JP6797539B2 - Foreign matter detection device and foreign matter detection method - Google Patents

Description

The present invention relates to a technique for detecting a foreign substance in an object to be inspected using X-rays.

At factories that manufacture food products, foreign matter detection devices are used to check whether foreign substances such as metals and plastics are mixed in the products.

Conventionally, as this foreign matter detecting device, X-rays are emitted to a passage path of an object to be inspected which is conveyed in a predetermined direction by a conveyor or the like, and the intensity of the X-rays transmitted through the object to be inspected is detected by a sensor (multiple X-ray sensors). Is detected by an integrated line sensor) that is lined up in a direction orthogonal to the passing direction, and a detection signal is detected by utilizing the fact that the detection signal changes locally due to the presence of a foreign substance.

However, as described above, in the method of detecting the intensity of X-rays transmitted through the object to be inspected by a sensor, foreign matter is accurately detected due to the difference in transmittance depending on the thickness in the direction in which the X-rays are transmitted and the material of which the material changes. Sometimes I couldn't.

As a technique for solving this, for example, in Patent Document 1, processing such as subtraction (difference processing of image data) for two transmitted X-ray data obtained by different energies of X-rays transmitted through an inspected object is performed. As a result, it has been proposed to improve the detection accuracy of foreign substances.

Japanese Unexamined Patent Publication No. 10-318943

However, in Patent Document 1, two detections in which X-rays output from a single X-ray source and transmitted through an inspected object are arranged side by side in the transport direction of the inspected object and have different energy sensitivities to X-rays. Two transmitted X-ray data are obtained by detecting with a device (line sensor).

Therefore, inevitably, the path through which the X-rays incident on one detector pass through the inspected object and the path through which the X-rays incident on the other detector pass through the inspected object do not match. Due to the influence, it is possible that the foreign matter to be inspected cannot be recognized correctly. It is also possible that accurate foreign matter detection cannot be performed due to the difference in the characteristics of the sensor elements of the two detectors.

It should be noted that Patent Document 1 also describes the use of two X-ray sources having different X-ray energies, but in that case, the X-ray source and the two corresponding X-ray sources so that the two X-rays do not interfere with each other. The distance between the detectors (line sensors) must be widened, the entire device becomes large, and the posture of the object to be inspected changes easily between them, and two detectors are used in the same manner as described above. Therefore, the detection accuracy of foreign matter may decrease.

As a method to solve this, paying attention to the variation in the energy of X-ray photons generated from X-ray tubes, etc., each time an X-ray photon is incident, a pulse signal with a peak value corresponding to that energy Using a photon detection type X-ray sensor that outputs, the pulse signals output from the X-ray sensor within a certain period of time are classified into multiple regions according to the difference in peak value, and the number of pulse signals for each region is accumulated. By doing so, it is conceivable to obtain transmitted image data when the X-ray energies are different. With this method, a plurality of X-ray sensors may be arranged in a row in a direction intersecting the passing direction of the object to be inspected, and the above problem can be solved.

Here, the energy of X-rays transmitted through the object to be inspected varies greatly depending on the material of the object to be inspected and the thickness in the X-ray transmission direction. If the material of the object to be inspected is made almost uniform and the thickness in the X-ray transmission direction is almost constant, the average emission energy of X-rays can be adjusted to be constant according to the thickness of the X-ray sensor. The dose of X-rays incident on the can be maintained within an appropriate range.

However, there are cases where objects of different thickness are carried into the inspection line in no particular order. In this case, for example, if the emission energy of X-rays is determined according to the object to be measured having a large thickness, the dose of X-rays becomes excessive with respect to the object to be inspected having a small thickness, and conversely, the thickness becomes large. If the emission energy of X-rays is determined according to the small object to be inspected, the dose of X-rays transmitted through the large object to be inspected becomes too small.

When the dose of X-rays transmitted through the object to be inspected becomes excessive in this way, the photon input frequency becomes excessive in the photon detection type X-ray sensor described above, and the X-ray sensor, for example, as shown in FIG. The output pulse signals P ₁ and P ₂ and the pulse signals P ₄ and P ₅ overlap each other, and only one peak value (peak value H ₁ and H ₃ ) can be obtained for each of the two pulse signals. The phenomenon occurs. This phenomenon is generally called a pile-up phenomenon, and if this phenomenon occurs with a high probability, a correct counting result for each region cannot be obtained, and as a result, foreign matter cannot be detected accurately.

Further, if the dose of X-rays transmitted through the object to be inspected is too small, the cumulative number of pulse signals becomes extremely small and cannot be distinguished from the noise component, and the S / N of the transmitted image data is lowered.

The present invention solves the above problems, and while using a photon detection type X-ray sensor, suppresses the influence of the pile-up phenomenon and S / N reduction caused by the difference in the thickness of the object to be inspected, and highly accurately removes foreign matter. It is an object of the present invention to provide a foreign matter detecting device and a foreign matter detecting method capable of detecting foreign matter.

In order to achieve the above object, the foreign matter detecting device according to claim 1 of the present invention is used.
An X-ray generator (22) that emits X-rays into the passage path through which the object to be inspected passes,
At the position where the X-ray is emitted from the X-ray generating portion to the passing path and passes through the inspected object, the X-rays are arranged so as to intersect the passing direction of the inspected object, and each receives the X-ray. Multiple X-ray sensors (31 _{1 to} 31 _N ) that convert to electrical signals,
While the object to be inspected is passing between the X-ray generating unit and the plurality of X-ray sensors, the signals output from the plurality of X-ray sensors are separated by a predetermined period and a predetermined signal processing is performed. , A transparent image data generation means for generating transparent image data of an inspected object, which is composed of two-dimensional position information determined by the passing direction of the inspected object and the arrangement direction of the X-ray sensors and signal processing results for each position. (40) and
In a foreign matter detecting device having a determination means (50) for determining the presence or absence of a foreign matter in an object to be inspected based on the transparent image data generated by the transparent image data generation means.
The X-ray sensor is a photon detection type that outputs a pulse signal having a peak value corresponding to the energy of the photon each time an X-ray photon is input.
The transparent image data generation means
For each of the X-ray sensors, it is determined in advance which of the regions in which the peak value of the pulse signal output from the X-ray sensor is divided into a plurality of predetermined ranges within the predetermined period, and within the predetermined period. The number of pulse signal inputs of the above is accumulated for each region, and the accumulated result for each region is used to generate a plurality of transmitted image data having different X-ray transmission energies.
The determination means
It is configured to determine the presence or absence of foreign matter in the object to be inspected by performing predetermined image processing including subtraction processing on a plurality of transparent image data obtained by the transparent image data generation means.
further,
A thickness detecting means (60) for detecting the thickness of the object to be inspected in the X-ray transmission direction before entering the position where the X-ray generating portion emits X-rays, and
Based on the thickness of the object to be inspected detected by the thickness detecting means, the number of pulse signal inputs within the predetermined period, which is transmitted through the object to be inspected and incident on the X-ray sensor and output, is predetermined. It is characterized in that an X-ray dose variable means (70) for varying the dose of X-rays emitted by the X-ray generating unit is provided so as to fall within an appropriate range set by the lower limit value and the upper limit value of .

Further, the foreign matter detecting apparatus請Motomeko 2 of the present invention, the foreign matter detecting apparatus according to claim 1,
The lower limit of the appropriate range is 40% of the standard maximum number of pulses that one X-ray sensor can output within the predetermined period.
The upper limit value of the appropriate range is 60% of the maximum number of pulses .

Further, the method for detecting a foreign substance according to claim 3 of the present invention is:
The stage of emitting X-rays from the X-ray generator (22) to the passage path through which the object to be inspected passes, and
The X-rays emitted from the passage path and transmitted through the object to be inspected are received by a plurality of X-ray sensors (31 _{1 to} 31 _N ) arranged in a direction intersecting the passing direction of the object to be inspected and converted into an electric signal. Stages and
While the object to be inspected is passing between the X-ray generating unit and the plurality of X-ray sensors, the signals output from the plurality of X-ray sensors are separated by a predetermined period and a predetermined signal processing is performed. , A step of generating transparent image data of the inspected object consisting of two-dimensional position information determined by the passing direction of the inspected object and the arrangement direction of the X-ray sensors and the signal processing result for each position.
In the foreign matter detection method including the step of determining the presence or absence of foreign matter in the object to be inspected based on the generated transparent image data.
As the X-ray sensor, a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the photon each time an X-ray photon is input is used.
At the stage of generating the transparent image data,
For each of the X-ray sensors, it is determined in advance which of the regions in which the peak value of the pulse signal output from the X-ray sensor is divided into a plurality of predetermined ranges within the predetermined period, and within the predetermined period. The number of pulse signal inputs of is accumulated for each region, and the cumulative result for each region is used to generate a plurality of transmitted image data having different X-ray transmission energies.
At the stage of determining the presence or absence of foreign matter in the object to be inspected,
By performing predetermined image processing including subtraction processing on the plurality of generated transparent image data, the presence or absence of foreign matter in the object to be inspected is determined.
Further, before the object to be inspected enters the X-ray irradiation position, the thickness of the object to be inspected in the X-ray transmission direction is detected, and the object is incident on the X-ray sensor according to the detected thickness. The dose of X-rays emitted from the X-ray generator is variable so that the number of pulse signal inputs within the predetermined period to be output is within the appropriate range set by the predetermined lower limit value and upper limit value. It is a feature.

As described above, in the present invention, as the X-ray sensor, a photon detection type that outputs a peak value pulse signal corresponding to the energy of the X-ray photon each time it is input is used, and X-ray irradiation is performed. The thickness of the X-ray transmission direction of the object to be inspected that enters the position is detected, and the dose of X-ray that passes through the object to be inspected and is incident on the X-ray sensor is within the appropriate range according to the thickness. In the state of being variable to, the object to be inspected is made to enter the X-ray irradiation position, and for each X-ray sensor, the peak value of the pulse signal output from the X-ray sensor within a predetermined period is set within a predetermined range in advance. It is determined which of the regions is divided into a plurality of regions, the number of pulse signal inputs within a predetermined period is accumulated for each region, and the cumulative result for each region is used to obtain a plurality of transmitted image data having different X-ray transmission energies. To generate. Then, by performing predetermined image processing including subtraction processing on these transparent image data, the presence or absence of foreign matter in the inspected object is determined.

Therefore, it is possible to generate a plurality of transmitted image data having different X-ray transmission energies while using a plurality of X-ray sensors arranged in a row in a direction intersecting the passing direction of the object to be inspected. Compared with the method of arranging a plurality of line sensors in the passing direction of the object to be inspected or the method of using a plurality of X-ray sources, the detection accuracy of foreign matter can be improved and the entire device can be miniaturized.

In addition, since the dose of X-rays emitted from the X-ray generating part is changed according to the thickness of the object to be inspected detected before entering the position where the X-rays are irradiated, the X-ray sensor can be used. When the dose of incident X-rays can be maintained within an appropriate range, transmission image data with suppressed pile-up phenomenon and accuracy deterioration due to S / N reduction can be obtained, and objects of different thickness are carried in in no particular order. Even so, foreign matter can be detected accurately.

Configuration diagram of the embodiment of the present invention The figure which shows the relationship between the pulse signal output from an X-ray sensor and a region. The figure which shows the example of three kinds of transparent image data obtained for each area of a crest value. The figure which shows the change example of the dose of the X-ray emitted from the X-ray generation part 22 when the object to be inspected with a different thickness is carried in. The figure which shows the waveform when the pulse signals output from an X-ray sensor overlap.

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

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

The transport device 21 is for transporting the object W to be inspected in a predetermined direction (direction orthogonal to the paper surface in the figure), and generally, the object W to be inspected is horizontally transported at a constant speed like a conveyor. However, it is not always necessary to use a conveyor having a power source, and a method of sliding on a ramp using the weight of the object to be inspected or a method of dropping from above may be used.

The X-ray generating unit 22 emits X-rays to a passing path through which the object W to be inspected, which is conveyed in a predetermined direction by the conveying device 21, passes. In this embodiment, it is assumed that X-rays spreading in the width direction of the transport path are emitted from above the object W to be transported by the transport device 21, but the emission direction of the X-rays is not limited to this and is to be inspected. It may be emitted from the side of the object W toward the side surface.

The X-ray source of the X-ray generator 22 includes a hot cathode X-ray tube that accelerates the electrons emitted from the heated filament and collides with the target of the anode to emit X-rays, and a lattice-controlled hot cathode X-ray. A tube is used and also includes the power supply needed to drive the X-ray tube.

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

Each of the plurality of N X-ray sensors 31 _{1 to} 31 _N receives X-rays and converts them into an electric signal, and is emitted from the X-ray generator 22 into the passage path of the object W to be inspected. At the position where the X-rays transmitted through the X-rays are received, they are lined up in a row with almost no gap in the direction in which the object W to be inspected passes (the direction orthogonal to the paper surface) and intersects (orthogonal in this example).

As an actual device, the plurality of N X-ray sensors 31 _{1 to} 31 _N are composed of one line sensor 30 in which each is integrally connected, and are arranged on the lower surface side of the transport path of the transport device 21. There is. Here, for example, if the width of the X-ray sensor is 1 mm, the gap between the X-ray sensors is negligibly small with respect to the width, and the width of the transport path for transporting the object W to be inspected is 200 mm, there are approximately 200 X-ray sensors. A line sensor having an X-ray sensor may be used.

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

The transmission image data generation means 40 outputs signals from the X-ray sensors 31 _{1 to} 31 _N while the object W to be inspected passes between the X-ray generator 22 and the X-ray sensors 31 _{1 to} 31 _N , respectively. Is divided by scan time and subjected to predetermined signal processing, and the inspected object consists of two-dimensional position information determined by the passing direction of the inspected object W and the arrangement direction of the X-ray sensors, and the signal processing result for each position. Generates transparent image data of.

As described above, the photon detection type X-ray sensors 31 _{1 to} 31 _N output one peak value pulse signal corresponding to the energy of the photon for each photon input, but X-rays are generated. Since the energy of the X-ray photons emitted from the unit 22 varies even if the tube current is constant, the pulse signal P output from each X-ray sensor corresponds to the energy, as shown in FIG. The peak values H ₁ , H ₂ , H ₃ , ... Of ₁ , P ₂ , P ₃ , ... Are varied.

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

In order to generate a plurality of transmitted image data having different ranges of the X-ray transmitted energy, the transmitted image data generating means 40 converts the output signals of the X-ray sensors 31 _{1 to} 31 _N into A / D converters 41 ₁ respectively. It is converted into a digital data string by ~ 41 _N and input to the peak value detecting means 42 _{1 to} 42 _N.

Each crest value detecting means 42 _{1 to} 42 _N is for detecting the crest value of the pulse signal from the input data string. For example, the input data string is subjected to differential processing to perform a differential value (signal). slope) detects a zero-cross timing when switched to a negative value of the predetermined or less from the positive value equal to or greater than a predetermined, detecting the data value at that zero-cross timing as the crest value of the pulse signals, respectively region determining means 43 ₁ Output to ~ 43 _N.

Region determining means ₄₃ 1 ~ 43 _N includes a boundary value region _{L 1 ~L M-1} for dividing the output range of the above-mentioned peak value in the region _R 1 to R _M of the plurality M, the peak value detecting means ₄₂ 1-42 _The crest value detected in _N is compared, it is determined which region the crest value falls into, and a region identification signal representing the region in which the crest value enters is output to the area-specific accumulation means 44 _{1 to} 44 _N.

The cumulative means 44 _{1 to} 44 _{N for} each region receive the region identification signals output from the region determining means 43 ₁ to 43 _N within the scan time, and accumulate the number of input of the region identification signals indicating the same region. , The cumulative number for each area within the scan time is calculated and output sequentially.

The cumulative number of the region identification signals is the cumulative number of pulse signals having the same peak value in the pulse signals output from one X-ray sensor within the scan time, and is the cumulative number of the pulse signals for each region. By storing the cumulative number of area identification signals output from 44 _{1 to} 44 _{N for} each scan time in the transparent image data memory 45 in parallel and in chronological order, X-ray transmission to the object to be inspected for each area is transmitted. Image data can be obtained.

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

Also, of the second X-ray sensor 31 pulse _{signal 2} is output in the same scan time within T1, the cumulative number of those whose peak value enters the area R ₁ A (1,1,2), in the region R ₂ the cumulative number of those entering a (2,1,2), the cumulative number of those entering the area R ₃ and a (3,1,2).

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

Similarly, in the next scan time T2, of the first X-ray sensor 31 pulse _{signal 1} is outputted, the cumulative number of those whose peak value enters the area R ₁ A (1,2,1), region The cumulative number of things that enter R ₂ is A (2,2,1), the cumulative number of things that enter region R ₃ is A (3,2,1), and the pulse signal output by the _second X-ray sensor 312 among them, the cumulative number of those whose peak value enters the area _{R 1 a (1,2,2), a} (2,2,2) the cumulative number of those entering the area R _2, the cumulative number of those entering the area R ₃ was the a (3,2,2), 3 th of pulse signals X-ray sensor ₃₁₃ has output, the cumulative number of those whose peak value enters the area R ₁ a (1,2,3), region the cumulative number of those entering the R ₂ a (2,2,3), the cumulative number of those entering the area R ₃ and a (3,2,3).

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

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

Similarly, nine cumulative number obtained for region R _2, if arranged in three rows and three columns as shown in (b) of FIG. 3, the object to be inspected by the X-ray energy range corresponding to the region R ₂ If the transparent image data is obtained and the nine cumulative numbers obtained for the region R ₃ are arranged in 3 rows and 3 columns as shown in FIG. 3 (c), the X-ray of the energy range corresponding to the region R ₃ is obtained. Transparent image data of the object to be inspected can be obtained.

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

In this way, if the transmitted image data for each energy range corresponding to each peak value region is obtained, the determination means 50 includes a predetermined subtraction process that has been conventionally performed on the plurality of transmitted image data. By performing the image processing of, it is possible to determine the presence or absence of foreign matter on the object to be inspected.

The method of dividing the peak value region is arbitrary, and as an example, the maximum value of the energy of the X-ray photon emitted from the X-ray generator 22 (in the case of an X-ray tube, the electron's). The peak value of the pulse signal output by the X-ray sensor and a predetermined reference value (for example, 0) may be equally divided into a plurality of values with respect to the theoretical value depending on the accelerating voltage. In addition, the number of regions is arbitrary with two or more, and transparent image data is first generated in many regions, and the optimum combination of transparent image data for detecting foreign matter is found for the object to be inspected, and the optimum combination is found. Predetermined image processing including subtraction processing using transparent image data may be performed.

Specifically, for example, the initial number of regions as 10, allocated in advance to generate a transmission image data in each region, the first region counted from the largest energy in the region R ₁ of the above, the third allocates a region in the region R ₂ of the above, and so ......, finally region selectively assigned from the initial region, using a plurality of transmission image data of the assigned area, predetermined image processing May be done. Further, by combining the transmission image data of the first and second regions counted from the larger energy, which was the previous region R ₁ of the transmitted image data, the transmitted image data of the third and fourth region synthesized and, this as a transmission image data in the above described region R _2, by combining the transmission image data of the initial plurality of regions so as ...... the transmitted image data of the final one region is the combined Predetermined image processing may be performed using a plurality of transparent image data or a composite of transparent image data and transparent image data in an initial region that does not include the transparent image data.

In the above specific example, transparent image data is generated for the number of initial regions, and regions are allocated and transparent image data is combined according to the optimum combination of transparent image data for detecting foreign matter. However, when the optimum combination of transparent image data for detecting foreign matter is known for the object to be inspected, only the transparent image data for the allocated area needs to be generated, and a plurality of transparent image data are combined. Alternatively, one transparent image data may be generated by adding the cumulative number of region identification signals of a plurality of regions. As a result, the storage area for transparent image data can be saved.

Here, to briefly explain the subtraction processing, when X-ray transmission data with different energies are obtained for the same part, the influence of the thickness of the part is removed by performing the difference processing, and the material (transmittance). The difference between the change in the transmittance of the material of the object to be inspected and the change in the transmittance of the material of the foreign matter becomes remarkable with respect to the difference in X-ray energy. As a result, the detection sensitivity for foreign matter is increased. In addition to this processing, the determination means 50 performs various filter processing and the like for removing noise and the like to detect foreign matter with higher accuracy.

Since the plurality of transmitted image data obtained by the above method is obtained from the outputs of a plurality of X-ray sensors arranged in a line in a direction orthogonal to the passing direction of the article, compared with the conventional method using two line sensors. Therefore, transparent image data with extremely high accuracy can be obtained, so that foreign matter can be detected accurately and the size can be reduced.

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

When a photon detection type X-ray sensor is used as described above, as described above, if the dose of X-rays incident on the X-ray sensor (the number of photons output per unit time) is too large, a pile-up phenomenon occurs. Will occur with a high probability, and correct counting results for each region will not be obtained. If the X-ray dose is too small, it will be indistinguishable from noise, and correct transmitted image data will not be obtained.

If the material of the object to be inspected is the same, the dose of X-rays that pass through the object to be inspected will decrease as the thickness in the transmission direction increases. Therefore, in general, it depends on the thickness of the object to be inspected. Although the dose of X-rays emitted from the X-ray generating unit 22 is set, it cannot be dealt with when objects to be inspected having the same material but not uniform thickness are carried into the inspection line in random order.

In order to solve this problem, the foreign matter detecting device 20 of the embodiment is provided with a thickness detecting means 60 and an X-ray dose variable means 70.

The thickness detecting means 60 detects the thickness of the object W to be inspected in the X-ray transmission direction in front of the X-ray irradiation position on the transport device 21. This thickness detection method is arbitrary, but in the case of an optical configuration example, for example, light is irradiated from one side of the side surface of the object to be inspected that has entered the thickness detection region, and the light is vertically transmitted to the opposite side. It is received by a plurality of receivers arranged in a direction, and is detected by the height of the receivers in which the incident of light is blocked by the object to be inspected. In addition, an optical reflection type sensor is placed above the passage path (transport surface), laser light is emitted, the reflected light reflected on the upper surface of the object to be inspected is received, the displacement is measured, and the passage path is measured from the sensor. A method may be used in which the difference between the distance to the (conveyed surface) and the distance from the sensor to the upper surface of the object to be inspected is detected as the thickness of the object to be inspected.

The thickness detected here may be any of the maximum value, the average value, and the like of the thickness of the object to be inspected obtained when passing through the thickness detection region.

In the X-ray dose variable means 70 that has received the thickness H detected by the thickness detecting means 60, the dose of X-rays that pass through the object to be inspected of the thickness H and enter the X-ray sensor is piled up. The dose of X-rays emitted from the X-ray generator 22 (specifically, the X-ray generator 22) so that the probability of occurrence of the phenomenon is low and the cumulative number of pulse signals falls within an appropriate range sufficiently larger than the noise level. The control value for controlling the tube current and tube voltage of the X-ray tube) is changed.

There are various methods of this variable processing. For example, the control value that gives the optimum X-ray dose according to the sample product is stored in advance for each type (material) and thickness classification of the object to be inspected, and the thickness is detected. The thickness detecting means 60 is described in a method of reading out a control value corresponding to a category including the thickness H detected by the means 60 and setting it in the X-ray generating unit 22, and an expression showing the relationship between the thickness and the optimum control value. A method of calculating a control value by substituting the thickness H detected in 1 and setting this in the X-ray generating unit 22 can be adopted.

FIG. 4 shows the relationship between the thickness of the object to be inspected detected by the thickness detecting means 60 and the dose of X-rays emitted by the X-ray generating unit 22, as shown in FIG. 4A. The object W1 to be inspected enters the thickness detection region and its thickness H1 (here, the thickness is constant, but as described above, the maximum value or the average value of the thicknesses obtained along the passing direction is used. When Td is detected for a predetermined time (when the object W1 to be inspected reaches immediately before the X-ray irradiation position and the scan time is started), (b) of FIG. As described above, the X-ray dose of the X-ray generating unit 22 is switched to an appropriate dose A1 corresponding to the thickness H1. As a result, transparent image data for the object W1 to be inspected having a thickness H1 can be accurately obtained, and foreign matter detection can be performed correctly.

Then, after the inspected object W1, a gap is opened and the next inspected object W2 enters the thickness detection region, and when the thickness H2 is detected, the inspected object W2 is X-rayed in the same manner as described above. The X-ray dose of the X-ray generating unit 22 is switched to an appropriate dose A2 corresponding to the thickness H2 according to the timing of entering the irradiation position. As a result, transparent image data for the object W2 to be inspected having a thickness H2 can be accurately obtained, and foreign matter can be detected correctly. The X-ray dose variable means 70 distinguishes the inspected object by determining the range B in which the thickness detected by the thickness detecting means 60 is equal to or less than a predetermined value as a gap of the inspected object.

The appropriate range of the dose of X-rays incident on the X-ray sensor is, for example, the maximum number of pulses according to the standard that one X-ray sensor can output within the scan time (for example, the scan time is 1 millisecond). It can be set to a range (for example, 400 to 600) set for (1000 pieces). In this case, the dose is set so that the cumulative number of the pulse signals output by one X-ray sensor for the entire region of the transmitted image data actually obtained for the object to be inspected is within the above-mentioned appropriate range. However, if the cumulative number of some areas is targeted instead of the entire area, the appropriate range may be changed accordingly.

In this way, the thickness of the X-ray emitted by the X-ray generating unit 22 is detected so that the thickness of the X-ray to be inspected is detected and the dose of the X-ray incident on the X-ray sensor falls within an appropriate range according to the thickness. By varying the dose, even when objects of different thickness are carried in in no particular order, foreign matter can be accurately detected for each object to be inspected.

Although the storage format of the transparent image data described above is arbitrary, a transparent image is obtained by assigning a different color to each peak value region and making the brightness of the color assigned to that region correspond to the cumulative number of pulse signals. It becomes easier for the observer to understand when observing.

For example, there are three peak value regions, three primary colors of red (R), green (G), and blue (B) are assigned to each region, and the cumulative number of pulses is assigned to the brightness value of each color. However, the value assigned to the brightness of each color is, for example, a range (0 to 255) that can be represented by 8 bits, and is normalized (compression processing or decompression processing) so that the range of the actual cumulative number of pulses falls within the range that can be represented by 8 bits. .. In this case, the three transparent image data can be saved as one RGB color image data. Therefore, the storage area of the transparent image data can be saved. Further, since the data format is general RGB color image data, image processing and image display can be easily performed.

Further, by using a data storage format in which different colors are assigned to each region and the brightness of the color is represented by the cumulative number of pulse signals, the transparent image of each region can be represented by an image of a different color. The distinctiveness is very high when the images are displayed side by side on a display device (not shown).

20 ... Foreign matter detection device, 21 ... Conveyor device, 22 ... X-ray generator, 30 ... Line sensor, 31 _{1 to} 31 _N ... X-ray sensor, 40 ... Transmission image data generation means, 41 ₁ to 41 _N …… A / D converter, 42 _{1 to} 42 _N …… Crest value detecting means, 43 ₁ to 43 _N …… Area determination means, 44 _{1 to} 44 _N …… Cumulative means by area, 45 …… Transparent image Data memory, 50 ... determination means, 60 ... thickness detection means, 70 ... X-ray dose variable means

Claims (3)

An X-ray generator (22) that emits X-rays into the passage path through which the object to be inspected passes,
At the position where the X-ray is emitted from the X-ray generating portion to the passing path and passes through the inspected object, the X-rays are arranged so as to intersect the passing direction of the inspected object, and each receives the X-ray. Multiple X-ray sensors (31 _{1 to} 31 _N ) that convert to electrical signals,
While the object to be inspected is passing between the X-ray generating unit and the plurality of X-ray sensors, the signals output from the plurality of X-ray sensors are separated by a predetermined period and a predetermined signal processing is performed. , A transparent image data generation means for generating transparent image data of an inspected object, which is composed of two-dimensional position information determined by the passing direction of the inspected object and the arrangement direction of the X-ray sensors and signal processing results for each position. (40) and
In a foreign matter detecting device having a determination means (50) for determining the presence or absence of a foreign matter in an object to be inspected based on the transparent image data generated by the transparent image data generation means.
The X-ray sensor is a photon detection type that outputs a pulse signal having a peak value corresponding to the energy of the photon each time an X-ray photon is input.
The transparent image data generation means
For each of the X-ray sensors, it is determined in advance which of the regions in which the peak value of the pulse signal output from the X-ray sensor is divided into a plurality of predetermined ranges within the predetermined period, and within the predetermined period. The number of pulse signal inputs of the above is accumulated for each region, and the cumulative result for each region is used to generate a plurality of transmitted image data having different X-ray transmission energies.
The determination means
It is configured to determine the presence or absence of foreign matter in the object to be inspected by performing predetermined image processing including subtraction processing on a plurality of transparent image data obtained by the transparent image data generation means.
further,
A thickness detecting means (60) for detecting the thickness of the object to be inspected in the X-ray transmission direction before entering the position where the X-ray generating portion emits X-rays, and
Based on the thickness of the object to be inspected detected by the thickness detecting means, the number of pulse signal inputs within the predetermined period, which is transmitted through the object to be inspected and incident on the X-ray sensor and output, is predetermined. Foreign matter detection is provided with an X-ray dose variable means (70) that changes the dose of X-rays emitted by the X-ray generating unit so as to fall within an appropriate range set by the lower limit value and the upper limit value of. apparatus. The lower limit of the appropriate range is 40% of the standard maximum number of pulses that one X-ray sensor can output within the predetermined period.
The foreign matter detecting device according to claim 1 , wherein the upper limit value in the appropriate range is 60% of the maximum number of pulses . The stage of emitting X-rays from the X-ray generator (22) to the passage path through which the object to be inspected passes, and
The X-rays emitted from the passage path and transmitted through the object to be inspected are received by a plurality of X-ray sensors (31 _{1 to} 31 _N ) arranged in a direction intersecting the passing direction of the object to be inspected and converted into an electric signal. Stages and
While the object to be inspected is passing between the X-ray generating unit and the plurality of X-ray sensors, the signals output from the plurality of X-ray sensors are separated by a predetermined period and a predetermined signal processing is performed. , A step of generating transparent image data of the inspected object consisting of two-dimensional position information determined by the passing direction of the inspected object and the arrangement direction of the X-ray sensors and the signal processing result for each position.
In the foreign matter detection method including the step of determining the presence or absence of foreign matter in the object to be inspected based on the generated transparent image data.
As the X-ray sensor, a photon detection type that outputs a pulse signal of a peak value corresponding to the energy of the photon each time an X-ray photon is input is used.
At the stage of generating the transparent image data,
For each of the X-ray sensors, it is determined in advance which of the regions in which the peak value of the pulse signal output from the X-ray sensor is divided into a plurality of predetermined ranges within the predetermined period, and within the predetermined period. The number of pulse signal inputs of is accumulated for each region, and the cumulative result for each region is used to generate a plurality of transmitted image data having different X-ray transmission energies.
At the stage of determining the presence or absence of foreign matter in the object to be inspected,
By performing predetermined image processing including subtraction processing on the plurality of generated transparent image data, the presence or absence of foreign matter in the object to be inspected is determined.
Further, before the object to be inspected enters the X-ray irradiation position, the thickness of the object to be inspected in the X-ray transmission direction is detected, and the object is incident on the X-ray sensor according to the detected thickness. The dose of X-rays emitted from the X-ray generator is changed so that the number of pulse signal inputs within the predetermined period to be output is within the appropriate range set by the predetermined lower limit value and upper limit value. Characteristic foreign matter detection method.

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