JP2016080662A - Surface inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an inspection of a cone-shaped mirror plane having an aperture formed in a bottom part to be more facilitated.SOLUTION: A surface inspection device 10 comprises: a stripe member 12; a photographing device 14; and a computation unit 18. The stripe member 12 is shaped into a cylinder or column, and is arranged in a bottom aperture 25 so that a central axis of the stripe member runs along a height direction of a cone-shaped mirror plane 24, and has a vertical stripe pattern 26 along a center axis direction arrayed on an outer peripheral face in a peripheral direction. The photographing device 14 is arranged so as to be spaced with respect to the stripe member 12 toward the height direction of the cone-shaped mirror plane 24, and photographs the cone-shaped mirror plane 24 having the vertical stripe pattern 26 reflected. The computation unit 18 detects presence or absence of flaws on the cone-shaped mirror plane 24 on the basis of the photographing image of the cone-shaped mirror plane 24.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface inspection apparatus capable of detecting flaws on a mirror surface.

  For the purpose of quality inspection and the like, a surface inspection apparatus that detects flaws and irregularities on a mirror surface is known. For example, in Patent Document 1, a plurality of strip-shaped organic EL elements are arranged in the width direction and irradiated onto the inspection surface, thereby projecting a striped pattern on the inspection surface and capturing the pattern and analyzing the captured image. Thus, a flaw on the mirror surface is detected. Further, Patent Document 2 discloses an appearance inspection apparatus that captures an image of a part of a lead using a mirror surface during an appearance inspection of an IC lead.

JP 2014-2041 A JP-A-6-265323

  By the way, when inspecting the presence of a flaw on a mirror surface of a member having a mortar-shaped mirror surface with an opening formed at the bottom, such as a light reflector (reflecting mirror) which is a part of a vehicle headlamp. If it is attempted to irradiate a planar stripe pattern as in the prior art, it is difficult to project the stripe pattern on the entire inspection surface as shown in the upper part of FIG. 13 due to the mirror shape, or FIG. As in the lower stage, it may be difficult to image the entire inspection surface. In such a case, it is conceivable that the irradiation area and the imaging area are sequentially changed to detect scratches for each part, but the imaging is performed a plurality of times, and the partial images of the inspection surface are combined into a full image. The work becomes complicated, such as requiring processing to synthesize. Then, an object of this invention is to provide the surface inspection apparatus which can perform the inspection of the mortar-shaped mirror surface in which the opening was formed in the bottom part more easily than before.

  The present invention relates to a surface inspection apparatus for inspecting the appearance of a mortar-shaped mirror surface having an opening formed at the bottom. The apparatus has a cylindrical or columnar shape and is arranged in the bottom opening so that its central axis is along the height direction of the mortar-shaped mirror surface, and vertical stripes along the central axis direction on the outer peripheral surface Are arranged so as to be spaced apart in the height direction of the mortar-shaped mirror surface, and the mirror surface in which the stripe pattern is reflected is imaged. And an arithmetic unit that detects the presence or absence of flaws on the mirror surface based on the captured image of the mirror surface.

  Further, in the above invention, the calculation unit is a rectangular coordinate system having a radius coordinate and an angle from a center point of a striped pattern arranged radially in the captured image, and an orthogonal coordinate system having the radius and angle as an orthogonal axis. It is preferable that the fringe pattern is arranged along one axis of the orthogonal coordinate system by converting the captured image so that

In the above invention, the mirror surface is an inclined surface having a linear cross section along the height direction, and the height Hc of the camera center of the imager from the bottom opening of the mirror surface is the imager. The angle of view θ _C , the maximum radius R _{W of the} mirror surface, the radius r _W of the bottom opening, and the angle φ of the slope with respect to the horizontal direction orthogonal to the height direction are in a range satisfying the following formula (1) It is preferable to set.

In the above invention, the mirror surface, the cross-sectional shape along the height direction is a curved inclined surface, the height H _C of the camera center of the imaging device from the mirror surface of the bottom opening, said imaging The angle of view θ _{C of the} vessel, the maximum radius R _{W of the} mirror surface, the radius r _W of the bottom opening, and the curvature radius a of the slope are preferably set in a range satisfying the following formula (2). .

  According to the present invention, it becomes possible to inspect a mortar-shaped mirror surface having an opening formed at the bottom more easily than in the past.

It is a perspective view which illustrates the surface inspection apparatus concerning this embodiment. It is a figure which illustrates the picked-up image by the surface inspection apparatus concerning this embodiment. It is a figure which shows the example of a setting of the surface inspection apparatus which concerns on this embodiment in case the cross section of a mortar mirror surface is a straight line. It is a figure which shows the example of a setting of the surface inspection apparatus which concerns on this embodiment in case the cross section of a mortar mirror surface is a straight line. It is a figure which shows the example of a setting of the surface inspection apparatus which concerns on this embodiment in case the cross section of a mortar mirror surface is a curve. It is a figure which shows the example of a setting of the surface inspection apparatus which concerns on this embodiment in case the cross section of a mortar mirror surface is a curve. It is a figure which illustrates the picked-up image by the surface inspection apparatus concerning this embodiment. It is a figure explaining the principle of a flaw detection by the surface inspection apparatus concerning this embodiment. It is a figure explaining the principle of a flaw detection by the surface inspection apparatus concerning this embodiment. It is a figure explaining the principle of a flaw detection by the surface inspection apparatus concerning this embodiment. It is a figure explaining the principle of a flaw detection by the surface inspection apparatus concerning this embodiment. It is a figure explaining the principle of a flaw detection by the surface inspection apparatus concerning this embodiment. It is a figure explaining the surface inspection which concerns on a prior art.

<Device configuration>
FIG. 1 illustrates a surface inspection apparatus 10 according to the present embodiment. The mirror surface member 22 to be subjected to appearance inspection by the surface inspection apparatus 10 is, for example, a vehicle light reflector, and a mortar-shaped mirror surface 24 (hereinafter simply referred to as a mortar mirror surface) is formed at the center. The mortar mirror surface 24 has an opening 25 formed at the bottom, and has a bottomed mortar shape. For example, the light source member is inserted from the bottom opening 25.

  Here, the mortar shape refers to a shape having an inclined surface whose radius decreases toward the bottom along the height direction, and the cross-sectional shape in the height direction is straight or curved. Contains.

  The surface inspection apparatus 10 includes a stripe member 12, an imager 14, a stage 15, an illuminator 16, a calculation unit 18, and a display unit 20. After the mirror member 22 is placed on the stage 15, the stripe member 12 is erected on the bottom opening 25 of the mortar mirror surface 24. The stripe pattern 26 formed on the outer peripheral surface of the stripe member 12 is reflected on the mortar mirror surface 24, and this is imaged by the imager 14. The calculation unit 18 analyzes the captured image and detects a flaw in the captured screen. The detection result is displayed on the display unit 20.

<Details of each configuration>
The striped member 12 is a cylindrical or columnar member, and stands in the bottom opening 25 of the mortar mirror surface 24 (on the stage 15), that is, its own central axis C is in the height direction of the mortar mirror surface 24 ( (Z direction). In this arrangement, the stripe member 12 may be arranged so that the center axis C of the stripe member 12 coincides with the center of the mortar mirror surface 24. The height and radius of the strip member 12 in the central axis C direction will be described later.

  On the outer peripheral surface of the stripe member 12, a stripe pattern 26 is formed in which vertical stripes along the central axis C direction are arranged in the circumferential direction. The fringe pattern 26 may be one in which the fringe density changes in a sine wave shape along the circumferential direction. The fringe pattern 26 functions as a so-called carrier stripe and has an effect of raising a flaw on the mortar mirror surface 24 as described later.

  The illuminator 16 is a light source that irradiates the entire surface of the mortar mirror surface 24. The illuminator 16 is composed of, for example, a ring-shaped LED illumination. The illuminator 16 is provided so as to be separated from the mirror member 22 in the height direction (Z direction). The height direction position of the illuminator 16 may be adjustable. For example, the illuminator 16 may be attached to a moving mechanism 28 in the Z-axis direction provided on the stage 15.

  In addition, in embodiment shown in FIG. 1, although the striped member 12 and the illuminator 16 were used as separate members, it is not restricted to this form. For example, the illuminator 16 may be incorporated in the stripe member 12 so that light is emitted from the stripe member 12 toward the mortar mirror surface 24.

  The imager 14 images the mortar mirror surface 24 on which the stripe pattern 26 is reflected. The imager 14 may be a CCD camera or a CMOS camera, for example. The imager 14 images the mortar mirror surface 24 at an angle that looks down on the mortar mirror surface 24. That is, the imaging device 14 is provided so as to be separated from the mortar mirror surface 24 and the stripe member 12 in the height direction (Z direction). In addition, the imager 14 may be arranged so that the optical axis of the imager 14 coincides with the center of the mortar mirror surface 24 and the center axis C of the stripe member 12. Further, like the illuminator 16, the imager 14 may be fixed to the moving mechanism 28 of the stage 15 and be adjustable in height direction position.

  FIG. 2 illustrates a captured image of the mortar mirror surface 24 by the imager 14. This captured image includes the mortar mirror surface 24 and the top surface of the columnar striped member 12. Specifically, in this captured image, a radial stripe pattern 26 reflected on the mortar mirror surface 24 and a peripheral portion 30 (outline portion) of the mortar mirror surface 24 on the outer periphery thereof are shown. The peripheral portion 30 includes a surface facing the illuminator 16 and substantially totally reflects the illumination of the illuminator 16, so that a clear image is obtained as compared with the stripe pattern 26 reflected on the mortar mirror surface 24. .

  Returning to FIG. 1, the calculation unit 18 detects the presence or absence of a flaw on the mortar mirror surface 24 based on the captured image of the mortar mirror surface 24 captured by the imager 14. The arithmetic unit 18 may be anything that can perform image processing, and may be a computer including an arithmetic circuit such as a CPU and a storage unit such as a memory. The storage means stores a program for executing image processing to be described later. The calculation result by the calculation unit 18 is displayed on the display unit 20 including a display.

<Installation conditions of the striped member 12 and the imaging device 14>
The conditions for allowing the fringe pattern 26 of the fringe member 12 to appear on the entire surface of the mortar mirror surface 24 and enabling the imager 14 to capture an image of the entire mirror surface 24 will be described below.

FIG. 3 shows a schematic diagram of the XZ cross section of FIG. Further, FIG. 3 shows a mortar mirror surface 24 whose cross-sectional shape along the height direction (Z-axis direction) is a linear slope shape. Further, the imager 14 is shown by a camera center _CC and a (virtual) image plane IP, following a so-called pinhole camera model. Further, in FIG. 3, the center of the mortar mirror surface 24, the central axis C of the stripe member 12, and the optical axis of the imager 14 are made to coincide. In addition, in the same figure, these central axes are set as the Z axis, and the mounting surface of the stage 15 is set as the XY plane.

First, conditions for enabling the imager 14 to image the entire surface of the mortar mirror surface 24 will be described. When the imager 14 can image the entire surface of the mortar mirror surface 24, light from the outermost point of the mortar mirror surface 24 is received by the image sensor of the imager 14. Therefore, as a boundary condition that allows the imager 14 to image the entire surface of the mortar mirror surface 24, a projection line having an angle equal to the angle of view θ _C of the imager 14 is an end point of the mortar mirror surface 24 as shown in FIG. 3. consider the case through the (outermost point) _{p R.} Here, the angle of view θ _C is obtained from the following formula (3) using the width w from the optical axis (Z axis) of the image sensor 14 to the end of the image sensor array and the focal length f of the image sensor 14. Can do.

The theta _C, (the radius of the _{p R)} maximum radius of mortar mirror 24 _{R W,} the radius _{r W} of the bottom opening 25 of the bowl mirror 24, the bottom height _{H C} of the center of the camera _{C C} from the opening 25, and, mortar mirror The following formula (4) is derived using the angle φ (of the inclined surface) of the mortar mirror surface 24 with respect to the horizontal direction (X axis) orthogonal to the height direction of 24.

The following equation (5) is derived by modifying the equation (4).

By setting the height H _C of the center of the camera C _C in the range satisfying the above equation (5), the imaging unit 14 is enabled image the entire surface of the mortar mirror 24. Of the above formula (5), the parameter θ _C related to the image pickup device 14 can be acquired from the specifications of the image pickup device 14, and the parameters R _W , r _W , and φ related to the mirror surface member 22 can be acquired from the design values of the mirror surface member 22. It is. From this, the imaging device 14 can be positioned before the inspection of the mirror surface member 22.

  Next, conditions of the stripe member 12 for reflecting the stripe pattern 26 of the stripe member 12 over the entire surface of the mortar mirror surface 24 will be described. When the projection line from the image pickup device 14 is reflected at a point p on the mortar mirror surface 24 and intersects at a point q on the outer peripheral surface of the striped member 12 as a light ray 32 in FIG. The vector n is expressed by the following formula (6).

  The incident vector e is expressed by the following formula (7), where θ is the angle of the projection line 32 with respect to the central axis (Z axis).

  Further, using the reflection vector v, the vector t orthogonal to the normal vector, and arbitrary coefficients α and β, the following equation (8) is derived.

  From the formula (8), the following formula (9) is derived.

  Here, since α is the inner product of the vectors e and n, the following formula (10) is derived.

  When the equations (6) and (7) are substituted into the equation (10), the vector v is expressed by the following equation (11).

  In addition, if the x coordinate of the point p is r, the point p is expressed by the following mathematical formula (12).

  The expression of the projection line from the reflection point p toward the point q on the stripe member 12 is expressed as v · s + p from the parameter s (parameter representing the expansion (magnification) of the vector) and equations (10) and (11). The This parameter s is expressed by the following equation (13), where l is the radius of the stripe member 12.

  From Expression (13), the height h of the point q where the light beam intersects the outer peripheral surface of the stripe member 12 is expressed by Expression (14) below.

  In the right side of Equation (14), the first term represents the height from the bottom opening 25 to the point p, and the second term represents the height from the point p to the point q. Regarding Expression (14), θ can be expressed as Expression (15) below using r.

  By substituting the formula (15) into the formula (14), the following formula (16) is derived.

As the above h obtained when substituting the maximum radius R _W of the mortar mirror 24 to r of Equation (16), by setting the height H _e of the fringe member 12, stripes on the entire surface of the bowl mirror 24 The pattern 26 can be reflected.

FIG. 4 shows a graph showing a change in h when r in Expression (16) is increased. Note that H _C = 300 mm, r _W = 30 mm, l = 25 mm, φ = 30 °, 45 °, and 60 °. As shown in this graph, the stripe pattern 26 can be reflected on the entire surface of the mortar mirror surface 24 by increasing the height h of the stripe member 12 as the radius r of the mortar mirror surface 24 increases. Become.

FIG. 5 is a schematic diagram for explaining the setting conditions of the imaging device 14 and the stripe member 12 with respect to the mortar mirror surface 24 whose cross-sectional shape along the height direction (Z-axis direction) is a curved slope. . This figure also shows the image pickup device 14 with a camera center _CC and an image plane IP, as in FIG. Further, the center of the mortar mirror surface 24, the central axis C of the stripe member 12, and the optical axis of the imager 14 are made to coincide. Further, these central axes are the Z-axis, and the mounting surface of the stage 15 is the XY plane. Note that description of the same parameters as those in FIG. 3 is omitted.

First, projection lines having the same angle as the angle theta _C imager 14, consider the case through the outermost point P _R of mortar mirror 24. Curvature radius a mortar mirror 24, a line connecting the outermost point p _R of curved surface center O _W and mortar mirror 24 of mortar mirror 24, the angle t _W with respect to the central axis (Z _axis), the curved center of the bottom openings 25 O _W heights I and, by using the height _{H C} of the center of the camera _{C C} from the bottom opening 25, the following equation (17) to (19) is derived.

From the formula (17-19), the following equation is a conditional expression relating to the height _{H C} of the center of the camera _{C C} (20) is derived.

By setting the height H _C of the center of the camera C _C in the range satisfying the above equation (20), the imaging unit 14 is enabled image the entire surface of the mortar mirror 24. Of the above formula (20), the parameter θ _C related to the image pickup device 14 can be acquired from the specification of the image pickup device 14, and the parameters a, R _W , r _{W related} to the mirror surface member 22 can be acquired from the design values of the mirror surface member 22. It is. From this, the imaging device 14 can be positioned before the inspection of the mirror surface member 22.

  Next, conditions of the stripe member 12 for reflecting the stripe pattern 26 of the stripe member 12 over the entire surface of the mortar mirror surface 24 will be described. When the projection line from the image pickup device 14 is reflected at a point p on the mortar mirror surface 24 and intersects at a point q on the outer peripheral surface of the striped member 12 like the light beam 34 in FIG. (21)

  From the equation (21), the normal vector n at the reflection point p is expressed as the following equation (22).

  The following formula (23) is derived from the formula (22), the formula (7) related to the incident vector e, and the formula (10) related to the reflection vector v.

  Similarly to Equation (14), the height h of the point q where the light beam intersects the outer peripheral surface of the stripe member 12 is expressed by Equation (24) below using Equations (21) and (23).

  Further, the angle t and the angle θ have a relationship as shown in the following formula (25).

  Therefore, the height h of the reflection point q is expressed as the following formula (26).

  Furthermore, when Expression (26) is expressed using the radius r of the mortar mirror surface 24, the following Expression (27) is derived.

As the above h obtained when substituting the maximum radius R _W of the mortar mirror 24 to r of Equation (27), by setting the height H _e of the fringe member 12, stripes on the entire surface of the bowl mirror 24 The pattern 26 can be reflected.

FIG. 6 is a graph showing a change in h when r in Expression (27) is increased. Note that H _C = 300 mm, l = 25 mm, I = 150 mm, a = 170 mm, 180 mm, and 200 mm.

  In this graph, the rate of increase of h decreases as the value of r increases, and further, the rate of change drops negatively. This is considered to be caused by the curved surface shape of the mortar mirror surface 24, and a plurality of reflection points of the mortar mirror surface 24 converge to the same point on the stripe member 12, that is, the mortar mirror surface as shown in FIG. The one-to-one relationship between the reflection point p on 24 and the point q on the stripe member 12 is broken. In such a case, as shown in the lower part of FIG. 7, the stripe pattern 26 reflected on the mortar mirror surface 24 becomes unclear and image analysis becomes difficult.

  Therefore, the plot of the mortar mirror surface 24 to be inspected is included in any position on the graph by substituting each parameter of Equation 27 from the specifications of the imaging device 14 and the stripe member 12 and the design value of the mirror member 22. It is preferable to obtain in advance. By doing in this way, it can be judged whether mirror surface member 22 used as a candidate for inspection suits inspection by surface inspection device 10 of this embodiment.

<Measurement principle>
Next, the measurement principle of the surface inspection apparatus according to the present embodiment will be described. FIG. 8 illustrates a captured image of the mortar mirror surface 24. The computing unit 18 obtains the center points (reference points) of the striped patterns 26 arranged radially based on this image. For example, the center point is obtained by obtaining the radius of curvature of the peripheral edge portion 30 (contour portion) of the mortar mirror surface 24. As described above, since the peripheral portion of the mortar mirror surface 24 is imaged relatively clearly, the image processing for obtaining the curvature radius can be performed relatively easily.

  Next, as illustrated in FIG. 9, the calculation unit 18 is configured so that the polar coordinate system including the moving radius and the angle from the obtained center point becomes an orthogonal coordinate system having the moving radius and the angle as orthogonal axes. A so-called Frieze expansion for converting the captured image is performed. Thereby, the fringe pattern 26 is rearranged along one axis of the orthogonal coordinate system.

  Further, as illustrated in FIG. 10, the calculation unit 18 detects a flaw on the mortar mirror surface 24 by extracting a high-frequency component from the captured image (original image) in which the stripe pattern 26 is rearranged. The fringe pattern reflected in the vicinity of the scratch shows a more complex projection image than the periphery, and includes a high frequency component in terms of spatial frequency. Therefore, a flaw on the mortar mirror surface 24 can be detected by extracting a high frequency component.

  The calculation unit 18 performs a Fourier transform (FT) on the image obtained in FIG. 9 (S10). If the luminance distribution of the original image is I (x), step S10 can be expressed as the following mathematical formulas (28) and (29). Note that the parameter x of the function I (x) of the luminance distribution is a vector and indicates arbitrary coordinates on the two-dimensional plane of the captured image.

  Here, F [] is a Fourier transform, and R {} and I {} are operators for obtaining a real part and an imaginary part from complex numbers in {}, respectively. Based on the real part A (f) and the imaginary part P (f), the calculation unit 18 obtains a power spectrum and a phase as shown in the following formulas (30) and (31) (S12).

  Here, L (f) represents a power spectrum and Q (f) represents a phase. Next, the calculation unit 18 duplicates (copies) the power spectrum L (f), and applies a Gaussian filter to this (S14). Alternatively, the power spectrum may be obtained after reducing the resolution of the original image, and a Gaussian filter may be applied to the power spectrum.

  In the Gaussian filter, a Gaussian function of the following formula (32) is used.

Here, f _x and f _y respectively indicate the horizontal and vertical spatial frequency of the image. W represents the width of the Gaussian distribution and is synonymous with the standard deviation (σ). In the present embodiment, the spatial frequency [m ⁻¹ ] of the stripe pattern 26 (carrier stripe) developed linearly as shown in FIG. 9 is used as the width w of this Gaussian function.

The spatial frequency of the fringe pattern 26 can be obtained by image processing of the power spectrum L (f). The left side of FIG. 11 illustrates an image of the power spectrum L (f). The horizontal axis and the vertical axis of the image both represent the spatial frequency (wave number) [m ⁻¹ ]. In the upper right of FIG. 11, an enlarged view around the center (origin) of the power spectrum L (f) is shown. The spatial frequency (carrier frequency) of the fringe pattern 26 (carrier fringe) corresponds to the point having the maximum value of the luminance of the power spectrum L (f). The computing unit 18 obtains the carrier frequency from the image of the power spectrum L (f) and substitutes this value for the width w of the Gaussian function.

In deriving the carrier frequency, pixels of the power spectrum L (f) image may be used. That is, the number of pixels from the center of the power spectrum L (f) image to the maximum point of luminance is counted, and the count value is multiplied by the pixel size or a predetermined unit length, and the reciprocal is multiplied by the carrier frequency [m ^−1. ] May be used. Further, for simplification of calculation, multiplication by the length unit may be omitted and the reciprocal of the pixel count may be handled as the carrier frequency.

  Returning to FIG. 10, the calculation unit 18 multiplies the power spectrum L (f) by a Gaussian filter in which the width w of the Gaussian distribution, which is a parameter of the Gaussian function, is set to a value equal to the carrier frequency. Further, the arithmetic unit 18 subtracts the Gaussian filtered power spectrum (filtered power spectrum) g (f) · L (f) from the power spectrum L (f) as shown in the following formula (34) (S16). ).

  The filtered power spectrum g (f) · L (f) is a power spectrum in which a high frequency component equal to or higher than the carrier frequency is suppressed. By subtracting the filtered power spectrum g (f) · L (f) from the original power spectrum L (f), the low frequency component is removed from the captured image (original image) and the high frequency component equal to or higher than the carrier frequency is obtained. Is obtained.

  Next, the calculation unit 18 uses the phase Q (f) and the power spectrum R (f) from which the high frequency component is extracted, as shown in the following formula (35), the inverse Fourier transform (IFT). .) Is performed (S18).

  Next, the calculation unit 18 extracts only the region of the mortar mirror surface 24 from the captured image obtained in FIG. 9, and generates an inspection region mask that removes the background region (S20). When attention is paid to the end of the stripe pattern 26 in FIG. 9, the stripe pattern 26 is cut off in the black portion of the background. If this is seen from a viewpoint of a luminance change, the luminance changes in a rectangular manner. Since the rectangular wave includes harmonic components, this boundary is extracted when the high-frequency components of the captured image are connected. In this way, the calculation unit 18 extracts the boundary portion of the fringe pattern 26 based on the image (original image) of FIG.

  In generating the inspection area mask, the boundary may be extracted after reducing the resolution of the captured image (original image).

  When the boundary portion is extracted, the calculation unit 18 gives an arbitrary value to the area of the stripe pattern 26 and gives an arbitrary value different from the background area to create an inspection area mask. For example, 1 is given to the area of the stripe pattern 26 and 0 is given to the background area.

  The calculation unit 18 performs boundary processing for thinning out luminance values on pixels at the boundary portion (contour portion) between the stripe pattern 26 region and the background (S22). As described above, the boundary portion between the stripe pattern 26 region and the background includes a high frequency component. Since the flaw in the fringe pattern 26 region also has a high-frequency component, there is a possibility that the boundary portion is erroneously detected in the flaw detection process. Therefore, the calculation unit 18 reduces the luminance value of the pixel at the boundary portion.

The calculation unit 18 reduces the luminance value for pixels within a predetermined width starting from the boundary extracted in step S20. For example, a parameter a satisfying 0 <a <1 is given to 10 pixels from the boundary to the stripe pattern 26. Alternatively, the parameter a may be increased (increased) from 0 to 1 as it goes from the boundary toward the stripe pattern 26. By doing so, the contour suppression filter _CF is generated in which the parameter 0 is given to the background area, the parameter a is given to the boundary area, and the parameter 1 is given to the fringe pattern 26 area excluding the boundary.

Then calculating unit 18, or the inverse Fourier transformed image data S (x) is multiplied by the contour suppression filter _{C F,} to power (S24). As a result, among the luminance values of the image data S (x), the luminance value of the background portion is 0 for multiplication and 1 for power, while the luminance value of the fringe pattern 26 region is S (x ) Original value. In addition, the luminance value of the boundary portion is multiplied by a decimal when multiplying and is multiplied by a decimal when it is a power.

Calculating section 18 performs binarization processing on the filtered image data _{S (x) · C F (} S26). For example, a predetermined margin is added to the luminance value of the pixel at the boundary portion to obtain a threshold value, luminance below the threshold value is set to 0, and luminance above the threshold value is set to the maximum luminance.

  Through the processes from S10 to S26 described above, the low frequency components are removed from the image of FIG. 9 and the high frequency components in the boundary region are also removed. Therefore, by executing these steps, an image in which flaws (high-frequency components) in the fringe pattern 26 region appear as shown in the lower part of FIG. 12 is obtained.

  DESCRIPTION OF SYMBOLS 10 Surface inspection apparatus, 12 Stripe member, 14 Image pick-up device, 15 Stage, 16 Illuminator, 18 Calculation part, 20 Display part, 22 Mirror surface member, 24 Mortar mirror surface, 25 Bottom part opening, 26 Stripe pattern.

Claims (4)

A surface inspection device for performing an appearance inspection of a mortar-shaped mirror surface having an opening formed at the bottom,
A cylindrical or columnar shape, the central axis of which is arranged in the bottom opening so as to be along the height direction of the mortar-shaped mirror surface, and the vertical stripes along the central axis direction on the outer peripheral surface in the circumferential direction A striped member in which an array of striped patterns is formed;
The stripe member is arranged so as to be spaced apart in the height direction of the mortar-shaped mirror surface, and an imaging device that images the mirror surface in which the stripe pattern is reflected,
Based on the captured image of the mirror surface, a calculation unit that detects the presence or absence of flaws on the mirror surface;
A surface inspection apparatus comprising: The surface inspection apparatus according to claim 1,
The arithmetic unit is configured to capture a polar coordinate system including a radius and an angle from a center point of a stripe pattern arranged radially in the captured image, and an orthogonal coordinate system having the radius and an angle as an orthogonal axis. A surface inspection apparatus, wherein the fringe pattern is arranged along one axis of the orthogonal coordinate system by converting an image. The surface inspection apparatus according to claim 1 or 2,
The mirror surface is a slope whose cross-sectional shape along the height direction is linear,
The height Hc of the camera center of the image pickup device from the bottom opening of the mirror surface is perpendicular to the angle of view θ _{C of} the image pickup device, the maximum radius R _{W of the} mirror surface, the radius r _{W of} the bottom opening, and the height direction. The surface inspection apparatus is set to a range satisfying the following formula (1) using the angle φ of the slope with respect to the horizontal direction.
The surface inspection apparatus according to claim 1 or 2,
The mirror surface is a slope with a curved cross-sectional shape along the height direction,
The height H _C of the camera center of the image pickup device from the bottom opening of the mirror surface is the angle of view θ _{C of} the image pickup device, the maximum radius R _{W of the} mirror surface, the radius r _{W of} the bottom opening, and the curvature radius of the slope. The surface inspection apparatus is set to a range satisfying the following formula (2) using a.