Mass estimation method and X-ray inspection device

Abstract

To provide a mass estimation method and an X-ray inspection device capable of accurately estimating the mass of an inspection object by calculating a weight vector using calibration X-ray transmission image data.SOLUTION: A mass estimation method includes: a step S7 of generating X-ray transmission image data for each transmission region of a sample of an inspection object; a step S8 of generating a histogram of a pixel value of a pixel corresponding to each transmission region included in each of the N pieces of X-ray transmission image data of the sample; a step S10 of generating a histogram matrix composed of N row vectors corresponding to the N histograms of the sample; a step S11 of calculating a weight vector that minimizes the variance of N relative mass estimation values obtained from the product of the histogram matrix and the weight vector composed of weight coefficients for each pixel value of the N pieces of X-ray transmission image data; and a step of estimating the mass of the inspection object using the weight vector.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a mass estimation method and an X-ray inspection apparatus for irradiating an object to be inspected with X-rays and estimating the mass based on the amount of transmitted X-rays. [Background technology]

[0002] X-ray inspection equipment generally emits X-rays with a width perpendicular to the direction of passage of the object being inspected, receives the X-rays that pass through the object with multiple sensor elements arranged in a direction perpendicular to the direction of passage of the object, obtains an X-ray transmission image that shows the difference in the amount of X-ray penetration for each part of the object with shades of gray, and performs various processing on this X-ray transmission image to determine whether there is any foreign matter or whether there are any missing or damaged contents.

[0003] Furthermore, in recent years, X-ray inspection devices have been proposed that can estimate the mass of an object to be inspected based on the amount of X-rays transmitted through the object to be inspected (see, for example, Patent Documents 1 and 2).

[0004] Here, we will explain the interaction between X-rays and the object being inspected. When X-rays pass through the object being inspected, they are attenuated by interactions with the object (absorption, scattering, etc.). The rate of this attenuation is expressed as the linear attenuation coefficient μ [1 / cm], which is expressed as the linear attenuation coefficient μ when multiplied by the density ρ [g / cm] of the object being inspected. 3 ] is the mass attenuation coefficient μ m [cm 2 / g].

[0005] Here, if the X-ray irradiation dose from the X-ray source is I0, the amount of X-ray transmission is I, and the thickness of the object to be inspected is t [cm], then the following equation (1) holds.

[0006] I=I0exp(-μ m ρt) (1)

[0007] Here, the X-ray transmission amount I is the product y(k)A of the transmission data y(k) of each unit transmission area obtained from the X-ray source and the correction coefficient A, so the above formula (1) becomes the following formula (2).

[0008] y(k)A=I0exp(-μ m ρt) (2)

[0009] Transforming equation (2) yields equation (3) below.

[0010] ρt=-1 / μ m ×ln[y(k)A / I0] (3)

[0011] Here, the unit of the left side of equation (3) is [g / cm 3 ]×[cm]=[g / cm 2 ], and the right side of equation (3) is a unit transmission area (unit area 1 cm 2 ) mass. In this equation (3), the measurement parameter μ m , I0, A and the transmission data y(k) are substituted to calculate the unit mass for each unit transmission area.

[0012] Then, the unit mass for each unit transmission area is added up over the entire transmission area of ​​the transmitted X-rays that have passed through the object to be inspected. That is, the unit masses calculated for each unit transmission area are summed up, and the total mass M of the object to be inspected is calculated using the following formula (4).

[0013]

number

[0014] [Patent Document 1] Patent No. 5651007 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-296022 Summary of the Invention [Problem to be solved by the invention]

[0015] However, in such X-ray inspection devices using X-rays, not only does the amount of transmitted X-ray change due to the presence or absence of foreign matter in the inspected object itself, or the presence or absence of missing or missing contents, but the intensity of the X-rays incident on each sensor element becomes non-uniform because the X-rays are emitted in a manner that spreads toward the inspection area.

[0016] Furthermore, there are differences in sensitivity between sensor elements, and in the case of arrays or modules each consisting of a plurality of sensor elements, there are differences in sensitivity between arrays or modules.

[0017] For this reason, conventionally, the measurement parameter μ m Attempts have been made to reduce the variability in the total mass M of the object to be inspected, which is calculated based on equation (4), by adjusting , I0, and A to change the shape of the curve in equation (3). However, this method has the problem that it is not possible to fully absorb, for example, differences in how the object is projected depending on the position on the conveyor belt where the object is placed, or differences in how the object is projected depending on the height of the object, by adjusting the measurement parameters.

[0018] The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a mass estimation method and an X-ray inspection apparatus that can accurately estimate the mass of an object to be inspected by calculating a weight vector using calibration X-ray transmission image data. [Means for solving the problem]

[0019] In order to solve the above problem, the mass estimation method according to the present invention includes a first transport step (S5) of transporting a sample of the same type as the object (100) and having a known mass N times while irradiating the sample with X-rays; a first X-ray transmission image data generation step (S7) of generating, for each transport, X-ray transmission image data corresponding to the amount of X-ray transmission for each transmission region of the sample transported by the first transport step; a first histogram generation step (S8) of generating a histogram of pixel values ​​of pixels corresponding to each transmission region included in each of the N pieces of X-ray transmission image data of the sample generated by the first X-ray transmission image data generation step; and a histogram of pixel values ​​of pixels corresponding to each transmission region generated by the first histogram generation step. The method includes a histogram matrix generation step (S10) of generating a histogram matrix consisting of N row vectors corresponding to the N histograms of a sample; a weight vector calculation step (S11) of calculating a weight vector that minimizes the variance of the N relative mass estimates, where the product of the histogram matrix and a weight vector consisting of weight coefficients for each pixel value of the N pieces of X-ray transmission image data is a relative mass estimate vector consisting of N relative mass estimates of the sample; and a mass estimation step (S25 to S27) of estimating the mass of the object to be inspected using the weight vector calculated in the weight vector calculation step during an inspection mode in which one or more objects to be inspected are transported.

[0020] As a result, the mass estimation method according to the present invention generates X-ray transmission image data of a sample of an object to be inspected N times during calibration mode, and can calculate a weight vector consisting of weight coefficients for each pixel value of a plurality of pixels contained in each of the N pieces of X-ray transmission image data. In other words, the mass estimation method according to the present invention does not approximate the relationship between pixel value and mass with a curve such as equation (3) as in the conventional method, but calculates a weight coefficient, which is a correction coefficient for calculating the mass of the object to be inspected, for each pixel value. As a result, the mass estimation method according to the present invention can estimate the mass of the object to be inspected with high accuracy using the weight vector during inspection mode.

[0021] Furthermore, the mass estimation method according to the present invention may further include a relative mass estimate vector calculation step (S12) of calculating the product of the histogram matrix and the weight vector calculated in the weight vector calculation step as the relative mass estimate vector, and a reference mass calculation step (S13) of calculating, as a reference mass, a representative value of the N relative mass estimates included in the relative mass estimate vector calculated in the relative mass estimate vector calculation step.

[0022] With this configuration, the mass estimation method according to the present invention can calculate a reference mass when estimating the mass of an object to be inspected.

[0023] Furthermore, the mass estimation method according to the present invention further includes, in the inspection mode, a second transport step (S21) of sequentially transporting one or more of the objects to be inspected while irradiating the objects with X-rays, a second X-ray transmission image data generation step (S23) of generating X-ray transmission image data corresponding to the amount of X-ray transmission for each of the transmission regions of the object to be inspected transported by the second transport step, and a second histogram generation step (S24) of generating a histogram of pixel values ​​of pixels corresponding to each of the transmission regions included in the X-ray transmission image data of the object to be inspected generated by the second X-ray transmission image data generation step, The mass estimation step may include a histogram vector generation step (S25) of generating a histogram vector consisting of one row vector corresponding to the histogram of the object under test generated by the second histogram generation step, a relative mass calculation step (S26) of calculating the product of the histogram vector and the weight vector calculated by the weight vector calculation step as the relative mass of the object under test, and a mass conversion step (S27) of converting the relative mass into the mass of the object under test based on the ratio of the known mass of the sample to the reference mass.

[0024] With this configuration, the mass estimation method of the present invention can calculate the relative mass of the test object using the weight vector and convert the relative mass to the mass of the test object based on the ratio of the known mass of the sample to the reference mass.

[0025] Furthermore, the mass estimation method according to the present invention may further include a mass pass / fail determination step (S28) for determining whether the mass converted by the mass conversion step is within a predetermined mass tolerance range corresponding to the object to be inspected.

[0026] With this configuration, the mass estimation method according to the present invention can determine whether the mass of the object to be inspected is within a predetermined mass tolerance range.

[0027] Further, the X-ray inspection apparatus according to the present invention is an X-ray inspection apparatus comprising: a transport unit (10) that transports a sample of the same type as an inspection object (100) and having a known mass N times; an X-ray source (21) that irradiates X-rays onto the sample transported by the transport unit; and an X-ray detector (24) that detects the X-rays that have passed through the sample for each transmission region of the sample, and further comprising: an X-ray transmission image data generation unit (31) that generates, for each transport, X-ray transmission image data corresponding to the amount of X-rays transmitted for each transmission region of the sample based on detection information from the X-ray detector; and a histogram generation unit ( a histogram matrix generator (33) that generates a histogram matrix consisting of N row vectors corresponding to the N histograms of the sample generated by the histogram generator; a weight vector calculator (34) that calculates a weight vector that minimizes the variance of the N relative mass estimates of the sample, where the product of the histogram matrix and a weight vector consisting of weight coefficients for each pixel value of the N pieces of X-ray transmission image data is a relative mass estimate vector consisting of N relative mass estimates of the sample; and a mass estimator (38) that estimates the mass of the object to be inspected using the weight vector calculated by the weight vector calculator in an inspection mode in which one or more objects to be inspected are transported by the transport unit.

[0028] Furthermore, the X-ray inspection apparatus according to the present invention may further include a relative mass estimation vector calculation unit (36) that calculates the product of the histogram matrix and the weight vector calculated by the weight vector calculation unit as the relative mass estimation vector, and a reference mass calculation unit (37) that calculates, as a reference mass, a representative value of the N relative mass estimation values ​​included in the relative mass estimation vector calculated by the relative mass estimation vector calculation unit.

[0029] Furthermore, in the X-ray inspection apparatus according to the present invention, the transport unit sequentially transports one or more of the objects to be inspected in the inspection mode, the X-ray source irradiates the objects to be inspected transported by the transport unit with X-rays in the inspection mode, the X-ray detector detects the X-rays that have passed through the object to be inspected for each of the transmission regions of the object to be inspected in the inspection mode, the X-ray transmission image data generation unit generates the X-ray transmission image data corresponding to the amount of X-rays that have passed through each of the transmission regions of the object to be inspected based on the detection information of the X-ray detector in the inspection mode, and the histogram generation unit generates the X-ray transmission image data of the object to be inspected generated by the X-ray transmission image data generation unit in the inspection mode. The mass estimation unit may be configured to generate a histogram of pixel values ​​of pixels corresponding to each of the transmission regions included in the transmission image data, and include: a histogram vector generation unit (39) that generates a histogram vector consisting of one row vector corresponding to the histogram of the object under test generated by the histogram generation unit; a relative mass calculation unit (40) that calculates the product of the histogram vector and the weight vector calculated by the weight vector calculation unit as the relative mass of the object under test; and a mass conversion unit (41) that converts the relative mass into the mass of the object under test based on the ratio of the known mass of the sample to the reference mass.

[0030] Furthermore, the X-ray inspection apparatus according to the present invention may be configured to further include a foreign matter determination unit (43) that determines whether or not the object to be inspected contains a foreign matter based on detection information from the X-ray detector.

[0031] With this configuration, the X-ray inspection apparatus according to the present invention can determine whether or not the object to be inspected contains a foreign substance. [Effects of the Invention]

[0032] The present invention provides a mass estimation method and an X-ray inspection apparatus that can accurately estimate the mass of an object to be inspected by calculating a weight vector using X-ray transmission image data for calibration. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a schematic configuration diagram of an X-ray inspection apparatus according to an embodiment of the present invention. [Figure 2] 3 is a diagram schematically showing an example of a plurality of X-ray transmission image data generated by an X-ray transmission image data generating unit in a calibration mode of the X-ray inspection apparatus according to the embodiment of the present invention. FIG. [Figure 3] 1 is a flowchart showing the processing of a mass estimation method using an X-ray inspection apparatus according to an embodiment of the present invention. [Figure 4] 4 is a flowchart showing details of the process of step S3 in the flowchart of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0034] Hereinafter, embodiments of a mass estimation method and an X-ray inspection apparatus according to the present invention will be described with reference to the drawings.

[0035] 1 is a diagram showing the configuration of an X-ray inspection apparatus 1. The X-ray inspection apparatus 1 has a function of estimating the mass of an inspection object 100 (article) being transported. The inspection object 100 is, for example, fruit, vegetables, seafood, packaged raw meat, processed food, medicine, etc.

[0036] As shown in FIG. 1, the X-ray inspection apparatus 1 includes a transport unit 10, an X-ray inspection unit 20, and a control unit 50 having a display unit 45 and an operation unit .

[0037] The transport unit 10 is a conveyor that winds a loop-shaped transport belt 11 around multiple transport rollers 12 and 13, and sequentially transports the object to be inspected 100 or a sample thereof placed on the transport surface 11a of the transport belt 11 to the right in FIG. 1 to pass through a predetermined inspection section of the X-ray inspection unit 20, and is supported by a housing (not shown). The sample is, for example, a typical non-defective product of the same type as the object to be inspected 100 and has a known mass. The object to be inspected 100 or a sample thereof may be placed on the transport belt 11 manually by the user, or may be placed by a dedicated device (not shown). Note that hereinafter, the object to be inspected 100 and its sample may be collectively referred to simply as the "object to be inspected 100."

[0038] The transport unit 10 transports the object 100 to the X-ray inspection unit 20 at a predetermined constant transport speed corresponding to the type of the object. When the operation mode of the X-ray inspection apparatus 1 is an inspection mode, which will be described later, the transport unit 10 transports one or more objects 100 to the right in Fig. 1 in sequence. On the other hand, when the operation mode of the X-ray inspection apparatus 1 is a calibration mode, which will be described later, the transport unit 10 transports a sample of the object 100 to the right in Fig. 1 N times.

[0039] The X-ray inspection unit 20 has an X-ray source 21 that irradiates the object 100 to be inspected, which is being transported by the transport unit 10, with X-rays in a predetermined energy band that can penetrate the object 100. The X-ray source 21 generates X-rays with a wavelength and intensity according to the tube current and tube voltage of a known X-ray tube 22, and is capable of irradiating the object 100 on the transport belt 11 with fan-beam-shaped X-rays that pass through an X-ray window 23a of an envelope 23 and are perpendicular to the transport direction of the transport unit 10.

[0040] The X-ray inspection unit 20 further includes an X-ray detector 24 disposed directly below the conveyor belt 11.

[0041] Although not shown, this X-ray detector 24 is composed of an X-ray line sensor camera in which detection elements consisting of a scintillator, which is a phosphor, and a photodiode or a charge-coupled device are arranged in an array at a predetermined pitch in the width direction of the conveying path of the conveying section 10, so as to detect X-rays at a predetermined resolution.

[0042] That is, the X-ray detector 24 detects the X-rays irradiated from the X-ray source 21 and transmitted through the object 100 for each predetermined transmission area of ​​the object 100 corresponding to the detection element, converts the detected X-rays into an electrical signal according to the amount of transmission, and outputs an X-ray detection signal for each transmission area.

[0043] The control unit 50 is configured to control the transport speed and transport interval of the inspection object 100 by the transport belt 11 in the transport unit 10. The control unit 50 also controls the X-ray irradiation intensity and irradiation period in the X-ray inspection unit 20, and controls the X-ray detection cycle and detection period of the inspection object 100 by the X-ray line sensor of the X-ray detector 24 according to the transport speed of the inspection object 100. Furthermore, the control unit 50 has a counter (not shown) that counts the number of times the inspection object 100 sample is transported by the transport unit 10, and displays the count result on the display unit 45.

[0044] The control unit 50 also has a mode switching unit 30, an X-ray transmission image data generation unit 31, a histogram generation unit 32, a histogram matrix generation unit 33, a weight vector calculation unit 34, a memory unit 35, a relative mass estimation value vector calculation unit 36, a reference mass calculation unit 37, a mass estimation unit 38, a mass pass / fail determination unit 42, and a foreign matter determination unit 43.

[0045] The mode switching unit 30 switches the operation mode of the X-ray inspection apparatus 1 between an inspection mode in which a normal inspection is performed on the inspection object 100 and a reference mass W Sm For example, mode switching unit 30 is configured to select the operation mode of X-ray inspection apparatus 1 in response to an operation input to operation unit 46 by the user.

[0046] The X-ray transmission image data generating unit 31 receives an X-ray detection signal from the X-ray detector 24 at a predetermined cycle and generates X-ray transmission image data of the object 100, which includes two-dimensional position information determined by the passing direction of the object 100 and the arrangement direction of the detection elements, and signal processing results for each position. The X-ray transmission image data is digital data with pixel values ​​of, for example, 4096 gradations from 0 to 4095, corresponding to the amount of X-ray transmission for each transmission area of ​​the object 100. For example, each pixel constituting the X-ray transmission image data corresponds to each transmission area of ​​the object 100. The X-ray transmission image data generating unit 31 generates X-ray transmission image data each time the object 100 is transported to the X-ray inspection unit 20 and passes through a predetermined inspection section. That is, when the operating mode of the X-ray inspection apparatus 1 is a calibration mode (described later), the X-ray transmission image data generating unit 31 generates N pieces of X-ray transmission image data for a sample of one object 100.

[0047] The configuration relating to the operation of X-ray inspection apparatus 1 in the calibration mode will be described below.

[0048] 2 is a diagram showing a schematic example of multiple X-ray transmission image data generated by the X-ray transmission image data generation unit 31 in the calibration mode. The upper, middle, and lower rows of FIG. 2 respectively show examples of X-ray transmission image data of a sample obtained in the first, second, and third transports by the transport unit 10. In this way, it is desirable to change the position and orientation of the sample placed on the transport belt 11 of the transport unit 10 for each transport by the transport unit 10, so that different X-ray transmission image data can be obtained for each transport.

[0049] The position and orientation of the sample placed on the conveyor belt 11 of the conveyor unit 10 may be changed by the user when placing the sample on the conveyor belt 11. Alternatively, the conveyor unit 10 may be equipped with any mechanism that changes the position and orientation of the sample on the conveyor belt 11.

[0050] The histogram generating unit 32 generates a histogram {h i,n Here, i is an index indicating the pixel value of I gradation and is an integer between 0 and the maximum pixel value I-1. Also, n is an index indicating the number of times the sample of the inspection object 100 has been transported and is an integer between 1 and the total number of times N it has been transported.

[0051] The histogram matrix generation unit 33 generates a histogram matrix consisting of N row vectors corresponding to the N histograms of the samples generated by the histogram generation unit 32. That is, the histogram matrix generated by the histogram matrix generation unit 33 is calculated based on the frequency h of the histograms generated by the histogram generation unit 32, as shown in the following equation (5): i,n is a matrix whose elements are

[0052]

number

[0053] Here, the frequency h of each pixel value of the X-ray transmission image data of the sample of the inspection object 100 is i,n weighting coefficient w i The sum of the products multiplied by is the relative mass estimate W n The weighting coefficient w i That is, as shown in the following equation (6), the N relative mass estimates W n The relative mass estimation value vector W is calculated by using the histogram matrix generated by the histogram matrix generator 33 and the weighting coefficients w for each pixel value of the N pieces of X-ray transmission image data. i and a weight vector w consisting of

[0054]

number

[0055] The weight vector calculation unit 34 calculates the N relative mass estimates W n The weight vector calculation unit 34 calculates a weight vector w that minimizes the variance of the weight vector w. The method for calculating the weight vector w by the weight vector calculation unit 34 will be described below.

[0056] The estimated relative mass W when the number of transfers is n n is expressed by the following equation (7). In addition, the N relative mass estimates W n The average value of is expressed by the following equation (8).

[0057]

number

[0058]

number

[0059] Therefore, the N relative mass estimates W n The variance V of is expressed by the following equation (9).

[0060]

number

[0061] Here, when formula (9) is expanded, the following formula (10) is obtained.

[0062]

number

[0063] Therefore, the minimum condition of variance V is, that is, variance V is w j The condition under which the value obtained by partial differentiation with respect to becomes 0 is expressed as in the following equation (11).

[0064]

number

[0065] Here, equation (11) is a component C of the covariance matrix C of the histogram shown in equation (12) below. j,i Using this, it can be rewritten as the following equation (13).

[0066]

number

[0067]

number

[0068] The unknown weighting coefficient w in equation (13) i is found as a solution to the homogeneous equation Cw=0 with the covariance matrix C as a coefficient. The covariance matrix C is calculated by the histogram bias H i,n The matrix H with I rows and N columns has the elements and its transpose matrix H t It is an I-row, I-column matrix consisting of the product of

[0069]

number

[0070] The number of rows I of matrix H is equal to the number of columns in the histogram, while the number of columns N of matrix H is equal to the number of X-ray image data. Usually, I>N. Since the rank of matrix H, i.e., the number of independent rows, is at most N, matrix C is a singular matrix. By finding a nontrivial solution w≠0 of this homogeneous equation Cw=0, we can determine the weight vector w that minimizes the variance V.

[0071] In the above calculation method of the weight vector w, for pixel values ​​below a predetermined noise cut threshold in the X-ray transmission image data and pixel values ​​outside the area corresponding to the object 100 (for example, the conveyor belt 11), the corresponding weight coefficient w i may be set to 0. This reduces the amount of calculation and allows the weighting coefficient w to be calculated accurately. ican be calculated.

[0072] The relative mass estimate vector calculation unit 36 ​​calculates the product of the histogram matrix generated by the histogram matrix generation unit 33 and the weight vector w calculated by the weight vector calculation unit 34 as the relative mass estimate vector W. That is, the relative mass estimate vector calculation unit 36 ​​calculates the relative mass estimate vector W by substituting the histogram matrix generated by the histogram matrix generation unit 33 and the final weight vector w calculated by the weight vector calculation unit 34 into equation (6).

[0073] The reference mass calculation unit 37 calculates the N relative mass estimates W included in the relative mass estimate vector W calculated by the relative mass estimate vector calculation unit 36. n The representative value of the reference mass W Sm where N relative mass estimates W n The representative value of is, for example, N relative mass estimates W n The reference mass W is either the mean, median, mode, maximum, or minimum value of Sm The user may select which of the representative values ​​to use as the relative mass estimated value W by inputting an operation to the operation unit 46. n If the average value of the N relative mass estimates W1 to W2 is N By substituting into equation (8), the reference mass W Sm Calculate.

[0074] The storage unit 35 stores the weight vector w calculated by the weight vector calculation unit 34 and the reference mass W calculated by the reference mass calculation unit 37. Sm and the known mass W of the sample of 100 specimens Km The system has a table (not shown) that stores the above in association with the type of the object 100 to be inspected.

[0075] The configuration relating to the operation of X-ray inspection apparatus 1 in the inspection mode in which one or more objects to be inspected 100 are transported sequentially by transport unit 10 will be described below.

[0076] The histogram generating unit 32 generates a histogram {h i Here, i is an index indicating the pixel value of I gradation, and is an integer ranging from 0 to the maximum pixel value I-1.

[0077] The mass estimation unit 38 calculates the weight vector w and the reference mass W stored in the table of the storage unit 35. Sm , and the known mass of the sample W Km The mass of the object to be inspected 100 is estimated using the above, and includes a histogram vector generating unit 39, a relative mass calculating unit 40, and a mass converting unit 41.

[0078] The histogram vector generating section 39 generates a histogram vector consisting of one row vector corresponding to the histogram of the object to be inspected 100 generated by the histogram generating section 32, as shown in the following equation (15).

[0079]

number

[0080] The relative mass calculation unit 40 calculates the product of the histogram vector and the weight vector w stored in the table of the storage unit 35 as the relative mass W of the object 100 to be inspected, as shown in the following equation (16): rm That is, the relative mass W rm is the frequency h of each pixel value of the X-ray transmission image data of the object 100 to be inspected. i weighting coefficient w i is the sum of the products multiplied by

[0081]

number

[0082] The mass conversion unit 41 converts the relative mass W calculated by the relative mass calculation unit 40 into rm is converted into the mass of the object to be inspected 100. The mass information calculated by the mass conversion unit 41 is displayed on the display unit 45.

[0083] For example, the mass conversion unit 41 converts the known mass W of the sample stored in the table of the storage unit 35 into Km and reference mass W Sm The ratio of the relative mass W rm By multiplying by the relative mass W rm is converted into the mass of the inspection object 100. That is, the mass of the inspection object 100 is expressed by the following formula (17).

[0084] Mass of the test object = relative mass W rm × mass of sample W Km / Reference mass W Sm (17)

[0085] The mass pass / fail determination unit 42 determines whether the mass measurement result is pass / fail based on whether the mass calculated by the mass conversion unit 41 is within a predetermined mass tolerance range corresponding to the inspection object 100. Information on whether the mass measurement result is pass / fail obtained by the mass pass / fail determination unit 42 is displayed on the display unit 45.

[0086] The foreign substance determination unit 43 determines whether or not the inspection object 100 contains foreign substances based on the detection information from the X-ray detector 24. For example, the foreign substance determination unit 43 performs image processing such as a filter on the X-ray transmission image data generated by the X-ray transmission image data generation unit 31 to emphasize foreign substance information and extract it as a foreign substance extracted image, thereby detecting the presence or absence of foreign substances mixed in the inspection object 100. As a filter for emphasizing foreign substance information, for example, a differential filter (Roberts filter, Prewitt filter, Sobel filter) or a feature extraction filter such as a Laplacian filter is used. The determination result by the foreign substance determination unit 43 is displayed on the display unit 45.

[0087] The control unit 50 is configured as a control device such as a computer including, for example, a central processing unit (CPU), a graphics processing unit (GPU), a field programmable gate array (FPGA), a read-only memory (ROM), a random access memory (RAM), and a hard disk drive (HDD). For example, the control unit 50 can configure at least a portion of the mode switching unit 30, the X-ray transmission image data generation unit 31, the histogram generation unit 32, the histogram matrix generation unit 33, the weight vector calculation unit 34, the relative mass estimation value vector calculation unit 36, the reference mass calculation unit 37, the mass estimation unit 38, the mass pass / fail determination unit 42, and the foreign matter determination unit 43 as software by executing a predetermined program using the CPU or GPU. The above programs are pre-stored in the ROM or HDD. Alternatively, the above programs may be provided or distributed in an installable or executable format recorded on a computer-readable recording medium such as a compact disc or DVD. Alternatively, the above program may be stored in a computer connected to a network such as the Internet, and provided or distributed by downloading via the network.

[0088] The display unit 45 is configured with a display device such as an LCD (Liquid Crystal Display) or a CRT (Cathode Ray Tube), and displays various determination results and measurement results based on a display control signal from the control unit 50. The display unit 45 may also have an operation function of the operation unit 46, such as soft keys on the display screen.

[0089] The operation unit 46 is for accepting operation inputs by the user, and is configured with a user interface such as, for example, an operation knob, various keys, switches, buttons, and soft keys on the display screen of the display unit 45. Alternatively, the operation unit 46 may be configured to include an input device such as a keyboard or a mouse.

[0090] For example, the user can input an operation to the operation unit 46 to select an operation mode of the X-ray inspection apparatus 1 in the mode switching unit 30 or select a table according to the type of the object 100 to be inspected.

[0091] An example of the processing of a mass estimation method using the X-ray inspection apparatus 1 will be described below with reference to the flowcharts of Figures 3 and 4. Note that descriptions that overlap with the above-described description of the configuration of the X-ray inspection apparatus 1 will be omitted as appropriate. The processing of each step in the flowcharts of Figures 3 and 4 is realized by the computer constituting the control unit 50 executing the above-described program.

[0092] First, the mode switching unit 30 switches the operation mode of the X-ray inspection apparatus 1 (step S1). The switching of the operation mode by the mode switching unit 30 is performed, for example, at the timing of an operation input by a user to the operation unit 46, at a pre-specified time, or several seconds after the start of operation of the X-ray inspection apparatus 1.

[0093] If the operation mode switched by the mode switching unit 30 in step S1 is the calibration mode (step S2: YES), the control unit 50 executes the calibration mode process from step S4 onwards.

[0094] If the operation mode switched by the mode switching unit 30 in step S1 is the inspection mode (step S2: NO), the control unit 50 executes the processing in the inspection mode (step S3).

[0095] In step S4, a sample of the inspection object 100 is placed on the conveyor belt 11 by a user or a dedicated device (step S4).

[0096] When a user inputs an operation to start measurement to the operation unit 46, the transport unit 10 starts transporting the sample of the inspection object 100 placed on the transport belt 11. Then, the X-ray source 21 irradiates the sample with X-rays as it is transported by the transport unit 10 and passes through a predetermined inspection section (first transport step S5).

[0097] Next, when a detection sensor (not shown) detects the entry of one sample into the inspection area (step S6: YES), the X-ray transmission image data generation unit 31 generates X-ray transmission image data corresponding to the amount of X-ray transmission for each transmission area of ​​the sample transported by the first transport step S5 (first X-ray transmission image data generation step S7).

[0098] Next, the histogram generating unit 32 generates a histogram of pixel values ​​of a plurality of pixels included in the sample X-ray transmission image data generated in the first X-ray transmission image data generating step S7 (first histogram generating step S8).

[0099] Next, if the sample has not been transported N times (step S9: NO), the processes from step S4 onwards are executed again.

[0100] On the other hand, when the samples have been transported N times (step S9: YES), the histogram matrix generation unit 33 generates a histogram matrix consisting of N row vectors corresponding to the N histograms of the samples generated in the first histogram generation step S8 (histogram matrix generation step S10).

[0101] Next, the weight vector calculation unit 34 calculates a weight vector w that minimizes the variance of the N relative mass estimate values ​​that make up the relative mass estimate value vector W obtained based on the histogram matrix (weight vector calculation step S11). At this time, the control unit 50 stores the weight vector w calculated in the weight vector calculation step S11 in a table in the storage unit 35 in association with the type of the object 100 to be inspected.

[0102] Next, the relative mass estimated value vector calculation unit 36 ​​calculates the product of the histogram matrix and the weight vector w calculated in the weight vector calculation step S11 as the relative mass estimated value vector W (relative mass estimated value vector calculation step S12).

[0103] Next, the reference mass calculation unit 37 calculates a representative value of the N relative mass estimates included in the relative mass estimate vector W calculated in the relative mass estimate vector calculation step S12 as the reference mass W Sm (reference mass calculation step S13). At this time, the control unit 50 calculates the reference mass W Sm are stored in a table in the storage unit 35 in association with the type of the object 100 to be inspected.

[0104] The process of step S3 will be described in detail below with reference to the flowchart of FIG.

[0105] First, a table corresponding to the type of the object to be inspected 100 is read from the storage unit 35 by a user's operation input to the operation unit 46 (step S20).

[0106] Next, when the user inputs an operation to the operation unit 46 to instruct the start of measurement, the transport unit 10 starts transporting one or more inspection objects 100 that have been sequentially placed on the transport belt 11 by the user or a dedicated device. Then, the X-ray source 21 irradiates X-rays onto the inspection objects 100 that are transported by the transport unit 10 and pass through a predetermined inspection section (second transport step S21).

[0107] Next, when a detection sensor (not shown) detects the entry of one inspection object 100 into the inspection section (step S22: YES), the X-ray transmission image data generation unit 31 generates X-ray transmission image data corresponding to the amount of X-ray transmission for each transmission area of ​​the inspection object 100 transported to the inspection section by the second transport step S21 (second X-ray transmission image data generation step S23).

[0108] Next, the histogram generating unit 32 generates a histogram of pixel values ​​of a plurality of pixels included in the X-ray transmission image data of the inspection object 100 generated in the second X-ray transmission image data generating step S23 (second histogram generating step S24).

[0109] Next, the histogram vector generating unit 39 generates a histogram vector consisting of one row vector corresponding to the histogram of the object under inspection 100 generated in the second histogram generating step S24 (histogram vector generating step S25).

[0110] Next, the relative mass calculation unit 40 calculates the product of the histogram vector and the weight vector w stored in the table of the storage unit 35 as the relative mass W of the object 100 to be inspected. rm (relative mass calculation step S26).

[0111] Next, the mass conversion unit 41 converts the known mass W of the sample stored in the table of the storage unit 35 into Km and reference mass W Sm The relative mass W calculated in the relative mass calculation step S26 based on the ratio rm is converted into the mass of the object to be inspected 100 (mass conversion step S27).

[0112] Next, the mass pass / fail determination unit 42 determines whether or not the mass converted in the mass conversion step S27 is within a predetermined mass tolerance range corresponding to the inspection object 100 (mass pass / fail determination step S28).

[0113] Next, the display unit 45 displays information on the mass of the inspection object 100 converted in the mass conversion step S27 and the determination result in the mass pass / fail determination step S28 (step S29).

[0114] Next, when mass information and determination results are acquired for all the objects 100 to be inspected, that is, when inspection of all the objects 100 to be inspected is completed (step S30: YES), the series of processes is completed. If inspection of all the objects 100 to be inspected is not completed (step S30: NO), the processes from step S22 onwards are executed again.

[0115] The histogram vector generation step S25, the relative mass calculation step S26, and the mass conversion step S27 constitute a mass estimation step that estimates the mass of the object 100 to be inspected using the weight vector w calculated by the weight vector calculation step S11 during an inspection mode in which one or more objects 100 to be inspected are transported.

[0116] As described above, the mass estimation method and X-ray inspection apparatus according to this embodiment generate X-ray transmission image data of a sample of the inspection object 100 N times in the calibration mode, and calculate weighting coefficients w for each pixel value of a plurality of pixels included in each of the N pieces of X-ray transmission image data. i In other words, the mass estimation method and X-ray inspection apparatus according to this embodiment do not approximate the relationship between pixel values ​​and mass with a curve such as equation (3) as in the conventional method, but calculate the weighting coefficient w, which is a correction coefficient for calculating the mass of the object 100 under inspection. i is calculated for each pixel value. As a result, the mass estimation method and X-ray inspection apparatus according to this embodiment can estimate the mass of the inspection object 100 with high accuracy using the weight vector w in the inspection mode.

[0117] Furthermore, the mass estimation method and X-ray inspection apparatus according to this embodiment use a reference mass W Sm can be calculated.

[0118] Furthermore, the mass estimation method and X-ray inspection apparatus according to this embodiment estimate the relative mass W of the object 100 using the weight vector w. rm Calculate the mass of the sample, W Km and reference mass W Sm Based on the ratio of W to W, the relative massrm can be converted into the mass of the object 100 to be inspected.

[0119] Furthermore, the mass estimation method and X-ray inspection apparatus according to this embodiment can determine whether the mass of the inspection object 100 is within a predetermined mass tolerance range.

[0120] Moreover, the X-ray inspection apparatus according to this embodiment can determine whether or not the object 100 to be inspected contains a foreign substance. [Explanation of symbols]

[0121] 1 X-ray inspection equipment 10 Conveying section 20 X-ray Inspection Department 21 X-ray source 24 X-ray detector 30 Mode switching section 31 X-ray transmission image data generation unit 32 Histogram generation unit 33 Histogram matrix generator 34 Weight vector calculation unit 35 Storage section 36 Relative mass estimation vector calculation section 37 Reference mass calculation section 38 Mass estimation section 39 Histogram Vector Generation Unit 40 Relative mass calculation section 41 Mass conversion section 42 Mass acceptance / rejection determination section 43 Foreign object determination section 45 Display section 46 Control section 50 control section 100 Test object (or sample)

Claims

1. a first transport step (S5) of transporting a sample N times, the sample being of the same type as the object (100) and having a known mass, while irradiating the sample with X-rays; a first X-ray transmission image data generating step (S7) of generating, for each conveyance, X-ray transmission image data corresponding to the amount of X-ray transmitted through each transmission region of the sample conveyed by the first conveyance step; a first histogram generating step (S8) of generating a histogram of pixel values ​​of pixels corresponding to each of the transmission regions included in each of the N pieces of X-ray transmission image data of the sample generated in the first X-ray transmission image data generating step; a histogram matrix generating step (S10) of generating a histogram matrix consisting of N row vectors corresponding to the N histograms of the samples generated by the first histogram generating step; a weight vector calculation step (S11) of calculating a weight vector that minimizes the variance of the N relative mass estimates of the sample, where the product of the histogram matrix and a weight vector consisting of weight coefficients for each pixel value of the N pieces of X-ray transmission image data is a relative mass estimate vector consisting of the N pieces of relative mass estimates of the sample; a mass estimation step (S25 to S27) of estimating the mass of the object to be inspected using the weight vector calculated by the weight vector calculation step during an inspection mode in which one or more object to be inspected are transported.

2. a relative mass estimation vector calculation step (S12) of calculating the product of the histogram matrix and the weight vector calculated in the weight vector calculation step as the relative mass estimation vector; 2. The mass estimation method according to claim 1, further comprising: a reference mass calculation step (S13) of calculating a reference mass as a representative value of the N relative mass estimate values ​​included in the relative mass estimate vector calculated in the relative mass estimate vector calculation step.

3. a second transport step (S21) of sequentially transporting one or more of the objects to be inspected while irradiating the objects with X-rays in the inspection mode; a second X-ray transmission image data generating step (S23) of generating X-ray transmission image data corresponding to the amount of X-ray transmitted through each of the transmission regions of the inspection object transported by the second transport step; a second histogram generating step (S24) of generating a histogram of pixel values ​​of pixels corresponding to each of the transmission regions included in the X-ray transmission image data of the object of inspection generated in the second X-ray transmission image data generating step, The mass estimation step includes: a histogram vector generating step (S25) of generating a histogram vector consisting of one row vector corresponding to the histogram of the object to be inspected generated in the second histogram generating step; a relative mass calculation step (S26) of calculating the product of the histogram vector and the weight vector calculated in the weight vector calculation step as the relative mass of the object to be inspected; 3. The mass estimation method according to claim 2, further comprising a mass conversion step (S27) of converting the relative mass into the mass of the object to be inspected based on a ratio between the known mass of the sample and the reference mass.

4. The mass estimation method according to claim 3, further comprising a mass pass / fail determination step (S28) of determining whether the mass converted by the mass conversion step is within a predetermined mass tolerance range corresponding to the object to be inspected.

5. a transport unit (10) that transports a sample of the same type as the object (100) to be inspected and having a known mass N times; an X-ray source (21) that irradiates the sample transported by the transport unit with X-rays; an X-ray detector (24) that detects X-rays that have passed through the sample for each transmission region of the sample, an X-ray transmission image data generating unit (31) that generates X-ray transmission image data corresponding to the amount of X-ray transmission for each transmission region of the sample for each transport based on detection information from the X-ray detector; a histogram generating unit (32) for generating a histogram of pixel values ​​of pixels corresponding to each of the transmission regions included in each of the N pieces of X-ray transmission image data of the sample generated by the X-ray transmission image data generating unit; a histogram matrix generator (33) for generating a histogram matrix consisting of N row vectors corresponding to the N histograms of the samples generated by the histogram generator; a weight vector calculation unit (34) that calculates the weight vector that minimizes the variance of the N relative mass estimates of the sample, where the product of the histogram matrix and a weight vector consisting of weight coefficients for each pixel value of the N pieces of X-ray transmission image data is a relative mass estimate vector consisting of the N pieces of relative mass estimates of the sample; and a mass estimation unit (38) that, during an inspection mode in which one or more of the objects to be inspected are transported by the transport unit, estimates the mass of the object to be inspected using the weight vector calculated by the weight vector calculation unit.

6. a relative mass estimation vector calculation unit (36) that calculates the product of the histogram matrix and the weight vector calculated by the weight vector calculation unit as the relative mass estimation vector; 6. The X-ray inspection apparatus according to claim 5, further comprising: a reference mass calculation unit (37) that calculates, as a reference mass, a representative value of the N relative mass estimate values ​​included in the relative mass estimate vector calculated by the relative mass estimate vector calculation unit.

7. the transport unit sequentially transports one or more of the objects to be inspected in the inspection mode; the X-ray source irradiates the object to be inspected that is being transported by the transport unit with X-rays in the inspection mode; the X-ray detector detects X-rays transmitted through the object under inspection for each of the transmission regions of the object under inspection in the inspection mode; the X-ray transmission image data generation unit generates the X-ray transmission image data corresponding to an amount of X-ray transmission for each of the transmission regions of the object to be inspected based on detection information from the X-ray detector in the inspection mode; the histogram generating unit generates a histogram of pixel values ​​of pixels corresponding to each of the transmission regions included in the X-ray transmission image data of the object to be inspected generated by the X-ray transmission image data generating unit in the inspection mode; The mass estimation unit a histogram vector generating unit (39) that generates a histogram vector consisting of one row vector corresponding to the histogram of the object to be inspected generated by the histogram generating unit; a relative mass calculation unit (40) that calculates the product of the histogram vector and the weight vector calculated by the weight vector calculation unit as the relative mass of the object to be inspected; 7. The X-ray inspection apparatus according to claim 6, further comprising: a mass conversion unit (41) that converts the relative mass into the mass of the object to be inspected based on a ratio between the known mass of the sample and the reference mass.

8. 8. The X-ray inspection apparatus according to claim 5, further comprising a foreign matter determination unit (43) that determines whether or not the object to be inspected contains a foreign matter based on detection information from the X-ray detector.

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