Pinhole detection device

Abstract

The present application solves the problem of providing a pinhole detection device with higher pinhole detection accuracy. In the pinhole detection device (10) of the present application, the detection unit (24) for detecting the pinhole (110) generated in the object (100) includes a plurality of optical fibers (30) for transmitting light through the object (100). The plurality of optical fibers (30) are arranged side by side and face the light source (20). When the maximum detectable angle relative to the optical axis of the light source (20) at which the pinhole (110) can be detected is defined as θ, the maximum incident angle of the light transmitted by the optical fiber (30) relative to the optical axis of the light source (20) is set within the range of θ+0° to θ+5°.

Description

Technical Field

[0001] This invention relates to a pinhole detection device. Background Technology

[0002] Patent Document 1 aims to provide a surface defect inspection device capable of accurately detecting penetrating defects that are inclined along the thickness direction of the material to be inspected (Column 3, Rows 10-13). To achieve this objective, the surface defect inspection device of Patent Document 1 includes: a light source that emits light onto the surface of the material to be inspected; and a detection unit that detects the amount of transmitted light emitted by the light source, wherein an optical lens that forms a focal point on the detection unit is provided between the material to be inspected and the light source (Column 3, Rows 15-20). Figure 1 ).

[0003] Patent Document 2 aims to provide a pinhole detection device that detects abnormal portions formed within a plate-like object, such as pinholes extending obliquely relative to the surface of the plate-like object (column 2, row 19 to column 3, row 2). To achieve this, the plate-like object abnormal portion detection device of Patent Document 2 includes: a laser source; a lens that disperses a laser beam from the laser source and converts the laser beam into a dispersed beam; a plate-like object disposed such that the dispersed beam is incident on one side of the plate-like object; and a photosensitive device disposed such that it responds to transmitted light of the dispersed beam located on the other side of the plate-like object (claims). The photosensitive device includes a light guiding element FO such as an optical fiber and a photoelectric conversion element PH (column 4, rows 12-14; figures).

[0004] Patent Document 3 aims to provide a pinhole detection device that detects pinholes in a board material with high detection accuracy (page 4, lines 7-8). To achieve this, in the board pinhole detection device of Patent Document 3, light is directed to one side of the scanned board material, while on the other side, the end faces of optical transmission fibers arranged in an array perpendicular to the scanning direction of the board material receive the light passing through the pinholes in the board material. This light is guided by the optical transmission fibers to a photodetector, wherein the light-receiving ends of the optical transmission fibers are arranged in multiple rows to form a trefoil pattern (claim 1; Figures 4 to 6).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: JP S61025042A

[0008] Patent Document 2: JP S50034586A

[0009] Patent Document 3: JP S55116256U Summary of the Invention

[0010] The technical problem solved by the invention

[0011] Although Patent Document 1 states that the detection unit (3) detects the amount of transmitted light of the emitted light (column 3, rows 16-17, etc.), Patent Document 1 does not describe the specific structure of the detection unit (3). Furthermore, although Patent Document 2 describes light guiding elements such as optical fibers (FO) and photoelectric conversion elements (PH) as photosensitive devices (column 4, rows 12-14; figure), Patent Document 2 does not specifically discuss the specifications of the light guiding element (FO, optical fiber).

[0012] Furthermore, although Patent Document 3 discloses the cross-sectional shape and arrangement of the optical transmission fiber 7 (optical fiber) (page 3, lines 16-20; Figures 4 to 6, etc.), Patent Document 3 does not discuss other specifications of the optical transmission fiber 7. Therefore, there is still room for improvement in the accuracy of pinhole detection.

[0013] The present invention addresses the above-mentioned problems and provides a pinhole detection device with higher pinhole detection accuracy.

[0014] Problem Solving Methods

[0015] A pinhole detection device according to the present invention includes:

[0016] A light source that emits light toward the object to be inspected;

[0017] An optical lens disposed between the light source and the object to be inspected; and

[0018] A detection unit that detects light focused by the optical lens and passing through a pinhole in the object under test.

[0019] The detection unit includes an optical fiber for transmitting light passing through the pinhole in the object under inspection, and

[0020] When the maximum detectable angle relative to the optical axis of the light source that can detect the pinhole is defined as θ, the maximum incident angle of the light that can be transmitted by the optical fiber relative to the optical axis of the light source is in the range of θ+0° to θ+5°.

[0021] According to the present invention, pinholes, as the target of detection, can be ensured to be detected, and interference light (or leakage light) can be easily prevented from entering the optical fiber. Therefore, the signal-to-noise ratio (S / N ratio) of transmitted light and interference light can be improved, and the pinhole detection accuracy can be enhanced. The present invention is preferably used, for example, when the object to be inspected is strip-shaped. Specifically, when the object to be inspected extends along the conveying direction (e.g., steel plate, opaque film, paper, etc.), inclined pinholes are easily generated. The present invention facilitates the detection of pinholes inclined in the conveying direction.

[0022] In this invention, the light source can be a line light source that linearly emits light toward the object to be inspected. The optical lens can converge the light from the light source that is propagating in a direction away from the optical axis of the light source, thereby causing the light to propagate in a direction close to the optical axis of the light source. The detection unit may include multiple optical fibers arranged side by side and facing the light source, and when the maximum polarization angle of the optical lens is defined as θ1, the maximum polarization angle θ1 can be set to be greater than or equal to the maximum detectable angle θ.

[0023] In this invention, when the maximum polarization angle of the optical lens is defined as θ1, the maximum incident angle of the light that can be transmitted by each optical fiber relative to the optical axis of the light source can be within the range of θ1+0° to θ1+5°.

[0024] The present invention may include a conveying device for moving the object to be inspected along a direction perpendicular to the longitudinal direction of the light source and orthogonal to the optical axis of the light source. The end face of the optical fiber facing the object to be inspected may be located at the focal position of the optical lens, or may be located closer to the object to be inspected than the focal position of the optical lens.

[0025] According to the present invention, pinhole detection can be easily achieved even when the object to be inspected moves relative to the pinhole detection device. That is, when the end face of the optical fiber is positioned at the focal point of the optical lens, the detection unit detects the light transmitted through the pinhole in a rapid upward motion, and the detection time for this upward motion is relatively short. Conversely, when the end face of the optical fiber is positioned closer to the object to be inspected than at the focal point of the optical lens, the upward motion detected by the detection unit due to light transmission through the pinhole is less than in the aforementioned configuration, and the detection time for this upward motion is relatively longer. Therefore, even if pinhole detection cannot be achieved in the former configuration (positioned at the focal point of the optical lens) due to the moving speed of the object to be inspected, pinhole detection can still be achieved in the latter configuration (positioned closer to the object to be inspected than at the focal point). Therefore, a higher moving speed of the object to be inspected can be set in the latter configuration.

[0026] In both of the above-described setup methods, a criterion for determining the presence or absence of pinholes needs to be set. Different criteria can be set for each of the two setup methods. The criteria used in this application may, for example, include the signal strength of the detection unit and the number of data points used to calculate the moving average.

[0027] In this invention, a first linear Fresnel lens and a second linear Fresnel lens may be provided between the light source and the detection unit. The first linear Fresnel lens is positioned closer to the light source along its longitudinal direction, and the second linear Fresnel lens is positioned closer to the detection unit than the first linear Fresnel lens along the same longitudinal direction. The first linear Fresnel lens refracts light from the light source into parallel light. Viewed along the longitudinal direction of the light source, the second linear Fresnel lens refracts the parallel light such that the maximum polarization angle of the light refracted by the second linear Fresnel lens is less than or equal to the maximum incident angle relative to the end face of the optical fiber. According to this invention, parallel light is generated between the first and second linear Fresnel lenses, thereby facilitating the adjustment of the distance between the two Fresnel lenses.

[0028] Effects of the present invention

[0029] According to the present invention, the accuracy of pinhole detection can be improved. Attached Figure Description

[0030] Figure 1 This is a three-dimensional structural diagram of a pinhole detection device according to an embodiment of the present invention.

[0031] Figure 2 This diagram illustrates the optical characteristics of the optical lens and optical fiber in this embodiment.

[0032] Explanation of reference numerals in the attached figures:

[0033] 10 Pinhole Detection Device

[0034] 20 Light Sources (Line Light Sources)

[0035] 22a Optical lens (first linear Fresnel lens)

[0036] 22b Optical lens (second linear Fresnel lens)

[0037] 24 detection units

[0038] 26 Conveying equipment

[0039] 30 fiber optic cables

[0040] 32 Detection elements

[0041] 50 light

[0042] 60 optical axis

[0043] 100 items to be inspected

[0044] 110 pinhole

[0045] θ Maximum detectable angle

[0046] θ₁ Maximum polarization angle

[0047] θ₂ Maximum incident angle DETAILED DESCRIPTION

[0048] <A. One Embodiment>

[0049] [A-1. Structure]

[0050] (A-1-1. Overall Structure)

[0051] Figure 1 is a schematic perspective structural view of a pinhole detecting apparatus 10 according to an embodiment of the present invention. The pinhole detecting apparatus 10 detects a pinhole 110 formed in an object 100 to be inspected. The pinhole detecting apparatus 10 includes a light source 20, optical lenses 22a, 22b, a detecting unit 24, and a conveying device 26. The detecting unit 24 includes a plurality of optical fibers 30 and at least one detecting element 32. The object 100 to be inspected is conveyed by the conveying device 26 along Figure 1 a direction shown by arrow 120.

[0052] (A-1-2. Light Source 20)

[0053] The light source 20 emits light 50 toward the object 100 to be inspected. For example, the light source 20 is a linear light source including a plurality of lamps (not shown), and these lamps are arranged in a straight line to linearly emit light toward the object 100 to be inspected.

[0054] (A-1-3. Optical Lenses 22a, 22b)

[0055] As Figure 1 shown, the optical lenses 22a, 22b are arranged between the light source 20 and the object 100 to be inspected. When viewed along the direction from the light source 20 to the detecting unit 24 ( Figure 1 the downward direction in [the drawing]), the optical lenses 22a, 22b converge the light 50 from the light source 20 in a direction perpendicular to the longitudinal direction of the light source 20. That is, the optical lenses 22a, 22b converge the light from the light source 20 that propagates in a direction away from the optical axis of the light source 20, so that the light propagates in a direction close to the optical axis of the light source 20.

[0056] The optical lens 22a is a first linear Fresnel lens (hereinafter also referred to as "first linear Fresnel lens 22a" or "first lens 22a"), and is arranged at a position closer to the light source 20 than the optical lens 22b. The first lens 22a is arranged along the longitudinal direction of the light source 20, and refracts the light 50 from the light source 20 into parallel light. That is, the first lens 22a refracts the light from the light source 20 that propagates in a direction away from the optical axis of the light source 20, so that the light becomes parallel to the optical axis.

[0057] Optical lens 22b is a second linear Fresnel lens (hereinafter also referred to as "second linear Fresnel lens 22b" or "second lens 22b"), and is positioned closer to the detection unit 24 than the first optical lens 22a. The second lens 22b is positioned along the longitudinal direction of the light source 20, and along the direction from the light source 20 to the detection unit 24 (…). Figure 1 Looking downwards from the center, the second lens 22b causes the parallel light from the first lens 22a to converge in a direction perpendicular to the longitudinal direction of the light source 20. In other words, the second lens 22b causes the light parallel to the optical axis to converge, thereby causing the light to propagate in a direction close to the optical axis of the light source 20.

[0058] Figure 2 This diagram illustrates the optical characteristics of the optical lens 22b and optical fiber 30 in this embodiment. Figure 2 In this context, θ1 is the maximum polarization angle of the light 50 refracted by the second lens 22b. θ2 is the maximum angle of incidence of the light 50 transmitted by the optical fiber 30 relative to the optical axis 60 of the light source 20. θ2′ is the angle θ2 + 5°. The second lens 22b refracts parallel light in such that the maximum polarization angle θ1 of the light 50 refracted by the second lens 22b is equal to the maximum angle of incidence θ2 relative to the end face of the optical fiber 30. Alternatively, the second lens 22b can refract parallel light in such that the maximum polarization angle θ1 is less than the maximum angle of incidence θ2.

[0059] (A-1-4. Detection Unit 24)

[0060] The detection unit 24 detects the light 50 that is focused by optical lenses 22a and 22b and passes through the pinhole 110 in the object to be inspected 100. In this embodiment, since the light 50 is focused by optical lenses 22a and 22b, the light 50 also passes through the tilted pinhole 110.

[0061] like Figure 1 As shown, the detection unit 24 includes multiple optical fibers 30, at least one detection element 32, and a pinhole determination section (not shown). Each optical fiber 30 transmits light 50 passing through the object to be inspected 100 to the detection element 32 (it should be noted that the optical fiber 30 does not transmit light 50 with an incident angle greater than the maximum incident angle θ2).

[0062] like Figure 1 As shown in magnified section 34, the optical fibers 30 are arranged in a straight line along the longitudinal direction of the light source 20. The end face of the optical fiber 30 near the object under inspection 100 is configured to be parallel to the optical lenses 22a, 22b and the object under inspection 100. Furthermore, in this embodiment, the end face of the optical fiber 30 facing the object under inspection 100 ( Figure 1 The top end face of the lens is positioned at the focal point of the optical lens 22b.

[0063] The detection element 32 is a component that converts light propagating through the optical fiber 30 into an electrical signal, and can be, for example, a photomultiplier tube or a cadmium sulfide (CdS) element. The pinhole detection section determines the presence or absence of a pinhole 110 based on the output of the detection element 32. The pinhole detection section can also be configured to switch the set values ​​(signal strength, number of data points used to calculate the moving average, etc.) of the criteria used to determine the pinhole 110 based on the type of the object under inspection 100, the transmission speed, etc.

[0064] (A-1-5. Conveying Equipment 26)

[0065] The conveying device 26 moves the object to be inspected 100 in a direction perpendicular to the longitudinal direction of the light source 20 and orthogonal to the optical axis of the light source 20. The conveying device 26 includes rollers rotated by an electric motor (not shown) and conveys the object to be inspected 100. Viewed from the light source 20 to the detection unit 24, the conveying device 26 moves in a direction perpendicular to the longitudinal direction of the light source 20. Figure 1 The object to be inspected 100 is moved in the direction indicated by the middle arrow 120. It should be noted that in this embodiment, the object to be inspected 100 moves, while the light source 20, optical lenses 22a, 22b and detection unit 24 are fixed.

[0066] (A-1-6. Item to be inspected 100)

[0067] The object to be inspected 100 is in the form of a strip, and may be, for example, a steel plate, an opaque film, or paper. The object to be inspected 100 may extend along the conveying direction (in the direction shown by arrow 120). When the object to be inspected 100 is a steel plate, its width (length in the direction perpendicular to the scanning direction) may be, for example, 50 centimeters to 1 meter.

[0068] [A-2. Manufacturing Methods (Design Methods)]

[0069] The following describes a manufacturing method (design method) for the pinhole detection device 10 according to this embodiment. In this embodiment, the specifications of each part of the pinhole detection device 10 are set in detail to improve the detection accuracy of the pinhole detection device 10. In one example, the following manufacturing method (design method) may be used.

[0070] The manufacturing personnel (designers) determine the maximum detectable angle θ of the pinhole 110 based on the thickness of the object to be inspected 100 (design value or measured value) and the aperture of the pinhole 110 (assumed value or previous measured value). The maximum detectable angle θ is the maximum angle formed between the pinhole 110, which is the detection target, and the optical axis 60 of the light source 20 when viewed along the longitudinal direction of the light source 20. Figure 2 Since the thickness of the object to be inspected 100 is greater and the aperture of the pinhole 110 is smaller, the possibility of the tilted light 50 passing through the pinhole 110 is smaller. Therefore, the maximum detectable angle θ is set to a smaller angle.

[0071] Subsequently, the manufacturing personnel (designers) determined the maximum incident angle θ2 of the light 50 that can be transmitted by the optical fiber 30 relative to the optical axis 60 of the light source 20. Figure 2 The maximum incident angle θ2 is, for example, within the range of the maximum detectable angle θ+0° to the maximum detectable angle θ+5°. After determining the maximum incident angle θ2, the manufacturer (designer) selects the specifications of the fiber 30 that can achieve the maximum incident angle θ2. The maximum incident angle θ2 is essentially synonymous with numerical aperture (NA) and varies with the material of the fiber 30, the core refractive index, the cladding refractive index, etc. The manufacturer (designer) selects the fiber 30 that can achieve the maximum incident angle θ2 based on this.

[0072] Following this, the manufacturing personnel (designers) set the specifications for the light source 20 and lenses 22a and 22b. For example, when the maximum polarization angle of the optical lens 22b is defined as θ1 ( Figure 2 When manufacturing (designing), the maximum polarization angle θ1 is set in such a way that the maximum incident angle θ2 is contained within the range of θ1+0° to θ1+5°.

[0073] [A-3. Advantages of this embodiment]

[0074] According to this embodiment, when viewed longitudinally along the light source 20 (line light source), if the maximum detectable angle formed between the pinhole 110 (the detection target) and the optical axis 60 of the light source 20 is defined as θ, the maximum incident angle θ2 of the light 50 transmitted by the optical fiber 30 relative to the optical axis 60 is set within the range of θ+0° to θ+5°. In other words, when the maximum detectable angle relative to the optical axis 60 of the light source 20 for detecting the pinhole 110 is defined as θ, the maximum incident angle of the light 50 transmitted by the optical fiber 30 relative to the optical axis 60 of the light source 20 is within the range of θ+0° to θ+5°. This ensures that the pinhole 110, as the detection target, is detected, and it is easy to prevent interference light (or leakage light) from entering the optical fiber 30. Therefore, the signal-to-noise ratio (S / N ratio) of the transmitted light and interference light can be improved, and the detection accuracy of the pinhole 110 can be improved.

[0075] In this embodiment, the light source 20 is a line light source that linearly emits light toward the object to be inspected 100. Optical lenses 22a and 22b converge the light from the light source 20 propagating in a direction away from the optical axis of the light source 20, thereby causing the light to propagate in a direction close to the optical axis of the light source 20. The detection unit 24 includes multiple optical fibers 30 arranged side-by-side and facing the light source 20, and when the maximum polarization angle of the optical lens 22b is defined as θ1, this maximum polarization angle θ1 is set to be greater than or equal to the maximum detectable angle θ. This easily ensures the amount of light required for detecting the pinhole 110.

[0076] In this embodiment, the end face of the optical fiber 30 facing the object to be inspected 100 is located at the focal point of the optical lens 22b. Figure 1 Alternatively, the end face of the optical fiber 30 facing the object 100 can be positioned closer to the object 100 than the focal point of the optical lens 22b. This allows for easy detection of the pinhole 110 even when the object 100 moves relative to the pinhole detection device 10. In other words, when the end face of the optical fiber 30 is positioned at the focal point of the optical lens 22b, the detection unit 24 detects the light transmitted through the pinhole 110 with a rapid rise, and the detection time for this rise is relatively short. Conversely, when the end face of the optical fiber 30 is positioned closer to the object 100 than the focal point of the optical lens 22b, the rise detected by the detection unit 24 due to light transmission through the pinhole 110 is less than in the above configuration, and the detection time for this rise is relatively longer. Therefore, even if the detection of pinhole 110 cannot be achieved in the first setting (located at the focal position of optical lens 22b) due to the moving speed of the object 100, the detection of pinhole 110 can still be achieved in the second setting (located at a position closer to the object 100 than the focal position). Therefore, a higher moving speed of the object 100 can be set in the second setting.

[0077] In this embodiment, the conveying device 26 moves the object to be inspected 100 in a direction perpendicular to the longitudinal direction of the light source 20 and orthogonal to the optical axis 60 of the light source 20 (in the direction shown by arrow 120). Figure 1 Thus, when the object to be inspected 100 is, for example, in the form of a strip, a preferred mode of use can be achieved. Specifically, when the object to be inspected 100 extends along the conveying direction (e.g., a steel plate, opaque film, paper, etc.), it is easy to generate slanted pinholes. This embodiment helps to detect pinholes 110 that are slanted in the conveying direction.

[0078] In this embodiment, a first linear Fresnel lens 22a is provided between the light source 20 and the detection unit 24, which is positioned closer to the light source 20 along its longitudinal direction and a second linear Fresnel lens 22b is positioned closer to the detection unit 24 along its longitudinal direction than the first linear Fresnel lens 22a. Figure 1 The first linear Fresnel lens 22a refracts light 50 from the light source 20 into parallel light. Figure 1 The second linear Fresnel lens 22b refracts parallel light such that the maximum polarization angle θ1 of the light refracted by the optical lens 22b is equal to or less than the maximum incident angle θ2 relative to the end face of the fiber 30. Figure 1 and Figure 2 Thus, parallel light is generated between the first linear Fresnel lens 22a and the second linear Fresnel lens 22b, which helps to adjust the distance between the two Fresnel lenses 22a and 22b.

[0079] <B. Change Plan>

[0080] Needless to say, the present invention is not limited to the embodiments described above, but can be constructed in various ways based on the contents of this specification. For example, the present invention can be constructed as follows.

[0081] [B-1. Light Source]

[0082] In the above embodiment, the light source 20 is a line light source ( Figure 1 However, light source 20 can also be a light source other than a line light source. In the above embodiment, a line light source is used ( Figure 1 However, for example, as shown in Figure 5 of Patent Document 1, multiple light sources 20 may also be used. In the above embodiment, the light source 20 is located on the top side, and the detection unit 24 is located on the bottom side. However, the positions of the light source 20 and the detection unit 24 may also be reversed.

[0083] [B-2. Optical Lens]

[0084] In the above embodiment, a first linear Fresnel lens 22a and a second linear Fresnel lens 22b are used. Figure 1 However, other lenses may also be used.

[0085] [B-3. Detection Unit]

[0086] In the above embodiment, the optical fibers 30 are arranged in a straight line. Figure 1 However, given the fact that pinhole 110 detection is performed over the entire width of the object to be inspected (the length along the longitudinal direction of the light source 20), the arrangement of the optical fibers 30 is not limited to this. Other arrangements of the optical fibers 30 are also possible. For example, the optical fibers 30 may be shifted relative to each other along the longitudinal direction of the light source 20.

[0087] In the above embodiment, the end face of the optical fiber 30 facing the object to be inspected 100 is positioned closer to the object to be inspected than the focal position of the optical lens 22b. Figure 1 However, depending on factors such as the transmission speed of the object to be inspected 100, the end face of the optical fiber 30 may also be located at the focal point of the optical lens 22b.

[0088] [B_4. Conveying Equipment]

[0089] In the above embodiment, the conveying device 26 is used to move the object to be inspected 100 ( Figure 1 However, when performing focused detection on pinhole 110, the transmission device 26 may not be required.

Claims

1. A pinhole detection device, characterized in that, include: A light source, used to emit light onto the object to be inspected; An optical lens is disposed between the light source and the object to be inspected; as well as The detection unit is used to detect the light that is focused by the optical lens and passes through the pinhole in the object to be inspected. The detection unit includes an optical fiber for transmitting light passing through the pinhole in the object under inspection, and When θ is defined as the maximum detectable angle relative to the optical axis of the light source that allows the detection of the pinhole, the maximum incident angle of the light transmitted by the optical fiber relative to the optical axis of the light source is in the range of θ+0° to θ+5°. The optical lens includes a first linear Fresnel lens and a second linear Fresnel lens. The first linear Fresnel lens is positioned closer to the light source along the longitudinal direction of the light source, and the second linear Fresnel lens is positioned closer to the detection unit than the first linear Fresnel lens along the longitudinal direction of the light source. The first linear Fresnel lens refracts light from the light source into parallel light, and Viewed along the longitudinal direction of the light source, the second linear Fresnel lens refracts the parallel light such that the maximum polarization angle of the light refracted by the second linear Fresnel lens is less than or equal to the maximum incident angle relative to the end face of the optical fiber.

2. The pinhole detection device according to claim 1, characterized in that, The light source is a line light source that emits light linearly toward the object to be inspected. The optical lens converges light from the light source that is propagating along the optical axis away from the light source, thereby bringing the light closer to the optical axis of the light source. The detection unit includes multiple optical fibers arranged side-by-side and facing the light source, and When the maximum polarization angle of the optical lens is defined as θ1, the maximum polarization angle θ1 is set to be greater than or equal to the maximum detectable angle θ.

3. The pinhole detection device according to claim 2, characterized in that, The maximum angle of incidence of the light that can be transmitted by each of the optical fibers relative to the optical axis of the light source is within the range of θ1+0° to θ1+5°.

4. The pinhole detection device according to any one of claims 1 to 3, characterized in that, The device includes a conveying device that moves the object to be inspected in a direction perpendicular to the longitudinal direction of the light source and orthogonal to the optical axis of the light source. The end face of the optical fiber facing the object under inspection is located at the focal point of the optical lens, or is located closer to the object under inspection than the focal point of the optical lens.

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