JP5596820B2 - Radiation detector - Google Patents

Description

  The present invention relates to a dual energy type radiation detection apparatus, and more particularly to a radiation foreign substance inspection apparatus.

  2. Description of the Related Art Radiation detection apparatuses that perform foreign object detection, component distribution measurement, weight measurement, and the like in in-line non-destructive inspection of inspected objects conveyed by a belt conveyor or the like are known. The radiation detection apparatus includes a radiation detector having a scintillator layer and pixels, and detects radiation transmitted through the object to be inspected to generate a radiation image.

  This type of radiation detection apparatus is disclosed in Patent Document 1. In the radiation detection apparatus described in Patent Document 1, two radiation detectors having different pixel areas are juxtaposed in the carrying direction of the belt conveyor. In this radiation detection apparatus, a large foreign object is detected by a radiation detector having a large pixel area, and a small foreign object is detected by a radiation detector having a small pixel area. As described above, the inspection accuracy of the foreign matter can be improved by selecting the pixel size in advance according to the size of the foreign matter to be detected.

  As another method for improving the inspection accuracy of foreign matter, a dual energy type radiation detection apparatus is known. The dual energy type radiation detection apparatus includes two radiation detectors having different energy sensitivities, and includes radiation in a low energy range (first energy range) transmitted through an object to be inspected and high energy range (second energy range). Detect radiation. According to this radiation detection apparatus, a radiation image in a low energy range and a radiation image in a high energy range are simultaneously acquired, and weighted subtraction processing, overlay processing, and the like (for example, subtraction processing) are performed based on these radiation images. A high-accuracy foreign matter inspection can be realized by creating an image and raising the foreign matter due to the contrast difference between the images.

JP 2009-85627 A

  For example, foreign matter inspection in food requires that bone, cartilage, metal, etc. in meat be inspected as foreign matter, and the difference between the amount of radiation absorbed by meat and the amount of radiation absorbed by foreign matter (bone, cartilage, metal, etc.) Is used to raise the foreign matter based on the contrast difference between the subtraction images of the radiation images that have passed through them, and determine the presence or absence of the foreign matter.

  Here, since bones and metals have greatly different (lower) radiolucency compared to meat, there is a large contrast difference in the radiation image by at least one of the radiation detectors. As a result, the contrast difference between the subtraction images of the two radiation images is large, and foreign matter inspection is easy. However, since cartilage has a high radiation transmittance as in meat, and the difference between the two is small, the contrast difference between the radiation images of both radiation detectors is small. As a result, the contrast difference between the subtraction images of these radiation images is small, and foreign matter inspection is difficult.

  In this regard, the inventors of the present application have made extensive studies, and as a result, contrast differences between light atoms such as meat and cartilage, that is, radiological images of substances having high radiation transparency, are found in a radiation image in a lower energy range. I found out that it can be bigger. Furthermore, the inventors of the present application reduce the area of the pixel in the radiation detector for detecting the low energy range and reduce the amount of charge converted by each pixel, thereby increasing the charge due to the radiation image of substances having high radiation transparency. The present inventors have found that the amount difference can be relatively increased, and the contrast difference between these radiation images can be increased.

  However, in order to reduce the area of the pixel in the low energy radiation detector, if the pixel width in the direction orthogonal to the pixel arrangement direction (image detection direction) is reduced to increase the number of pixels (number of line outputs), The number of pixels output from the energy radiation detector (number of line outputs) differs from the number of pixels output from the high energy radiation detector (number of line outputs), and as a result, subtraction processing, that is, differential processing is performed. Becomes difficult.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a radiation foreign substance inspection apparatus that facilitates arithmetic processing based on a radiation image by these radiation detectors even if the number of pixels in the two radiation detectors is different.

  The radiation foreign object inspection apparatus according to the present invention includes a belt conveyor that conveys an object to be inspected in a conveyance direction, a radiation irradiation apparatus that irradiates radiation in a radiation irradiation direction orthogonal to the conveyance direction, and an upstream side with respect to the radiation irradiation direction. A first radiation detector that detects radiation in the first energy range and generates first image data corresponding to the image of the radiation; A second radiation detector that detects radiation in a second energy range higher than the radiation in the range and generates second image data corresponding to the radiation image; detection timing of the first radiation detector; A timing control unit that controls the detection timing of the radiation detector; and an image processing unit that performs subtraction processing based on the first image data and the second image data. The first radiation detector includes a first line sensor having a plurality of first pixels arranged along the image detection direction, and the second radiation detector includes a plurality of arrays arranged along the image detection direction. A second line sensor having a second pixel. The pixel width Wb1 in the orthogonal direction orthogonal to the image detection direction of the first pixel is smaller than the pixel width Wb2 in the orthogonal direction of the second pixel, and the image processing unit has a ratio between the pixel width Wb1 and the pixel width Wb2. Based on the above, a correction process for correcting the first image data to the image data for the subtraction process is performed.

  When the subtraction method is used, it is necessary for the two radiation detectors to image the same position on the inspection object both spatially and temporally. Therefore, in the type in which two radiation detectors are arranged side by side as described in Patent Document 1, the detection timing of each radiation detector must be adjusted. Moreover, even if the detection timing is adjusted, it is difficult to image the same position on the inspection object, that is, the exact same area, and the position accuracy may be low. Thus, when a subtraction image in which a part of the end of the detection area is shifted is created, a pseudo edge such as a bright edge (white edge) or a dark edge (black edge) is generated at the end of the detection object in the subtraction image. There is.

  On the other hand, in this radiation foreign substance inspection apparatus, the first radiation detector and the second radiation detector are arranged so as to overlap with each other in the radiation incident direction, that is, because they are of a vertically stacked type, the detection timing control is performed. Therefore, it is possible to easily image the same position on the inspection object at the same time in time.

  According to this radiation foreign object inspection apparatus, the timing control unit controls the detection timing of the first radiation detector and the detection timing of the second radiation detector, so that the second radiation detector can be used at one detection timing. The pixel data of the ratio of the pixel width Wb1 and the pixel width Wb2 is acquired for the first radiation detector. Then, the image processing unit performs correction processing for correcting the first image data to image data for subtraction processing based on the ratio between the pixel width Wb1 and the pixel width Wb2, and thus the corrected first radiation detector And the number of pixels of the image from the second radiation detector can be made equal. Therefore, even when the pixel width in the orthogonal direction orthogonal to the image detection direction of the image in the first radiation detector is smaller than the pixel width in the orthogonal direction of the pixel in the second radiation detector, that is, the first radiation. Even if the number of pixels in the detector and the number of pixels in the second radiation detector are different, arithmetic processing based on the radiation image by the first radiation detector and the radiation image by the second radiation detector, for example, subtraction processing is facilitated. be able to.

  The timing control unit described above may synchronize the detection timing of the second radiation detector with the detection timing of the first radiation detector. According to this, since the detection timing of the second radiation detector is synchronized with the detection timing of the first radiation detector by the timing control unit, the second radiation detector detects the first radiation detection at one detection timing. The pixel data of the ratio Wb2 / Wb1 times of the first pixel width Wb1 and the second pixel width Wb2 is acquired. Then, the image correction unit adds Wb2 / Wb1 pieces of continuous pixel data in the image from the first radiation detector based on the ratio Wb2 / Wb1 between the first pixel width Wb1 and the second pixel width Wb2. The number of pixels of the image from the first radiation detector after correction and the number of pixels of the image from the second radiation detector can be made equal. Therefore, even when the first pixel width in the orthogonal direction orthogonal to the image detection direction of the image in the first radiation detector is smaller than the second pixel width in the orthogonal direction of the pixel in the second radiation detector, that is, Even if the number of pixels in the first radiation detector and the number of pixels in the second radiation detector are different, arithmetic processing based on the radiation image by the first radiation detector and the radiation image by the second radiation detector, for example, subtraction processing Can be made easier.

  The timing control unit described above may delay either the detection timing of the first radiation detector or the detection timing of the second radiation detector. Due to the arrangement of the first radiation detector and the second radiation detector, the detection position of the inspection object at the detection timing of the first radiation detector and the detection position of the inspection object at the detection timing of the second radiation detector are large. It may shift. Then, in the subtraction image based on the radiation image by the first radiation detector and the radiation image by the second radiation detector, white edges and black edges may occur before and after the portion corresponding to this detection position. However, according to this, due to the arrangement of the first radiation detector and the second radiation detector, depending on the detection position of the inspection object by the detection timing of the first radiation detector and the detection timing of the second radiation detector. The detection position of the inspection object can be reduced. Therefore, in the subtraction image based on the radiation image by the first radiation detector and the radiation image by the second radiation detector, it is possible to suppress the occurrence of white edges and black edges before and after the portion corresponding to this detection position. A good subtraction image can be obtained.

  The first radiation detector and the second radiation detector described above are the detection position of the inspection object based on the detection timing of the first radiation detector and the detection of the inspection object based on the detection timing of the second radiation detector. It may be arranged so that the positional deviation from the position is 0.3 times or less of the pixel width. According to this, the displacement between the detection position of the inspection object at the detection timing of the first radiation detector and the detection position of the inspection object at the detection timing of the second radiation detector is 0.3 times the first pixel width. When the first radiation detector and the second radiation detector are arranged as follows, the subtraction image based on the radiation image by the first radiation detector and the radiation image by the second radiation detector corresponds to this detection position. It is possible to suppress the occurrence of white edges and black edges before and after the portion to be performed, and a good subtraction image can be obtained.

  The first radiation detector described above extends in the image detection direction, and converts the radiation image in the first energy range into an optical image, and light converted by the first scintillator layer. A first line sensor that acquires first image data based on an image, and the second radiation detector described above extends along the image detection direction, and converts an image of radiation in the second energy range into an optical image. And a second scintillator layer for converting to a second scintillator layer, and a second line sensor for acquiring second image data based on the light image converted by the second scintillator layer.

The image processing unit described above may perform addition processing of the first image data as the correction processing.

  Further, the pixel width Wa1 in the image detection direction of the first pixel may be smaller than the pixel width Wa2 in the image detection direction of the second pixel.

  According to the present invention, even if the number of pixels in the two radiation detectors is different in the dual energy type radiological foreign body inspection apparatus using the subtraction method, arithmetic processing based on the radiation image by these radiation detectors, for example, subtraction processing is performed. Can be easily.

It is a perspective view of the X-ray foreign material inspection apparatus which concerns on this embodiment. It is a schematic block diagram of the X-ray foreign material inspection apparatus which concerns on this embodiment. It is a schematic structure figure of the dual energy sensor in the radiation detection instrument concerning this embodiment. It is a figure which shows the X-ray entrance plane of the low energy detector and high energy detector in the dual energy sensor shown in FIG. It is a conceptual diagram which shows the image process in the low energy image correction part and high energy image correction part which are shown in FIG. It is a conceptual diagram of the detection timing control by the timing control part shown in FIG. It is a figure which shows the pixel data of the image output from the low energy detector and high energy detector which are shown in FIG. It is a conceptual diagram which shows the image correction process by the low energy image correction part shown in FIG. It is a figure which shows the image detected by the low energy detector and high energy detector when not performing detection timing control and image correction processing of this embodiment. It is a figure which shows the image detected by the low energy detector and high energy detector at the time of performing the detection timing control and image correction process of this embodiment. It is a subtraction image based on the image shown in FIG. It is a figure which shows the luminance file of an image when the same to-be-inspected object is detected. It is a figure which shows the luminance file of the subtraction image by the image which has a luminance file shown in FIG. It is a figure which shows an example of the subtraction image by two images from which detection timing differs. It is a figure which shows the X-ray entrance plane of the low energy detector and high energy detector in the dual energy sensor of the modification of this embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a perspective view of an X-ray foreign substance inspection apparatus according to the present embodiment, and FIG. 2 is a schematic configuration diagram of the X-ray foreign substance inspection apparatus according to the present embodiment. As shown in FIG. 1 and FIG. 2, the X-ray foreign substance inspection apparatus 1 irradiates the inspection object S with X-rays (radiation) from an X-ray source in an irradiation direction Z, and Among these, the apparatus detects transmitted X-rays transmitted through the inspection object S in a plurality of energy ranges. The X-ray foreign matter inspection apparatus 1 performs foreign matter inspection, baggage inspection, and the like included in the inspection object S using the transmitted X-ray image. Such an X-ray foreign substance inspection apparatus 1 includes a belt conveyor 10, an X-ray irradiator 20, a low energy image acquisition unit 30, a high energy image acquisition unit 40, a timing control unit 50, a timing calculation unit 60, and an image processing device 70. I have. The low energy image acquisition unit 30, the high energy image acquisition unit 40, and the timing control unit 50 constitute the dual energy type radiation detection apparatus 80 according to the present embodiment.

  As shown in FIG. 1, the belt conveyor 10 includes a belt portion 12 on which the inspection object S is placed. The belt conveyor 10 conveys the inspection object S in the conveyance direction Y at a predetermined conveyance speed by moving the belt portion 12 in the conveyance direction Y. The conveyance speed of the inspection object S is 48 m / min, for example. The belt conveyor 10 can change the speed to a conveyance speed such as 24 m / min or 96 m / min by the belt conveyor control unit 14 as necessary. Further, the belt conveyor control unit 14 can change the height position of the belt unit 12. By changing the height position of the belt part 12, the distance between the X-ray irradiator 20 and the inspection object S can be changed. By this change, it is possible to change the resolution of the X-ray transmission image acquired by the low energy image acquisition unit 30 and the high energy image acquisition unit 40. Examples of the inspection object S conveyed by the belt conveyor 10 include food products such as meat, rubber products such as tires, baggage inspection and cargo inspection for security and safety, and other resin products, metal products, and minerals. Such as resource materials, waste for sorting and resource recovery (recycling), electronic parts, etc.

  The X-ray irradiator 20 is an apparatus that irradiates the inspection object S in the irradiation direction Z as an X-ray source. The X-ray irradiator 20 is a point light source, and irradiates the X-ray by diffusing it in a predetermined angle range in the detection direction X orthogonal to the irradiation direction Z and the transport direction Y. The X-ray irradiator 20 has a predetermined distance from the belt portion 12 so that the X-ray irradiation direction Z is directed to the belt portion 12 and diffused X-rays extend over the entire width direction (detection direction X) of the inspection object S. It is arranged above the belt portion 12 at a distance. Further, in the X-ray irradiator 20, in the length direction (conveying direction Y) of the inspection object S, a predetermined division range in the length direction is an irradiation range, and the inspection object S is conveyed in the belt conveyor 10. By being conveyed to Y, X-rays are irradiated to the entire length direction of the inspection object S.

  The low energy image acquisition unit 30 includes a low energy detector (first radiation detector) 32 and a low energy image correction unit (image correction unit) 34.

  The low energy detector 32 is located on the upstream side with respect to the X-ray incident direction Z, and a low energy range (first energy range) in which X-rays irradiated from the X-ray irradiator 20 pass through the inspection object S. X-rays are detected and low energy image data (first radiation image data) is generated.

  The low energy image correction unit 34 amplifies and corrects the low energy image data generated by the low energy detector 32. The low energy image correction unit 34 is converted by an amplifier 34a that amplifies low energy image data, an A / D conversion unit 34b that performs A / D conversion on the low energy image data amplified by the amplifier 34a, and an A / D conversion unit 34b. A correction circuit 34c that performs a predetermined correction process on the low energy image data and an output interface 34d that externally outputs the image data corrected by the correction circuit 34c are provided. Details of the low energy image correction unit (image correction unit) 34 will be described later.

  The high energy image acquisition unit 40 includes a high energy detector (second radiation detector) 42 and a high energy image correction unit 44.

  The high energy detector 42 is located on the downstream side with respect to the X-ray incident direction Z, is irradiated from the X-ray irradiator 20, and has passed through the inspection object S and the low energy detector 32 among the X-rays. X-rays in a range (second energy range) are detected, and high energy image data (second radiation image data) is generated. The low energy range detected by the low energy detector 32 and the high energy range detected by the high energy detector 42 are not clearly distinguished, and the energy ranges overlap to some extent. .

  The high energy image correction unit 44 is a part that amplifies and corrects the high energy image data generated by the high energy detector 42. The high energy image correction unit 44 converts the high energy image data amplified by the amplifier 44a, the A / D conversion unit 44b that performs A / D conversion on the high energy image data amplified by the amplifier 44a, and the A / D conversion unit 44b. A correction circuit 44c that performs a predetermined correction process on the high-energy image data and an output interface 44d that outputs the image data corrected by the correction circuit 44c to the outside are provided.

  The timing control unit 50 controls the transmission X-ray detection timing at the low energy detector 32 and the transmission X-ray detection timing at the high energy detector 42. The timing control unit 50 reduces the image shift in the following subtraction process according to the detection timing calculated by the timing calculation unit 60 so that the low energy image data and the high energy image data correspond to each other. Details of the timing control unit 50 and the timing calculation unit 60 will be described later.

  The image processing apparatus 70 performs arithmetic processing (subtraction processing) for obtaining difference data between the low energy image data detected and generated by the low energy detector 32 and the high energy image data detected and generated by the high energy detector 42. This is a device for generating a subtraction image that is a composite image. The detection timing of both energy image data input to the image processing device 70 is controlled by the timing control unit 50 so that the image data corresponds to each other. The image processing device 70 outputs and displays the subtraction image generated by the arithmetic processing on a display or the like. By this output display, foreign matter or the like contained in the inspection object S can be visually confirmed. Note that the foreign matter contained in the inspection object S may be directly detected from the image data by performing only the data output without performing the output display of the subtraction image and performing the detection process on the image data.

  Next, the low energy detector 32 and the high energy detector 42 will be described in detail. FIG. 3 is a schematic structural diagram of a dual energy sensor 86 including the low energy detector 32 and the high energy detector 42 in the radiation detection apparatus 80 shown in FIG. 2, and FIG. 4 is an X-ray diagram of the low energy detector 32. It is a figure which shows the entrance plane (a) and the X-ray entrance plane (b) of the high energy detector 42.

  As shown in FIGS. 3 and 4, the low energy detector 32 includes a low energy scintillator layer (first scintillator layer) 322 and a low energy line sensor (first pixel unit) 324. The low energy scintillator layer 322 extends along the image detection direction X, and converts an X-ray image in the low energy range into an optical image. The low energy line sensor 324 includes a plurality of pixels 326 arranged along the image detection direction X, and acquires a low energy image (first image) based on the light image converted by the low energy scintillator layer 322. In this way, the low energy detector 32 detects X-rays in the low energy range.

  Similarly, the high energy detector 42 includes a high energy scintillator layer (second scintillator layer) 422 and a high energy line sensor (second pixel unit) 424. The high energy scintillator layer 422 extends along the image detection direction X, and converts an X-ray image in the high energy range into an optical image. The high energy line sensor 424 includes a plurality of pixels 426 arranged along the image detection direction X, and acquires a high energy image (second image) based on the light image converted by the high energy scintillator layer 422. In this way, the high energy detector 42 detects X-rays in the high energy range.

  Here, the pixel width (first image detection direction width) Wa1 in the image detection direction X of each of the plurality of pixels 326 in the low energy line sensor 324 is the image detection direction X of each of the plurality of pixels 426 in the high energy line sensor 424. This is the same as the pixel width (second image detection direction width) Wa2. On the other hand, the pixel width (first orthogonal direction width) Wb1 in the orthogonal direction (conveyance direction Y) orthogonal to the image detection direction X of each of the plurality of pixels 326 in the low energy line sensor 324 is the plurality of pixels in the high energy line sensor 424. Each pixel 426 is smaller than the pixel width (second orthogonal direction width) Wb2 in the orthogonal direction Y. In this way, the area (first area) S1 of each of the plurality of pixels 326 in the low energy line sensor 324 is smaller than the area (second area) S2 of each of the plurality of pixels 426 in the high energy line sensor 424. . That is, the number of pixels (number of line outputs) in the low energy line sensor 324 is larger than the number of pixels (number of line outputs) in the high energy line sensor 424.

  The material of the low energy scintillator layer 322 and the material of the high energy scintillator layer 422 may be the same, but different materials may be used for the low energy scintillator layer 322 and the high energy scintillator layer 422. For example, as materials for the low energy scintillator layer 322 and the high energy scintillator layer 422, Gd2O2S: Tb, CsI: Tl, CdWO4, CaWO4, GSO, LGSO, BGO, LSO, YSO, YAP, Y2O2S: Tb, YTaO4: Tm, etc. Can be applied, and a combination of materials may be selected in accordance with the X-ray to be detected. The low energy detector 32 and the high energy detector 42 may be X-ray detectors having an energy discrimination function by a direct conversion method such as CdTe (cadmium telluride).

  Here, in the inspection of foreign matter in food, it is required to inspect bone, cartilage, metal, etc. in meat as foreign matter, and the amount of radiation absorbed by meat and the amount of radiation absorbed by foreign matter (bone, cartilage, metal, etc.) Using the difference, foreign matter is raised by the contrast difference of the subtraction image of the radiation image that has passed through these, and the presence or absence of the foreign matter is determined.

  Here, since bones and metals have greatly different (lower) radiolucency compared to meat, there is a large contrast difference in the radiation image by at least one of the radiation detectors. As a result, the contrast difference between the subtraction images of the two radiation images is large, and foreign matter inspection is easy. However, since cartilage has a high radiation transmittance as in meat, and the difference between the two is small, the contrast difference between the radiation images of both radiation detectors is small. As a result, the contrast difference between the subtraction images of these radiation images is small, and foreign matter inspection is difficult.

  However, in each of the low energy detectors 32 for detecting a radiation image in a low energy range capable of relatively increasing a contrast difference between light atoms such as meat and cartilage, that is, a radiation image between substances having high radiation permeability, When the pixel width Wb1 in the transport direction Y of the pixel 326 is reduced, that is, when the area S1 of each pixel 326 in the low energy detector 32 is reduced, the amount of charge converted by each pixel 326 is reduced, and meat, cartilage, and the like The difference in the amount of charge due to the radiation image between the light atoms, that is, between the substances having high radiation transparency can be relatively increased, and the contrast difference between these radiation images can be increased. As a result, foreign matter inspection can be facilitated.

  Next, the correction circuit 34c, the timing control unit 50, and the timing calculation unit 60 in the low energy image correction unit 34 will be described in detail.

  FIG. 5 is a conceptual diagram showing image processing (a) by the low energy image correction unit 34 and image processing (b) by the high energy image correction unit 44.

  As shown in FIG. 5A, the image output from the low energy detector 32 is subjected to two-dimensional image processing of M pixels (detection direction X) × N line output (conveyance direction Y), and the number of pixels is M × N pixels. On the other hand, according to FIG. 5B, the image output from the high energy detector 42 is subjected to two-dimensional image processing of M pixels (detection direction X) × N ′ line output (conveyance direction Y), and the number of pixels. Becomes M × N ′ pixels (N ′ <N).

  Thus, when the pixel area S1 of the low energy detector 32 and the pixel area S2 of the high energy detector 42 are different, that is, the pixel width Wb1 in the transport direction Y of the low energy detector 32 and the high energy detector 42 When the pixel width Wb2 in the transport direction Y is different, the line output number N of the image output from the low energy detector 32 is different from the line output number N ′ of the image output from the high energy detector 42, that is, The number N of pixels in the conveyance direction Y of the image from the low energy detector 32 and the number N of pixels N ′ in the conveyance direction Y of the image from the high energy detector 42 are different, and the subtraction image is obtained by performing these difference processing. Difficult to create.

  Therefore, the timing control unit 50 synchronizes the detection timing of the low energy detector 32 and the detection timing of the high energy detector 42 to detect the number N of line outputs of the image output from the low energy detector 32 and the high energy detection. The line output number N ′ of the image output from the device 42 is made equal. That is, the number N of pixels in the image conveyance direction Y from the low energy detector 32 is made equal to the number of pixels N ′ in the image conveyance direction Y from the high energy detector 42.

  FIG. 6 is a conceptual diagram of detection timing control by the timing control unit 50, and FIG. 7 is an image pixel data (a) output from the low energy detector 32 and output from the high energy detector 42. It is a figure which shows the pixel data (b) of an image.

  For example, the timing control unit 50 supplies a repetitive pulse signal for detection timing to the low energy detector 32 and the high energy detector 42. The timing control unit 50 synchronizes these repeated pulse signals to synchronize the detection timing. The repetitive pulse signal is controlled according to the control signal from the timing calculation unit 60 using, for example, a PLL (Phase Locked Loop). In the timing calculation unit 60, for example, the conveyance speed V of the belt conveyor 10, the pixel width Wb1 or Wb2 in the pixel conveyance direction Y, the distance FOD from the light source 20 to the inspection object S, and the detector 32 from the light source 20 Alternatively, the value of the control signal, that is, the detection timing is adjusted in consideration of the distance FDD to 42 or the like. Each value may be set in advance by the user, for example.

  Specifically, the timing control unit 50 controls the cycle of the repetitive pulse signal for the low energy detector 32 to the pixel width Wb1 in the transport direction Y of the pixel 326 in the low energy detector 32 to detect high energy. The period of the repetitive pulse signal for the detector 42 is synchronized with the period of the repetitive pulse signal for the low energy detector 32. As described above, in this embodiment, the detection timing of the high energy detector 42 having the larger pixel width in the transport direction Y is not the pixel width Wb2 of its own pixel 426, but the pixel of the pixel 326 in the low energy detector 32. Adjustment is made with the width Wb1.

  Then, for example, as shown in FIGS. 6 and 7, at the detection timing of the first line, the low energy detector 32 detects the pixel data A and the high energy detector 42 detects the pixel data A + noise N. be able to. Next, at the detection timing of the second line, the pixel data B can be detected by the low energy detector 32 and the pixel data B + A can be detected by the high energy detector 42. Next, at the detection timing of the third line, the low energy detector 32 can detect the pixel data C and the high energy detector 42 can detect the pixel data C + B. Next, at the detection timing of the fourth line, the low energy detector 32 can detect the pixel data D and the high energy detector 42 can detect the pixel data D + C. Next, at the detection timing of the fifth line, the low energy detector 32 can detect the pixel data E and the high energy detector 42 can detect the pixel data E + D. Next, at the detection timing of the sixth line, the low energy detector 32 can detect the pixel data F and the high energy detector 42 can detect the pixel data F + E. Next, at the detection timing of the seventh line, the low energy detector 32 can detect the pixel data G and the high energy detector 42 can detect the pixel data G + F. Next, at the detection timing of the eighth line, the noise N can be detected by the low energy detector 32 and the noise N + pixel data G can be detected by the high energy detector 42.

  Then, for the difference processing, the correction circuit 34c in the low energy image correction unit 34 performs correction processing for aligning the pixel data on the low energy detector 32 side and the pixel data on the high energy detector 42 side. Specifically, the correction circuit 34c in the low energy image correction unit 34 is based on the ratio Wb2 / Wb1 between the pixel width Wb1 of the pixel 326 in the low energy detector 32 and the pixel width Wb2 of the pixel 426 in the high energy detector 42. Thus, the continuous Wb2 / Wb1 pixel data in the image from the low energy detector 32 is added.

  In this embodiment, since Wb2 / Wb1 = 2, as shown in FIG. 8, the correction circuit 34c adds the pixel data A detected one line before to the pixel data B detected on the second line and corrects it. Data B + A is generated, and pixel data B detected one line before is added to pixel data C detected on the third line to generate correction data C + B, and pixel data D detected on the fourth line is generated one line before The detected pixel data C is added to generate correction data D + C, and the pixel data E detected one line before is added to the pixel data E detected in the fifth line to generate correction data E + D. In the sixth line The correction data F + E is generated by adding the pixel data E detected one line before to the detected pixel data F, and the pixel data F detected one line before is added to the pixel data G detected at the seventh line. Generating the correction data G + F. In this way, the correction circuit 34c generates correction data B + A, C + B, D + C, E + D, F + E, and G + F corresponding to each of the pixel data B + A, C + B, D + C, E + D, F + E, and G + F on the high energy detector 42 side. To do.

  As described above, according to the radiation detection apparatus 80 of the present embodiment, the timing control unit 50 synchronizes the detection timing of the high energy detector 42 with the detection timing of the low energy detector 32, so at one detection timing. The high energy detector 42 acquires pixel data having a ratio Wb2 / Wb1 times of the pixel width Wb1 and the pixel width Wb2 in the transport direction Y to the low energy detector 32. Then, by the correction circuit 34c in the low energy image correction unit 34, continuous Wb2 / Wb1 pixel data in the image from the low energy detector 32 is obtained based on the ratio Wb2 / Wb1 between the pixel width Wb1 and the pixel width Wb2. Since the addition is performed, the number of pixels of the image from the low energy detector 32 after correction and the number of pixels of the image from the high energy detector 42 can be made equal. Therefore, even when the pixel width Wb1 in the image conveyance direction Y in the low energy detector 32 is smaller than the pixel width Wb2 in the pixel conveyance direction Y in the high energy detector 42, that is, the low energy detector 32. Even if the number of pixels in the high-energy detector 42 is different from the number of pixels in the high-energy detector 42, arithmetic processing based on the radiation image by the low-energy detector 32 and the radiation image by the high-energy detector 42, for example, subtraction processing can be facilitated. it can.

  FIG. 9 is a diagram illustrating an image (a) detected by the low energy detector 32 and an image (b) detected by the high energy detector 42 when the detection timing control and the image correction processing of the present embodiment are not performed. FIG. 10 shows an image (a) detected by the low energy detector 32 and an image (b) detected by the high energy detector 42 when the detection timing control and image correction processing of this embodiment are performed. FIG. FIG. 11 is a subtraction image based on the image shown in FIG.

  As shown in FIG. 9, the number of pixels in the conveyance direction Y of the image from the low energy detector 32 and the number of pixels in the conveyance direction Y of the image from the high energy detector 42 are different. It is difficult to generate a subtraction image.

  As shown in FIG. 10, by equalizing the number of pixels in the conveyance direction Y of the image from the low energy detector 32 and the number of pixels in the conveyance direction Y of the image from the high energy detector 42, FIG. As shown, it can be seen that a subtraction image in which only a desired substance is raised can be easily obtained.

  The present invention is not limited to the above-described embodiment, and various modifications can be made.

  In the present embodiment, the timing control unit 50, the low energy image correction unit 34, and the high energy image correction unit 44 are configured by hardware. However, the timing control unit 50, the low energy image correction unit 34, and the high energy image correction unit 44 are configured by hardware. The image correction unit 44 may be realized by software processing in an external computer, for example. That is, the timing control unit and the image correction unit of the present invention may be realized by a computer program, and the detection timing control process and the pixel correction process of the present invention may be processed by software.

  In the present embodiment, the case where the low energy detector 32 and the high energy detector 42 are arranged so that the left ends are aligned is illustrated. However, the arrangement of the low energy detector 32 and the high energy detector 42 is as follows. Various forms are possible. For example, the low energy detector 32 and the high energy detector 42 may be arranged so that the central axes are aligned.

  As described above, various arrangements of the low energy detector 32 and the high energy detector 42 can be considered. Depending on the arrangement, the detection timing of the low energy detector 32 and the high energy detection can be determined. It is preferable to delay one of the detection timings of the detector 42.

  FIG. 12 is a diagram showing a luminance file of an image when the same inspection object is detected. The inspection object has a high transmittance portion having a length corresponding to three pixels. In FIG. 12A, the high transmittance portion of the inspection object can be detected at the detection time points 4 to 7. The detection timing is adjusted. On the other hand, 12 (b) is a luminance file when the detection timing is shifted by 1/2 pixel with respect to FIG. 12 (a), and FIG. 12 (c) is detected with respect to FIG. 12 (a). This is a luminance file when the timing is shifted by 1/4 pixel.

  FIG. 13 is a diagram illustrating a luminance file of a subtraction image based on an image having the luminance file shown in FIG. FIG. 13A shows a luminance file of a subtraction image based on an image having the luminance file shown in FIG. 12A and an image having the luminance file shown in FIG. 12B, that is, an image whose detection timing is shifted by 1/2 pixel. This is a luminance file of a subtraction image by. According to FIG. 13A, a pseudo edge in the positive direction is generated before and after the high transmittance portion of the inspection object. The occurrence of the pseudo edge in the positive direction causes the generation of a white edge, which will be described later, in the subtraction image. On the other hand, FIG. 13B shows the luminance file of the subtraction image by the image having the luminance file of FIG. 12A and the image having the luminance file shown in FIG. 12C, that is, the detection timing is shifted by 1/4 pixel. It is a luminance file of the subtraction image by the obtained image. According to FIG. 13B, a pseudo edge in the positive direction occurs before the high transmittance portion of the inspection object, and a pseudo edge in the negative direction occurs after the high transmittance portion of the inspection object. Yes. The occurrence of a pseudo edge in the positive direction causes a white edge to be described later in the subtraction image, and the occurrence of a pseudo edge in the negative direction causes a black edge to be described later in the subtraction image.

  FIG. 14 is a diagram illustrating an example of a subtraction image using two images having different detection timings. According to FIG. 14, a white edge is generated in the lower part of each substance in the inspection object, and a black edge is generated in the upper part. As described above, when the detection timings of the detection points of the inspection object are greatly different in the two detectors, a good subtraction image may not be obtained.

  In such a case, the low energy detector 32 can reduce the displacement between the detection position of the inspection object at the detection timing of one detector and the detection position of the inspection object at the detection timing of the other detector. It is preferable to delay either the detection timing or the detection timing of the high energy detector 42. For example, as shown in FIG. 6, when the low energy detector 32 detects the third line, only the pixel data C is detected without including the adjacent pixel data B and D, and the high energy detector 42 detects the third line. It is only necessary to give a delay time to one of the detection timings so that only the pixel data B + C is detected without detecting the adjacent pixel data A and D at the time of detection.

  According to the study by the inventors of the present application, the position shift between the detection position of the inspection object at the detection timing of one detector and the detection position of the inspection object at the detection timing of the other detector is low energy detection. If the pixel width Wb1 of the pixel 326 in the device 32 is 0.3 times or less, the generation of white edges and black edges in the subtraction image can be reduced. In other words, the displacement between the detection position of the inspection object at the detection timing of one detector and the detection position of the inspection object at the detection timing of the other detector is the pixel width of the pixel 326 in the low energy detector 32. When it exceeds 0.3 times Wb1, as described above, the displacement between the detection position of the inspection object at the detection timing of one detector and the detection position of the inspection object at the detection timing of the other detector Therefore, it is necessary to adjust the delay time of one of the detection timing of the low energy detector 32 and the detection timing of the high energy detector 42.

  In the present embodiment, the area S1 of each of the plurality of pixels 326 in the line sensor 324 of the low energy detector 32 is made smaller than the area S2 of each of the plurality of pixels 426 in the line sensor 424 of the high energy detector 42. Although the pixel width Wb1 of each pixel 326 is made smaller than the pixel width Wb2 of each pixel 426, the pixel width Wa1 of each pixel 326 may be made smaller than the pixel width Wa2 of each pixel 426 as shown in FIG. Good. In this way, when the number of pixels in the detection direction X is different, image thinning processing is performed in one radiation detector or image interpolation processing is performed in the other radiation detector so that the number of pixels is the same. You may go.

  DESCRIPTION OF SYMBOLS 1 ... X-ray foreign material inspection apparatus, 10 ... Belt conveyor, 12 ... Belt part, 14 ... Belt conveyor control part, 20 ... X-ray irradiator, 30 ... Low energy image acquisition part, 32 ... Low energy detector (1st radiation) Detector), 322 ... Low energy scintillator layer (first scintillator layer), 324 ... Low energy line sensor (first pixel unit), 326 ... Pixel, 34 ... Low energy image correction unit (image correction unit), 34a ... Amplifier 34b ... A / D converter, 34c ... correction circuit, 34d ... output interface, 40 ... high energy image acquisition unit, 42 ... high energy detector (second radiation detector), 422 ... high energy scintillator layer (second Scintillator layer), 424 ... high energy line sensor (second pixel unit), 426 ... pixel, 44 ... high energy image correction unit, 44a ... amplifier, 44b ... A / Conversion unit, 44c ... correction circuit, 44d ... output interface, 50 ... timing controller, 60 ... timing calculation unit, 70 ... image processing apparatus, 80 ... radiation detection device, 86 ... dual energy sensor.

Claims (7)

A belt conveyor that conveys the inspection object in the conveying direction;
A radiation irradiation device that irradiates radiation in a radiation irradiation direction orthogonal to the transport direction;
A first radiation detector positioned upstream from the radiation irradiation direction, detecting radiation in a first energy range, and generating first image data corresponding to the radiation image;
A second detector that is positioned downstream of the radiation irradiation direction and detects radiation in a second energy range higher than radiation in the first energy range, and generates second image data corresponding to the radiation image. Two radiation detectors;
A timing controller for controlling the detection timing of the first radiation detector and the detection timing of the second radiation detector;
An image processing unit that performs subtraction processing based on the first image data and the second image data,
The first radiation detector includes a first line sensor having a plurality of first pixels arranged along an image detection direction,
The second radiation detector includes a second line sensor having a plurality of second pixels arranged along the image detection direction,
The pixel width Wb1 in the orthogonal direction orthogonal to the image detection direction of the first pixel is smaller than the pixel width Wb2 in the orthogonal direction of the second pixel,
The image processing unit performs correction processing for correcting the first image data to image data for subtraction processing based on a ratio between the pixel width Wb1 and the pixel width Wb2.
A foreign matter inspection apparatus characterized by the above. The timing control unit synchronizes the detection timing of the second radiation detector with the detection timing of the first radiation detector,
The radiation foreign material inspection apparatus according to claim 1. The timing control unit delays either one of the detection timing of the first radiation detector and the detection timing of the second radiation detector,
The radiation foreign material inspection apparatus according to claim 1. The first radiation detector and the second radiation detector are a detection position of the inspection object based on a detection timing of the first radiation detector and detection of the inspection object based on a detection timing of the second radiation detector. It is arranged so that the positional deviation from the position is 0.3 times or less of the pixel width Wb1,
The radiation foreign material inspection apparatus according to claim 1. The first radiation detector extends along the image detection direction, and converts a radiation image in the first energy range into an optical image, and light converted by the first scintillator layer. The first line sensor for acquiring the first image data by an image;
The second radiation detector extends along the image detection direction, converts a radiation image in the second energy range into an optical image, and light converted by the second scintillator layer. The second line sensor for acquiring the second image data by an image,
The radiological foreign material inspection apparatus of any one of Claims 1-4. The image processing unit performs addition processing of the first image data as the correction processing.
The radiation foreign material inspection apparatus of any one of Claims 1-5. A pixel width Wa1 in the image detection direction of the first pixel is smaller than a pixel width Wa2 in the image detection direction of the second pixel.
The radiation foreign material inspection apparatus of any one of Claims 1-6.