JP2016114362A - Double image inspection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double image inspection system capable of precisely inspecting a double image.SOLUTION: A double image inspection system includes: a light source unit; a camera unit; and a processing part. The light source unit includes a projection optical system for projecting linear light emitted from a light source via a slit to a subject glass as projection light. The camera unit includes: an objective lens for condensing light emitted from the light source unit, and reflected by the subject glass; and an image sensor for receiving light condensed by the objective lens. The processing part is configured to perform predetermined data conversion processing to image data to obtain an intensity distribution pattern corresponding to an interference fringe pattern generated on the light reception surface of the image sensor. The processing part is further configured to obtain the view angle of a double image generated when the projection light is reflected by the subject glass on the basis of the obtained intensity distribution pattern.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a double image inspection system that inspects a double image generated on a subject glass such as a laminated glass.

  In recent years, laminated glass has been used for windshields of passenger cars in place of conventional tempered glass. The virtual image head-up display (HUD) using the windshield as a screen is becoming widespread. In the virtual image viewing HUD, since the projection image from the projector is reflected by the two interfaces of the laminated glass, a double image is generally generated. Thus, for example, Patent Document 1 proposes correcting a double image by giving an appropriate wedge angle to an intermediate layer between two bonded glasses.

Patent No. 5315358

  According to the description in Patent Document 1, by setting that the viewing angle of the double image generated by the curved glass and the viewing angle of the double image generated by the flat glass having the wedge angle are set to be equal to each other, It seems that the conditions that can eliminate the image can be derived. However, in this application, even if the wedge angle is set so that the viewing angle of the double image becomes 0 ° or the laminated glass is replaced with flat glass, the double image may be generated. The person discovered. This cannot be explained by the theory described in Patent Document 1. In order to verify this problem, it is necessary to inspect the generated double image precisely. However, in the conventional inspection system, it is difficult to accurately inspect the double image.

  The present invention has been made in view of such problems, and an object thereof is to provide a double image inspection system capable of inspecting a double image accurately.

  A double image inspection system according to an embodiment of the present invention includes a light source unit, a camera unit, and a processing unit. The light source unit includes a light source, a slit that is illuminated by the light source, and a projection optical system that projects linear light emitted from the light source via the slit onto the subject glass as projection light. The camera unit includes an objective lens that collects light emitted from the light source unit and reflected by the subject glass, and an image sensor that receives the light collected by the objective lens. The processing unit processes image data obtained by the camera unit. Specifically, the processing unit obtains a line image intensity distribution of the double image corresponding to the interference fringe pattern generated on the light receiving surface of the image sensor by performing predetermined data conversion processing on the image data. ing. The processing unit further obtains the viewing angle of the double image generated when reflecting the projection light on the subject glass based on the obtained line image intensity distribution.

  According to the double image inspection system as one embodiment of the present invention, a double image can be inspected precisely.

It is a schematic diagram showing an example of the functional block of the double image inspection system which concerns on one embodiment of this invention. It is a schematic diagram showing an example of schematic structure of the interference experiment apparatus of Young. It is a schematic diagram showing an example of the interference fringe model of the double image in the double image inspection system of FIG. FIG. 2 is a contour map representing a double image intensity distribution calculated using a spatial frequency response in the double image inspection system of FIG. 1. It is a graph showing an example of the measured value and calculated value of the vertical section of the line image intensity distribution of a double image. It is a graph showing an example of the calculated value of the vertical cross section of the line image intensity distribution of a double image. It is a graph showing an example of the calculated value of the vertical cross section of the line image intensity distribution of a double image. It is a graph showing an example of the calculated value of the vertical cross section of the line image intensity distribution of a double image. It is a graph showing an example of the calculated value of the vertical cross section of the line image intensity distribution of a double image. It is a graph showing an example of the calculated value of the vertical cross section of the line image intensity distribution of a double image. It is a graph showing the calculation value of the vertical cross section of double image intensity distribution when the interference fringe by repeated reflection is not superimposed at a focal distance of 135 mm. It is a graph showing the calculated value of the vertical cross section of double image intensity distribution when the interference fringe by repeated reflection is not superimposed at a focal distance of 50 mm. 2 is a graph showing a relationship between an integrated value of an autocorrelation function of a line image intensity distribution of a double image obtained using a spatial frequency response in the double image inspection system of FIG. 1 and a viewing angle θ of the double image. . It is a flowchart showing an example of the process sequence in the double image inspection system of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is one specific example of the present invention, and the present invention is not limited to the following embodiment. Further, the present invention is not limited to the arrangement, dimensions, dimensional ratios, and the like of the components shown in the drawings.

[Constitution]
FIG. 1 schematically shows an overall configuration example of a double image inspection system 1 according to an embodiment of the present invention. The double image inspection system 1 inspects the viewing angle θ of the double image of the subject glass 100 and includes a light source unit 10, a camera unit 20, and an image processing unit 30. The light source unit 10 corresponds to a specific example of “light source unit” of the present invention. The camera unit 20 corresponds to a specific example of “camera unit” of the invention. The image processing unit 30 corresponds to a specific example of a “processing unit” of the present invention. The subject glass 100 is, for example, a laminated glass, and is arranged in a direction in which the projection light L emitted from the light source unit 10 can be divided by wavefront division. The subject glass 100 is, for example, a laminated glass arranged so that the projection light L is incident at 60 °. The subject glass 100 corresponds to a specific example of “subject glass” of the present invention.

  The light source unit 10 emits linear projection light L. The light source unit 10 includes, for example, the LED light source 11, the slit 12, the lens 13, and the projection lens 14 in this order on the optical path of the light emitted from the LED light source 11. The LED light source 11 corresponds to a specific example of “light source” of the present invention. The slit 12 corresponds to a specific example of “slit” of the present invention. The projection lens 14 corresponds to a specific example of “projection optical system” of the invention.

  The LED light source 11 is a light emitting diode that emits incoherent light, and emits light having a wavelength in the visible region. The LED light source 11 is, for example, a white light emitting diode. The LED light source 11 illuminates the slit 12 uniformly. The slit 12 shapes the spot light emitted from the LED light source 11 into linear light. The slit 12 converts light emitted from the LED light source 11 into light having a uniform phase. That is, the slit 12 emits linear light having a uniform wavefront. The opening width of the slit 12 is, for example, 0.01 mm. The slit 12 is arranged so that a line segment parallel to the longitudinal direction of the slit 12 is orthogonal to the optical axis of the light emitted from the LED light source 11 and parallel to the surface of the subject glass 100. That is, the slit 12 extends in a direction perpendicular to the paper surface of FIG. The lens 13 condenses the light emitted from the LED light source 11. The lens 13 has, for example, a convex lens 13a and a concave lens 13b in this order on the optical path of the light emitted from the LED light source 11. The convex lens 13a is, for example, a condenser lens. The projection lens 14 projects linear light emitted from the LED light source 11 through the slit 12 onto the subject glass 100 as projection light L. Specifically, the projection lens 14 projects linear light generated by the slit 12 and collected by the lens 13 onto the subject glass 100 as projection light L.

  The light source unit 10 may further include a mechanism (first mechanism) that moves the light emitted from the LED light source 11 along the focal plane of the convex lens 13a. The light source unit 10 can scan the projection light L over a wide range of the subject glass 100 by scanning the light emitted from the LED light source 11 along the focal plane of the convex lens 13a using the first mechanism. . The first mechanism includes, for example, an optical fiber that connects the LED light source 11 and the first mechanism to each other, and a stage that moves the light emitting portion of the optical fiber. The lens 13 may have two concave lenses 13b. In this case, the light source unit 10 may have a mechanism (second mechanism) that changes the interval between the convex lens 13a and one concave lens 13b. The light source unit 10 is generated by changing the distance between the convex lens 13a and the single concave lens 13b using the second mechanism, and the light emitted from the LED light source 11 is repeatedly reflected at the interface of the subject glass 100. The position of the virtual image Iv can be changed.

  The camera unit 20 receives the projection light L emitted from the light source unit 10 and reflected by the subject glass 100, and generates image data D. The camera unit 20 includes, for example, an objective lens 21, an image sensor 22, and an image processing unit 23. The objective lens 21 condenses the projection light L emitted from the light source unit 10 and reflected by the subject glass 100. The objective lens 21 forms an image at a position (1 + 1 / m) when the focal length of the objective lens 21 is f and the imaging magnification of the objective lens 21 is m. The two-point resolution of Rayleigh of the objective lens 21 is proportional to the reciprocal of the numerical aperture of the objective lens 21 and is, for example, 0.1 '. The image sensor 22 receives the light collected by the objective lens 21 by the light receiving surface 22A and generates image data D. The image sensor 22 is, for example, a CCD (Charge Coupled Device) image sensor. The objective lens 21 and the image sensor 22 preferably have an angular resolution higher than the angular resolution (eg, 1 ') of the human eye.

  The image processing unit 30 processes the image data D obtained by the camera unit 20 and obtains the viewing angle θ of the double image generated when the projection light L is reflected on the specimen glass 100. The image processing unit 23 performs a predetermined data conversion process on the image data D to obtain a double image line image intensity distribution corresponding to the interference fringe pattern generated on the light receiving surface 22A of the image sensor 22. It has become. The image processing unit 23 further obtains the viewing angle θ of the double image generated when the projection light L is reflected on the subject glass 100 based on the obtained line image intensity distribution.

  The image processing unit 23 uses the spatial frequency response in Fourier imaging theory equivalent to the two pinholes 230a in Young's interference experiment apparatus 200 as a model function of the double image intensity distribution, thereby obtaining the above line image intensity distribution. And the viewing angle θ of the double image is obtained based on the derived line image intensity distribution. The image processing unit 23 obtains the viewing angle θ of the double image by fitting the profile of the line image intensity distribution indicated by the model function to the profile of the line image intensity distribution derived based on the image data D. It has become.

  The image processing unit 23 obtains the viewing angle θ of the double image based on the integral value of the autocorrelation function of the line image intensity distribution of the double image indicated by the model function. Specifically, the image processing unit 23 uses a known function indicating the correlation between the autocorrelation function of the line image intensity distribution of the double image indicated by the model function and the viewing angle θ of the double image. Thus, the viewing angle θ of the double image is obtained. The known function is a monovalent approximation function in a predetermined viewing angle θ range, and is, for example, a cubic polynomial as will be described later.

  Hereinafter, the model function and approximate function of the double image intensity distribution will be described in detail.

[Model function of double image intensity distribution]
First, the model function of the double image intensity distribution will be described. Double image resolution is typically measured with Rayleigh two-point resolution. Rayleigh's two-point resolution describes that when the aperture diameter of the lens of the detection system becomes as large as the wavelength of light, the resolution is limited by the diffraction effect of the aperture due to the wave nature of the light. For example, in a telescope having a focal length f and an aperture radius w, the Rayleigh two-point resolution ε is expressed by the following equation (1). Therefore, the condition for resolving the viewing angle θ = 1 ′ is derived by setting ε = fθ.

Thus, the aperture radius w corresponding to the Rayleigh two-point resolution ε is obtained regardless of the focal length f. That is, the opening radius w is expressed by the following formula (2).

  However, even if the aperture radius w of the objective lens 21 that actually measures the double image generated on the laminated glass is larger than 1.153 mm, the effective aperture diameter is limited to about 1.15 mm. Therefore, Rayleigh's two-point resolution ε does not become 1 'or less. In order to explain such a complex spatial frequency response, the present applicant has devised a model expression of the double image intensity distribution based on the expression of the interference image in Young's interference experiment apparatus 200 of FIG.

  As shown in FIG. 2, Young's interference experiment apparatus 200 includes a lens 220, a pinhole screen 230, a lens 240, and a screen 250 in this order from the light source 210 side on the optical path of light emitted from the light source 210. Yes. The pinhole screen 230 is provided with two pinholes 230a. In the interference experiment apparatus 200, the two light beams that have passed through the two pinholes 230a interfere with each other on the screen 250, thereby generating interference fringes on the screen 250. However, when the pinhole screen 230 is removed in the interference experiment apparatus 200, no interference fringes are generated on the screen 250. Therefore, it is understood that there is wavefront division as one of the functions of the two pinholes 230a.

  On the other hand, even in the double image inspection apparatus 1 using the model formula devised by the present applicant, a double image is generated on the light receiving surface 22A when the subject glass 100 is irradiated with light. However, the double image inspection apparatus 1 has no structure corresponding to the two pinholes 230a in Young's interference experiment apparatus 200. The double image inspection apparatus 1 is equivalent to the two pinholes 230a in the Young interference experimental apparatus 200 by combining the slit 12, the wavefront division by repeated reflection in the subject glass 100, and the aperture radius of the objective lens 21. The spatial frequency response in Fourier imaging theory is realized as a model function of the double image intensity distribution.

  The spatial frequency response in the double image inspection apparatus 1 is expressed by the following equation (3). Further, the spatial frequency response in the double image inspection apparatus 1 is explained by the double image interference fringe model 300 shown in FIG. The interference image model 300 includes a slit 12, a lens 13, a projection lens 14, a subject glass 100, a virtual pinhole screen 310, an objective lens 21, and a light receiving surface 22 </ b> A on an optical path of light emitted from the LED light source 11. It has in order from the 11 side. The virtual pinhole screen 310 has two virtual pinholes H1 corresponding to the two pinholes 230a.

Here, J ₁ is a first-order first-type Bessel function. λ is an average wavelength of light emitted from the LED light source 11. z is the image plane distance. δ is the diameter of the virtual pinhole H1. {X, y} are coordinates on the light receiving surface 22A. x ₀ is the image height of the double image. h ′ is a multiple of the interval h between two virtual pinholes H1 adjacent to each other. Light L1 emitted from the LED light source 11 and transmitted through the subject glass 100 enters one virtual pinhole H1. The other virtual pinhole H1 is incident with the light L2 that is reflected by the back surface of the subject glass 100 and then emitted toward the light receiving surface 22A. μ ₁₂ is the visibility of interference fringes and takes a value between 0 and 1. alpha ₁₂ is the phase of the light L2, takes a value in the range of -Pai～pai.

  By the way, in the well-known Young's interference fringe formula, there is one point image on the right side. This is because the observation position of the interference fringes of the light diffracted by the two pinholes 230a is at infinity. On the other hand, in the spatial frequency response in the double image inspection apparatus 1, the position of the virtual image Iv of the LED light source 11 is finite. As a result, it is observed that interference fringes are superimposed on the double image on the light receiving surface 22A. In the interference image type model 300, two virtual pinholes H1 are provided corresponding to the two pinholes 230a in Young's interference experiment apparatus 200. The diameter δ of the two virtual pinholes H1 is defined by the following formula (4). When the thickness t of the subject glass 100 is 4 mm and the incident angle ψ of the light L1 with respect to the subject glass 100 is 60 °, the diameter δ of the pinhole H1 is 2.77 mm. At this time, by applying the following conditions, the double image line image intensity distribution obtained from the spatial frequency response in the double image inspection apparatus 1 is the double image line obtained by the Young interference experiment apparatus 200. The Applicant has found that the image intensity distribution is a good approximation.

-Condition-
Width a of slit 12: 0.01 mm
Aperture radius w of objective lens 21: 12 mm
Interval h between two virtual pinholes H1: 2.77 mm

  FIG. 4 shows the line image intensity distribution of the double image calculated using the spatial frequency response in the double image inspection apparatus 1 by contour lines. In FIG. 4, interference fringes are superimposed in the tilt direction of the subject glass 100 in the double image line image intensity distribution. FIG. 5 is a graph showing the measured values and the calculated values of the vertical section of the double image line image intensity distribution. In FIG. 5, the measured value is represented by a point, and the calculated value is represented by a solid line. The measurement value is a value of a vertical section of the intensity distribution derived based on the image data obtained from the image sensor 22. The calculated value is a line image intensity distribution value of the double image calculated using the spatial frequency response in the double image inspection apparatus 1. Note that the viewing angle θ of the double image is assumed to be about 0.75 '. The horizontal axis of FIG. 5 is the spatial coordinates of the image plane (light receiving surface 22A), and the unit thereof is the pixel pitch of the image sensor 22, and specifically, 4.65 μm. As shown in FIG. 5, the line image intensity distribution profile of the double image obtained from the spatial frequency response in the double image inspection apparatus 1 is derived based on the image data obtained from the image sensor 22. It can be seen that it closely approximates the profile of the intensity distribution. 6, 7, 8, 9, and 10, it is assumed that the viewing angle θ of the double image is 0.866444 ′, 0.649833 ′, 0.433222 ′, 0.216611 ′, and 0 ′. 2 shows a line image intensity distribution of a double image obtained when the image is recorded. In FIG. 10, it can be seen that the double images are separated.

  The spatial frequency response in the double image inspection apparatus 1 is derived as follows. Following the concept of OTF (Optical Transfer Function) of double pinhole optical system described in “Fourier Imaging Theory” by Teruo Kose (reissued in Kyoritsu Shuppan 2013), multiple repetitive reflections by the glass surface and the glass back surface Of the light, consider a virtual pinhole H1 into which the front surface reflected light is incident and a virtual pinhole H1 into which the primary back surface reflected light is incident with an inclination of the double image viewing angle θ. At this time, the diameter δ of the virtual pinhole H1 is made equal to the distance between the optical axis of the front surface reflected light and the optical axis of the primary back surface reflected light. In addition, it is defined that the opening radius w of the objective lens 21 is a plurality of intervals h of the virtual pinhole H1. Finally, the spatial frequency response in the double image inspection apparatus 1 is derived from the autocorrelation functions of the plurality of virtual pinholes H1. The Fourier transform of the spatial frequency response obtained in this way should be a line image intensity distribution of a double image on which interference fringes are superimposed.

  The size of the diameter δ of the virtual pinhole H1 determines the point image size. In the sense of Rayleigh's two-point decomposition, the angular resolution corresponding to half the point image size should give a limit value. When the diameter δ of the virtual pinhole H1 is 2.77 mm, if the focal length f of the objective lens 21 is 135 mm, the Airy diameter d of the point image is 1.22λz / δ = 65.4 μm. Here, the image plane distance z was approximated to (1 + 1 / m) f. In FIG. 5, since the pixel pitch is 4.65 μm, the Airy diameter d corresponds to the 14 pixel pitch, and corresponds to the range from the 95th pixel to the 109th pixel. On the other hand, since the expected viewing angle θ of the double image is 0.75 ′, the image height fθ is 29.4 μm. Here, FIG. 11 shows a double image intensity distribution when no interference fringes are superimposed by repeatedly reflected light. FIG. 12 shows a double image intensity distribution when the focal length is 50 mm and the interference fringes are not superimposed by the reflected light repeatedly. Thus, it can be seen that the long focal length is more advantageous in that the angular resolution can be increased. However, in FIG. 5, the multibeam interference effect, convolution, and aberration are taken into consideration, whereas in FIGS. 11 and 12, these are not taken into consideration.

  As described above, it is possible to fit the spatial frequency response shown by the equation (3) to the measurement value. However, in the spatial frequency response shown in Equation (3), there are many degrees of freedom of parameters, so enormous calculation is required to fit the measurement value. Therefore, the present applicant has found a method for deriving the viewing angle θ of the double image by using the following approximate function instead of fitting the spatial frequency response shown in the above equation (3) to the measurement value. .

[Approximate function]
Next, the approximate function will be described. FIG. 13 shows the relationship between the integrated value of the autocorrelation function of the line image intensity distribution of the double image obtained by using the spatial frequency response expressed by the above equation (3) and the viewing angle θ of the double image. It is a thing. FIG. 13 shows a graph when the viewing angle θ of the double image is on the horizontal axis and the integrated value of the autocorrelation function is on the vertical axis. From FIG. 13, the viewing angle θ of the double image can be obtained based on the integral value of the autocorrelation function of the line image intensity distribution of the double image indicated by the spatial frequency response expressed by the above equation (3). The graph shown in FIG. 13 is represented by a monovalent approximation function in which the integrated value of the autocorrelation function monotonously increases as the viewing angle θ of the double image increases. For example, as shown in FIG. 13, this approximate function is represented by a third-order polynomial of Y = aX ³ + bX + c. In the range where the viewing angle θ of the double image is at least in the range from 0 ° to 0.9 ′, this approximate function is a monovalent approximate function. Therefore, the viewing angle θ of the double image of 1 ′ or less can be obtained using this approximate function which is a known function.

[Processing procedure]
Next, an example of a processing procedure in the double image inspection apparatus 1 will be described. FIG. 14 shows an example of a processing procedure in the double image inspection apparatus 1. When the projection light L is emitted from the light source unit 10, it is reflected by the subject glass 100 and enters the light receiving surface 22A. The light incident on the light receiving surface 22A is received by the light receiving surface 22A, and image data D is generated. The image data D is taken into the image processing unit 30 (step S101). The image data D is processed by the image processing unit 30 as follows. Specifically, first, noise of the image data D is removed using a window function (step S102). Next, after the image data D is normalized, complex Fourier transform is performed (step S103). Thereby, a complex pupil function corresponding to the line image intensity distribution of the double image corresponding to the interference fringe pattern generated on the light receiving surface 22A of the image sensor 22 is obtained. Next, inverse Fourier transform is performed on the square of the absolute value of the obtained complex pupil function (steps S104 and S105). Thereby, the autocorrelation function of the line image intensity distribution is obtained. Bracewell equivalent width calculation is performed (step S106). That is, an integral value of the obtained autocorrelation function is obtained. Finally, the double image viewing angle θ is obtained using a known function indicating the correlation between the integrated value of the autocorrelation function and the double image viewing angle θ (step S107). Instead of performing steps S104 to S107, the profile of the line image intensity distribution indicated by the model function is fitted to the profile of the line image intensity distribution derived based on the image data D, so that a double image is obtained. The viewing angle θ may be obtained.

[effect]
Next, the effects of the double image inspection system 1 will be described in comparison with the invention described in Patent Document 1.

According to the description of Patent Document 1, the angle of incidence ψ is fixed, the viewing angle η1 (formula (5)) of the double image generated by the curved glass, and the double image generated by the flat glass having the wedge angle α. By setting the viewing angle η2 (formula (6)) to be equal to each other, the glass thickness t, the glass radius of curvature Rc, and the wedge angle α capable of eliminating the double image are expressed by the formula (7). ) Seems to be derived from.

However, even if the wedge angle α is set so that the viewing angle of the double image becomes 0 °, or the laminated glass is replaced with flat glass, the double image may be generated. Applicant discovered. This is because Patent Document 1 assumes that the virtual image distance is infinite when the equation (6) is derived. When the virtual image distance is finite, there is no wedge angle α of the flat glass. This is because the double image becomes finite. When the virtual image distance is d and the distance between the optical axis of the front surface reflected light and the optical axis of the back surface reflected light is h, the following equation (8) is obtained. Accordingly, the wedge angle α necessary for eliminating the double image at the finite virtual image distance is expressed by the following equation (9). In equation (9), if d → ∞, the result is equation (7).

  On the other hand, in the double image inspection system 1, the spatial frequency response in Fourier imaging theory equivalent to the two pinholes 230a in Young's interference experiment apparatus 200 is used as a model function of the line image intensity distribution of the double image. It is done. Thus, a double image line image corresponding to the interference fringe pattern generated on the light receiving surface 22A of the image sensor 22 in spite of the absence of a structure corresponding to the two pinholes 230a in Young's interference experiment apparatus 200. An intensity distribution can be derived. Further, based on the obtained line image intensity distribution, the viewing angle θ of the double image generated when the projection light L is reflected on the subject glass 100 is obtained. As described above, the double image inspection system 1 does not derive the double image viewing angle θ from the geometric optical approach, but derives the double image viewing angle θ from the wave optical approach. . Thereby, a double image can be inspected precisely.

  Further, in the double image inspection system 1, instead of fitting the spatial frequency response expressed by the above equation (3) to the measured value, the integrated value of the autocorrelation function of the double image linear image intensity distribution indicated by the model function Based on the above, the viewing angle θ of the double image is obtained. Thereby, the viewing angle θ of the double image can be derived with a small amount of calculation without performing the enormous calculation required for fitting the spatial frequency response shown in Expression (3) to the measurement value.

DESCRIPTION OF SYMBOLS 1 ... Double image inspection system, 10 ... Light source unit, 11 ... LED light source, 12 ... Slit, 13 ... Lens, 13a ... Convex lens, 13b ... Concave lens, 14 ... Projection lens, 20 ... Camera unit, 21 ... Objective lens, 22 DESCRIPTION OF SYMBOLS ... Image sensor, 30 ... Image processing apparatus, 100 ... Sample glass, 200 ... Interference experiment apparatus, 210 ... Light source, 220 ... Lens, 230 ... Pinhole screen, 230a ... Pinhole, 24 ... Lens, 250 ... Screen, 300 ... Interference fringe model, 310 ... Virtual pinhole screen, a ... Slit width, D ... Image data, f ... Focal length, H1 ... Virtual pinhole, h ... Spacing between two adjacent virtual pinholes, Iv ... Virtual image, J ₁ ... 1 order Bessel function of the first kind, L ... projection light, L1, L2 ... light, opening radius w ... objective lens, lambda ... LED Mean wavelength of the light emitted from the source, {x, y} ... coordinates on the light receiving surface, x ₀ ... double image image height, z ... image surface distance, alpha ... wedge angle, alpha ₁₂ ... phase of light L2 Δ is the diameter of the virtual pinhole, θ is the viewing angle of the double image, and μ _{12 is} the visibility of the interference fringes.

Claims (7)

A light source unit including a light source, a slit illuminated by the light source, and a projection optical system that projects linear light emitted from the light source through the slit as projection light onto a subject glass;
An objective lens that collects light emitted from the light source unit and reflected by the subject glass; and a camera unit that includes an image sensor that receives the light collected by the objective lens;
A processing unit for processing image data obtained by the camera unit,
The processor is
By performing a predetermined data conversion process on the image data, a line image intensity distribution of a double image corresponding to an interference fringe pattern generated on the light receiving surface of the image sensor is obtained,
A double image inspection system for obtaining a viewing angle of a double image generated upon reflection of the projection light on the subject glass based on the obtained line image intensity distribution. The processing unit obtains the line image intensity distribution by using, as a model function of the line image intensity distribution of the double image, a spatial frequency response in Fourier imaging theory equivalent to a plurality of pinholes in Young's interference experiment. The double image inspection system according to claim 1. The double image inspection system according to claim 2, wherein the model function is represented by the following expression (1).

J1: First-order first-order Bessel function λ: Average wavelength of light emitted from the light source z: Image plane distance δ: Diameter of a virtual pinhole corresponding to the pinhole {x, y}: On the light receiving surface X _0: Image height of the double image h ′: Plurality of the interval h between two virtual pinholes adjacent to each other μ ₁₂ : Visibility of interference fringes α ₁₂ is the front and back surfaces of the subject glass The phase of the light emitted to the light receiving surface after being repeatedly reflected at The processing unit obtains a viewing angle of the double image by fitting a profile of a line image intensity distribution indicated by the model function to a profile of a line image intensity distribution derived based on the image data. 4. The double image inspection system according to 3. The double image inspection system according to claim 3, wherein the processing unit obtains a viewing angle of the double image based on an integral value of an autocorrelation function of a line image intensity distribution of the double image indicated by the model function. . The processing unit uses the known function indicating a correlation between an integrated value of an autocorrelation function of the line image intensity distribution of the double image indicated by the model function and a viewing angle of the double image. The double image inspection system according to claim 5, wherein an image viewing angle is obtained. The double image inspection system according to claim 6, wherein the known function is a cubic polynomial.

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