Tolerance error estimation device, method, program, reconstruction device, and control device

Abstract

To provide a tolerance error estimation device, a method, a program, a reconstruction device and a control device that are able to estimate deviation of a drive shaft from a reference position with respect to a drive time.SOLUTION: A tolerance error estimation device (A processing device 300) for estimating a tolerance error of a rotary drive shaft of an X-ray analysis device, includes: a specific position calculation unit 320 that obtains a specific position from an X-ray detection image of a standard sample at each rotary drive time; and a deviation amount calculation unit 330 that, based on the specific position, calculates an amount Δx of displacement in an x direction and an amount Δy of displacement in a y direction from a reference position of a central position of the rotary drive shaft at each rotary drive time when a direction parallel to the rotary drive shaft is set as a z direction of an orthogonal coordinate system fixed to a sample.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a tolerance error estimation device, method, program, reconstruction device, and control device for estimating a tolerance error of a rotation drive shaft in an X-ray analysis device. [Background technology]

[0002] In X-ray CT scanners, image degradation occurs when the gantry rotation axis or the sample rotation axis (hereafter referred to as the "CT rotation axis") shifts during measurement. This shift is called tolerance error, and various methods have been tried to correct it.

[0003] For example, a method of correcting tolerance errors by aligning images is known (see Patent Document 1). In this method, the confirmed misalignment is corrected by superimposing a two-dimensional projection image and a three-dimensional reconstructed image. As a result, it is possible to correct the center shift and SOD (source-sample distance). In this case, accuracy can be improved by repeatedly reconstructing and aligning the projection images of the reconstructed images.

[0004] Also, a method of correcting tolerance errors using sensors is known (see Patent Document 2). With this method, deviations in the radial direction and thrust direction can be corrected using distance sensors. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-193965 A [Patent Document 2] JP 2018-99175 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when correcting tolerance errors by aligning images, a reconstructed image is required, and the reconstruction process takes time. In addition, when using a sensor, it does not take much time to check the error, but the manufacturing cost increases depending on the measurement accuracy required for the sensor itself and how the sensor is installed.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a tolerance error estimation device, method, program, reconstruction device, and control device that can estimate the deviation of the drive axis from a reference position over drive time. [Means for solving the problem]

[0008] (1) In order to achieve the above object, the tolerance error estimation device of the present invention is a tolerance error estimation device that estimates the tolerance error of a rotation drive shaft of an X-ray analysis device, and is characterized by comprising: a specific position calculation unit that determines a specific position of a standard sample at each rotation drive time from an X-ray detection image, and a deviation amount calculation unit that calculates a deviation amount Δx in the x direction and a deviation amount Δy in the y direction of the center position of the rotation drive shaft from a reference position at each rotation drive time based on the specific position when the z direction of an orthogonal coordinate system fixed to the sample is set to a direction parallel to the rotation drive shaft. In this way, by calculating the deviation of the drive shaft from the reference position with respect to the drive time using the X-ray detection image, high-quality data can be obtained quickly and at low cost.

[0009] (2) In addition, the tolerance error estimation device of the present invention is characterized in that the deviation calculation unit assumes a function form of each of Δx and Δy for each rotation drive time, determines a function Δx(t) used to calculate Δx and a function Δy(t) used to calculate Δy by optimizing parameters of the assumed function form, and calculates Δx and Δy at each rotation drive time using the determined Δx(t) and Δy(t). This makes it possible to estimate Δx and Δy, which vary depending on the rotation angle, with high accuracy.

[0010] (3) The tolerance error estimation device of the present invention is characterized in that the deviation calculation unit optimizes parameters of the assumed function form so as to minimize an evaluation function that represents a degree of coincidence between a specific position determined from the X-ray detection image and a specific position calculated using the assumed function forms of Δx and Δy, respectively. This makes it possible to easily estimate Δx and Δy with high accuracy using the X-ray detection image.

[0011] (4) In addition, the tolerance error estimation device of the present invention is characterized in that the deviation calculation unit calculates Δx and Δy by assuming that the functional forms of Δx and Δy are periodic functions whose period is the rotation drive. In this way, Δx and Δy can be easily estimated by assuming that they are periodic functions by utilizing the fact that Δx and Δy return to the same value in one rotation.

[0012] (5) The tolerance error estimation device of the present invention is characterized in that the X-ray detection image is acquired by a two-dimensional detector having detection elements of 50 μm or less. This makes it applicable to the inspection of industrial products that require CT images with micron-level accuracy.

[0013] (6) The tolerance error estimation device of the present invention is characterized by further comprising a table storage unit for storing a table including correction parameters based on the calculated Δx and Δy, which makes it possible to eliminate the need to recalculate the specific position or calculate the corrected SOD when correcting data or drive control.

[0014] (7) The tolerance error estimation device of the present invention is characterized by further comprising a display processing unit that displays Δx and Δy over one rotation calculated by the deviation amount calculation unit as a tolerance error locus. This allows a user to understand the state of the X-ray analysis device at the time when the data used to calculate the deviation amount was obtained from the shape of the displayed locus.

[0015] (8) The tolerance error estimation device of the present invention further comprises a designation receiving unit that receives a designation of a means for applying Δx and Δy, and starts a reconfiguration function or a control function according to the designation received. This allows the user to select whether to correct the tolerance error on software or on hardware.

[0016] (9) Furthermore, the reconstruction device of the present invention is characterized in that the X-ray analysis device is an X-ray CT device, and includes a reconstruction unit that reconstructs a three-dimensional image using a CT projection image in which the deviation amount calculated by the tolerance error estimation device described in any one of (1) to (8) above has been corrected. This makes it possible to generate a corrected reconstructed image using a projection image containing a tolerance error, without requiring any particular adjustment of the optical system, etc.

[0017] (10) The control device of the present invention is characterized by including a correction control unit that performs correction control of the X-ray analysis device based on the deviation amount calculated by the tolerance error estimation device described in any one of (1) to (8) above. This allows the sample to be imaged while adjusting the relative position during measurement, thereby enabling high-precision measurement using the obtained X-ray detection image.

[0018] (11) A method of the present invention is a method for estimating a tolerance error of a rotation drive shaft of an X-ray analysis device, and is characterized by including the steps of: determining a specific position from an X-ray detection image of a standard sample at each rotation drive time; and calculating, based on the specific position, an amount of deviation Δx in the x direction and an amount of deviation Δy in the y direction of the center position of the rotation drive shaft from a reference position at each rotation drive time when a direction parallel to the rotation drive shaft is defined as the z direction of an orthogonal coordinate system fixed to the sample. This makes it possible to obtain high-quality data quickly and at low cost.

[0019] (12) A program of the present invention is a program for estimating a tolerance error of a rotation drive shaft of an X-ray analysis device, characterized in that the program causes a computer to execute a process of determining a specific position from an X-ray detection image of a standard sample at each rotation drive time, and a process of calculating, based on the specific position, a deviation amount Δx in the x direction and a deviation amount Δy in the y direction of the center position of the rotation drive shaft from a reference position at each rotation drive time when a direction parallel to the rotation drive shaft is the z direction of an orthogonal coordinate system fixed to the sample. This makes it possible to obtain high-quality data quickly and at low cost. Effect of the Invention

[0020] According to the present invention, the burden of correcting tolerance errors can be reduced by estimating the deviation of the rotary drive shaft from a reference position with respect to drive time. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an X-ray CT apparatus in which a tolerance error occurs. [Diagram 2] 13(a) and 13(b) are schematic diagrams of projection images obtained when a tolerance error occurs. [Diagram 3] 13 is a graph showing the variation in the u direction of the center of gravity of a projected image due to a tolerance error. [Figure 4] (a) and (b) are projections in the z-axis direction showing the coordinate systems before and after an error occurs, respectively. [Diagram 5] FIG. 1 is a schematic diagram showing the configuration of the entire system. [Figure 6] FIG. 2 is a block diagram showing a configuration of a processing device (a tolerance error estimating device, a reconstruction device, and a control device). [Figure 7] 3 is a flowchart illustrating a method for estimating tolerance errors of the present invention. [Figure 8] FIG. 13 is a diagram showing an image of a table. [Figure 9] 1 is a graph showing the position of the center of gravity in the u direction of a projected image of a steel ball versus the rotation angle. [Figure 10]13 is a graph showing Δx, Δy, and the calculated center of gravity position in the u direction relative to the rotation angle. [Figure 11] 1 is a graph showing the trajectory of Δx and Δy over one rotation. [Figure 12] 1 is a graph showing Δz versus rotation angle. [Figure 13] 1 is a graph showing the rate of change in SOD versus rotation angle. [Figure 14] (a) and (b) are reconstructed images of the steel ball without and with correction, respectively. [Figure 15] (a) and (b) are reconstructed images of the X-ray test chart without and with correction, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Next, an embodiment of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are used to refer to the same components in each drawing, and duplicated description will be omitted.

[0023] [principle] X-ray CT scanners irradiate a sample with cone-shaped or parallel beams of X-rays from all angles, and obtain the distribution of X-ray absorption coefficients, i.e., a projection image, using a detector. To irradiate X-rays from all angles, X-ray CT scanners are configured to rotate the sample stage or the gantry in which the X-ray source and detector are integrated, relative to a fixed X-ray source and detector. The rotation is relative, and the rotation angle refers to the angle between the gantry and the sample, and is also called the projection angle. The rotation angle is basically proportional to the rotation drive time.

[0024] X-ray CT scanners are a type of X-ray analysis device, equipped with a CT rotation axis as a rotation drive axis, and acquire X-ray CT projection images as X-ray detection images. When estimating the tolerance error of an X-ray CT scanner, the standard sample used to acquire the X-ray detection image is a sphere with uniform density, and the specific position used to calculate the amount of deviation is the center of gravity of the absorption coefficient.

[0025] In this way, projections are made from various angles, and the distribution of the linear absorption coefficient of the sample can be inferred from the shade of the projected image of the sample obtained. The process of obtaining a three-dimensional linear absorption coefficient distribution from a two-dimensional projected image is called reconstruction. Basically, the projected images are back-projected.

[0026] In the above-mentioned X-ray CT device, the CT rotation axis is adjusted so that it is located at the reference position of the sample, which is placed on the straight line connecting the radiation source and the center of the detector. When the CT rotation axis is rotated during measurement, it may deviate from the reference position of the sample (tolerance error). Figure 1 is a schematic diagram showing the configuration of an X-ray CT device in which a tolerance error has occurred. When the CT rotation axis is rotated by a rotation angle θ (gantry rotation angle), the X-ray source F0 attached to the gantry and Detector D0 moves to positions F1 and D1. At this time, the CT rotation axis (gantry rotation axis) initially coincides with the reference position of the sample at position P0, but as the CT rotation axis rotates, the position of the CT rotation axis shifts from P0 to P1. This shift is the tolerance error.

[0027] Figures 2(a) and (b) are schematic diagrams of the projection image acquired when a tolerance error occurs. The rectangular frame indicates the entire area of ​​the projection image detected on the detection surface. In the projection image, the direction parallel to the CT rotation axis is defined as v, and the direction perpendicular to v is defined as u. The outline and center of gravity position (u0,v0) of the projection image of a sample when a sphere of uniform density is used as the standard sample are shown. The projection image when the CT rotation axis is adjusted to be located at the reference position of the sample is shown by the dashed line.

[0028] Figure 3 is a graph showing the fluctuation of the center of gravity of the projected image in the u direction due to tolerance errors. The direction and amount of movement of the center of gravity of the projected image changes with respect to the rotation drive time (t) relative to the center position of the detector. The impact on the projected image is different between the deviation of the CT rotation axis in the direction parallel to the detector plane (u direction) and the deviation in the SOD direction.

[0029] When the CT rotation axis is shifted parallel to the detection surface (Fig. 2(a)), the outline of the projected image does not change, and only the center of gravity moves on the detector plane. When there is also a shift in the SOD direction (Fig. 2(b)), even if the amount of movement of the center of gravity is the same, the magnification rate changes when a shift occurs in the SOD direction, and the size of the outline of the projected image also changes accordingly. Therefore, when the amount of movement of the center of gravity of the projected image is corrected as a tolerance error, the shift in the SOD direction remains, and even if reconstruction is performed using such a projection image, the reconstructed image will still have blurring due to the tolerance error. Therefore, when making corrections, it is necessary to consider in which direction and how much the CT rotation axis moves relative to the rotation drive time.

[0030] The present invention is characterized in that the position where the sample is placed is taken as the reference position, and the deviation of the center position of the CT rotation axis from the reference position is expressed as a function of the rotation drive time (t). By determining the optimal parameters of the assumed function, the deviation amount (Δx, Δy, Δz) of the center position of the CT rotation axis from the reference position at each rotation drive time can be estimated.

[0031] When optimizing the parameters of the function, CT measurements are performed using a sphere of uniform density as a standard sample, and the position of the center of gravity of the absorption coefficient of the projection image of the sphere reflected in the acquired CT projection image is used. The sphere of uniform density is preferably a metal sphere, and more preferably a steel sphere. If the amount of deviation with respect to the drive time is reproducible, it can be reflected in the deviation correction of the actual measurement by estimating the amount of deviation with respect to the drive time from highly reliable data. In addition, if the sample has a clear contrast in the projection image and an isotropic shape, such as a steel sphere, the calculation of the center of gravity position is simple.

[0032] Figures 4(a) and (b) are projections in the z-axis direction showing each coordinate system before and after an error occurs. Figures 4(a) and (b) show the principle of estimating the amount of deviation in an X-ray CT scanner. The reference coordinate system is set at the position where the sample is placed, with the origin position set as (0,0,0). If the coordinate system is set with the center position of the CT rotation axis as the origin, at the initial time of rotation drive, the reference position of the sample and the center position of the CT rotation axis coincide. The center position of the detector on the projected image and the center of gravity of the projected image also coincide.

[0033] During CT measurement, when the CT rotation axis is arranged at a rotation angle (θ(t)) during a certain rotation drive time, the center position (origin of the coordinate system) of the CT rotation axis shifts by (-Δx(t), -Δy(t), -Δz). At this time, the shift in the center position of the CT rotation axis is expressed by the vector β(t). Furthermore, if the unit vector in the u direction parallel to the detection surface is expressed as in relationship (1), then u0(t) will be as shown in relationship (2).

[0034]

number

number

[0035] The length v0(t) in the v direction parallel to the detection surface corresponds to the deviation in the z direction of the center position of the CT rotation axis. The relationship between these is expressed by the following formula (Helgason-Ludwig condition).

number

number

[0036] (1) Assume the functional forms of Δx(t) and Δy(t) The causes of tolerance error vary depending on the assembly and material of the drive shaft. Therefore, the function is specified based on the tendency of the direction and amount of deviation. For example, when the direction and amount of deviation are constant, such as when the drive shaft components expand and contract due to the temperature and other environmental factors, or when it is affected by stress applied in one direction, it can be expressed in a simple functional form such as a linear function. In the case of X-ray CT equipment, it is expected that a certain amount of deviation or the same amount will be repeated for each rotation period for a certain range around the CT rotation axis, so it is preferable to assume a periodic function.

[0037] If the deviations Δx(t) and Δy(t) during a certain rotational drive time (t) are periodic functions of the rotation angle (θ(t)) during the certain rotational drive time, then they can be expressed by the following equations through Fourier series expansion.

number

number

[0038] Parameters i}{b j By defining} for Δx and Δy, respectively, it is possible to reproduce the change in the amount of deviation over time in two perpendicular directions. In addition, the parameter i max , j max can be taken to higher degrees to define a more precise function.

[0039] (2) Optimize the parameters of the assumed function using the evaluation function In order to calculate Δx and Δy at each rotation drive time, the parameters of the function assumed above, {a i}{b j} is optimized. The parameters of the assumed function form {a i}{b j} is an arbitrary constant, and this parameter is optimized so that a specific position of the X-ray detection image coincides with a specific position calculated using a function representing Δx(t) and Δy(t). It is preferable to define an evaluation function representing the degree of coincidence of each specific position as an optimization index.

[0040] For example, in estimating the tolerance error of an X-ray CT scanner, the rotation drive time (t k ), the parameters {a i ,b j When the parameters are optimized, the difference between the left side of equation (3) and the right side is minimized when the left side is set to the center of gravity of the absorption coefficient of the CT projection image of the standard sample.

[0041] The sum of the squared residuals of the left and right sides for all projection numbers (k) is used as the evaluation function. The evaluation function is expressed by the following formula. The parameters {a i ,b j} to determine

number

[0042] (3) Create a table to store the amount of deviation along with related information, and then perform corrections by referencing the stored values. The optimized parameters {ai,bj} are substituted into Δx(t) (equation (5)) and Δy(t) (equation (6)), and Δx, Δy, SODa Then, the functions Δx(t), Δy(t), and SODa(t) for calculating the above are determined. This makes it possible to calculate Δx, Δy, and SODa for each rotation drive time t.

[0043] Furthermore, it is preferable to store the calculated values ​​used for correction as t, θ(t), Δx(t), Δy(t), u0(t), v0(t), and SODa(t) in a single table. In that case, the values ​​are stored for each combination of t and θ(t). This allows the amount of correction to be selected according to the correction method.

[0044] By storing the deviation amount for the rotation drive time t and the rotation angle θ, it is possible to correct the deviation amount by taking into account the change in the tolerance error when the scan time is changed. u0(t), v0(t), and SODa(t) are also stored.

[0045] By storing the center of gravity of the absorption coefficient of the projection image of the standard specimen used to estimate the amount of deviation, the value can be directly referenced when correcting the reconstruction. As a result, the reconstruction device or control device can eliminate the need to recalculate the center of gravity of the absorption coefficient of the projection image of the standard specimen or calculate SODa, which is the corrected SOD. It is also preferable to store the results as inspection results during equipment inspection such as shipment inspection and maintenance of the equipment, or as periodic inspection results, for example, once a month. From the stored data table, Δx and Δy over one rotation during CT measurement may be plotted to output a graph showing the trajectory.

[0046] This trajectory indicates how far the rotation drive shaft moves in the x and y directions during one rotation, based on the state when the reference position of the sample and the center position of the CT rotation axis are aligned. The shape of this trajectory makes it possible to understand the state of the X-ray analysis equipment at the time when the data used to calculate the amount of deviation was obtained. By storing the change in the shape of the trajectory as equipment management information, it is possible to determine, for example, the deterioration or abnormality of parts related to the rotation drive, such as worn bearings.

[0047] In controlling the CT rotation axis during measurement, the estimated deviation is consistent with the movement of the CT rotation axis, so the deviation can be used as the correction amount and the movement controlled to cancel the deviation. Since data can be acquired while correcting the deviation during measurement, correction during data processing is not required.

[0048] In addition, if the acquired data is affected by tolerance errors, the data can be corrected by converting the amount of deviation into a correction amount. The coordinates are recalculated so that the center position of the detector before correction is moved by u0(t) and v0(t). The conversion can be done using the following formula.

number

number

[0049] Since this deviation includes information on the direction and amount of movement of the CT rotation axis, the deviation in the SOD direction can also be calculated. SODa, which is the corrected SOD, can be calculated using the following formula.

number

[0050] By referring to these values ​​during reconstruction and correcting the data, it is possible to reduce blurring of the reconstructed image caused by the misalignment of the CT rotation axis in the directions parallel to the detector plane (u and v directions) and in the SOD direction.

[0051] [Entire system] Fig. 5 is a schematic diagram showing the configuration of the entire system 100 including the X-ray CT device 200, the processing device 300, the input device 410, and the display device 420. Here, the X-ray CT device 200 shown in Fig. 5 is configured to rotate a gantry in which an X-ray source 260 and a detector 270 are integrated with each other relative to a sample, but is not limited to this and may be configured to rotate the sample.

[0052] The processing device 300 (tolerance error estimation device) is connected to the X-ray CT device 200, and controls the X-ray CT device 200 and processes acquired data. The processing device 300 may be a PC terminal or a server on the cloud. The processing device 300 estimates the tolerance error of the CT rotation axis in the X-ray CT data. The input device 410 is, for example, a keyboard and a mouse, and performs input to the processing device 300. The display device 420 is, for example, a display, and is used to show the processing results by the processing device 300 to the user by displaying them on a screen.

[0053] [X-ray CT device] 5, the X-ray CT apparatus 200 includes a rotation control unit 210, a sample position control unit 220, a sample stage 250, an X-ray source 260, and a detector 270. The X-ray source 260 and the detector 270 are installed on a gantry (not shown), and X-ray CT imaging is performed by rotating the gantry with respect to a sample fixed to the sample stage 250. Note that the sample stage 250 installed between the X-ray source 260 and the detector 270 may also be rotated.

[0054] The X-ray CT device 200 rotates the gantry at a timing instructed by the processing device 300 to obtain a projection image of the sample. The measurement data is transmitted to the processing device 300. The X-ray CT device 200 is suitable for use in precision industrial products such as semiconductor devices, but can also be applied to veterinary devices as well as industrial devices.

[0055] The X-ray source 260 irradiates X-rays toward the detector 270. The detector 270 is a two-dimensional detector having a light receiving surface that receives X-rays, and can measure the intensity distribution of X-rays that have passed through a sample using a large number of pixels. The X-ray CT projection image is preferably acquired using a two-dimensional detector having detection elements of 50 μm or less (e.g., pixels of 50×50 μm or less). For example, when the magnification is 50 times, the size of one pixel is 1 μm. When image blurring occurs on the order of microns due to tolerance errors, errors occur in grasping shapes and measuring dimensions, so this is particularly effective for X-ray CT devices for industrial products that perform analysis with micron-level accuracy.

[0056] The rotation control unit 210 rotates the gantry at a speed set during CT measurement. The sample position control unit 220 controls the sample position by adjusting the position of the sample stage 250 during CT measurement. The sample position control unit 220 can adjust the sample position according to Δx, Δy, and Δz at each rotation position according to instructions from the processing device 300.

[0057] [Processing device] 6 is a block diagram showing the configuration of a processing device 300 (a tolerance error estimation device, a reconstruction device, and a control device). The processing device 300 is configured by a computer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and a memory connected to a bus. The processing device 300 is connected to the X-ray CT device 200 and receives information. In the example shown in FIG. 6, the processing device 300 functions independently as each of the tolerance error estimation device, reconstruction device, and control device, but each of them may be a separate processing device. In any case, each device is connected so that information can be transmitted and received between them.

[0058] (Tolerance error estimation device) The processing device 300 includes a measurement data storage unit 311, a device information storage unit 312, a specific position calculation unit 320, a deviation amount calculation unit 330, a display processing unit 332, a correction amount calculation unit 335, a table storage unit 340, and a designation reception unit 345. Each unit can transmit and receive information via a control bus L. The input device 410 and the display device 420 are connected to the CPU via an appropriate interface.

[0059] The measurement data storage unit 311 stores the measurement data acquired from the X-ray CT device 200. The measurement data includes a rotation drive time (including information corresponding to the rotation drive time such as rotation angle information) and a projection image corresponding thereto. The device information storage unit 312 stores the device information acquired from the X-ray CT device 200. The device information includes the geometry at the time of measurement, etc.

[0060] The specific position calculation unit 320 obtains the center of gravity position of the absorption coefficient from the X-ray CT projection image of a sphere of uniform density at each rotation drive time. This makes it possible to recognize the transition of the center of the sphere with respect to the change in the rotation drive time in the projection image. The center of the sphere on the projection image represents the projection of the deviation of the center of the CT rotation axis from the original reference position of the sample, but Δx and Δy cannot be obtained directly from the projection of the deviation, so they must be estimated.

[0061] The deviation amount calculation unit 330 calculates the deviation Δx in the x direction and the deviation Δy in the y direction of the central position of the CT rotation axis from the reference position of the sample at each rotation drive time when the direction parallel to the CT rotation axis is the z direction of the Cartesian coordinate system fixed to the sample, based on the position of the center of gravity in the u direction. In this way, by calculating the deviation of the central position of the CT rotation axis from the reference position of the sample using the projection image without reconstruction, high-quality data can be obtained quickly and at low cost. The calculation of Δx and Δy will be described in detail later.

[0062] Specifically, it is preferable to assume the respective function forms of Δx and Δy for each rotation drive time, and optimize the parameters of the assumed functions to determine the function Δx(t) used to calculate Δx and the function Δy(t) used to calculate Δy, and to calculate Δx and Δy at each rotation drive time using the determined Δx(t) and Δy(t). This makes it possible to estimate the amount of deviation caused by the tolerance error and calculate values ​​that can be used for correction. In addition, it is preferable to optimize the parameters included in the assumed function form so as to minimize an evaluation function that indicates the degree of coincidence between a specific position of an X-ray detection image and a specific position calculated using Δx and Δy. This makes it possible to estimate Δx and Δy, which vary depending on the rotation drive time, with high accuracy.

[0063] Δx and Δy return to the same value in one cycle of the CT rotation. Using this, it is preferable to calculate Δx and Δy by assuming them to be periodic functions with the CT rotation as a period. This makes it possible to easily estimate Δx and Δy by assuming them to be periodic functions. The deviation amount calculation unit 330 further calculates Δz from the transition of the center of gravity position in the v direction with respect to the rotation drive time on the projection image.

[0064] The display processing unit 332 displays Δx and Δy over one rotation calculated by the deviation amount calculation unit 330 as a trajectory of the tolerance error on the display device 420. This allows the user to understand the state of the X-ray analysis device at the time when the data used to calculate the deviation amount was obtained from the shape of the displayed trajectory.

[0065] The correction amount calculation unit 335 calculates values ​​required for correction using the calculated deviation amounts Δx and Δy. It is preferable to use a stored table when making the correction.

[0066] The table storage unit 340 stores the values ​​calculated by the specific position calculation unit 320, the deviation amount calculation unit 330, and the correction amount calculation unit 335 as a table. In the table, the specific position, deviation amount, and correction value of the X-ray image are specified for each combination of each rotation drive time and the corresponding rotation angle.

[0067] The designation reception unit 345 is x and y directions The processing device 300 receives a screen for specifying the means for applying the deviation amount. The processing device 300 starts a reconfiguration function or a control function according to the received specification. This allows the user to select whether to correct the tolerance error on software or on hardware.

[0068] (reconstruction device) The reconstruction device 350 includes a reconstruction unit 360. The reconstruction device 350 causes the reconstruction unit 360 to reconstruct a three-dimensional image based on the corrected X-ray CT projection image of the sample. This makes it possible to generate a corrected reconstructed image using a projection image including a tolerance error without requiring adjustment of the optical system or the like. The reconstruction unit 360 reconstructs the three-dimensional image based on the X-ray CT projection image.

[0069] (Control device) The control device 370 includes a correction control unit 380, which corrects and controls the position of the sample during CT measurement using the calculated Δx, Δy, and Δz. It is preferable to use a stored table for correction. This allows the sample to be imaged while adjusting its relative position during measurement, so that a highly accurate reconstructed image can be generated without correction using the obtained projection image.

[0070] [Tolerance error estimation method] A method for estimating tolerance errors using the entire system 100 configured as described above will be described. Fig. 7 is a flowchart showing the method for estimating tolerance errors. First, a CT projection image is obtained using a steel ball as a standard sample, which is a sphere of uniform density (step S1). Next, the positions of the centers of gravity u0(t) and v0(t) of the absorption coefficients are calculated from the obtained CT projection image (step S2).

[0071] Next, the function forms of the deviations Δx and Δy during the rotation drive time are assumed (step S3). Because the cause of the tolerance error differs depending on the state of the parts that make up the device, it is preferable to be able to select a function form that can reproduce the change in the deviation amount for each rotation drive time. For example, a screen may be displayed that allows the user to select a function form such as a linear function or a periodic function.

[0072] Next, an evaluation function is set for the parameters to be optimized (step S4). The evaluation function is set based on the specific position of the X-ray detection image, the specific position calculated using Δx and Δy, and information on the number of projections. Then, the parameters are optimized by a gradient method (step S5). At this time, a graph may be output in which the specific position of the X-ray detection image and the specific position calculated using Δx and Δy are plotted against each rotation drive time or the rotation angle at each rotation drive time. This allows visual confirmation of the accuracy of the optimized parameters.

[0073] Next, the functions Δx(t) and Δy(t) are determined using the optimized parameters (step S6). The determined function is used to calculate the amount of deviation (Δx, Δy) (step S7). A correction value (SODa) is calculated from the calculated amount of deviation (step S8). Then, the specific position of the X-ray image, the amount of deviation, and the correction value calculated are stored as a table (step S9). In this way, the tolerance error can be estimated.

[0074] [Correction method] A reconstructed image can be generated by correcting the tolerance error estimated as described above. There are two correction methods: a method using software and a method controlling the X-ray CT device during measurement. It is preferable that the processing device 300 displays a screen that allows the user to select which method to use for correction, whether to apply correction, etc.

[0075] When using the software, first perform CT measurement of the desired sample. The obtained projection image is corrected using tables of Δx, Δy, and Δz. Specifically, center shift and SOD are corrected. A 3D image is reconstructed using the corrected projection image. This allows a reconstructed image with tolerance errors corrected easily by just processing.

[0076] When controlling the X-ray CT device during measurement, the Δx, Δy, and Δz tables are used to correct and control the sample position during CT measurement of the desired sample. The projection images obtained in this way have tolerance errors corrected. A 3D image is reconstructed using the projection images obtained. This allows for a highly accurate reconstructed image with reduced errors due to the equipment.

[0077] In this way, it is preferable to store the estimated Δx, Δy, and Δz as a table. FIG. 8 is a diagram showing an image of the table. As shown in FIG. 8, for each drive time (t1, t2, t3, ...) at a certain step, the rotation angle (θ1, θ2, θ3, ...), the center of gravity position of the absorption coefficient in the u direction (u 01 ,u 02 ,u 03 ,…), the center of gravity of the absorption coefficient in the v direction (v 01 (Δz1),v 02 (Δz2),v 03 The amount of deviation in the X direction (Δx1, Δx2, Δx3, ...), the amount of deviation in the Y direction (Δy1, Δy2, Δy3, ...), and corrected SOD (SODa1, SODa2, SODa3, ...) are stored. As each rotation drive time for each fixed step, for example, each rotation drive time for acquiring a projection image may be used.

[0078] [Other embodiments] Although the above embodiment is directed to the estimation and correction of tolerance errors in an X-ray CT device, the present invention can also be applied to other X-ray analysis devices. An X-ray diffraction device is equipped with a rotary drive shaft that rotates the detector around a reference position on which a sample is placed. If a tolerance error occurs in the rotary drive shaft, it may affect the acquired data. For example, if the camera length (distance between the sample and the detector) changes due to a tolerance error, the capture angle changes. Even if the same diffraction beam is acquired, the position detected on the detector surface changes, resulting in an angle error.

[0079] In an X-ray diffraction apparatus, when a diffraction image is obtained using a powder sample with a known diffraction position as a standard sample, the Debye center (specific position) can be calculated from the observed Debye rings. By applying the present invention with this Debye center as (u0, v0), the amount of deviation can be calculated and the data or rotation drive control can be corrected.

[0080] [Example 1] A gantry-rotating X-ray CT scanner for testing was used to perform CT measurements of the steel ball. The center of gravity position was calculated from the obtained projection image of the steel ball, and Δx and Δy were calculated from the obtained measured center of gravity position in the u direction. Optimization was performed using the Helgason-Ludwig condition to calculate Δx and Δy. Figure 9 is a graph showing the measured and calculated center of gravity positions in the u direction versus the rotation angle. As shown in Figure 9, the parameter {a i}{b j It was confirmed that when { was optimized, the measured value for the center of gravity position in the u direction coincided with the calculated value.

[0081] Figure 10 is a graph showing Δx, Δy, and the calculated center of gravity position (center shift) in the u direction versus the rotation angle. Figure 11 is a graph showing the trajectories of Δx and Δy over one rotation. The deviations of Δx and Δy in a test gantry-rotating X-ray CT device were confirmed. Figure 12 is a graph showing deviations Δz in the v direction versus the rotation angle. The deviation of Δz was confirmed by plotting v0 calculated from the CT projection image.

[0082] Using the Δx and Δy obtained above, SOD(t) Figure 13 shows the relationship between the rotation angle and SOD(t) 13 is a graph showing the rate of change in the amount of correction used to correct the reconstructed image.

[0083] [Example 2] We confirmed the difference in reconstructed images with and without correction. First, a reconstructed image was generated using an uncorrected projection image of the steel ball used to calculate Δx, Δy, and Δz. Next, a reconstructed image was generated using a projection image corrected using the calculated Δx, Δy, and Δz. Figures 14(a) and (b) are reconstructed images of the steel ball without and with correction, respectively. In Figure 14(a), it was confirmed that the steel ball was not displayed as a sphere due to blurring, whereas in Figure 14(b), the steel ball was displayed as a sphere.

[0084] [Example 3] Next, the X-ray test chart was measured by CT, and a reconstructed image was generated first using a projection image without correction. Next, a reconstructed image was generated using a projection image corrected using Δx, Δy, and Δz calculated using a steel ball. Figures 15(a) and (b) show the reconstructed images of the X-ray test chart without correction and with correction, respectively. In Figure 15(a), the boundary of the pattern of the X-ray test chart is not clear, whereas in Figure 15(b), it can be confirmed that the boundary is clear. [Explanation of symbols]

[0085] 100 Systems 200 X-ray CT device 210 Rotation control unit 220 Sample position control unit 250 Sample stage 260 X-ray source 270 Detector 300 Processing Equipment 310 Tolerance error estimation device 311 Measurement data storage unit 312 Device information storage unit 320 Specific position calculation unit 330 Displacement calculation unit 332 Display processing unit 335 Correction amount calculation unit 340 Table storage section 345 Designated Reception Department 350 Reconfiguration device 360 Reconstruction part 370 Control device 380 Correction control section 410 Input Device 420 Display device L Control bus

Claims

1. A tolerance error estimation device that estimates a tolerance error of a rotation drive shaft of an X-ray analysis device, comprising: a specific position calculation unit that sets a standard sample, which is a sphere of uniform density, so that a reference position of the standard sample coincides with a central position of a rotation drive shaft, and rotates a sample stage relative to an X-ray source and a detector on a plane perpendicular to the rotation drive shaft, and calculates a center position of an absorption coefficient as a specific position of the standard sample at each rotation drive time from an X-ray detection image obtained by the detector using X-rays irradiated by the X-ray source during each rotation drive time; and a deviation calculation unit that calculates, based on the specific position, a deviation Δx in the x direction and a deviation Δy in the y direction of the center position of the rotation drive shaft from a reference position during each rotation drive time when the z direction of a Cartesian coordinate system fixed to the sample is set to a direction parallel to the rotation drive shaft.

2. The deviation amount calculation unit Assuming the function forms of Δx and Δy for each rotation drive time, determining a function Δx(t) used to calculate Δx and a function Δy(t) used to calculate Δy by optimizing parameters of the assumed function form; 2. The tolerance error estimating device according to claim 1, wherein the determined .DELTA.x(t) and .DELTA.y(t) are used to calculate .DELTA.x and .DELTA.y at each rotation drive time.

3. The deviation amount calculation unit 3. The tolerance error estimation device according to claim 2, wherein parameters of the assumed function form are optimized so as to minimize an evaluation function representing a degree of coincidence between the specific position determined from the X-ray detection image and the specific position calculated using each of the assumed functional forms of Δx and Δy.

4. The deviation amount calculation unit 4. The tolerance error estimating device according to claim 2, wherein said .DELTA.x and .DELTA.y are calculated by assuming that the functional forms of said .DELTA.x and .DELTA.y are periodic functions whose period is the rotational drive.

5. 5. The tolerance error estimation device according to claim 1, wherein the X-ray detection image is acquired by a two-dimensional detector having detection elements of 50 μm or less.

6. 6. The tolerance error estimating device according to claim 1, further comprising a table storage unit that stores a table including correction parameters based on the calculated Δx and Δy.

7. 7. The tolerance error estimating device according to claim 1, further comprising a display processing unit that displays Δx and Δy over one rotation calculated by the deviation amount calculation unit as a locus of the tolerance error.

8. A designation receiving unit that receives a designation of a means for applying the Δx and Δy is further provided, 8. The tolerance error estimating device according to claim 1, further comprising:activating a reconfiguration function or a control function in accordance with the received designation.

9. the X-ray analysis device is an X-ray CT device, 9. A reconstruction device comprising: a reconstruction unit that reconstructs a three-dimensional image using a CT projection image in which a deviation amount calculated by the tolerance error estimation device according to claim 1 has been corrected.

10. 9. A control device comprising: a correction control unit that performs correction control of the X-ray analysis device based on an amount of deviation calculated by the tolerance error estimating device according to claim 1.

11. 1. A method for estimating tolerance errors of a rotary drive shaft of an X-ray analysis device, comprising: a step of setting a standard sample, which is a sphere of uniform density, so that a reference position of the standard sample coincides with a central position of a rotation drive shaft, and rotating a sample stage relative to an X-ray source and a detector on a plane perpendicular to the rotation drive shaft, and determining a center position of an absorption coefficient as a specific position from an X-ray detection image of the standard sample at each rotation drive time, which is acquired by the detector using X-rays irradiated by the X-ray source during each rotation drive time; and calculating, based on the specific position, an x-direction deviation Δx and a y-direction deviation Δy of the center position of the rotation drive shaft from a reference position during each rotation drive time when a direction parallel to the rotation drive shaft is defined as the z-direction of an orthogonal coordinate system fixed to the sample.

12. A program for estimating a tolerance error of a rotation drive shaft of an X-ray analysis device, comprising: a process of setting a standard sample, which is a sphere of uniform density, so that a reference position of the standard sample coincides with a central position of a rotation drive shaft, and rotating a sample stage relative to an X-ray source and a detector on a plane perpendicular to the rotation drive shaft, and determining a center position of an absorption coefficient as a specific position from an X-ray detection image of the standard sample at each rotation drive time, which is acquired by the detector using X-rays irradiated by the X-ray source during each rotation drive time; and calculating, based on the specific position, an x-direction deviation Δx and a y-direction deviation Δy of the center position of the rotation drive shaft from a reference position at each rotation drive time when a direction parallel to the rotation drive shaft is defined as the z-direction of an orthogonal coordinate system fixed to the sample.

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