Slit design method, chopper wheel, backscatter imaging device and signal correction method

Abstract

The present invention provides a slit design method, a chopper wheel, a backscatter imaging device, and a signal correction method. The slit design method first obtains the narrow side width of the slit based on the design imaging resolution spot height of the surface of the slit to be measured; then constructs a beam exit area model related to the chopper wheel, wherein the beam exit area is related to the wide side width of the slit and the rotation angle θ of the slit, and the rotation angle of the slit is between -θ max °~θ max °; control the rotation angle θ so that the rotation angle is θ max The beam exit area at a rotation angle of 0° is equal to the beam exit area at a rotation angle of 0°, thereby obtaining the wide side width of the slit. The slit design method, chopper wheel, backscatter imaging device, and signal correction method provided by the present invention solve the problem of uneven signal intensity after imaging caused by different exit areas of the flying spot beam emitted by existing backscatter imaging devices.

Description

Technical Field

[0001] The present invention relates to the technical field of radiation imaging inspection, and in particular to a slit design method, a chopper wheel, a backscatter imaging device and a signal correction method. Background Art

[0002] An X-ray backscatter imager is a non-contact inspection instrument based on Compton scattering. It illuminates the object under inspection with X-rays, collects the backscattered X-ray signals for imaging, and obtains information about the electron density of the object's shallow layers. Its features allow for co-location of the detector and the target, as well as its enhanced organic matter loading effect, making it ideal for inspecting large objects, interlayered objects, and contraband such as drugs and explosives. It has been widely deployed in civil aviation, customs, and public security border control departments.

[0003] Pencil beam scanning is a classic method for backscatter imaging. Prior art pencil beam generation mechanisms primarily utilize a disc-shaped chopper wheel. Typically, the chopper wheel features evenly spaced equiangular centripetal slits. The X-ray beam emitted by an X-ray machine is a cone-shaped beam, which passes through a pre-collimator before being transformed into a fan-shaped beam that irradiates the chopper disk. Except for the intersection with the slits, where X-rays are transmitted, the chopper disk absorbs the fan-shaped X-ray beam at all other locations. Driven by a chopper motor, the slits and the source's fan-shaped collimating slits form an upward and downward moving intersection. Rays emerge from this intersection as a flying-spot beam that scans upward and downward, while the object simultaneously moves left and right, enabling scanning of different locations on the target.

[0004] To achieve effective shielding, the chopper disk requires a certain thickness. Therefore, if the slit is designed as a standard concentric rectangle, the cross-section of the beam will be significantly affected by the chopper disk's rotation angle during the scanning process. The resulting X-ray flying spot will be smaller at the ends and larger in the middle, or even result in no signal at the ends. Failure to compensate for this shortcoming will lead to a serious degradation of imaging quality. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the object of the present invention is to provide a slit design method, a chopper wheel, a backscatter imaging device and a signal correction method, which are used to solve the problem that the flying spot light beams emitted by the existing backscatter imaging device have different exit areas, resulting in uneven signal intensity after imaging.

[0006] To achieve the above and other related objectives, the present invention provides a slit design method, the design method comprising:

[0007] S1): Based on the spot height of the surface of the object to be measured, the narrow side width d of the slit is obtained. min ;

[0008] S2): Construct a beam exit area model for the chopper wheel, where the beam exit area S θ The wide side width d of the slit max is related to the rotation angle θ of the slit, and the rotation angle of the slit is between -θ max °~θ max °; control the rotation angle θ in the beam exit area model so that the rotation angle is θ max The beam exit area S at ° θmax The beam exit area S0 is equal to the beam exit area S0 when the rotation angle is 0°, so the wide side width d of the slit is obtained. max ;

[0009] The opening shape of the slit is an isosceles trapezoid, the central axis of which passes through the center of the chopper wheel, and the distance from the narrow side of the slit to the center of the chopper wheel is smaller than the distance from the wide side of the slit to the center of the chopper wheel.

[0010] Optionally, the narrow side width d of the slit in S1) is min satisfy:

[0011]

[0012] Wherein, V represents the spot height on the surface of the object to be measured, L2 represents the distance between the chopper wheel and the light source, and L3 represents the distance between the surface of the object to be measured and the light source.

[0013] Optionally, the narrow side width d of the slit min Between 0.1mm and 0.8mm.

[0014] Optionally, the beam exit area model satisfies:

[0015]

[0016] in,

[0017] Wherein, a perpendicular line is drawn from the center of the chopper wheel to the optical axis of the incident light beam, D represents the distance between the projection of the incident area of ​​the slit on the perpendicular line and the center of the chopper wheel, and D min Denotes the shortest distance between the projection and the center of the chopper wheel, D max represents the farthest distance between the projection and the center of the chopper wheel; d L It is expressed as the thickness of the impeller, d θrepresents the average slit width of the slit located in the light beam incident area, L2 represents the distance between the chopper wheel and the light source, r1 represents the distance between the wide side of the slit and the center of the chopper wheel; r0 represents the distance between the narrow side of the slit and the center of the chopper wheel.

[0018] Optionally, the slit design method further includes:

[0019] S3): Based on the narrow side width d of the slit min and the wide side width d of the slit max Constructing a particle transport simulation model to simulate the process in which a light beam emitted by a light source is incident on the slit and emerges as a flying spot beam, wherein the light flux of the flying spot beam is related to the rotation angle θ;

[0020] S4): Fine-tune the wide side width d of the slit in the particle transport simulation model max until the rotation angle is θ max The outgoing luminous flux at the rotation angle of 0° is equal to the outgoing luminous flux at the rotation angle of 0°, and the adjusted wide side width d max As the final broadside width d max .

[0021] The present invention further provides a chopper wheel, wherein the chopper wheel is provided with at least one slit, and the slit is obtained by adopting the slit design method as described above.

[0022] Optionally, the chopper wheel is provided with N slits, and the N slits are distributed at equal angles on the chopper wheel, where N is an integer greater than or equal to 2.

[0023] Optionally, the thickness of the chopper wheel is greater than or equal to 3 mm.

[0024] The present invention further provides a backscatter imaging device, comprising a light source, a sector collimator, a detector, and a chopper wheel as described in any one of the preceding items; wherein,

[0025] The light beam emitted by the light source is a cone-shaped light beam;

[0026] The sector collimator is provided with a collimating diaphragm, and the cone-shaped light beam is emitted as a fan-shaped light beam after passing through the collimating diaphragm, and the optical axis of the sector collimator is coaxial with the optical axis of the light source;

[0027] The fan-shaped light beam is emitted as a flying-spot light beam after passing through the slit;

[0028] The flying spot light beam is scattered after being irradiated on the surface to be detected, and forms scattered light which enters the detector.

[0029] The present invention also provides a signal correction method, wherein the signal correction method comprises:

[0030] K1): imaging the standard test plate using the backscatter imaging device described above, measuring the signal intensity value of the surface of the object to be tested on the standard test plate, and obtaining measurement data of different test points in different slits;

[0031] K2): classifying the measurement data according to the different slits to obtain classification data for each slit;

[0032] K3): determining a standard value for each slit based on the measurement data of each test point in the classification data, and dividing the standard value of each slit by the measurement data of each test point in the classification data to obtain a correction template for each test point;

[0033] K4): Obtain a corrected signal strength value based on the correction template and the signal strength value actually collected at the corresponding measurement point.

[0034] As described above, the slit design method, chopper wheel, backscatter imaging device and signal correction method of the present invention are

[0035] 1) By setting an isosceles trapezoidal slit on the chopper wheel, the problem of no light beam emission when the rotation angle θ is large is solved;

[0036] 2): Optimize the wide side width of the slit so that the rotation angle is θ max The beam exit area when the rotation angle is 0° is equal to the beam exit area when the rotation angle is 0°, avoiding the problem of large difference in the exit light flux between the flying point beams generated by the same slit;

[0037] 3): The signal correction method provided can make the light signal intensity value detected by the detector more uniform and the imaging quality higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Shown is a flow chart of the slit design method described in the first embodiment of the present invention.

[0039] Figure 2 It shows a schematic structural diagram of the backscatter imaging device described in the first and second embodiments of the present invention.

[0040] Figure 3 The diagram shows the effect of the fan-shaped light beam incident on the chopper wheel when the slit rotation angle is θ in the first embodiment of the present invention.

[0041] Figure 4 The diagram shows the optical path of the light beam entering the slit and exiting the slit in the first embodiment of the present invention.

[0042] Figure 5 The wide side width d calculated in step S2) in the first embodiment of the present invention is displayed. max Substituting into Equation 6 yields the relationship curve between the beam exit area and the rotation angle.

[0043] Figure 6 The wide side width d calculated in step S2) in the first embodiment of the present invention is displayed. max The relationship curve between the output light flux and the rotation angle was obtained by modeling and simulation using Geant4 software.

[0044] Figure 7 The data displayed is the signal strength value data measured by the detector before the signal correction method described in the third embodiment of the present invention is adopted.

[0045] Figure 8 The display shows the signal strength value measured by the detector and the signal strength value data after correction after the signal correction method described in the third embodiment of the present invention is adopted.

[0046] Component number description

[0047] 10 Backscatter imaging device

[0048] 100 light sources

[0049] 200 Sector Collimator

[0050] 210 Collimating aperture

[0051] 300 Chopping Wheel

[0052] 310 Slit

[0053] 400 detectors

[0054] 500 objects to be detected

[0055] 510 Surface to be detected DETAILED DESCRIPTION

[0056] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0057] See also Figures 1 to 8. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they have no substantive technical significance. Any modification of the structure, change in the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0058] Example 1

[0059] like Figure 2 As shown, the backscatter imaging device 10 is generally composed of a light source 100 , a sector collimator 200 , a chopper wheel 300 and a detector 400 .

[0060] The light source 100 is an X-ray source, which can be regarded as a point light source, and its emission angle is less than 180°, so the X-ray beam it emits is a cone-shaped beam. The center of the collimating aperture 210 provided in the sector collimator 200 is located on the optical axis, and the opening of the collimating aperture 210 is perpendicular to the incident surface of the cone-shaped beam. The collimating aperture 210 blocks a portion of the incident cone-shaped beam, and the beam is emitted as a fan-shaped beam. The fan-shaped beam emitted by the collimating aperture 210 is incident on the chopper wheel 300, that is, on the slit 310. However, as shown in FIG. Figure 3 As shown, only a part of the slit 310 can overlap with the incident light beam, and the rest will be blocked. In this embodiment, the part where the incident light beam overlaps with the slit 310 is defined as the light beam incident area. Since the chopper wheel 300 is in a rotating state when working, it drives the rotation of the slit 310. When the slit 310 is at different rotation angles θ, the position where it overlaps with the incident light beam is different, that is, the position of the light beam incident area is different; and the incident light beam is a fan-shaped light beam, and the outgoing light beam will appear as a flying spot light beam, wherein the light beam exit area S of the flying spot light beam is 1 / 4. θ There will be a periodic change pattern (the beam exit area S θ The periodic change of corresponds to the periodic change of the rotation angle θ).

[0061] The rotation angle when the central axis of the slit 310 passes through the optical axis of the fan beam is defined as 0°, and the limit angle at which the slit 310 can overlap with the incident beam is defined as the maximum rotation angle ±θ max , when the slit is a long rectangular shape and satisfies -θ max °≤θ≤+θmax °, the larger the rotation angle θ is, the larger the beam exit area S of the flying spot beam is. θ Therefore, in this embodiment, the slit 310 is designed to be an isosceles trapezoidal shape to solve the problem that the larger the rotation angle θ, the larger the light beam exit area S θ wherein the central axis of the isosceles trapezoidal slit 310 passes through the center of the chopper wheel 300, and the distance from the narrow side of the slit 310 to the center is smaller than the distance from the wide side of the slit 310 to the center.

[0062] In order to better solve the problem that the larger the rotation angle θ, the larger the beam exit area S θ To further avoid the problem of too large difference in the light flux of the flying spot beams generated by the same slit 310, it is necessary to adjust the narrow side width d of the isosceles trapezoidal slit 310. min and wide side width d max Design, so Figure 1 As shown, this embodiment further provides a design method for the slit 310, and the design method for the slit 310 includes steps S1) to S2); it should be noted that, in order to briefly describe the embodiment, the slit 310 described hereafter specifically refers to a slit 310 in an isosceles trapezoidal shape.

[0063] Step S1): Obtain the narrow side width d of the slit 310 based on the spot height of the surface 510 of the object to be measured. min .

[0064] In this embodiment, since the slit 310 is provided on the chopper wheel 300, and the chopper wheel 300 is provided in the backscatter imaging device 10, the dimensional design of the wide side width and the narrow side width of the slit 310 needs to be considered based on the overall design of the backscatter imaging device 10. First, the spacing between the light source 100, the sector collimator 200, the chopper wheel 300, and the imaging surface 510 should be determined. Then, the distance between the narrow side of the slit 310 and the center of the chopper wheel, the distance between the wide side of the slit 310 and the center of the chopper wheel, and the spot height of the surface of the object to be measured 510 should be determined. The narrow side width d of the slit 310 can be further calculated and confirmed based on these parameters. min .

[0065] Specifically, the narrow side width d of the slit 310 in step S1) is min Satisfies the formula:

[0066]

[0067] Wherein, V represents the light spot height, L2 represents the distance between the chopper wheel 300 and the light source 100 , and L3 represents the distance between the surface of the object to be measured 510 and the light source 100 .

[0068] In this embodiment, when the distance L2 between the light source 100 and the chopper wheel 300 and the distance L3 between the light source 100 and the surface 510 of the object to be measured are determined, the spot height V on the surface 510 of the object to be measured is determined by the slit width 310. The two are linearly related. Therefore, the narrow side width d of the slit 310 can be calculated using the spot height V. min .

[0069] Step S2): Construct a beam exit area model for the chopper wheel 300, wherein the beam exit area S θ The width d of the wide side of the slit 310 max is related to the rotation angle θ of the slit 310, and the rotation angle of the slit 310 is between -θ max °~θ max °; control the rotation angle θ in the beam exit area model so that the rotation angle is θ max The beam exit area S at ° θmax The width d of the slit 310 is equal to the light beam exit area S0 when the rotation angle is 0°. max .

[0070] In this embodiment, Figure 3 and Figure 4 As shown, a perpendicular line is drawn from the center of the chopper wheel 300 to the optical axis of the incident fan-shaped light beam, and the slit 310 is rotated to form an angle θ with the perpendicular line. Figure 3 The rectangular box in the middle represents the area where the fan-shaped light beam irradiates the chopper wheel 300. Figure 3 The trapezoidal box diagram in the middle represents the opening shape of the slit, and the area where the rectangular box diagram and the trapezoidal box diagram overlap is the incident area of ​​the light beam, and, Figure 3 The shaded area in the middle represents the beam exit area, and the area of ​​the shaded area is the beam exit area S of the flying spot beam. θ .

[0071] The beam exit area S of the flying spot beam can be obtained by performing area integration along the vertical direction starting from the center of the chopper wheel 300. θ , its function expression is as follows:

[0072]

[0073] Where D represents the distance between the projection of the light beam incident area of ​​the slit 310 on the vertical line and the center of the chopper wheel 300, and D min represents the shortest distance between the projection and the center of the chopper wheel 300, D max represents the farthest distance between the projection and the center of the chopper wheel 300 , d2 represents the distance between the upper edge of the light beam exit area and the vertical line, and d3 represents the distance between the lower edge of the light beam exit area and the vertical line.

[0074] Furthermore, d3 can be expressed as the following functional relationship:

[0075]

[0076] Where D is the distance between the projection of the light beam incident area of ​​the slit 310 on the vertical line and the center of the chopper wheel 300, θ is the rotation angle of the slit 310, and d is θ represents the average slit width of the slit located in the light beam incident area.

[0077] And, d θ It can be expressed as the following functional relationship:

[0078]

[0079] Wherein, θ represents the rotation angle of the slit 310, r1 represents the distance between the wide side of the slit 310 and the center of the chopper wheel 300, r0 represents the distance between the narrow side of the slit and the center of the chopper wheel, and d max It is represented as the wide side width of the slit 310, d min It is represented as the narrow side width of the slit 310 .

[0080] Let d1 be the distance between the upper edge of the beam incident area and the vertical line, then d1 can be expressed as the following functional relationship:

[0081]

[0082] Then, d2 can be expressed as the following functional relationship:

[0083]

[0084] Where, d L represents the thickness of the chopper wheel 300 , and L2 represents the distance between the chopper wheel 300 and the light source 100 .

[0085] Substituting Equations 2, 3, 4, and 5 into Equation 1, we can obtain the following functional relationship:

[0086]

[0087] Where D represents the distance between the projection of the light beam incident area of ​​the slit 310 on the vertical line and the center of the chopper wheel 300, and D min represents the shortest distance between the projection and the center of the chopper wheel 300, D max represents the farthest distance between the projection and the center of the chopper wheel 300, L2 represents the distance between the chopper wheel 300 and the light source 100, d LIt is represented by the thickness of the pulsator 300, θ max Expressed as the maximum rotation angle of the slit.

[0088] Assuming the rotation angle θ = 0°, the beam exit area S0 when the rotation angle is 0° can be obtained from Equation 6; max °, then the rotation angle is θ obtained from formula 6 max The beam exit area S at ° θmax ; Let S0 = S θmax , then the width of the wide side of the slit d can be obtained max .

[0089] It should be noted that, for the backscatter imaging device 10, the light beam exit area calculated by Formula 6 can represent the light flux of the flying spot light beam irradiated on the inspected surface 510. However, in actual applications, due to the diffraction and interference of the slit, the diffraction and interference of the collimating aperture, and the reaction between the X-ray photons and the atoms of the material, there will be a certain error between the light flux of the flying spot light beam and the light beam exit area calculated by Formula 6. Therefore, the wide side width d calculated in step S2) max This is a rough value only.

[0090] In this embodiment, the design method in step S3) and step S4) is also required to adjust the width d of the wide side. max Further fine-tuning is performed to confirm a more accurate broadside width d max value, so that the rotation angle is θ max The outgoing luminous flux when the rotation angle is 0° is equal to the outgoing luminous flux when the rotation angle is 0°.

[0091] Step S3): Based on the narrow side width d of the slit min and the wide side width d of the slit max A particle transport simulation model is constructed to simulate the process in which a light beam emitted by a light source is incident on the slit and emerges as a flying spot beam, wherein the emitted light flux of the flying spot beam is related to the rotation angle θ.

[0092] In this embodiment, the particle transport simulation model can be produced using software such as Geant4 and MCNP to simulate the conical X-ray of the equal photon beam emitted by the light source 100. The X-ray passes through the collimating aperture 200 and is emitted as a fan-shaped beam. The fan-shaped beam passes through the slit 310 and is emitted as a flying spot beam. The number of photons in the finally detected flying spot beam is recorded as the emitted light flux of θ at the rotation angle.

[0093] Step S4): fine-tuning the wide side width d of the slit in the particle transport simulation model max until the rotation angle is θ maxThe outgoing luminous flux at the rotation angle of 0° is equal to the outgoing luminous flux at the rotation angle of 0°, and the adjusted wide side width d max As the final broadside width d max .

[0094] In this embodiment, the width d of the slit is fine-tuned by a step-by-step fine-tuning method. max For example, with 0.05mm as the step accuracy for fine-tuning, the width d of the slit is adjusted step by step. max In actual operation, we can refer to Figure 6 The simulation curve shown in the figure confirms the fine-tuning direction and fine-tuning results in real time. When the wide side width d of the slit is adjusted step by step max Make the two ends of the curve (rotation angle is ±θ max °) deviates further from the center of the curve (rotation angle is 0°), the width of the slit d is adjusted in the opposite direction. max After confirming the adjustment direction, fine-tune the width d of the slit. max .

[0095] As an example, Figure 5 As shown, the wide side width d calculated in step S2) is max Substituting the relationship curve between the beam exit area and the rotation angle into equation 6, it can be seen that the beam exit area at both ends of the curve is basically the same as the beam exit area at the center of the curve; Figure 6 As shown, the wide side width d calculated in step S2) is max The relationship curve between the outgoing luminous flux and the rotation angle is obtained by modeling and simulating using Gent4 software. It can be seen that the outgoing luminous flux at both ends of the curve is significantly lower than the outgoing luminous flux at the center of the curve. Therefore, for the wide side width d calculated in step S2), max It is also necessary to use the design method in steps S3) to S4) to adjust the width of the wide side d max Fine-tuning.

[0096] Example 2

[0097] This embodiment provides a chopper wheel 300 , in which the chopper wheel 300 uses the slits 310 obtained by the slit 310 design method described in the first embodiment.

[0098] In this embodiment, the thickness of the chopper wheel 300 should be greater than 3 mm. It is made of high-density metal, such as lead, tin, etc., which can effectively shield X-rays and prevent X-rays from penetrating the blocking area. The slits 310 are set on the chopper wheel 300. They can be one or more. When the number of slits 310 is greater than or equal to two, each slit 310 is set at equal intervals. As an example, the number of slits 310 is 5, and each slit 310 is set at equal intervals at an angle of 72°. In addition, the narrow side width d of the slit 310 is 1 / 4 of the width of the slit 310. min The value of is between 0.1 mm and 0.8 mm to meet the design requirements of the spot height of the backscatter imaging device 10.

[0099] This embodiment further provides a backscattering imaging device 10, which uses the chopper wheel 300 as described above. The flying spot light beam emitted by the backscattering imaging device 10 does not have a distribution situation where the light is small at both ends and large in the middle (or even where there is no signal at both ends of the flying spot light beam). In addition, the flying spot light beams generated by the same slit 310 do not have a problem of excessive difference in the emitted light flux.

[0100] Example 3

[0101] This embodiment provides a signal correction method, which is used to perform signal correction on the backscatter imaging device 10 as described in the second embodiment. The signal correction method includes steps K1) to K4).

[0102] Step K1): Use the backscatter imaging device 10 described in Example 2 to image the standard test plate 500, measure the signal intensity value of the surface 510 of the object to be tested on the standard test plate 500, and obtain measurement data of different test points in different slits 310.

[0103] In this embodiment, the side of the standard test plate 500 facing the light source 100 is the surface 510 of the object to be tested, and its thickness distribution and density are uniform, ensuring the accuracy of the measurement data; as an example, the chopper wheel 300 rotates at a constant speed, and 5 slits are set at equal angles on it, and each slit is set with 720 test points (that is, the chopper wheel sets a test point every 0.1°). Every time the chopper wheel 300 rotates one circle, 3600 points of test data can be obtained, wherein, it can be rotated only one circle to obtain one circle of test data, or it can be rotated several circles to obtain the average value of several circles of test data for each test point.

[0104] Step K2): classifying the measurement data according to the different slits 310 to obtain classification data for each slit 310 .

[0105] As an example, there are five slits set on the chopper wheel 300, 720 test data between 0°-72° belong to the classification data of the first slit, 720 test data between 72°-144° belong to the classification data of the second slit, 720 test data between 144°-216° belong to the classification data of the third slit, 720 test data between 216°-288° belong to the classification data of the fourth slit, and 720 test data between 288°-360° belong to the classification data of the fifth slit.

[0106] Step K3): determining a standard value for each slit based on the measurement data of each test point in the classification data, dividing the standard value of each slit by the test data of each test point in the classification data to obtain a correction template for each test point.

[0107] As an example, taking the classification data of the first slit as an example, a standard value is obtained based on the 720 test data it has (for example, the mean or median of the 720 test data can be directly calculated, and the obtained mean or median is the standard value), and the obtained standard value is divided by the 720 test data to obtain 720 correction values. These 720 correction values ​​are used as the correction templates for the 720 test points; the method for obtaining the correction templates for the second, third, fourth and fifth slits is the same as that for the first slit, that is, a correction value will be calculated for each test point of each slit.

[0108] Step K4): Based on the correction template and the signal strength values ​​actually collected at the corresponding measurement points, a corrected signal strength value is obtained.

[0109] In this embodiment, the backscatter imaging device 10 is used to image the surface of the object, and the signal strength value actually detected by the detector will also be differentiated according to the angle correspondence, and then multiplied by the correction value of the corresponding measurement point to obtain the corrected signal strength value; for example, the signal strength value measured when the chopper wheel rotation angle is 0.1° is multiplied by the correction value of the measurement point when the chopper wheel rotation angle is 0.1° to obtain the corrected signal strength value of 0.1°; the signal strength value actually measured within the rotation angle of 0°-72° is multiplied by the correction template of the first slit to obtain the corrected signal strength value of the first slit.

[0110] As an example, Figure 7 As shown in FIG. 1 , before the signal correction method of this embodiment is used, the surface of a standard test plate with uniform thickness and density is imaged by the detector 400, and the signal intensity value data is measured. Figure 7The signal intensity data of 5 slits are displayed in FIG. 1 . The difference between the peak value and the valley value of the signal intensity value of each slit is large, which affects the final imaging quality of the detector 400. Figure 8 As shown, the detector 400 is used to image the surface of a standard test plate with uniform thickness and uniform density, and after adopting the signal correction method described in this embodiment, the signal intensity value measured by the detector 400 is corrected data. Figure 8 The display also shows the signal intensity value data of 5 slits. The difference between the peak value and the valley value of the signal intensity value of each slit is relatively small, and the final imaging quality of the detector 400 is high.

[0111] In summary, the slit design method, chopper wheel, backscatter imaging device and signal correction method provided by the present invention solve the problem of no light beam emission when the rotation angle θ is large by setting an isosceles trapezoidal slit on the chopper wheel; optimize the wide side width of the slit so that the rotation angle θ is max The beam exit area at a rotation angle of 0° is equal to the beam exit area at a rotation angle of 0°, avoiding the problem of large differences in the exiting light flux between flying spot beams generated by the same slit. The provided signal correction method can make the light signal intensity values ​​detected by the detector more uniform, thereby improving imaging quality. Therefore, the present invention effectively overcomes various shortcomings of the existing technology and has high industrial application value.

[0112] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for designing a slit, characterized in that: The design method includes: S1): Based on the spot height of the surface of the object to be measured, the narrow side width d of the slit is obtained. min ; S2): Construct a beam exit area model for the chopper wheel, where the beam exit area S θ The wide side width d of the slit max is related to the rotation angle θ of the slit, and the rotation angle of the slit is between -θ max °~θ max °; control the rotation angle θ in the beam exit area model so that the rotation angle is θ max The beam exit area S at ° θmax The beam exit area S0 is equal to the beam exit area S0 when the rotation angle is 0°, so the wide side width d of the slit is obtained. max ; The opening shape of the slit is an isosceles trapezoid, the central axis of which passes through the center of the chopper wheel, the distance from the narrow side of the slit to the center of the chopper wheel is smaller than the distance from the wide side of the slit to the center of the chopper wheel; the incident light beam is a fan-shaped light beam; the maximum angle at which the slit can overlap with the incident light beam is ±θ max The rotation angle of the slit when the central axis passes through the optical axis of the fan-shaped beam is 0°.

2. The method for designing a slit according to claim 1, wherein: S1) The narrow side width d of the slit min satisfy: Wherein, V represents the spot height on the surface of the object to be measured, L2 represents the distance between the chopper wheel and the light source, L3 represents the distance between the surface of the object to be measured and the light source.

3. The method for designing a slit according to claim 1, wherein: The narrow side width d of the slit min Between 0.1mm and 0.8mm.

4. The method for designing a slit according to claim 1, wherein: The beam exit area model satisfies: in, Wherein, a perpendicular line is drawn from the center of the chopper wheel to the optical axis of the incident light beam, D represents the distance between the projection of the incident area of ​​the slit on the perpendicular line and the center of the chopper wheel, and D min Denotes the shortest distance between the projection and the center of the chopper wheel, D max represents the farthest distance between the projection and the center of the chopper wheel; d L Expressed as the thickness of the chopper wheel, d θ represents the average slit width of the slit located in the light beam incident area, L2 represents the distance between the chopper wheel and the light source, r1 represents the distance between the wide side of the slit and the center of the chopper wheel; r0 represents the distance between the narrow side of the slit and the center of the chopper wheel.

5. The method for designing a slit according to any one of claims 1 to 4, characterized in that: The slit design method further includes: S3): Based on the narrow side width d of the slit min and the wide side width d of the slit max Constructing a particle transport simulation model to simulate the process in which a light beam emitted by a light source is incident on the slit and emerges as a flying spot beam, wherein the light flux of the flying spot beam is related to the rotation angle θ; S4): Fine-tune the wide side width d of the slit in the particle transport simulation model max until the rotation angle is θ max The outgoing luminous flux at the rotation angle of 0° is equal to the outgoing luminous flux at the rotation angle of 0°, and the adjusted wide side width d max As the final broadside width d max .

6. A chopper wheel, characterized in that: The chopper wheel is provided with at least one slit, and the slit is obtained by adopting the slit design method according to any one of claims 1 to 5.

7. The chopper wheel according to claim 6, characterized in that: The chopper wheel is provided with N slits, and the N slits are distributed at equal angles on the chopper wheel, where N is an integer greater than or equal to 2.

8. The chopper wheel according to claim 6, characterized in that: The thickness of the chopper wheel is greater than or equal to 3 mm.

9. A backscatter imaging device, characterized in that: The backscatter imaging device comprises a light source, a sector collimator, a detector and a chopper wheel according to any one of claims 6 to 8; wherein, The light beam emitted by the light source is a cone-shaped light beam; The sector collimator is provided with a collimating diaphragm, and the cone-shaped light beam is emitted as a fan-shaped light beam after passing through the collimating diaphragm, and the optical axis of the sector collimator is coaxial with the optical axis of the light source; The fan-shaped light beam is emitted as a flying-spot light beam after passing through the slit; The flying spot light beam is scattered after being irradiated on the surface to be detected, and forms scattered light which enters the detector.

10. A signal correction method, characterized in that: The signal correction method comprises: K1): imaging a standard test plate using the backscatter imaging device according to claim 9, measuring the signal intensity value of the surface of the object to be tested on the standard test plate, and obtaining measurement data of different test points in different slits; K2): classifying the measurement data according to different slits to obtain classification data for each slit; K3): determining a standard value for each slit based on the measurement data of each test point in the classification data, and dividing the standard value for each slit by the measurement data of each test point in the classification data to obtain a correction template for each test point; K4): Obtaining a corrected signal strength based on the correction template and the signal strength values ​​actually collected at the corresponding measurement points.

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