CN110411346B - Method for quickly positioning surface micro-defects of aspheric fused quartz element - Google Patents

Abstract

The invention relates to a method for quickly locating micro-defects on the surface of aspherical fused silica elements, belonging to the technical field of engineering optics. The invention solves the problems of low detection efficiency and low positioning accuracy of the surface micro-defects of the existing optical elements. The invention establishes the machine tool coordinate system, and obtains the coordinates of the geometric center of the aspheric surface of the fused silica element to be measured under the machine tool coordinate system according to the positions of the four boundary lines of the aspheric surface of the fused silica element to be measured under the machine tool coordinate system; The fused silica element to be measured is moved to the spectral confocal displacement range finder, and the characteristic points of the aspheric surface of the fused silica element to be measured are measured. The equation of the aspheric surface in the component coordinate system; after the image is collected by the CMOS area scan camera, the two-dimensional information of the image is restored to the three-dimensional, so as to obtain the position information of the defect points on the aspheric surface of the fused silica component to be measured. The invention can be applied to the technical field of detection of micro-defects on the surface of optical elements.

Description

A rapid localization method for micro-defects on the surface of aspherical fused silica components

technical field

The invention belongs to the technical field of engineering optics, in particular to a method for quickly locating micro-defects on the surface of an aspherical fused silica element.

Background technique

The large-diameter aspherical fused silica element is the key element of the terminal optical component of the high-power solid-state laser system. It can focus the parallel-injected triple-frequency laser on the target point of the vacuum target chamber, thereby obtaining a high focusing power density. Fig. 1 is a schematic diagram of a three-dimensional structure of a large-diameter aspherical optical element, the light incident surface is an aspherical surface, and the material is fused silica. As a typical hard and brittle material, fused silica is prone to micro-cracks, pits and other surface micro-defects during processing. Strong laser irradiation aggravates the generation and growth of defects. Studies have shown that if the micro-defects on the fused silica surface are not repaired or suppressed in time, the size of the defects will increase exponentially under laser irradiation. This will result in a reduction in the quality of the beam passing through the fused silica, making the optics unsuitable for production and scrapping. Therefore, a high-precision and high-efficiency method must be designed to quickly locate micro-defects on the surface of aspheric optical components, so as to facilitate subsequent laser repair of the defects.

The common methods for detecting and locating micro-defects on the surface of optical components include visual inspection and machine vision inspection. The visual inspection method is to irradiate the surface of the component with a light beam at a certain angle, and the inspector observes the defects with bright spots in the beam reflection or transmission direction. This method is widely used in early detection due to its simple operation. However, it is impossible to obtain accurate position and size information of defects simply by visual recognition, and the efficiency is low and the error rate is high.

With the development of technology, machine vision has been introduced into the detection of surface defects of optical components. The detection method uses a high-resolution camera to collect the surface image of the optical element, obtains the specific position and size of the surface micro-defect through image processing, and can locate the micro-defect by combining with the electronic control platform, which is easy to realize the precision and automation of the repair. However, at present, large-diameter optical components are mostly scanned and detected by a line scan camera, which requires progressive scanning and photographing of optical components and stitching of images, resulting in low detection efficiency. And at this stage, most of the detection elements are flat elements, while the detected surface of aspheric elements is a curved surface. According to the mapping relationship, the curved surface information will be converted into plane information when the camera is imaged. During this process, the depth information along the optical axis will be compressed. This results in low positioning accuracy.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problems of low detection efficiency and low positioning accuracy of the surface micro-defects of the existing optical elements, and proposes a rapid positioning method for the surface micro-defects of the aspherical fused silica element.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is: a method for quickly locating micro-defects on the surface of an aspherical fused silica element, the method comprising the following steps:

Step 1. Take the machine zero point of the machine tool as the original center O, establish the machine tool coordinate system O-XYZ, and the three axes of the machine tool coordinate system point to the same three axes of the space rectangular coordinate system;

Step 2. Based on Step 1, the fused silica element to be tested is located in the center of the bright field field of view, and the image of the fused silica element to be tested is collected by an area array CCD camera. to obtain the coordinates of the machine tool in the machine tool coordinate system when the aspheric geometric center of the fused silica element to be measured moves to the center of the bright field field of view;

Step 3: Move the fused silica element to be measured to the spectral confocal displacement range finder, measure the characteristic points of the aspherical surface of the fused silica element to be measured, and obtain the coordinate values of the characteristic points of the aspherical surface;

And use the coordinate values of the feature points on the aspheric surface to fit the equation of the aspheric surface of the fused silica element to be measured in the element coordinate system;

Step 4: Based on Step 2 and Step 3, move the fused silica element to be measured to the CMOS area scan camera station to take a single picture, and after processing the collected image, restore the two-dimensional information of the image to three-dimensional, so as to obtain the The position information of the defect points on the aspheric surface of the fused silica element is measured, and the defect points on the aspheric surface of the fused silica element to be measured are repaired.

The beneficial effects of the present invention are as follows: the present invention proposes a method for quickly locating micro-defects on the surface of an aspherical fused silica element; After the measuring element is moved to the photographing station, the acquisition of the full aperture image can be completed with a single photographing. Through the distortion correction and three-dimensional surface restoration methods, the detection efficiency and the positioning accuracy are improved. and,

(1) The present invention adopts a high-resolution area array camera to realize dark-field imaging and full-aperture single-frame photography, and the detection speed is greatly improved compared with the linear array scanning method;

(2) The present invention utilizes a bright-field microscope system to realize rapid positioning of the component to be tested and visual online monitoring of defects;

(3) The present invention uses the spectral confocal displacement range finder to correct the rotation error during the installation of the component to be measured, and obtains the accurate equation of the component surface in the component coordinate system;

(4) The present invention performs three-dimensional surface restoration on the two-dimensional images collected by the high-resolution area array camera, thereby improving the positioning accuracy of defects;

(5) The process method of the present invention realizes the detection and positioning of the surface defects of the aspherical element to be tested, and satisfies the use requirements of subsequent laser repair.

Description of drawings

Fig. 1 is a three-dimensional structural schematic diagram of a large-diameter aspherical optical element;

2 is a schematic diagram of a micro-defect detection and positioning device on the surface of an aspherical element of the present invention;

Fig. 3 is the schematic diagram of the three-dimensional model of the component to be tested and the standard coordinate system of the present invention;

Figure 4 is a schematic diagram of the rotation error of the component to be tested;

Fig. 5 is the ranging fitting diagram of the feature points of the aspherical surface of the element to be measured;

1, 2, 3, 4, and 5 in the figure represent the positions of the five feature points respectively;

Fig. 6 is the detection principle diagram of the defect point on the aspheric surface of the component to be tested;

FIG. 7 is a schematic diagram of imaging an aspheric surface in a CMOS area scan camera;

FIG. 8 is a schematic diagram of the imaging plane being restored to a curved surface;

FIG. 9 is a schematic diagram of the image captured by the camera when the defect point is located in the bright field station.

Detailed ways

Embodiment 1: The method for quickly locating micro-defects on the surface of an aspheric fused silica element described in this embodiment includes the following steps:

Step 1. Take the machine zero point of the machine tool as the original center O, establish the machine tool coordinate system O-XYZ, and the three axes of the machine tool coordinate system point to the same three axes of the space rectangular coordinate system;

Step 2. Based on Step 1, the fused silica element to be tested is located in the center of the bright field field of view, and the image of the fused silica element to be tested is collected by an area array CCD camera. to obtain the coordinates of the machine tool in the machine tool coordinate system when the aspheric geometric center of the fused silica element to be measured moves to the center of the bright field field of view;

Due to the different sizes of the fused silica components to be tested and the positioning error during the installation process, the coordinates of the components in the machine tool coordinate system need to be re-determined after each installation.

The coordinates of the geometric center of the component in the machine tool coordinate system are obtained by the bright field array microscope system, which is composed of an area array CCD camera, a zoom microscope head and a ring light source. The resolution of the area array CCD camera is 2456 × 2058, the pixel size is 3.45 μm × 3.45 μm, the zoom range of the variable-focus optical microscope is 0.87 × ~ 10.5 ×, and its working distance is 105mm. The brightfield microscope system CCD adopts Reflected light imaging, so the black area in the field of view represents the location of micro-defects or no reflection, and the white area is the defect-free position of the fused silica optical element to be tested, according to which the boundary of the optical element can be observed in the field of view of the brightfield CCD camera.

Step 3: Move the fused silica element to be measured to the spectral confocal displacement range finder, measure the characteristic points of the aspherical surface of the fused silica element to be measured, and obtain the coordinate values of the characteristic points of the aspherical surface;

And use the coordinate values of the feature points on the aspheric surface to fit the equation of the aspheric surface of the fused silica element to be measured in the element coordinate system;

Step 4: Based on Step 2 and Step 3, move the fused silica element to be measured to the CMOS area scan camera station to take a single picture, and after processing the collected image, restore the two-dimensional information of the image to three-dimensional, so as to obtain the The position information of the defect points on the aspheric surface of the fused silica element is measured, and the defect points on the aspheric surface of the fused silica element to be measured are repaired.

The schematic diagram of the micro-defect detection and positioning device on the surface of the aspherical element used in the present invention is shown in Figure 2. The device is divided into a bright field monitoring station, a spectral confocal ranging station, and a high-resolution area array camera dark field photography station , CO ₂ infrared laser repair station. First, the position of the aspheric optical element in the machine tool coordinate system is determined by the bright field monitoring station, and then the spectral confocal rangefinder is used to measure the distance of the surface feature points of the optical element and fit the surface equation, and then move to the photographing station to measure the distance. The surface of the component is photographed, and the accurate position and size information of the defect can be obtained through image processing and three-dimensional surface restoration. The repair platform moves the optical component to the repair station to complete the laser repair of the defect according to this information.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the specific process of the second step is:

Move the fused silica element to be tested to the center of the brightfield field of view through the X and Y two-dimensional high-precision motion platforms, and record the Y-axis coordinates y _T of the aspherical upper and lower boundary lines of the fused silica element to be tested in the machine tool coordinate system. and y _D , and the X-axis coordinates x _L and x _R of the left and right boundary lines of the aspheric surface in the machine coordinate system;

In Figure 3, the upper boundary line refers to the boundary located in the positive direction of the Y" axis and parallel to the X" axis, the lower boundary line refers to the boundary located in the negative direction of the Y" axis and parallel to the X" axis, and the left boundary line refers to the boundary located in the X" axis. The boundary of the "negative axis" and parallel to the Y" axis, and the right boundary line refers to the boundary located in the positive direction of the X" axis and parallel to the Y" axis;

Then when the aspheric geometric center of the fused silica element to be measured moves to the center of the bright field field of view, the coordinates (x ₀ , y ₀ ) of the machine tool in the machine tool coordinate system are:

Aspherical fused silica components have high machining accuracy and accurate surface equations. However, due to the limited assembly adjustment accuracy during installation, there is a rotation error between the component coordinate system and the machine tool coordinate system. Therefore, it is necessary to establish the component aspheric surface in the machine tool coordinate system. Surface equation.

Embodiment 3: The difference between this embodiment and Embodiment 2 is that the specific process of the third step is:

Taking the geometric center of the aspheric surface of the fused silica element to be measured as the origin O', the standard coordinate system O'-X"Y"Z" and the component coordinate system O'-X'Y'Z' are established, as shown in Figure 4, The three axes of the component coordinate system point to the same three axes of the machine tool coordinate system, the X" axis of the standard coordinate system is parallel to the upper and lower boundary lines of the aspheric surface of the fused silica element to be measured, and the Y" axis is parallel to the The left boundary line and the right boundary line of the aspheric surface of the fused silica element are parallel, and the direction of the Z" axis is the normal direction of the aspheric surface of the fused silica element to be measured through the origin O';

Then the aspheric equation of the fused silica element to be tested in the standard coordinate system is:

Where: 1/c is the radius of curvature at the geometric center of the aspheric surface, k is the conic coefficient, and x", y", and z" are the coordinates of the aspheric surface in the X", Y", and Z" axis directions, respectively;

Due to the limited assembly adjustment accuracy of the fused silica component to be tested during installation, there is a rotation error between the three axes of the standard coordinate system and the three axes of the component coordinate system, as shown in Figure 4. Therefore, it is necessary to change the standard coordinate system of formula (2) into The spherical equation is transformed into the aspheric equation in the element coordinate system;

Assuming that there is a defect point A on the aspheric surface of the fused silica component to be tested, the coordinates of the defect point A in the component coordinate system and the standard coordinate system are (x', y', z'), (x", y", z respectively "), according to the principle of rotation transformation, there is the following formula (3) relationship between the component coordinate system and the standard coordinate system:

为标准坐标系Y″轴与工件坐标系Y′轴的旋转误差角度，ρ为标准坐标系Z″轴与工件坐标系Z′轴的旋转误差角度；R(x″,θ)为标准坐标系X″轴与工件坐标系X′轴的旋转矩阵，

为标准坐标系Y″轴与工件坐标系Y′轴的旋转矩阵，R(z″,ρ)为标准坐标系Z″轴与工件坐标系Z′轴的旋转矩阵；Where: θ is the rotation error angle between the X″ axis of the standard coordinate system and the X′ axis of the workpiece coordinate system,

is the rotation error angle between the Y″ axis of the standard coordinate system and the Y′ axis of the workpiece coordinate system, ρ is the rotation error angle between the Z″ axis of the standard coordinate system and the Z′ axis of the workpiece coordinate system; R(x″, θ) is the standard coordinate system The rotation matrix between the X" axis and the X' axis of the workpiece coordinate system,

is the rotation matrix of the Y″ axis of the standard coordinate system and the Y′ axis of the workpiece coordinate system, and R(z″, ρ) is the rotation matrix of the Z″ axis of the standard coordinate system and the Z′ axis of the workpiece coordinate system;

的表达式为：where: rotation matrix

The expression is:

Since the rotation direction of the Z axis is positioned by the plane, there is no rotation in the direction of the Z″ axis, that is, ρ=0, then the expression of the rotation matrix R is transformed into formula (5):

θ两个未知数，因此只需要3个测量点就可以求解出旋转矩阵R。这里用到了非球面在空间中旋转不改变形状的原理，由于暗场相机景深较小，着重关注z′值的大小，通过上述旋转矩阵可知，只有最后一行对z′值有影响，由旋转矩阵得到：There is only one left in the rotation matrix R

θ has two unknowns, so only 3 measurement points are needed to solve the rotation matrix R. The principle that the aspheric surface rotates in space does not change its shape is used here. Since the depth of field of the dark field camera is small, the focus is on the size of the z' value. From the above rotation matrix, we can see that only the last row has an impact on the z' value. The rotation matrix get:

The formula for calculating the z' value of the fused silica element to be measured in the element coordinate system is:

sinθ＝tanθ，

cosθ＝1，则待测熔石英元件在元件坐标系下的非球面方程为：In practical use, it can be approximated

sinθ=tanθ,

cosθ=1, then the aspherical equation of the fused silica element to be measured in the element coordinate system is:

两个未知量，本发明采用光谱共焦测距仪对非球面表面的五个特征点进行测距的方法，对未知参数进行拟合，五个特征点在非球面上的分布如图5所示。In equation (7), only θ,

For two unknown quantities, the present invention uses a spectral confocal rangefinder to measure the distance of five characteristic points on the aspheric surface, and fits the unknown parameters. The distribution of the five characteristic points on the aspheric surface is shown in Figure 5. Show.

The spectral confocal displacement rangefinder is used to measure the distance of the feature point 1, feature point 2, feature point 3, feature point 4 and feature point 5 of the aspheric surface, wherein: feature point 1 is the geometric center of the aspheric surface, and the feature point 2. Feature point 3, feature point 4 and feature point 5 are the four vertices of a rectangle centered on the aspheric geometric center, and the four sides of the rectangle are respectively parallel to the X and Y axes of the machine tool coordinate system. Within the range of the confocal displacement rangefinder, the aspheric surface area covered by the rectangle should be as large as possible;

When the geometric center of the aspheric surface is clearly imaged in the bright field field of view, the coordinate z ₀ of the machine tool in the Z-axis direction of the machine tool coordinate system is:

z ₀ =l ₁ +z _c -σ ₁ (8)

Among them: l ₁ is the measurement result of the spectral confocal displacement range finder at feature point 1, z _c is the coordinate of the spectral confocal displacement range finder in the Z-axis direction of the machine tool coordinate system during ranging, and σ ₁ is the area array CCD The object distance when the camera is clearly imaged;

和θ的值；Move the three-dimensional motion platform to measure the distance between the spectral confocal displacement rangefinder and feature point 2, feature point 3, feature point 4 and feature point 5, and record feature point 2, feature point 3, feature point 4 and The raster feedback value of feature point 5 on the X axis and the Y axis, that is, the three-dimensional coordinates of feature point 2, feature point 3, feature point 4 and feature point 5 of the aspheric surface in the machine tool coordinate system are obtained by using the least square method. The coordinate values of feature point 2, feature point 3, feature point 4 and feature point 5 are processed to calculate

and the value of θ;

和θ值代入公式(7)，求得待测熔石英元件在元件坐标系下的非球面方程。will be calculated

Substitute the value of θ and θ into formula (7) to obtain the aspherical equation of the fused silica element to be measured in the element coordinate system.

Embodiment 4: The difference between this embodiment and Embodiment 3 is that the specific process of the fourth step is:

Step 41. Move the fused silica element to be tested to the CMOS area scan camera station. The scattered light emitted by the defect point A on the aspheric surface of the fused silica element to be tested enters the imaging system, and the CMOS area scan camera of the imaging system will be able to detect under the dark background. image acquisition of bright defects;

After the top hat transformation is performed on the collected image, the background information is removed, and then the Laplacian weighted adaptive binarization is used to achieve image segmentation to obtain the target image; The minimum circumscribed circle diameter is taken as the pixel size of defect point A;

Step 42: If the pixel coordinates of the defect point A are (x _pixel , y _pixel ), according to the imaging principle of the camera, the imaging surface coordinates (x ₁ , y ₁ ) corresponding to the defect point A are:

Wherein: k _x and _ky are the conversion coefficients from the pixel coordinates of the defect point A to the imaging surface coordinates; the conversion coefficients can be obtained by calibration with a standard scale plate;

Step 43: The imaging surface of the CMOS area scan camera is a plane. According to the mapping relationship, the curved surface information will be converted into plane information when the CMOS area scan camera is imaging. As shown in Figure 7, when the CMOS area scan camera collects images, the curved surface abcd The actual imaging surface is a plane a ₁ b ₁ c ₁ d ₁ . During this process, the depth information along the optical axis is compressed, so a method is needed to restore the two-dimensional image; Analysis, the coordinates of defect point A in the component coordinate system are (x', y', z'), the point corresponding to defect point A on the imaging surface is A ₁ , and the coordinates of point A ₁ in the component coordinate system are ( x ₁ , y ₁ , z ₁ ); combined with Fig. 8, the imaging plane is restored to a surface schematic diagram;

From geometric optics, y' and y ₁ have the following correspondence:

Where: L represents the distance between the optical center of the incident imaging system and the geometric center of the aspheric surface;

Approximately consider z′=z ₁ , then

Similarly get:

Then the corresponding relationship between the coordinates of defect point A in the component coordinate system and the coordinates of defect point A in the imaging plane is:

Step 44: Establish the relationship between the coordinates of the defect point A in the component coordinate system and the pixel coordinates of the defect point A;

When the machine tool moves to (x ₀ , y ₀ ), the geometric center of the aspheric surface of the fused silica element to be tested is in the center of the bright field field of view. Therefore, when the machine tool moves to the position shown in equation (15), the defect point A is in the bright field The center of the field of view can be used to observe the defect point A with the area array CCD camera;

Similarly, when the machine tool moves to the position shown in formula (16), the defect point A is in the laser repair station, and the defect point A can be repaired;

Among them: σ _x and σ _y are the distances from the laser head to the center of the brightfield field of view in the X and Y axes, and σ ₂ is the coordinates of the laser head in the machine tool coordinate system during laser repair.

By formulas (15) and (16), the pixel coordinates of the defect points are converted into the corresponding bright field station coordinates and repair station coordinates, and the geometric center of the aspheric surface of the fused silica element is moved to the repair station coordinates to realize the fusion Repair the surface defects of the quartz element, and then move the geometric center of the aspheric surface of the fused quartz element to the coordinates of the bright field station to check the repair results.

FIG. 6 is a schematic diagram of the dark field detection adopted in the present invention. When there is a defect on the surface of the element, according to geometric optics, the scattered light of the incident light A0 is A1. If there is no defect, the reflected light is A2. Only the scattered light A1 can enter the imaging system, so that the dark background can be measured. Bright defects. The pixel coordinates and size of the defects can be obtained by processing the collected images, and a certain method is used to convert the pixel coordinates of the defects into coordinates in the machine tool coordinate system, and the positioning of the defects can be realized through the motion system of the detection platform.

The high-resolution camera used is a CMOS area scan camera with a sensor size of 31mm × 22mm, a resolution of 10000 × 7096 pixels, and a pass light field size of 636 × 450mm, so the magnification is 0.0487. The working distance is 1730mm, corresponding to the focal length of the lens. The light source is a high-brightness linear array light source, the light source size is 600×20mm, and the power is 0-48W, which can be adjusted by the controller. In the process of black and white imaging, the quantum effect curve of the camera reaches a peak value between 500nm and 580nm, and the camera has the best sensitivity to this wavelength, so the color of the light source is selected as green light.

The repair platform used in the present invention has a positioning accuracy of ±10 μm, includes three motion axes of X/Y/Z, and can be equipped with optical elements to realize X/Y two-dimensional high-precision movement. Move the repair platform to the installation station to complete the installation of aspheric components. The fixture used during installation is a quick-clamp accompanying fixture for repairing micro-defects on the surface of large-diameter curved optical components. 500mm x 500mm fused silica optics for clamping.

Embodiment 5: The difference between this embodiment and Embodiment 4 is that the resolution of the area array CCD camera used in the second step is 2456×2058, and the pixel size is 3.45 μm×3.45 μm.

Embodiment 6: This embodiment differs from Embodiment 5 in that the working distance of the spectral confocal rangefinder used in the third step is 222.3 mm, the effective range is 24 mm, and the axial measurement accuracy is 3 μm.

Embodiment 7: This embodiment is different from Embodiment 6 in that the resolution of the CMOS area scan camera used in the fourth step is 10000×7096 pixels.

Example

Example analysis of micro-defect detection and positioning method on the surface of aspheric components. The above method is used to detect a batch of aspheric components. The diameter of the component is 430mm × 430mm, and the detection surface is an aspheric surface (light incident surface). The surface equation is as follows:

where:

The radius of curvature at the geometric center of the incident surface: 1/c=1899.75mm;

Cone coefficient: k=-2.180721;

Quadratic term coefficient: a=4.34336×10 ^-10 ;

Before testing components, the following parameters need to be calibrated:

Conversion coefficients k _x and ky from pixel coordinates to imaging plane coordinates, k _x =0.06360, _{ky =} 0.06365;

The distance L from the optical center to the imaging surface, L=1730mm;

The distances σ _x , σ _y from the laser head to the center of the brightfield field of view in the X and Y directions, the object distance when the brightfield camera is clearly imaged, and the coordinates σ ₁ , σ ₂ of the laser head in the machine tool coordinate system during laser repair, σ _x = 371.46mm, σ _y =47.96mm, σ ₁ =17.205mm, σ ₂ =58.8mm

Automatically initialize the machine tool to zero the machine tool, and move the machine tool to the installation station to complete the installation of optical components. After installation, move the optical element to the brightfield field of view, move the upper, lower, left, and right boundaries of the optical element to the center of the brightfield field of view, respectively, and record the corresponding coordinate values: y _T = -213.75990, y _D = 216.24011, x _L =375.16701, x _R =-54.83382, the machine tool coordinates when the geometric center of the component moves to the center of the bright field view are:

Move the optical element to the spectral confocal ranging station, and the automatic measurement of five points and automatic fitting of parameters can be realized by repairing the platform software. The measurement and fitting results are:

Move the optical element to the dark field photographing station for image acquisition, and process the collected images to obtain the pixel coordinates and pixel dimensions of all defects. Take the No. 312 defect obtained by image processing as an example for analysis, and its pixel coordinates are (- 3262, 2275). Convert it to imaging plane coordinates as:

According to the formula (13), the imaging plane coordinates of the defect point are transformed into the coordinates under the workpiece coordinate system:

It can be seen from formula (15) that when the defect is moved to the center of the bright field field of view, the machine tool coordinates should be:

It can be seen from formula (16) that when the defect is moved to the repair station, the coordinates of the machine tool should be:

Move the machine to (-49.25, 142.41, 6.44) to locate the defect to the brightfield station, and move the machine to (-420.71, 94.45, 58.50) to locate the defect to the repair station. Figure 9 shows the image captured by the brightfield camera when the defect is located in the brightfield station. It can be seen from the image that the defect is successfully located in the center of the brightfield field of view.

The above steps use the positioning method provided by the present invention to realize the rapid positioning of micro-defects on the surface of the aspherical fused silica element.

The above calculation examples of the present invention are only to illustrate the calculation model and calculation process of the present invention in detail, but are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, on the basis of the above description, other different forms of changes or changes can also be made, and it is impossible to list all the embodiments here. Obvious changes or modifications are still within the scope of the present invention.

Claims (4)

1. a method for quickly locating micro-defects on the surface of aspherical fused silica elements, is characterized in that, the method comprises the following steps: Step 1. Take the machine zero point of the machine tool as the original center O, establish the machine tool coordinate system O-XYZ, and the three axes of the machine tool coordinate system point to the same three axes of the space rectangular coordinate system; Step 2. Based on Step 1, the fused silica element to be tested is located in the center of the bright field field of view, and the image of the fused silica element to be tested is collected by an area array CCD camera. to obtain the coordinates of the machine tool in the machine tool coordinate system when the aspheric geometric center of the fused silica element to be measured moves to the center of the bright field field of view; The specific process of the second step is: Move the fused silica element to be tested to the center of the brightfield field of view, and record the Y-axis coordinates y _T and y _D of the upper and lower boundary lines of the aspheric surface of the fused silica element to be tested in the machine tool coordinate system, and the left boundary line of the aspheric surface. and the X-axis coordinates x _L and x _R of the right boundary line in the machine coordinate system; Then when the aspheric geometric center of the fused silica element to be measured moves to the center of the bright field field of view, the coordinates (x ₀ , y ₀ ) of the machine tool in the machine tool coordinate system are:

Step 3: Move the fused silica element to be measured to the spectral confocal displacement range finder, measure the characteristic points of the aspherical surface of the fused silica element to be measured, and obtain the coordinate values of the characteristic points of the aspherical surface; And use the coordinate values of the feature points on the aspheric surface to fit the equation of the aspheric surface of the fused silica element to be measured in the element coordinate system; The specific process of the third step is: Taking the geometric center of the aspheric surface of the fused silica element to be measured as the origin O', the standard coordinate system O'-X"Y"Z" and the component coordinate system O'-X'Y'Z' are established. The three axes point to the three axes of the machine tool coordinate system, the X″ axis of the standard coordinate system is parallel to the upper and lower boundary lines of the aspheric surface of the fused silica element to be tested, and the Y″ axis is parallel to the aspheric surface of the fused silica element to be tested. The left boundary line and the right boundary line are parallel, and the Z″ axis direction is the normal direction of the aspheric surface of the fused silica element to be measured passing through the origin O’; Then the aspheric equation of the fused silica element to be tested in the standard coordinate system is:

Where: 1/c is the radius of curvature at the geometric center of the aspheric surface, k is the conic coefficient, and x", y", and z" are the coordinates of the aspheric surface in the X", Y", and Z" axis directions, respectively; Due to the limited adjustment accuracy of the fused silica component to be tested during installation, there is a rotation error between the three axes of the standard coordinate system and the three axes of the component coordinate system. Therefore, it is necessary to convert the aspheric equation in the standard coordinate system of formula (2) into component coordinates. The aspheric equation under the system; Assuming that there is a defect point A on the aspheric surface of the fused silica component to be tested, the coordinates of the defect point A in the component coordinate system and the standard coordinate system are (x', y', z'), (x", y", z respectively "), according to the principle of rotation transformation, there is the following formula (3) relationship between the component coordinate system and the standard coordinate system:

Where: θ is the rotation error angle between the X″ axis of the standard coordinate system and the X′ axis of the workpiece coordinate system,

is the rotation error angle between the Y″ axis of the standard coordinate system and the Y′ axis of the workpiece coordinate system, ρ is the rotation error angle between the Z″ axis of the standard coordinate system and the Z′ axis of the workpiece coordinate system; R(x″, θ) is the standard coordinate system The rotation matrix between the X" axis and the X' axis of the workpiece coordinate system,

is the rotation matrix of the Y″ axis of the standard coordinate system and the Y′ axis of the workpiece coordinate system, and R(z″, ρ) is the rotation matrix of the Z″ axis of the standard coordinate system and the Z′ axis of the workpiece coordinate system; where: rotation matrix

The expression is:

Since there is no rotation in the direction of the Z″ axis, that is, ρ=0, the expression of the rotation matrix R is transformed into formula (5):

The formula for calculating the z' value of the fused silica element to be measured in the element coordinate system is:

sinθ=tanθ,

cosθ=1, then the aspherical equation of the fused silica element to be measured in the element coordinate system is:

The spectral confocal displacement rangefinder is used to measure the distance of the feature point 1, feature point 2, feature point 3, feature point 4 and feature point 5 of the aspheric surface, wherein: feature point 1 is the geometric center of the aspheric surface, and the feature point 2. Feature point 3, feature point 4 and feature point 5 are the four vertices of a rectangle centered on the aspheric geometric center, and the four sides of the rectangle are respectively parallel to the X and Y axes of the machine tool coordinate system. Within the range of the confocal displacement rangefinder, the aspheric surface area covered by the rectangle should be as large as possible; When the geometric center of the aspheric surface is clearly imaged in the bright field field of view, the coordinate z ₀ of the machine tool in the Z-axis direction of the machine tool coordinate system is: z ₀ =l ₁ +z _c -σ ₁ (8) Among them: l ₁ is the measurement result of the spectral confocal displacement range finder at feature point 1, z _c is the coordinate of the spectral confocal displacement range finder in the Z-axis direction of the machine tool coordinate system during ranging, and σ ₁ is the area array CCD The object distance when the camera is clearly imaged; Measure the distance between the spectral confocal displacement rangefinder and feature point 2, feature point 3, feature point 4 and feature point 5 respectively, and record feature point 2, feature point 3, feature point 4 and feature point 5 in X The raster feedback value of the axis and the Y axis, that is, to obtain the three-dimensional coordinates of the feature point 2, feature point 3, feature point 4 and feature point 5 of the aspheric surface in the machine tool coordinate system, and use the least square method to obtain the feature point 2, The coordinate values of feature point 3, feature point 4 and feature point 5 are processed to calculate

and the value of θ; will be calculated

Substitute the value of θ and θ into formula (7) to obtain the aspheric equation of the fused silica element to be measured in the element coordinate system; Step 4: Based on Step 2 and Step 3, move the fused silica element to be measured to the CMOS area scan camera station to take a single picture, and after processing the collected image, restore the two-dimensional information of the image to three-dimensional, so as to obtain the Measure the position information of the defect points on the aspheric surface of the fused silica element, and repair the defect points on the aspheric surface of the fused silica element to be measured; The specific process of the step 4 is: Step 41. Move the fused silica element to be tested to the CMOS area scan camera station. The scattered light emitted by the defect point A on the aspheric surface of the fused silica element to be tested enters the imaging system, and the CMOS area scan camera of the imaging system will be able to detect under the dark background. image acquisition of bright defects; After the top hat transformation is performed on the collected image, the background information is removed, and then the Laplacian weighted adaptive binarization is used to achieve image segmentation to obtain the target image; The minimum circumscribed circle diameter is taken as the pixel size of defect point A; Step 42: If the pixel coordinates of the defect point A are (x _pixel , y _pixel ), according to the imaging principle of the camera, the imaging surface coordinates (x ₁ , y ₁ ) corresponding to the defect point A are:

Where: k _x and _ky are the conversion coefficients from the pixel coordinates of the defect point A to the imaging surface coordinates; Step 43: The imaging surface of the CMOS area scan camera is a plane. According to the mapping relationship, the curved surface information will be converted into plane information when the CMOS area scan camera is imaging, and the depth information along the optical axis direction is compressed; Analyze the direction, the coordinates of defect point A in the component coordinate system are (x', y', z'), the point corresponding to defect point A on the imaging surface is A ₁ , and the coordinates of point A ₁ in the component coordinate system is (x ₁ , y ₁ , z ₁ ); From geometric optics, y' and y ₁ have the following correspondence:

Where: L represents the distance between the optical center of the incident imaging system and the geometric center of the aspheric surface; z'=z ₁ , then

Similarly get:

Then the corresponding relationship between the coordinates of defect point A in the component coordinate system and the coordinates of defect point A in the imaging plane is:

Step 44: Establish the relationship between the coordinates of the defect point A in the component coordinate system and the pixel coordinates of the defect point A;

When the machine tool moves to (x ₀ , y ₀ ), the geometric center of the aspheric surface of the fused silica element to be tested is in the center of the bright field field of view. Therefore, when the machine tool moves to the position shown in equation (15), the defect point A is in the bright field The center of the field of view can be used to observe the defect point A with the area array CCD camera;

Similarly, when the machine tool moves to the position shown in formula (16), the defect point A is in the laser repair station, and the defect point A can be repaired;

Among them: σ _x and σ _y are the distances from the laser head to the center of the bright field field of view in the X and Y axes, and σ ₂ is the coordinates of the laser head in the machine tool coordinate system during laser repair; By formulas (15) and (16), the pixel coordinates of the defect points are converted into the corresponding bright field station coordinates and repair station coordinates, and the geometric center of the aspheric surface of the fused silica element is moved to the repair station coordinates to realize the fusion Repair the surface defects of the quartz element, and then move the geometric center of the aspheric surface of the fused quartz element to the coordinates of the bright field station to check the repair results. 2. The method for quickly locating micro-defects on the surface of an aspheric fused silica element according to claim 1, wherein the resolution of the area array CCD camera adopted in the step 2 is 2456×2058, and the pixel size is 3.45μm×3.45μm. 3. a kind of aspherical fused silica element surface micro-defect quick positioning method according to claim 2, is characterized in that, the working distance of the spectral confocal displacement distance meter that adopts in described step 3 is 222.3mm, effective range is 24mm, and the axial measurement accuracy is 3μm. 4 . The method for quickly locating micro-defects on the surface of an aspherical fused silica element according to claim 3 , wherein the resolution of the CMOS area scan camera used in the fourth step is 10000×7096 pixels. 5 .

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