A coaxial dual-mode x-ray ct detection control method and system

Abstract

This invention discloses a coaxial dual-mode X-ray CT detection control method and system, relating to the field of industrial X-ray CT nondestructive testing control technology. The method establishes a three-dimensional spatial coordinate system with the X-ray source focal point as the origin and the Z-axis vertically upward as the unified spatial reference. The cone-beam CT rotation axis Rx is parallel to the X-axis, and the focal point, the cone-beam CT rotation center, and the flat panel detector reference position are collinear on the Z-axis. After geometric calibration, the distance FOD from the source focal point to the cone-beam CT rotation center and the distance FDD from the source focal point to the flat panel detector are obtained. In planar CT mode, the detector swings along an arc sliding trajectory to acquire projected images, and the geometric calibration parameters are called using the sliding angle as a variable for projection mapping. This invention, by having the focal point, rotation center, and detector reference position collinear on the Z-axis, allows the two modes to share the same spatial reference and geometric calibration parameters, eliminating the need for recalibration during mode switching.

Description

Technical Field

[0001] This invention relates to the field of industrial X-ray CT nondestructive testing control technology, specifically a coaxial dual-mode X-ray CT testing control method and system. Background Technology

[0002] In the field of non-destructive testing in electronic manufacturing, X-ray computed tomography (CT) technology is widely used for detecting internal defects in printed circuit boards, semiconductor packages, electronic components, and electromechanical assemblies. Depending on the shape of the object being inspected and the required inspection cycle, existing X-ray CT inspections typically include planar CT inspection methods suitable for rapid screening of plate-shaped workpieces, and cone-beam CT inspection methods suitable for three-dimensional reconstruction of three-dimensional workpieces.

[0003] The limitations of existing technologies include at least the following problems: existing planar CT and cone-beam CT are usually built based on different acquisition geometry and motion control benchmarks, and there are differences between the two in motion axis settings, coordinate benchmarks, calibration parameters and projection mapping relationships; when integrating the two types of CT detection methods into the same device, if there is a lack of unified spatial benchmarks and control benchmarks, it is still necessary to establish and maintain geometric calibration parameter systems separately, which makes it difficult to reuse calibration parameters in the dual-mode detection process, affecting the rapid switching control between rapid planar CT detection and complete cone-beam CT reconstruction on the same platform. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a coaxial dual-mode X-ray CT detection control method and system, which solves the problem that in existing industrial X-ray CT detection, planar CT and cone-beam CT are constructed based on different spatial and control references, resulting in difficulty in reusing geometric calibration parameters and low mode switching control efficiency during dual-mode detection.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a coaxial dual-mode X-ray CT detection control method, comprising the following steps: establishing a unified spatial reference, with the X-ray source focus as the origin, the vertical direction as the Z-axis, and the horizontal directions as the X-axis and Y-axis respectively, establishing a three-dimensional spatial coordinate system as the unified spatial reference, the cone-beam CT rotation axis Rx being parallel to the X-axis, the cone-beam CT rotation center located on the Z-axis, the arc sliding trajectory of the flat panel detector located on an arc with the X-ray source focus as the center and the distance FDD from the source focus to the detector as the radius, the reference position of the flat panel detector located directly above the X-ray source focus, and the X-ray source focus, the cone-beam CT rotation center, and the reference position of the flat panel detector collinear on the Z-axis; completing geometric calibration based on the unified spatial reference to obtain geometric calibration parameters, the geometric calibration parameters including at least the distance FOD from the source focus to the cone-beam CT rotation center and the distance FDD from the source focus to the flat panel detector, the cone-beam CT detection mode and the planar CT detection mode sharing these geometric calibration parameters; in the planar CT detection mode, the plate-shaped workpiece to be tested... The workpiece is placed horizontally on the stage. The stage is moved along the X and Y axes to align the area to be measured directly above the X-ray source focal point. The flat panel detector is controlled to slide along an arc trajectory within a preset angle range and acquire planar CT projection images. During the sliding process, the normal of the flat panel detector always points to the X-ray source focal point. The sliding angle of the flat panel detector is used as the angle variable for projection mapping, and geometric calibration parameters are called for projection mapping. In cone-beam CT detection mode, the cone-beam CT shaft is mounted on the cone-beam CT rotation axis, and the workpiece to be measured is fixed on the cone-beam CT shaft. The cone-beam CT shaft is controlled to move along the Z-axis to adjust the distance FOD from the source focal point to the cone-beam CT rotation center. The cone-beam CT rotation axis Rx is controlled to rotate and acquire cone-beam CT projection images. The rotation angle of Rx is used as the angle variable for projection mapping, and the same geometric calibration parameters as in the planar CT detection mode are called for projection mapping. When switching between planar CT detection mode and cone-beam CT detection mode, the unified spatial reference remains unchanged, and the geometric calibration parameters are reused without repeating the geometric calibration process.

[0006] Furthermore, geometric calibration based on a unified spatial reference includes: placing a calibration phantom containing known feature points at the rotation center of the cone-beam CT; controlling the rotation axis Rx of the cone-beam CT in cone-beam CT detection mode to acquire calibration projection images of the calibration phantom at multiple rotation angles; solving for geometric calibration parameters based on the actual coordinates of the known feature points under the unified spatial reference and their pixel coordinates in the calibration projection images, where the projection magnification ratio satisfies the relationship: μ=FDD / FOD; where μ is the projection magnification ratio, FDD is the distance from the source focus to the flat panel detector, and FOD is the distance from the source focus to the rotation center of the cone-beam CT; the geometric calibration parameters include at least the distance FOD from the source focus to the rotation center of the cone-beam CT and the distance FDD from the source focus to the flat panel detector; verifying the geometric calibration parameters based on the deviation between the theoretical pixel coordinates and the actual pixel coordinates of the known feature points, and updating the geometric calibration parameters when the deviation exceeds a preset threshold.

[0007] Furthermore, in the planar CT detection mode, the projection mapping by calling geometric calibration parameters includes: obtaining the real-time sliding angle of the flat panel detector along the arc sliding trajectory; determining the spatial position and orientation of the flat panel detector under a unified spatial reference based on the real-time sliding angle and the distance FDD from the source focus to the flat panel detector in the geometric calibration parameters; establishing the correspondence between the workpiece spatial coordinates and the detector pixel coordinates by using the sliding angle of the flat panel detector as the angle variable for projection mapping; performing geometric correction on the planar CT projection image based on the correspondence, and performing tomographic synthesis reconstruction.

[0008] Furthermore, in cone-beam CT detection mode, the projection mapping using geometric calibration parameters includes: obtaining the real-time rotation angle of the cone-beam CT rotation axis Rx; determining the spatial position of the workpiece under a unified spatial reference based on the real-time rotation angle and the distance FOD from the source focus to the cone-beam CT rotation center in the geometric calibration parameters; using the rotation angle of the cone-beam CT rotation axis Rx as the angle variable for projection mapping, calling the same geometric calibration parameters as in planar CT detection mode to establish the correspondence between the workpiece spatial coordinates and the detector pixel coordinates; performing geometric correction on the cone-beam CT projection image based on the correspondence, and performing cone-beam CT reconstruction.

[0009] Furthermore, the switching between planar CT detection mode and cone-beam CT detection mode includes: receiving a mode switching command and determining the target detection mode; when the target detection mode is cone-beam CT detection mode, moving the flat panel detector to the reference position and locking it, installing the cone-beam CT shaft, and connecting the cone-beam CT rotation axis Rx to the rotation drive mechanism; when the target detection mode is planar CT detection mode, disassembling the cone-beam CT shaft or rotating the cone-beam CT shaft to a position that does not interfere with the planar CT optical path and locking it, and releasing the locked state of the flat panel detector; during the switching process, maintaining a unified spatial reference, directly calling the stored geometric calibration parameters, starting the projection acquisition process of the target detection mode, and not repeating the geometric calibration process; the movement of the cone-beam CT shaft along the Z-axis direction and the movement of the stage along the Z-axis direction are controlled in conjunction or independently.

[0010] Furthermore, controlling the flat panel detector to swing along an arc-shaped sliding trajectory in planar CT detection mode includes: setting the sliding start angle, end angle, and acquisition angle interval of the flat panel detector according to the size of the plate-shaped workpiece and the detection requirements, with the sliding start angle and end angle being symmetrical about the Z-axis; controlling the flat panel detector to move along an arc-shaped sliding trajectory between the start angle and the end angle, with the normal of the flat panel detector always pointing towards the focal point of the X-ray source during the sliding process; controlling the X-ray source to emit X-rays and acquire the planar CT projection image at the corresponding angle position when the flat panel detector reaches each acquisition angle position; and recording the sliding angle of the flat panel detector corresponding to each planar CT projection image.

[0011] Furthermore, controlling the rotation of the cone-beam CT rotation axis Rx in cone-beam CT detection mode includes: setting the preset rotation range, rotation direction, and acquisition angle interval of the cone-beam CT rotation axis Rx according to the three-dimensional reconstruction requirements of the three-dimensional workpiece; controlling the cone-beam CT rotation axis Rx to rotate within the preset rotation range; controlling the X-ray source to emit X-rays and acquire the cone-beam CT projection image at the corresponding angle position when the cone-beam CT rotation axis Rx reaches each acquisition angle position; and recording the rotation angle of the cone-beam CT rotation axis Rx corresponding to each cone-beam CT projection image.

[0012] Further, the verification of geometric calibration parameters includes: selecting multiple known feature points on the calibration model and recording the actual coordinates of each known feature point under a unified spatial reference; substituting the actual coordinates of each known feature point into the projection mapping model corresponding to the geometric calibration parameters to calculate the theoretical pixel coordinates of each known feature point; extracting the actual pixel coordinates of each known feature point in the calibration projection image; calculating the deviation between the theoretical pixel coordinates and the actual pixel coordinates of each known feature point; when all deviation values ​​are less than a preset threshold, the geometric calibration parameters are deemed qualified; when at least one deviation value exceeds the preset threshold, the calibration projection image is re-acquired and the geometric calibration parameters are updated until the deviation value meets the preset threshold.

[0013] Furthermore, in cone-beam CT detection mode, the flat panel detector is fixed at a reference position as the projection receiving surface of the cone-beam CT. The plane of the flat panel detector is parallel to the XY plane, and the projection mapping of the cone-beam CT shares the pixel coordinate system of the flat panel detector.

[0014] A coaxial dual-mode X-ray CT detection and control system includes: a unified spatial reference establishment module for establishing a unified spatial reference, using the X-ray source focal spot as the origin, the vertical direction as the Z-axis, and the horizontal directions as the X-axis and Y-axis respectively, to establish a three-dimensional spatial coordinate system. The cone-beam CT rotation axis Rx is parallel to the X-axis, the cone-beam CT rotation center is located on the Z-axis, and the circular sliding trajectory of the flat panel detector is located on an arc with the X-ray source focal spot as the center and the distance FDD from the source focal spot to the detector as the radius. The X-ray source focal spot, the cone-beam CT rotation center, and the reference position of the flat panel detector are collinear on the Z-axis; and a geometric calibration module for performing geometric calibration based on the unified spatial reference to obtain geometric calibration parameters, which include at least the distance FOD from the source focal spot to the cone-beam CT rotation center, the distance FDD from the source focal spot to the flat panel detector, and the cone-beam CT detection mode. The geometric calibration parameters are shared with the planar CT detection mode. The planar CT detection control module is used to control the flat panel detector to swing along the arc sliding trajectory within a preset angle range and acquire planar CT projection images in the planar CT detection mode. The sliding angle of the flat panel detector is used as the angle variable for projection mapping, and the geometric calibration parameters are called for projection mapping. The cone-beam CT detection control module is used to control the rotation of the cone-beam CT rotation axis Rx and acquire cone-beam CT projection images in the cone-beam CT detection mode. The rotation angle of Rx is used as the angle variable for projection mapping, and the same geometric calibration parameters as the planar CT detection mode are called for projection mapping. The mode switching control module is used to maintain a unified spatial reference when switching between the planar CT detection mode and the cone-beam CT detection mode, and reuse the geometric calibration parameters without repeating the geometric calibration process.

[0015] The present invention has the following beneficial effects:

[0016] (1) The coaxial dual-mode X-ray CT detection control method establishes a three-dimensional spatial coordinate system with the X-ray source focus as the origin and the Z-axis vertically upward as a unified spatial reference, and makes the X-ray source focus, cone-beam CT rotation center, and flat panel detector reference position collinear on the Z-axis, so that the cone-beam CT subsystem and the planar CT subsystem describe their respective spatial geometric relationships in the same coordinate system. In cone-beam CT mode, the cone-beam CT axis moves along the Z-axis to adjust the distance FOD from the source focus to the rotation center to change the magnification ratio, and rotates around the rotation axis Rx parallel to the X-axis to complete multi-angle projection acquisition. In planar CT mode, the stage moves the area to be measured along the X-axis and Y-axis to the Z-axis direction, and the detector slides along the arc with the source focus as the center and keeps the normal always pointing to the source focus. The movements of the two subsystems are independent, but they share the FOD and FDD parameters in the same coordinate system, so that the equipment does not need to establish independent spatial references for the two detection modes at the hardware level, and the control system does not need to maintain different coordinate transformation logic.

[0017] (2) The coaxial dual-mode X-ray CT detection control method completes a geometric calibration under a unified spatial reference, uses cone-beam CT rotation to acquire multi-angle projections of the calibration phantom, and determines the distance FOD from the source focus to the rotation center of the cone-beam CT and the distance FDD from the source focus to the flat panel detector based on the projection magnification ratio, forming geometric calibration parameters that can be directly called by both detection modes; in planar CT mode, the detector slides along the arc, and the FDD parameters are called to determine the spatial position of the detector and establish the mapping between the workpiece spatial coordinates and pixel coordinates; in cone-beam CT mode, the cone-beam CT rotation axis rotates, and the same FOD and FDD parameters are called to determine the spatial position of the workpiece and establish the mapping; if the production line needs to perform cone-beam CT precision analysis on suspicious samples after rapid screening by planar CT, it can directly switch the detection mode without repositioning the calibration phantom or repeating the acquisition of calibration projections, and the continuity of the detection process and the efficiency of on-site response are substantially improved.

[0018] (3) The coaxial dual-mode X-ray CT detection control method achieves rapid switching between two detection modes by designing the cone-beam CT shaft as a detachable structure or a biased structure that can be rotated to a position that does not interfere with the planar CT optical path. When switching to cone-beam CT mode, the cone-beam CT shaft is installed or the biased cone-beam CT shaft is rotated to the working position in the Z-axis direction, and the flat panel detector is fixed at the reference position as the projection receiving surface of the cone-beam CT. When switching to planar CT mode, the cone-beam CT shaft is disassembled or rotated to the biased position and locked, releasing the sliding degree of freedom of the flat panel detector. During the entire switching process, the X-ray source focal point position remains fixed, the unified spatial reference does not change, and the stored FOD and FDD parameters are directly reused without repeating the geometric calibration process. This switching method is suitable for mixed-line scenarios in electronic manufacturing production lines where plate-shaped workpieces and three-dimensional workpieces are alternately detected, avoiding repeated interruptions of the production line for calibration due to mode switching.

[0019] (4) The coaxial dual-mode X-ray CT detection and control system initializes the three-dimensional spatial coordinate system through the unified spatial reference establishment module and determines the collinear relationship between the cone-beam CT rotation center, the flat panel detector reference position and the source focus. The geometric calibration module completes one-time calibration using cone-beam CT rotation acquisition and outputs FOD and FDD parameter sets. The planar CT detection control module and the cone-beam CT detection control module execute motion control and projection acquisition of their respective modes and both call the parameters output by the same geometric calibration module. The mode switching control module coordinates the state transition of each module and keeps the spatial reference unchanged. After the system completes one calibration during the factory commissioning stage, the two detection modes can use the calibration results for operation. If the relative geometric relationship between the X-ray source, detector and rotation center does not change during subsequent use, the operator can complete the detection tasks of different workpieces without repeating the calibration, thus reducing the workload of daily maintenance.

[0020] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0021] Figure 1 This is a flowchart of a coaxial dual-mode X-ray CT detection control method according to the present invention.

[0022] Figure 2 This is a flowchart illustrating the steps of geometric calibration based on a unified spatial reference in a coaxial dual-mode X-ray CT detection and control method of the present invention.

[0023] Figure 3 This is a block diagram of a coaxial dual-mode X-ray CT detection and control system according to the present invention. Detailed Implementation

[0024] Please see Figure 1This invention provides a technical solution: a coaxial dual-mode X-ray CT detection control method, comprising the following steps: establishing a unified spatial reference, with the X-ray source focus as the origin, the vertical direction as the Z-axis, and the horizontal directions as the X-axis and Y-axis respectively, establishing a three-dimensional spatial coordinate system as the unified spatial reference, the cone-beam CT rotation axis Rx being parallel to the X-axis, the cone-beam CT rotation center located on the Z-axis, the circular sliding trajectory of the flat panel detector located on an arc with the X-ray source focus as the center and the distance FDD from the source focus to the detector as the radius, the reference position of the flat panel detector located directly above the X-ray source focus, and the X-ray source focus, the cone-beam CT rotation center, and the reference position of the flat panel detector collinear on the Z-axis; completing geometric calibration based on the unified spatial reference to obtain geometric calibration parameters, the geometric calibration parameters including at least the distance FOD from the source focus to the cone-beam CT rotation center and the distance FDD from the source focus to the flat panel detector, the cone-beam CT detection mode and the planar CT detection mode sharing the geometric calibration parameters; in the planar CT detection mode, the plate-shaped workpiece to be tested is placed horizontally. Placed on the stage, the stage is moved along the X and Y axes to align the area to be measured directly above the X-ray source focal point. The flat panel detector is controlled to slide along an arc trajectory within a preset angle range and acquire planar CT projection images. During the sliding process, the normal of the flat panel detector always points to the X-ray source focal point. The sliding angle of the flat panel detector is used as the angle variable for projection mapping, and geometric calibration parameters are called for projection mapping. In cone-beam CT detection mode, the cone-beam CT shaft is mounted on the cone-beam CT rotation axis, and the three-dimensional workpiece to be measured is fixed on the cone-beam CT shaft. The cone-beam CT shaft is controlled to move along the Z-axis to adjust the distance FOD from the source focal point to the cone-beam CT rotation center. The cone-beam CT rotation axis Rx is controlled to rotate and acquire cone-beam CT projection images. The rotation angle of Rx is used as the angle variable for projection mapping, and the same geometric calibration parameters as in the planar CT detection mode are called for projection mapping. When switching between planar CT detection mode and cone-beam CT detection mode, the unified spatial reference remains unchanged, and the geometric calibration parameters are reused without repeating the geometric calibration process.

[0025] Among them, the X-ray source focal point, the cone-beam CT rotation center, and the flat panel detector reference position are collinear on the Z-axis, so that the cone-beam CT subsystem and the planar CT subsystem describe their respective geometric relationships under the same spatial reference.

[0026] When the cone-beam CT axis moves along the Z-axis, the distance FOD from the source focus to the cone-beam CT rotation center changes, thereby adjusting the geometric magnification ratio of different objects.

[0027] When the flat panel detector slides along an arc centered on the source focus, the distance FDD from the source focus to the flat panel detector remains constant.

[0028] Specifically, such as Figure 2As shown, geometric calibration based on a unified spatial reference includes:

[0029] The calibration phantom containing known feature points is placed at the rotation center of cone-beam CT. Specifically, the calibration phantom is a dot matrix high-precision calibration phantom made of high-density metal. Multiple sets of metal markers with fixed spacing and known spatial coordinates are arranged in a regular array inside the phantom.

[0030] In one embodiment, the markers are arranged in a 5×5 dot matrix, with a horizontal spacing of 0.5 mm, a vertical spacing of 0.5 mm, and a marker diameter of 0.1 mm.

[0031] When placing the calibration phantom, ensure that its center coincides with the rotation center of the cone-beam CT, so that the calibration phantom is in the central region of a unified spatial reference.

[0032] In cone-beam CT detection mode, the cone-beam CT rotation axis Rx is controlled to rotate, and calibration projection images of the calibration phantom at multiple rotation angle positions are acquired, specifically as follows:

[0033] In one implementation, Rx is rotated 360°, and the angle interval is 1°, so a total of 360 projection images at the calibrated angle positions are collected. The collected projection data completely covers the angle range required for solving the geometric parameters.

[0034] Based on the known actual coordinates of feature points under a unified spatial reference and their pixel coordinates in the calibration projection image, the geometric calibration parameters are solved, specifically as follows:

[0035] By combining the geometric relationship of a unified spatial reference and utilizing the triangulation principle of X-ray projection, the optical path parameters are calculated in reverse by using the actual spatial coordinates of known feature points and the pixel coordinates in the projected image.

[0036] The projection magnification ratio satisfies the following relationship:

[0037] μ = FDD / FOD;

[0038] Where μ is the projection magnification ratio, FDD is the distance from the source focus to the flat panel detector, and FOD is the distance from the source focus to the center of rotation of the cone-beam CT.

[0039] This relationship is used to associate spatial coordinates with pixel coordinates, and all geometric calibration parameters are solved based on this relationship.

[0040] The geometric calibration parameters include at least the distance FOD from the source focal spot to the cone-beam CT rotation center and the distance FDD from the source focal spot to the flat panel detector, specifically:

[0041] The distance from the source focal point to the center of rotation of the cone-beam CT (FOD) determines the geometric magnification ratio of the cone-beam CT, which is adjusted by moving the cone-beam CT shaft along the Z-axis.

[0042] In one implementation, the FOD adjustment range is 80mm to 200mm;

[0043] The distance from the source focal point to the flat panel detector (FDD) determines the geometric magnification ratio of planar CT.

[0044] In one implementation, the FDD value is 300 mm.

[0045] Based on the deviation between the theoretical and actual pixel coordinates of known feature points, the geometric calibration parameters are verified, and updated when the deviation exceeds a preset threshold. Specifically:

[0046] Substitute the actual spatial coordinates of each known feature point into the projection mapping model corresponding to the solved geometric calibration parameters, calculate the theoretical pixel coordinates of the feature point, extract the actual pixel coordinates of the feature point in the projected image, and calculate the lateral and longitudinal deviations between the two.

[0047] The preset deviation threshold is 0.2 pixels. If the deviation of all feature points is less than this threshold, the geometric calibration parameters are considered to be qualified.

[0048] If the deviation of any feature point exceeds the threshold, the calibrated projection image is re-acquired, the geometric calibration parameters are solved and verified again, until the deviation of all feature points meets the preset threshold.

[0049] Specifically, in planar CT detection mode, calling geometric calibration parameters for projection mapping includes:

[0050] The real-time sliding angle of the flat panel detector along the circular arc sliding trajectory is obtained as follows:

[0051] An angle encoder is installed on the sliding mechanism of the flat panel detector. The angle encoder moves synchronously with the detector and collects the sliding angle value of the detector in real time. The data acquisition frequency is synchronized with the X-ray exposure frequency, and the accuracy of the acquired angle data is 0.01°.

[0052] Based on the real-time sliding angle and the distance FDD from the source focus to the flat panel detector in the geometric calibration parameters, the spatial position and attitude of the flat panel detector under a unified spatial reference are determined, specifically as follows:

[0053] Based on a three-dimensional coordinate system with a unified spatial reference, the detector is located on an arc with the source focus as the center and FDD as the radius, and its normal always points to the center of the circle;

[0054] In one embodiment, the sliding angle range of the flat panel detector is ±70°, that is, from position D5 to position D3, with a total angle coverage of approximately 140°.

[0055] Using the sliding angle of the flat panel detector as the angle variable for projection mapping, a correspondence between the workpiece spatial coordinates and the detector pixel coordinates is established. The sliding angle of the flat panel detector is substituted into the projection mapping model established based on geometric calibration parameters. When the sliding angle changes, the angle parameters in the projection mapping model are updated synchronously to adjust the correspondence between the workpiece spatial coordinates and the detector pixel coordinates.

[0056] Geometric correction is performed on the planar CT projection image based on the correspondence, and finite-angle tomographic reconstruction is then carried out, specifically as follows:

[0057] Distortion correction is performed on the projected image. The projected images under different sliding angles are offset and aligned according to the geometric calibration parameters. The tomographic synthesis and reconstruction algorithm is used to stack the aligned multiple projected images and output the tomographic image of the plate-shaped workpiece along the Z-axis.

[0058] In one implementation, the reconstruction layer thickness is between 0.1 mm and 0.5 mm.

[0059] Specifically, in cone-beam CT detection mode, calling geometric calibration parameters for projection mapping includes:

[0060] The real-time rotation angle of the cone-beam CT rotation axis Rx is obtained as follows:

[0061] An angle encoder is installed on the cone-beam CT rotation drive mechanism to collect the rotation angle signal of Rx in real time. The acquisition frequency is 200Hz and the angle accuracy reaches 0.005°.

[0062] Based on the real-time rotation angle and the distance FOD from the source focus to the rotation center of the cone-beam CT in the geometric calibration parameters, the spatial position of the workpiece under a unified spatial reference is determined, specifically as follows:

[0063] Using the cone-beam CT rotation center as a reference and combining the real-time rotation angle of Rx, the absolute coordinates of every spatial point around the workpiece are determined by three-dimensional coordinate system conversion.

[0064] Using the rotation angle of the cone-beam CT rotation axis Rx as the angle variable for projection mapping, and calling the same geometric calibration parameters as the planar CT detection mode, the correspondence between the workpiece spatial coordinates and the detector pixel coordinates is established.

[0065] Without changing any geometric calibration parameters or resetting the projection mapping model, the FOD and FDD parameters that have been calibrated in the planar CT detection mode are directly used. Only the angle variable of the projection mapping is replaced by the sliding angle of the flat panel detector and the rotation angle of the cone-beam CT rotation axis Rx, so as to realize the cross-mode reuse of calibration parameters.

[0066] Geometric correction is performed on cone-beam CT projection images based on correspondence, and cone-beam CT reconstruction is then performed;

[0067] Distortion correction is performed on the projected images. Spatial positioning correction is performed on each projected image based on geometric calibration parameters and real-time rotation angle. The FDK cone-beam reconstruction algorithm is used to calculate the projection data acquired from all angles to generate a complete three-dimensional voxel model of the workpiece.

[0068] Specifically, switching between planar CT detection mode and cone-beam CT detection mode includes:

[0069] The receiver receives the mode switching command and determines the target detection mode, specifically as follows:

[0070] The host computer of the equipment issues a mode switching command. After receiving the command, the control system first pauses all actions in the current detection mode, and then parses the command to determine the target detection mode.

[0071] When the target detection mode is cone-beam CT detection mode, move the flat panel detector to the reference position and lock it, install the cone-beam CT shaft, and connect the cone-beam CT rotation axis Rx to the rotation drive mechanism, specifically as follows:

[0072] The reference position of the flat panel detector is directly above the source focus on the Z-axis. After locking, the detector plane is parallel to the XY plane and serves as the projection receiving surface for cone-beam CT.

[0073] The cone-beam CT shaft is mounted on the cone-beam CT rotating shaft via a mechanical interface;

[0074] When the target detection mode is planar CT detection mode, disassemble the cone-beam CT shaft or rotate the cone-beam CT shaft to a position that does not interfere with the planar CT optical path and lock it to release the locked state of the flat panel detector. Specifically:

[0075] When the cone-beam CT shaft has a detachable structure, the shaft is removed from the cone-beam CT rotating shaft.

[0076] When the cone-beam CT shaft adopts an offset structure, the shaft is rotated to a position off the Z-axis and locked by mechanical or manual means to avoid obstructing the imaging optical path of the planar CT.

[0077] During the switching process, the unified spatial reference remains unchanged. The stored geometric calibration parameters are directly called to start the projection acquisition process of the target detection mode, without repeating the geometric calibration process. Specifically:

[0078] During mode switching, the three-dimensional spatial coordinate system remains unchanged, the source focus position is not changed, and the collinearity relationship of the three points is not adjusted. The control system directly calls the stored FOD and FDD parameters without re-executing the geometric calibration process.

[0079] The movement of the cone-beam CT axis along the Z-axis is controlled in conjunction with or independently of the movement of the stage along the Z-axis.

[0080] Specifically, controlling the flat panel detector to swing along a circular arc trajectory in planar CT detection mode includes:

[0081] Based on the size of the plate-shaped workpiece and the detection requirements, the sliding start angle, end angle, and acquisition angle interval of the flat panel detector are set as follows:

[0082] The sliding start and end angles are symmetrical about the Z-axis to ensure bilateral angle coverage required for planar CT tomography.

[0083] In one implementation, for a printed circuit board with a thickness of 1mm to 5mm, the starting angle is set to -70°, the ending angle is set to +70°, the angle interval is 2°, and a total of 71 angular positions of projected images are collected.

[0084] The flat panel detector is controlled to move along an arc sliding trajectory between the starting angle and the ending angle. The detector is controlled to slide at a constant speed along an arc centered on the source focus through the detector sliding drive mechanism. During the sliding process, the normal of the flat panel detector always points to the X-ray source focus. Limit protection is set at the starting angle and the ending angle to prevent the sliding from exceeding the range and damaging the mechanical structure.

[0085] When the flat panel detector reaches each acquisition angle position, the X-ray source is controlled to emit X-rays and acquire the corresponding planar CT projection image at the angle position. Specifically:

[0086] After the detector reaches the acquisition angle position, it remains stationary. After a delay to eliminate the inertial jitter of the mechanism, the X-ray source is controlled to emit X-rays.

[0087] In one embodiment, the X-ray energy is set to 50kV to 100kV, and the exposure time is set to 10ms.

[0088] The sliding angle of the flat panel detector corresponding to each plane of the CT projection image is recorded, specifically as follows:

[0089] After each projected image is acquired, the sliding angle data of the current detector is bound to the projected image and stored in ascending order of sliding angle.

[0090] Specifically, controlling the rotation of the cone-beam CT rotation axis Rx in cone-beam CT detection mode includes:

[0091] Based on the 3D reconstruction requirements of the workpiece, the preset rotation range, rotation direction, and acquisition angle interval of the cone-beam CT rotation axis Rx are set as follows:

[0092] To achieve complete 3D reconstruction of the three-dimensional workpiece, the preset rotation range covers 360°;

[0093] The rotation direction is set to unidirectional rotation to avoid mechanical clearance errors caused by reverse rotation;

[0094] In one implementation, the angle interval for acquisition is 1°, and a total of 360 angular positions of projected images are acquired;

[0095] The cone-beam CT rotation axis Rx is controlled to rotate within a preset rotation range, specifically as follows:

[0096] Rx is controlled to rotate at a constant speed in one direction by a rotary drive mechanism, and the rotation speed is uniform during the rotation process.

[0097] It automatically stops when it reaches the end of the preset rotation range, and the limit protection is set outside the preset range;

[0098] When the cone-beam CT rotation axis Rx reaches each acquisition angle position, the X-ray source is controlled to emit X-rays and acquire cone-beam CT projection images at the corresponding angle positions;

[0099] In one embodiment, the X-ray energy is set to 80kV to 150kV, and the exposure time is set to 5ms;

[0100] Record the rotation angle of the cone-beam CT rotation axis Rx corresponding to each cone-beam CT projection image, specifically as follows:

[0101] After each projected image is acquired, the rotation angle data of the current Rx is bound to the projected image and archived and stored in ascending order of rotation angle.

[0102] Specifically, verifying the geometric calibration parameters includes:

[0103] Select multiple known feature points on the calibration model and record the actual coordinates of each known feature point under a unified spatial reference. Specifically:

[0104] From the point matrix feature points of the calibration model, select multiple feature points evenly, including feature points at different positions such as the edge, center, and four corners of the model. The number of selected points should not be less than 20 to avoid local deviations from affecting the overall parameter accuracy.

[0105] Record the actual coordinates of each selected feature point under a unified spatial reference. These coordinates are the standard coordinates of the calibration model at the time of manufacture, with an accuracy of 0.001mm.

[0106] Substituting the actual coordinates of each known feature point into the projection mapping model corresponding to the geometric calibration parameters, the theoretical pixel coordinates of each known feature point are calculated, specifically as follows:

[0107] Substitute the actual spatial coordinates of each feature point into the projection mapping model established based on geometric calibration parameters, and obtain the theoretical pixel coordinates (horizontal and vertical coordinates) of the feature point in the projected image through spatial geometric transformation and pixel scaling. The calculation precision of the theoretical pixel coordinates is retained to two decimal places.

[0108] The actual pixel coordinates of each known feature point in the calibrated projection image are extracted as follows:

[0109] A subpixel edge recognition algorithm is used to accurately locate feature points in the calibrated projection image and extract the actual pixel coordinates of each feature point, achieving a positioning accuracy of 0.01 pixels and avoiding verification errors caused by feature point positioning deviations.

[0110] At the same time, blurry or occluded feature points in the projected image are removed to ensure that the extracted actual pixel coordinates are valid.

[0111] Calculate the deviation between the theoretical pixel coordinates and the actual pixel coordinates of each known feature point, specifically as follows:

[0112] Calculate the horizontal and vertical deviations between the theoretical and actual pixel coordinates of each feature point, and then calculate the comprehensive deviation value of the feature point using the Pythagorean theorem. Record the deviation values ​​of all feature points one by one.

[0113] When all deviation values ​​are less than the preset threshold, the geometric calibration parameters are deemed qualified, specifically as follows:

[0114] The preset deviation threshold is 0.2 pixels. If the comprehensive deviation value of all selected feature points is less than this threshold, the geometric calibration parameters are deemed qualified. Qualified geometric calibration parameters are directly stored in the non-volatile memory of the control system, which can be stored for a long time and retrieved at any time without the need for repeated geometric calibration.

[0115] When at least one deviation value exceeds a preset threshold, the calibration projection image is reacquired and the geometric calibration parameters are updated until the deviation value meets the preset threshold, specifically as follows:

[0116] If the overall deviation value of any feature point exceeds 0.2 pixels, the geometric calibration is deemed unqualified. The control system will automatically restart the geometric calibration process, re-acquire the projection image of the calibration model, solve the geometric calibration parameters again, and perform verification.

[0117] If a single calibration fails, the system can recalibrate a maximum of three times. If all three recalibrations fail, an equipment malfunction signal will be reported, reminding the operator to check the calibration phantom, detector, X-ray source, and other components. The system should be troubleshooted before recalibrating.

[0118] Specifically, coordinate transformation based on a unified spatial reference for projection mapping includes:

[0119] With the X-ray source focus as the origin, the vertical direction as the Z-axis, and the horizontal direction as the X-axis and Y-axis respectively, the coordinate components of the three-dimensional spatial coordinate system are set, and the spatial position of any point under the unified spatial reference is described by the three-dimensional rectangular coordinates.

[0120] Based on the distance FDD from the source focus to the flat panel detector and the distance FOD from the source focus to the rotation center of the cone-beam CT in the geometric calibration parameters, the transformation relationship between spatial coordinates and detector pixel coordinates in the three-dimensional spatial coordinate system is established; with the source focus as the projection center, the spatial coordinates are transformed into the detector pixel coordinates through projection transformation, and the projection magnification ratio is determined by FDD during the transformation process;

[0121] In planar CT detection mode, the sliding angle of the flat panel detector is substituted into the transformation model as a variable to update the projection mapping relationship in real time; in cone-beam CT detection mode, the rotation angle of the cone-beam CT rotation axis Rx is substituted into the transformation model, and the same FOD and FDD parameters as in planar CT detection mode are called to complete the mapping transformation from spatial coordinates to detector pixel coordinates.

[0122] Distortion correction is performed on the mapped detector pixel coordinates to restore the true geometry of the workpiece.

[0123] Please see Figure 3This invention provides a technical solution: a coaxial dual-mode X-ray CT detection and control system, comprising: a unified spatial reference establishment module, used to establish a unified spatial reference, with the X-ray source focus as the origin, the vertical direction as the Z-axis, and the horizontal directions as the X-axis and Y-axis respectively, establishing a three-dimensional spatial coordinate system, the cone-beam CT rotation axis Rx being parallel to the X-axis, the cone-beam CT rotation center located on the Z-axis, and the arc sliding trajectory of the flat panel detector located on an arc with the X-ray source focus as the center and the distance from the source focus to the detector FDD as the radius, the X-ray source focus, the cone-beam CT rotation center, and the flat panel detector reference position being collinear on the Z-axis; and a geometric calibration module, used to complete geometric calibration based on the unified spatial reference, obtaining geometric calibration parameters, the geometric calibration parameters including at least the distance from the source focus to the cone-beam CT rotation center FOD and the distance from the source focus to the flat panel detector FDD. The cone-beam CT detection mode and the planar CT detection mode share the same geometric calibration parameters. The planar CT detection control module is used to control the flat panel detector to swing along the arc sliding trajectory within a preset angle range and acquire planar CT projection images in the planar CT detection mode. The sliding angle of the flat panel detector is used as the angle variable for projection mapping, and the geometric calibration parameters are called for projection mapping. The cone-beam CT detection control module is used to control the rotation of the cone-beam CT rotation axis Rx and acquire cone-beam CT projection images in the cone-beam CT detection mode. The rotation angle of Rx is used as the angle variable for projection mapping, and the same geometric calibration parameters as in the planar CT detection mode are called for projection mapping. The mode switching control module is used to maintain a unified spatial reference when switching between the planar CT detection mode and the cone-beam CT detection mode, and reuse the geometric calibration parameters without repeating the geometric calibration process.

[0124] The system also includes an X-ray generation and control unit, a projection image acquisition and storage unit, a three-dimensional image reconstruction and calculation unit, a parameter storage unit, and an abnormal alarm unit.

[0125] The X-ray generation control unit is used to control the start and stop of the X-ray source, energy adjustment and exposure time setting, and to set X-ray parameters according to the detection mode and workpiece type;

[0126] The projection image acquisition and storage unit is used to receive the projection images output by the detector, preprocess the images, and store them according to the detection mode.

[0127] The 3D image reconstruction operation unit is used to perform planar CT tomographic reconstruction and cone-beam CT FDK reconstruction operations, and outputs tomographic images and 3D voxel models;

[0128] The parameter storage unit is used for long-term storage of geometric calibration parameters;

[0129] The abnormal alarm unit is used to issue alarm signals and report abnormal information to the host computer when calibration is unqualified, equipment malfunctions, or mode switching is abnormal.

[0130] When the cone-beam CT shaft adopts a detachable structure, it is installed on the cone-beam CT rotating shaft through a mechanical interface and removed from the rotating shaft in planar CT mode;

[0131] When the cone-beam CT shaft adopts an offset structure, it is connected to the cone-beam CT rotating shaft through a rotating mechanism. In planar CT mode, the shaft is rotated to a position offset from the Z-axis and locked.

[0132] The movement of the cone-beam CT shaft along the Z-axis and the movement of the stage along the Z-axis can be linked and controlled, that is, the cone-beam CT shaft and the stage move up and down synchronously.

[0133] It can also be controlled independently, meaning that the cone-beam CT shaft and the stage are each controlled by their own drive mechanism for lifting and lowering.

[0134] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0135] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A coaxial dual-mode X-ray CT detection control method, characterized in that, Includes the following steps: A three-dimensional spatial coordinate system with the X-ray source focal point as the origin and the Z-axis vertically upward is established as a unified spatial reference. The cone-beam CT rotation axis Rx is parallel to the X-axis, and the X-ray source focal point, the cone-beam CT rotation center, and the flat panel detector reference position are collinear on the Z-axis. Geometric calibration is performed based on a unified spatial reference to obtain the distance FOD from the source focus to the cone-beam CT rotation center and the distance FDD from the source focus to the flat panel detector. The cone-beam CT detection mode and the planar CT detection mode share this geometric calibration parameter. In planar CT detection mode, the flat panel detector is controlled to swing along an arc trajectory with the X-ray source focus as the center and FDD as the radius and to acquire projected images. During the swing, the normal of the flat panel detector always points to the X-ray source focus. The geometric calibration parameters are called to perform projection mapping with the swing angle as the variable. In cone-beam CT detection mode, the flat panel detector is controlled to be in and maintained at the reference position as the projection receiving surface, the cone-beam CT rotation axis Rx is controlled to rotate and the projected image is acquired, and the same geometric calibration parameters as the planar CT detection mode are called to perform projection mapping with the Rx rotation angle as the variable. When switching modes, the unified spatial reference remains unchanged, the geometric calibration parameters are reused, and the geometric calibration process is not repeated. Geometric calibration based on a unified spatial reference includes: Place the calibration phantom containing known feature points at the center of rotation of cone-beam CT. In cone-beam CT detection mode, the cone-beam CT rotation axis Rx is controlled to rotate, and calibration projection images of the calibration phantom at multiple rotation angle positions are acquired; Based on the actual coordinates of known feature points under a unified spatial reference and their pixel coordinates in the calibration projection image, the geometric calibration parameters are solved, where the projection magnification ratio satisfies the following relationship: μ = FDD / FOD; Where μ is the projection magnification ratio, FDD is the distance from the source focus to the flat panel detector, and FOD is the distance from the source focus to the center of rotation of the cone-beam CT. The geometric calibration parameters include at least the distance from the source focus to the cone-beam CT rotation center (FOD) and the distance from the source focus to the flat panel detector (FDD). Based on the deviation between the theoretical pixel coordinates and the actual pixel coordinates of known feature points, the geometric calibration parameters are verified, and the geometric calibration process is re-executed or the geometric calibration parameters are corrected when the deviation exceeds a preset threshold.

2. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, In planar CT detection mode, calling geometric calibration parameters for projection mapping includes: Obtain the real-time sliding angle of the flat panel detector along the circular arc sliding trajectory; Based on the real-time sliding angle and the distance FDD from the source focus to the flat panel detector in the geometric calibration parameters, the spatial position and attitude of the flat panel detector under the unified spatial reference are determined. Using the sliding angle of the flat panel detector as the angle variable for projection mapping, a correspondence between the workpiece spatial coordinates and the detector pixel coordinates is established. Geometric correction is performed on the planar CT projection image based on the correspondence, and tomographic reconstruction is then performed.

3. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, In cone-beam CT mode, calling geometric calibration parameters for projection mapping includes: Obtain the real-time rotation angle of the cone-beam CT rotation axis Rx; Based on the real-time rotation angle and the distance FOD from the source focus to the rotation center of the cone-beam CT in the geometric calibration parameters, the spatial position of the workpiece under a unified spatial reference is determined. Using the rotation angle of the cone-beam CT rotation axis Rx as the angle variable for projection mapping, and calling the same geometric calibration parameters as the planar CT detection mode, the correspondence between the workpiece spatial coordinates and the detector pixel coordinates is established. Geometric correction is performed on cone-beam CT projection images based on the correspondence, and cone-beam CT reconstruction is then performed.

4. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, Switching between planar CT and cone-beam CT modes includes: Receive mode switching instructions and determine the target detection mode; When the target detection mode is cone-beam CT detection mode, control the flat panel detector to move to the reference position and lock it, and activate the rotation drive function of the cone-beam CT rotation axis Rx. When the target detection mode is planar CT detection mode, control the flat panel detector to unlock; During the switching process, the unified spatial reference remains unchanged. The stored geometric calibration parameters are directly called to start the projection acquisition process of the target detection mode, without repeating the geometric calibration process. The movement of the cone-beam CT axis along the Z-axis is controlled in conjunction with or independently of the movement of the stage along the Z-axis.

5. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, Controlling the flat panel detector to swing along a circular arc trajectory in planar CT detection mode includes: Based on the size of the plate-shaped workpiece and the detection requirements, the sliding start angle, end angle, and acquisition angle interval of the flat panel detector are set. The sliding start angle and end angle are symmetrical about the Z-axis. The flat panel detector is controlled to move along a circular arc sliding trajectory between the starting angle and the ending angle. During the sliding process, the normal of the flat panel detector always points to the focal point of the X-ray source. When the flat panel detector reaches each acquisition angle position, the X-ray source is controlled to emit X-rays and acquire the corresponding planar CT projection image at the angle position; Record the sliding angle of the flat panel detector corresponding to each plane CT projection image.

6. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, Controlling the rotation of the cone-beam CT rotation axis Rx in cone-beam CT detection mode includes: Based on the 3D reconstruction requirements of the three-dimensional workpiece, the preset rotation range, rotation direction, and acquisition angle interval of the cone-beam CT rotation axis Rx are set. Control the rotation axis Rx of the cone-beam CT to rotate within a preset rotation range; When the cone-beam CT rotation axis Rx reaches each acquisition angle position, the X-ray source is controlled to emit X-rays and acquire cone-beam CT projection images at the corresponding angle positions; Record the rotation angle of the cone-beam CT rotation axis Rx corresponding to each cone-beam CT projection image.

7. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, Verification of geometric calibration parameters includes: Select multiple known feature points on the calibration model and record the actual coordinates of each known feature point under a unified spatial reference. Substitute the actual coordinates of each known feature point into the projection mapping model corresponding to the geometric calibration parameters to calculate the theoretical pixel coordinates of each known feature point. Extract the actual pixel coordinates of each known feature point in the calibrated projection image; Calculate the deviation between the theoretical pixel coordinates and the actual pixel coordinates of each known feature point; When all deviation values ​​are less than the preset threshold, the geometric calibration parameters are deemed to be qualified. When at least one deviation value exceeds the preset threshold, the calibration projection image is reacquired and the geometric calibration parameters are updated until the deviation value meets the preset threshold.

8. The coaxial dual-mode X-ray CT detection and control method according to claim 1, characterized in that, In cone-beam CT detection mode, the flat panel detector is fixed at the reference position as the projection receiving surface of the cone-beam CT. The plane of the flat panel detector is parallel to the XY plane, and the projection mapping of the cone-beam CT shares the pixel coordinate system of the flat panel detector.

9. A coaxial dual-mode X-ray CT detection and control system, employing the coaxial dual-mode X-ray CT detection and control method according to any one of claims 1-8, characterized in that, include: The unified spatial reference establishment module is used to establish a three-dimensional spatial coordinate system with the X-ray source focus as the origin and the Z-axis vertically upward as the unified spatial reference. The cone-beam CT rotation axis Rx is parallel to the X-axis, and the X-ray source focus, the cone-beam CT rotation center, and the flat panel detector reference position are collinear on the Z-axis. The geometric calibration module is used to complete geometric calibration based on a unified spatial reference, and obtain the distance FOD from the source focus to the rotation center of cone-beam CT and the distance FDD from the source focus to the flat panel detector. The cone-beam CT detection mode and the planar CT detection mode share this geometric calibration parameter. The planar CT detection control module is used to control the flat panel detector to swing along an arc trajectory with the X-ray source focus as the center and FDD as the radius in the planar CT detection mode and acquire projected images. During the swing, the normal of the flat panel detector always points to the X-ray source focus. The geometric calibration parameters are called to perform projection mapping with the swing angle as the variable. The cone-beam CT detection control module is used to control the flat panel detector to be in and maintain the reference position as the projection receiving surface in cone-beam CT detection mode, control the rotation axis Rx of the cone-beam CT to rotate and acquire the projection image, and call the same geometric calibration parameters as the planar CT detection mode to perform projection mapping with the Rx rotation angle as the variable. The mode switching control module is used to maintain a unified spatial reference during mode switching, reuse geometric calibration parameters, and avoid repeating the geometric calibration process.

Images