ₁ is A (1,3,1), and the region R the cumulative number of those entering ₂ a (2,3,1), the cumulative number of those entering the area R ₃ and a (3,3,1), of the second X-ray sensor ₃₁₂ is a pulse signal output , the cumulative number of those whose peak value enters the area R ₁ a (1,3,2), the cumulative number of those entering the area R ₂ a (2,3,2), the cumulative number of those entering the area R ₃ and a (3,3,2), 3 th of pulse signals X-ray sensor ₃₁₃ has output, the cumulative number of those whose peak value enters the region R ₁ a (1,3,3), a region R the cumulative number of those entering ₂ a (2,3,3), the cumulative number of those entering the area R ₃ and a (3,3,3).

Thus from the obtained data in the composed nine cumulative number obtained for region R _1, as in FIG. 3 (a), transverse to the scan time of the order, the longitudinal and order of the sensor if arranged in three rows and three columns as the transmission image data for the nine sites of the object by the X-ray energy range corresponding to the region R ₁ is obtained.

Similarly, nine cumulative number obtained for region R _2, if arranged in three rows and three columns as shown in (b) of FIG. 3, the object to be inspected by the X-ray energy range corresponding to the region R ₂ transmission image data is obtained, nine cumulative number obtained for region R _3, be arranged in three rows and three columns as shown in (c) of FIG. 3, according to X-ray energy range corresponding to the region R ₃ Transmission image data of the inspection object is obtained.

  In practice, the number of scans required for foreign substance inspection is obtained by dividing the transport time (for example, 0.5 seconds) obtained by dividing the length of the article in the transport direction by the transport speed by the scan time (for example, 1 millisecond). It becomes a value (for example, 500), and the number of divisions in the sensor arrangement direction corresponds to the number N (for example, 200) of X-ray sensors.

  In this manner, if transmission image data for each energy range corresponding to the peak value area is obtained, the determination unit 50 determines a predetermined value including a subtraction process conventionally performed on the plurality of transmission image data. By performing the above image processing, it is possible to determine the presence or absence of a foreign substance in the inspection object.

  The method of dividing the peak value area is arbitrary. As one example, the maximum value of the energy of the photon of the X-ray emitted from the X-ray generation unit 22 (in the case of the X-ray tube, the What is necessary is just to divide the pulse signal output from the X-ray sensor with respect to the acceleration value (theoretical value depending on the acceleration voltage) into a plurality of values between a peak value of the pulse signal and a predetermined reference value (for example, 0). Also, the number of regions is arbitrary with two or more, and transmission image data is generated in many regions first, and the optimum combination of transmission image data for foreign object detection for the inspection object is found. Predetermined image processing including subtraction processing using transmitted image data may be performed.

Specifically, for example, the initial number of regions as 10, allocated in advance to generate a transmission image data in each region, the first region counted from the largest energy in the region R ₁ of the above, the third allocates a region in the region R ₂ of the above, and so ..., from the initial area to the final area allocated selectively, by using a plurality of transmission image data of the allocated space, the predetermined image processing You may do it. Further, by combining the transmission image data of the first and second regions counted from the larger energy, which was the previous region R ₁ of the transmitted image data, the transmitted image data of the third and fourth region synthesized and, this as a transmission image data in the above described region R _2, the transmitted image data of the initial plurality of areas combined with the transmitted image data of the final one area and so ... was their synthesis The predetermined image processing may be performed using a plurality of transmission image data or combining transmission image data and transmission image data of an initial region not including the transmission image data.

  In the above specific example, as many transmission image data as the number of initial regions are generated, and areas are allocated and the transmission image data is synthesized in accordance with a combination of transmission image data that is optimal for detecting foreign matter. However, if the optimum combination of transmission image data for foreign matter detection with respect to the object to be inspected is known, only transmission image data for the assigned area need be generated, and a plurality of transmission image data are synthesized. Alternatively, one transmission image data may be generated by adding the cumulative numbers of the area identification signals of a plurality of areas. Thereby, the storage area of the transmission image data can be saved.

  Here, the subtraction processing will be briefly described. When X-ray transmission data with different energies is obtained for the same part, when the difference processing is performed, the influence of the thickness of the part is removed, and the material (transmittance) is obtained. Only, the difference between the change in the transmittance of the material of the inspection object itself and the change in the transmittance of the material of the foreign substance with respect to the difference in the X-ray energy becomes remarkable. As a result, the detection sensitivity for foreign matter is increased. In addition to this processing, the determination means 50 performs various kinds of filter processing and the like for removing noise and the like, and detects foreign matter with higher accuracy.

  Since the plurality of transmission image data obtained by the above method is obtained from the outputs of the plurality of X-ray sensors arranged in a line in a direction orthogonal to the passing direction of the article, compared to the conventional method using two line sensors. This makes it possible to obtain transmission image data with extremely high accuracy, thereby enabling accurate detection of foreign matter and a small size.

  The determination result (the signal indicating the presence or absence of a foreign substance) by the determination means 50 is sent to a subsequent sorting device (not shown), and the article determined to have the foreign substance is excluded from the path of a good product.

Here, the energy of the X-ray transmitted through the inspection object greatly changes depending on the material of the inspection object and the thickness in the X-ray transmission direction. If the material of the object to be inspected is substantially uniform and the thickness in the X-ray transmission direction is substantially constant, the X-ray sensor can be adjusted by adjusting the average emission energy of X-rays to be constant according to the thickness. The dose of X-rays incident on the substrate can be maintained in an appropriate range. However, when the thickness of the inspection object varies greatly depending on the part, the dose of X-rays incident on the X-ray sensor cannot be maintained in an appropriate range. For example, if the emission energy of X-rays is determined in accordance with a portion having a large thickness, the dose of X-rays transmitted through a portion having a small thickness becomes excessively large. When the emission energy of the ray is determined, the dose of the X-ray that passes through a thick part becomes too small. When the dose of the X-ray transmitted through the inspection object becomes excessive in this way, in the above-described X-ray sensor of the photon detection type, the input frequency of the photon becomes excessive, and for example, as shown in FIG. The output pulse signals P ₁ and P ₂ and the pulse signals P ₄ and P ₅ overlap each other, and only one peak value (peak value H ₁ or H ₃ ) is obtained for each of the two pulse signals. The phenomenon occurs. This phenomenon is generally called a pile-up phenomenon. If this phenomenon occurs with a high probability, a correct counting result for each region cannot be obtained, and as a result, it is impossible to accurately detect foreign matter. Further, when the dose of X-rays transmitted through the inspection object becomes too small, the cumulative number of pulse signals becomes extremely small, so that it is difficult to distinguish the noise components from the noise components, and the S / N of transmitted image data is reduced. When the photon detection type X-ray sensor is used as described above, as described above, if the dose of the X-rays incident on the X-ray sensor (the number of photons output per unit time) is too large, the pile-up phenomenon occurs. Occurs with a high probability, and a correct counting result for each region cannot be obtained. If the X-ray dose is too small, it cannot be distinguished from noise, and correct transmission image data cannot be obtained.

  The dose of X-rays that pass through the test object decreases as the thickness in the transmission direction increases if the material of the test object is the same, so that the dose generally depends on the thickness of the test object. Although the dose of the X-ray emitted from the X-ray generation unit 22 is set, it is not possible to cope with an inspection object having the same material but having a shape that changes along the thickness passing direction.

  In order to solve this, in the foreign matter detection device 20 of the embodiment, the thickness detection means 60 and the X-ray dose variation means 70 are provided.

  The thickness detecting means 60 detects the thickness of the inspection object W in the X-ray transmission direction just before the X-ray irradiation position on the transport device 21. The method of detecting the thickness is arbitrary.For example, in the case of an optical configuration example, light is irradiated from one side of the side surface of the inspection object that has entered the thickness detection area, and the light is vertically transmitted to the opposite side. The light is received by a plurality of light receivers arranged in the direction, and the light is detected by the height of the light receivers whose light incidence is blocked by the inspection object. Alternatively, an optical reflective sensor is arranged above the passage, emits laser light, receives reflected light reflected on the upper surface of the inspection object, measures displacement, and measures the distance from the sensor to the passage and the sensor. Alternatively, the difference from the distance to the upper surface of the inspection object may be detected as the thickness of the inspection object.

  The thickness detecting means 60 detects the thickness of the object to be inspected, and sequentially outputs the thickness H, which is the detection result, to the X-ray dose varying means 70, thereby detecting the thickness of the object to be inspected in the passing direction of the object. Although a change in thickness is detected, it is desirable that the cycle of this operation be the same as or shorter than the scan time.

  The X-ray dose varying means 70 having received the thickness H detected by the thickness detecting means 60 transmits the X-ray dose transmitted through the inspection object having the thickness H and incident on the X-ray sensor to the pile-up. The dose of X-rays emitted from the X-ray generation unit 22 (specifically, the X-ray generation unit 22) is set so that the probability of occurrence of the phenomenon is low and the cumulative number of pulse signals falls within an appropriate range sufficiently larger than the noise level. The control value for controlling the tube current and the tube voltage of the X-ray tube is changed for each scan time.

  There are various methods of this variable processing. For example, a control value for giving an optimal X-ray dose depending on the sample product is stored in advance for each type (material) and thickness of the inspection object, and the thickness is detected. The method of reading out the control value corresponding to the section including the thickness H detected by the means 60 and setting the control value in the X-ray generation unit 22 and the expression indicating the relationship between the thickness and the optimum control value are included in the thickness detection means 60. A method of calculating a control value by substituting the thickness H detected in step (1) and setting the control value in the X-ray generation unit 22 can be adopted.

FIG. 4 shows a relationship between a change in the thickness of the inspection object detected by the thickness detecting means 60 and a change in the dose of the X-ray emitted from the X-ray generation unit 22. The thickness detecting means 60 detects the thickness of the inspection object at a period equal to or shorter than the scan time and outputs a detection result. The X-ray dose varying means 70 receives the detection result, determines the values of the tube current and the tube voltage corresponding to the dose of the X-ray to be emitted, and controls each scan time so as to obtain the values. As a result, the X-ray generation unit 22 emits X-rays at a dose corresponding to a change in thickness in the passing direction of the inspection object.

  Incidentally, it is desirable that the thickness detecting means 60 is disposed immediately before the X-ray irradiation position. However, for reasons such as the structure of the foreign matter detecting device 20 and protection of the thickness detecting means 60 from X-rays, the thickness detecting means 60 is disposed at a position away from the X-ray irradiation position along the passage. May need to be done. Assuming that the processing time from when the thickness detecting means 60 performs detection to when the X-ray generation unit 22 emits X-rays of a dose corresponding to this detection result is negligibly short, the object to be inspected has a thickness of The timing is shifted by the moving time from the passage of the detection position of the detection means 60 to the arrival of the X-ray irradiation position. In order to solve this problem, the X-ray dose varying means 70 can set the above moving time as a delay time in advance. Upon receiving the detection result from the thickness detecting means 60, the X-ray dose changing means 70 changes the X-ray dose to an amount corresponding to the detection result after the delay time has elapsed.

  The appropriate range of the dose of X-rays incident on the X-ray sensor is, for example, the maximum number of pulses (for example, scan time of 1 millisecond) in a standard that one X-ray sensor can output within the scan time. In the range (for example, 400 to 600).

  As described above, the foreign object detection device 20 of this embodiment detects a change in the thickness of the inspection object and adjusts the dose of the X-ray incident on the X-ray sensor according to the thickness so as to fall within an appropriate range. By changing the dose of the X-ray emitted by the X-ray generation unit 22 for each predetermined time (scan time), even if the inspection target has a shape whose thickness changes along the passing direction, Foreign matter detection can be performed accurately.

  The storage format of the plurality of transmission image data is arbitrary, but different colors are assigned to each peak value area, and the brightness of the color assigned to the area is made to correspond to the cumulative number of pulse signals. When observing, the observer can easily understand.

  For example, three peak value areas are set, three primary colors of red (R), green (G), and blue (B) are assigned to each area, and the cumulative number of pulses is assigned to the luminance value of each color. However, the value assigned to the luminance of each color is, for example, a range (0 to 255) that can be represented by 8 bits, and normalization (compression processing or expansion processing) is performed so that the range of the actual number of accumulated pulses falls within the range that can be represented by 8 bits. . In this case, three pieces of transmission image data can be stored as one piece of RGB color image data. For this reason, the storage area of the transmission image data can be saved. In addition, since the data format is general RGB color image data, image processing and image display can be easily performed.

  Also, by assigning a different color to each region and using a data storage format in which the luminance of the color is represented by the cumulative number of pulse signals, the transmission image of each region can be represented by an image of a different color. Are very high when displayed side by side on a display device (not shown) in parallel.

Reference Signs List 20 foreign matter detection device 21 conveyance device 22 X-ray generation unit 30 line sensor 31 _{1 to} 31 _N X-ray sensor 40 transmission image data generation means 41 ₁ to 41 41 _N ... A / D converter, 42 _{1 to} 42 _N ... Peak value detecting means, 43 ₁ to 43 _N ... Area determining means, 44 _{1 to} 44 _N ... Area accumulating means, 45. Data memory, 50: determination means, 60: thickness detection means, 70: X-ray dose variable means

Claims (7)

An X-ray generator (22) that emits X-rays into a passage through which the inspection object passes;
At a position for receiving X-rays emitted from the X-ray generator to the passage and transmitted through the inspection object, the X-ray generation units are arranged so as to be arranged in a direction intersecting with the passing direction of the inspection object, and receive X-rays, respectively. A plurality of X-ray sensors (31 _{1 to} 31 _N ) for converting into electric signals;
While the inspection object is passing between the X-ray generating unit and the plurality of X-ray sensors, a signal output from each of the plurality of X-ray sensors is divided for a predetermined period to perform predetermined signal processing. A two-dimensional position information determined by a passing direction of the inspection object and a direction in which the X-ray sensors are arranged, and transmission image data generating means for generating transmission image data of the inspection object based on a signal processing result for each position; (40)
A foreign matter detection device having a determination means (50) for determining the presence or absence of a foreign matter in the inspection object based on the transmission image data generated by the transmission image data generation means;
The X-ray sensor is a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the photon every time a photon of the X-ray is input,
The transmission image data generating means,
For each of the X-ray sensors, it is determined whether the peak value of the pulse signal output from the X-ray sensor within the predetermined period falls into any of a plurality of regions in which the predetermined range is divided in advance. Is configured to accumulate the number of input pulse signals for each of the regions, and to generate a plurality of transmission image data that is a combination of regions optimal for detecting foreign matter with respect to the inspection object using the accumulation result for each of the regions. And
The determining means includes:
By performing predetermined image processing including subtraction processing on a plurality of transmission image data obtained by the transmission image data generating means, it is configured to determine the presence or absence of foreign matter in the inspection object. Characteristic foreign matter detection device.   2. The foreign matter detection device according to claim 1, wherein the number of regions in which the predetermined range is previously divided into a plurality of regions is three or more.   The transmission image data generation unit is configured to generate transmission image data for each of the plurality of areas divided in advance in the predetermined range, and to find a combination of transmission image data that is optimal for detecting a foreign substance with respect to the inspection object. The foreign matter detection device according to claim 1 or 2, wherein   The transmission image data generating means generates transmission image data for each area obtained by previously dividing the predetermined range into a plurality of areas, and synthesizes a part of the plurality of the generated transmission image data to form new transmission image data. The foreign matter detection device according to claim 3, wherein   The transmission image data generating means, when a combination of transmission image data that is optimal for foreign object detection with respect to the inspection object is known, generates only transmission image data for an area related to the combination. The foreign matter detection device according to claim 1 or 2, wherein   6. The foreign matter detection device according to claim 5, wherein the transmission image data generation means generates new transmission image data by adding the cumulative number of area identification signals of a plurality of areas. Emitting X-rays from the X-ray generator (22) to a passage through which the inspection object passes;
X-rays emitted to the passage and transmitted through the inspection object are received by a plurality of X-ray sensors (31 _{1 to} 31 _N ) arranged in a direction intersecting the passing direction of the inspection object and converted into electric signals. Stages and
While the inspection object is passing between the X-ray generating unit and the plurality of X-ray sensors, a signal output from each of the plurality of X-ray sensors is divided for a predetermined period to perform predetermined signal processing. Generating two-dimensional position information determined by a passing direction of the inspection object and a direction in which the X-ray sensors are arranged, and transmitting image data of the inspection object including a signal processing result for each position;
Based on the generated transmission image data, determining the presence or absence of a foreign substance in the inspection object,
Each time an X-ray photon is input, a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the photon is used as the X-ray sensor,
In the step of generating the transmission image data,
For each of the X-ray sensors, it is determined whether the peak value of the pulse signal output from the X-ray sensor within the predetermined period falls into any of a plurality of regions in which the predetermined range is divided in advance. The number of pulse signal inputs is accumulated for each region, and using the accumulation result for each region, a plurality of transmission image data that is a combination of regions optimal for detecting a foreign substance with respect to the inspection object is generated.
In the step of determining the presence or absence of foreign matter in the inspection object,
A foreign matter detection method, comprising: performing predetermined image processing including subtraction processing on the plurality of generated transmission image data to determine the presence or absence of foreign matter in the inspection object.