Transparent piece double-surface defect imaging method and device based on short coherent lightTechnical Field
The invention relates to the technical field of optical imaging, in particular to a transparent piece double-surface defect imaging method and device based on short coherent light.
Background
At present, the quality detection technology for surface defects of transparent media such as glass is greatly demanded, for example, the mobile phone cover plate glass is the glass on the outermost surface of a mobile phone touch screen, and the production process comprises processes such as substrate cutting, flat grinding and polishing, screen printing and the like, wherein each process can possibly generate surface defects such as ink residues, dirt, dust impurities and the like, so that effective defect detection on the front surface and the rear surface of the mobile phone cover plate glass plays an important role in controlling the screen yield of mobile phones and liquid crystal products.
The existing mainstream defect detection is to detect the defects on the surface of glass by using machine vision, and the method can quickly identify the defects, but cannot determine that the defects are particularly positioned on the front surface or the rear surface, so that the method becomes a technical short plate for detecting the defects of the transparent medium. At present, a scanning frequency type optical tomography method is used, the defect positions on the surface and in the glass can be accurately positioned, but a scanning frequency type short coherent light source is needed, the detection thickness is limited, the design is mainly aimed at the internal defect of the conductive glass, and the efficiency for detecting the surface defect is low. There are also cases where thermal stress is applied to a transparent material, the refractive index of which is changed, and the specific location of a defect is determined by examining the refractive index distribution information of the measured material, but the sample may be damaged by heating the sample. The single-sided imaging of the defects on the surface of the glass is realized by utilizing the propagation rule of linearly polarized light in a transparent medium based on a polarization extinction method, but the method can only record imaging information of a single surface by one-time imaging, and the other surface needs to be rotated or replaced with an analyzer.
Disclosure of Invention
The invention aims to provide a transparent piece double-surface defect imaging method and device based on short coherent light. The invention can record the front and back surface defect imaging of the transparent piece to be measured through one exposure, can synchronously separate and read defect information, and has the advantages of convenient use and high efficiency.
According to the technical scheme, the method comprises the steps of dividing an output light beam generated by a short-coherence light source into a detection light beam and a reference light beam, dividing the reference light beam into a front surface reference light beam and a rear surface reference light beam, respectively reflecting the front surface reference light beam and the rear surface reference light beam through a reference mirror, returning the front surface reference light beam and the rear surface reference light beam to an original path, transmitting the detection light beam to a transparent piece to be detected, receiving a front surface reflected light beam and a rear surface reflected light beam of the transparent piece to be detected, respectively interfering the front surface reflected light beam and the rear surface reflected light beam with the front surface reference light beam and the rear surface reference light beam, recording interference images by utilizing a CCD, and respectively obtaining front surface defect images and rear surface defect images through filtering treatment.
In the method for imaging the double-surface defects of the transparent piece based on the short coherent light, in a polarized light path, an output light beam generated by the short coherent light source is polarized by a polarizer and then is divided into a detection light beam and a reference light beam by a first polarization beam splitting prism after passing through a half-wave plate; the reference beam is divided into a front surface reference beam and a rear surface reference beam by a second polarization beam splitting prism after passing through a first quarter wave plate, the front surface reference beam is reflected by a front surface reference mirror and returns in an original way after passing through a third quarter wave plate, the rear surface reference beam is reflected by a rear surface reference mirror and returns in an original way after passing through a fourth quarter wave plate, the returned front surface reference beam and rear surface reference beam are combined by a second polarization beam splitting prism, the detection beam irradiates on a transparent piece to be detected after passing through the second quarter wave plate and a glass brick, the front surface reflected beam and the rear surface reflected beam reflected by the transparent piece to be detected return in an original way, and the front surface reference beam and the rear surface reference beam respectively interfere with the front surface reflected light and the rear surface reflected light of glass to be detected by the first polarization beam splitting prism by adjusting the optical path difference of each interference light arm, the interference image is obtained in the CCD through an imaging lens, and the defect images of the two surfaces are respectively extracted by filtering.
In the non-polarized light path, an output beam generated by a short coherent light source is divided into a detection beam and a reference beam by a first beam splitting prism, wherein the reference beam is divided into a front surface reference beam and a rear surface reference beam by a second beam splitting prism, the front surface reference beam is reflected by a front surface reference mirror after passing through a first attenuation sheet and returns back to the original path after passing through a rear surface reference mirror after passing through a second attenuation sheet, the returned front surface reference beam and rear surface reference beam are combined by the second beam splitting prism, the detection beam irradiates on a transparent piece to be detected after passing through a second quarter wave plate and a glass brick, the front surface reflected beam and the rear surface reflected beam reflected by the transparent piece to be detected return to the original path by the first polarization beam splitting prism, the front surface reference beam and the rear surface reference beam respectively interfere with the front surface reflected light and the rear surface reflected light of glass to be detected by the imaging lens by adjusting the optical path difference of each interference light arm, and the interference image is obtained in a CCD after passing through the filtering and the interference image of the double surface is extracted.
The optical path difference of the front surface reference mirror and the back surface reference mirror interference light arm is adjusted to enable the optical path of the front surface reference mirror and the back surface reference mirror interference light arm to be consistent with the optical path of a front surface reflection light beam and a back surface reflection light book of the transparent piece to be detected respectively, and two groups of interference fringes are received on a CCD, wherein the interference equation is expressed as follows:
Wherein A, B is the light field reflected by the front surface and the rear surface, RA、RB is the reference beam corresponding to the front surface and the rear surface, gamma (l) l represents the coherence of the light path difference l and is related to the light source selection, the subscript of l is the light field corresponding to the light path difference l, and Re { } represents the real part.
According to the transparent piece double-surface defect imaging method based on the short coherent light, after the obtained interference fringe pattern is subjected to Fourier transform, a spectrogram is obtained, so that two groups of fringes are separated, then signals imaged on the two surfaces are respectively extracted through band-pass filtering, squares of modes are obtained after inverse Fourier transform is respectively carried out, and front and rear surface defect images are obtained after dividing the signals by respective reference light fields.
The device of the transparent piece double-surface defect imaging method based on the short coherent light comprises a short coherent light source, wherein the short coherent light source is connected with a half-wave plate through a polarizer, the half-wave plate is connected with a first polarization beam splitter prism, the first polarization beam splitter prism is connected with a first quarter-wave plate, a second quarter-wave plate and an analyzer, the first quarter-wave plate is connected with a third quarter-wave plate and a fourth quarter-wave plate through the second polarization beam splitter prism, the third quarter-wave plate is connected with a front surface reference mirror, the fourth quarter-wave plate is connected with a rear surface reference mirror, the second quarter-wave plate is connected with a glass brick, and the analyzer is connected with a CCD through an imaging lens.
The device of the transparent piece double-surface defect imaging method based on the short coherent light comprises a short coherent light source, wherein the short coherent light source is connected with a second beam splitter prism, a glass brick and an imaging lens through a first beam splitter prism, the second beam splitter prism is connected with a first attenuation sheet and a second attenuation sheet, the first attenuation sheet is connected with a front surface reference mirror, the second attenuation sheet is connected with a rear surface reference mirror, and the imaging lens is connected with a CCD through a third attenuation sheet.
Compared with the prior art, the invention utilizes the finite coherence length of the coherence of the short coherence light source, the output light beam generated by the short coherence light source is divided into the detection light beam and the reference light beam, the reference light beam is divided into the front surface reference light beam and the rear surface reference light beam, the two reference light beams are respectively and simultaneously interfered with the double surfaces of the transparent piece to be tested, and the double surface defect imaging information is simultaneously recorded and synchronously separated and extracted through one exposure, so that the front surface defect image and the rear surface defect image are obtained. The invention can carry out assembly line detection after the surface type, the refractive index and the thickness of the transparent piece to be detected are determined, the corresponding light source is selected and the light path is modulated, and compared with the prior method, the invention has the advantages of high efficiency, convenient use and capability of acquiring the three-dimensional information of the defect, and has good application prospect.
Drawings
FIG. 1 is a schematic view showing the structure of a device in embodiment 1 of the present invention;
FIG. 2 is a schematic view showing the structure of the apparatus in embodiment 2 of the present invention;
FIG. 3 is an image of a scratch before separation in example 2 of the present invention;
FIG. 4 is a front surface scratch image obtained by separation;
fig. 5 is a rear surface scratch image obtained by separation.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not intended to be limiting.
In the embodiment 1, an output beam generated by a short-coherence light source is divided into a detection beam and a reference beam, the reference beam is divided into a front surface reference beam and a rear surface reference beam, the front surface reference beam and the rear surface reference beam are respectively reflected by a reference mirror and returned in the original path, the detection beam is transmitted to a transparent piece to be detected and received by the front surface reflection beam and the rear surface reflection beam of the transparent piece to be detected, the front surface reflection beam and the rear surface reflection beam respectively interfere with the front surface reference beam and the rear surface reference beam, interference images are recorded by using a CCD, and front surface defect images and rear surface defect images are respectively acquired through filtering treatment.
In this embodiment, as shown in fig. 1, a device for implementing the method includes a short coherent light source 1, where the short coherent light source 1 is connected with a half-wave plate 3 through a polarizer 2, the half-wave plate 3 is connected with a first polarization beam splitter prism 4, the first polarization beam splitter prism 4 is connected with a first quarter-wave plate 5, a second quarter-wave plate 11 and an analyzer 14, the first quarter-wave plate 5 is connected with a third quarter-wave plate 7 and a fourth quarter-wave plate 9 through the second polarization beam splitter prism 5, the third quarter-wave plate 7 is connected with a front surface reference mirror 8, the fourth quarter-wave plate 9 is connected with a rear surface reference mirror 10, the second quarter-wave plate 11 is connected with a glass brick 12, a transparent piece 13 to be tested is in front of the glass brick 12, and the analyzer 14 is connected with a CCD16 through an imaging lens 15. The polarizer and the half-wave plate are used for adjusting the light intensity of a detection light beam and a reference light beam, the first quarter-wave plate is used for adjusting the polarization state of the reference closed beam so that the reference closed beam can be split through the second beam splitting prism, the first beam splitting prism can interfere with the detection light beam after the original path is returned, the second quarter-wave plate is used for adjusting the polarization state of the detection light beam so that the detection light beam reflected by the transparent piece to be detected can interfere with the reference light through the first beam splitting prism and can adjust the light intensity of measurement light, the third quarter-wave plate and the fourth quarter-wave plate are respectively used for adjusting the light intensity of the reference light on the front surface and the back surface, the brightness of the two groups of interference fringes can be adjusted by rotating the polarizer and each quarter-wave plate so that the brightness of the interference fringes is approximately equal, the glass block is used for compensating the optical path difference generated by the reference light passing through the second beam splitting prism, and the analyzer is used for adjusting the light intensity ratio of the interference of the reference light and the measurement light.
In the polarized light path formed by the device, an output light beam generated by the short coherent light source is polarized by a polarizer, then is divided into a detection light beam and a reference light beam by a first polarization beam splitting prism after passing through a half wave plate, the reference light beam is divided into a front surface reference light beam and a rear surface reference light beam by a second polarization beam splitting prism after passing through a first quarter wave plate, the front surface reference light beam is reflected by a front surface reference mirror and returns in the original path after passing through a third quarter wave plate, the rear surface reference light beam is reflected by a rear surface reference mirror and returns in the original path after passing through a fourth quarter wave plate, the returned front surface reference light beam and rear surface reference light beam are combined by a second polarization beam splitting prism, the detection light beam is irradiated on a transparent piece to be detected after passing through a second quarter wave plate and a glass brick, the front surface reflected light beam and the rear surface reflected by the transparent piece to be detected returns in the original path, the front surface reference light beam and the rear surface reference light beam respectively interfere with the front surface reflected by the rear surface of glass to be detected by the first polarization beam splitting prism after adjusting the optical path difference of each interference light arm, and the front surface reference light and the rear surface reference light respectively interfere with the front surface reflected light and the rear surface reflected light of the glass to be detected by the imaging lens through the imaging lens, and the image is extracted through the interference lens to obtain the double-image defect images.
The optical path length of the front surface reference mirror and the optical path length of the back surface reference mirror interference light arm are respectively consistent with the optical path length of the front surface reflection light beam and the back surface reflection light book of the transparent piece to be tested by adjusting the optical path length difference of the front surface reference mirror and the back surface reference mirror interference light arm, and two groups of interference fringes are received on the CCD, wherein the interference equation is expressed as follows:
Wherein A, B is the light field reflected by the front surface and the rear surface, RA、RB is the reference beam corresponding to the front surface and the rear surface, gamma (l) l represents the coherence of the light path difference l and is related to the light source selection, the subscript of l is the light field corresponding to the light path difference l, and Re { } represents the real part.
For different transparent pieces to be tested, the interference item can be realized by matching a short coherent light source with the coherent length smaller than the optical path difference of the upper surface and the lower surface2Re { AB*}|γ(lAB) | is much smaller than the target termAnd |RA|2、|RB|2、|A|2、|B|2 is a DC term.
Performing two-dimensional Fourier transform on the obtained interference image by using a computer, and respectively extracting target itemsAnd performing inverse fourier transform, and taking squares of the modes respectively (RAA)2、(RBB)2, dividing by the front and rear surface reference light images respectively to obtain front and rear surface defect images a2 and B2 of the sample to be measured).
In embodiment 2, an output beam generated by a short-coherence light source is divided into a detection beam and a reference beam, the reference beam is divided into a front surface reference beam and a rear surface reference beam, the front surface reference beam and the rear surface reference beam are respectively reflected by a reference mirror and returned in the original path, the detection beam is transmitted to a transparent member to be detected and received by the front surface reflected beam and the rear surface reflected beam of the transparent member to be detected, the front surface reflected beam and the rear surface reflected beam respectively interfere with the front surface reference beam and the rear surface reference beam, interference images are recorded by using a CCD, and front surface defect images and rear surface defect images are respectively acquired through filtering processing.
In this embodiment, as shown in fig. 1, the device for implementing the method includes a short-coherence light source 1, wherein the short-coherence light source is connected with a second beam splitter prism 3, a glass block 8 and an imaging lens 10 through a first beam splitter prism 2, a transparent member 9 to be tested is arranged in front of the glass block 8, the second beam splitter prism 3 is connected with a first attenuation sheet 4 and a second attenuation sheet 6, the first attenuation sheet 4 is connected with a front surface reference mirror 5, the second attenuation sheet 6 is connected with a rear surface reference mirror 7, and the imaging lens 10 is connected with a CCD12 through a third attenuation sheet 11. The first attenuation sheet and the second attenuation sheet are respectively used for adjusting the light intensity of the reference light beam on the front surface and the back surface, the third attenuation sheet is used for adjusting the light intensity of the interference pattern fringes, the brightness of the two groups of interference fringes can be adjusted by rotating the attenuation sheets so that the brightness is approximately equal, and the glass brick is used for compensating the optical path difference generated by the reference light passing through the second light splitting prism.
In the unpolarized light path formed by the device, an output light beam generated by a short coherent light source is divided into a detection light beam and a reference light beam by a first beam splitting prism, wherein the reference light beam is divided into a front surface reference light beam and a rear surface reference light beam by a second beam splitting prism, the front surface reference light beam is reflected by a front surface reference mirror and returns in an original path after passing through a first attenuation sheet, the rear surface reference light beam is reflected by a rear surface reference mirror and returns in an original path after passing through a second attenuation sheet, the returned front surface reference light beam and rear surface reference light beam are combined by the second beam splitting prism, the detection light beam irradiates on a transparent piece to be detected after passing through a second quarter wave plate and a glass brick, the front surface reflected light beam and the rear surface reflected light beam reflected by the transparent piece to be detected return in an original path, and are combined by the first polarization beam splitting prism, and the front surface reference light beam and the rear surface reference light beam reflected by the glass to be detected respectively interfere with the front surface reflected by the rear surface through the rear surface of the transparent piece after adjusting the optical path difference of each interference light arm.
As shown in fig. 3, by adjusting the optical path difference between the front surface reference mirror and the back surface reference mirror, the optical path of the front surface reference mirror and the back surface reference mirror is respectively consistent with the optical path of the light beam reflected by the front surface of the transparent piece to be measured and the optical path of the light book reflected by the back surface, and two sets of interference fringes are received on the CCD, wherein the interference equation is expressed as:
Wherein A, B is the light field reflected by the front surface and the rear surface, RA、RB is the reference beam corresponding to the front surface and the rear surface, gamma (l) l represents the coherence of the light path difference l and is related to the light source selection, the subscript of l is the light field corresponding to the light path difference l, and Re { } represents the real part.
For different transparent pieces to be tested, the interference item can be realized by matching a short coherent light source with the coherent length smaller than the optical path difference of the upper surface and the lower surface2Re { AB*}|γ(lAB) | is much smaller than the target termAnd |RA|2、|RB|2、|A|2、|B|2 is a DC term.
Performing two-dimensional Fourier transform on the obtained interference image by using a computer, and respectively extracting target itemsAnd performing inverse fourier transform, and taking squares of the modes respectively (RAA)2、(RBB)2, dividing by the front and rear surface reference light images respectively to obtain front and rear surface defect images a2 and B2 of the sample to be measured).
In this embodiment, the separation effect is shown in fig. 3 to 5, wherein the thickness of the sample to be measured is 0.55mm, fig. 3 is a scratch image before separation, fig. 4 is a front surface scratch image after separation, and fig. 5 is a rear surface scratch image after separation. As can be seen from fig. 3 to fig. 5, the invention can image defects on the front and rear surfaces of the transparent member at one time and separate the defects after imaging, and the defects are obviously visible in the imaging diagrams in fig. 3 and fig. 4, which shows that the invention has the advantages of high efficiency, convenient use and capability of acquiring three-dimensional information of the defects, and has good application prospect.