Telecentric lens and mechanical vision inspection apparatus
By using a combination of a beam splitter and multiple lens modules in a telecentric lens, the problem of low imaging quality was solved, achieving high-precision and high-resolution imaging effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENZHEN DONGZHENG OPTICAL TECH CO LTD
- Filing Date
- 2023-02-09
- Publication Date
- 2026-06-23
AI Technical Summary
Existing telecentric lenses have low imaging quality and low precision, mainly due to light interference causing a decline in imaging quality.
A beam splitter is used to reflect the light emitted by the light source onto the object being measured. By combining the first lens module, the first lens group, the second lens group, and the third lens module, light interference is reduced, and measurement accuracy and imaging quality are improved.
By reducing light interference, imaging quality and measurement accuracy are improved, chromatic aberration and distortion are reduced, and high-resolution imaging is achieved.
Smart Images
Figure CN116149032B_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the technical field of machine vision, and more specifically, relates to a telecentric lens and a machine vision inspection device. Background Technology
[0002] Machine vision, a branch of artificial intelligence, uses machines to perform measurements and judgments instead of human eyes. With the rapid development of artificial intelligence, the requirements for machine vision imaging systems are becoming increasingly stringent. Various industrial lenses have emerged on the market, among which telecentric lenses, due to their unique technological advantage of maintaining image magnification regardless of object distance, are widely used in precision measurement, non-contact optical measurement, and other fields.
[0003] Existing telecentric lenses typically include a first lens, a second lens, a beam splitter, and a light source. The first lens, second lens, and beam splitter are arranged sequentially along the direction of light propagation, with the light source located above the beam splitter. The beam splitter reflects the light emitted from the light source and transmits it through the first and second lenses to the object being measured, thus illuminating the object. At the same time, the beam splitter directly reflects some light onto the image plane, causing interference with the light reflected from the object, interfering with imaging and resulting in low image quality. Summary of the Invention
[0004] The purpose of this application is to provide a telecentric lens and a machine vision inspection device to solve the technical problems of low imaging quality and low accuracy in the prior art.
[0005] To achieve the above objectives, one of the technical solutions adopted in this application is: providing a telecentric lens, comprising:
[0006] The first lens module has a positive optical power.
[0007] The second lens module includes a light source, a beam splitter, and a first lens group and a second lens group for reducing the chromatic aberration of the telecentric lens. The light source is disposed on the beam splitter, which is used to reflect the light emitted by the light source to illuminate the object under test and to transmit the light from the first lens group to the second lens group. The optical power of the second lens module is negative.
[0008] The third lens module has a positive optical power.
[0009] The first lens module, the first lens group, the beam splitter, the second lens group, and the third lens module are arranged sequentially along the direction of light propagation.
[0010] By adopting the above technical solution, the beam splitter reflects the light emitted by the light source onto the object to be measured so that the object to be measured is illuminated. The light reflected by the object to be measured is converged by the first lens module, and then the chromatic aberration is reduced by the first lens group. Then, it passes through the second lens group to further reduce the chromatic aberration of the telecentric lens. Finally, it is directed to the third lens module for converging imaging. Among them, the beam splitter is located between the first lens group and the second lens group. On the one hand, the beam splitter is closer to the object to be measured, so that the light emitted by the light source reaches the object to be measured through the transmission of fewer lenses, which can better illuminate the object to be measured, reduce the generation and propagation of stray light, and improve the measurement accuracy. On the other hand, there is a second lens group between the beam splitter and the image side, which reduces the number of times that the light is directly reflected to the image side without being reflected by the object to be measured, and avoids the light emitted by the light source directly hitting the imaging plane and interfering with the imaging, thereby improving the imaging quality.
[0011] In one embodiment, the first lens group includes a second lens and a third lens for reducing the chromatic aberration of the telecentric lens; the third lens is connected to the side of the second lens close to the beam splitter;
[0012] The second lens is a biconvex lens with positive optical power, and the refractive index of the second lens satisfies: 1.43 < n < 1.50, and the Abbe number of the second lens satisfies: 81 < v < 96;
[0013] The third lens is a concave lens with negative optical power, and the refractive index of the third lens satisfies: 1.71 < n < 1.8, and the Abbe number of the third lens satisfies: 41 < v < 49.
[0014] By adopting the above technical solution, the light is first converged and then diverged, removing a part of the stray light and reducing the chromatic aberration. The combination of the second lens with a high Abbe number and the third lens with a low Abbe number, as well as different refractive indices, forms a doublet achromatic lens group, which greatly reduces the chromatic aberration of the telecentric lens.
[0015] Optionally, the second lens is made of an anomalous dispersion material, and the anomalous dispersion material includes calcium fluoride, silica glass containing an inorganic phosphorous oxide / boron compound, fluorite, etc.
[0016] By adopting the above technical solution, the lens made of the above materials can effectively eliminate the chromatic aberration of the telecentric lens and improve the resolution.
[0017] In one embodiment, the first lens group further includes a fourth lens disposed between the third lens and the beam splitter. The fourth lens is a meniscus lens with positive optical power, and the concave surface of the fourth lens faces the side where the third lens is located.
[0018] By adopting the above technical solutions, in the first aspect, the fourth lens with positive optical power utilizes its meniscus shape to converge the incident light beam, reduce its divergence, and thus reduce the chromatic aberration of the lens; in the second aspect, the cooperation between the fourth lens and the first lens group can reduce the spherical aberration and lateral chromatic aberration of the lens.
[0019] Optionally, the refractive index of the fourth lens satisfies: 1.78 < n < 1.85, and the Abbe number of the fourth lens satisfies: 23 < v < 26.
[0020] By adopting the above technical solutions, the positive distortion generated by the fourth lens is complementary to the negative distortion generated by the second and third lenses, thereby reducing the distortion of the lens, reducing the image distortion, and improving the imaging quality.
[0021] In one embodiment, the second lens group includes a fifth lens and a sixth lens for reducing the chromatic aberration of the telecentric lens, and the sixth lens is connected to the side of the fifth lens away from the beam splitter; the fifth lens has positive optical power, and the sixth lens has negative optical power.
[0022] By adopting the above technical solutions, similar to the function of the first lens group, it can further reduce the chromatic aberration of the telecentric lens.
[0023] Optionally, the refractive index of the fifth lens satisfies: 1.59 < n < 1.64, and the Abbe number of the fifth lens satisfies: 65 < v < 69; the refractive index of the sixth lens satisfies: 1.59 < n < 1.62, and the Abbe number of the sixth lens satisfies: 38 < v < 45.
[0024] By adopting the above technical solutions, the combination of lenses with high and low Abbe numbers further reduces the chromatic aberration of the telecentric lens.
[0025] In one embodiment, the second lens group further includes an aperture for constraining the width and intensity of light and a seventh lens for diffusing the light constrained by the aperture, and the aperture, the seventh lens, and the third lens module are arranged in sequence along the light propagation direction; the seventh lens has negative optical power.
[0026] By adopting the above technical solutions, the aperture constrains the light transmitted through the first lens group, controls the width and intensity of the light, and the seventh lens diffuses the light constrained by the aperture, preventing all stray light from entering the third lens module and causing image distortion or forming ghost images.
[0027] Optionally, the distance between the aperture and the sixth lens is less than the distance between the aperture and the seventh lens.
[0028] By adopting the above technical solution, this distance allows light with a width and intensity within a better range to enter the aperture, thereby controlling the quality of the image.
[0029] Optionally, the aperture stop is an aperture stop.
[0030] By adopting the above technical solution, the aperture stop can block rays that are significantly deviated from the paraxial direction in the beam, which helps to improve the clarity, brightness and depth of field of the image.
[0031] In one embodiment, the seventh lens is a biconvex lens;
[0032] Alternatively, the seventh lens may be a plano-concave lens, with the concave surface of the seventh lens facing the side where the aperture is located.
[0033] By adopting the above technical solution, it is beneficial to diffuse light and prevent stray light from flooding into the third lens module and causing ghosting.
[0034] In one embodiment, the third lens module is a meniscus lens, and the concave surface of the third lens module faces the side where the second lens module is located; the third lens module and the second lens group form a quasi-symmetrical structure about the aperture to correct coma and dispersion.
[0035] By adopting the above technical solution, on the one hand, the positive and negative distortions produced by the third lens module and the seventh lens complement each other, reducing lens distortion and thus improving image quality and accuracy; on the other hand, the second lens group composed of the fifth and sixth lenses, with the aperture stop as the boundary, forms a quasi-symmetrical structure with the seventh lens and the third lens module, reducing coma and chromatic aberration in the telecentric lens. The so-called quasi-symmetrical structure means that the four lenses are approximately symmetrical about each other on both sides of the aperture stop, and the optical power of the four lenses is symmetrical on both sides, namely positive, negative, negative, and positive respectively. After being converged by the fifth lens, the light is diffused by the sixth lens, constrained by the aperture stop, and then diffused by the seventh lens, preventing stray light from flooding into the third lens module and causing ghosting. The light enters the third lens module for convergence, so that the imaging light converges on the ideal imaging plane, thereby correcting coma.
[0036] In one embodiment, the third lens module further includes an eighth lens for converging the light transmitted through the second lens group and a ninth lens for reducing the light deflection angle.
[0037] The eighth lens is a meniscus lens with positive optical power, and the concave surface of the eighth lens faces the side where the second lens module is located.
[0038] The ninth lens is a meniscus lens with a positive optical power; the concave surface of the ninth lens faces away from the side where the second lens module is located; the refractive index of the ninth lens satisfies: 1.70 < n < 1.92, and the Abbe number of the ninth lens satisfies: 35 < v < 53.
[0039] By adopting the above technical solution, the eighth lens performs the first convergence on light rays, enabling the imaging light rays to converge on the ideal imaging plane as much as possible; the ninth lens uses a material with a high refractive index and low dispersion to cope with the large deflection angle of light rays. Using a material with a low refractive index will result in an overly large lens curvature or an overly thick lens, making it difficult to process.
[0040] In one embodiment, the first lens module includes a first lens with a positive optical power, and the diameter of the first lens is between 40 mm and 73.76 mm;
[0041] Or, the first lens module includes a cemented lens with a positive optical power, and the diameter of the cemented lens is between 40 mm and 73.76 mm.
[0042] By adopting the above technical solution, with a diameter between 40 mm and 73.76 mm, it can ensure the large target surface, large aperture, and high telecentricity of the telecentric lens, while reducing the conjugate distance and making the overall volume of the telecentric lens smaller.
[0043] Optionally, the full image height and the overall optical length of the telecentric lens satisfy the following conditional formula: 0.088 ≤ H / L ≤ 0.127;
[0044] Where, H is the full image height of the telecentric lens, and L is the overall optical length of the telecentric lens.
[0045] By adopting the above technical solution, H / L satisfying the above conditional formula can ensure the proportion of the telecentric lens and meet the volume requirements of the telecentric lens.
[0046] The embodiment of the present application further provides a machine vision detection device, including the above telecentric lens.
[0047] By adopting the above technical solution, only by adjusting the lens surface types and materials of the first lens module and the third lens module and sharing the second lens module, the magnification change of the lens can be achieved; thus, for the research and development and manufacturing of products in the same series, the cost can be effectively reduced and the research and development difficulty can be reduced. Description of the Drawings
[0048] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0049] Figure 1 This is a 2D structural schematic diagram of a telecentric lens with a magnification of 0.64x in an embodiment of this application;
[0050] Figure 2 The MTF diagram is shown for a telecentric lens with a magnification of 0.64x in this embodiment of the application.
[0051] Figure 3 The distortion diagram is shown for a telecentric lens with a magnification of 0.64x in the example of this application.
[0052] Figure 4 This is an axial chromatic aberration diagram of a telecentric lens with a magnification of 0.64x in the example of this application;
[0053] Figure 5 This is a 2D structural diagram of a telecentric lens with a magnification of 0.91x in an embodiment of this application;
[0054] Figure 6 The MTF diagram is shown for a telecentric lens with a magnification of 0.91x in this embodiment of the application.
[0055] Figure 7 The distortion diagram is shown for a telecentric lens with a magnification of 0.91x in the example of this application.
[0056] Figure 8 This is an axial chromatic aberration diagram of a telecentric lens with a magnification of 0.91x in the example of this application.
[0057] The following are the labeling elements in the figure:
[0058] 10. First lens module; 11. First lens;
[0059] 20. Second lens module; 21. First lens group; 211. Second lens; 212. Third lens; 213. Fourth lens section; 22. Beam splitter; 23. Second lens group; 231. Fifth lens; 232. Sixth lens; 233. Aperture stop; 234. Seventh lens;
[0060] 30. Third lens module; 31. Eighth lens; 32. Ninth lens;
[0061] 100, object side; 200, image side; 300, imaging plane. Detailed Implementation
[0062] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.
[0063] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.
[0064] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0065] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.
[0066] Please see Figure 1 or Figure 5 The telecentric lens provided in this application includes a first lens module 10, a second lens module 20, and a third lens module 30. The optical power of the first lens module 10 is positive, the optical power of the second lens module 20 is negative, and the optical power of the third lens module 30 is positive. The second lens module 20 includes a first lens group 21, a beam splitter 22, a second lens group 23, and a light source 24. The first lens group 21 and the second lens group 23 are used to reduce the chromatic aberration of the telecentric lens. The beam splitter 22 is used to reflect the light emitted by the light source 24 to illuminate the object under test and to transmit the light emitted by the first lens group 21 to the second lens group 23. The first lens module 10, the first lens group 21, the beam splitter 22, the second lens group 23, and the third lens module 30 are arranged sequentially along the direction of light propagation.
[0067] The beam splitter 22 reflects the light emitted by the light source 24 onto the object to be measured so that the object to be measured is illuminated. The light reflected by the object to be measured is converged by the first lens module 10, and then the chromatic aberration is reduced by the first lens group 21. Then, it is transmitted through the second lens group 23 to further reduce the chromatic aberration of the telecentric lens. Finally, it is directed to the third lens module 30 for converging imaging. Among them, the beam splitter 22 is located between the first lens group 21 and the second lens group 23. The beam splitter 22 partially reflects the light emitted by the light source 24 onto the object to be measured (i.e., the object side 100), and part of the light is reflected to the image side 200. On the one hand, the beam splitter 22 is closer to the object to be measured, so that the light emitted by the light source 24 reaches the object side 100 through the transmission of fewer lenses, which can better illuminate the object to be measured to improve the measurement accuracy. The first lens group 21 diffuses the light reflected by the object to be measured, and cooperates with the beam splitter 22 to reduce the stray light entering the second lens group 23. On the other hand, there is a second lens group 23 between the beam splitter 22 and the third lens module 30. The second lens group 23 diffuses the light, reducing the number of times the light is directly reflected to the third lens module 30 without being reflected by the object to be measured, avoiding the light emitted by the light source from directly hitting the third lens module 30 and interfering with imaging, thereby improving the imaging quality.
[0068] In an embodiment of the present application, please continue to refer to Figure 1 or Figure 5 , the first lens group 21 includes a second lens 211 and a third lens 212. The third lens 212 is connected to the side of the second lens 211 close to the beam splitter 22. The second lens 211 is a biconvex lens, and the optical power of the second lens 211 is positive. The refractive index of the second lens 211 satisfies 1.43 < n < 1.50, and the Abbe number of the second lens 211 satisfies: 81 < v < 96. The second lens 211 is used to reduce the chromatic aberration of the telecentric lens. The third lens 212 is a concave lens, and the optical power of the third lens 212 is negative. The refractive index of the third lens 212 satisfies 1.71 < n < 1.8, and the Abbe number of the third lens 212 satisfies: 41 < v < 49. The third lens 212 is used to reduce the chromatic aberration of the telecentric lens. In this way, the second lens 211 with a high Abbe number and the third lens 212 with a low Abbe number, as well as the settings of different refractive indices, form the first lens group 21 that is beneficial to achromatism. The convex lens with positive optical power generates positive spherical aberration, and the concave lens with negative optical power generates negative spherical aberration, and the two are offset. At the same time, the edge thickness of the meniscus lens is larger than the center thickness, which can effectively reduce spherical aberration.
[0069] Optionally, the second lens 211 and the third lens 212 are glued to form a double-glued achromatic first lens group 21, and the gluing method is simple and stable.
[0070] Optionally, the second lens 211 is made of an anomalous dispersion material, which includes materials such as calcium fluoride, silica glass containing an inorganic phosphorous oxide / boron compound, and fluorite. By using the above materials, the chromatic aberration of the telecentric lens can be effectively eliminated, the resolution can be improved, and the imaging can be made clearer.
[0071] In an embodiment of the present application, please refer to Figure 1 or Figure 5 , the first lens group 21 further includes a fourth lens, the fourth lens is disposed between the third lens 212 and the beam splitter 22, the fourth lens is a meniscus lens, and the concave surface of the fourth lens faces the side where the third lens 212 is located, and the optical power of the fourth lens is positive. The fourth lens converges the light rays transmitted through the second lens 211 and the third lens 212, reduces the divergence of the light rays, and thus reduces the chromatic aberration of the lens; by using the meniscus shape, it is beneficial to reduce the spherical aberration and lateral chromatic aberration of the lens in cooperation with the second lens 211 and the third lens 212; in addition, the positive distortion generated by the fourth lens is complementary to the negative distortion generated by the second lens 211 and the third lens 212, thereby reducing the distortion of the lens, reducing the image distortion, and improving the imaging quality.
[0072] Optionally, the refractive index of the fourth lens satisfies: 1.78 < n < 1.85, and the Abbe number satisfies: 23 < v < 26. This is beneficial to the diffusion of light.
[0073] In an embodiment of the present application, please refer to Figure 1 or Figure 5 , the second lens group 23 includes a fifth lens 231 and a sixth lens 232, the sixth lens 232 is connected to the side of the fifth lens 231 away from the beam splitter 22; the optical power of the fifth lens 231 is positive, and the optical power of the sixth lens 232 is negative. It has the same function as the second lens 211 and the third lens 212, and further reduces the chromatic aberration of the lens.
[0074] Optionally, the refractive index of the fifth lens 231 satisfies: 1.59 < n < 1.64, and the Abbe number of the fifth lens 231 satisfies: 65 < v < 69; the refractive index of the sixth lens 232 satisfies: 1.59 < n < 1.62, and the Abbe number of the sixth lens 232 satisfies: 38 < v < 45. The combination of high and low Abbe numbers and different refractive indices forms a doublet achromatic lens group, which is the same as the combination of the second lens 211 and the third lens 212, and is beneficial to reducing the chromatic aberration of the telecentric lens.
[0075] In an embodiment of the present application, please refer to Figure 1 or Figure 5The second lens group 23 also includes an aperture stop 233 and a seventh lens 234. The aperture stop 233, the seventh lens 234, and the third lens module 30 are arranged sequentially along the direction of light propagation. The aperture stop 233 is used to constrain the width and intensity of the light. The seventh lens 234 has a negative optical power and is used to diffuse the light constrained by the aperture stop 233. With this configuration, the aperture stop 233 constrains the light transmitted through the first lens group 21, controlling the width and intensity of the light, while the seventh lens 234 diffuses the light constrained by the aperture stop 233, preventing stray light from entering the third lens module 30 and causing image distortion or ghosting.
[0076] Optionally, the distance between aperture 233 and the sixth lens 232 is less than the distance between aperture 233 and the seventh lens 234. This distance range allows light rays with a favorable width and intensity to enter aperture 233, thereby controlling the image quality. Specifically, the ratio of the distance between aperture 233 and the sixth lens 232 to the distance between aperture 233 and the seventh lens 234 is less than 1 / 6.
[0077] Optionally, the aperture stop 233 is an aperture stop 233. The aperture stop 233 can block rays in the beam that are significantly off-axis, which helps to improve the sharpness, brightness and depth of field of the image.
[0078] In one embodiment of this application, please refer to Figure 1 or Figure 5 The seventh lens 234 is a biconvex lens; it facilitates the diffusion of light and prevents stray light from flooding into the third lens module 30 and causing ghost images.
[0079] In another embodiment of this application, the seventh lens 234 is a plano-concave lens, with its concave surface facing the side where the aperture stop 233 is located. This facilitates the diffusion of light and prevents stray light from flooding into the third lens module 30, thus avoiding ghosting.
[0080] In one embodiment of this application, please refer to Figure 1 or Figure 5, the third lens module 30 is a meniscus lens, and the concave surface of the third lens module 30 faces the side where the second lens module 20 is located; the third lens module 30 and the second lens group 23 form a quasi-symmetric structure for correcting coma and chromatic aberration with respect to the aperture stop 233. That is, the fifth lens 231, the sixth lens 232, the seventh lens 234, and the third lens module 30 are approximately symmetric in pairs about the aperture stop 233 from left to right. Secondly, the optical powers of the four lenses are symmetric from left to right, being positive, negative, negative, and positive respectively. First, it is converged by the fifth lens 231, and then diffused by the sixth lens 232; then it is restricted by the aperture stop 233; it enters the seventh lens 234 for diffusion to prevent all stray light from pouring into the third lens module 30 and causing ghost images, and the light enters the third lens module 30 for convergence; so that the imaging light converges on the ideal imaging plane 300, thereby correcting coma.
[0081] In an embodiment of the present application, please refer to Figure 1 or Figure 5 , the third lens module 30 further includes an eighth lens 31 and a ninth lens 32; the eighth lens 31 is a meniscus lens with a positive optical power, and the concave surface of the eighth lens 31 faces the side where the second lens module 20 is located; the eighth lens 31 is used to converge the light transmitted by the second lens group 23;
[0082] The ninth lens 32 is a meniscus lens with a positive optical power; the concave surface of the ninth lens 32 faces away from the side where the second lens module 20 is located; the refractive index of the ninth lens 32 satisfies: 1.70 < n < 1.92, and the Abbe number of the ninth lens 32 satisfies: 35 < v < 53; the ninth lens 32 is used to reduce the light deflection angle. The advantage of such a setting is that the eighth lens 31 first converges the light, so that the imaging light can converge on the ideal imaging plane 300 as much as possible; the ninth lens 32 uses a material with a high refractive index and low dispersion to cope with the large light deflection angle. Using a low refractive index material will make the lens curvature too large or the lens too thick, making it difficult to process.
[0083] In an embodiment of the present application, the first lens module 10 includes a first lens 11 with a positive optical power, and the diameter of the first lens 11 is between 40 mm and 73.76 mm. In another embodiment, the first lens module 10 includes a cemented lens with a positive optical power, and the diameter of the cemented lens is between 40 mm and 73.76 mm. With a diameter between 40 mm and 73.76 mm, it can ensure a large target surface, a large aperture, and a high telecentricity of the telecentric lens, while reducing the conjugate distance and making the overall volume of the telecentric lens smaller.
[0084] Optionally, the full image height and the overall optical length of the telecentric lens provided in the present application satisfy the following conditional formula:
[0085] 0.088 ≤ H / L ≤ 0.127;
[0086] Where H is the holographic height of the telecentric lens, and L is the total optical length of the telecentric lens. The H / L ratio satisfying the above condition ensures the proportionality of the telecentric lens and meets its volume requirements.
[0087] In one embodiment of this application, reference is made to... Figure 1 This invention provides specific parameters for each lens element of a telecentric lens with a magnification of 0.64. The first lens module 10 includes a first lens element 11; the second lens module 20 includes a first lens group 21 and a second lens group 23; the first lens group 21 includes a second lens element 211, a third lens element 212, and a fourth lens element; the second lens group 23 includes a fifth lens element 231, a sixth lens element 232, an aperture stop 233, and a seventh lens element 234; and the third lens module 30 includes an eighth lens element 31 and a ninth lens element 32.
[0088] First lens 11: The radius of curvature facing the object side 100 is 481.98 mm, the radius of curvature facing the image side 200 is 153.19 mm, the lens thickness is 8.14 mm, the refractive index is 1.62, and the Abbe number is 60.34.
[0089] The second lens 211 has a surface radius of 47.60 mm facing the object side 100 and a surface radius of 51.86 mm facing the image side 200. The lens thickness is 10.45 mm, the refractive index is 1.44, and the Abbe number is 95.10. The distance between the second lens 211 and the first lens 11 is 87.01 mm.
[0090] The third lens 212 has a surface radius of 51.86 mm facing the object side 100 and a surface radius of 1777.48 mm facing the image side 200. The lens thickness is 1.57 mm, the refractive index is 1.80, and the Abbe number is 42.25.
[0091] The fourth lens has a surface radius of 77.05 mm facing the object side 100 and a surface radius of 55.50 mm facing the image side 200. The lens thickness is 6.56 mm, the refractive index is 1.85, and the Abbe number is 23.78. The distance between the fourth lens and the third lens 212 is 5.51 mm.
[0092] Beam splitter 22: a beam splitter prism with a flat surface; the lens thickness is 25.40 mm, the refractive index is 1.52, and the Abbe number is 64.20; the distance between beam splitter 22 and the fourth lens is 16.45 mm.
[0093] Fifth lens 231: The radius of curvature facing the object side 100 is 18.86 mm, the radius of curvature facing the image side 200 is 60.36 mm, the lens thickness is 4.12 mm, the refractive index is 1.59, and the Abbe number is 68.34; the distance between the fifth lens 231 and the beam splitter 22 is 0.49 mm.
[0094] The sixth lens 232 has a surface radius of 60.36 mm facing the object side 100 and a surface radius of 26.34 mm facing the image side 200. The lens thickness is 1.20 mm, the refractive index is 1.61, and the Abbe number is 44.11.
[0095] Aperture stop 233: The distance between aperture stop 233 and the sixth lens 232 is 3.11mm.
[0096] The seventh lens 234 has a surface radius of 13.37 mm facing the object side 100 and a surface radius of 162.86 mm facing the image side 200. The lens thickness is 1.15 mm, the refractive index is 1.74, and the Abbe number is 27.76. The distance between the aperture stop 233 and the seventh lens 234 is 19.39 mm.
[0097] The eighth lens 31 has a surface radius of 72.10 mm facing the object side 100 and a surface radius of 30.08 mm facing the image side 200. The lens thickness is 9.27 mm, the refractive index is 1.95, and the Abbe number is 32.31. The distance between the eighth lens 31 and the seventh lens 234 is 8.93 mm.
[0098] Ninth lens 32: The radius of curvature facing the object side 100 is 30.08 mm, the radius of curvature facing the image side 200 is 65.80 mm, the lens thickness is 5.31 mm, the refractive index is 1.76, and the Abbe number is 52.32; the distance between the ninth lens 32 and the eighth lens 31 is 0.08 mm, and the distance between the ninth lens 32 and the imaging plane 300 is 48.69 mm.
[0099] This application provides an embodiment of a telecentric lens with an optical system total length TTL = 400mm, a magnification of 0.64x, and a lens light transmission parameter FNO = 8. See also... Figure 2 It is known that the MTF (Modulation Transfer Function) is close to the diffraction limit, which can guarantee extremely high image quality. (Refer to...) Figure 3 As can be seen, the maximum distortion is only 0.029%, a negligible amount that is sufficient to ensure that the object under test does not deform, thus improving the accuracy of the detection. Figure 4 It can be seen that when the pupil is 0.7, the axial chromatic difference is 0.043mm, and no colored edge texture will be produced at the edge of the main image.
[0100] In another embodiment of this application, reference is made to... Figure 5 This provides specific parameters for each lens element of a telecentric lens with a magnification of 0.91.
[0101] First lens 11: The radius of curvature facing the object side 100 is 245.55 mm, the radius of curvature facing the image side 200 is 164.01 mm, the lens thickness is 6.77 mm, the refractive index is 1.62, and the Abbe number is 60.34.
[0102] The second lens 211 has a surface radius of 47.60 mm facing the object side 100 and a surface radius of 51.86 mm facing the image side 200. The lens thickness is 10.45 mm, the refractive index is 1.44, and the Abbe number is 95.10. The distance between the second lens 211 and the first lens 11 is 59.53 mm.
[0103] The third lens 212 has a surface radius of 51.86 mm facing the object side 100 and a surface radius of 1777.48 mm facing the image side 200. The lens thickness is 1.57 mm, the refractive index is 1.80, and the Abbe number is 42.25.
[0104] The fourth lens has a surface radius of 77.05 mm facing the object side 100 and a surface radius of 55.50 mm facing the image side 200. The lens thickness is 6.56 mm, the refractive index is 1.85, and the Abbe number is 23.78. The distance between the fourth lens and the third lens 212 is 5.51 mm.
[0105] Beam splitter 22: a beam splitter prism with a flat surface; the lens thickness is 25.40 mm, the refractive index is 1.52, and the Abbe number is 64.20; the distance between beam splitter 22 and the fourth lens is 16.45 mm.
[0106] Fifth lens 231: The radius of curvature facing the object side 100 is 18.86 mm, the radius of curvature facing the image side 200 is 60.36 mm, the lens thickness is 4.12 mm, the refractive index is 1.59, and the Abbe number is 68.34; the distance between the fifth lens 231 and the beam splitter 22 is 0.49 mm.
[0107] The sixth lens 232 has a surface radius of 60.36 mm facing the object side 100 and a surface radius of 26.34 mm facing the image side 200. The lens thickness is 1.20 mm, the refractive index is 1.61, and the Abbe number is 44.11.
[0108] Aperture stop 233: The distance between aperture stop 233 and the sixth lens 232 is 3.11mm.
[0109] The seventh lens 234 has a surface radius of 13.37 mm facing the object side 100 and a surface radius of 162.86 mm facing the image side 200. The lens thickness is 1.15 mm, the refractive index is 1.74, and the Abbe number is 27.76. The distance between the aperture stop 233 and the seventh lens 234 is 19.39 mm.
[0110] The eighth lens 31 has a surface radius of 62.84 mm facing the object side 100 and a surface radius of 30.35 mm facing the image side 200. The lens thickness is 8.15 mm, the refractive index is 1.95, and the Abbe number is 32.31. The distance between the eighth lens 31 and the seventh lens 234 is 12.41 mm.
[0111] Ninth lens 32: The radius of curvature facing the object side 100 is 72.34 mm, the radius of curvature facing the image side 200 is 564.79 mm, the lens thickness is 6.98 mm, the refractive index is 1.76, and the Abbe number is 52.32; the distance between the ninth lens 32 and the eighth lens 31 is 25.90 mm, and the distance between the ninth lens 32 and the imaging plane 300 is 43.70 mm.
[0112] This application provides an embodiment of a telecentric lens with an optical system total length TTL = 395.5 mm, a magnification of 0.91x, and a lens light transmission parameter FNO = 8. (The last sentence appears to be incomplete and possibly refers to a different application.) Figure 6 It can be seen that MTF is close to the diffraction limit, which can guarantee extremely high image quality requirements. From... Figure 7 As can be seen, the maximum distortion is only 0.042%, a negligible amount that is sufficient to ensure the object under test does not deform, thus improving the accuracy of the detection. Figure 8 It can be seen that when the pupil is 0.7, the axial chromatic difference is 0.046mm, and no colored edge texture will be produced at the edge of the main image.
[0113] A comparison of the specific data of the two sets of lenses shows that the magnification can be changed simply by altering the surface shape and material of the first lens 11, the eighth lens 31, and the ninth lens 32. This allows for the reuse of most lenses, effectively reducing costs and simplifying the development and manufacturing of similar products. This application offers advantages such as a large target surface, high telecentricity, high resolution, low distortion, low cost, achromaticity, and small size.
[0114] This application also provides a machine vision inspection device, including the aforementioned telecentric lens, a display device for displaying images, and a mounting base for mounting the telecentric lens. The magnification of the lens can be varied simply by adjusting the lens surface shape and material of the first lens module 10 and the third lens module 30, while sharing the second lens module 20. This effectively reduces costs and development difficulty for the research and manufacturing of similar products. This application can achieve a target surface of 38mm across the entire field of view, providing clear imaging without significant purple fringing or chromatic aberration, resulting in high image quality. It meets the object-side telecentricity requirement, exhibiting an extremely high level of telecentricity. Through the combination of high- and low-dispersion refractive index cemented lenses and meniscus lenses, it can significantly improve the formation of a central bright spot from the coaxial light source, avoiding imaging problems caused by halos from the light source.
[0115] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A telecentric lens, characterized in that, It consists of a first lens module, a second lens module and a third lens module. The optical power of the first lens module is positive. The first lens module consists of a first lens with positive optical power, or the first lens module consists of a cemented lens with positive optical power. The second lens module consists of a light source, a beam splitter, a first lens group and a second lens group for reducing the chromatic aberration of the telecentric lens. The light source is disposed on the beam splitter. The beam splitter is used to reflect the light emitted by the light source to illuminate the object to be measured and to transmit the light from the first lens group to the second lens group. The optical power of the second lens module is negative. The optical power of the third lens module is positive. The first lens module, the first lens group, the beam splitter, the second lens group and the third lens module are arranged in sequence along the light propagation direction. The first lens group consists of a second lens, a third lens and a fourth lens. The third lens is connected to the side of the second lens close to the beam splitter. The fourth lens is disposed between the third lens and the beam splitter. The fourth lens is a meniscus lens with positive optical power, and the concave surface of the fourth lens faces the side where the third lens is located. The second lens is a biconvex lens with positive optical power, and the third lens is a concave lens with negative optical power. The second lens group consists of a fifth lens, a sixth lens, an aperture stop and a seventh lens. The sixth lens is connected to the side of the fifth lens away from the beam splitter. The optical power of the fifth lens is positive, the optical power of the sixth lens is negative, and the optical power of the seventh lens is negative. The third lens module consists of an eighth lens and a ninth lens. The eighth lens is a meniscus lens with positive optical power, and the concave surface of the eighth lens faces the side where the second lens module is located. The ninth lens is a meniscus lens with positive optical power, and the concave surface of the ninth lens faces away from the side where the second lens module is located.
2. The telecentric lens as described in claim 1, characterized in that, The refractive index of the second lens satisfies: 1.43 < n < 1.50, and the Abbe number of the second lens satisfies: 81 < v < 96.
3. The telecentric lens as described in claim 1, characterized in that, The aperture stop, the seventh lens and the third lens module are arranged in sequence along the light propagation direction.
4. The telecentric lens as described in claim 1, characterized in that, The seventh lens is a plano-concave lens, and the concave surface of the seventh lens faces the side where the aperture stop is located.
5. The telecentric lens as described in claim 1, characterized in that, The refractive index of the ninth lens satisfies: 1.70 < n < 1.92, and the Abbe number of the ninth lens satisfies: 35 < v < 53.
6. A machine vision inspection device, characterized in that, It includes the telecentric lens according to any one of claims 1-5.