CN114460110B - Servo system error compensation method - Google Patents

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

A Servo System Error Compensation Method

technical field

The invention relates to the technical field of motion mechanism calibration, in particular to a servo system error compensation method.

Background technique

The X-ray inspection device is mainly oriented to the reliability inspection of integrated circuit packaging, inspecting the circuit and its packaging to check the existence of defects so as to determine the cause of the defects. The Chinese invention patent with the patent application number CN201910592325.6 discloses an X-ray detection device based on a five-axis motion platform, which can obtain multiple two-dimensional images or three-dimensional models of areas of interest from different perspectives or projections. The servo system allows the detector to move relative to the spherical surface, and the sample moves linearly with the stage in three-dimensional space.

Two-dimensional imaging of the region of interest is effective, but usually provides insufficient information due to reasons such as occlusion, and the region of interest needs to be imaged from different perspectives. However, in the actual operation process, due to the non-orthogonal error of the shaft system and the installation error of the ray source, the sphere center of the spherical motion of the detector and the source center of the ray source are not concentric errors, indication errors, detector installation errors and other error sources. When the height of the stage moves and the detector rotates for detection, the area of interest will deviate from the center of the field of view, and it is necessary to reposition the area of interest. re-locate.

Aiming at this problem, the existing X-ray detection devices generally have two solutions. One is to adjust the height of the stage and the tilt and rotation angle of the detector at a small angle, and then adjust the horizontal position of the stage so that the area of interest is always in the center of the field of view. Repeat several times to achieve the desired magnification ratio and tilt angle. Focus on the imaging of the area; this method is cumbersome to adjust, the user experience is poor, and it is difficult to meet the automatic detection requirements during batch processing. Another approach relies on high-precision mechanical systems for relatively high-precision movement between the X-ray source, region of interest, and detector. This need for high-precision mechanical equipment makes the X-ray inspection device expensive. Therefore, a servo system error compensation method is proposed.

Contents of the invention

The technical problem to be solved by the present invention is: how to solve the problem of compensating the systematic error of the servo system, realize that the center of the field of view is always kept constant under different magnification ratios and different viewing angles, and image the area of interest, providing a servo system error compensation method.

The present invention solves the above-mentioned technical problems through the following technical solutions, and the present invention comprises the following steps:

S1: Use X-rays to identify fiducial marks with known geometric shapes on the surface of the stage, and acquire images in real time;

S2: Move the stage height z, the detector tilt angle θ, and the detector rotation angle γ, through the horizontal position x and y of the stage, so that the position of the feature of the fiducial mark in the image remains unchanged, and the sequence {x, y,z,θ,γ};

S3: Extract the sequence {x, y, z, θ, γ=0} when γ is 0, and use the method of data fitting to establish the relationship between x, y, z and θ respectively:

Among them, p _x00 and p _y00 are constants, f _x and f _y are corresponding fitting functions;

S4: Perform circle fitting on {x, y} in the sequence of the same z and θ, different γ, and obtain the sequence {z, θ, x _c , y _c , r}, where x _c and y _c are fitting The x and y values corresponding to the center of the circle, r is the radius of the fitted circle;

S5: Use the method of data fitting to establish the relationship between r, γ ₀ and z and θ:

Among them, γ ₀ is the initial angle of the fitting circle, y _d is the offset of y relative to y _c when γ = 0, f _r and f _yd are the corresponding fitting functions;

S6: Use the fitted function to compensate the error of the servo system. If the stage moves horizontally, dynamically correct p _x00 and p _y00 :

If the stage height z, detector tilt angle θ, and detector rotation angle γ change, then:

Among them, x _T , y _T are the follow-up positions after the height z of the stage, the tilt angle θ of the detector, and the rotation angle γ of the detector change.

Furthermore, in the step S1, the reference mark with a known geometric shape is a metal ball.

Furthermore, in the step S2, the features of the reference mark are the geometric center, the centroid, and the center of the smallest circumscribed circle.

Furthermore, in the steps S3 and S5, the data fitting methods are polynomial fitting, neural network fitting and the like.

Compared with the prior art, the present 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, uses metal microspheres as markers, and uses X-rays to image the markers, so that The position of the center of the imaging circle in the field of view remains unchanged as a constraint condition, and the horizontal position of the stage, the height of the stage, the tilt angle and the rotation angle of the detector are counted, and the five-axis motion relationship is established by using a polynomial fitting method. According to the motion relationship, the load The horizontal position of the object stage changes with the height of the stage, the inclination angle and the rotation angle of the detector, so that the center of the field of view is always kept constant under different magnification ratios and different viewing angles, and the area of interest is imaged; the absolute position of the point image in space can be established. The positional relationship can not only meet the requirement of keeping the center of the field of view constant under different magnification ratios and different viewing angles, but also can be applied to planar CT imaging, and can realize three-dimensional imaging of the measured object without additional planar CT modules; The software method compensates the error of the servo system, does not require additional high-precision mechanical equipment and testing equipment, is cost-effective, and is worthy of promotion and use.

Description of drawings

Fig. 1 is the flow chart of data acquisition and fitting of the servo system error compensation method in the second embodiment of the present invention;

Fig. 2 is the error compensation flowchart of the servo system error compensation method in the second embodiment of the present invention;

Fig. 3 a is a schematic diagram of f _x (z, θ) data fitting results in Example 2 of the present invention;

Fig. 3b is a schematic diagram of the data fitting residual in Fig. 3a;

Fig. 4A is a schematic diagram of the data fitting results of f _y (z, θ) in Example 2 of the present invention;

Figure 4a is a schematic diagram of the data fitting residuals in Figure 4A;

Fig. 4B is a schematic diagram of the data fitting results of f _r (z, θ) in Example 2 of the present invention;

Fig. 4b is a schematic diagram of the data fitting residual in Fig. 4B;

Fig. 4C is a schematic diagram of the data fitting results of f _yd (z, θ) in Example 2 of the present invention;

Figure 4c is a schematic diagram of the data fitting residuals in Figure 4C.

Detailed ways

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Embodiment one

This embodiment provides a technical solution: a servo system error compensation method, including the following steps:

S1: Use X-rays to identify fiducial marks with known geometric shapes on the surface of the stage, and acquire images in real time, which contain fiducial marks;

S2: Move the stage height z, the detector tilt angle θ, and the detector rotation angle γ. By adjusting the horizontal position x and y of the stage, the position of the feature of the fiducial mark in the image remains unchanged, and the sequence {x ,y,z,θ,γ};

S3: Extract the sequence {x, y, z, θ, γ=0} when γ is 0, and use the method of data fitting to establish the relationship between x, y, z and θ respectively:

Among them, p _x00 and p _y00 are constants, f _x and f _y are corresponding fitting functions;

S4: Perform circle fitting on {x, y} in the sequence of the same z and θ, different γ, and obtain the sequence {z, θ, x _c , y _c , r}, where x _c and y _c are fitting The x and y values corresponding to the center of the circle, r is the radius of the fitted circle;

S5: Use the method of data fitting to establish the relationship between r, γ ₀ and z and θ:

Among them, γ ₀ is the initial angle of the fitting circle, y _d is the offset of y relative to y _c when γ = 0, f _r and f _yd are the corresponding fitting functions;

S6: Use the fitted function to compensate the error of the servo system. If the stage moves horizontally, dynamically correct p _x00 and p _y00 :

If the stage height z, the detector tilt angle θ, and the detector rotation angle γ change, then

Among them, x _T , y _T are the follow-up positions after changes in the height z of the stage, the tilt angle θ of the detector, and the rotation angle γ of the detector.

In this embodiment, in the steps S3 and S5, the data fitting methods are polynomial fitting, neural network fitting and the like.

In this embodiment, in the step S1, the reference mark with a known geometric shape is a metal ball.

In this embodiment, in the step S2, the feature of the reference mark is the center of the smallest circumscribed circle.

In this embodiment, under the control of the servo system, the stage can move in two axes (x-axis and y-axis, the two axes are perpendicular to each other) in the horizontal direction, and can move in the vertical direction (z-axis). move.

Embodiment two

According to the method shown in Figure 1 for data acquisition and processing, the height z of the stage varies from 20 to 50 mm, the tilt angle θ of the detector ranges from 0 to 45°, and the rotation angle γ of the detector ranges from -180° to 180° , using the polynomial fitting method and the circle fitting method to process the sampled data to obtain f _x , f _y , f _r and f _yd functions, and the fitting conditions are shown in Fig. 3a, Fig. 4A, Fig. 4B, and Fig. 4C , the fitting residuals are shown in Figure 3b, Figure 4a, Figure 4b and Figure 4c, and the residual error is less than 50 μm, which shows the effectiveness of the method.

In summary, the servo system error compensation method of the above-mentioned embodiment is applicable to an X-ray detection device based on a five-axis motion platform, using metal microspheres as markers, imaging the markers with X-rays, and using the imaged circle center When the position of the field of view remains unchanged as a constraint condition, the horizontal position of the stage, the height of the stage, the tilt angle and the rotation angle of the detector are counted, and the polynomial fitting method is used to establish the five-axis motion relationship. According to the motion relationship, the level of the stage The position follows the height of the stage, the tilt angle and rotation angle of the detector, and realizes that the center of the field of view remains unchanged under different magnification ratios and different viewing angles, and the area of interest is imaged; the absolute position relationship of the point image in space can be established, Not only can it meet the requirement of keeping the center of field of view constant under different magnification ratios and different viewing angles, but it can also be used in planar CT imaging, and it can realize three-dimensional imaging of the measured object without additional planar CT modules; using software methods Compensating the error of the servo system does not require additional high-precision mechanical equipment and testing equipment. It is cost-effective and worthy of promotion and use.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

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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