Surface inspection method and surface inspection apparatus

Abstract

Spherical surfaces are batch inspected at the same sensitivity. A surface inspection method in which a light shining device 50 is used to shine a light at a spherical surface of a spherical body 100 having said spherical surface, reflected light that has been reflected by the spherical surface is projected onto an annular screen 105 to form an optical image, and a surface condition of the spherical surface is inspected on the basis of the brightness of the optical image. In this surface inspection method, the light shining device 50 is used to shine a circular ring beam 10b, which results from forming a parallel beam so as to become a circular ring with the optical axis 10a of the parallel beam as the center, onto the spherical surface such that the optical axis 10a passes through the center O of the spherical surface, and the reflected light reflected by the spherical surface is projected onto an irradiation surface, which is the concave surface of the annular screen 105.

Description

Technical Field

[0001] The present invention relates to a surface inspection method and a surface inspection apparatus for inspecting the surface state of a spherical surface.

Background Art

[0002] Spherical parts made of metal or ceramic are widely used in rotating mechanisms and sliding parts of industrial machines, transportation machines, and precision instruments. In order to ensure the rotational accuracy and sliding performance, they are required to be precise true spheres. For example, steel balls for ball bearings are required to have high dimensional accuracy such as a sphericity of 0.5 μm or less and a surface roughness Ra of 0.040 μm or less as one of the general standards. For quality assurance, precise surface inspection is essential. Therefore, various inspection methods and inspection apparatuses have been conventionally proposed for industrial spherical parts.

[0003] Patent Document 1 describes a surface inspection apparatus that inspects the surface of a sphere by irradiating the sphere of an object to be inspected with a laser beam while simultaneously rotating the sphere and the laser beam axis, and detecting the amount of reflected light from the sphere.

[0004] In addition, Patent Document 2 describes a surface inspection method for a cylindrical part, although it is not a spherical surface. In Patent Document 2, using the magic mirror principle, a sheet-shaped irradiation light having a predetermined width and a predetermined thickness is irradiated on the surface of the cylindrical part, and the reflected light from the surface of the cylindrical part is projected onto a screen, and the surface state of the cylindrical part is inspected by observing the optical image formed on the screen.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the surface inspection of a spherical surface, the reflection angle on the spherical surface changes depending on the position where light is irradiated and the incident angle of the irradiated light. In the prior art described in Patent Document 1, which targets a sphere, the light irradiated from the focus A of the ellipse irradiates a point on the spherical surface arranged at the position of the other focus B of the ellipse. However, in Patent Document 1, since the reflection angle of the light at the focus B is not uniform, the spherical surface could not be inspected with the same sensitivity. Also, in Patent Document 1, since the illumination light irradiates only one point (focus B) on the spherical surface, the spherical surface could not be inspected collectively.

[0007] Also, although Patent Document 2 discloses a method for inspecting the surface of a cylindrical component, it does not disclose a method for inspecting the surface of a spherical surface.

[0008] The present invention proposes a technique for collectively inspecting a spherical surface with the same sensitivity.

Means for Solving the Problems

[0009] In order to solve the above problems, one of the typical surface inspection methods of the present invention is a surface inspection method in which, for the spherical surface of an inspection object having a spherical surface, light is irradiated using a light irradiation device, the reflected light reflected by the spherical surface is projected onto a screen to form an optical image, and the surface state of the spherical surface is inspected based on the luminance of the optical image. In this method, the light irradiation device forms circular light by shaping parallel light into a circular shape centered on the optical axis of the parallel light, irradiates the spherical surface so that the optical axis passes through the center of the spherical surface, and projects the reflected light reflected by the spherical surface onto the irradiated surface that is the concave surface of the screen.

Effects of the Invention

[0010] According to the present invention, it becomes possible to collectively inspect the spherical surface with the same sensitivity. Problems, methods, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0011]

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Best Mode for Carrying Out the Invention

[0012] Hereinafter, examples will be described with reference to the drawings.

[0013] <Example 1> Hereinafter, a surface inspection apparatus and a surface inspection method according to Example 1 will be described with reference to FIGS. 1 to 8. FIG. 1 is a side view showing the configuration of the surface inspection apparatus according to Example 1, and FIG. 2 is a front view showing the configuration of the surface inspection apparatus according to Example 1. The surface inspection apparatus 1 irradiates light onto the spherical surface of the sphere 100, and projects the reflected light reflected by the spherical surface onto a screen (hereinafter referred to as an annular screen in this Example and Examples 3, 6, and 7 described later) 105 having an annular and belt-shaped irradiated surface to form an optical image. Then, the surface inspection apparatus 1 inspects the surface state of the spherical surface based on the luminance of the optical image.

[0014] The surface inspection apparatus 1 includes a light irradiation device 50 that irradiates the sphere 100 with light. The light irradiation device 50 includes a light generation device (including a laser oscillator that generates laser light in this Example) 101 that generates parallel light, and an optical device 51 that includes a beam expander 102, an axicon lens 103, and an axicon lens 104. The surface inspection apparatus 1 further includes an annular screen 105, a line sensor camera 106, a lens 107, a line sensor camera 108, a lens 109, an image processing device 113, a determination device 114, and a holding device 115 (see FIG. 6) for the sphere 100. Details of the holding device 115 will be described later. At least one of the axicon lens 103 and the axicon lens 104 is movable in the Y-axis direction, and the distance (distance between axicon lenses) a between the axicon lens 103 and the axicon lens 104 can be set to an arbitrary distance. That is, the optical device 51 has a configuration capable of adjusting the distance between the axicon lens 103 and the axicon lens 104. In addition, line sensor cameras 106 and 108 are held by a holding mechanism (not shown) and are variable in the Y-axis direction. By making line sensor cameras 106 and 108 variable in the Y-axis direction, the positions of line sensor cameras 106 and 108 can be adjusted. Further, surface inspection device 1 has a controller (not shown) that controls the operations of the above-described devices and mechanisms.

[0015] In this embodiment, the inspection object was sphere 100. However, the inspection object may not be a sphere as long as it has a spherical surface. For example, the inspection object may be a piston. An example of rotating the piston will be described in detail in Example 6. Also, sphere 100 may be made of any material such as metal, ceramics, or wood as long as it has a predetermined reflectivity.

[0016] In this embodiment, the radius r of sphere 100 is 15 mm. Laser oscillator 101 constitutes a light generation device 101 that generates parallel light (hereinafter, the case where the light generation device is a laser oscillator will be described). Laser oscillator 101 outputs parallel beam 10 having a wavelength of 670 nm and a beam diameter of 0.48 mm, and the optical axis 10a of parallel beam 10 passes through the center point O of sphere 100. Parallel beam 10 is parallel light parallel to optical axis 10a. Parallel light refers to light in which any ray within the beam is parallel to other rays. The output of laser oscillator 101 is, for example, about 1 mW. Parallel beam 10 is in single mode, and the intensity distribution of the output beam is Gaussian distribution, with 1 / e 2 diameter being taken as the beam diameter. That is, the beam diameter is the width at the intensity when it has dropped to 1 / e 2 (13.6%) of the peak intensity. Parallel beam 10 is expanded to a beam diameter of t0 via beam expander 102. In this embodiment, t0 = 1 mm is set.

[0017] The axicon lenses 103 and 104, which are the optical devices 51, are conical prism lenses and have the same shape and the same material as each other. Also, the optical axis 10a passes through the vertices of the cones of the axicon lenses 103 and 104, and the vertices of the cones face each other. When the parallel beam 10 enters from the plane side of the axicon lens 103 and exits from the conical surface, the parallel beam 10 is refracted at the ridge line of the cone and travels toward the optical axis 10a. After the parallel beam 10 crosses the optical axis 10a, the parallel beam 10 becomes an annular beam (annular light). The outer diameter of the annular beam increases as the irradiation distance from the axicon lens 103 increases, but the thickness of the annulus is constant. This beam characteristic is close to the characteristic of the Bessel beam, and the beam intensity forming the annulus is constant regardless of the irradiation distance. Subsequently, the annular beam enters the conical surface of the axicon lens 104. At this time, since the prism angle α of the axicon lens 104 is the same as that of the axicon lens 103, the annular beam is refracted at the ridge line of the cone, and the optical path of the annular beam becomes parallel to the optical axis 10a again. The annular beam parallel to the optical axis 10a is hereinafter referred to as the annular beam 10b. The annular beam 10b is annular with the optical axis 10a as the center, and the optical axis 10a passes through the center O of the sphere 100. Therefore, the annular beam 10b is irradiated on the spherical surface of the sphere 100 at the same incident angle. This incident angle indicates the angle formed by the optical axis 10a of the annular beam 10b and the normal direction on the spherical surface of the sphere 100 where the annular beam 10b is irradiated. Also, with respect to the radius r of the sphere 100, when the thickness t1 of the annular beam 10b satisfies t1 << r, the incident angle of the annular illumination region 110 of the sphere 100 is substantially the same incident angle, as shown by the following formula (7)'. Although the details will be described later, in the case of this embodiment, since t1 = 0.502 mm with respect to r = 15 mm, the range of the incident angle of the annular beam 10b on the illumination region 110 is 42.3° to 45°. Since the change in the luminance on the annular screen 105 due to the change in the incident angle remains below 0.5%, it is possible to perform the inspection with substantially the same sensitivity.

[0018] Next, the thickness t1 of the annular beam 10b formed in this embodiment will be described. In this embodiment, the prism angles α of the axicons 103 and 104 are α = 10°, and the refractive index n with respect to the illumination light with a wavelength of 670 nm is n = 1.456. Since the optical axis 10a of the parallel beam 10 passes through the apex of the cone of the axicon 103, the thickness of the annular beam after passing through the axicon 103 is half of the beam diameter t0 of the parallel beam 10, that is, 0.5 mm. Also, the thickness t1 of the annular beam 10b after passing through the axicon 104 is constant regardless of the irradiation distance from the axicon 104. If the angle formed by the optical path of the annular beam after passing through the axicon 103 and the optical axis 10a is α' as shown in FIG. 1, then t1 = t0 / (2cosα'). Also, since α' = sin -1 (n × sinα) - α, substituting α = 10° and n = 1.456, we get t1 = 0.502 mm.

[0019] Next, the relationship between the outer diameter dr of the annular beam 10b and the distance a between the axicons will be described. Using the refractive index n and the prism angle α of the axicons 103 and 104, the outer diameter dr of the annular beam 10b is obtained from Equation (1). dr = 2a × tan((n - 1)α)) …(1) As shown in Equation (1), by adjusting the distance a between the axicons, the outer diameter dr can be adjusted. In FIG. 2, the illumination area 110 on the spherical surface of the sphere 100 is shown with diagonal hatching. By adjusting the outer diameter dr, the illumination area 110 can be arbitrarily changed.

[0020] Next, the arrangement of the screen that projects the reflected light from the spherical surface of the sphere 100 and the camera that detects the optical image on the screen will be described with reference to FIGS. 2 and 3. The annular beam 10b is reflected by the spherical surface of the sphere 100, travels radially around the point O' on the optical axis 10a, and is projected onto the annular screen 105. The annular screen 105 is a screen configured such that the irradiated surface (the optical axis 10a side in this embodiment) irradiated with the reflected light is concave. The annular screen 105 of the first embodiment is an annular screen arranged along the circumferential direction of a circle centered on the optical axis 10a. FIG. 3 is a side view showing the illumination state of the sphere. The annular screen 105 has a hollow cylindrical shape with a radius L0 and a width W in the Y-axis direction. Also, the cylindrical axis of the annular screen 105 coincides with the optical axis 10a. The annular screen 105 is installed at a location that is separated from the center O of the sphere 100 by a distance u0 toward the laser oscillator 101 side. Also, the annular screen 105 has diffuse reflection characteristics. In this embodiment, the screen radius L0 = 50 mm, the screen width W = 15 mm, and the screen distance u0 = 5 mm.

[0021] In the first embodiment, the reflected light is projected onto the annular screen 105 with a concave surface on the optical axis 10a side, but the screen does not have to be annular. For example, the annular screen 105 only needs to have a concave surface on the optical axis 10a side and may be hemispherical.

[0022] As shown in FIG. 2, the optical image formed by the reflected light projected onto the annular screen 105 is scanned and observed in the circumferential direction of the annular screen 105 by the line sensor cameras 106 and 108 via the lenses 107 and 109. The line sensor cameras 106 and 108 are arranged on the same side of the rotation axis 11 on the X-Z plane as shown in FIG. 2. Also, the circumferential field of view range 111 of the annular screen 105 with the line sensor cameras 106 and 108 combined covers at least the range of 180° from 0° to (90°) to 180° of the annular screen 105 as shown in FIG. 2. In this case, when the sphere 100 is rotated once around the rotation axis 11, the line sensor cameras 106 and 108 also include the axially symmetric region of the circumferential field of view range 111 on the annular screen 105 in the field of view. For this reason, the 360° in the circumferential direction on the annular screen 105 can be included in the field of view range with the line sensor cameras 106 and 108 combined. Thereby, all of the illumination region 110 of the sphere 100 can be observed. In this embodiment, the observation optical axes 12a and 12b of the line sensor camera 106 and the line sensor camera 108 are arranged to pass through the optical axis 10a, and as shown in FIG. 2, are arranged to intersect at the 45° and 135° positions of the annular screen 105. Also, the lens 107 and the line sensor camera 106 are coaxially arranged, and similarly, the lens 109 and the line sensor camera 108 are coaxially arranged.

[0023] In this embodiment, the line sensor cameras 106 and 108 are arranged to image the outside of the annular screen 105, but at least one of the line sensor cameras 106 and 108 may be arranged to image the inside of the annular screen 105.

[0024] Next, with reference to FIG. 3, the relationship between the outer diameter dr of the annular beam 10b and the radius r of the sphere 100 and the relationship between the outer diameter dr and the axicon lens distance a in this embodiment will be described. In FIG. 3, the two intersection points of the sphere 100 and the rotation axis 11 are defined as vertex T and vertex T', respectively. Assuming that the position where the parallel light corresponding to the outer ring of the annular beam 10b irradiates the spherical surface of the sphere 100 is point A, in this embodiment, the angle TOA = 45°. In this case, the parallel light irradiated at point A is reflected in a direction perpendicular to the optical axis 10a and projected onto point A' of the annular screen 105. Further, since the annular beam 10b is axially symmetric about the optical axis 10a passing through the center of the sphere 100, if the position axisymmetric with point A is point C, then the angle TOC = 135° (angle T'OC = 45°). The light irradiated on point C on the spherical surface of the sphere 100 is reflected in a direction perpendicular to the optical axis 10a, similar to the reflected light from point A, and projected onto point C' on the annular screen 105. If the angle TOA is less than 45°, the reflected light from the spherical surface of the sphere 100 is reflected in a direction approaching the rotation axis 11 and may interfere with the holding device 115. To avoid this, in this embodiment, the annular beam 10b is shaped such that the angle TOA = 45°. In this case, the outer shape dr of the annular beam 10b is 2×r×cos45° = 1.414r.

[0025] FIG. 4 is a perspective view of FIG. 3. With reference to FIGS. 3 and 4, the inspection region 112 of the sphere 100 in this embodiment will be described. In FIG. 4(a), the illumination region 110 of the annular beam 10b irradiated on the surface of the sphere 100 is shown by diagonal hatching. Further, when the sphere 100 is rotated once about the rotation axis 11, the surface region of the sphere 100 passing through the illumination region 110 is the region shown by the diagonal hatching in FIG. 4(b). The region shown by the hatching in FIG. 4(b) is called the inspection region 112. In this embodiment, the inspection region 112 is a strip-shaped range with an angle AOC = 90° sandwiched between point A and point C.

[0026] In this case, the ratio S of the inspection region 112 to the entire surface of the sphere 100 is obtained by Equation (2) using the radius r of the sphere 100 and the outer diameter dr of the annular beam 10b. S = 2πr×dr / 4πr 2=dr / 2r …(2) In this embodiment, since dr = 2r × cos(45°), substituting this into Equation (2) gives S = 2r × cos(45°) / 2r = cos(45°) = 0.707.

[0027] Thus, in this embodiment, it can be seen that if the annular beam 10b is formed such that the angle TOA = 45°, regardless of the radius r of the sphere 100, the inspection area 112 is approximately 70% of the entire surface of the sphere 100.

[0028] Also, the outer diameter dr of the annular beam 10b can be adjusted by the axicon lens distance a according to Equation (1). In the case of this embodiment, the outer diameter dr of the annular beam 10b and the radius r of the sphere 100 are in the relationship of dr = 1.414r. Therefore, the axicon lens distance a is obtained by Equation (3) using the refractive indices n of the axicon lenses 103 and 104, the prism angle α, and the radius r of the sphere 100. a = 0.707r / tan((n - 1)α) …(3)

[0029] In this embodiment, since n = 1.456, α = 10°, and r = 15 mm, the axicon lens distance a is determined to be 133.00 mm. Even if the size of the sphere 100 changes and the radius r changes, by adjusting the axicon lens distance a according to Equation (3), the outer diameter dr of the annular beam 10b can be made to satisfy the relationship of dr = 1.414r. In this case, the reflected light from point A is perpendicularly projected onto point A' on the annular screen 105 with respect to the optical axis 10a. The observation optical axes 12a and 12b of the line sensor cameras 106 and 108 are within the band-shaped range surrounded by the circumferences passing through points A' and C' on the annular screen 105 and the circumferences passing through points B' and D'. Or, the line sensor cameras 106 and 108 are moved in the Y-axis direction so that the observation optical axes 12a and 12b are within the band-shaped range. Thereby, even if the radius r of the sphere 100 changes, the spherical surface can be inspected with the same inspection apparatus. Also, from Equation (2), a certain ratio of the entire surface of the sphere 100 can be inspected.

[0030] Next, with reference to FIGS. 3 and 5, the range of the incident angle of the annular beam 10b to the illumination area 110 and the magnification effect of the optical image of the illumination area 110 will be described. The reflected light reflected by the spherical surface of the sphere 100 is expanded in the width direction (sphere rotation direction) and the circumferential direction (sphere rotation axis direction) of the annular screen 105 due to the curvature of the spherical surface, and is projected onto the annular screen 105. FIG. 3 shows the optical path of the reflected light in the Y-Z plane of the reflected light that irradiates the spherical surface of the sphere 100 with the annular beam 10b and is reflected from the spherical surface. The parallel light hitting the outer ring of the annular beam 10b is irradiated to point A, and the reflected light reflected from point A is reflected perpendicular to the optical axis 10a and projected onto point A' of the annular screen 105. On the other hand, the parallel light hitting the inner ring of the annular beam is irradiated to point B, and the reflected light irradiated from point B is projected onto point B' of the annular screen 105. In FIG. 3, let the angle of the arc AB be β and the distance between the optical axis 10a and the annular screen 105 be L0. The range of the incident angle of the annular beam 10b to the illumination area 110 is 45° - β to 45°, and the incident angle of the reflected light from point B to the annular screen 105 is 2β.

[0031] Assuming the length of the arc AB is dAB and the length between A' and B' on the annular screen 105 is dA'B', the magnification ratio M_YZ in the width direction of the annular screen, that is, on the Y-Z plane, by the spherical surface of the sphere 100 is represented by Equation (4). M_YZ = dA'B' / dAB …(4) Also, dAB and dA'B' are obtained from Equation (5) and Equation (6), respectively. dAB = βr …(5) dA'B' = r×(sin(45° + β) - sin(45°)) +(L0 - r×cos(45° + β))×tan2β …(6) Also, the angle β of the arc AB is obtained from the thickness t1 of the annular beam 10b by Equation (7). t1 = r×(cos45° - cos(45° + β)) …(7) When t1 << r, the trigonometric functions in Equation (7) are Taylor-expanded and terms of the second order and higher are ignored, then it can be converted to Equation (7)'. β = 1.414×t1 / r (rad) =80.78×t1 / r (°) …(7)' In this embodiment, r = 15 mm, t1 = 0.502 mm, and L0 = 50 mm. From equations (4) to (7), M_YZ = 5.99 times and β = 2.7° are obtained. Also, the range of the incident angle of the annular beam 10b on the illumination area 110 is 42.3° to 45°, and the incident angle of the reflected light from point B on the annular screen 105 is 5.4°. The reflected light is incident vertically on point A'. On the other hand, the reflected light is incident obliquely on point B' at an incident angle of 5.4°, and the luminance decreases with respect to point A'. However, the decrease in the luminance of point B' is (1 - cos5.4°) × 100 = 0.44%, which is very small, and the inspection area 112 can be inspected with substantially the same sensitivity.

[0032] Figure 5 shows the optical path in the X-Z plane of a part of the reflected light reflected from the spherical surface of the sphere 100 when the annular beam 10b is irradiated on the spherical surface of the sphere 100. The light hitting the outer ring of the annular beam is irradiated on points P and Q, and the reflected light reflected from points P and Q is reflected radially around point O' on the optical axis 10a and projected onto points P' and Q' on the annular screen 105. The magnification M_XZ in the circumferential direction of the annular screen 105, that is, in the X-Z plane, by the spherical surface of the sphere 100 is equal to the ratio of the distance from point O' to point P to the distance from point O' to point P'. In the case of this embodiment, the distance r1 between O' and P is r×cos45°, and the distance between O' and P' is L0. Therefore, M_XZ is represented by equation (8). M_XZ = 1.414×L0 / r …(8) Substituting r = 15 mm and L0 = 50 mm gives M_XZ = 4.71 times. From the above, it can be seen that the optical image on the annular screen 105 is enlarged in the circumferential direction and the width direction of the annular screen by the spherical surface of the sphere 100.

[0033] Further, when the line scan rates f of the line sensor cameras 106 and 108 are appropriately adjusted, it becomes possible to inspect the optical image at a magnification corresponding to the magnification in the width direction of the annular screen 105 of the optical image. When the rotation time per rotation of the sphere 100 is set to T, the minimum value of the scan rate f of the line sensor cameras 106 and 108 is calculated from Equation (9). Here, let the radius of the sphere 100 be r, the radius of the annular screen 105 be L0, the magnification be M, and the pixel size c on the annular screen 105 corresponding to one pixel of the line sensor cameras 106 and 108. f ≧ 2πr × M / (T × c) …(9) Here, when r = 15 mm, M = M_YZ = 5.99, T = 3 s, and c = 0.1 mm, the scan rate f of the line sensor cameras 106 and 108 needs to be driven at 1882 Hz or more. In this embodiment, it is assumed that the pixel size c is constant regardless of the observation position on the annular screen 105 and is calculated.

[0034] Next, the holding device 115 of the first embodiment will be described with reference to FIG. 6. The holding device 115 is a device that holds the sphere 100 so as to have a configuration capable of rotating the sphere 100 about the rotation axis 11. The holding device 115 rotates the sphere 100 about the rotation axis 11 that passes through the center of the sphere 100 and is orthogonal to the optical axis 10a. More specifically, the holding device 115 includes a holder 116 that holds the sphere 100, and a rotation mechanism (for example, a rotation stage) 117 that rotates the holder 116 about the rotation axis 11. The holder 116 is a hollow cylinder. The outer diameter dc of the holder 116 satisfies the condition dc / 2 < r × sin 45°. This is because the holder 116 would interfere with the annular beam 10b.

[0035] FIG. 7 is a schematic diagram of the optical image acquired by the line sensor camera 106, and is an optical image of the upper half of the sphere 100 inspected in the range of 0° to 90° from the vertex T to the vertex T' of the sphere 100, that is, when the vertex T is defined as above and the vertex T' is defined as below. The vertical axis of the optical image in FIG. 7 is the direction of the rotation axis of the sphere 100 from the vertex T to the vertex T', and the horizontal axis indicates the rotation direction of the sphere 100. FIG. 7 simulates the reflected light intensity distribution on the annular screen 105 detected by rotating the sphere 100 with a radius r = 15 mm in 3 s and setting the scan rate f = 1882 Hz of the line sensor camera 106 according to the conditions of this embodiment. The optical image is enlarged 4.71 times in the sphere rotation axis direction and 5.99 times in the sphere rotation direction.

[0036] In the optical image of FIG. 7, the uneven defects on the spherical surface of the sphere 100 are manifested as luminance changes due to the magic mirror principle. In this optical image, images 31 and 32 are detected as bright spots. Image 31 is a defect near the middle between the vertex T and the vertex T' of the sphere 100, that is, near the equator of the earth. Image 32 is a defect near the vertex T of the sphere 100. As it approaches the vertex T, the optical image is detected in a shape extending in the rotation direction of the sphere 100. This is because distortion occurs when the reflected light from the spherical surface is projected onto a plane for observation. When the sphere 100 is rotated once around the rotation axis 11, in the upper half of the spherical surface of the sphere 100, the closer it is to the vertex T, the shorter the length of one circumference, so the length per pixel in the rotation direction becomes shorter, and the apparent pixel resolution increases. The images 31 and 32 shown in FIG. 7 are extracted by the image processing device 113, and defect information such as defect coordinates and defect dimensions is recorded in a storage means (not shown). The image processing device 113 outputs defect information such as defect coordinates and defect dimensions based on the luminance of the images acquired by the line sensor cameras 106 and 108. This image processing device 113 functions as a detection device for detecting defects on the surface of the sphere 100.

[0037] The determination device 114 determines the presence or absence of a defect based on the defect dimensions (defect size, defect depth) stored in a storage means (not shown). For example, if the determination device 114 detects a defect with a size equal to or greater than a predetermined size or a depth equal to or greater than a predetermined depth, it determines that there is a defect and that the inspection object is defective. Further, the determination device 114 can output information indicating whether the inspection object is good or defective, information indicating the dimensions and depth of the defect of the inspection object, etc. to a display unit or the like. Note that an inspection processing device that executes the surface inspection processing of the sphere 100 includes the image processing device 113 and the determination device 114. This inspection processing device may be mounted, for example, in a controller (not shown) that controls the overall operation of the surface inspection device 1, or may be provided as a separate information processing device.

[0038] Finally, the relationship between the radius L0 of the annular screen 105 and the defect detection performance will be described. Fig. 8(a) shows the condensing action when light is irradiated on the concave defect 41. The reflected light from the concave defect 41 becomes brighter near the focal point because the light rays are condensed. The focal length F of a concave mirror with a depth d and a width Ld is expressed by Equation (10). F = Ld 2 / 8d …(10) Note that when a screen is installed at a position L1 away from the concave defect, the relative reflected light intensity of the condensing part from the concave defect with respect to the reflected part from the flat surface without a defect is expressed by Equation (11). I(L1) = F 2 / (F - L1) 2 …(11)

[0039] I(L1) represents the luminance on the magic mirror image. The larger I(L1) is, the brighter the condensing part is, indicating a higher sensitivity to defects. However, in this embodiment, since a laser beam with high coherence is used as the light source, speckle-like random noise (speckles) is generated on the annular screen 105. Let 2σ of this speckle intensity be set to ±N% of the average luminance of the optical image on the annular screen 105. In this embodiment, as a criterion for separating the condensing action due to defects from the speckles, it is made detectable when the brightness of the condensing part due to defects becomes about (1 + N / 100) times that of the surroundings. That is, when I(L1) ≥ (1 + N / 100), defects can be detected. When the focal length F of the concave defect is known from Equation (11), defects can be expected to be detected as bright spots when Equation (12) is satisfied. F×(1+N / 100-(1+N / 100) 0.5 ) / (1+N / 100)≦L1≦F×(1+N / 100+(1+N / 100) 0.5 ) / (1+N / 100) …(12)

[0040] In this embodiment, for example, 2σ of the speckle intensity is estimated to be ±50%. In this case, substituting N = 50 into Equation (12), defects can be expected to be detected as bright spots when the condition 0.184F ≤ L1 ≤ 1.82F is satisfied.

[0041] Also, FIG. 8(b) shows the diffusion action when light is irradiated on the concave defect 41. The reflected light from the concave defect 41 is condensed at the focal point and then diffused. When the optical path exceeds twice the focal length, the corresponding part becomes dark. The reflected light intensity at the part that becomes dark due to the diffusion effect of the concave defect is also expressed by Equation (11) as in the case of light condensation. I(L1)=F 2 / (F-L1) 2 …(11) However, in Fig. 8(b), since L1 > 2F, I(L1) < 1. When I(L1) approaches 0 and is darker than the surroundings, the defect can still be detected. However, since it is detected separately from the speckle noise this time, it can be detected when I(L1) ≤ 1 - N / 100. From Equation (11), when the focal length F of the concave defect is known, when the condition of Equation (13) is satisfied, the defect can be expected to be detected as a dark spot. F × (1 - N / 100 + (1 - N / 100) 0.5 ) / (1 - N / 100) ≤ L1 …(13) That is, L1 is determined so as to satisfy Equation (12) or Equation (13).

[0042] Similar to the case of detecting the defect as a bright spot, in this embodiment, when N = 50 is substituted into Equation (13) and the condition of 2.41F ≤ L1 is satisfied, the defect can be expected to be detected as a dark spot. From the above, when the focal length F1 of the concave defect to be inspected is known, assuming that 2σ of the speckle intensity is ±50%, by designing the annular screen 105 so that the screen distance L1 satisfies Equation (14), the defect can be detected as a bright spot or a dark spot. 0.184F ≤ L1 ≤ 1.82F, 2.41F ≤ L1 …(14)

[0043] In this embodiment, conversely, the screen distance L1 is known. The distance from the defect to the screen corresponds to AA' in Fig. 3, for example. The distance of AA' is obtained from Equation (15) based on the radius L0 of the annular screen 105 and the radius r of the sphere 100. AA' = L0 - r × cos45° …(15) Substituting L0 = 50mm and r = 15mm, AA' = L1 = 39.4mm is obtained. Substituting this into Equation (14), the range of the focal length F of the defect with sensitivity is Equation (16). F ≤ 16.34mm (range detected as a dark spot), 21.64mm ≤ F ≤ 214.1mm (range detected as a bright spot) …(16) For example, in the case of a concave-shaped defect with a diameter of 0.5 mm and a depth of 1 μm, F = 31.25 mm, and it is detected as a bright spot by the apparatus of this embodiment.

[0044] According to the form of this embodiment, the following effects can be obtained. (1) By irradiating the spherical body 100 with the annular beam 10b and projecting the reflected light from the spherical surface onto the annular screen 105 and observing the surface of the annular screen 105, minute unevenness on the spherical surface can be detected with high sensitivity. (2) By irradiating the spherical body 100 with the annular beam 10b having a thickness of t1 such that t1 << r with respect to the radius r of the spherical body 100, the incident angles of the illumination light within the illumination region 110 become substantially the same. Therefore, the inspection region 112 of the spherical body 100 can be inspected with substantially the same sensitivity. (3) By changing the distance a between the axicons 103 and 104, the outer diameter dr of the annular beam 10b can be adjusted. Thereby, spherical bodies with different diameters can also be inspected with the same inspection apparatus. (4) Since the annular screen 105 is annular, all of the annular beam 10b reflected by the spherical surface can be projected onto the annular screen 105. Further, since it is projected onto the annular screen 105 having diffuse reflection characteristics, stable optical image observation is possible without depending on the reflection characteristics of the spherical body 100. (5) When the dimensions and shape of the defect to be detected are known, the defect detection sensitivity can be increased by adjusting the radius L0 of the annular screen 105. (6) By making the light irradiated onto the spherical body 100 annular, the energy efficiency is better than making it circular. Since the energy density of the light is higher in the annular shape than in the circular shape, the spherical surface can be inspected with high sensitivity. (7) By projecting the reflected light reflected by the spherical surface onto the annular screen 105 whose light axis 10a side is concave, the spherical surface can be inspected with the same sensitivity. By making the outer diameter of the annular beam 10b constant regardless of the optical path length and shaping the outer diameter of the annular beam 10b to be 0.707 times the diameter of the sphere 100, the annular beam 10b can be reflected in a direction perpendicular to the optical axis 10a.

[0045] In the surface inspection method of Example 1, for the spherical surface of the sphere 100 having a spherical surface, light is irradiated using the light irradiation device 50, the reflected light reflected by the spherical surface is projected onto the annular screen 105 to form an optical image, and based on the luminance of the optical image, in the surface inspection method for inspecting the surface state of the spherical surface, the light irradiation device 50 forms an annular beam 10b by shaping the parallel beam 10 into a circular shape centered on the optical axis 10a of the parallel beam 10, irradiates the spherical surface so that the optical axis 10a passes through the center of the spherical surface, and projects the reflected light reflected by the spherical surface onto the irradiated surface that is the concave surface of the annular screen 105.

[0046] In the surface inspection method of Example 1, the annular beam 10b is annular.

[0047] In the surface inspection method of Example 1, the outer diameter of the annular beam 10b is constant regardless of the optical path length, and is shaped so that the outer diameter is 0.707 times the diameter of the sphere having the spherical surface.

[0048] In the surface inspection method of Example 1, the sphere 100 is held by a rotatable holding device 115 and rotated about a rotation axis 11 that passes through the center of the spherical surface and is orthogonal to the optical axis 10a.

[0049] In the surface inspection method of Example 1, the optical image projected onto the annular screen 105 is detected by the line sensor cameras 106 and 108. When the radius of the sphere 100 having the spherical surface is r, the distance between the optical axis 10a and the annular screen 105 is L0, the pixel size on the annular screen 105 for one pixel of the line sensor camera is c, the rotation time per rotation of the sphere is T, and the scan rate of the line sensor cameras 106 and 108 is f, the line sensor cameras 106 and 108 are driven under the condition that f ≧ 2πr × M / (T × c).

[0050] In the surface inspection method of Example 1, when the focal length is F when a defect on the spherical surface is regarded as a concave mirror and the distance from the spherical surface to the annular screen 105 is L1, in the optical image on the annular screen 105, as a condition for separating and detecting the luminance change due to the defect from the speckle noise on the annular screen 105, when 2σ of the intensity of the speckle noise is ±N% with respect to the average luminance of the optical image on the annular screen 105, F×(1+N / 100-(1+N / 100) 0.5 ) / (1+N / 100)≦L1≦F×(1+N / 100+(1+N / 100) 0.5 ) / (1+N / 100) Or, (1-N / 100+(1-N / 100) 0.5 ) / (1-N / 100)≦L1 Determine L1 so as to satisfy.

[0051] The surface inspection apparatus 1 of Example 1 includes a holding device 115 that holds a sphere 100 having a spherical surface, a light generation device 101 that generates parallel light, an optical device 51 that forms the parallel beam 10 into a circular shape around the optical axis 10a of the parallel beam 10 and irradiates the spherical surface with an annular beam 10b formed into a circular shape so that the optical axis 10a passes through the center of the spherical surface, an annular screen 105 configured such that the reflected light from the spherical surface is projected and the irradiated surface irradiated with the reflected light is a concave surface, and an image processing device 113 that detects a defect on the surface of the spherical surface based on the luminance of the optical image formed on the annular screen 105.

[0052] In the surface inspection apparatus 1 of Example 1, the optical device 51 includes an axicon lens 103 that forms the parallel beam 10 into an annular shape and an axicon lens 104 that forms the annular light formed into an annular shape into a shape parallel to the optical axis 10a and having a predetermined diameter.

[0053] In the surface inspection apparatus 1 of Example 1, the optical device 51 has a configuration in which the distance between the axicon lens 103 and the axicon lens 104 can be adjusted.

[0054] In the surface inspection apparatus 1 of the first embodiment, the holding device 115 is configured to be able to rotate the sphere 100 about a rotation axis 11 that passes through the center of the spherical surface and is orthogonal to the optical axis 10a.

[0055] <Second Embodiment> In the first embodiment, a surface inspection apparatus has been described that can inspect a spherical surface with substantially the same sensitivity and can be inspected by the same inspection apparatus even when the diameter of the sphere to be inspected changes. However, in the first embodiment, among the entire spherical surface, the inspection area was limited to a part.

[0056] In the second embodiment, a surface inspection apparatus 2 capable of inspecting the entire spherical surface will be described with reference to FIGS. 9 to 11. FIG. 9 is a plan view showing the configuration of the surface inspection apparatus of the second embodiment. In the present embodiment, in addition to the apparatus configuration of the first embodiment, another set of the same light irradiation device for irradiating an annular beam of the same shape is added as the light irradiation device 60. That is, as shown in FIG. 9, the surface inspection apparatus 2 includes two light irradiation devices 50 and 60, two light generation devices (laser oscillators in the present embodiment) 101 and 201, two beam expanders 102 and 202, two axicon lenses 103 and 203, and two axicon lenses 104 and 204, which respectively form two optical devices 51 and 61. Further, the surface inspection apparatus 2 includes two screens (hereinafter referred to as semi-annular screens in the present embodiment) 105b and 205b having semi-annular and strip-shaped irradiated surfaces corresponding to the two light irradiation devices 50 and 60, two line sensor cameras 106 and 206, two lenses 107 and 207, two line sensor cameras 108 and 208, and two lenses 109 and 209. Further, in the surface inspection apparatus 2, light shielding plates 121 and 221 for forming the annular beams 10b and 20b into semi-annular shapes are respectively added to the first light irradiation device 50 (light generation device 101 and optical device 51) and the second light irradiation device (other light irradiation device) 60 (other light generation device 201 and other optical device 61).

[0057] Each of the optical axis 10a of the first light irradiation device 50 and the optical axis 20a of the second light irradiation device 60 passes through the center O of the sphere 100 and forms an angle of 90° with each other. The rotation axis 11b is set to form angles of 135° and 45° with the optical axes 10a and 20a respectively, and the optical axes 10a and 20a are arranged on the same side with respect to the plane including the rotation axis 11b. Also, the rotation axis 11b exists on the plane formed by the optical axis 10a and the optical axis 20a. As a result, when the vertex T of the sphere 100 is defined as above the sphere 100 and the vertex T' is defined as below the sphere 100, the inspection range of the annular beam 10b is the lower half of the sphere 100, and the inspection range of the annular beam 20b is the upper half of the sphere 100. As a result, in the second embodiment, it is possible to inspect the entire spherical surface of the sphere 100.

[0058] FIG. 10 is a perspective view showing the illumination state of the sphere 100. In FIG. 10(a), for the sake of explanation, the description of the screen is omitted. In this embodiment, a light shielding plate 121 is disposed between the sphere 100 and the axicon lens 104, and a light shielding plate 221 is disposed between the sphere 100 and the axicon lens 104. The light shielding plates 121 and 221 shape the annular beams 10b and 20b into semi-annular beams 10c and 20c. In FIG. 10(a), the illumination area 110c of the semi-annular beam 10c irradiated on the spherical surface of the sphere 100 is indicated by oblique hatching. Also, the illumination area 210c of the semi-annular beam 20c irradiated on the spherical surface of the sphere 100 is indicated by the area surrounded by the dotted line.

[0059] In this embodiment, as shown in FIG. 10(b), the semi-annular screens 105b and 205b are semi-annular. The spherical surface of the sphere 100 is irradiated with the semi-annular beams 10c and 20c, and the reflected light thereof is projected onto the semi-annular screens 105b and 205b. Thereby, the reflected lights of the semi-annular beams 10c and 20c from the spherical surface of the sphere 100 interfere with each other on the screen, and physical interference between the screens is prevented.

[0060] FIG. 11 is a plan view of the sphere 100 observed from the direction of the optical axis 10a or 20a, showing the positional relationship between the line sensor camera and the screen. Also, the illumination regions 110c and 210c are shown with diagonal hatching. The positional relationship between the line sensor cameras 106 and 108 and the semi-circular screen is shown in FIG. 11(a). The line sensor cameras 106 and 108 are arranged at positions outside the semi-circular screen 105b. Similar to Example 1, the circumferential field-of-view ranges 111 of the line sensor cameras 106 and 108 cover at least the range of 180° from 0° to (90°) to 180° of the semi-circular screen 105b in FIG. 11(a). In this embodiment, the observation optical axes 12a and 12b of the line sensor camera 106 and the line sensor camera 108 are set to intersect at the positions of 45° and 135° of the semi-circular screen 105b, respectively, similar to Example 1. FIG. 11(b) shows the positional relationship between the line sensor cameras 206 and 208 and the semi-circular screen 205b. The positional relationship between the line sensor cameras 206 and 208 and the semi-circular screen 205b, and the circumferential field-of-view ranges 211 of the line sensor cameras 206 and 208 are the same as the relationship between the line sensor cameras 106 and 108 and the semi-circular screen 105b. Also, the angles of the observation optical axes 22a and 22b of the line sensor cameras 206 and 208 are the same as the relationship between the line sensor cameras 106 and 108 and the semi-circular screen 105b.

[0061] In this embodiment, the sphere 100 is irradiated with the annular semi-circular beams 10c and 20c, and the reflected light from the spherical surface is projected onto the semi-circular screens 105b and 205b. Thereby, by observing the surfaces of the semi-circular screens 105b and 205b, in addition to the effects of Example 1, it becomes possible to inspect the entire spherical surface.

[0062] Next, a surface inspection apparatus 2' which is a modification of Example 2 will be described with reference to FIGS. 12 and 13. FIG. 12 is a plan view showing the surface inspection apparatus 2' which is a modification of the present embodiment. In the surface inspection apparatus 2', the optical axis 10a and the optical axis 20a are coaxial and pass through the center O of the sphere 100. Further, the laser oscillator 101 and the laser oscillator 201 are located on opposite sides across the center O of the sphere 100. The rotation axis 11b forms an angle of 45° with the optical axis 10a or 20a, and the optical axis 10a, the rotation axis 11b, and the cylindrical axis of the semi-annular screen 105c exist on the same plane. FIG. 13 is an enlarged perspective view for explaining a state in which the semi-annular beams 10c and 20c are irradiated onto the spherical surface of the sphere 100. In FIG. 12, the illumination regions 110c and 210c of the semi-annular beams 10c and 20c irradiated onto the spherical surface of the sphere 100 are indicated by hatching. In the surface inspection apparatus 2', the semi-annular beams 10c and 20c irradiate the same side with respect to the plane formed by the optical axis 10a and the rotation axis 11b. With this structure, since a space is created on the side opposite to the semi-annular screen 105c across the optical axis 10a, it becomes easy to convey the sphere 100 to the inspection region.

[0063] The surface inspection method of Example 2 uses a light irradiation device 60 different from the light irradiation device 50 to form an annular beam 20b different from the annular beam 10b into a circular shape around the optical axis 20a of the annular beam 20b, and irradiates the spherical surface so that the optical axis 20a passes through the center of the spherical surface, and projects the reflected light of the annular beam 20b reflected by the spherical surface onto the irradiated surface which is the concave surface of a semi-annular screen 205b different from the semi-annular screen 105b.

[0064] The surface inspection apparatuses 2 and 2' of Example 2 include, in addition to the light generation device 101 and the optical device 51, a light generation device 201 for generating the annular beam 20b, and an optical device 61 for shaping the annular beam 20b into a circular shape around the optical axis 20a of the annular beam 20b and irradiating the spherical surface so that the optical axis 20a of the circularly shaped annular beam 20b passes through the center of the spherical surface.

[0065] <Example 3> In Example 1, a surface inspection apparatus that can inspect a spherical surface with substantially the same sensitivity and can be inspected by the same inspection apparatus even when the diameter of the spherical object to be inspected changes was described. However, in Example 1, among the entire spherical surface, the inspection area is only a part. Further, in Example 2 and its modified examples, an apparatus capable of inspecting the entire spherical surface of the sphere 100 was described by combining two optical systems that irradiate an annular beam. However, in Example 2 and its modified examples, since two optical systems are required, the apparatus becomes large-sized.

[0066] In Example 3, a surface inspection apparatus 3 that can expand the inspection area more than in Example 1 without increasing the size of the inspection apparatus will be described with reference to FIGS. 14 to 16. FIG. 14 is a side view of the surface inspection apparatus 3. In the surface inspection apparatus 3, the light irradiation device 70 has an optical device 71 including an axicon lens 301 disposed between the axicon lens 104 of the surface inspection apparatus of Example 1 and the sphere 100. In Example 3, the axicon lens 301 has the same shape and the same material as the axicon lenses 103 and 104 of Example 1. Further, the axicon lens 301 is configured to be movable in the Y-axis direction by a moving mechanism (not shown). The conical axis of the axicon lens 301 coincides with the optical axis 10a, and the apex of the cone faces the sphere 100. In this case, the annular beam 10b passing through the ridge line of the cone of the axicon lens 301 is refracted in the direction toward the optical axis 10a, and the outer diameter dr of the axicon lens 103 decreases in proportion to the optical path length around the optical axis 10a.

[0067] FIG. 15 is an enlarged view showing the illumination state of the sphere 100. In FIG. 15, only the light 10d' corresponding to the outer ring among the annular beam 10b after passing through the axicon lens 301 is shown. Let the angle formed by the light 10d' and the optical axis 10a be γ. That is, the incident angle of the light 10d' with respect to the spherical surface of the sphere 100 is 45° - γ. In the case of Example 3, since the axicon lens 301 has the same shape and the same material as the axicon lenses 103 and 104, γ is equal to α' in FIG. 1 of Example 1 or FIG. 14 of Example 3, and γ = α' = sin -1It becomes (n×sinα). In Example 3, since α = 10° and n = 1.456, γ = 4.65°. When the axicon lens distance a and the axicon lens 301 are moved to appropriate positions and the light 10d’ irradiates a point A1 which is at a position 45° - γ away from the vertex T of the sphere 100, the reflected light from the point A1 reflects in the vertical direction with respect to the optical axis 10a. As a result, the reflected light is projected onto the point A1’ on the annular screen 105 without interfering with the rotation axis 11.

[0068] Next, with reference to FIG. 16, an example of the axicon lens distance a and the distance b between the vertex of the cone of the axicon lens 301 and the center point O of the sphere 100 for irradiating the point A1 with the light 10d’ will be described. For example, if the outer diameter dr of the annular beam 10b is 30 mm, substituting n = 1.456 and α = 10° into Equation (1), a = 188.07 mm is obtained. dr = 2a×tan((n−1)α)) …(1)

[0069] Next, when the annular beam 10b passes through the axicon lens 301, it becomes an annular beam 10d whose outer diameter of the annulus shrinks toward the optical axis 10a. This reduction amount is proportional to the distance between the axicon lens 301 and the sphere 100. If the outer diameter when the annular beam 10d reaches the point A1 is dr’, then from FIG. 16, Equations (17) and (18) hold. dr’ = 2r×cos(45° - γ) …(17) (dr - dr’) / 2 = (dr / 2×sinα + b - r×sin(45° - γ))×tanγ …(18)

[0070] Substituting dr = 30 mm, α = 10°, and γ = 4.65° into Equations (17) and (18), b = 50.98 mm is obtained. In Example 3, if the distance between the axicon lenses 103 and 104 is a = 188.07 mm and the distance between the vertex of the cone of the axicon lens 301 and the center O of the sphere 100 is b = 50.98 mm, the reflected light from the sphere 100 does not interfere with the rotation axis 11. As a result, the inspection area can be enlarged compared to the inspection area 112 of Example 1. In this case, the ratio S of the inspection area of the spherical body 100 is obtained by deforming Equation (2) using the radius r of the spherical body 100, the central angle 45° - γ of the arc TA1', and γ = 4.65° with respect to the entire spherical surface of the spherical body 100. S = dr’ / 2r = 2r×cos(45° - γ) / 2r = cos(45° - γ) = 0.762 > 0.707 …(2)'

[0071] From the result of Equation (2)', when the axicon lens 301 is added to Example 1 and the incident angle of γ is given to the annular beam 10b, the inspection area can be expanded as compared with the case of Example 1. The surface inspection apparatus 3 of the third embodiment can expand the inspection area without further increasing the size of the apparatus in addition to the effects of Example 1.

[0072] In the surface inspection method of Example 3, the outer diameter of the annular beam 10b is reduced in proportion to the optical path length. When the angle formed by the annular beam 10d and the optical axis 10a is γ (where 0° < γ < 45°) and the radius of the spherical body having a spherical surface is r, the circular light is shaped so that the outer diameter of the circular light when the annular beam 10d irradiates the spherical body 100 becomes 2r×cos(45° - γ).

[0073] In the surface inspection apparatus 3 of Example 3, the optical device 71 includes an axicon lens 301 that reduces the outer diameter of the annular beam 10b in proportion to the optical path length.

[0074] <Example 4> The surface inspection apparatus 4 of Example 4 will be described with reference to FIG. 17. In Example 1, since the annular screen 105 is curved and dead angles are formed, the optical image on the annular screen 105 was observed using two line sensor cameras. In Example 4, the optical image projected onto the annular screen 105 is detected by a single line sensor camera without dead angles.

[0075] The surface inspection device 4 replaces the annular screen 105 of the surface inspection device 1 in the first embodiment with a screen having an arc-shaped and belt-shaped irradiated surface (hereinafter referred to as an arc screen 105d in this embodiment). FIG. 17 is a front view of the surface inspection device 4 as seen from the laser oscillator 101. The arc screen 105d is a part of an arc having a sufficiently large radius L0', and the optical axis 10a side is concave. The center point Od of the arc screen 105d is located at a position far from the center point O of the sphere 100 compared to the line sensor camera 106, and O and Od are separated by L0'-u1. The light reflected from points A and B on the spherical surface of the sphere 100 becomes reflected light parallel to the rotation axis 11, and the locations projected onto the arc screen 105d are denoted as points A1' and B1' respectively. If the reflected light from the arc AB can be observed, when the sphere 100 is rotated about the rotation axis 11, the regions symmetric with respect to the rotation axis 11 can also be observed, so that all regions of the illumination region 110 can be inspected. The reflected light from the arc AB is projected onto the illumination region of the arc A'B' on the arc screen 105d. In the fourth embodiment, since the angle δ of the arc A'B' is relatively small, an optical image of the necessary region on the arc screen 105d can be observed without dead angles by a single line sensor camera 106. For example, when L0 = 120 mm and L0'-u1 = 90 mm, using the fact that the radius of the sphere 100 is r = 15 mm and the outer diameter dr of the annular beam 10b is 1.414r, δ = 82.8°. And if the distance between the line sensor camera 106 and the arc screen 105d is sufficiently large, the arc A1'B1' on the arc screen 105d becomes within the field of view by one unit.

[0076] <Example 5> In the fifth embodiment, a surface inspection device 5 that can be inspected at the same magnification even when the radius r of the sphere 100 changes will be described with reference to FIG. 18. In this embodiment, as in the first embodiment, the reflected light from the sphere 100 is enlarged in the rotation axis direction and the rotation direction of the sphere 100 and projected onto the annular screen. In particular, the rotation axis direction of the sphere 100 is obtained from the distance L0 between the annular screen and the optical axis 10a and the radius r of the sphere 100 according to Equation (8). M_XZ = 1.414 × L0 / r …(8)

[0077] In Example 5, the screen is a truncated cone screen 105e having a hollow truncated cone shape and a strip-shaped irradiated surface, and the cone axis of the truncated cone screen 105e coincides with the optical axis 10a. The truncated cone screen 105e is configured to be movable in the Y-axis direction (the direction of the optical axis 10a). With this structure, even if the radius r of the sphere 100 changes, by moving the truncated cone screen 105e in the Y-axis direction (the optical axis direction), the distance L0 to the projection surface of the truncated cone screen 105e can be adjusted, and the magnification M_XZ in the rotation axis direction of the optical image projected onto the truncated cone screen 105e can be made constant. Also, in the surface inspection apparatus 5, the holding device 401 of the sphere 100 is configured to be insertable from the direction opposite to the irradiation direction of the annular beam 10b into the hollow of the truncated cone screen 105e.

[0078] With the above structure, in the surface inspection apparatus 5, in addition to the effects of Example 1, the surface of the sphere 100 can be inspected at the same magnification regardless of the radius r of the sphere 100.

[0079] The truncated cone screen 105e of the surface inspection apparatus 5 of Example 5 has a hollow truncated cone shape and is configured to be movable in the direction of the optical axis 10a so that the distance from the optical axis 10a to the projection surface of the truncated cone screen 105e is variable.

[0080] <Example 6> The holding device 115 of Example 1 is configured to rotate the sphere 100. The inspection object of the present invention is not limited to the sphere 100 and is not limited to a sphere as long as it is a member having a spherical surface. For example, a piston having a spherical surface may be the specimen object. FIG. 19 is a diagram showing the configuration of the holding device 615 of the surface inspection apparatus of Example 6. The holding device 615 of Example 6 can rotatably hold the piston 100b.

[0081] The piston 100b has a shape in which a spherical body portion 100c having a spherical surface is integrally formed on a tapered main body portion. The surface inspection apparatus 1 can use the piston 100b as an inspection object and this spherical body portion 100c as an inspection target portion by adapting the configuration and arrangement of the holding apparatus 615 to the piston 100b. That is, the light irradiation apparatus 50 can be configured such that an annular beam is irradiated onto the spherical body portion 100c of the piston 100b. More specifically, the holding apparatus 615 installs the piston 100b on a rotatable holder 617 including a rotation mechanism. The line sensor camera 108 and the lens 109 are arranged such that the observation optical axis 12b forms an angle of 45° with respect to the annular screen 105. Also, the line sensor camera 106 and the lens 107 are arranged such that the observation optical axis 12a forms an angle of 45° with respect to the annular screen 105.

[0082] In addition to the holder 617, the holding apparatus 615 has a swingable swing mechanism (for example, a goniostage in this embodiment) 618. In this embodiment, the rotation mechanism (for example, a rotation stage) of the holder 617 and the goniostage of the swing mechanism 618 are integrally formed. By swinging the rotation axis 11 (tilting the piston 100b) by the swing mechanism 618, the inspection range can be expanded up to the apex T of the spherical body portion 100c.

[0083] <Example 7> The surface inspection apparatus 7 of Example 7 has a light irradiation device 80 that irradiates the spherical body 100 with light formed in a circular shape. The surface inspection apparatus 7 of Example 7 will be described with reference to FIG. 20. Different from Example 1 in which the spherical body 100 is irradiated with an annular ring beam 10b, in this example, the light irradiated onto the spherical body 100 is circular light shaped to be circular. As shown in FIG. 20, the surface inspection apparatus 7 includes a light generation device (laser oscillator) 101, an optical device 702 consisting only of a beam expander, an annular screen 105, a line sensor camera 106, a lens 107, a line sensor camera 108, and a lens 109. In the surface inspection apparatus 7, the optical device 702 does not include the axicon lenses 103 and 104 shown in Example 1. The optical device 702 is a beam expander (optical system) that enlarges or reduces the beam diameter. The optical device 702 may be a Keplerian beam expander or a Galilean beam expander. The optical device 702 of Example 6 has an objective lens 702a and an image-side lens 702b. The parallel light incident on the objective lens 702a is focused at a focal point between the objective lens 702a and the image-side lens 702b, and the diameter of the circular light increases as the irradiation distance from the objective lens 702a increases. Then, the circular light incident on the image-side lens 702b becomes circular light 10e that is parallel to the optical axis 10a and circular again when passing through the image-side lens 702b. The optical axis 10a of the circular light 10e passes through the center O of the spherical surface.

[0084] As in this example, by making the light irradiated onto the spherical body 100 circular, it is also possible to perform a surface inspection of the spherical body 100 in the same manner as in the case of irradiating annular light. Further, for example, when performing a surface inspection using circular light as in Example 7, or when irradiating the spherical body 100 with light from a plurality of positions as in the various examples described above, or when inspecting only a part of the spherical body 100, etc., there may be a case where it is not necessary to rotate the spherical body 100. The same applies to the swing mechanism 618. That is, the holding devices 115, 401, and 615 do not necessarily have a rotation mechanism 117 or a swing mechanism 618, and may be configured to hold the inspection object at a predetermined position.

[0085] Note that the present invention is not limited to the above-described embodiments, and various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, for a part of the configuration of each embodiment, addition, deletion, or replacement with other configurations is possible.

Description of Reference Numerals

[0086] 1, 2, 2', 3, 4, 5, 7 Surface inspection device 10, 20 Parallel beam 10a, 20a Optical axis 10b, 10d, 20b Annular beam 10c, 20c Semi-annular beam 11, 11b Rotation axis 12a, 12b, 22a, 22b Observation optical axis 31 Image 41 Concave defect 50, 60, 70, 80 Light irradiation device 51, 61, 71, 702 Optical device 100 Sphere 100b Piston 101, 201 Laser oscillator (light generation device) 102, 202 Beam expander 103, 104, 203, 204, 301 Axicon lens 105 Annular screen 105b, 105c Semi-annular screen 105d Arc screen 105e Frustum of a cone screen 106, 108, 206, 208 Line sensor camera 107, 109, 207, 209 Lens 110, 110c, 210c Illumination area 111, 211 Field of view 112 Inspection area 121 and 222 light shields 115, 401, and 615 holding devices

Claims

1. In a surface inspection method for inspecting the surface state of a spherical surface of an object to be inspected having a spherical surface, by irradiating the spherical surface with light using a light irradiation device, projecting the reflected light reflected by the spherical surface onto a screen to form an optical image, and inspecting the surface state of the spherical surface based on the luminance of the optical image, by the light irradiation device, irradiating the spherical surface such that the optical axis passes through the center of the spherical surface with circular light obtained by shaping parallel light into a circular shape centered on the optical axis of the parallel light, projecting the reflected light reflected by the spherical surface onto the irradiated surface that is the concave surface of the screen, the circular light is annular, A surface inspection method characterized by this.

2. In a surface inspection method for inspecting the surface state of a spherical surface of an object to be inspected having a spherical surface, by irradiating the spherical surface with light using a light irradiation device, projecting the reflected light reflected by the spherical surface onto a screen to form an optical image, and inspecting the surface state of the spherical surface based on the luminance of the optical image, by the light irradiation device, irradiating the spherical surface such that the optical axis passes through the center of the spherical surface with circular light obtained by shaping parallel light into a circular shape centered on the optical axis of the parallel light, projecting the reflected light reflected by the spherical surface onto the irradiated surface that is the concave surface of the screen, the outer diameter of the circular light is reduced in proportion to the optical path length, and when the angle formed by the circular light and the optical axis is γ (where 0° < γ < 45°) and the radius of the sphere having the spherical surface is r, the circular light is shaped such that the outer diameter of the circular light when the spherical surface is irradiated is 2r × cos(45° - γ), A surface inspection method characterized by this.

3. In a surface inspection method for inspecting the surface state of a spherical surface of an object to be inspected having a spherical surface, by irradiating the spherical surface with light using a light irradiation device, projecting the reflected light reflected by the spherical surface onto a screen to form an optical image, and inspecting the surface state of the spherical surface based on the luminance of the optical image, by the light irradiation device, Circular light formed by shaping parallel light into a circular shape around the optical axis of the parallel light is irradiated onto the spherical surface so that the optical axis passes through the center of the spherical surface. The reflected light reflected by the spherical surface is projected onto the irradiated surface that is the concave surface of the screen. By another light irradiation device different from the light irradiation device. Another circular light formed by shaping other parallel light different from the parallel light into a circular shape around the optical axis of the other parallel light is irradiated onto the spherical surface so that its optical axis passes through the center of the spherical surface. Projecting the reflected light of the other circular light reflected by the spherical surface onto the irradiated surface that is the concave surface of another screen different from the screen. A surface inspection method characterized by the above.

4. In the surface inspection method according to claim 1 or 3, the outer diameter of the circular light is constant regardless of the optical path length, and is shaped so that the outer diameter is 0.707 times the diameter of the sphere having the spherical surface. A surface inspection method.

5. In the surface inspection method according to any one of claims 1 to 3, the inspection object is held by a rotatable holding device and rotated about a rotation axis passing through the center of the spherical surface and orthogonal to the optical axis. A surface inspection method having the above.

6. In the surface inspection method according to claim 5, the optical image projected onto the screen is detected by a line sensor camera, the radius of the sphere having the spherical surface is r, the magnification on the screen of the optical image is M, and the pixel size on the screen for one pixel of the line sensor camera is c. When the rotation time per rotation of the sphere is T and the scan rate of the line sensor camera is f, driving the line sensor camera under the condition that f ≧ 2πr × M / (T × c). A surface inspection method having the above.

7. In the surface inspection method according to claim 5, when the focal length when the defect on the spherical surface is regarded as a concave mirror is F and the distance from the spherical surface to the screen is L1, in the optical image on the screen, as a condition for separating and detecting the luminance change due to the defect from the speckle noise on the screen, when 2σ of the intensity of the speckle noise is ±N% with respect to the average luminance of the optical image on the screen, F×(1 + N / 100 - (1 + N / 100) ０．５ ) / (1 + N / 100) ≤ L1 ≤ F×(1 + N / 100 + (1 + N / 100) ０．５ ) / (1 + N / 100) Or, (1 - N / 100 + (1 - N / 100) ０．５ ) / (1 - N / 100) ≤ L1 A surface inspection method for determining L1 so as to satisfy the above.

8. A holding device for holding an inspection object having a spherical surface, A light generating device for generating parallel light, An optical device that shapes the parallel light into a circular shape around the optical axis of the parallel light and irradiates the spherical surface with the circular light shaped into a circular shape so that the optical axis passes through the center of the spherical surface, A screen configured such that the reflected light from the spherical surface is projected and the irradiated surface irradiated with the reflected light is a concave surface, A detection device for detecting a defect on the surface of the spherical surface based on the luminance of the optical image formed on the screen, comprising: The optical device has a first axicon lens that shapes the parallel light into an annular shape and a second axicon lens that shapes the annular light formed into an annular shape into a shape parallel to the optical axis and having a predetermined diameter. A surface inspection device characterized by the above.

9. In the surface inspection device according to claim 8, the optical device has a configuration capable of adjusting the distance between the first axicon lens and the second axicon lens.

10. The surface inspection apparatus according to claim 8, wherein the holding device has a configuration capable of rotating the object to be inspected about a rotation axis passing through the center of the spherical surface and orthogonal to the optical axis.

11. In the surface inspection apparatus according to claim 8, another light generation device that generates other parallel light, another optical device that shapes the other parallel light into a circular shape about the optical axis of the other parallel light and irradiates the spherical surface so that the circular light shaped into a circular shape has its optical axis passing through the center of the spherical surface, a surface inspection apparatus.

12. In the surface inspection apparatus according to claim 8, the optical device includes a third axicon lens that reduces the outer diameter of the annular light in proportion to the optical path length.

13. a holding device that holds an object to be inspected having a spherical surface, a light generation device that generates parallel light, an optical device that shapes the parallel light into a circular shape about the optical axis of the parallel light and irradiates the spherical surface so that the optical axis passes through the center of the spherical surface, a screen configured such that the reflected light from the spherical surface is projected and the irradiated surface irradiated with the reflected light is a concave surface, a detection device that detects a defect on the surface of the spherical surface based on the luminance of the optical image formed on the screen, and the screen is in the shape of a hollow truncated cone and has a configuration that is movable in the direction of the optical axis so that the distance from the optical axis to the projection surface of the screen is variable.

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