Lens surface defect detection method and device

Abstract

This invention discloses a method and apparatus for detecting surface defects in lenses, specifically for Fresnel lenses. Illumination light is transmitted through a baffle to the lens under test. The baffle has multiple parallel slits for light transmission, creating an alternating light and dark environment. An image of the lens is acquired from the side furthest from the illumination light source. Based on this image, surface defects of the lens are identified. Compared to existing detection methods, this invention makes defects in the acquired image of the lens more readily apparent, enabling the detection of more defects and thus reducing the likelihood of missed defects in the lens surface.

Description

Technical Field

[0001] This invention relates to the field of optical component inspection, and in particular to a method for detecting surface defects in lenses. This invention also relates to an apparatus for detecting surface defects in lenses. Background Technology

[0002] Fresnel lenses are commonly used optical components in the field of optics. For example, with the development of the mobile internet, head-mounted VR devices are being used more and more widely, and Fresnel lenses are an important component in VR devices.

[0003] For manufactured Fresnel lenses, it is necessary to inspect them for defects, such as scratches, dirt, or stuck teeth on the lens surface. Using defective lenses in optical equipment will affect the functionality of the equipment. Based on manual inspection results and experience with Fresnel lenses, it is known that due to the inherent characteristics of Fresnel lenses, Fresnel fringes can also severely affect defects during the inspection process, potentially causing some defects to remain undetected. Therefore, only some defects can be detected, resulting in missed defects and a high defect rate. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting surface defects in lenses and an apparatus for detecting surface defects in lenses, which can reduce the number of missed detections of surface defects in lenses.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for detecting surface defects in Fresnel lenses, comprising:

[0007] Illumination light is passed through a baffle and then irradiated onto the lens under test. An image of the lens under test is acquired from the side of the lens under test away from the illumination light. The baffle is provided with a plurality of parallel slits that allow light to pass through the parallel slits and irradiate the lens under test.

[0008] Based on the image of the lens being tested, defects on the surface of the lens being tested are identified in the image.

[0009] Optionally, the lens under test includes a first region located in the central region, and the illumination light shines on the first region after passing through the baffle, and the optical axis of the illumination light is parallel to the optical axis of the lens under test;

[0010] Identifying defects on the surface of the lens under test in the image includes: identifying defects on the surface of the first region of the lens under test in the image.

[0011] Optionally, the lens being tested includes a second region located in a non-central region, the illumination light is transmitted through the baffle to the second region, and the angle between the optical axis of the illumination light and the optical axis of the lens being tested is greater than 0 degrees;

[0012] Identifying defects on the surface of the lens under test in the image includes: identifying defects on the surface of the second region of the lens under test in the image.

[0013] Optionally, the non-central region of the lens being tested is divided into a plurality of second regions.

[0014] Optionally, the second region is an annular region centered on the center of the lens being tested, and different second regions are at different distances from the center of the lens being tested.

[0015] Optionally, the lens under test is divided into multiple regions by multiple horizontal lines and multiple vertical lines, the multiple regions including a first region containing the center of the lens under test and a second region not containing the center of the lens under test.

[0016] Optionally, acquiring an image of the lens under test includes: focusing an image on any surface of the lens under test;

[0017] Identifying defects on the surface of the lens under test in the image includes: identifying the defects on the surface of the lens under test in the image.

[0018] An apparatus for detecting surface defects in a lens, specifically for Fresnel lenses, includes a light source, a baffle, and an image acquisition device.

[0019] The baffle is disposed between the light source and the lens to be tested. The baffle is provided with a plurality of parallel slits that allow light emitted from the light source to pass through the parallel slits of the baffle and illuminate the lens to be tested.

[0020] The image acquisition device is disposed on the side of the lens being tested away from the illumination light, and is used to acquire an image of the lens being tested from the side of the lens being tested away from the illumination light, so as to identify defects on the surface of the lens being tested in the image.

[0021] Optionally, the width of the slit in the baffle is equal to the width of the interval between two adjacent slits.

[0022] Optionally, an image of the lens under test is acquired through an optical lens, wherein the optical axis extension of the optical lens passes through the slit of the baffle, or the optical axis extension of the optical lens passes through the portion between two adjacent slits of the baffle.

[0023] As can be seen from the above technical solution, the lens surface defect detection method provided by the present invention is used for Fresnel lenses. Specifically, illumination light is emitted through a baffle and then onto the lens under test. The baffle is provided with multiple parallel slits for light transmission. The illumination light shines through the parallel slits onto the lens under test, forming an alternating light and dark lighting environment. An image of the lens under test is acquired from the side of the lens away from the illumination light, and then the defects on the surface of the lens under test are identified in the image. Compared with existing detection methods, the present invention makes the defects of the lens under test more easily visible in the obtained image of the lens under test, and can detect more defects on the lens under test, thus reducing the missed detection of lens surface defects.

[0024] The present invention provides a device for detecting defects on the surface of lenses, which can achieve the above-mentioned beneficial effects. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A flowchart of a method for detecting surface defects of a lens provided in an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of a lens surface defect detection method provided in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of lens inspection using a device for detecting surface defects in lenses provided in an embodiment of the present invention;

[0029] Figure 4 This is a side sectional view of a Fresnel lens according to an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram illustrating the division of the lens to be tested into multiple regions in one embodiment of the present invention;

[0031] Figure 6 This is yet another schematic diagram of lens inspection using a device for detecting surface defects in lenses provided in an embodiment of the present invention;

[0032] Figure 7 This is a schematic diagram illustrating the division of the lens to be tested into multiple regions in another embodiment of the present invention;

[0033] Figure 8-1 This is a schematic diagram showing the optical axis extension of the optical lens passing through the baffle slit during detection in one embodiment of the present invention;

[0034] Figure 8-2 To adopt Figure 8-1 A schematic diagram of an image obtained by focusing imaging on the surface of the lens under test in the manner shown.

[0035] Figure 9-1 This is a schematic diagram showing the portion of the optical axis extension line of the optical lens passing between two adjacent slits of the baffle during detection in another embodiment of the present invention;

[0036] Figure 9-2 To adopt Figure 9-1 The image obtained by focusing the imaging of the surface of the lens being tested is shown in the diagram. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0038] Based on previous manual inspection results and experience with Fresnel lenses, the inventors know that due to the inherent characteristics of Fresnel lenses—their surface has a serrated structure and a certain curvature—the resulting Fresnel fringes during inspection can severely affect defects, potentially preventing some defects from being detected. Existing technologies cannot effectively remove these Fresnel fringes, thus only some defects can be detected, leading to missed detections and a high defect rate. To address this, the present invention provides a method and apparatus for detecting lens surface defects. The method creates an alternating light and dark illumination environment for the lens under inspection and acquires images of the lens. The inventors have found that, compared to existing inspection methods, defects in the acquired images of the lens are more easily revealed, enabling the detection of more defects, reducing missed detections, and improving lens yield.

[0039] Please refer to Figure 1 , Figure 1 A flowchart of a lens surface defect detection method provided in this embodiment is shown in the figure. The lens surface defect detection method for Fresnel lenses includes the following steps:

[0040] S11: The illumination light passes through the baffle and illuminates the lens under test. An image of the lens under test is acquired from the side of the lens under test away from the illumination light. The baffle is provided with a plurality of parallel slits that allow the illumination light to pass through the parallel slits and illuminate the lens under test.

[0041] For reference Figure 2 , Figure 2 This is a schematic diagram of a lens surface defect detection method provided in this embodiment. A baffle 101 is disposed on one side of the lens 100 to be tested. Illumination light passes through the baffle 101 and illuminates the lens 100 to be tested. An image of the lens 100 to be tested is obtained from the other side of the lens 100.

[0042] The baffle 101 is provided with multiple parallel slits that allow light to pass through. When the illumination light reaches the baffle 101, at least part of the light can pass through when it shines on the parallel slits of the baffle 101, while the light is blocked when it shines on the gaps between the parallel slits of the baffle 101. Therefore, after the illumination light passes through the baffle 101, it forms an alternating bright and dark lighting environment and illuminates the lens 100 being tested.

[0043] S12: Based on the image of the lens being tested, identify defects on the surface of the lens being tested in the image.

[0044] Compared with existing detection methods, the lens surface defect detection method of this embodiment makes the defects of the lens more visible in the obtained image of the lens being tested, and can detect more defects on the lens being tested, thus reducing the chance of missed detection of lens surface defects.

[0045] The lens 100 under test typically comprises multiple surfaces, and each surface of the lens 100 can be inspected separately. Specifically, acquiring an image of the lens 100 under test includes focusing an image on any surface of the lens 100 under test. Correspondingly, identifying defects on the surface of the lens 100 under test in the image includes identifying the defects on that surface of the lens 100 under test in the image. For example, when illumination light is shone on the lens 100 under test, focusing an image on the upper surface of the lens 100 under test obtains an image of the upper surface, and checking whether there are defects on that surface of the lens 100 under test based on the image; if defects are found, they are identified.

[0046] In some embodiments, the lens 100 under test includes a first region located in its central area, and the illumination light, after passing through the baffle 101, illuminates the first region, with the optical axis of the illumination light parallel to the optical axis of the lens 100 under test. Accordingly, identifying defects on the surface of the lens 100 under test in the image includes: identifying defects on the surface of the first region of the lens 100 under test in the image. Examples may be referenced. Figure 3 , Figure 3 This is a schematic diagram of a lens inspection using a device for detecting surface defects of a lens provided in this embodiment. As shown in the figure, the optical axis of the light source 102 is parallel to the optical axis of the lens being inspected 100, so that the optical axis of the illumination light emitted by the light source 102 is parallel to the optical axis of the lens being inspected 100.

[0047] For Fresnel lenses, one surface is etched with concentric rings of increasing size, while the other surface is a smooth, curved surface, either spherical or aspherical. Examples are available for reference. Figure 4 , Figure 4 The figure shows a side cross-sectional view of a Fresnel lens according to an embodiment. The first surface 104 of the lens is smooth, and the second surface 105 is etched with a serrated texture. This texture is designed based on light interference and perturbation, as well as relative sensitivity and receiving angle requirements. The curvature of the central and edge regions of the same surface of the Fresnel lens will differ, and the edge region of the lens is thinner. An example can be referenced. Figure 5 , Figure 5 This is a schematic diagram illustrating the division of the lens under test into multiple regions in one embodiment. As shown in the figure, the lens under test 100 is divided into a first region (i.e., region A in the figure) and multiple second regions (including regions B and C in the figure). The first region, region A, is located in the central region of the lens under test 100, and the second regions are annular regions centered on the center of the lens under test 100. For the first region, region A, of the lens under test 100, defects in the first region can be detected using the method described in the above embodiments. More specifically, for the first region, region A, of the lens under test 100, a surface with serrated edges in region A can be focused and imaged, and the defects of this surface in region A can be detected based on the obtained image; alternatively, another smooth surface in region A can be focused and imaged, and the defects of this smooth surface in region A can be detected based on the obtained image.

[0048] In other embodiments, the lens 100 under test includes a second region located in a non-central area, the illumination light passing through the baffle 101 and illuminating the second region, the angle between the optical axis of the illumination light and the optical axis of the lens 100 under test being greater than 0 degrees. Accordingly, identifying defects on the surface of the lens 100 under test in the image includes: identifying defects on the surface of the second region of the lens 100 under test in the image. Examples are available for reference. Figure 6 , Figure 6 As shown in the figure, the optical axis of the light source 102 is not parallel to the optical axis of the lens 100 being tested, and the angle between them is greater than 0 degrees. This causes the optical axis of the illumination light emitted by the light source 102 to be non-parallel to the optical axis of the lens 100 being tested, resulting in the illumination light being obliquely irradiated onto the lens 100 being tested.

[0049] Fresnel lenses have different curvatures in the central and edge regions of the same surface, and the edge region is thinner. The inventors discovered that when inspecting the non-central region of the lens 100 under test, if the optical axis of the illumination light is still parallel to the optical axis of the lens 100, the non-central region of the lens 100 will be relatively dark in the acquired image, failing to form a normal image and thus failing to reveal surface defects. To address this, when inspecting the non-central region of the lens 100, if the angle between the optical axis of the illumination light and the optical axis of the lens 100 is set greater than 0 degrees (i.e., the illumination light is tilted towards the lens 100), the acquired image is clearer.

[0050] In this embodiment, the angle between the optical axis of the illumination light and the optical axis of the lens under test 100 is determined by the surface curvature of the second region and the angle of the teeth set in the second region. The angle of the teeth can be understood as the angle between the line connecting the top and bottom ends of the teeth and the normal to the lens surface. During inspection, the angle between the optical axis of the illumination light and the optical axis of the lens under test 100 must be such that defects on the surface of the second region are displayed as clearly as possible in the acquired image. In practical applications, for a non-central region of the lens, a suitable angle can be found through multiple experiments and adjustments to the angle between the optical axis of the illumination light and the optical axis of the lens under test 100.

[0051] More preferably, the non-central region of the lens 100 under test can be divided into multiple second regions. The non-central region of the lens 100 is relatively large, and the surface curvature may differ at different locations. By dividing it into multiple regions, each second region of the lens 100 can be tested sequentially. In this embodiment, the number of second regions into which the non-central region of the lens 100 under test is divided is not limited; it can be determined based on the size and curvature of the lens 100 in practical applications. For different second regions on the lens 100 under test, the angle between the optical axis of the illumination light and the optical axis of the lens 100 under test can be different during testing.

[0052] In some embodiments, the first region is the region encompassing the center of the lens 100 being tested, and the second region can be an annular region centered on the center of the lens 100 being tested. Different second regions are located at different distances from the center of the lens 100 being tested. Examples are available for reference. Figure 5 The lens 100 under test is divided into two second regions, namely region B and region C. Region B is located outside region A, and region C is located outside region B. Regions B and C of the lens 100 under test can be imaged and tested by tilting the illumination light.

[0053] In other embodiments, the lens under test 100 can be divided into multiple regions by multiple horizontal lines and multiple vertical lines, including a first region containing the center of the lens under test 100 and a second region not containing the center of the lens under test 100. Examples are available for reference. Figure 7 , Figure 7 This is a schematic diagram illustrating the division of the lens under test into multiple regions in another embodiment. As shown, the lens under test 100 is divided into nine regions by two horizontal lines and two vertical lines. The region containing the center of the lens under test 100 is the first region. The remaining eight are the second regions, including regions 1 to 8. For regions 1 to 8, illumination is applied with the optical axis of the illumination light tilted relative to the optical axis of the lens under test 100.

[0054] This embodiment provides a device for detecting surface defects in lenses, specifically for Fresnel lenses. (See reference for details.) Figure 3 or Figure 6 The device includes a light source 102, a baffle 101, and an image acquisition device 103;

[0055] The baffle 101 is disposed between the light source 102 and the lens 100 to be tested. The baffle 101 is provided with a plurality of parallel slits that allow light emitted from the light source 102 to pass through the parallel slits of the baffle 101 and illuminate the lens 100 to be tested.

[0056] The image acquisition device 103 is disposed on the side of the lens 100 to be tested that is away from the illumination light, and is used to acquire an image of the lens 100 to be tested from the side of the lens 100 to be tested that is away from the illumination light, so as to identify defects on the surface of the lens 100 to be tested in the image.

[0057] Compared with existing detection methods, the apparatus for detecting surface defects of lenses according to this embodiment makes it easier to show the defects of the lens in the obtained image of the lens being tested, thereby enabling the detection of more defects on the lens and reducing the chance of missed detection of surface defects of lenses.

[0058] In this embodiment, the type and structure of the light source 102 are not limited, nor is the wavelength range of the illumination light limited. Blue light is preferred, as it has a better effect on revealing defects on the lens.

[0059] Preferably, the width of the slits in the baffle 101 is equal to the width of the interval between two adjacent slits, so that the illumination light passing through the baffle 101 forms an alternating light intensity distribution of light and dark, and the light intensity distribution is relatively uniform. In this embodiment, the width of the slits on the baffle 101 and the width of the interval between two adjacent slits are not specifically limited. In practical applications, the width of the slits on the baffle 101 and the width of the interval between two adjacent slits should be such that defects can be displayed as clearly as possible in the acquired image.

[0060] Optionally, during inspection, an image of the lens 100 under inspection can be acquired via an optical lens, wherein the optical axis extension of the optical lens passes through the slit of the baffle 101, or the optical axis extension of the optical lens passes through the portion between two adjacent slits of the baffle 101. An example may be referenced. Figure 8-1 and Figure 8-2 , Figure 8-1 This is a schematic diagram showing the optical axis extension of the optical lens passing through the baffle slit during detection in one embodiment. Figure 8-2 To adopt Figure 8-1 The diagram shows an image obtained by focusing the image onto the surface of the lens being tested. Figure 9-1 and Figure 9-2 , Figure 9-1 This is a schematic diagram showing the portion of the optical axis extension of the optical lens passing through the space between two adjacent slits of the baffle during detection in another embodiment. Figure 9-2 To adopt Figure 9-1 This diagram illustrates an image obtained by focusing the image onto the surface of the lens being tested. Figure 8-1 The optical axis extension line of the optical lens 106 passes through the slit of the baffle 101, in Figure 9-1 The optical axis extension line of the optical lens 106 passes through the portion between two adjacent slits of the baffle 101. (Comparison) Figure 8-2 and Figure 9-2 As can be seen, the grayscale display of bright and dark stripes in the acquired images is exactly opposite under these two methods, and the appearance of defects in the two images is not significantly different when all other conditions are the same. In practical applications, both image acquisition methods can be used.

[0061] In addition, regarding the lighting method for different areas of the lens 100 under test and the specific implementation method for detecting different surfaces of the lens 100 under test in this embodiment, please refer to the detailed description of the implementation method of the lens surface defect detection method above, and will not be repeated here.

[0062] The present invention has provided a detailed description of a method and apparatus for detecting surface defects in lenses. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of these embodiments are merely illustrative of the method and its core concepts. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for detecting surface defects in lenses, used for Fresnel lenses, characterized in that, include: The lens under test includes a first region located in the central area. Illumination light is emitted onto the first region after passing through a baffle. The optical axis of the illumination light is parallel to the optical axis of the lens under test. An image of the lens under test is acquired from the side of the lens under test away from the illumination light. The baffle is provided with a plurality of parallel slits that allow the illumination light to pass through the parallel slits and illuminate the lens under test. Defects on the surface of the first region of the lens under test are identified in the image of the lens under test. The lens under test includes a second region located in a non-central area. The second region is an annular area centered on the center of the lens under test. Illumination light is emitted into the second region after passing through the baffle. The angle between the optical axis of the illumination light and the optical axis of the lens under test is greater than 0 degrees. The angle between the optical axis of the illumination light and the optical axis of the lens under test is determined by the surface curvature of the second region and the angle of the teeth set in the second region. The angle of the teeth is the angle between the line connecting the top and bottom ends of the teeth and the normal of the lens surface. An image of the lens under test is acquired from the side of the lens under test away from the illumination light. In the image of the lens under test, defects on the surface of the second region of the lens under test are identified. When inspecting the second region, the angle between the optical axis of the illumination light and the optical axis of the lens under test must satisfy the requirement that as many defects on the surface of the second region as possible are clearly displayed in the acquired image. Through multiple experiments and multiple adjustments to the angle between the optical axis of the illumination light and the optical axis of the lens under test, the angle that makes as many defects on the surface of the second region as possible clearly displayed in the acquired image is found.

2. The method for detecting surface defects of a lens according to claim 1, characterized in that, The non-central region of the lens being tested is divided into multiple second regions.

3. The method for detecting surface defects of a lens according to claim 2, characterized in that, The distance from the second region to the center of the lens being tested varies.

4. The method for detecting surface defects of a lens according to claim 1, characterized in that, The lens under test is divided into multiple regions by multiple horizontal lines and multiple vertical lines. The multiple regions include a first region containing the center of the lens under test and a second region not containing the center of the lens under test.

5. The method for detecting surface defects of a lens according to any one of claims 1-4, characterized in that, Acquiring an image of the lens under test includes: focusing and imaging any surface of the lens under test; Identifying defects on the surface of the lens under test in the image includes: identifying the defects on the surface of the lens under test in the image.

6. An apparatus for detecting surface defects in lenses, specifically for Fresnel lenses, characterized in that, Includes a light source, a baffle, and an image acquisition device; The baffle is disposed between the light source and the lens to be tested. The baffle has a plurality of parallel slits that allow light emitted from the light source to pass through the parallel slits of the baffle and illuminate the lens to be tested. The image acquisition device is disposed on the side of the lens being tested away from the illumination light, and is used to acquire an image of the lens being tested from the side of the lens being tested away from the illumination light, so as to identify defects on the surface of the lens being tested in the image based on the image of the lens being tested; The lens under test includes a first region located in the central region. The illumination light passes through the baffle and illuminates the first region. The optical axis of the illumination light is parallel to the optical axis of the lens under test. Identifying defects on the surface of the lens under test in the image includes: identifying defects on the surface of the first region of the lens under test in the image; The lens under test includes a second region located in a non-central area. The second region is an annular region centered on the center of the lens under test. The illumination light passes through the baffle and illuminates the second region. The angle between the optical axis of the illumination light and the optical axis of the lens under test is greater than 0 degrees. The angle between the optical axis of the illumination light and the optical axis of the lens under test is determined by the surface curvature of the second region and the angle of the teeth set in the second region. The angle of the teeth is the angle between the line connecting the top and bottom ends of the teeth and the normal of the lens surface. Identifying defects on the surface of the lens under test in the image includes: identifying defects on the surface of the second region of the lens under test in the image. When detecting the second region, the angle between the optical axis of the illumination light and the optical axis of the lens under test must satisfy the requirement that as many defects on the surface of the second region as possible are clearly displayed in the acquired image. Through multiple experiments and multiple adjustments to the angle between the optical axis of the illumination light and the optical axis of the lens under test, the angle that makes as many defects on the surface of the second region as possible clearly displayed in the acquired image is found.

7. The apparatus for detecting surface defects of a lens according to claim 6, characterized in that, The width of the slit in the baffle is equal to the width of the interval between two adjacent slits.

8. The apparatus for detecting surface defects of a lens according to claim 6, characterized in that, An image of the lens under test is acquired through an optical lens, wherein the optical axis extension of the optical lens passes through the slit of the baffle, or the optical axis extension of the optical lens passes through the portion between two adjacent slits of the baffle.

Images