JP6625470B2 - Foreign object detection device and foreign object detection method - Google Patents

Description

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

  In a factory that manufactures 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 detection 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. Are 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 with 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, in Patent Document 1, processing such as subtraction (difference processing of image data) is performed 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 Patent Document 1, X-rays output from a single X-ray source and transmitted through an 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 of the detectors 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 a foreign substance in the inspection object cannot be correctly recognized. Further, it is 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, the 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, easily changes the posture of the test object being transported between them, and uses two detectors as described above. For this reason, there is a possibility that the detection accuracy of the foreign matter is reduced.

As a method for solving this problem, attention is paid to the fact that the energy of X-ray photons generated from an X-ray tube or the like varies, and each time an X-ray photon is incident, a pulse signal of a peak value corresponding to the energy is taken. 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. In this method, the plurality of X-ray sensors may be arranged in a row in a direction intersecting with the passing direction of the inspection object, and the above problem can be solved.

  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 made substantially uniform and the thickness in the X-ray transmission direction is almost constant, the X-ray sensor can be adjusted by adjusting the average emission energy of X-rays in accordance with the thickness. X-ray dose 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 portion having a large thickness 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 becomes impossible to distinguish the noise components from the noise components, and the S / N of transmitted image data is reduced.

  The present invention solves the above-mentioned problems, and uses an X-ray sensor of a photon detection type to cause a pile-up phenomenon caused by a difference in the thickness of an inspected object whose thickness changes along the passing direction. It is an object of the present invention to provide a foreign substance detection device and a foreign substance detection method capable of performing the foreign substance detection with high accuracy while suppressing the influence of the S / N reduction.

In order to achieve the above object, a foreign object detection device according to claim 1 of the present invention comprises:
An X-ray generator (22) that emits X-rays to a passage through which the inspection object passes;
At a position for receiving X-rays emitted from the X-ray generation unit 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. A plurality of X-ray sensors (311-31N) for converting into electric signals;
While the inspection object is passing between the X-ray generation 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. Means for generating two-dimensional position information determined by the direction in which the inspection object passes and the direction in which the X-ray sensors are arranged, and transmission image data generating means for generating transmission image data of the inspection object, comprising signal processing results for each position (40)
A foreign matter detection device comprising: 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 X-ray photon each time the photon is input,
The transmission image data generation 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, and within the predetermined period, Is configured to accumulate the number of pulse signal inputs for each of the regions, and to generate a plurality of transmission image data having different X-ray transmission energies using the accumulation result for each region,
The determining means includes:
By performing a predetermined image processing including a subtraction process on the 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,
further,
Thickness detection means (60) for sequentially detecting the thickness of the inspection object in the X-ray transmission direction before entering the position irradiated with the X-ray emitted by the X-ray generation unit;
X-ray dose varying means (70) for changing the dose of X-rays emitted by the X-ray generation unit every predetermined period based on the thickness of the inspection object detected by the thickness detection means. It is characterized by having.

According to a second aspect of the present invention, there is provided a foreign matter detecting device according to the first aspect.
As the X-ray generation unit, a hot cathode X-ray tube that accelerates electrons emitted from a heated filament to collide with a target of an anode to emit X-rays is used,
The X-ray dose varying unit changes at least one of a tube current and a tube voltage of the hot cathode X-ray tube according to a thickness of the inspection object detected by the thickness detecting unit. .

According to a third aspect of the present invention, there is provided a foreign substance detection device according to the first or second aspect.
The X-ray dose variable unit is configured to calculate a time difference between when the thickness detecting unit detects the thickness of a part of the inspection object and when the part of the inspection object reaches a position irradiated with the X-ray. The delay time can be set in advance, and the dose of the X-ray is changed to an amount corresponding to the detected thickness after the delay time elapses after the thickness detection unit performs the detection. And

Further, the foreign matter detection method according to claim 4 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 through 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 generation 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 an arrangement direction of the X-ray sensors, and generating transmission 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 foreign matter in the inspection object,
Each time an X-ray photon is input, a photon detection type that outputs a pulse signal having 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, and within the predetermined period, The pulse signal input number is accumulated for each region, and a plurality of transmission image data having different X-ray transmission energies is generated using the accumulation result for each region,
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, it is determined whether there is a foreign substance in the inspection object,
Further, before the inspection object enters the irradiation position of the X-ray, the thickness of the inspection object in the X-ray transmission direction is sequentially detected, and according to the detected thickness, The dose of the emitted X-ray is changed every predetermined period.

  The present invention uses, as an X-ray sensor, a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the X-ray photon every time a photon of the X-ray is input, and enters a position irradiated with the X-ray. The dose of the X-ray emitted from the X-ray generator is varied according to the change in the thickness of the inspection object detected before the X-ray detection. , And it is possible to obtain transmission image data in which a decrease in accuracy due to a pile-up phenomenon or a decrease in S / N is suppressed, and to detect a foreign object with respect to an inspection object having a shape whose thickness changes along a passing direction. It can be performed accurately.

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 object 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 N 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 transports the inspection object W in a predetermined direction (in the figure, a direction orthogonal to the paper surface, hereinafter, referred to as a passing direction or a transport direction), and is generally an inspection target like a conveyor. A device that horizontally transports the object W at a constant speed is used. However, it is not always necessary to use a transport device having a power source. 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-controlled hot cathode X-ray. A tube is used, and additionally contains the power supply required to drive the X-ray tube.

  The dose of X-rays (sum of energy per unit time) emitted from 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 dose of the X-ray emitted from the X-ray generator 22 is varied by the X-ray dose varying means 70, which will be described later.

Each of the plurality of N X-ray sensors 31 _{1 to} 31 _N receives X-rays and converts the X-rays into an electric signal. X transmitted through
At the position where the line is received, they are arranged in a row with almost no gap in a direction intersecting (in this example, orthogonal) with the passing direction of the inspection object 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 one 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 object 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 received light into an electric signal. The X-ray sensors 31 _{1 to} 31 _N used by the foreign object 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 generating 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. Is 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 signal processing results 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 part 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, A plurality of transmission image data having different X-ray transmission energy ranges for a portion corresponding to the scan time can be generated.

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. 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 detection 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, and performs 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 and outputs it to the ~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 same pulse signal in the region where the peak value is included among the pulse signals output from one X-ray sensor during the scan time. _By storing the cumulative number of region 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 region is stored. Data is obtained.

As a simple example, assume that 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, of 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 represented by 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, in 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 means 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 The peak value of the pulse signal output from the X-ray sensor may be equally divided into a plurality of values between a peak value of the pulse signal output from the X-ray sensor and a predetermined reference value (for example, 0). Also, the number of regions is arbitrary with two or more. 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 pieces 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 transmission image data are 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 inspection object is known, only transmission image data for the assigned area needs to 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. In the case where 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 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 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 with the conventional method using two line sensors, Thus, transmitted image data with extremely high accuracy can be obtained, whereby foreign matter detection can be performed accurately, and the apparatus can be made compact.

  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.

  When a photon detection type X-ray sensor is used as described above, as described above, if the dose of 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.

  Since the dose of X-rays transmitted through the inspection object decreases as the thickness in the transmission direction increases if the material of the inspection object is the same, the X-ray dose generally depends on the thickness of the inspection 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 region, 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 from the object 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, so that the thickness in the passing direction of the object to be inspected is obtained. Although the change in thickness is detected, the cycle of this operation is desirably the same as or shorter than the scan time.

  Upon receiving the thickness H detected by the thickness detecting means 60, the X-ray dose varying means 70 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 X-ray dose (specifically, the X-ray generation unit 22) emitted from 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 tube voltage of the X-ray tube is changed for each scan time.

  There are various methods of the variable processing. For example, a control value for giving an optimum 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 (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 detection unit 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 be 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 detection 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 have to be done. Assuming that the processing time from the detection by the thickness detecting means 60 to the emission of the X-ray of the dose corresponding to the detection result by the X-ray generation unit 22 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 varying means 70 changes the X-ray dose to an amount corresponding to the detection result after the delay time has elapsed.

  Note that 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, 1 millisecond scan time) that can be output by one X-ray sensor within the scan time. In the range (for example, 400 to 600).

  As described above, the foreign matter 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 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 object has a shape whose thickness changes along the passing direction, Foreign matter detection can be performed accurately.

  Although the storage format of the plurality of transmission image data is arbitrary, 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. Further, 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. Is very high when displayed side by side on a display device (not shown) in parallel.

20 ...... foreign substance detecting device, 21 ...... conveying device, 22 ...... X-ray generating unit, 30 ...... line _sensor, 31 1 to 31 _N ...... X-ray sensor, 40 ...... transmission image data generating unit, ₄₁ 1 ~ 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. Data memory, 50 determination means, 60 thickness detection means, 70 X-ray dose variable means

Claims (4)

An X-ray generator (22) that emits X-rays to a passage through which the inspection object passes;
At a position for receiving X-rays emitted from the X-ray generation unit 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. 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 generation 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. Means for generating two-dimensional position information determined by the direction in which the inspection object passes and the direction in which the X-ray sensors are arranged, and transmission image data generating means for generating transmission image data of the inspection object, comprising signal processing results for each position (40)
A foreign matter detection device comprising: 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 X-ray photon each time the photon is input,
The transmission image data generation 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, and within the predetermined period, Is configured to accumulate the number of pulse signal inputs for each of the regions, and to generate a plurality of transmission image data having different X-ray transmission energies using the accumulation result for each region,
The determining means includes:
By performing a predetermined image processing including a subtraction process on the 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,
further,
Thickness detection means (60) for sequentially detecting the thickness of the inspection object in the X-ray transmission direction before entering the position irradiated with the X-ray emitted by the X-ray generation unit;
X-ray dose varying means (70) for changing the dose of X-rays emitted by the X-ray generation unit every predetermined period based on the thickness of the inspection object detected by the thickness detection means. A foreign matter detection device, characterized in that: As the X-ray generation unit, a hot cathode X-ray tube that accelerates electrons emitted from a heated filament to collide with a target of an anode to emit X-rays is used,
The X-ray dose varying unit changes at least one of a tube current and a tube voltage of the hot cathode X-ray tube according to a thickness of the inspection object detected by the thickness detecting unit. The foreign matter detection device according to claim 1.   The X-ray dose variable unit is configured to calculate a time difference between when the thickness detecting unit detects the thickness of a part of the inspection object and when the part of the inspection object reaches a position irradiated with the X-ray. The delay time can be set in advance, and the dose of the X-ray is changed to an amount corresponding to the detected thickness after the delay time elapses after the thickness detection unit performs the detection. The foreign matter detection device according to claim 1 or 2, wherein Emitting X-rays from the X-ray generator (22) to a passage through which the inspection object passes;
The 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 with the passing direction of the inspection object and converted into electric signals. Stages and
While the inspection object is passing between the X-ray generation 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 an arrangement direction of the X-ray sensors, and generating transmission 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 foreign matter in the inspection object,
Each time an X-ray photon is input, a photon detection type that outputs a pulse signal having 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, and within the predetermined period, The pulse signal input number is accumulated for each region, and a plurality of transmission image data having different X-ray transmission energies is generated using the accumulation result for each region,
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, it is determined whether there is a foreign substance in the inspection object,
Further, before the inspection object enters the irradiation position of the X-ray, the thickness of the inspection object in the X-ray transmission direction is sequentially detected, and according to the detected thickness, A foreign matter detection method, wherein the emitted dose of X-rays is changed every predetermined period.