JP2009080030A - X-ray inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand the size range of an foreign material detectable by a same X-ray detection device more than conventional range. <P>SOLUTION: An X-ray inspection device 10 includes a conveyer 12, an X-ray irradiator 13, an X-ray line sensor module 14 and a control computer 20. The conveyer 12 delivers a commodity G to a predetermined delivery direction. The X-ray irradiator 13 irradiates an X-ray to the commodity G while being delivered. The X-ray line sensor module 14 includes a photo diode 14a. The photo diode 14a outputs an X-ray fluoroscopic image signal in accordance with an intensity of the X-ray transmitted through the commodity G with an predetermined scanning interval Ts. The control computer 20 inspects a contamination of a foreign material to the commodity G based on the X-ray fluoroscopic image signal. A first value is shortened or prolonged than a second value. The first value is a Ps value which is the scanning interval Ts converted to the length of the delivery direction. The second value is L representing the length of the photo diode 14a in the delivery direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an X-ray inspection apparatus, and more particularly to an X-ray inspection apparatus characterized by a scanning interval of an X-ray detection unit.

In a production line for commodities such as food, inspection may be performed by an X-ray inspection apparatus as shown in Patent Document 1, for example, so as not to ship commodities mixed with foreign matters. In such an X-ray inspection apparatus, an X-ray is irradiated to an article (product) conveyed by a conveyor (conveying unit), and the intensity of the X-ray transmitted through the article is detected. An X-ray fluoroscopic image signal corresponding to the strength is output, and based on the X-ray fluoroscopic image signal, it is determined whether or not a foreign substance that greatly attenuates X-rays is mixed in the article.
Japanese Patent Laid-Open No. 10-318943

  An example of an X-ray detection element often used in a conventional X-ray inspection apparatus is a photodiode. In many cases, an X-ray detection module including a photodiode includes a scintillator that emits light according to the intensity of received X-rays. The photodiode generates and accumulates current according to the amount of light from the scintillator, converts the accumulated charge amount into an electrical signal (X-ray fluoroscopic image signal) at a predetermined time interval (scanning interval), and outputs it. .

  Normally, this time interval is set in advance to a time required for the article to be moved by the distance L by the conveyance unit, where L is the length of the photodiode in the conveyance direction of the article. That is, each time the article is moved by the distance L, the photodiode outputs an X-ray fluoroscopic image signal corresponding to the amount of charge accumulated during that time. By doing so, it is considered that any part of the article can be imaged without omission and duplication.

  Therefore, in the conventional X-ray inspection apparatus, the size range of the foreign matter that can be detected is determined by the size of the X-ray detection element. In other words, the size range of the foreign matter that can be detected is determined when the X-ray detection module is provided in the main body of the X-ray inspection apparatus. With this, one X-ray detection module cannot sufficiently cope with a wide variety of foreign matters.

  An object of the present invention is to expand the range of the size of a foreign object that can be detected by the same X-ray detection element as compared with the prior art.

  The X-ray inspection apparatus according to the first invention includes a transport unit, an X-ray irradiation unit, an X-ray detection unit, and a signal processing unit. The conveyance unit conveys the article in a predetermined conveyance direction. The X-ray irradiation unit irradiates the article being conveyed with X-rays. The X-ray detection unit has an element. The element outputs a detection signal corresponding to the intensity of the X-ray transmitted through the article at a predetermined scanning interval. The signal processing unit inspects contamination of the article based on the detection signal. The first value is shorter or longer than the second value. The first value is a value obtained by converting the scanning interval into a length in the transport direction. The second value is a value indicating the length of the element in the transport direction.

  Here, the scanning interval of the X-ray detection unit is set to a value shorter or longer than in the past. When the scanning interval of the X-ray detection unit is shortened and the resolution is increased, the detection accuracy of relatively small foreign matters (particularly, foreign matters having a diameter smaller than the length L in the element transport direction) by the signal processing unit is improved. If the scanning interval of the detection unit is increased and the resolution is lowered, the detection accuracy of relatively large foreign matters (particularly, foreign matters having a diameter larger than the length L in the element transport direction) by the signal processing portion is improved. That is, the range of the size of the foreign matter that can be detected by the same X-ray detection element is expanded as compared with the conventional case.

  The X-ray inspection apparatus according to the second invention is the X-ray inspection apparatus according to the first invention, wherein the first value is shorter than the second value.

  As described above, in the conventional X-ray inspection apparatus, every time the article is moved by the transport unit by the distance L (same as the length in the transport direction of the element), the element responds to the intensity of the X-ray received during that time. The detection signal is output. On the other hand, the inventors of the present application have found that when the scanning interval of the X-ray detection unit is shortened, detection accuracy of small foreign matters, particularly foreign matters having a diameter smaller than the length L in the transport direction of the element, is increased. This was confirmed by experiments. Details of the experimental results will be described later. “Reducing the scanning interval” means that each time the article is moved a predetermined distance shorter than the distance L by the transport unit (in other words, a predetermined time shorter than the time required for the article to move the distance L). Is to output an X-ray detection signal to the element.

  Here, as a device for improving the detection accuracy of the foreign matter, a technique is adopted in which the element is left as it is and the scanning interval of the X-ray detection unit is shortened instead of downsizing the element.

  As a result, it is possible to improve the detection accuracy of small foreign matters, particularly foreign matters having a diameter smaller than the length L of the element in the transport direction.

  An X-ray inspection apparatus according to a third aspect is the X-ray inspection apparatus according to the first aspect, wherein the first value is extended from the second value.

  As described above, in the conventional X-ray inspection apparatus, every time the article is moved by the transport unit by the distance L (same as the length in the transport direction of the element), the element responds to the intensity of the X-ray received during that time. The detection signal is output. On the other hand, here, every time the article is moved a predetermined distance longer than the distance L by the transport unit (in other words, a predetermined time longer than the time required for the article to move the distance L elapses). The device outputs an X-ray detection signal. When the resolution is lowered in this way, detection accuracy of a large foreign object, particularly a foreign object having a diameter larger than the length L in the transport direction of the element is improved.

  In addition, it is considered that the reason why the detection accuracy of a relatively large foreign object is improved when the resolution is lowered is as follows.

  When the resolution is lowered, that is, the pixel size is increased, one foreign object image is easily contained in one pixel. Then, the influence of the X-ray attenuated by one foreign substance is reflected in the density value of one pixel. On the other hand, when the resolution is high and the pixel size is small, the influence of one foreign substance is distributed to a large number of pixels, and the influence of the foreign substance appearing in the density value of one pixel is relatively reduced. Therefore, when the resolution is high, the presence of a foreign object is stably detected when trying to detect the presence of a foreign object based on the difference between the density value of a pixel that captures a foreign object and the density value of a pixel that does not capture a foreign object. I can't do that.

  Conventionally, under the technical idea that “if the resolution is high, a small foreign object can be detected, and a large foreign object can be detected,” a large foreign object has been subjected to detection processing at a high resolution. However, in the present application, for a large foreign matter, a new technique that the accuracy of foreign matter inspection is improved by reducing the resolution so as to increase the size of one pixel, that is, the size of the element, rather than the size of the foreign matter. An X-ray inspection apparatus is configured based on the idea.

  Thereby, it is possible to improve the detection accuracy of a large foreign object, particularly a foreign object having a diameter larger than the length L in the carrying direction of the element.

  An X-ray inspection apparatus according to a fourth invention is the X-ray inspection apparatus according to any one of the first to third inventions, further comprising a setting changing unit. The setting change unit is for changing the scanning interval.

  Here, the setting of the scanning interval of the X-ray detector can be changed. Note that this setting change may be performed, for example, by manual input by an operator, or may be automatically performed when a predetermined condition is satisfied. Further, when the setting is changed by manual input, it may be possible to directly input the change of the scanning interval, or to input the change of the parameter that can indirectly specify the scanning interval. You may be able to. The parameters that can indirectly specify the scanning interval include, for example, the scanning pitch (the distance traveled by the article at each scanning interval) and the exposure time (the time during which the article is irradiated with X-rays at each scanning interval). To tell. Thereby, one X-ray inspection apparatus can be used for detection of various foreign substances.

  An X-ray inspection apparatus according to a fifth aspect is the X-ray inspection apparatus according to the fourth aspect, wherein the setting changing unit changes the dose of the X-ray irradiation unit according to the set scanning interval.

  Here, when the scanning interval of the X-ray detection unit is changed, the X-ray irradiation amount from the X-ray irradiation unit is automatically changed accordingly. For example, when the scanning interval is lengthened, the irradiation amount is decreased so that the element is not saturated. Conversely, when the scanning interval is shortened, the irradiation amount is increased. As a result, foreign objects can be detected with high accuracy while avoiding overexposure and underexposure.

  An X-ray inspection apparatus according to a sixth aspect of the present invention is the X-ray inspection apparatus according to any of the first to fifth aspects of the present invention, further comprising an image generation unit. The image generation unit generates an X-ray image by connecting density values indicated by detection signals obtained at scanning intervals in time series. The signal processing unit inspects contamination of the article by performing image processing on the X-ray image.

  Here, the presence of a foreign object is detected by image processing on an X-ray image.

  An X-ray inspection apparatus according to a seventh aspect of the present invention is the X-ray inspection apparatus according to the sixth aspect of the present invention, further comprising a display unit. The display unit deforms and displays the X-ray image in the transport direction at a predetermined magnification. The predetermined magnification is a value obtained by dividing the first value by the second value.

  When the scanning interval of the X-ray inspection unit is shortened or extended, the obtained X-ray image is also stretched or compressed in the transport direction. Here, when the scanning interval is shortened and the X-ray image is stretched, the display image is compressed by that amount, while when the scanning interval is extended and the X-ray image is compressed, Enlarge the display image accordingly. This makes it easier for a person viewing the X-ray image on the display unit to recognize the actual state of the article.

  An X-ray inspection apparatus according to an eighth invention is the X-ray inspection apparatus according to any one of the first to seventh inventions, wherein the first value is 2/3 or less of the second value.

  Here, the ratio of the value obtained by converting the scanning interval to the length in the transport direction and the length in the transport direction of the element is 2: 3.

  In the present invention, the scanning interval of the X-ray detection unit is set to a value that is shorter or longer than the conventional one. When the scanning interval of the X-ray detection unit is shortened and the resolution is increased, the detection accuracy of relatively small foreign matters (particularly, foreign matters having a diameter smaller than the length L in the element transport direction) by the signal processing unit is improved. If the scanning interval of the detection unit is increased and the resolution is lowered, the detection accuracy of relatively large foreign matters (particularly, foreign matters having a diameter larger than the length L in the element transport direction) by the signal processing portion is improved. That is, the range of the size of the foreign matter that can be detected by the same X-ray detection element is expanded as compared with the conventional case.

  Hereinafter, an X-ray inspection apparatus 10 according to an embodiment of the present invention will be described with reference to the drawings.

<Configuration of X-ray inspection apparatus>
FIG. 1 shows the appearance of the X-ray inspection apparatus 10. The X-ray inspection apparatus 10 is an apparatus for inspecting the quality of the product G by irradiating the product G that is continuously conveyed with X-rays, which is incorporated in the production line of the product G such as food. is there. The X-ray inspection apparatus 10 inspects the presence or absence of foreign matter in the product G as one quality inspection. The foreign substance to be detected in this foreign substance contamination inspection is a substance that can greatly attenuate X-rays, and is mainly metal.

  As shown in FIG. 6, the product G as a specimen is carried to the X-ray inspection apparatus 10 by the front conveyor 60. The product G is classified as a non-defective product or a defective product in the X-ray inspection apparatus 10. The inspection result in the X-ray inspection apparatus 10 is sent to a distribution mechanism 70 disposed on the downstream side of the X-ray inspection apparatus 10. The distribution mechanism 70 sends the product G determined to be a non-defective product in the X-ray inspection apparatus 10 to the regular line conveyor 80, and the product G determined to be a defective product in the X-ray inspection apparatus 10 to the defective product storage conveyor 90. And send.

  As shown in FIGS. 1, 2 and 5, the X-ray inspection apparatus 10 includes a shield box 11, a conveyor 12, an X-ray irradiator 13, an X-ray line sensor module 14, an LCD monitor 30 with a touch panel function, and a control computer. 20 or the like.

[Shield box]
On both side surfaces of the shield box 11, openings 11 a for allowing the product G to be carried in and out of the shield box 11 are formed. The opening 11 a is blocked by a shielding nolen 16 in order to prevent leakage of X-rays to the outside of the shield box 11. The shielding nolen 16 is molded from rubber containing lead, and is pushed away by the product G when the product G passes through the opening 11a.

  The shield box 11 contains a conveyor 12, an X-ray irradiator 13, an X-ray line sensor module 14, a control computer 20, and the like. Further, in addition to the LCD monitor 30, a key slot, a power switch, and the like are disposed on the upper front portion of the shield box 11.

〔Conveyor〕
The conveyor 12 conveys the commodity G in the shield box 11 and is disposed so as to penetrate through the openings 11a formed on both side surfaces of the shield box 11 as shown in FIG. And the conveyor 12 conveys the goods G mounted on the belt, rotating an endless belt with the drive roller driven by the conveyor motor 12a (refer FIG. 5).

  The conveyance speed by the conveyor 12 is finely controlled by the inverter control of the conveyor motor 12a by the control computer 20 so as to be the set speed input by the operator. The conveyor motor 12a is equipped with an encoder 12b (see FIG. 5) that detects the conveying speed of the conveyor 12 and sends it to the control computer 20.

[X-ray irradiator]
As shown in FIG. 2, the X-ray irradiator 13 is an X-ray source disposed above the central portion of the conveyor 12, and the X-ray irradiator 13 enters the fan-shaped irradiation range X toward the X-ray line sensor module 14 below. Irradiate the line.

[X-ray line sensor module]
As shown in FIG. 4, the X-ray line sensor module 14 is disposed below the conveyor 12 and detects X-rays that pass through the product G and the conveyor 12. As shown in FIGS. 2 and 4, the X-ray line sensor module 14 includes a number of photodiodes 14 a (in a straight line in a direction perpendicular to the conveying direction of the conveyor 12 and parallel to the conveying surface of the conveyor 12. Pixel sensor). The photodiode 14a is mounted on the substrate. The X-ray line sensor module 14 has a scintillator 14b as shown in FIG. The scintillator 14b is disposed on the photodiode 14a. In the present embodiment, fluorescent paper is used as the scintillator 14b. The scintillator 14b converts X-rays incident from above into light, and causes the light to enter the photodiode 14a below. The photodiode 14a generates and accumulates current in accordance with the amount of light from the scintillator 14b, converts the accumulated amount of electric charge into an electric signal, and outputs it to the control computer 20 as an X-ray fluoroscopic image signal. The X-ray line sensor module 14 repeats such scanning processing at a preset scanning interval Ts.

  As shown in FIG. 3, in this embodiment, the length L of each photodiode 14a is 0.6 mm, and the width W is 0.3 mm. Note that the length L is based on the direction of conveyance by the conveyor 12, and the width W is based on the direction in which many photodiodes 14a are aligned. The pitch P between the multiple photodiodes 14a arranged in a row is 0.4 mm.

[LCD monitor]
The LCD monitor 30 is a full-dot liquid crystal display, and displays an X-ray image and a determination result of the presence or absence of foreign matter. The LCD monitor 30 also has a touch panel function, displays a screen that prompts the operator to input inspection parameters necessary for inspection, and accepts input of inspection parameters from the operator.

[Control computer]
As shown in FIG. 5, the control computer 20 inserts a CPU (Central Processing Unit) 21, ROM (Read Only Memory) 22, RAM (Random Access Memory) 23, HDD (Hard Disk) 25, storage media, and the like. The drive 24 is mounted.

  In the CPU 21, various programs stored in the ROM 22 and the HDD 25 are executed. The HDD 25 stores and accumulates inspection parameters and inspection results. The inspection parameter can be changed by an input from the operator using the touch panel function of the LCD monitor 30. The operator can set so that these data are stored and accumulated not only in the HDD 25 but also in a storage medium inserted in the drive 24.

  Further, the control computer 20 includes a display control circuit (not shown) for controlling data display on the LCD monitor 30, and a key input circuit (not shown) for fetching key input data input by the operator via the LCD monitor 30. A communication port (not shown) that enables connection with an external device such as a printer or a network such as a LAN (local area network) is also provided.

  And each part 21-25 of the control computer 20 is mutually connected via bus lines, such as an address bus and a data bus.

  The control computer 20 is connected to a conveyor motor 12a, an encoder 12b, a photoelectric sensor 15, an X-ray irradiator 13, an X-ray line sensor module 14, an LCD monitor 30, and the like.

  The photoelectric sensor 15 is a synchronous sensor for detecting the timing when the product G as a specimen passes through the fan-shaped X-ray irradiation range X (see FIG. 2), and is mainly a pair of sensors arranged with the conveyor 12 interposed therebetween. It consists of a projector and a light receiver.

<Operation of X-ray inspection apparatus>
[Setting change of scanning interval Ts by operator]
The operator can change the setting of the scanning pitch Ps (first value) of the X-ray line sensor module 14 using the touch panel function of the LCD monitor 30 at the time of calibration prior to actual inspection processing. The scanning pitch Ps is the moving distance of the product G by the conveyor 12 from the time when the photodiode 14a outputs the X-ray fluoroscopic image signal to the next time it outputs it. That is, each time the product G is moved by the conveyor 12 by a distance equal to the scanning pitch Ps, the photodiode 14a outputs an X-ray fluoroscopic image signal corresponding to the amount of charge accumulated during that time.

  The default value of the scanning pitch Ps is set to a value equal to the length L (second value) of the photodiode 14a (0.6 mm in this embodiment). The operator can change the scanning pitch Ps so as to be shorter or longer than the default value according to the size of the foreign object to be detected. More specifically, the scanning pitch Ps is changed to 1/4 times, 1/3 times, 1/2 times, 2/3 times, 3/2 times, 2 times, 3 times, 4 times the default value. be able to.

  When the scanning pitch Ps is changed to any one of the default value 1/4, 1/3, 1/2, and 2/3, that is, the scanning interval Ts of the X-ray line sensor module 14 is shortened, When the resolution of the X-ray image of the product G is increased, a relatively small foreign object in the foreign object detection process by the control computer 20 (particularly, a foreign object having a smaller diameter in the conveying direction by the conveyor 12 than the length L of the photodiode 14a). The detection accuracy will be improved. On the other hand, when the scanning pitch Ps is changed to any one of 3/2 times, 2 times, 3 times, and 4 times of the default value, that is, the scanning interval Ts of the X-ray line sensor module 14 is increased, When the resolution of the line image is lowered, the detection accuracy of a relatively large foreign object (particularly, a foreign object having a diameter larger in the conveyance direction by the conveyor 12 than the length L of the photodiode 14a) in the foreign object detection process by the control computer 20 is improved. Will improve.

  When the operator inputs a change in the scanning pitch Ps via the LCD monitor 30, the input information is sent from the LCD monitor 30 to the control computer 20. On the other hand, the control computer 20 converts the scanning pitch Ps into the scanning interval Ts of the X-ray line sensor module 14 based on the conveying speed of the conveyor 12, and performs the scanning process at the scanning interval Ts. The control parameters relating to the scanning process are changed. Note that the operator can also change the conveying speed of the conveyor 12 using the touch panel function of the LCD monitor 30 by the operator.

  Further, the control computer 20 determines the irradiation amount by the X-ray irradiator 13 in accordance with the calculated scanning interval Ts, and changes the control parameter of the X-ray irradiator 13 so as to perform irradiation with the irradiation amount. It is assumed that the control computer 20 holds in advance a calculation formula that can calculate the dose based on the scanning interval Ts. According to this calculation formula, the longer the scanning pitch Ps, the smaller the irradiation amount so that the pixels of the X-ray image do not overshoot, and the shorter the scanning pitch Ps, the smaller the pixels of the X-ray image. The amount of irradiation increases so as not to black out.

[X-ray image creation processing and display processing]
The control computer 20 determines the X-ray fluoroscopic image signals output from the photodiodes 14a of the X-ray line sensor module 14 when the product G passes the fan-shaped X-ray irradiation range X (see FIG. 2) at fine time intervals. An X-ray image of the product G is created based on the acquired X-ray fluoroscopic image signal acquired at (scan interval Ts). The timing at which the product G passes through the fan-shaped X-ray irradiation range X is determined by a signal from the photoelectric sensor 15. That is, the control computer 20 connects the data for each scanning interval Ts related to the X-ray density value obtained from each photodiode 14a of the X-ray line sensor module 14 in a matrix form in time series, thereby copying the product G. Create a line image.

  The control parameters used for the X-ray image creation process are not changed by changing the setting of the scanning pitch Ps. Therefore, in the X-ray image obtained, when the scanning pitch Ps is set to be shorter than the default value (L = 0.6 mm), L / Ps (> 1) in the conveyance direction of the product G If the scanning pitch Ps is set to be longer than the default value (L = 0.6 mm), the ratio of L / Ps (<1) in the conveyance direction of the product G Will be compressed.

  Therefore, when displaying the X-ray image of the product G on the LCD monitor 30, the control computer 20 stretches or compresses the X-ray image to be displayed in the conveyance direction of the product G. More specifically, when the scanning pitch Ps is set to be shorter than the default value (L = 0.6 mm), the X-ray image is Ps / L (<1) in the conveyance direction of the product G. When the scanning pitch Ps is set to be longer than the default value (L = 0.6 mm), the X-ray image is Ps / L (> 1) in the conveyance direction of the product G. Stretch at a rate of. Thereby, the operator who visually recognizes the X-ray image displayed on the LCD monitor 30 can grasp the actual state of the product G more accurately.

[Foreign matter detection processing]
The control computer 20 performs image processing on the X-ray image obtained by the image creation processing to determine whether foreign matter is mixed in the product G. There are two determination methods (trace detection method and binarization detection method) as image processing methods employed in the foreign object inspection. As a result of the determination based on these determination methods, if a foreign object is detected in the process based on at least one method, the product G is handled as a defective product. In this case, the control computer 20 displays a defective product on the LCD monitor 30 and sends an instruction to the distribution mechanism 70 to distribute the product G to the defective product storage conveyor 90.

  In the trace detection method, a threshold value is set in advance along the rough thickness of the product G, and foreign matter is mixed into the product G when there is an area that appears darker than the threshold on the X-ray image of the product G. It is a method to judge that. In this method, it is possible to detect a relatively small foreign object.

  The binarization detection method is a method for determining that a foreign matter is mixed in the product G when there is an area that appears darker than a preset threshold on the X-ray image of the product G. With this method, it is possible to detect a relatively large foreign object.

  It is also possible to set a mask on the X-ray image. A mask is set with respect to the container part etc. of the goods G, for example. When a mask is set, processing similar to the above method is performed on an unmasked region of the X-ray image.

  Note that the threshold value and mask in each method can be changed by the operator using the touch panel function of the LCD monitor 30.

<Characteristics of X-ray inspection equipment>
In the conventional method, the scanning interval Ts of the X-ray line sensor module 14 is set in advance to the time required for the conveyor 12 to move the product G by a distance equal to the length L of the photodiode 14a. Each time the product G moves a distance L, X-rays (more specifically, X-rays transmitted through a minute part of the product L of length L in the movement direction) by the photodiode 14a of length L in the movement direction. This is because, if it is detected, it is considered that any part of the article is imaged without omission and duplication.

  However, the inventor of the present application has found that the size of the foreign matter that can be detected in the foreign matter detection process is reduced when the scanning interval Ts is shorter than a value set under such a conventional idea. The X-ray inspection apparatus 10 is designed based on such a discovery, and the setting of the scanning interval Ts can be changed.

  Conventionally, as a device for increasing the sharpness of an X-ray image in order to increase the detection accuracy of small foreign matter, a method of downsizing a photodiode has been employed. However, such a method increases the processing load, decreases the inspection speed, and requires a more expensive X-ray line sensor module. Moreover, the range of the size of the foreign matter that can be detected without replacing the X-ray line sensor module is also narrow.

  On the other hand, in the present application, by changing the setting in software so as to shorten the scanning interval Ts, the X-ray line sensor module is not replaced, and the foreign matter, in particular, the length L of the photodiode 14a is exceeded. It is possible to improve the detection accuracy of foreign matters having a small diameter. In particular, the present invention improves the detection accuracy of minute foreign substances contained in a specimen with a large background change such as udon and pilaf.

  On the contrary, if the setting is changed by software so as to increase the scanning interval Ts and the resolution is lowered, the X-ray line sensor module is not replaced, and a larger foreign matter, in particular, the length L of the photodiode 14a. In addition, it is possible to improve the detection accuracy of foreign matters having a large diameter.

  In addition, it is considered that the reason why the detection accuracy of a relatively large foreign object is improved when the resolution is lowered is as follows.

  When the resolution is lowered, that is, the pixel size is increased, one foreign object image is easily contained in one pixel. Then, the influence of the X-ray attenuated by one foreign substance is reflected in the density value of one pixel. On the other hand, when the resolution is high and the pixel size is small, the influence of one foreign substance is distributed to a large number of pixels, and the influence of the foreign substance appearing in the density value of one pixel is relatively reduced. Therefore, when the resolution is high, the presence of a foreign object is stably detected when trying to detect the presence of a foreign object based on the difference between the density value of a pixel that captures a foreign object and the density value of a pixel that does not capture a foreign object. I can't do that.

  Conventionally, under the technical idea that “if the resolution is high, a small foreign object can be detected, and a large foreign object can be detected,” a large foreign object has been subjected to detection processing at a high resolution. However, in the present application, “For a large foreign matter, the accuracy of foreign matter inspection is improved by reducing the resolution so that the size of one pixel, that is, the size of the X-ray detection element is larger than the size of the foreign matter”. The X-ray inspection apparatus 10 is configured based on a new technical idea.

<Modification>
[1]
In the above embodiment, the LCD monitor 30 receives an input for changing the scanning pitch Ps of the X-ray line sensor module 14, and the control computer 20 automatically calculates the scanning interval Ts based on the inputted scanning pitch Ps. Yes. However, the LCD monitor 30 may directly receive a change input of the scanning interval Ts, or may receive a change input of another parameter that can indirectly specify the scanning interval Ts. May be. As other parameters, for example, the exposure time during one scan and the size of the detection target foreign matter can be considered.

[2]
The length L, width W, and pitch P of the photodiode 14a are not limited to the values described above, and may be other sizes.

[3]
In the X-ray inspection apparatus 10, the scanning pitch Ps can be changed to 1/4 times, 1/3 times, 1/2 times, 2/3 times, 3/2 times, 2 times, 3 times, 4 times the default value. However, the setting may be changed at other magnifications. That is, for example, the scanning pitch Ps may be set to 1/4 times or less of the default value, or may be set to 4 times or more of the default value. Further, instead of the magnification, a specific value of the scanning pitch Ps may be set directly.

  Furthermore, the default value of the scanning pitch Ps is not limited to that described above. That is, the default value of the scanning pitch Ps may not be equal to the length L of the photodiode 14a.

[4]
In the foreign object detection process, a method other than the method described above can be adopted.

[5]
The processing related to the control computer 20 may be executed in an apparatus provided separately from the main body of the X-ray inspection apparatus 10. For example, various data may be sent from the control computer 20 to a separate computer via a network, and all or part of the above processing may be executed in the computer.

<Experimental result>
Hereinafter, the results of two experiments conducted to examine the relationship between the scanning pitch Ps of the X-ray line sensor module and the foreign matter detection accuracy will be described with reference to FIGS.

[Experiment 1]
In Experiment 1, two types of X-ray line sensor modules having photodiodes of length L were used, and the relationship between the modulation transfer function and the spatial frequency was examined while changing the scanning pitch Ps in four stages. The length L is based on the sample transport direction. More specifically, (L, Ps) = (0.60 mm, 0.60 mm), (0.60 mm, 0.40 mm), (0.60 mm, 0.30 mm), (0.60 mm, 0.20 mm) ), (0.90 mm, 0.90 mm), (0.90 mm, 0.60 mm), (0.90 mm, 0.45 mm), and (0.90 mm, 0.30 mm). FIG. 7 shows a plot of the relationship between the modulation transfer function and the spatial frequency. Note that the horizontal axis of the graph shown in FIG. 7, that is, the spatial frequency [LP / mm], indicates how many pairs of black and white line pairs are included per unit length (1.00 mm). That is, 1.00 LP / mm means that one black line of 0.50 mm and one white line of 0.50 mm are included in 1.00 mm.

  FIG. 8 summarizes the values of the spatial frequencies when the value of the modulation transfer function is 0.05 in each of the above eight cases. The resolution limit [mm] in FIG. 8 is a value obtained by dividing the reciprocal of the spatial frequency (total width of one line pair) by 2 (number of lines in one line pair). In general, it is said that the place where the value of the modulation transfer function is 0.05 is the human eye identification limit. Therefore, it can be said that the resolution limit shown in FIG. 8 represents the limit value of the width of the foreign matter that can be identified by the human eye.

  Further, FIG. 9 is a graph plotting the relationship between the resolution limit and the scanning pitch Ps shown in FIG.

  From Experiment 1, it can be seen that when the scanning pitch Ps is shortened, the resolution limit is also lowered, and the detection of a foreign substance having a smaller size becomes possible.

[Experiment 2]
In Experiment 2, a frozen udon pack mixed with six types of SUS (stainless steel) balls having diameters M = 0.30 mm, 0.40 mm, 0.50 mm, 0.60 mm, 0.70 mm, and 0.80 mm was used as a specimen. Whether a foreign object is actually detected after using an X-ray line sensor module having a photodiode with a length L = 0.60 mm and setting the scanning pitch Ps = 0.30 mm and 0.60 mm. No was measured. The length L is based on the sample transport direction.

  FIG. 10 shows the number of times a foreign object is detected when the measurement is performed 20 times for each condition.

  Similar to Experiment 1, it can also be seen from Experiment 2 that if the scanning pitch Ps is shortened, a foreign object with a smaller size can be detected. In particular, it can be seen that the detection accuracy of a foreign substance having a diameter smaller than the length L of the photodiode is increased.

  The present invention has an effect that the range of the size of a foreign object that can be detected by the same X-ray detection element is expanded as compared with the conventional technique, and is characterized by an X-ray inspection apparatus, in particular, an X-ray detection unit having a scanning interval. It is useful as a line inspection device.

1 is an external perspective view of an X-ray inspection apparatus. The schematic block diagram inside the shield box of a X-ray inspection apparatus. (A) A schematic plan view of an X-ray line sensor module. (B) A schematic side view of an X-ray line sensor module. The schematic diagram which shows the principle of a X-ray inspection. The control block diagram of a X-ray inspection apparatus. The figure which shows the mode before and behind an X-ray inspection apparatus. The figure which shows the graph which plotted the relationship between the spatial frequency in Experiment 1, and a modulation transfer function. The figure which shows the table | surface which shows the relationship between the scanning pitch in Experiment 1, a spatial frequency, and the resolution limit. The figure which shows the graph which plotted the relationship between the scanning pitch in Experiment 1, and a resolution limit. The figure which shows the result of the experiment 2. FIG.

Explanation of symbols

10 X-ray inspection device 12 Conveyor (conveyance unit)
13 X-ray irradiator (X-ray irradiation unit)
14 X-ray line sensor module (X-ray detector)
14a Photodiode (element)
14b Scintillator 20 Control computer (signal processing unit, setting change unit)
30 LCD monitor (display unit, setting change unit)
G Product (article)
L Photodiode length W Photodiode width P Photodiode pitch Ps Scanning pitch Ts Scanning interval

Claims (8)

A transport unit for transporting articles in a predetermined transport direction;
An X-ray irradiation unit for irradiating the article being conveyed with X-rays;
An X-ray detector having an element for outputting a detection signal corresponding to the intensity of the X-ray transmitted through the article at a predetermined scanning interval;
A signal processing unit for inspecting contamination of the article based on the detection signal;
With
The first value obtained by converting the scanning interval into the length in the transport direction is shorter or extended than the second value indicating the length of the element in the transport direction.
X-ray inspection equipment. The first value is shorter than the second value;
The X-ray inspection apparatus according to claim 1. The first value is longer than the second value,
The X-ray inspection apparatus according to claim 1. A setting changing unit for changing the scanning interval;
Further comprising
The X-ray inspection apparatus according to claim 1. The setting change unit changes an irradiation amount of the X-ray irradiation unit according to the set scanning interval.
The X-ray inspection apparatus according to claim 4. An image generating unit that generates an X-ray image by connecting the density values indicated by the detection signals obtained at the scanning interval in time series;
Further comprising
The signal processing unit inspects the contamination of the article by performing image processing on the X-ray image;
The X-ray inspection apparatus according to claim 1. A display unit that displays the X-ray image by deforming the X-ray image at a predetermined magnification in the transport direction;
Further comprising
The predetermined magnification is a value obtained by dividing the first value by the second value.
The X-ray inspection apparatus according to claim 6. The first value is 2/3 or less of the second value.
The X-ray inspection apparatus according to claim 1.

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