A high-precision telecentric imaging device for machine vision

Abstract

The application relates to the technical field of machine vision, and discloses a high-precision telecentric imaging device for machine vision, which comprises a high-precision telecentric imaging lens, the high-precision telecentric imaging lens is installed in the interior of a lens barrel, the rear end of the lens barrel is provided with a C interface, the high-precision telecentric imaging lens comprises two groups of lens groups arranged from the object side to the imaging surface along the optical axis, the first lens group comprises a first lens with positive focal power, a second lens with positive focal power and a third lens with negative focal power, the second lens group comprises a fourth lens with positive focal power and a fifth lens with negative focal power, the second lens and the third lens are cemented together, the first lens, the second lens and the third lens are installed at the front end in the interior of the lens barrel, and the fourth lens and the fifth lens are installed at the rear end in the interior of the lens barrel.The high-precision telecentric imaging device can ensure that the chief rays enter the lens at an angle close to parallel to the optical axis within a certain working distance range, so that the measurement error caused by the slight change of the object position can be effectively eliminated.

Description

Technical Field

[0001] This invention relates to the field of machine vision technology, and in particular to a high-precision telecentric imaging device for machine vision. Background Technology

[0002] In the field of machine vision, especially in high-precision applications such as precision measurement, semiconductor inspection, and electronic manufacturing, telecentric imaging lenses, with their unique optical design of parallel principal ray incidence, can effectively eliminate perspective errors and ensure the consistency of image size at different object distances, becoming a core optical component for achieving high-accuracy detection and measurement. With the rapid development of industrial automation, the requirements for recognition and alignment in machine vision are constantly increasing.

[0003] Traditional telecentric lenses typically employ a fixed optical path structure to ensure telecentricity and resolution, limiting their working distance and depth of field. When the object being inspected experiences height fluctuations or positional shifts, the aperture must be reduced to increase the depth of field. However, this directly reduces the amount of light entering the lens, further lowering the imaging resolution and image signal-to-noise ratio. If a mechanical structure is used to adjust the lens position for focusing, there are issues with response lag and mechanical wear, making it unsuitable for the dynamic inspection scenarios of high-speed production lines. Summary of the Invention

[0004] The purpose of this application is to provide a high-precision telecentric imaging device for machine vision, addressing the technical deficiencies existing in the prior art.

[0005] The technical solution adopted to achieve the purpose of this application is:

[0006] A high-precision telecentric imaging device for machine vision includes a high-precision telecentric imaging lens, which is installed inside a lens barrel. A C-interface is provided at the rear end of the lens barrel. The high-precision telecentric imaging lens includes two lens groups arranged sequentially along the optical axis from the object side to the imaging plane. The first lens group includes a first lens with positive optical power, a second lens with positive optical power, and a third lens with negative optical power. The second lens group includes a fourth lens with positive optical power and a fifth lens with negative optical power. The second lens and the third lens are cemented together. The first, second, and third lenses are installed at the front end inside the lens barrel, and the fourth and fifth lenses are installed at the rear end inside the lens barrel.

[0007] The first lens, second lens, third lens, fourth lens, and fifth lens all include an object-side surface and an image-side surface; the object-side surface of the first lens is convex, and the image-side surface of the first lens is convex; the object-side surface of the second lens is convex, and the image-side surface of the second lens is convex; the object-side surface of the third lens is concave, and the image-side surface of the third lens is concave; the object-side surface of the fourth lens is convex, and the image-side surface of the fourth lens is convex; the object-side surface of the fifth lens is concave, and the image-side surface of the fifth lens is concave.

[0008] In the above technical solution, the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are made of the same material, which is glass.

[0009] In the above technical solution, the radius of curvature of the object-side surface of the first lens is 133.388 mm, and the radius of curvature of the image-side surface of the first lens is -50.765 mm; the radius of curvature of the object-side surface of the second lens is 26.529 mm, and the radius of curvature of the image-side surface of the second lens is -51.211 mm; the radius of curvature of the object-side surface of the third lens is -51.211 mm, and the radius of curvature of the image-side surface of the third lens is 49.886 mm; the radius of curvature of the object-side surface of the fourth lens is 18.739 mm, and the radius of curvature of the image-side surface of the fourth lens is -24.267 mm; the radius of curvature of the object-side surface of the fifth lens is -23.254 mm, and the radius of curvature of the image-side surface of the fifth lens is 26.458 mm.

[0010] In the above technical solution, the thickness of the object-side surface of the first lens is 5.216 mm, and the thickness of the image-side surface of the first lens is 1.99 mm; the thickness of the object-side surface of the second lens is 6.9 mm, and the thickness of the image-side surface of the second lens is 0.001 mm; the thickness of the object-side surface of the third lens is 1.1 mm, and the thickness of the image-side surface of the third lens is 68.119 mm; the thickness of the object-side surface of the fourth lens is 4.291 mm, and the thickness of the image-side surface of the fourth lens is 3.279 mm; the thickness of the object-side surface of the fifth lens is 5.02 mm, and the thickness of the image-side surface of the fifth lens is 20.348 mm.

[0011] In the above technical solution, the focal length, refractive index and Abbe number of the object side and the image side of the first lens are the same. The focal length of the object side and the image side of the first lens is 59.915 mm, the refractive index of the object side and the image side of the first lens is 1.6172, and the Abbe number of the object side and the image side of the first lens is 53.914.

[0012] In the above technical solution, the focal length, refractive index and Abbe number of the object side and the image side of the second lens are the same. The focal length of the object side and the image side of the second lens is 54.389 mm, the refractive index of the object side and the image side of the second lens is 1.497, and the Abbe number of the object side and the image side of the second lens is 81.605.

[0013] In the above technical solution, the focal length, refractive index and Abbe number of the object side and the image side of the third lens are the same. The focal length of the object side and the image side of the third lens is -150.326 mm, the refractive index of the object side and the image side of the third lens is 1.8348, and the Abbe number of the object side and the image side of the third lens is 42.725.

[0014] In the above technical solution, the focal length, refractive index, and Abbe number of the object side and the image side of the fourth lens are the same. The focal length of the object side and the image side of the fourth lens is 15.081 mm, the refractive index of the object side and the image side of the fourth lens is 1.7292, and the Abbe number of the object side and the image side of the fourth lens is 54.685.

[0015] In the above technical solution, the focal length, refractive index and Abbe number of the object side and the image side of the fifth lens are the same. The focal length of the object side and the image side of the fifth lens is -18.262 mm, the refractive index of the object side and the image side of the fifth lens is 1.6477, and the Abbe number of the object side and the image side of the fifth lens is 33.84.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. The second lens of the present invention has a convex image side and the third lens has a concave object side. The second lens and the third lens are cemented together, which can reduce the chromatic aberration of refracted light and improve the resolution of the high-precision telecentric imaging lens.

[0018] 2. The high-precision telecentric imaging lens of the present invention uses five lenses with specific optical power. By rationally allocating the optical power of the five lenses and rationally controlling the surface shape of the lenses, the optical lens can achieve high resolution while maintaining low cost under the condition of satisfying the object space. Moreover, the high-precision telecentric imaging device of the present invention can ensure that within a certain working distance range, the main light rays enter the lens at an angle almost parallel to the optical axis, thereby effectively eliminating measurement errors caused by small changes in the position of the object.

[0019] 3. The high-precision telecentric imaging lens of the present invention operates in an independent mode, achieving excellent telecentricity and low distortion performance without the need for additional optical components. Furthermore, the standard configuration of the high-precision telecentric imaging lens is a C-mount interface, ensuring that it can be quickly and reliably integrated with most industrial cameras on the market that use a C-mount interface to form a complete imaging system. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this application 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 The diagram shown is a schematic of the high-precision telecentric imaging lens structure described in this invention.

[0022] Figure 2 The figure shown is a schematic diagram of the MTF curve of the high-precision telecentric imaging lens described in this invention.

[0023] Figure 3 The diagram shown is a dot plot of the high-precision telecentric imaging lens described in this invention.

[0024] Figure 4 The diagram shown is a schematic representation of the high-precision telecentric imaging device of the present invention.

[0025] In the diagram: 1-First lens, S1-Object side of first lens, S2-Image side of first lens, 2-Second lens, S3-Object side of second lens, S4-Image side of second lens, 3-Third lens, S5-Object side of third lens, S6-Image side of third lens, 4-Fourth lens, S7-Object side of fourth lens, S8-Image side of fourth lens, 5-Fifth lens, S9-Object side of fifth lens, S10-Image side of fifth lens, 6-Lens barrel, 7-C interface. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below with reference to specific embodiments.

[0027] Example 1

[0028] A high-precision telecentric imaging device for machine vision, see [link to relevant documentation] Figure 1 , Figure 4It includes a high-precision telecentric imaging lens, which is installed inside the lens barrel 6. The rear end of the lens barrel 6 is provided with a C-mount interface 7. The high-precision telecentric imaging lens includes two lens groups arranged sequentially along the optical axis from the object side to the imaging plane.

[0029] The first lens group includes a first lens 1 with positive optical power, a second lens 2 with positive optical power, and a third lens 3 with negative optical power. The second lens group includes a fourth lens 4 with positive optical power and a fifth lens 5 with negative optical power. The second lens 2 and the third lens 3 are cemented together to reduce chromatic aberration of the refracted light. The first lens 1, the second lens 2, and the third lens 3 are installed at the front end inside the lens barrel 6, and the fourth lens 4 and the fifth lens 5 are installed at the rear end inside the lens barrel 6.

[0030] The first lens 1, second lens 2, third lens 3, fourth lens 4, and fifth lens 5 all include an object-side surface and an image-side surface. Specifically, the object-side surface S1 of the first lens is convex, and the image-side surface S2 of the first lens is convex; the object-side surface S3 of the second lens is convex, and the image-side surface S4 of the second lens is convex; the object-side surface S5 of the third lens is concave, and the image-side surface S6 of the third lens is concave; the object-side surface S7 of the fourth lens is convex, and the image-side surface S8 of the fourth lens is convex; the object-side surface S9 of the fifth lens is concave, and the image-side surface S10 of the fifth lens is concave. The image-side surface S4 of the second lens cooperates with the object-side surface S5 of the third lens to cement the second lens 2 and the third lens 3 together, reducing chromatic aberration of refracted light and improving the resolution of the high-precision telecentric imaging lens. By employing five lenses with specific optical powers, and by rationally allocating the optical powers of the five lenses and rationally controlling the lens surface shape, the optical lens achieves high resolution while meeting object-side requirements.

[0031] As shown in Table 1, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5 are all made of the same material: glass. The radius of curvature of the object-side surface S1 of the first lens is 133.388 mm, and the radius of curvature of the image-side surface S2 of the first lens is -50.765 mm (the radius of curvature disclosed for the first lens 1 in this embodiment helps reduce spherical aberration and coma, improving the quality of light imaging). The thickness of the object-side surface S1 of the first lens is 5.216 mm, and the thickness of the image-side surface S2 of the first lens is 1.99 mm. The focal length, refractive index, and Abbe number of the object-side surface S1 and the image-side surface S2 of the first lens are the same, and the focal length of the object-side surface S1 and the image-side surface S2 is 59.915 mm. The object-side surface S1 and image-side surface S2 of the first lens have a refractive index of 1.6172, and their Abbe numbers are 53.914 (the Abbe number disclosed for the first lens 1 in this embodiment enables the first lens 1 to work with the second lens 2, third lens 3, fourth lens 4, and fifth lens 5 as a field lens to initially correct light imaging errors and provide good light incident conditions for the second lens 2, third lens 3, fourth lens 4, and fifth lens 5). The object-side surface S3 of the second lens has a radius of curvature of 26.529 mm, and the image-side surface S4 of the second lens has a radius of curvature of -51.211 mm. The object-side surface S3 of the second lens has a thickness of 6.9 mm, and the image-side surface S4 of the second lens has a thickness of 0.001 mm. The object-side surface S3 and the image-side surface S4 of the second lens have the same focal length, refractive index, and Abbe number, and their focal length is 54.389 mm. The object-side surface S3 and image-side surface S4 of the second lens have a refractive index of 1.497 and an Abbe number of 81.605. The object-side surface S5 of the third lens has a radius of curvature of -51.211 mm and the image-side surface S6 has a radius of curvature of 49.886 mm. The object-side surface S5 has a thickness of 1.1 mm and the image-side surface S6 has a thickness of 68.119 mm. The object-side surface S5 and the image-side surface S6 of the third lens have the same focal length, refractive index, and Abbe number. The focal length of the object-side surface S5 and the image-side surface S6 is -150.326 mm, the refractive index is 1.8348, and the Abbe number is 42.725. The object-side surface S7 of the fourth lens has a radius of curvature of 18.739 mm. mm, the radius of curvature of the image side surface S8 of the fourth lens is -24.The radius of curvature of the first lens 1 in this embodiment is 267 mm (which is capable of strong optical focusing). The thickness of the object-side surface S7 of the fourth lens is 4.291 mm, and the thickness of the image-side surface S8 of the fourth lens is 3.279 mm. The focal length, refractive index, and Abbe number of the object-side surface S7 and the image-side surface S8 of the fourth lens are the same. The focal length of the object-side surface S7 and the image-side surface S8 of the fourth lens is 15.081 mm, the refractive index of the object-side surface S7 and the image-side surface S8 of the fourth lens is 1.7292, and the Abbe number of the object-side surface S7 and the image-side surface S8 of the fourth lens is 54.685. The radius of curvature of the object-side surface S9 of the fifth lens is -23.254 mm. The radius of curvature of the image-side surface S10 of the fifth lens is 26.458 mm. The thickness of the object-side surface S9 of the fifth lens is 5.02 mm. The thickness of the image-side surface S10 of the fifth lens is 20.348 mm. mm; the object-side surface S9 and the image-side surface S10 of the fifth lens have the same focal length, refractive index, and Abbe number. The focal length of the object-side surface S9 and the image-side surface S10 of the fifth lens is -18.262 mm, the refractive index of the object-side surface S9 and the image-side surface S10 of the fifth lens is 1.6477, and the Abbe number of the object-side surface S9 and the image-side surface S10 of the fifth lens is 33.84 (the refractive index and Abbe number disclosed in the fifth lens 5 of this embodiment help control higher-order aberrations).

[0032] Table 1. Design parameters of high-precision telecentric imaging lens;

[0033] ;

[0034] See Figure 2 Comprehensive modulation transfer function (MTF) analysis shows that the MTF curve of the high-precision telecentric imaging lens of the present invention is very close to the theoretical value of the diffraction limit of the optical system in the entire working band and the entire field of view. This indicates that the high-precision telecentric imaging lens has excellent imaging consistency and near-perfect aberration balance capability, and can achieve a resolution performance close to the physical theoretical limit across the entire image plane.

[0035] Figure 3 The diagram shows the results of the optical system's dot plot analysis. In all fields of view (including the central and peripheral fields of view), the diffuse spots formed by the combined effects of various monochromatic aberrations (such as spherical aberration, coma, astigmatism, etc.) are all spatially distributed within the diameter of the Airy disk. This means that the aberration correction of the high-precision telecentric imaging lens of this invention has reached an extremely high level, and most aberrations have been successfully eliminated. The overall imaging energy concentration of the system is extremely high, and its resolution performance is very close to the diffraction limit at this aperture.

[0036] The imaging method of the high-precision telecentric imaging lens includes the following steps:

[0037] Step 1: Light first enters the first lens 1 of the high-precision telecentric imaging lens. The first lens 1 collects, converges, and refracts the light, ensuring that the light is telecentric (telecentricity less than 0.4°). In this embodiment, the first lens 1 is a positive lens with a focal length of 59.915mm. As the first lens in the first lens group, it mainly provides positive optical power, collects and converges light. The radius of curvature of the object-side surface S1 of the first lens is 133.388, which helps the first lens 1 reduce spherical aberration and coma, improving the quality of light imaging.

[0038] Step 2: Light rays that are telecentric on the object side are incident on the cemented second lens 2 and third lens 3, which reduce chromatic aberration. In this embodiment, the second lens 2 is a positive lens with a focal length of 54.389 mm, working in conjunction with the first lens 1 to further converge the light rays and balance aberrations. The third lens 3 is a negative lens with a focal length of -150.326 mm, forming a chromatic aberration correction pair with the second lens 2 to reduce chromatic aberration. The third lens 3 also introduces negative optical power to control Petzval curvature and field curvature and distortion, thereby improving surface flatness.

[0039] Step 3: Light with reduced chromatic aberration is incident on the fourth lens 4 (the fourth lens 4 is responsible for correcting the overall spherical aberration of the lens), and the fourth lens 4 is used to compensate for the refraction deviation of the edge light rays. In this embodiment, the fourth lens 4 is a positive lens with a focal length of 15.081 mm. As the first lens in the first lens group, it provides positive optical power to form a sharp image point; and the Abbe number of the fourth lens 4 is 54.685, which can further correct astigmatism and coma, optimizing image quality.

[0040] Step 4: The light emitted from the fourth lens 4 enters the fifth lens 5. The fifth lens 5 optimizes the path of light deflection, ensuring that the angle of the emitted light can achieve the maximum efficiency of CMOS. In this embodiment, the fifth lens 5 has an Abbe number of 33.84 (low Abbe number). The fifth lens 5, in conjunction with the fourth lens 4, positions the aperture stop, preparing for image-side telecentrism. Furthermore, the fifth lens 5 is a negative lens; its negative optical power ensures that the principal ray is parallel to the optical axis, guaranteeing image-side telecentrism and reducing measurement errors.

[0041] For ease of explanation, spatial relative terms such as “up,” “down,” “left,” and “right” are used in the embodiments to describe the relationship of one element or feature shown in the figures relative to another element or feature. It should be understood that, in addition to the orientations shown in the figures, spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figures is inverted, an element described as being “down” of other elements or features would be positioned “up” of those other elements or features. Therefore, the exemplary term “down” can encompass both up and down orientations. The device may be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0042] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component from another that has the same name, without necessarily requiring or implying any such actual relationship or order between the components.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-precision telecentric imaging device for machine vision, characterized in that, The system includes a high-precision telecentric imaging lens, which is installed inside the lens barrel. A C-interface is provided at the rear end of the lens barrel. The high-precision telecentric imaging lens consists of two lens groups arranged sequentially along the optical axis from the object side to the imaging plane. The first lens group consists of a first lens with positive optical power, a second lens with positive optical power, and a third lens with negative optical power. The second lens group consists of a fourth lens with positive optical power and a fifth lens with negative optical power. The second lens and the third lens are cemented together. The first, second, and third lenses are installed at the front end inside the lens barrel, and the fourth and fifth lenses are installed at the rear end inside the lens barrel. The first lens, second lens, third lens, fourth lens, and fifth lens all include an object-side surface and an image-side surface; the object-side surface of the first lens is convex, and the image-side surface of the first lens is convex; the object-side surface of the second lens is convex, and the image-side surface of the second lens is convex; the object-side surface of the third lens is concave, and the image-side surface of the third lens is concave; the object-side surface of the fourth lens is convex, and the image-side surface of the fourth lens is convex; the object-side surface of the fifth lens is concave, and the image-side surface of the fifth lens is concave. The first lens has an object-side radius of curvature of 133.388 mm and an image-side radius of curvature of -50.765 mm; the second lens has an object-side radius of curvature of 26.529 mm and an image-side radius of curvature of -51.211 mm; the third lens has an object-side radius of curvature of -51.211 mm and an image-side radius of curvature of 49.886 mm; the fourth lens has an object-side radius of curvature of 18.739 mm and an image-side radius of curvature of -24.267 mm; the fifth lens has an object-side radius of curvature of -23.254 mm and an image-side radius of curvature of 26.458 mm. The first lens has the same focal length on both its object-side and image-side surfaces, which is 59.915 mm. The second lens has the same focal length on both its object-side and image-side surfaces, which is 54.389 mm. The third lens has the same focal length on both its object-side and image-side surfaces, which is -150.326 mm. The fourth lens has the same focal length on both its object-side and image-side surfaces, which is 15.081 mm. The fifth lens has the same focal length on both its object-side and image-side surfaces, which is -18.262 mm.

2. The high-precision telecentric imaging device according to claim 1, characterized in that, The first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all made of the same material, which is glass.

3. The high-precision telecentric imaging device according to claim 1, characterized in that, The thickness of the object-side surface of the first lens is 5.216 mm, and the thickness of the image-side surface of the first lens is 1.99 mm; the thickness of the object-side surface of the second lens is 6.9 mm, and the thickness of the image-side surface of the second lens is 0.001 mm; the thickness of the object-side surface of the third lens is 1.1 mm, and the thickness of the image-side surface of the third lens is 68.119 mm; the thickness of the object-side surface of the fourth lens is 4.291 mm, and the thickness of the image-side surface of the fourth lens is 3.279 mm; the thickness of the object-side surface of the fifth lens is 5.02 mm, and the thickness of the image-side surface of the fifth lens is 20.348 mm.

4. The high-precision telecentric imaging device according to claim 1, characterized in that, The object side and the image side of the first lens have the same refractive index and Abbe number. The refractive index of the object side and the image side of the first lens is 1.6172, and the Abbe number of the object side and the image side of the first lens is 53.

914.

5. The high-precision telecentric imaging device according to claim 1, characterized in that, The object side and the image side of the second lens have the same refractive index and Abbe number. The refractive index of the object side and the image side of the second lens is 1.497, and the Abbe number of the object side and the image side of the second lens is 81.

605.

6. The high-precision telecentric imaging device according to claim 1, characterized in that, The object side and the image side of the third lens have the same refractive index and Abbe number. The refractive index of the object side and the image side of the third lens is 1.8348, and the Abbe number of the object side and the image side of the third lens is 42.

725.

7. The high-precision telecentric imaging device according to claim 1, characterized in that, The object side and the image side of the fourth lens have the same refractive index and Abbe number. The refractive index of the object side and the image side of the fourth lens is 1.7292, and the Abbe number of the object side and the image side of the fourth lens is 54.

685.

8. The high-precision telecentric imaging device according to claim 1, characterized in that, The object side and the image side of the fifth lens have the same refractive index and Abbe number. The refractive index of the object side and the image side of the fifth lens is 1.6477, and the Abbe number of the object side and the image side of the fifth lens is 33.84.

Images