JPH01296146A - Method of detecting substance with small x ray absorption and x ray sensor used therefor - Google Patents

Abstract

PURPOSE:To enable inspection of a sequence of a substance even with a small X ray transmissivity, by employing soft X rays with a low energy and a photodiode array having a sensitivity to a low energy to allow an accurate measurement of the substance. CONSTITUTION:This invention relates to the inspection of an object wherein a first substance with a small X-ray absorption has a second substance with a small X-ray absorption though different in amount buried therein, for example a plycord for a tire. Here, soft X rays with a low energy as controlled by X-ray controller 1 is radiated from an X-ray tube 2 to the plycord 3 as object to be measured moving horizontally. A photodiode having a sensitivity to a low energy is employed as X-ray sensor 4 for measuring the X rays and a measuring waveform outputted by the measurement is inputted into a measuring circuit 11. Then, a difference in X-ray absorption is detected for rubber and polyester in the plycord 3 and an arithmetic processing of the results and the movement of the plycord 3 is performed thereby detecting the second substance polyester.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to coated cords (hereinafter referred to as coated cords) using materials with low X-ray absorption such as rubber and organic fibers, especially organic fibers used as tire components. The present invention relates to a method for inspecting a cable (such as a cable) and detecting the pitch and amount of ear rubber of a cord embedded therein, as well as the amount of joints at a joint, and an X-ray sensor used in the method.

(Prior art) In tire manufacturing, cords made of fiber materials, thin steel wires, etc. embedded in rubber sheets are generally used as reinforcing materials to support the internal pressure. If there is an abnormality in the amount of joint in the joint, or if the joint is not properly connected, there is a risk that stress will be concentrated inside the tire during driving, leading to tire damage. In order to prevent such ply cord abnormalities, it is necessary to accurately detect the pitch of the cord embedded in the rubber sheet, the amount of ear rubber, the amount of joint at the joint, etc.

In particular, in order to improve the uniformity and quality of tires, there is a recent trend of connecting the joints of ply cords by butting, which requires more accurate inspection of the cord pitch and amount of ear rubber. It has become.

Regarding the detection of steel cords, Japanese Patent Application Laid-Open No. 53-181
As stated in the publication, the X-ray transmittance of the steel cord is higher than the X-ray transmittance of the rubber sheet, so the X-ray transmission image of the steel cord is detected and the cord is inspected. There is something to do.

However, with this method, in the case of coated code,
Since the radiation transmission coefficient was small and not much different from that of rubber, it was not possible to obtain an effective X-ray transmission image and it was not possible to inspect it.

The conventional inspection method for tire coated cords is as follows:
An inspection method that takes advantage of the presence of unevenness on the ply cord surface due to the cord embedded in rubber, shines light on the ply cord surface, detects the reflected light, and performs arithmetic processing on the output according to the amount of light. There is.

Furthermore, as described in JP-A No. 61-102543, a method has been proposed for detecting the cord by utilizing the fact that since the degree of crystallinity is different between rubber and coated cord, the diffraction images are different when exposed to X-rays. has been done.

However, the former method of optically inspecting the cord has the disadvantage that measurement errors may occur due to variations in the size of the irregularities on the surface of the ply cord, and that it cannot be used for ply cords with few irregularities.

Further, in the latter method using XvA diffraction, there is a problem that the degree of crystallinity of the cord is not necessarily constant.

(Problems to be Solved by the Invention) As mentioned above, when detecting the cord of a ply cord, the method of detecting irregularities on the rubber surface using an optical sensor cannot be used for ply cords with few surface irregularities. However, the method of detecting the cord by projecting X-rays onto the ply cord and using X-ray diffraction based on the difference in crystallinity between the rubber and the cord has the problem that the crystallinity of the cord material is not constant. Ta. Furthermore, in the method of detecting a cord using an X-ray transmission image that does not cause measurement errors, it can only be used for steel cords whose X-ray transmittance is significantly different from that of rubber.

The first object of the present invention is to eliminate the above-mentioned drawbacks, and to accurately measure the cord even for materials with low X-ray transmittance, such as coated cords embedded in rubber, and to improve the cord arrangement. The purpose is to provide a method for testing.

In this case, a photodiode array is used as an X-ray sensor for measuring the -dimensional X-rays. However, the field of view of commercially available photodiode arrays is approximately several tens of mm. On the other hand, in joint inspection of coated cords, the cord length of the ply cord, which is the treasure to be measured, varies by about 100 m at most, and therefore the joint position also shifts by about 100 mm at most. If you try to measure the joint position with a commercially available photodiode array when the cord is stopped, the field of view is small and it will not be possible to cover the displacement of the joint of the bright cord.

A second object of the present invention is to provide an X-ray sensor that can sufficiently cover the deviation width of the joint using a commercially available photodiode array that has a limited field of view.

(Means for Solving the Problems) In order to achieve the above-mentioned first object, the method of detecting a substance with a small amount of X-ray absorption according to the present invention is based on the method of detecting a substance with a small amount of X-ray absorption. Although the X-ray absorption amount is different,
When inspecting an object in which a second material with a small amount of radiation absorption is buried, low-energy X-rays are projected onto the object while moving the object in the horizontal direction, and the X-rays of both materials are The difference in the amount of X-ray absorption of both substances is detected using an X-ray sensor that can detect the difference in absorption amount with high sensitivity, and the amount of movement of the object and the amount of X of both substances detected by the X-ray sensor are calculated.
The second substance is detected by calculating the difference in the amount of radiation absorption.

Furthermore, in order to achieve the second object, the X-ray sensor of the present invention includes an X-ray source that projects soft X-rays onto an object to be measured, and an X-ray sensor that receives the soft X-rays that have passed through the object to be measured. The X-ray sensor is provided with a plurality of photodiode arrays, and these photodiode arrays are arranged so as to be shifted in a first direction and overlapped in a second direction by the width of the frame of the photodiode array, and The photodiode array is characterized in that it is arranged so that there is no gap between the light-receiving parts of the photodiode array. a conveyance means for conveying the object to be measured within the X-ray radiation range; and an
a radiation source; an X-ray sensor that receives the X-rays that have passed through the object to be measured within the X-ray radiation range; The X-ray sensor is characterized by comprising a driving means for driving the X-ray sensor along an arcuate trajectory centered on the X-ray source so that the X-ray sensor is incident on the X-ray source.

(Function) According to the method of detecting a substance with a small amount of X-ray absorption according to the first invention described above, it is possible to detect a substance with a low energy (X'vA generation voltage of 8
To detect these X-rays, a photodiode array that is particularly sensitive to low energy is used. It is possible to detect the difference even in objects where both materials have low X-ray absorption rates, such as buried coated cords, and it is possible to inspect the cord arrangement and the amount of ear rubber without error. .

The second and third inventions are X-rays using a commercially available photodiode array sensitive to low energy used in the method of detecting a substance with a small amount of X-ray absorption, which is the first invention.
This relates to line sensors.

That is, according to the X-ray sensor of the second invention, a plurality of commercially available photodiode arrays are arranged in the above-mentioned manner so that a range of about 100 mm in which the position of the joint part changes is such that there is no gap between the light receiving parts. Because they are arranged side by side, the field of view can be expanded while maintaining the resolution of the individual photodiode arrays. Furthermore, since two rows of sensors are arranged in the direction in which the cord extends,
Since the same cord can be measured at two points at the same time, the reliability of the measurement can be improved.

Further, according to the X-ray sensor of the third aspect of the invention, in order to perform inspection with higher precision, the photodiode used is provided with a collimator slit to set a high resolution. Therefore, it is difficult to arrange multiple photodiodes as in the first invention, and since one photodiode is used,
The field of view does not cover the deviation width of the joint position. Therefore, a mechanism is required to measure the cord width in advance and move the inspection machine to the joint position each time a measurement is made. In the third aspect of the present invention, this moving mechanism is simple and only the sensor is moved, so that measurement accuracy does not deteriorate due to vibrations or the like. Furthermore, since the sensor is always positioned facing the X-ray source during scanning, highly accurate measurement with the above-mentioned resolution is possible without being affected by the radiation angle of the X-rays.

(Example) FIG. 1 is a diagram for explaining a method for detecting a substance with a small amount of X-ray absorption according to the first invention.

From the X-ray tube 2, an X-ray control device 1 connected to the X-ray tube 2 is connected.
For example, the output voltage is 9.5KV and the output current is 0.
．． Soft X-rays controlled at 85 mA are emitted toward the thread-filled rubber sheet 3, which is the object to be measured.

The distance between the X-ray tube 2 and the object to be measured 3 is 95 mm, and the distance between the thread-filled rubber sheet 3 and the X-ray sensor is 7 mm.

The X-ray sensor 4 is a photodiode array sensitive to low energy, such as RLD 512 manufactured by Reticon.
In order to further increase the sensitivity of T, the light receiving window is removed and used.

The attenuation characteristic of X-rays is generally Ix=I. It is expressed by the formula e-. FIG. 2A is a graph representing this equation. Here, X is the distance that X-rays pass through the material, μ is the X-ray absorption coefficient, a value unique to the material that indicates the degree to which X-rays are attenuated within the material, and IX is the X-ray after passing through the material. The strength of,■. is the intensity of the X-rays before they pass through the substance. Now, based on Figure 2B, we will discuss the amount of attenuation of X-rays when they pass through a certain thickness for a material with a large amount of X-ray absorption (the first material) and a material with a small amount of absorption (the second material). explain. As is clear from Figure 2B, when the difference in X-ray absorption rate between the first substance and the second substance is large (μ2.μ
2') The difference in X-ray attenuation between both substances is (IμzXo−1μ
z'
+Xo IμI'xo). Therefore, it is clear from FIG. 2B that the greater the difference in the absorption coefficients of the two materials, the greater the difference in the amount of attenuation.

Applying this relationship to tire ply cord, the difference in X-ray attenuation between rubber and cord will be thicker if the difference in X-ray absorption coefficient between the two materials is large, such as between rubber and steel cord. Therefore, it is easy to measure the code arrangement.

However, since the tire braking cord that is the subject of measurement in the present invention is a composite of rubber and polyester or synthetic fibers such as nylon, the X-ray absorption rate of both materials is extremely low, and therefore the difference is small. . Therefore, if ordinary X-rays are used, the amount of X-ray attenuation required to accurately detect the code arrangement cannot be obtained.

However, according to experiments conducted by the present inventors, it is possible to irradiate a coated cord with soft X-rays with an X-ray generation voltage of approximately 8 to 18 KV, and to use a photodiode array sensitive to low energy as an X-ray sensor. It turns out that it is possible to detect code sequences by

As shown in Figure 3, the photodiode array used here has its light-receiving window removed to further increase its sensitivity. In order to prevent this, parts other than the light receiving section are covered with a lead film 12, and an opaque film 13 through which X-rays are transmitted is provided below to protect the light receiving section.

FIG. 4 shows a measurement waveform obtained when the coated cord is measured with the above-mentioned X-ray sensor. As is clear from this figure, this waveform is not rectangular but looks like a sine wave.

One reason for this is that the XvA source has a certain area rather than a point, which blurs the X-ray image on the sensor, but since the cross section of the thread to be measured is close to a circle, the This is because the dose is larger than that at both ends of the thread.

The measurement waveform measured and output by the X-ray sensor 4 is manually input to the measurement circuit 11. In the measurement circuit 11, the A/D converter 5 digitizes the signal output from the X-ray sensor.
The waveform is shaped by the waveform shaping circuit 6.

After that, in the peak detection circuit 7, first the center point between the peaks (represented by the O mark in Fig. 4) is found, then the center of these points (represented by the Δ mark in Fig. 4) is found, and this is determined as the true point. Take the peak, i.e. the center of the cord or the center of the rubber. In the yarn pitch and yarn both end position calculation circuit 8, the yarn diameter of the cord to be measured is stored as a unique value. Now, if the thread diameter is d, the positions of both ends of the thread are X2±d/2,
The positions of both ends of the cord are determined from the center position of the cord determined by the peak detection circuit 7 and the yarn diameter stored in advance.

In determining the thread pitch, a standard value comparison circuit 9 is used.
The standard yarn pitch p is stored in advance as a unique value. The actual yarn pitch is determined by the calculation process of (X2-X+). Now, assuming that the pitch tolerance is Δp, if p-Δp≦IXZXII≦p+Δp is satisfied, the test is passed, and if not, the test is judged to be failed.

Further, when determining the amount of ear rubber, the standard ear rubber Ng is stored in advance in the comparator circuit 9 as a standard value as a unique value. The actual amount of ear rubber is (e − (xz+ −)
) is obtained by the calculation process. Now, if the allowable value of the amount of ear rubber is Δg, then g-Δg≦1e −(xt+ −)
If l≦g+Δg is satisfied, the test is passed; otherwise, the test is failed.

The determination result output circuit 10 outputs pass/fail signals for each of the yarn pitch and the amount of selvage.

Next, the X-ray sensor used in the first invention will be explained.

FIG. 5 is a diagram showing the configuration of an embodiment of the X-ray sensor of the second invention. In this embodiment, an X-ray control device 1, an X-ray tube 2,
The arrangement of the thread-containing rubber sheet 3, the X-ray sensor 4, and the measurement circuit 11 is the same as that in Fig. 1, but the
The line sensor has a plurality of photodiode arrays arranged alternately as shown in FIG. 5, with four photodiode arrays A arranged in the X-axis direction, that is, in the longitudinal direction of the ply cord.

Four photodiode arrays E and F are arranged in a similar manner so that there are no gaps between the light receiving sections B, C, and D indicated by the hatched areas, and are arranged in the same manner.

G and H are lined up next to each other and fixed on the printed circuit board. Therefore, in the y-axis direction, that is, the direction in which the cord extends, each cord must be inspected at two points, such as A and E, B and F, C and G, and D and H, using two photodiode arrays. It is located in

The photodiode array used here is commercially available and is housed in a photodiode package measuring 40 mm in length and 101 mm in width, and the size of the light receiving part is N25 m.
m width is 2.0 mm. When the photodiode array is arranged in this way, as shown in FIG. 6A, by eliminating the gap between the light receiving sections, the field of view can be increased to four in the X-axis direction while maintaining the resolution of one photodiode array. It is possible to double the amount. That is, in this example, since the vertical field of view of one photodiode array is 251, the field of view expands to 100+I1 m, and can sufficiently cover the width of the joint portion of the ply cord pointed out in the above problem.

Furthermore, in the y direction, since two rows of sensors are lined up, the same code is measured at two locations at the same time.

This is because if measurements are taken at only one location, noise in the measurement signal may disrupt the waveform that distinguishes yarn from rubber, leading to misjudgment of yarn pitch, but if this is measured at two locations, Since it is rare that noise occurs in the measurement signals of two places at the same time, erroneous recognition can be prevented by comparing and determining the measured values of these two places. That is, by adding the waveforms (1) and (2) shown in FIG. 6B and further performing waveform processing, a measurement result with a high S/N can be obtained.

As explained in the first invention above, in each photodiode array, the light receiving window is removed to increase X-ray sensitivity, and the area other than the light receiving part is covered with a lead film to prevent the sensor from deteriorating due to X-rays. In order to deal with gas and light noise, an opaque film that transmits X-rays is provided.

FIG. 7A is a flowchart for explaining a signal processing method when a coated cord is measured with the X-ray sensor of the second invention.

From the X-ray generator, output voltage 6.3KV, output current 0
．． X-rays controlled at 9 mA are emitted to the object to be measured at a radiation angle of 30°, and the distance between the X-ray source and the object to be measured is 15
5mm, and the distance between the object to be measured and the X-ray sensor is 35rnm.
is set to . As the X-ray sensor, eight commercially available photodiode arrays are used, as shown in FIG. The object to be measured is a tire ply cord in which a cord made of organic fibers such as nylon, rayon, polyester, or Kepler is embedded in a rubber sheet. The X-rays projected from the X-ray generator and transmitted through the object to be measured are detected by a sensor consisting of 8 photodiode arrays with a field of view of 100 mm to the object.
(Step 2)
1).

The signals extracted from each array in this way are A/D
The signal is converted into a digital signal in a conversion step 22, and the waveform is shaped in a waveform shaping step 23.

FIG. 7B is a diagram showing the measured waveform of the signal obtained in this manner. As explained in the first invention, this waveform is like a sine wave. Next, in a peak-to-peak center point detection step 24, the center point between the peaks of this measured waveform is determined, as indicated by the circles in FIG. 7C. Furthermore, in the peak detection step 25, the center between these center points is determined as indicated by the Δ mark in the seventh diagram, and this is determined as the center point XI+ of the thread.
Find it as xz. In the yarn both end value calculation step 26, the positions of both ends of the cord are determined as follows.

That is, if the thread diameter of the cord to be measured is stored as an eigenvalue and this is set as d, the positions of both ends of the thread can be found by calculating x2±□.

Note that the position of the rubber end is represented by e.

Next, in the ear rubber amount determination step 27, it is determined whether the ear rubber amount is acceptable or not. That is, the standard amount of ear rubber g and the allowable value Δg of the amount of ear rubber are stored as unique values, and the actual amount of ear rubber is determined by the calculation process of e - (XZ+2). The standard amount of ear rubber is g, and the allowable value of the amount of ear rubber is Δg, so if g-Δg≦1e-(χ,+-)l≦g+Δg, the amount of ear rubber is passed, and if it is not, it is rejected. do.

Furthermore, in the yarn pitch determination step 28, the standard yarn pitch p and the yarn pitch tolerance Δp are stored as unique values, and the actual yarn pinch is determined by the difference between the values of the yarn center point x and x2 determined in step 25. (X2 XI) is obtained through arithmetic processing.

Therefore, as in the case of the amount of ear rubber, if p-Δp≦1xzx+l≦p+Δp is satisfied, the test is passed, and if not, the test is judged to be rejected.

In the determination result output step 29, a signal indicating whether the amount of selvedge rubber and the yarn pitch is acceptable or not is output based on the above-mentioned determination result.

As shown in step 2, inspect whether the pinch of the threads arranged in the rubber is within the specifications, and whether the amount of rubber between the endmost thread and the end of the rubber (the amount of selvedge rubber) is within the specifications. be able to.

Next, the third invention will be explained.

The third invention also relates to the X-ray sensor used in the first invention, but the third invention uses only one photodiode array, and therefore a mechanism for moving the sensor to cover the field of view is required. has.

FIG. 8 is a diagram showing the configuration of an embodiment of the third invention.

In this embodiment, the X-rays emitted from the X-ray tube 2 are
As in the first and second embodiments, the X-ray control device 1 controls the output voltage to 6.3 KV and the current to 0.9 mA. A commercially available photodiode is used as an X-ray sensor for detecting this soft X-ray, and its field of view is narrow as described above, and cannot cover variations in the cord length of the ply cord. Therefore, a mechanism is required that measures the cord length in advance and moves the inspection machine to the joint position prior to measuring the joint portion.

As shown in FIG. 8, the ply cords 3 are joined by a joint machine 12 and conveyed in the direction of the arrow in order to measure the joints. A cord length measuring device 13 is installed behind the position of the joint machine 12 by a standard cord length, and measures the position of the cord end 15 when the conveyance of the cord is stopped at the time of joining in the joint machine 13.

In this embodiment, the cord length measuring device 13 is connected to the cord end 15.
A photoelectric type is used that measures by shining a parallel light beam on the cord, and its width is approximately equal to the variation in the cord width to be measured, that is, approximately
Any material that can cover 00 mm is sufficient. Furthermore, since the measurement here only needs to include the joint position within the field of view of the X-ray sensor as will be described later, it is sufficient to have an accuracy of about 1 to 2 mm.

The cord length measuring device 13 measures the position of the cord end 15 in advance, calculates the amount of variation in the cord length from the reference cord length, and outputs an electrical signal according to the amount of variation. The X-ray sensor 4 is moved to the joint position in accordance with this output, and at this time, the X-ray sensor is controlled so as to stop 10 mm before the estimated joint position.

After the X-ray sensor has stopped, it is moved at a speed of 20 m - 7 seconds from the stopped position for 20 seconds to capture the joint part in its field of view.
Scan mm width.

FIG. 9 is a diagram showing the configuration of an X-ray sensor according to the third invention of the present application. As can be seen from this figure, the X-ray sensor is attached to a screw 17 that is rotated by a stepping motor 16, and is configured to move along a guide 18.

The distance between the X-ray source and the ply cord is set to 200 mm, the distance between the ply cord and the X-ray sensor is set to 351, and when the X-ray projection angle is 30°, the X-ray is projected onto the ply cord 3. The width is 108 mm, which covers the maximum variation of the ply cord length from the standard length of 100 mm. Therefore, the joint position will stop at any position within this width, and this position is estimated as described above and scanned by the X-ray sensor 4.

A commercially available photodiode is used as the X-ray sensor in order to simplify the circuit and reduce costs, but in order to perform inspection with high precision, a lead collimator slit is installed in parallel with the cord, as shown in Figure 10, to increase the resolution. is set to 0.05 mm. Since this collimator has a thickness, if the sensor is simply moved parallel to the code, the amount of X-rays on the light receiving surface will change depending on the difference in the radiation angle, as shown in FIG.

In other words, in the shaded area in FIG. 11, the collimator blocks the X-rays and cannot be received. For example, if the thickness of the collimator is 0.05 mm, the angle of incidence of the X-rays and the wall on the slit side of the collimator make Approximately 16%X for a 15° angle
Dose decreases. In order to eliminate measurement errors due to the difference in X-rays, while keeping the sensor perpendicular to the X-ray source,
It is necessary to scan at a constant speed. For this reason, a guide 18 is provided on the circumference around the X-ray source so that the X-ray sensor 4 rotates around the X-ray source 12. It is configured to scan at a constant speed while maintaining a distance. Note that, in consideration of safety and economy, the X-ray generator is configured to operate only when the sensor scans.

The signal of the joint portion thus measured is passed through the measuring circuit 11 and judged as pass/fail, as in the case of the first invention.

(Effect of the invention) In the first invention described above, the cord arrangement of a coated cord in which organic fibers with a low X-ray absorption capacity are embedded in a rubber sheet with a low X-ray absorption capacity can be inspected using X-rays. This has made it possible to discover defects in components before they occur.

Furthermore, by measuring and controlling the amount of rubber on the coated cord's selvage, a stable joint can be achieved, and it is also possible to inspect the thread arrangement of the product tire, thereby preventing the shipment of defective tires due to open cords, etc.

The second invention relates to an X-ray sensor used in the method of the first invention, which achieves a wide field of view that could not be obtained with conventional one-dimensional sensors with a simple mechanism using a commercially available photodiode array. Is possible. or,
Since a plurality of photodiode arrays are arranged in the direction in which the threads of the cord extend, the reliability of the measurement can be increased without increasing the measurement time.

According to the third invention, a 1001 width scan required for joint inspection can be achieved using a commercially available photodiode and a simple mechanism. Further, joints can be inspected in 1 second with a width of 20 mm at a high resolution of 0.05 mm. Furthermore, since the mechanism used in the present invention moves only the sensor, the mechanism of the inspection machine can be simple and inexpensive.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the first invention; Figure 2 A and B are graphs for explaining X-ray attenuation and X-ray transmittance; Figure 3 is a block diagram showing an embodiment of the first invention. A cross-sectional view of the photodiode array used; FIG. 4 is a graph showing a waveform obtained when a coated cord is measured using the first invention; FIG. 5 is a diagram showing the configuration of an embodiment of the second invention. Figures; Figures 6A and B are diagrams for explaining the effect of arranging photodiode arrays in a special arrangement; Figure 7 is a block diagram showing the operation of the second invention; Figure 8 is a diagram showing the operation of the third invention; Fig. 9 is a diagram showing the structure of the X-ray sensor of the third invention; Fig. 10 is a perspective view of a photodiode used in the third invention; Fig. 11 is a diagram for explaining changes in the X-ray dose when the photodiode is moved parallel to the cord. l...X-ray control device 2...X-ray tube 3...ply cord 4...X-ray sensor 11...measuring circuit 12...joint machine 13...
Code width detector 14...Joint part 15...
Cord end 16...Stemping motor 17
...Screw screw 18...Guide Fig. 2A Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 A Fig. 9

Claims (1)

[Claims] 1. In the first substance with a small amount of X-ray absorption, the substance is
When inspecting an object in which a second material with a different amount of radiation absorption but also a smaller amount of X-ray absorption is buried, low-energy X-rays are projected onto the object while moving the object in the horizontal direction. Then, the difference in the amount of X-ray absorption between the two substances is detected using an X-ray sensor that can detect the difference in the amount of X-ray absorption between the two substances, and the difference in the amount of X-ray absorption between the two substances is detected. A method for detecting a substance with a small amount of X-ray absorption, characterized in that the second substance is detected by calculating the difference in the amount of X-ray absorption of both the detected substances. 2. Equipped with an X-ray source that projects soft X-rays onto the object to be measured and an X-ray sensor that receives the soft X-rays that have passed through the object to be measured,
This X-ray sensor is provided with a plurality of photodiode arrays, and these photodiode arrays are arranged so as to be shifted in a first direction and overlapped in a second direction by the width of the frame of the photodiode arrays, and 2. The X-ray sensor used in the method for detecting a substance that absorbs a small amount of X-rays according to claim 1, wherein the X-ray sensor is arranged so that a gap is not formed between the light-receiving parts. 3. A measuring means for measuring an object to be measured, a conveying means for transporting the object to be measured within an X-ray radiation range based on the output of the measuring means, and emitting soft X-rays at least within the X-ray radiation range. an X-ray source that receives the X-rays that have passed through the object to be measured within the X-ray emission range; and a driving means for driving the X-ray sensor along an arcuate trajectory centered on the X-ray source so that the X-rays are incident almost perpendicularly. X-ray sensor used in the detection method.