CN111830043A - Surface defect detection device and detection method based on spatial frequency shift regulation - Google Patents
Surface defect detection device and detection method based on spatial frequency shift regulation Download PDFInfo
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- 238000003384 imaging method Methods 0.000 claims abstract description 20
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- 238000005259 measurement Methods 0.000 description 2
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
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Abstract
The invention discloses a surface defect detection device and a detection method based on spatial frequency shift regulation. According to the detection method, the illuminating light with higher wave vector is used for moving the higher-frequency components of the sample in the frequency spectrum space, so that when the detection is carried out in a far field, the high-frequency components reflecting defect information can enter a lens field of an image acquisition system, and the defects are effectively detected. The method can realize the amplification effect on the tiny defects which are difficult to obtain in the traditional illumination mode, so that the tiny defects can be obtained through a simple image obtaining system, and the characteristic of high-resolution imaging is realized.
Description
Technical Field
The invention relates to the field of machine vision and surface defect detection, in particular to a surface defect detection device and a detection method based on spatial frequency shift regulation.
Background
The mobile phone heat dissipation film is arranged at the bottommost layer of the mobile phone display screen and is used for effectively dissipating heat of the mobile phone screen. However, when the surface of the film has defects, the display effect and the heat dissipation effect of the mobile phone screen are seriously affected. In addition, the display effect of the screen can be seriously affected by the tiny defects on the polaroid and the display panel of the mobile phone. At present, the detection of the surface defects of the film can be realized by a machine vision method, and with the improvement of the requirement of mobile phone manufacturers on the screen quality, the defects of the film surface smaller than 45 micrometers are required to be effectively detected, which cannot be realized by the traditional machine vision method at present. The invention provides a method for detecting tiny defects based on spatial frequency shift regulation, which uses illumination light with higher wave vector to move higher-frequency components of a sample in a frequency spectrum space so as to realize far-field detection, so that high-frequency components reflecting defect information can enter a lens field of an image acquisition system, and thus, the defects are effectively detected. The method can realize the amplification effect on the tiny defects which are difficult to obtain in the traditional illumination mode, so that the tiny defects can be obtained through a simple image obtaining system, and the characteristic of high resolution is realized.
Disclosure of Invention
The invention discloses a method for regulating and controlling space optical frequency shift quantity, and a device and a method for detecting surface defects of a thin film based on the method. The detection of the surface defects of the film is realized by acquiring the reflected light image passing through the surface of the sample to be detected through a line scanning camera or an area array camera, and the problems of low efficiency, low machine detection accuracy and the like of the existing manual visual inspection method are solved.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a surface defect detection device is characterized by comprising a light source 1, a sample transmission mechanism 2, a sample to be detected 3, a linear array or area array camera 4, an image acquisition card 5 and a computer 6.
The light source is a bar light source.
The length of the strip-shaped light source is 3 times longer than that of the sample to be measured.
The wavelength of the light source is short wavelength light to obtain large lateral light wave vector, and the wavelength range is 330-700 nm.
The light source irradiates the surface of the sample to be measured at oblique incidence with an incidence angle ranging from 10 degrees to 80 degrees.
The light source is irradiated to the sample to be measured, and the light and shade boundary of the reflected light is in the imaging field of the camera.
A method of surface defect detection, comprising: high-resolution imaging is realized by regulating and controlling input light frequency shift quantity, and transverse wave vector of illumination light is increased, so that a high-frequency space part of reflected light passing through a sample can enter a field range of a camera lens during far-field imaging.
The defects of the sample to be detected are amplified by increasing the transverse wave vector of the incident light, so that super-resolution imaging is realized.
The high frequency space portion of the reflected light of the illumination light passing through the sample can enter the field of view of the camera lens.
The light source is illuminated on the sample to be measured such that the bright-dark boundary of the reflected light is within the imaging field of view of the camera.
The invention has the beneficial effects that: the integration is good, can produce in batches, easy to operate. The method has the characteristics of large view field, fast imaging and ultrahigh resolution when being applied to super-resolution imaging. According to the invention, the most clear defect image can be obtained by selecting the incident light with a proper incident angle and a reasonable wavelength and enabling the light and shade boundary of the reflected light to be in the imaging field of the camera when the light source irradiates the sample to be detected, so that the efficiency is high and the accuracy is high.
Drawings
FIG. 1 is a diagram of the relationship between the incident light transverse wave vector and the incident angle according to the present invention.
Fig. 2 is a calculated image contrast map under different illuminations.
FIG. 3 is a block diagram of a measuring device according to an embodiment of the present invention.
FIG. 4 is a comparison of defect detection results for different wavelengths of illumination light.
FIG. 5 is a comparison of defect detection at different incident light angles.
FIG. 6 contrast of alternating bright and dark and uniform light field illumination.
Detailed Description
The embodiment of the invention provides a device and a method for detecting surface defects of a film, which are used for detecting the surface defects of the film by acquiring a reflected light image passing through the surface of a sample to be detected through a line scanning camera or an area array camera, and solving the problems of low efficiency, large influence of human factors and the like of the conventional manual visual inspection method.
In order to make the objects, features and advantages of the present invention obvious, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, but the scope of the present invention should not be limited thereby.
According to the Abbe imaging principle, an object is a set of information of a series of different spatial frequencies, and the frequency spectrum information is displayed on a back focal plane of a lens through the lens. These spectral components include a direct current component having the same frequency as the incident light and a high frequency component including object detail information. And the surface defects of the object to be measured are all reflected by high-frequency information. When light with a wavelength λ is incident on the surface of the sample to be measured, assuming that there is a defect with a width d on the surface of the sample, the transverse wave vector of the reflected light after passing through the defect can be expressed as: the frequency information of the object reflected light that the camera can receive can be expressed as:
in the above formula
Is the wave vector of incident light and has
Is the wave vector of reflected light caused by the defect of the sample to be measured and has
From the diffraction limit, when the numerical aperture of the imaging lens is NA, the frequency components of the object that can be received by the camera satisfy the following relationship:
the left two wave vectors in the above formula are added to exceed the frequency receiving range of the imaging lens, the two wave vectors are subtracted from each other, and the subtracted part can be received by the lens and imaged in the camera, and (2) the right side of the formula represents the light collected by the lensThe cut-off frequency. From the equation (2), when the lateral wave vector of the incident light is increased, the wave vector of the reflected light of the sample is increased, that is, the spatial frequency is also increased, and the subtraction of the two can be kept smaller than the cut-off frequency of the lens. An increase in the spatial frequency of the sample means a decrease in the size of the sample, equivalent to the effect of amplifying the defects. According to
It can be known that the use of short wavelength light or increased incidence angle (the angle between the incident light and the normal of the detection surface increases the wave vector in the lateral direction of the incident light, so as to achieve the purpose of amplifying the surface defect of the sample to be detected and detecting the micro-defect, and the relationship between the lateral wave vector and the angle of the incident light is shown in fig. 1.
Contrast is as important as clarity and resolution if the defect is to be clearly visible. Contrast ratio: refers to the measurement of different brightness levels between the brightest white and darkest black in the bright and dark areas in an image, and the larger the difference range is, the larger the contrast is. Definition: is the sharpness of edge variations in image detail. At the edges of the image detail, the sharper (faster) and sharper (greater contrast) the change in optical density or brightness with position, the sharper and more distinguishable the edges of the detail. For local details, the decision should be in the form of sharpness rather than contrast. Sharpness may be defined herein as local contrast, i.e., the magnitude of contrast within a small range. According to the weber's law,
wherein I is the signal strength, IbIs the background intensity. The highest contrast between the bright and dark phases can be found by calculation, as shown in fig. 2. As can be seen from fig. 2, the light field pattern on the left is a light field pattern and the local contrast pattern on the right is a light field pattern with a sinusoidal distribution, it can be seen that the light field changes most strongly at the point A, B where the peak and valley are separated, in the contrast pattern, the contrast at point A, B is a peak and the contrast at the point located at the intensity peak or valley is equal to zero. The light field at the gap between the peak and the valley is the light field at the interval between the light and the dark.
Based on the above analysis, the present invention provides a detection apparatus and method for detecting surface defects of a thin film, as shown in fig. 3, the detection apparatus comprises a light source 1, a sample transmission mechanism 2, a thin film sample 3 to be detected, a linear or area camera 4, an image acquisition card 5 and a computer 6.
The light source 1 is incident on a sample to be detected at a certain angle, the incident light enters the camera 4 through the reflected light of the sample after reflection, so that the camera can image the sample to be detected, the camera 4 transmits the obtained image of the sample to be detected to the image acquisition card 5, and the defects on the surface of the sample to be detected are automatically judged through an image processing algorithm in the computer 6. During measurement, the sample to be measured is moved through the transmission mechanism, so that the camera can effectively image all areas of the sample, and a complete image of the sample is obtained.
The light source 1 of the detection device is a bar light source. In order to achieve the best imaging effect, the length of the selected strip-shaped light source is 3 times longer than that of the sample to be detected.
The core of the linear array or area array camera 4 is a lens, the basic function of which is to realize light beam transformation (modulation), and in a machine vision system, the lens mainly functions to image a target on a photosensitive surface of an image sensor. The quality of the lens directly affects the overall performance of the machine vision system, and the reasonable selection and installation of the lens are important links of the design of the machine vision system. When evaluating the quality of an industrial lens, the quality of the industrial lens is generally judged from several practical parameters such as resolution, sharpness and depth of field: 1. resolution (Resolution): the reason that the resolution of the industrial lens is limited is the diffraction phenomenon of light, namely diffraction spots (airy spots). The resolution is in units of "line pairs/millimeter" (lp/mm). 2. Sharpness (Acutance): also called contrast, refers to the contrast of the brightest and darkest parts of the image. Depth of field (DOF): in the scenery space, the scenery in a certain distance in front of and behind the focusing object plane can be combined into a relatively clear image. The depth distance between the above-mentioned scenery which can be combined into relatively clear image and is positioned in front of and behind the focusing object plane, that is, the scenery space depth range which can obtain relatively clear image on the actual image plane is called depth of field. 4. Maximum relative aperture and aperture ratio: relative aperture, which is the ratio of the incident pupil diameter (denoted by D) to the focal length (denoted by f) of the industrial lens, is: the relative pore diameter is D/f. The reciprocal of the relative aperture is called the aperture ratio (aperture scale), also known as the f/stop ratio or aperture number. The relative aperture of a typical lens is adjustable, and the maximum relative aperture or aperture ratio is often indicated on industrial lenses, such as 1:1.2 or f/1.2. If the light of the shooting site is dark or the exposure time is short, an industrial lens with a large maximum relative aperture needs to be selected as much as possible. Comprehensively considered, VST VS-L10028/F model of the VS-L (F) series of the Japan VST industrial lens is selected.
The light wavelength of the light source selects short wavelength light to obtain a large transverse light wave vector, and the reasonable wavelength range is 330-700 nm. Fig. 4 shows the difference in defect detection effect of illumination light of different wavelengths. As shown in fig. 4, when the light source emits ultraviolet light, the wavelength range of the ultraviolet light is 330-400 nm, the detected defect image is clear, when the light source emits red light, the wavelength range of the red light is 620-700 nm, the detected defect image is visible, and when the ultraviolet light with shorter wavelength is used, a larger lateral light wave vector can be obtained.
The light source irradiates the surface of the sample to be measured to be oblique incidence, so that large transverse light wave vectors can be obtained, and the reasonable incidence angle range is 10-80 degrees. Fig. 5 shows the difference of defect detection effect by different incident angles of illumination light. As shown in fig. 5, when the light source uses ultraviolet light, the defect image photo at an incident angle of 10 degrees shows that the moire defect is invisible, the defect image photo at an incident angle of 80 degrees shows that the moire defect is invisible, and the defect image photo at an incident angle of 45 ± 5 degrees shows that the moire defect is clear.
As shown in fig. 6, a comparison graph of alternate bright and dark and uniform light field illumination is shown. As can be seen from the figure, the defect image obtained during illumination of the light and dark alternating light field is more clearly visible.
During detection, the light source and the camera are installed on a movable mechanical structure main body, and meanwhile, the light source and the camera need to be installed on a mechanical structure main body capable of achieving angle adjustment such as pitching and swing angles, and the two mechanical structure main bodies are installed in a mutually nested mode.
High-resolution imaging is realized by regulating and controlling the input light frequency shift quantity. And the transverse wave vector of the illuminating light is increased, so that the high-frequency space part of the reflected light passing through the sample can enter the field range of the camera lens when a far field is imaged.
In order to improve the contrast of defect identification, the light source should make the light-dark boundary of the reflected light in the imaging field of the camera when irradiating the sample to be detected.
Although the illustrative embodiments of the present invention have been described above to enable those skilled in the art to understand the present invention, the present invention is not limited to the scope of the embodiments, and it is apparent to those skilled in the art that all the inventive concepts using the present invention are protected as long as they can be changed within the spirit and scope of the present invention as defined and defined by the appended claims.
Claims (10)
1. A surface defect detection device is characterized by comprising a light source 1, a sample transmission mechanism 2, a sample to be detected 3, a linear array or area array camera 4, an image acquisition card 5 and a computer 6.
2. The surface defect detecting apparatus according to claim 1, wherein the light source is a bar light source.
3. The surface defect detecting apparatus according to claim 2, wherein the length of the strip light source is greater than 3 times of the length of the sample to be detected.
4. The surface defect detecting device of claim 1, wherein the light source has a wavelength selected from short wavelengths to obtain a large lateral light wave vector, the wavelength range is 330-700 nm.
5. The apparatus of claim 1, wherein the light source is obliquely incident on the surface of the sample to be measured, and the incident angle is in the range of 10 to 80 degrees.
6. A surface defect detecting apparatus according to claim 1, wherein the light source irradiates the sample to be measured such that the light and dark boundary of the reflected light is within the imaging field of view of the camera.
7. A method of surface defect detection, comprising: high-resolution imaging is realized by regulating and controlling input light frequency shift quantity, and transverse wave vector of illumination light is increased, so that a high-frequency space part of reflected light passing through a sample can enter a field range of a camera lens during far-field imaging.
8. The method of claim 7, wherein the amplification of the defects of the sample to be measured is achieved by increasing the transverse wave vector of the incident light, thereby achieving super-resolution imaging.
9. The method of claim 7, wherein a high frequency spatial portion of the reflected light of the illumination light passing through the sample is allowed to enter a field of view of a lens of the camera.
10. A surface defect detecting method according to claim 7, characterized in that the boundary between the dark and bright areas of the reflected light is within the imaging field of the camera when the light source is irradiated to the sample to be measured.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116993653A (en) * | 2022-09-28 | 2023-11-03 | 腾讯科技（深圳）有限公司 | Camera lens defect detection method, device, equipment, storage medium and product |
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| US20080144023A1 (en) * | 2006-11-07 | 2008-06-19 | Yukihiro Shibata | Apparatus for inspecting defects |
| US20090059216A1 (en) * | 2007-08-29 | 2009-03-05 | Yukihiro Shibata | Defect inspection method and defect inspection apparatus |
| JP2009251412A (en) * | 2008-04-09 | 2009-10-29 | Renesas Technology Corp | Device and method for inspecting mask blank, method of manufacturing reflection type exposure mask, and method of manufacturing semiconductor integrated circuit |
| CN103048272A (en) * | 2013-01-08 | 2013-04-17 | 浙江大学 | Frequency-shift super-resolution microimaging method and device based on evanescent field illumination |
| CN106296585A (en) * | 2016-08-12 | 2017-01-04 | 浙江大学 | Fourier iteration splicing super-resolution microscopic method based on surface wave illumination and device |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20080144023A1 (en) * | 2006-11-07 | 2008-06-19 | Yukihiro Shibata | Apparatus for inspecting defects |
| US20090059216A1 (en) * | 2007-08-29 | 2009-03-05 | Yukihiro Shibata | Defect inspection method and defect inspection apparatus |
| JP2009251412A (en) * | 2008-04-09 | 2009-10-29 | Renesas Technology Corp | Device and method for inspecting mask blank, method of manufacturing reflection type exposure mask, and method of manufacturing semiconductor integrated circuit |
| CN103048272A (en) * | 2013-01-08 | 2013-04-17 | 浙江大学 | Frequency-shift super-resolution microimaging method and device based on evanescent field illumination |
| CN106296585A (en) * | 2016-08-12 | 2017-01-04 | 浙江大学 | Fourier iteration splicing super-resolution microscopic method based on surface wave illumination and device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116993653A (en) * | 2022-09-28 | 2023-11-03 | 腾讯科技（深圳）有限公司 | Camera lens defect detection method, device, equipment, storage medium and product |
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