Manufacturing method for conical mirrors

Abstract

This invention provides a method for manufacturing a conical mirror capable of obtaining a high-quality annular beam. [Solution] A method for manufacturing a conical mirror 11B with an apex angle φ. This method includes a step of polishing the reflective surface 25 of the conical mirror 11B so that when the incident beam incident on the reflective surface 25 of the conical mirror 11B is a collimated light 26 having a beam width w, the inclination of the reflective surface 25 at a position where the distance r from the central axis Ax of the conical mirror 11B is at least w / 4 is φ / 2 with respect to the central axis Ax.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a conical mirror. [Background technology]

[0002] Conventionally, inspection devices are known that perform inspection of the inner surface of a tubular object by irradiating its inner surface with an annular laser beam while moving the device along the axial direction of the object, thereby obtaining a light section image from an annular beam image (see, for example, Patent Document 1).

[0003] This inspection device uses an annular beam that extends circumferentially from a point on the central axis of the object being inspected, into the internal space of the object. The annular beam is incident on the inner surface of the object, and an annular beam image is acquired by a camera positioned on the central axis of the object. By analyzing this annular beam image, information such as the inner diameter, surface shape, and presence or absence of defects on the inner surface of the object can be obtained. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-60722 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In the inspection apparatus described above, a laser beam output from a laser light source is incident on the apex of a cone mirror (a cone mirror) having a conical reflective surface, and an annular beam is obtained by reflection from the cone-shaped reflective surface. For example, if the apex angle φ of the cone mirror is 90°, a laser beam incident parallel to the central axis of the cone mirror will, by design, be reflected perpendicular to the direction of incidence. Also, for example, if the apex angle φ of the cone mirror is 60°, a laser beam incident parallel to the central axis of the cone mirror will, by design, be reflected at a direction of 120° to the direction of incidence.

[0006] However, conical mirrors that are actually manufactured are formed with a rounded tip compared to an ideal cone. Therefore, the laser beam incident on the tip of the conical mirror is reflected in a direction different from the designed direction, and the annular beam reflected by the conical mirror contains not only the component reflected in the designed direction, but also the component reflected in a different direction. Such a component propagating in a different direction than the designed direction in the annular beam is undesirable because it leads to measurement errors.

[0007] This invention has been made in view of these circumstances, and its purpose is to provide a method for manufacturing a conical mirror that can obtain a high-quality annular beam. [Means for solving the problem]

[0008] To solve the above problems, a method for manufacturing a conical mirror according to one aspect of the present invention is a method for manufacturing a conical mirror with an apex angle φ, comprising the step of polishing the reflective surface of the conical mirror such that, when the incident beam incident on the reflective surface of the conical mirror is collimated light having a beam width w, the inclination of the reflective surface at a position where the distance r from the central axis of the conical mirror is at least w / 4 is φ / 2 with respect to the central axis. [Effects of the Invention]

[0009] According to the present invention, a method for manufacturing a conical mirror capable of obtaining a high-quality annular beam can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of an inspection device using a conical mirror manufactured by the method according to the embodiment. [Figure 2] This is a schematic perspective view of the optical probe. [Figure 3] This is a schematic cross-sectional view of a conical mirror. [Figure 4] This figure shows the simulation results of the reflection intensity of a conical mirror. [Figure 5]Figs. 5(a) to 5(d) are diagrams for explaining the conical mirror according to the first embodiment. [Figure 6] Figs. 6(a) to 6(d) are diagrams for explaining the conical mirror according to the second embodiment.

Mode for Carrying Out the Invention

[0011] Hereinafter, the same or equivalent components and members shown in each drawing are denoted by the same reference numerals, and repeated explanations are omitted as appropriate. In addition, the dimensions of the members in each drawing are appropriately enlarged or reduced for easy understanding. Also, a part of the members that are not important for explaining the embodiments in each drawing is omitted and shown.

[0012] Fig. 1 is a schematic cross-sectional view of an inspection apparatus 100 using a conical mirror manufactured by the method according to the embodiment. The inspection apparatus 100 irradiates an annular beam on the inner peripheral surface of the inspection object 60 to inspect the inner peripheral surface.

[0013] The inspection apparatus 100 includes a housing 50 and a support plate 51 disposed in the internal space of the housing 50. The housing 50 can move on the floor surface by wheels 53. The internal space of the housing 50 is partitioned by the support plate 51 into two upper and lower spaces. The upper space is called an inspection chamber 50A, and the lower space is called a standby chamber 50B. In the present embodiment, the positional relationship between the inspection chamber 50A and the standby chamber 50B is an up-and-down relationship, but it does not necessarily have to be an up-and-down relationship. For example, they may be arranged side by side horizontally. Or the up-and-down relationship between the inspection chamber 50A and the standby chamber 50B may be reversed.

[0014] A work installation portion 52 is fixed on the support plate 51, and, for example, a tubular inspection object 60 is held on the work installation portion 52. The inspection object 60 is fixed in a posture in which its central axis is parallel to the vertical direction. An opening 54 penetrating the support plate 51 and the work installation portion 52 in the vertical direction is provided at a position directly below the internal space of the inspection object 60.

[0015] The inspection device 100 includes an optical probe 10. The optical probe 10 is supported by a support mechanism 18 so as to be movable along the central axis of the inspection object 60. In a standby state where no inspection is being performed, the optical probe 10 waits in a standby chamber 50B below the inspection object 60 (below the support plate 51). During inspection, the optical probe 10 rises through the opening 54 by the support mechanism 18 and enters the inspection chamber 50A, and enters the space inside the inspection object 60.

[0016] The optical probe 10 includes an optical module 11, an imaging device 12, and an optical module fixing member 13. The optical module 11 is supported directly above the imaging device 12 by the optical module fixing member 13, and its position with respect to the imaging device 12 is fixed.

[0017] A laser light source 15 and a control unit 42 are housed in the standby chamber 50B of the housing 50. As the laser light source 15, for example, a laser diode that outputs a laser beam having a wavelength within the range of 370 nm or more and 1100 nm or less is used. Laser light is introduced from the laser light source 15 to the optical module 11 via an optical fiber 16. The control unit 42 controls the laser light source 15 and the support mechanism 18 according to a command from the upper controller 40. The image captured by the imaging device 12 is input to the analysis unit 41 of the upper controller 40, and the analysis unit 41 analyzes the image. Based on the analysis result of the image, the inner diameter of the inspection object 60 can be measured.

[0018] FIG. 2 is a schematic perspective view of the optical probe 10. The optical probe 10 includes an optical module 11 and an imaging device 12. The optical module 11 includes a collimating lens 11A and a conical mirror 11B. The position of the conical mirror 11B is fixed with respect to the collimating lens 11A by, for example, a transparent member (not shown) or a plurality of support columns.

[0019] Laser light is guided from the laser light source 15 to the optical module 11 via the optical fiber 16. The laser light output from the output end of the optical fiber 16 is collimated by the collimating lens 11A.

[0020] A conical mirror 11B is positioned where the collimating light is incident. The conical mirror 11B has a conical reflective surface. The axis of rotation of this conical surface coincides with the optical axis of the collimating light (the optical axis of the collimating lens 11A). The conical mirror 11B reflects the collimating light to generate an annular beam 20 that spreads in the circumferential direction on the inner surface of the object to be inspected 60.

[0021] When the apex angle of the conical reflective surface of the conical mirror 11B is 90°, the annular beam 20 spreads out in a disc shape (sheet shape). The inner surface of the object to be inspected 60 is a rough surface with irregularities equal to or larger than the wavelength of the annular beam 20. When the annular beam 20 is incident on the inner surface of the object to be inspected 60, diffuse reflection occurs. The location where diffuse reflection occurs is called the diffuse reflection location 21. The diffuse reflection location 21 lies along the intersection line of a plane perpendicular to the central axis of the object to be inspected 60 and the inner surface of the object to be inspected 60. If the inner surface is a cylindrical surface, the diffuse reflection location 21 will be circumferential in shape. Some of the reflected light 22 diffusely reflected at the diffuse reflection location 21 is incident on the imaging device 12. The imaging device 12 receives the reflected light 22 and generates an image.

[0022] Figure 3 is a schematic cross-sectional view of the conical mirror 11B. Here, we will explain using the case where the apex angle φ of the conical mirror 11B is 90° as an example. As shown in Figure 3, the conical mirror 11B that is actually manufactured is formed with a rounded tip portion 24 compared to an ideal cone (shown by the dashed line). This rounding of the tip portion 24 is caused by the polishing process of the reflective surface 25 when manufacturing the conical mirror 11B.

[0023] Figure 3 illustrates the collimated light 26 incident on the reflective surface 25 of the conical mirror 11B. The collimated light 26 is parallel to the central axis Ax of the conical mirror 11B. Of the collimated light 26, the beam 27 incident on the reflective surface 25, excluding the rounded tip portion 24, is reflected by the reflective surface 25 in a direction perpendicular to the direction of incidence (reflected beam 28). The direction of this reflected beam 28 is the designed reflection direction of the conical mirror 11B.

[0024] On the other hand, the beam 29 of the collimated light 26 that enters the rounded tip portion 24 is reflected in an angle smaller than perpendicular to the incident direction (reflected beam 30). That is, the direction of this reflected beam 30 is different from the designed reflection direction. Here, the angle θ of the reflected beam 30 with respect to the designed reflection direction (in this case, perpendicular to the incident direction) is defined as the "shift angle θ". If the annular beam generated by the conical mirror 11B contains a component with such a shift angle θ, a nonlinear distortion dependent on the measurement diameter relative to the inner diameter of the object being inspected occurs, leading to measurement errors. The shift angle θ can be reduced by adjusting the distance between the collimated lens 11A and the output port of the optical fiber 16, but this causes the beam to diverge or converge, worsening the cross-sectional profile of the annular beam and making it difficult to determine the optimal focus.

[0025] Since the measurement error due to the misalignment angle θ is nonlinear, if the region of the tip portion 24 that produces the misalignment angle θ can be kept within a certain range, its impact on the measurement error can be reduced.

[0026] Figure 4 shows the simulation results of the reflection intensity of the conical mirror. This simulation shows how the intensity of the reflected beam changes depending on the distance r from the central axis Ax of the conical mirror 11B when a parallel Gaussian beam is incident on the conical mirror 11B. The beam width w of the parallel Gaussian beam (intensity is 1 / e of the peak intensity) 2 The distance between the two points was set to 0.6 mm.

[0027] From the simulation results, it can be seen that when the distance r is near 0 mm, the reflection intensity is very small. As the distance r increases, the reflection intensity increases, and the reflection intensity reaches its maximum when the distance r is 0.15 mm. Such a reflection intensity distribution is caused by the perimeter of the reflecting surface of the conical mirror 11B. When the distance r is near 0 mm, although the intensity of the incident beam is maximum, the perimeter of the reflecting surface is short, so the reflection intensity is small. On the other hand, for example, when the distance r is 0.5 mm, the perimeter is long but the intensity of the incident beam is weak, so the reflection intensity is small. When the distance r is 0.15 mm, due to the good balance between the perimeter and the incident beam intensity, the reflection intensity is maximum. The beam reflected at the position of the distance r where the reflection intensity is maximum is called the principal ray, and the distance r where the reflection intensity is maximum is denoted as the principal ray position r max Let it be.

[0028] In the above simulation, when the incident light is a parallel Gaussian beam with a beam width w = 0.6 mm, the principal ray position r max is 0.15 mm. Generalizing this, when a parallel Gaussian beam with a beam width w is incident on the conical mirror 11B, the principal ray position r max is w / 4. r max = w / 4 ···(1)

[0029] If the inclination of the reflecting surface 25 at the principal ray position r represented by the above equation (1) max is 45°, the principal ray can be reflected in a direction perpendicular to the incident direction. That is, the deviation angle θ with respect to the principal ray can be made zero. Therefore, by performing the polishing process of the reflecting surface 25 when manufacturing the conical mirror 11B such that the inclination of the reflecting surface 25 at a position where the distance r from the central axis Ax is at least the principal ray position r max or more is 45° with respect to the central axis Ax, the measurement error can be suppressed. Here, it is stated that as a criterion when performing the polishing process, the inclination of the reflecting surface at a distance r of "at least" the principal ray position r max or more is set to 45°. Naturally, in the manufactured product, the principal ray position r maxNote that the inclination of the reflective surface may be 45° at a distance r less than r. Establishing standards for the polishing process is very beneficial in manufacturing stable conical mirrors 11B.

[0030] In this specification, it should be noted that a 45° inclination of the reflective surface includes cases where the inclination of the reflective surface is 45° ± 0.1°.

[0031] Figures 5(a) to 5(d) are diagrams illustrating the conical mirror 11B according to the first embodiment. Figure 5(a) is a schematic cross-sectional view of the conical mirror 11B according to the first embodiment. Figure 5(b) shows the intensity profile of the collimated light 26 (Gaussian beam) incident on the conical mirror 11B according to the first embodiment. Figure 5(c) shows the reflection intensity distribution by the conical mirror 11B according to the first embodiment. Figure 5(d) is a schematic diagram of the annular beam formed by the conical mirror 11B according to the first embodiment. In Figure 5(d), only the annular beam reflected perpendicular to the direction of incidence is shown.

[0032] In the conical mirror 11B shown in Figure 5(a), the reflective surface 25 is formed in a rounded shape up to a distance r=r0 from the central axis Ax, and at a distance r>r0, the inclination of the reflective surface is 45°. A parallel Gaussian beam of width w having the intensity profile shown in Figure 5(b) is incident on the conical mirror 11B formed in this way. The conical mirror 11B shown in Figure 5(a) is formed at the principal ray position r expressed by equation (1) above. max =w / 4 is greater than r0, and the principal ray position r max The inclination of the reflective surface at the above distance r is formed at 45°.

[0033] The conical mirror 11B formed in this manner according to the first embodiment yields an annular beam 20 as shown in Figure 5(d). Figure 5(d) shows the annular beam 20a formed by the principal ray. The annular beam 20a formed by the principal ray has the maximum reflectivity, as shown in Figure 5(c). In this way, the tip portion 24, which is rounded by polishing, is positioned at the principal ray position r maxBy keeping the beam within a distance r of less than 1, the principal ray with the highest reflectivity can be reliably directed perpendicular to the incident direction, resulting in a high-quality annular beam that reduces measurement errors.

[0034] Figures 6(a) to 6(d) are diagrams illustrating the conical mirror 11B according to the second embodiment. Figure 6(a) is a schematic cross-sectional view of the conical mirror 11B according to the second embodiment. Figure 6(b) shows the intensity profile of the collimated light 26 (Gaussian beam) incident on the conical mirror 11B according to the second embodiment. Figure 6(c) shows the reflection intensity distribution by the conical mirror 11B according to the second embodiment. Figure 6(d) is a schematic diagram of the annular beam formed by the conical mirror 11B according to the second embodiment. In Figure 6(d), only the annular beam reflected perpendicular to the direction of incidence is shown.

[0035] In the conical mirror 11B shown in Figure 6(a), the reflective surface 25 is formed in a rounded shape up to a distance r=r0 from the central axis Ax, and at a distance r>r0, the inclination of the reflective surface is 45°. Here, in this second embodiment, the rounded tip portion 24 is narrower compared to the first embodiment. Specifically, in this second embodiment, r0 is r max Less than half (r0 <r max / 2). In other words, when manufacturing the conical mirror 11B according to this second embodiment, the polishing process of the reflective surface 25 is performed so that the inclination of the reflective surface 25 at a position where the distance r from the central axis Ax is at least w / 8 or more (r>w / 8) is 45° with respect to the central axis Ax. If the tip portion 24 that is formed by being rounded in this way can be narrowed, the intensity of the annular beam 20 that flies perpendicular to the direction of incidence can be increased as shown in Figures 6(c) and (d), so a higher quality annular beam can be obtained with a greater effect in reducing measurement errors.

[0036] The above description concerns the case where the apex angle φ of the conical mirror 11B is 90°, but the manufacturing method of the conical mirror 11B described above is also applicable to conical mirrors with apex angles φ other than 90°. Generally, a laser beam incident parallel to the central axis of a conical mirror is designed to reflect in a direction of 180°-φ relative to the incident direction. This direction is the designed reflection direction for a conical mirror with an apex angle φ. For example, if the apex angle φ of the conical mirror is 60°, the designed reflection direction is 180°-60°=120° relative to the incident direction. Also, for example, if the apex angle φ of the conical mirror is 120°, the designed reflection direction is 180°-120°=60° relative to the incident direction. Even with a conical mirror with an apex angle φ, if the tip is rounded, the annular beam obtained by the conical mirror will contain a component that reflects in a direction different from the designed reflection direction, and this component may cause measurement errors.

[0037] Therefore, in the polishing process when manufacturing a conical mirror with an apex angle φ, when the incident beam incident on the reflective surface of the conical mirror is collimated light with a beam width w, the reflective surface 25 of the conical mirror is polished so that the inclination of the reflective surface 25 at a position where the distance r from the central axis Ax of the conical mirror is at least w / 4 (r>w / 4) is φ / 2 with respect to the central axis. This ensures that the principal ray with the maximum reflection intensity is reliably directed in the designed reflection direction (preventing a deviation angle θ from occurring in the principal ray), thus enabling the production of a high-quality annular beam that reduces measurement errors.

[0038] Furthermore, in the polishing process when manufacturing a conical mirror with an apex angle of φ, the reflective surface 25 may be polished such that the inclination of the reflective surface 25 at a position where the distance r from the central axis Ax is at least w / 8 (r>w / 8) is φ / 2 with respect to the central axis Ax. In this case, the intensity of the annular beam projected in the designed reflection direction can be increased, making it possible to obtain a higher quality annular beam with a greater effect in reducing measurement errors.

[0039] Any combination of the embodiments and modifications described above is also useful as an embodiment of the present invention. The new embodiments resulting from these combinations possess the combined effects of the respective embodiments and modifications. [Explanation of symbols]

[0040] 10 Optical probe, 11 Optical module, 11A Collimating lens, 11B Conical mirror, 12 Imaging device, 13 Optical module fixing member, 15 Laser light source, 16 Optical fiber, 18 Support mechanism, 20 Annular beam, 21 Diffuse reflection point, 24 Tip section, 25 Reflecting surface, 26 Collimated light, 30 Reflected beam, 40 Higher-level controller, 41 Analysis unit, 42 Control unit, 50 Housing, 50A Inspection room, 50B Waiting room, 51 Support plate, 52 Workpiece installation section, 53 Wheels, 54 Aperture, 60 Object to be inspected, 100 Inspection device.

Claims

1. A method for manufacturing a conical mirror with an apex angle of φ, A method for manufacturing a conical mirror, characterized by comprising the step of polishing the reflective surface of the conical mirror such that, when the incident beam incident on the reflective surface of the conical mirror is collimated light having a beam width w, the inclination of the reflective surface at a position where the distance r from the central axis of the conical mirror is at least w / 4 is φ / 2 with respect to the central axis.

2. The method for manufacturing a cone mirror according to claim 1, characterized in that, in the polishing step, the reflective surface of the cone mirror is polished such that the inclination of the reflective surface at a position where the distance r from the central axis of the cone mirror is at least w / 8 is φ / 2 with respect to the central axis.

Images