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

Method for quickly positioning surface micro-defects of aspheric fused quartz element Download PDF

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CN110411346B
CN110411346B CN201910740204.1A CN201910740204A CN110411346B CN 110411346 B CN110411346 B CN 110411346B CN 201910740204 A CN201910740204 A CN 201910740204A CN 110411346 B CN110411346 B CN 110411346B
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陈明君
尹朝阳
赵林杰
程健
张德志
蒋晓东
廖威
王海军
张传超
栾晓雨
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Harbin Institute of Technology
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    • G01—MEASURING; TESTING
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Abstract

A method for quickly positioning micro defects on the surface of an aspheric fused quartz element belongs 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 element. According to the method, a machine tool coordinate system is established, and the coordinate of the geometric center of the aspheric surface of the fused quartz element to be detected under the machine tool coordinate system is obtained according to the positions of the boundary lines of the four sides of the aspheric surface of the fused quartz element to be detected under the machine tool coordinate system; moving the fused quartz element to be measured to a spectrum confocal displacement distance measuring instrument, measuring the distance of the characteristic points of the aspheric surface of the fused quartz element to be measured, and fitting an equation of the aspheric surface of the fused quartz element to be measured in an element coordinate system according to the coordinates of the characteristic points of the aspheric surface; and after the CMOS area array camera is adopted to collect the image, the two-dimensional information of the image is restored to be three-dimensional, so that the position information of the defect point on the aspheric surface of the fused quartz element to be detected is obtained. The invention can be applied to the technical field of optical element surface micro-defect detection.

Description

Method for quickly positioning surface micro-defects of aspheric fused quartz element
Technical Field
The invention belongs to the technical field of engineering optics, and particularly relates to a method for quickly positioning micro defects on the surface of an aspheric fused quartz element.
Background
The large-caliber aspheric fused quartz element is a key element of a high-power solid laser system terminal optical component, and can focus the triple-frequency laser which is injected in parallel on a target point of a vacuum target chamber, so that high focusing power density is obtained. Fig. 1 is a schematic diagram of a three-dimensional structure of a large-caliber aspheric optical element, in which an incident surface is aspheric and a material is fused quartz. As a typical hard and brittle material, the fused quartz is very easy to generate surface microdefects such as microcracks, pits and the like in the processing process, and the generation and growth of the microdefects are further aggravated by strong laser irradiation. Research shows that if micro defects on the surface of the fused quartz are not repaired or inhibited in time, the size of the defects grows exponentially under laser irradiation. This results in a reduced quality of the light beam transmitted through the fused silica, which makes the optical element unusable for production. Therefore, a high-precision and high-efficiency method must be designed to realize the rapid positioning of the surface micro-defects of the aspheric optical element, so as to facilitate the subsequent laser repair of the defects.
Common methods for detecting and positioning the micro-defects on the surface of the optical element include a visual detection method and a machine vision detection method. The visual inspection method is to irradiate the surface of the element with light beams at a certain angle, and the detection personnel observes the defect of bright spots in the direction of light beam reflection or transmission. But the accurate position and size information of the defect can not be obtained by only visual identification, and the efficiency is low and the error rate is high.
As technology has evolved, machine vision has been introduced in the detection of surface defects on optical elements. According to the detection method, the surface image of the optical element is acquired by means of the high-resolution camera, the specific position and size of the surface micro-defect are obtained through image processing, the micro-defect can be positioned through combination with the electric control platform, and precision and automation of repair are easy to achieve. However, at present, a linear array camera is mostly adopted for scanning and detecting a large-aperture optical element, the optical element needs to be scanned and photographed line by line and images need to be spliced, so that the detection efficiency is low. And most of the detection elements at the present stage are planar elements, the detected surface of the aspheric element is a curved surface, curved surface information can be converted into planar information when the camera images according to the mapping relation, and depth information along the optical axis direction is compressed in the process, so that the positioning accuracy is low.
Disclosure of Invention
The invention aims to solve the problems of low detection efficiency and low positioning accuracy of the surface micro-defects of the conventional optical element, and provides a method for quickly positioning the surface micro-defects of an aspheric fused quartz element.
The technical scheme adopted by the invention for solving the technical problems is as follows: a method for quickly positioning micro defects on the surface of an aspheric fused quartz element comprises the following steps:
establishing a machine tool coordinate system O-XYZ by taking a mechanical zero point of a machine tool as a centroid O, wherein three axes of the machine tool coordinate system point to three axes of a rectangular coordinate system in the same space;
secondly, based on the first step, enabling the fused quartz element to be detected to be located at the center of a bright field visual field, acquiring an image of the fused quartz element to be detected by using an area array CCD camera, and obtaining the coordinate of a machine tool under a machine tool coordinate system when the geometric center of the aspheric surface of the fused quartz element to be detected moves to the center of the bright field visual field according to the positions of four boundary lines of the aspheric surface of the fused quartz element to be detected under the machine tool coordinate system;
moving the fused quartz element to be measured to a spectrum confocal displacement distance measuring instrument, and measuring the distance of the characteristic points of the aspheric surface of the fused quartz element to be measured to obtain the coordinate values of the characteristic points of the aspheric surface;
fitting an equation of the aspheric surface of the fused quartz element to be tested in an element coordinate system by using the coordinate values of the aspheric surface characteristic points;
and step four, based on the step two and the step three, moving the fused quartz element to be detected to a CMOS area array camera station for single shooting, processing the acquired image, reducing the two-dimensional information of the image to be three-dimensional, thereby obtaining the position information of the aspheric surface defect point of the fused quartz element to be detected, and repairing the aspheric surface defect point of the fused quartz element to be detected.
The invention has the beneficial effects that: the invention provides a method for quickly positioning surface micro defects of an aspheric fused quartz element, and provides a detection method for carrying out full-aperture single-shot shooting on an element to be detected by adopting a high-resolution area-array camera. Furthermore, it is possible to provide a liquid crystal display device,
(1) according to the invention, the dark field imaging and the full-aperture single-frame shooting are realized by adopting the high-resolution area-array camera, and the detection speed is greatly improved compared with a linear array scanning mode;
(2) the invention realizes the rapid positioning of the element to be detected and the visual online monitoring of the defects by using a bright field microscope system;
(3) the invention adopts the spectrum confocal displacement distance measuring instrument to correct the rotation error of the element to be measured in the installation process, and obtains the accurate equation of the curved surface of the element in the element coordinate system;
(4) the invention carries out three-dimensional curved surface reduction on the two-dimensional image acquired by the high-resolution area-array camera, thereby improving the positioning precision of defects;
(5) the process method provided by the invention realizes detection and positioning of the surface defects of the aspheric surface element to be detected, and meets the use requirements of subsequent laser repair.
Drawings
FIG. 1 is a schematic three-dimensional structure diagram of a large-caliber aspheric optical element;
FIG. 2 is a schematic view of the positioning apparatus for detecting surface micro-defects of aspheric elements according to the present invention;
FIG. 3 is a schematic diagram of a three-dimensional model of a DUT and a standard coordinate system according to the present invention;
FIG. 4 is a schematic diagram of a rotation error of the DUT;
FIG. 5 is a distance measurement fitting graph of aspheric surface feature points of the device under test;
in the figure, 1, 2, 3, 4 and 5 respectively represent the positions of five feature points;
FIG. 6 is a schematic diagram of the detection of defect points on the aspheric surface of the device under test;
FIG. 7 is a schematic diagram of imaging of an aspheric surface in a CMOS area-array camera;
FIG. 8 is a schematic representation of the reduction of the imaging plane to a curved surface;
FIG. 9 is a schematic view of a camera capturing an image with a defect point located at a brightfield station.
Detailed Description
The first embodiment is as follows: the method for quickly positioning the surface micro-defects of the aspheric fused quartz element comprises the following steps of:
establishing a machine tool coordinate system O-XYZ by taking a mechanical zero point of a machine tool as a centroid O, wherein three axes of the machine tool coordinate system point to three axes of a rectangular coordinate system in the same space;
secondly, based on the first step, enabling the fused quartz element to be detected to be located at the center of a bright field visual field, acquiring an image of the fused quartz element to be detected by using an area array CCD camera, and obtaining the coordinate of a machine tool under a machine tool coordinate system when the geometric center of the aspheric surface of the fused quartz element to be detected moves to the center of the bright field visual field according to the positions of four boundary lines of the aspheric surface of the fused quartz element to be detected under the machine tool coordinate system;
because the fused quartz component to be measured has different sizes and positioning errors exist in the installation process, the coordinates of the component in the machine tool coordinate system need to be determined again after the component is installed every time.
The coordinate of the geometric center of the element in the machine tool coordinate system is obtained by using a bright field area array microscope system, and the bright field area array microscope system consists of an area array CCD camera, a variable focus microscope lens and an annular light source. The resolution of the area array CCD camera is 2456 multiplied by 2058, the pixel size is 3.45 multiplied by 3.45, the zoom range of the variable focus optical microscope lens is 0.87 multiplied by 10.5 multiplied by 105mm, the bright field microscope system CCD adopts reflected light for imaging, therefore, a black area in a visual field represents the position of a micro defect or a non-reflection position, a white area is the non-defect position of the fused quartz optical element to be detected, and the boundary of the optical element can be observed in the visual field of the bright field CCD camera.
Moving the fused quartz element to be measured to a spectrum confocal displacement distance measuring instrument, and measuring the distance of the characteristic points of the aspheric surface of the fused quartz element to be measured to obtain the coordinate values of the characteristic points of the aspheric surface;
fitting an equation of the aspheric surface of the fused quartz element to be tested in an element coordinate system by using the coordinate values of the aspheric surface characteristic points;
and step four, based on the step two and the step three, moving the fused quartz element to be detected to a CMOS area array camera station for single shooting, processing the acquired image, reducing the two-dimensional information of the image to be three-dimensional, thereby obtaining the position information of the aspheric surface defect point of the fused quartz element to be detected, and repairing the aspheric surface defect point of the fused quartz element to be detected.
The schematic diagram of the device for detecting and positioning the surface microdefects of the aspheric surface element adopted by the invention is shown in figure 2, and the device comprises a bright field monitoring station, a spectrum confocal distance measuring station, a high-resolution area-array camera dark field photographing station, a CO2And (5) infrared laser repairing stations. The method comprises the steps of firstly determining the position of an aspheric optical element in a machine tool coordinate system through a bright field monitoring station, then ranging characteristic points on the surface of the optical element by using a spectrum confocal range finder and fitting a curved surface equation, moving to a photographing station to photograph the surface of the element, obtaining accurate position and size information of a defect through image processing and three-dimensional curved surface reduction, and moving the optical element to a repairing station by a repairing platform according to the information to complete laser repairing of the defect.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the specific process of the second step is as follows:
moving the fused quartz element to be measured to the center of a bright field view through an X-dimensional and Y-dimensional high-precision motion platform, and respectively recording a Y-axis coordinate Y of an upper boundary line and a lower boundary line of the aspheric surface of the fused quartz element to be measured under a machine tool coordinate systemTAnd yDAnd X-axis coordinate X of the left and right boundary lines of the aspherical surface in the machine coordinate systemLAnd xR；
In FIG. 3, the upper boundary line refers to a boundary located in the positive direction of the Y 'axis and parallel to the X' axis, the lower boundary line refers to a boundary located in the negative direction of the Y 'axis and parallel to the X' axis, the left boundary line refers to a boundary located in the negative direction of the X 'axis and parallel to the Y' axis, and the right boundary line refers to a boundary located in the positive direction of the X 'axis and parallel to the Y' axis;
when the aspheric geometric center of the fused quartz element to be measured moves to the center of the bright field view, the coordinate (x) of the machine tool under the machine tool coordinate system0,y0) Comprises the following steps:
Figure BDA0002163671690000041
the aspheric fused quartz element has high processing precision and an accurate curved surface equation, but because the assembly adjustment precision is limited during installation, a rotation error exists between an element coordinate system and a machine tool coordinate system, and therefore the curved surface equation of the aspheric surface of the element under the machine tool coordinate system must be established.
The third concrete implementation mode: the second embodiment is different from the first embodiment in that: the specific process of the third step is as follows:
establishing a standard coordinate system O ' -X ' Y ' Z ' and an element coordinate system O ' -X ' Y ' Z ' by taking the geometric center of the aspheric surface of the fused quartz element to be detected as an original point O ', wherein three axes of the element coordinate system point to three axes of the machine tool coordinate system as shown in figure 4, an X ' axis of the standard coordinate system is parallel to an upper boundary line and a lower boundary line of the aspheric surface of the fused quartz element to be detected, a Y ' axis is parallel to a left boundary line and a right boundary line of the aspheric surface of the fused quartz element to be detected, and a Z ' axis direction is a normal direction of the aspheric surface of the fused quartz element to be detected passing through the original point O ';
then the aspheric equation of the fused quartz component to be measured in the standard coordinate system is:
Figure BDA0002163671690000051
wherein: 1/c is the curvature radius at the geometric center of the aspheric surface, k is the cone coefficient, and X ', Y', Z 'are the coordinates of the aspheric surface in the X', Y ', Z' axis directions respectively;
because the assembly and adjustment precision of the fused quartz element to be measured is limited during installation, and rotation errors exist between the three axes of the standard coordinate system and the three axes of the element coordinate system, as shown in fig. 4, the aspheric equation under the standard coordinate system of the formula (2) needs to be converted into the aspheric equation under the element coordinate system;
assuming that a defect point A is arranged on the aspheric surface of the fused quartz element to be detected, the coordinates of the defect point A under an element coordinate system and a standard coordinate system are (x ', y ', z '), (x ", y", z "), respectively, and according to the rotation transformation principle, the relationship of the following formula (3) exists between the element coordinate system and the standard coordinate system:
Figure BDA0002163671690000052
wherein: theta is the rotation error angle of the X 'axis of the standard coordinate system and the X' axis of the workpiece coordinate system,
Figure BDA0002163671690000053
the rotation error angle between the Y 'axis of the standard coordinate system and the Y' axis of the workpiece coordinate system is defined, and rho 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 ', theta) is a rotation matrix of the X ' axis of the standard coordinate system and the X ' axis of the workpiece coordinate system,
Figure BDA0002163671690000054
the rotation matrix of the Y 'axis of the standard coordinate system and the Y' axis of the workpiece coordinate system is used as R (Z ', rho), and the rotation matrix of the Z' axis of the standard coordinate system and the Z 'axis of the workpiece coordinate system is used as R (Z', rho);
wherein: rotation matrix
Figure BDA0002163671690000055
The expression of (a) is:
Figure BDA0002163671690000056
since the Z-axis rotation direction is located by a plane, there is no rotation in the Z "axis direction, i.e., ρ is 0, the expression of the rotation matrix R is transformed into formula (5):
Figure BDA0002163671690000057
only the rotation matrix R is left
Figure BDA0002163671690000058
θ two unknowns, so only 3 measurement points are needed to solve for the rotation matrix R. The principle that the aspheric surface rotates in space without changing the shape is used, the depth of field of the dark field camera is small, the size of the z 'value is focused, and the rotation matrix shows that only the last row has influence on the z' value and is obtained by the rotation matrix:
the calculation formula of the z' value of the fused quartz element to be measured in the element coordinate system is as follows:
Figure BDA0002163671690000061
in practical use, can approximate
Figure BDA0002163671690000062
sinθ＝tanθ，
Figure BDA0002163671690000063
And cos θ is 1, the aspheric equation of the fused quartz element to be measured in the element coordinate system is:
Figure BDA0002163671690000064
in equation (7), only θ,
Figure BDA0002163671690000065
Two unknown quantities, the method of the invention adopts the spectrum confocal distance measuring instrument to measure the distance of five characteristic points on the aspheric surface, the unknown parameters are fitted, and the distribution of the five characteristic points on the aspheric surface is shown in figure 5.
The confocal displacement distancer of adoption spectrum is to aspheric surface's characteristic point 1, characteristic point 2, characteristic point 3, characteristic point 4 and characteristic point 5 carry out the range finding, wherein: the characteristic point 1 is the geometric center of an aspheric surface, the characteristic point 2, the characteristic point 3, the characteristic point 4 and the characteristic point 5 are respectively four vertexes of a rectangle taking the geometric center of the aspheric surface as the center, four sides of the rectangle are respectively parallel to an X axis and a Y axis of a machine tool coordinate system, and the area of the aspheric surface covered by the rectangle is required to be as large as possible within the measuring range of the spectral confocal displacement distance measuring instrument;
when the geometric center of the aspheric surface is clearly imaged in a bright field view, the machine tool has a Z-axis direction coordinate Z of a machine tool coordinate system0Comprises the following steps:
z0＝l1+zc-σ1 (8)
wherein: l1For the measurement of the spectral confocal displacement range finder at characteristic point 1, zcFor measuring the coordinate, sigma, of the spectral confocal displacement range finder in the Z-axis direction of the machine tool coordinate system1The object distance is the object distance when the area array CCD camera clearly images;
moving the three-dimensional motion platform, respectively measuring the distance values between the spectral confocal displacement range finder and the characteristic points 2, 3, 4 and 5, simultaneously respectively recording the grating feedback values of the characteristic points 2, 3, 4 and 5 in the X axis and the Y axis, namely obtaining the three-dimensional coordinates of the characteristic points 2, 3, 4 and 5 on the aspheric surface in the machine tool coordinate system, processing the coordinate values of the characteristic points 2, 3, 4 and 5 by adopting a least square method, and calculating to obtain the coordinate values of the characteristic points 2, 3, 4 and 5
Figure BDA0002163671690000066
And the value of θ;
will be calculated
Figure BDA0002163671690000067
And substituting the theta value into the formula (7) to obtain an aspheric surface equation of the fused quartz element to be measured in the element coordinate system.
The fourth concrete implementation mode: the third difference between the present embodiment and the specific embodiment is that: the specific process of the step four is as follows:
moving the fused quartz element to be detected to a CMOS area array camera station, and enabling scattered light emitted by the defect point A on the aspheric surface of the fused quartz element to be detected to enter an imaging system, so that the CMOS area array camera of the imaging system acquires images of bright defects under a dark background;
removing background information after top hat transformation is carried out on the collected image, and then realizing image segmentation by adopting Laplace weighting self-adaptive binarization to obtain a target image; taking the center of a minimum circumscribed circle of the target image as a pixel coordinate of the defect point A, and taking the diameter of the minimum circumscribed circle as the pixel size of the defect point A;
step four, if the pixel coordinate of the defect point A is (x)pixel，ypixel) According to the camera imaging principle, the imaging plane coordinate (x) corresponding to the defect point A1,y1) Comprises the following steps:
Figure BDA0002163671690000071
wherein: k is a radical ofx、kyThe conversion coefficient from the pixel coordinate of the defect point A to the imaging plane coordinate is obtained; the conversion coefficient can be obtained by calibrating a standard scale plate;
step four and three, the imaging surface of the CMOS area-array camera is a plane, curved surface information can be converted into plane information when the CMOS area-array camera images according to the mapping relation, as shown in figure 7, when the CMOS area-array camera collects images, the actual imaging surface of the curved surface abcd is a plane a1b1c1d1In this process, depth information in the optical axis direction is compressed, and thus a method is required to restore a two-dimensional image; analyzing the Y-axis direction of the defect point A, wherein the coordinates of the defect point A under the element coordinate system are (x ', Y ', z '), and the point corresponding to the defect point A on the imaging plane is A1，A1The coordinates of the point in the element coordinate system are (x)1,y1,z1) (ii) a The imaging plane is reduced into a curved surface schematic diagram by combining with the imaging plane of FIG. 8;
from geometrical optics, y' and y1The following correspondence exists:
Figure BDA0002163671690000072
wherein: l represents the distance between the optical center of the incident imaging system and the aspheric geometric center;
z' is approximately regarded as z1Then, then
Figure BDA0002163671690000073
Obtaining the following by the same method:
Figure BDA0002163671690000074
the corresponding relationship between the coordinates of the defect point a in the element coordinate system and the coordinates of the defect point a in the imaging plane is as follows:
Figure BDA0002163671690000081
fourthly, establishing a relation between the coordinates of the defect point A and the pixel coordinates of the defect point A in the element coordinate system;
Figure BDA0002163671690000082
when the machine tool moves to (x)0，y0) When the machine tool moves to the position shown in the formula (15), the defect point A is positioned at the center of the bright field visual field, and the defect point A can be observed by using the area array CCD camera;
Figure BDA0002163671690000083
similarly, when the machine tool moves to the position shown in the formula (16), the defect point A is located at the laser repair station, and the defect point A can be repaired;
Figure BDA0002163671690000084
wherein: sigmax、σyDistance in the direction of the X, Y axis, σ, from the laser head to the center of the bright field view2Is the coordinate of the laser head in the machine tool coordinate system during laser repair.
And (3) converting pixel coordinates of the defect points into corresponding bright field station coordinates and repairing station coordinates by formulas (15) and (16), moving the geometric center of the aspheric surface of the fused quartz element to the repairing station coordinates to repair the surface defects of the fused quartz element, moving the geometric center of the aspheric surface of the fused quartz element to the bright field station coordinates, and checking a repairing result.
Fig. 6 is a diagram of the dark field detection principle employed in the present invention. When the surface of the element has defects, the scattered light of the incident light A0 is A1 according to geometrical optics, the reflected light is A2 if no defects exist at the position, and only the scattered light A1 can enter an imaging system, so that bright defects under a dark background can be detected. The pixel coordinates and the size of the defect can be obtained by processing the acquired image, the pixel coordinates of the defect are converted into coordinates under a machine tool coordinate system by a certain method, and the defect can be positioned by a motion system of the detection platform.
The high-resolution camera used is a CMOS area-array camera, the sensor size of the camera is 31mm multiplied by 22mm, the resolution is 10000 multiplied by 7096 pixels, the light-passing domain size is 636 multiplied by 450mm, and the magnification is 0.0487. The working distance 1730mm, the corresponding lens focal length lens f 1-1730 × 0.0487/1.0487-80.34 mm, and the Canon company EF 70-200mm f/2.8LII USM zoom lens is selected. The light source is a high-brightness linear array light source, the light emitting size of the light source is 600 mm multiplied by 20mm, the power is 0-48W, and the light emitting size can be adjusted through a controller. The quantum effect curve of the camera reaches the peak value between 500nm and 580nm in the black and white imaging process, the camera has the best sensitivity to the wavelength, and therefore the color of the light source is selected to be green light.
The repair platform used in the invention has a positioning precision of +/-10 mu m, comprises three motion axes of X/Y/Z, and can carry an optical element to realize X/Y two-dimensional high-precision movement. The repairing platform is moved to an installation station to complete the installation of the aspheric surface element, the fixture used during the installation is a rapid clamping follow fixture for repairing the surface micro-defects of the large-caliber curved surface optical element, and the clamping of the curved surface optical element and the plane optical element with the caliber not more than 500mm multiplied by 500mm can be realized.
The fifth concrete implementation mode: the fourth difference between this embodiment and the specific embodiment is that: the resolution of the area array CCD camera adopted in the second step is 2456 multiplied by 2058, and the pixel size is 3.45 multiplied by 3.45 mu m.
The sixth specific implementation mode: the fifth embodiment is different from the fifth embodiment in that: the working distance of the spectrum confocal distance measuring instrument adopted in the third step is 222.3mm, the effective measuring range is 24mm, and the axial measuring precision is 3 mu m.
The seventh embodiment: the sixth embodiment is different from the sixth embodiment in that: the resolution of the CMOS area-array camera used in the fourth step is 10000 × 7096 pixels.
Examples
The method for detecting and positioning the surface microdefects of the aspheric element is an example analysis, the method is used for detecting a batch of aspheric elements, the caliber of each aspheric element is 430mm × 430mm, the detection surface is an aspheric surface (light incident surface), and the equation of the surface is as follows:
Figure BDA0002163671690000091
in the formula:
curvature radius at geometric center of light incident surface: 1899.75mm for 1/c;
cone coefficient: -2.180721;
coefficient of quadratic term: a is 4.34336 x 10-10；
Before the component is detected, the following parameters need to be calibrated:
conversion coefficient k from pixel coordinates to imaging plane coordinatesx、ky，kx＝0.06360，ky＝0.06365；
The distance L between the optical center and the imaging plane is 1730 mm;
laser head to bright fieldDistance σ in the direction of the center X, Y of the field of viewx、σyObject distance when bright field camera clearly images and coordinate sigma of laser head in machine tool coordinate system when laser is repaired1、σ2，σx＝371.46mm、σy＝47.96mm、σ1＝17.205mm、σ2＝58.8mm
And performing automatic initialization operation on the machine tool to enable the machine tool to return to zero, and moving the machine tool to the mounting station to complete the mounting of the optical element. After the installation is finished, the optical element is moved to the bright field visual field, the upper, lower, left and right boundaries of the optical element are respectively moved to the center of the bright field visual field, and corresponding coordinate values are recorded as follows: y isT＝-213.75990、yD＝216.24011、xL＝375.16701、xRWhen the geometric center of the element is moved to the bright field view center position, the machine coordinates are-54.83382:
Figure BDA0002163671690000101
the optical element is moved to a spectrum confocal distance measuring station, automatic measurement of five points and automatic fitting of parameters can be realized through restoring platform software, and the measurement and fitting results are as follows:
Figure BDA0002163671690000102
and moving the optical element to a dark field photographing station for image acquisition, processing the acquired image to obtain pixel coordinates and pixel sizes of all defects, and analyzing the defect No. 312 obtained by image processing as an example, wherein the pixel coordinate is (-3262,2275). Converting the coordinate of the imaging plane into the coordinate of:
Figure BDA0002163671690000103
and (3) converting the coordinates of the imaging plane of the defect point into the coordinates of the workpiece coordinate system according to the formula (13):
Figure BDA0002163671690000104
from equation (15), when the defect is moved to the center of the bright field view, the machine coordinates should be:
Figure BDA0002163671690000105
from equation (16), when the defect is moved to the repair station, the machine coordinates should be:
Figure BDA0002163671690000106
the defect can be positioned to the bright field station by moving the machine tool to (-49.25,142.41,6.44), and the defect can be positioned to the repair station by moving the machine tool to (-420.71,94.45, 58.50). FIG. 9 is an image of a brightfield camera capturing a defect as it is positioned to a brightfield station, from which it can be seen that the defect is successfully positioned to the center of the brightfield view.
The steps use the positioning method provided by the invention to realize the rapid positioning of the surface micro-defects of the aspheric fused quartz element.
The above-described calculation examples of the present invention are merely to explain the calculation model and the calculation flow of the present invention in detail, and are not intended to limit the embodiments of the present invention. It will be apparent to those skilled in the art that other variations and modifications of the present invention can be made based on the above description, and it is not intended to be exhaustive or to limit the invention to the precise form disclosed, and all such modifications and variations are possible and contemplated as falling within the scope of the invention.

Claims (4)

1. A method for quickly positioning micro defects on the surface of an aspheric fused quartz element is characterized by comprising the following steps:
establishing a machine tool coordinate system O-XYZ by taking a mechanical zero point of a machine tool as a centroid O, wherein three axes of the machine tool coordinate system point to three axes of a rectangular coordinate system in the same space;
secondly, based on the first step, enabling the fused quartz element to be detected to be located at the center of a bright field visual field, acquiring an image of the fused quartz element to be detected by using an area array CCD camera, and obtaining the coordinate of a machine tool under a machine tool coordinate system when the geometric center of the aspheric surface of the fused quartz element to be detected moves to the center of the bright field visual field according to the positions of four boundary lines of the aspheric surface of the fused quartz element to be detected under the machine tool coordinate system;
the specific process of the second step is as follows:
moving the fused quartz element to be measured to the center of the bright field view, and respectively recording the Y-axis coordinate Y of the upper boundary line and the lower boundary line of the aspheric surface of the fused quartz element to be measured under the machine tool coordinate systemTAnd yDAnd X-axis coordinate X of the left and right boundary lines of the aspherical surface in the machine coordinate systemLAnd xR；
When the aspheric geometric center of the fused quartz element to be measured moves to the center of the bright field view, the coordinate (x) of the machine tool under the machine tool coordinate system0,y0) Comprises the following steps:
Figure FDA0002764431030000011
moving the fused quartz element to be measured to a spectrum confocal displacement distance measuring instrument, and measuring the distance of the characteristic points of the aspheric surface of the fused quartz element to be measured to obtain the coordinate values of the characteristic points of the aspheric surface;
fitting an equation of the aspheric surface of the fused quartz element to be tested in an element coordinate system by using the coordinate values of the aspheric surface characteristic points;
the specific process of the third step is as follows:
establishing a standard coordinate system O ' -X ' Y ' Z ' and an element coordinate system O ' -X ' Y ' Z ' by taking the geometric center of the aspheric surface of the fused quartz element to be detected as an original point O ', wherein three axes of the element coordinate system point to three axes of the machine tool coordinate system, an X ' axis of the standard coordinate system is parallel to the upper boundary line and the lower boundary line of the aspheric surface of the fused quartz element to be detected, a Y ' axis is parallel to the left boundary line and the right boundary line of the aspheric surface of the fused quartz element to be detected, and the Z ' axis direction is the normal direction of the aspheric surface of the fused quartz element to be detected passing through the original point O ';
then the aspheric equation of the fused quartz component to be measured in the standard coordinate system is:
Figure FDA0002764431030000012
wherein: 1/c is the curvature radius at the geometric center of the aspheric surface, k is the cone coefficient, and X ', Y', Z 'are the coordinates of the aspheric surface in the X', Y ', Z' axis directions respectively;
because the assembly and adjustment precision of the fused quartz element to be measured is limited during installation, and rotation errors exist between the three axes of the standard coordinate system and the three axes of the element coordinate system, the aspheric equation under the standard coordinate system of the formula (2) needs to be converted into the aspheric equation under the element coordinate system;
assuming that a defect point A is arranged on the aspheric surface of the fused quartz element to be detected, the coordinates of the defect point A under an element coordinate system and a standard coordinate system are (x ', y ', z '), (x ", y", z "), respectively, and according to the rotation transformation principle, the relationship of the following formula (3) exists between the element coordinate system and the standard coordinate system:
Figure FDA0002764431030000021
wherein: theta is the rotation error angle of the X 'axis of the standard coordinate system and the X' axis of the workpiece coordinate system,
Figure FDA0002764431030000022
the rotation error angle between the Y 'axis of the standard coordinate system and the Y' axis of the workpiece coordinate system is defined, and rho 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 ', theta) is a rotation matrix of the X ' axis of the standard coordinate system and the X ' axis of the workpiece coordinate system,
Figure FDA0002764431030000023
the rotation matrix of the Y 'axis of the standard coordinate system and the Y' axis of the workpiece coordinate system is used as R (Z ', rho), and the rotation matrix of the Z' axis of the standard coordinate system and the Z 'axis of the workpiece coordinate system is used as R (Z', rho);
wherein: rotation matrix
Figure FDA0002764431030000024
The expression of (a) is:
Figure FDA0002764431030000025
since there is no rotation in the Z "axis direction, that is, ρ is 0, the expression of the rotation matrix R is transformed into formula (5):
Figure FDA0002764431030000026
the calculation formula of the z' value of the fused quartz element to be measured in the element coordinate system is as follows:
Figure FDA0002764431030000027
Figure FDA0002764431030000028
sinθ＝tanθ，
Figure FDA0002764431030000029
and cos θ is 1, the aspheric equation of the fused quartz element to be measured in the element coordinate system is:
Figure FDA0002764431030000031
the confocal displacement distancer of adoption spectrum is to aspheric surface's characteristic point 1, characteristic point 2, characteristic point 3, characteristic point 4 and characteristic point 5 carry out the range finding, wherein: the characteristic point 1 is the geometric center of an aspheric surface, the characteristic point 2, the characteristic point 3, the characteristic point 4 and the characteristic point 5 are respectively four vertexes of a rectangle taking the geometric center of the aspheric surface as the center, four sides of the rectangle are respectively parallel to an X axis and a Y axis of a machine tool coordinate system, and the area of the aspheric surface covered by the rectangle is required to be as large as possible within the measuring range of the spectral confocal displacement distance measuring instrument;
when the geometric center of the aspheric surface is clearly imaged in a bright field view, the machine tool has a Z-axis direction coordinate Z of a machine tool coordinate system0Comprises the following steps:
z0＝l1+zc-σ1 (8)
wherein: l1For the measurement of the spectral confocal displacement range finder at characteristic point 1, zcFor measuring the coordinate, sigma, of the spectral confocal displacement range finder in the Z-axis direction of the machine tool coordinate system1The object distance is the object distance when the area array CCD camera clearly images;
respectively measuring the distance values between the spectral confocal displacement distance measuring instrument and the characteristic points 2, 3, 4 and 5, simultaneously respectively recording the grating feedback values of the characteristic points 2, 3, 4 and 5 on the X axis and the Y axis, namely obtaining the three-dimensional coordinates of the characteristic points 2, 3, 4 and 5 on the aspheric surface under the machine tool coordinate system, processing the coordinate values of the characteristic points 2, 3, 4 and 5 by adopting the least square method, and calculating to obtain the coordinate values of the characteristic points 2, 3, 4 and 5
Figure FDA0002764431030000032
And the value of θ;
will be calculated
Figure FDA0002764431030000033
Substituting the theta value into the formula (7) to obtain an aspheric surface equation of the fused quartz element to be measured in the element coordinate system;
step four, based on the step two and the step three, moving the fused quartz element to be detected to a CMOS area array camera station for single shooting, processing the collected image, reducing the two-dimensional information of the image to be three-dimensional, thereby obtaining the position information of the aspheric surface defect point of the fused quartz element to be detected, and repairing the aspheric surface defect point of the fused quartz element to be detected;
the specific process of the step four is as follows:
moving the fused quartz element to be detected to a CMOS area array camera station, and enabling scattered light emitted by the defect point A on the aspheric surface of the fused quartz element to be detected to enter an imaging system, so that the CMOS area array camera of the imaging system acquires images of bright defects under a dark background;
removing background information after top hat transformation is carried out on the collected image, and then realizing image segmentation by adopting Laplace weighting self-adaptive binarization to obtain a target image; taking the center of a minimum circumscribed circle of the target image as a pixel coordinate of the defect point A, and taking the diameter of the minimum circumscribed circle as the pixel size of the defect point A;
step four, if the pixel coordinate of the defect point A is (x)pixel,ypixel) According to the camera imaging principle, the imaging plane coordinate (x) corresponding to the defect point A1,y1) Comprises the following steps:
Figure FDA0002764431030000041
wherein: k is a radical ofx、kyThe conversion coefficient from the pixel coordinate of the defect point A to the imaging plane coordinate is obtained;
step three, the imaging surface of the CMOS area-array camera is a plane, curved surface information can be converted into plane information when the CMOS area-array camera images according to the mapping relation, and depth information along the optical axis direction is compressed; analyzing the Y-axis direction of the defect point A, wherein the coordinates of the defect point A under the element coordinate system are (x ', Y ', z '), and the point corresponding to the defect point A on the imaging plane is A1，A1The coordinates of the point in the element coordinate system are (x)1,y1,z1)；
From geometrical optics, y' and y1The following correspondence exists:
Figure FDA0002764431030000042
wherein: l represents the distance between the optical center of the incident imaging system and the aspheric geometric center;
z′＝z1then, then
Figure FDA0002764431030000043
Obtaining the following by the same method:
Figure FDA0002764431030000044
the corresponding relationship between the coordinates of the defect point a in the element coordinate system and the coordinates of the defect point a in the imaging plane is as follows:
Figure FDA0002764431030000045
fourthly, establishing a relation between the coordinates of the defect point A and the pixel coordinates of the defect point A in the element coordinate system;
Figure FDA0002764431030000046
when the machine tool moves to (x)0，y0) When the machine tool moves to the position shown in the formula (15), the defect point A is positioned at the center of the bright field visual field, and the defect point A can be observed by using the area array CCD camera;
Figure FDA0002764431030000051
similarly, when the machine tool moves to the position shown in the formula (16), the defect point A is located at the laser repair station, and the defect point A can be repaired;
Figure FDA0002764431030000052
wherein: sigmax、σyDistance in the direction of the X, Y axis, σ, from the laser head to the center of the bright field view2The coordinate of the laser head in a machine tool coordinate system during laser repair;
and (3) converting pixel coordinates of the defect points into corresponding bright field station coordinates and repairing station coordinates by formulas (15) and (16), moving the geometric center of the aspheric surface of the fused quartz element to the repairing station coordinates to repair the surface defects of the fused quartz element, moving the geometric center of the aspheric surface of the fused quartz element to the bright field station coordinates, and checking a repairing result.
2. The method for rapidly positioning the surface micro defects of the aspheric fused quartz component as claimed in claim 1, wherein the resolution of the area array CCD camera adopted in the second step is 2456 x 2058, and the pixel size is 3.45 μm x 3.45 μm.
3. The method for rapidly positioning the surface micro-defects of the aspheric fused quartz component as claimed in claim 2, wherein the working distance of the spectral confocal displacement distance measuring instrument adopted in the third step is 222.3mm, the effective measuring range is 24mm, and the axial measuring precision is 3 μm.
4. The method for rapidly positioning the surface micro defects of the aspheric fused quartz component as claimed in claim 3, wherein the resolution of the CMOS area-array camera adopted in the fourth step is 10000 x 7096 pixels.
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