CN114460110B - Servo system error compensation method - Google Patents
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Abstract
The invention discloses a servo system error compensation method, which belongs to the technical field of calibration of a motion mechanism, wherein X-rays are adopted to image a marker, the position of an imaged reference marker in an image is kept unchanged to serve as a constraint condition, the horizontal position of an objective table, the height of the objective table, the inclination angle and the rotation angle of a detector are counted, a five-axis motion relation is established by adopting a polynomial fitting method, the horizontal position of the objective table follows the change of the height of the objective table, the inclination angle and the rotation angle of the detector according to the motion relation, the fact that the center of a field of view is always kept unchanged under different amplification ratios and different visual angles is realized, and the region of interest is imaged; the invention can establish the absolute position relation of the point object image in space, can not only meet the requirement of keeping the center of the field of view unchanged all the time under different amplification ratios and different visual angles, but also be applied to planar CT imaging, and can realize the three-dimensional imaging of the measured object without an additional planar CT module.
Description
Technical Field
The invention relates to the technical field of calibration of a motion mechanism, in particular to a servo system error compensation method.
Background
The X-ray inspection apparatus is mainly directed to integrated circuit package reliability inspection, inspecting a circuit and its package to inspect the presence of defects in order to determine the cause of the defects. The Chinese patent application No. CN201910592325.6 discloses an X-ray detection device based on a five-axis motion platform, which can acquire a plurality of two-dimensional images or three-dimensional models of a region of interest from different view angles or projections. The servo system may allow relative movement of the detector within the sphere and linear movement of the sample with the stage in three dimensions.
Two-dimensional imaging of a region of interest is effective, but often provides insufficient information due to shadowing or the like, requiring imaging of the region of interest from different perspectives. However, in the actual operation process, due to the error sources such as the non-orthogonal axis error, the non-concentric center of the spherical motion of the detector and the source center of the radiation source, the indication error, the detector installation error, and the like, which are caused by the installation error of the radiation source, when the stage is moved in height and the detector is rotated for detection, the region of interest deviates from the center of the field of view, and the region of interest needs to be repositioned, especially when the imaging with high magnification is performed, the magnification or the viewing angle is greatly adjusted, the region of interest deviates from the field of view completely, and the repositioning is difficult.
To solve this problem, there are two general solutions for the existing X-ray detection apparatus. One is to adjust the height of the objective table and the inclination and rotation angles of the detector at a small angle, then adjust the horizontal position of the objective table to ensure that the region of interest is always positioned in the center of the field of view, and repeatedly adjust for several times to realize the imaging of the region of interest under the expected amplification ratio and inclination angle; the method is complicated in adjustment, poor in user experience, and difficult to meet the automatic detection requirement in batch processing. Another approach is to rely on a high precision mechanical system for relatively high precision movement between the X-ray source, the region of interest, and the detector. This need for high precision mechanical equipment makes the X-ray detection device expensive. For this purpose, a servo error compensation method is proposed.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: how to solve the system error of the compensation servo system, the method realizes that the center of the visual field is always kept unchanged under different amplification ratios and different visual angles, images the region of interest, and provides a servo system error compensation method.
The invention solves the technical problems through the following technical proposal, and the invention comprises the following steps:
s1: acquiring an image in real time using X-rays to identify fiducial markers on the stage surface having a known geometry;
s2: moving the object stage height z, the detector inclination angle theta and the detector rotation angle gamma, and keeping the position of the characteristic of the reference mark in the image unchanged through the horizontal positions x and y of the object stage to obtain a sequence { x, y, z, theta, gamma };
s3: extracting a sequence { x, y, z, θ, γ=0 } when γ is 0, and respectively establishing the relationship between x, y, z and θ by adopting a data fitting method:
wherein p is x00 And p y00 Is constant, f x And f y A corresponding fitting function;
s4: performing circle fitting on { x, y } in the sequences of the same z, the same θ and different γ to obtain the sequences { z, θ, x } c ,y c R }, where x c And y c The values of x and y corresponding to the fitted circle center are obtained, and r is the radius of the fitted circle;
s5: establishing r and gamma by adopting data fitting method 0 Relationship with z and θ:
wherein, gamma 0 To fit the initial angle of the circle, y d Y is relative to y when γ=0 c Offset of f r And f yd A corresponding fitting function;
s6: compensating for servo errors using fitted functions, dynamically correcting p if the stage moves horizontally x00 And p y00 ：
If the stage height z, the detector inclination angle θ, and the detector rotation angle γ change, then:
wherein x is T 、y T The following position is the following position after the object stage height z, the detector inclination angle theta and the detector rotation angle gamma are changed.
Still further, in said step S1, said fiducial markers of known geometry are metal balls.
Still further, in the step S2, the reference mark is characterized by a geometric center, a centroid, and a minimum circumscribing center.
Further, in the steps S3 and S5, the data fitting method is a polynomial fitting method, a neural network fitting method, or the like.
Compared with the prior art, the invention has the following advantages: the servo system error compensation method is suitable for an X-ray detection device based on a five-axis motion platform, takes metal microspheres as markers, adopts X-rays to image the markers, takes the position of the imaged circle center in the visual field as a constraint condition, counts the horizontal position, the height and the inclination angle of a detector of an objective table, and adopts a polynomial fitting method to establish a five-axis motion relation, and according to the motion relation, the horizontal position of the objective table changes along with the height, the inclination angle and the rotation angle of the objective table, so that the central of the visual field is always kept unchanged under different amplification ratios and different visual angles, and the imaging of a concerned region is realized; the method can establish the absolute position relation of the point object image in space, can meet the requirement of keeping the center of the field of view unchanged all the time under different amplification ratios and different visual angles, can be applied to planar CT imaging, and can realize three-dimensional imaging of an object to be measured without an additional planar CT module; the servo system error is compensated by adopting a software method, no additional high-precision mechanical equipment and detection equipment are needed, the cost performance is high, and the servo system error compensation method is worthy of popularization and use.
Drawings
FIG. 1 is a flow chart of data acquisition and fitting of a servo system error compensation method in a second embodiment of the present invention;
FIG. 2 is a flow chart of error compensation of a servo system error compensation method according to a second embodiment of the invention;
FIG. 3a shows f in a second embodiment of the invention x (z, θ) data fitting results schematic;
FIG. 3b is a schematic diagram of the data fitting residuals in FIG. 3 a;
FIG. 4A is a diagram of f in a second embodiment of the invention y (z, θ) data fitting results schematic;
FIG. 4A is a schematic diagram of the data fit residuals in FIG. 4A;
FIG. 4B is f in a second embodiment of the invention r (z, θ) data fitting results schematic;
FIG. 4B is a schematic diagram of the data fit residuals in FIG. 4B;
FIG. 4C is f in a second embodiment of the invention yd (z, θ) data fitting results schematic;
fig. 4C is a schematic diagram of the data fit residuals in fig. 4C.
Detailed Description
The following describes in detail the examples of the present invention, which are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of protection of the present invention is not limited to the following examples.
Example 1
The embodiment provides a technical scheme: a method for compensating for errors in a servo system, comprising the steps of:
s1: identifying a reference mark with a known geometric shape on the surface of the object stage by utilizing X-rays, and acquiring an image in real time, wherein the image contains the reference mark;
s2: moving the object stage height z, the detector inclination angle theta and the detector rotation angle gamma, and adjusting the horizontal positions x and y of the object stage to ensure that the position of the characteristic of the reference mark in the image is unchanged, so as to obtain a sequence { x, y, z, theta, gamma };
s3: extracting a sequence { x, y, z, θ, γ=0 } when γ is 0, and respectively establishing the relationship between x, y, z and θ by adopting a data fitting method:
wherein p is x00 And p y00 Is constant, f x And f y A corresponding fitting function;
s4: performing circle fitting on { x, y } in the sequences of the same z, the same θ and different γ to obtain the sequences { z, θ, x } c ,y c R }, where x c And y c The values of x and y corresponding to the fitted circle center are obtained, and r is the radius of the fitted circle;
s5: establishing r and gamma by adopting data fitting method 0 Relationship with z and θ:
wherein, gamma 0 To fit the initial angle of the circle, y d Y is relative to y when γ=0 c Offset of f r And f yd A corresponding fitting function;
s6: compensating for servo errors using fitted functions, dynamically correcting p if the stage moves horizontally x00 And p y00 ：
If the stage height z, the detector inclination angle θ, and the detector rotation angle γ change, then
Wherein x is T 、y T The position is the follow-up position after the object stage height z, the detector inclination angle theta and the detector rotation angle gamma are changed.
In this embodiment, in the steps S3 and S5, the data fitting method is a polynomial fitting method, a neural network fitting method, or the like.
In this embodiment, in said step S1, said fiducial markers of known geometry are metal balls.
In this embodiment, in the step S2, the reference mark is characterized by a minimum circumscribing circle center.
In this embodiment, the stage is movable in the horizontal direction (x-axis and y-axis, two axes being perpendicular to each other) and in the vertical direction (z-axis) under the control of the servo system.
Example two
Data acquisition and processing are carried out according to the method shown in FIG. 1, the range of the change of the stage height z is 20-50 mm, the range of the detector inclination angle theta is 0-45 degrees, the range of the detector rotation angle gamma is-180 degrees, and the sampling data are processed by adopting a polynomial fitting method and a circle fitting method to obtain f x 、f y 、f r And f yd The function, the fitting conditions of which are shown in fig. 3a, 4B and 4C, and the fitting residuals are shown in fig. 3B, 4A, 4B and 4C, the residuals are less than 50 μm, which illustrates the effectiveness of the method.
In summary, the method for compensating the error of the servo system in the embodiment is suitable for an X-ray detection device based on a five-axis motion platform, uses metal microspheres as markers, uses X-rays to image the markers, uses the position of the imaged circle center in the field of view as a constraint condition, counts the horizontal position of an objective table, the height of the objective table, the inclination angle and the rotation angle of a detector, adopts a polynomial fitting method to establish a five-axis motion relationship, and realizes that the horizontal position of the objective table changes along with the height of the objective table, the inclination angle and the rotation angle of the detector according to the motion relationship, so that the center of the field of view is always kept unchanged under different amplification ratios and different visual angles, and images a region of interest; the method can establish the absolute position relation of the point object image in space, can meet the requirement of keeping the center of the field of view unchanged all the time under different amplification ratios and different visual angles, can be applied to planar CT imaging, and can realize three-dimensional imaging of an object to be measured without an additional planar CT module; the servo system error is compensated by adopting a software method, no additional high-precision mechanical equipment and detection equipment are needed, the cost performance is high, and the servo system error compensation method is worthy of popularization and use.
While embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives and variations may be made to the above embodiments by one of ordinary skill in the art within the scope of the invention.
Claims (3)
1. A method for compensating for errors in a servo system, comprising the steps of:
s1: acquiring an image in real time using X-rays to identify fiducial markers on the stage surface having a known geometry;
s2: moving the object stage height z, the detector inclination angle theta and the detector rotation angle gamma, and adjusting the horizontal positions x and y of the object stage to ensure that the position of the characteristic of the reference mark in the image is unchanged, so as to obtain a sequence { x, y, z, theta, gamma };
s3: extracting a sequence { x, y, z, θ, γ=0 } when γ is 0, and respectively establishing the relationship between x, y, z and θ by adopting a data fitting mode:
wherein p is x00 And p y00 Is constant, f x And f y A corresponding fitting function;
s4: performing circle fitting on { x, y } in the sequences of the same z, the same θ and different γ to obtain the sequences { z, θ, x } c ,y c R }, where x c And y c The values of x and y corresponding to the fitted circle center are obtained, and r is the radius of the fitted circle;
s5: adopting a data fitting mode to establish r and gamma 0 Relationship with z and θ:
wherein, gamma 0 To fit the initial angle of the circle, y d Y is relative to y when γ=0 c Offset of f r And
a corresponding fitting function;
s6: compensating for servo errors using fitted functions, dynamically correcting p if the stage moves horizontally x00 And p y00 ：
If the stage height z, the detector inclination angle θ, and the detector rotation angle γ change, then:
wherein x is T 、y T The position is a follow-up position after the object stage height z, the detector inclination angle theta and the detector rotation angle gamma are changed;
in the step S2, the reference mark is characterized by a geometric center, a centroid, and a minimum circumscribing circle center.
2. A method of compensating for servo errors as recited in claim 1, wherein: in the step S1, the fiducial markers having a known geometry are metal balls.
3. A method of compensating for servo errors as recited in claim 1, wherein: in the steps S3 and S5, the data fitting method is a polynomial fitting method and a neural network fitting method.
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| EP2645701A1 (en) * | 2012-03-29 | 2013-10-02 | Axis AB | Method for calibrating a camera |
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