Object-side telecentric lens and machine vision system

Abstract

The present application provides an object-side telecentric lens and a machine vision system. The object-side telecentric lens includes a first lens group, an aperture, and a second lens group arranged in sequence from the object side to the image side. The first lens group has a positive focal power, and the first lens group includes a plurality of positive focal power lenses. The second lens group has a positive focal power. The focal powers of the first lens group and the second lens group of the object-side telecentric lens are both positive, and the first lens group includes a plurality of positive focal power lenses, which can collect light of a large field of view, effectively expand the field of view of the object-side telecentric lens without increasing distortion, and the number of lens groups is small, and the overall volume is small.

Description

Technical Field

[0001] The present application belongs to the field of optical lenses, and more specifically, to an object-side telecentric lens and a machine vision system. Background Art

[0002] With the widespread application of machine vision systems in the field of precision detection, ordinary industrial lenses are difficult to meet the detection requirements. In order to make up for the shortcomings of ordinary lens applications and adapt to the needs of precision detection, telecentric lenses came into being. Telecentric lenses are mainly designed to correct the parallax of traditional industrial lenses. It can keep the image magnification unchanged within a certain object distance range. This is a very important application for the situation where the objects being measured are not on the same object plane. Telecentric lenses can be divided into object-side telecentric lenses, image-side telecentric lenses, and two-sided telecentric optical paths. Among them, object-side telecentric lenses are more widely used. At present, object-side telecentric lenses on the market often have problems with inaccurate measurements caused by excessive distortion. Although some lenses have solved the problem of excessive distortion, they still have the problem of small field of view. Utility Model Content

[0003] The purpose of the embodiments of the present application is to provide an object-side telecentric lens and a machine vision system to solve the technical problem of the small field of view of the object-side telecentric lens existing in the prior art.

[0004] To achieve the above-mentioned purpose, the technical solution adopted in the present application is: to provide an object-side telecentric lens, which includes a first lens group, an aperture and a second lens group arranged in sequence from the object side to the image side, the optical focal length of the first lens group is positive, the first lens group includes a plurality of positive optical focal length lenses, and the optical focal length of the second lens group is positive.

[0005] Optionally, the object-side telecentric lens satisfies the following conditional formula:

[0006] 0.2≤PMAG≤0.3

[0007] PMAG is the vertical axis magnification of the object-side telecentric lens.

[0008] Optionally, the first lens group includes a first lens, a second lens, a third lens and a fourth lens from the object side to the image side, the first lens, the second lens and the fourth lens are all positive power lenses, the third lens is a negative power lens, and the second lens and the third lens form a doublet lens.

[0009] Optionally, the shape of the object side of the first lens is convex toward the object surface, the shape of the second lens from the object side to the image side is convex toward the object surface and concave toward the object surface, the shape of the third lens from the object side to the image side is concave toward the object surface and convex toward the object surface, and the shape of the fourth lens from the object side to the image side is convex toward the object surface and convex toward the object surface.

[0010] Optionally, the second lens group includes a fifth lens, a sixth lens and a seventh lens in sequence from the object side to the image side, the fifth lens is a negative power lens, and the sixth lens and the seventh lens are positive power lenses.

[0011] Optionally, the shapes of the fifth lens from the object side to the image side are concave toward the object surface and concave toward the object surface, the shapes of the sixth lens from the object side to the image side are concave toward the object surface and concave toward the object surface, and the shapes of the seventh lens from the object side to the image side are convex toward the object surface and concave toward the object surface.

[0012] Optionally, the object-side telecentric lens meets the following conditions:

[0013] 1.65≤f L01 / f G1 ≤2.75

[0014] where f L01 is the focal length of the first lens from the object side to the image side, f G1 is the focal length of the first lens group.

[0015] Optionally, the refractive index and Abbe number of the second lens and the third lens satisfy the following relationship:

[0016] 1.40≤nd L2 ≤1.63

[0017] 60.0≤vd L2 ≤98.0

[0018] 1.70≤nd L3 ≤1.95

[0019] 20.0≤vd L3 ≤35.0

[0020] Among them, n L2 represents the refractive index of the second lens, vd L2 represents the Abbe number of the second lens, nd L3 represents the refractive index of the third lens, vd L3 It represents the Abbe number of the third lens.

[0021] Optionally, the object-side telecentric lens satisfies the following conditional formula:

[0022] 0.2≤T L01-L2 / L≤0.4

[0023] Where T L01-L2 is the air space between the first lens and the second lens of the object side telecentric lens, and L is the total optical length of the object side telecentric lens.

[0024] Optionally, the object-side telecentric lens satisfies the following conditional formula:

[0025] Angle 物方 ≤0.1°

[0026] Where Angle 物方 It is the object telecentricity of the object telecentric lens.

[0027] The present application also provides a machine vision system, comprising the above-mentioned object-space telecentric lens.

[0028] The beneficial effects of the object-side telecentric lens and machine vision system provided by the present application are as follows: compared with the prior art, the optical focal lengths of the first lens group and the second lens group of the present application are both positive, and the first lens group includes a plurality of positive optical focal length lenses, which can collect light of a large field of view, effectively expanding the field of view of the object-side telecentric lens without increasing distortion, and the number of lens groups is relatively small, so the overall volume is relatively small. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 2D structural diagram of the object-side telecentric lens of the first embodiment of the present application;

[0031] Figure 2 This is the MTF diagram of Example 1 of the present application;

[0032] Figure 3 This is the focal shift curve of Example 1 of this application;

[0033] Figure 4 This is a vertical axis chromatic aberration diagram of Example 1 of the present application;

[0034] Figure 5 The field curvature diagram and distortion diagram of Example 1 of the present application;

[0035] Figure 6 2D structural diagram of the object-side telecentric lens of the second embodiment of the present application;

[0036] Figure 7 This is the MTF diagram of Example 2 of the present application;

[0037] Figure 8 This is the focal shift curve of Example 2 of this application;

[0038] Fig. 9 This is a vertical axis chromatic aberration diagram of Example 2 of the present application;

[0039] Fig.10 The field curvature diagram and distortion diagram of Example 2 of the present application;

[0040] Fig.11 This is a 2D structural diagram of the object-side telecentric lens of Example 3 of the present application;

[0041] Fig.12 This is the MTF diagram of Example 3 of the present application;

[0042] Fig.13 This is the focal shift curve of Example 3 of this application;

[0043] Fig.14 This is a vertical axis chromatic aberration diagram of Example 3 of the present application;

[0044] Fig.15 The field curvature diagram and distortion diagram of Example 3 of this application are shown;

[0045] In the figures, reference numerals are: first lens group G1, first lens group G2, aperture STOP, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7. DETAILED DESCRIPTION

[0046] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0047] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0048] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0049] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0050] See also Figure 1 , Figure 6 and Fig.11 The object-side telecentric lens provided in the embodiment of the present application is now described. The object-side telecentric lens includes a first lens group G1, a stop STOP, and a second lens group G2 arranged in sequence from the object side to the image side. The first lens group G1 has a positive focal power, and includes a plurality of positive focal power lenses. The second lens group G2 has a positive focal power.

[0051] The object-side telecentric lens is to place the aperture stop STOP on the image-side focal plane of the optical system, and the convergence center of the object-side principal ray parallel to the optical axis principal ray is located at infinity on the object side, so that even if the object distance changes, the image distance also changes, but the image height does not change, that is, the measured object size does not change. The object-side telecentric lens of this embodiment includes a first lens group G1, an aperture stop STOP and a second lens group G2 from the object side to the image side, with a total of two lens groups. The first lens group G1 and the second lens group G2 are usually lens systems formed by arranging multiple lenses. Among them, the optical power of the first lens group G1 and the second lens group G2 are both positive, and the optical power refers to the measure of the focusing ability of a lens or a lens group on light, also known as the curvature focal length. The optical power of the lens group is formed by combining the lenses it contains, that is, the optical power formed by the optical power of all lenses in the first lens group G1 superimposed and offset is positive, and similarly, the optical power formed by the optical power of all lenses in the second lens group G2 superimposed and offset is also positive, which can reduce chromatic aberration and distortion. The first lens group G1 includes a plurality of positive power lenses that can collect light of a large field of view, so that the object telecentric lens can obtain a larger viewing angle range and improve the imaging quality. In general, the object telecentric lens in this embodiment has a larger viewing angle range with smaller chromatic aberration and distortion.

[0052] In some embodiments of the present application, the object-side telecentric lens satisfies the following conditional formula:

[0053] 0.2≤PMAG≤0.3

[0054] PMAG is the vertical axis magnification of the object-side telecentric lens.

[0055] The vertical axis magnification refers to the ratio of the vertical axis size of the image to the vertical axis size of the object, and can be used to evaluate the ability of the optical system to magnify or reduce the image. In this embodiment, the vertical axis magnification of the object-side telecentric lens is controlled within the range of 0.2-0.3, which can achieve a large field of view of the lens and meet many scenarios where high-magnification lenses cannot be used. For example, in some embodiments, the field of view of the object-side telecentric lens can be greater than 60mm.

[0056] See also Figure 1 , Figure 6 and Fig.11 In some embodiments of the present application, the first lens group G1 includes the first lens L1, the second lens L2, the third lens L3 and the fourth lens L4 from the object side to the image side. The first lens L1, the second lens L2 and the fourth lens L4 are all positive power lenses, the third lens L3 is a negative power lens, and the second lens L2 and the third lens L3 form a doublet lens. As mentioned above, the first lens group G1 includes a plurality of positive power lenses. In this embodiment, it includes three positive power lenses, namely the first lens L1, the second lens L2 and the fourth lens L4. The third lens L3 is a negative power lens, but the second lens L2 and the third lens L3 form a doublet lens. The doublet lens is formed by gluing the second lens L2 and the third lens L3 together to form an integral lens. The doublet lens has excellent light transmittance, which allows more light to pass through and be fully utilized. The object-side telecentric lens of this embodiment can not only collect light of a large field of view, but also effectively reduce the aberration generated by the system, improve the imaging quality of the system, and ensure a small object-side telecentricity.

[0057] See also Figure 1 , Figure 6 and Fig.11 In some embodiments of the present application, the shape of the first lens L1 on the object side is a convex object surface, the shape of the second lens L2 from the object side to the image side is a convex object surface and a concave object surface, the shape of the third lens L3 from the object side to the image side is a concave object surface and a convex object surface, and the shape of the fourth lens L4 from the object side to the image side is a convex object surface and a convex object surface. The convex object surface is a surface that is convex toward the object side, and the concave object surface is a surface that is concave toward the object side. The second lens L2 and the third lens L3 form a double cemented lens, so the surfaces that are bonded to each other are all concave object surfaces. The object-side telecentric lens of this embodiment can further reduce the aberrations generated by the system and improve the imaging quality.

[0058] See also Figure 1 , Figure 6 and Fig.11In some embodiments of the present application, the second lens group G2 includes a fifth lens L5, a sixth lens L6 and a seventh lens L7 from the object side to the image side, the fifth lens L5 is a negative power lens, and the sixth lens L6 and the seventh lens L7 are positive power lenses. The fifth lens L5 is a negative power lens, and the sixth lens L6 and the seventh lens L7 with positive power can converge the light converged by the first lens group G1, while ensuring the sensitivity of the system light and achieving a higher resolution.

[0059] See also Figure 1 , Figure 6 and Fig.11 In some embodiments of the present application, the shape of the fifth lens L5 from the object side to the image side is concave toward the object surface, concave toward the object surface, the shape of the sixth lens L6 from the object side to the image side is concave toward the object surface, concave toward the object surface, and the shape of the seventh lens L7 from the object side to the image side is convex toward the object surface, concave toward the object surface. The specific lens structure of this embodiment can further improve the sensitivity of light and improve the resolution.

[0060] In some embodiments of the present application, the object-side telecentric lens satisfies the following conditions:

[0061] 1.65≤f L01 / f G1 ≤2.75

[0062] where f L01 is the focal length of the first lens from the object side to the image side, f G1 is the focal length of the first lens group G1. L01 / f G1 Meeting the above conditional expression can effectively converge light of a large field of view while allowing the light to pass through the first lens group G1 and the aperture STOP more smoothly, thereby reducing sensitivity, ensuring the stability of the optical system front and back, and achieving a smaller object-side telecentricity.

[0063] In some embodiments of the present application, the refractive index and Abbe number of the second lens L2 and the third lens L3 satisfy the following relationship:

[0064] 1.40≤nd L2 ≤1.63

[0065] 60.0≤vd L2 ≤98.0

[0066] 1.70≤nd L3 ≤1.95

[0067] 20.0≤vd L3 ≤35.0

[0068] Among them, n L2represents the refractive index of the second lens L2, vd L2 represents the Abbe number of the second lens L2, nd L3 represents the refractive index of the third lens L3, vd L3 It represents the Abbe number of the third lens L3.

[0069] The Abbe number, also known as the relative dispersion number or dispersion coefficient, is used to represent the inverse proportional exponent of the dispersion ability of a transparent material. The second lens L2 and the third lens L3 are double-cemented lenses. When the refractive index and the Abbe number of the second lens L2 and the third lens L3 satisfy the above relationship, the system chromatic aberration can be effectively corrected and the imaging quality of the system can be improved.

[0070] In some embodiments of the present application, the object-side telecentric lens satisfies the following conditional formula:

[0071] 0.2≤T L01-L2 / L≤0.4

[0072] Where T L01-L2 is the air space between the first lens L1 and the second lens L2 of the object telecentric lens, and L is the total optical length of the object telecentric lens. The total optical length refers to the length from the first lens to the imaging surface. The object telecentric lens satisfies the above conditional formula, which can effectively control the aperture of the rear lens, thereby achieving a small size and low cost of the object telecentric lens.

[0073] In some embodiments of the present application, the object-side telecentric lens satisfies the following conditional formula:

[0074] Angle 物方 ≤0.1°

[0075] Where Angle 物方 The object telecentricity of the object telecentric lens. The object telecentricity mainly describes the angle at which the main light deviates from the optical axis. The smaller the angle, the better the telecentricity. The object telecentricity of this embodiment can be less than 0.1°.

[0076] Based on the above object space telecentric lens, the present application also provides a machine vision system, including the above object space telecentric lens. The machine vision system of this embodiment can take into account the advantages of low distortion, achromatism, small size, large field of view, etc., and can meet the needs of various industrial inspections.

[0077] Three specific embodiments of the present application are introduced below.

[0078] Embodiment 1:

[0079] like Figure 1 As shown, the object-side telecentric lens data of the first embodiment is as follows:

[0080]

[0081]

[0082] The total length of the optical system of the object side telecentric lens is TTL=178.06, the vertical axis magnification is 0.2X, and its field of view can reach a maximum of 88mm.

[0083] Refractive index and Abbe number of the second lens L2 of the first lens group G1:

[0084] nd L2 =1.5

[0085] vd L2 =81.6

[0086] Refractive index and Abbe number of the third lens L3 of the first lens group G1:

[0087] nd L3 =1.8

[0088] vd L3 =23.8

[0089] like Figure 2 The MTF diagram of the first embodiment, that is, the modulation transfer function diagram, is shown. It can be seen that the curve is close to the diffraction limit, and the MTF of 100lp / mm is greater than 0.4.

[0090] Figure 3 As shown in the focal shift curve of Example 1, the focal shift difference of the three colors of light is about 43um, which achieves a small axial chromatic aberration and meets the use requirements of the telecentric lens.

[0091] Figure 4 This is the vertical axis chromatic aberration diagram of Example 1. The maximum vertical axis chromatic aberration is about 2.5um, which is smaller than 1 pixel of the camera used, thus avoiding the phenomenon such as purple fringing caused by vertical axis chromatic aberration.

[0092] Figure 5 The field curvature diagram and distortion diagram of Example 1 are shown in Figure 1. The distortion is about 0.04%, which is basically distortion-free and meets industrial detection requirements.

[0093] Embodiment 2:

[0094] like Figure 6 As shown, the object-side telecentric lens data of Implementation 2 is as follows:

[0095]

[0096]

[0097] The total length of the optical system of the object side telecentric lens is TTL=175.37, the vertical axis magnification is 0.25X, and its field of view can reach a maximum of 70.4mm.

[0098] Refractive index and Abbe number of the second lens L2 of the first lens group G1: nd L2 =1.5, vd L2 =81.6.

[0099] Refractive index and Abbe number of the third lens L3 of the first lens group G1: nd L3 =1.8, vd L3 =23.8.

[0100] Figure 7 This is the MTF diagram of Example 2. It can be seen that the curve is close to the diffraction limit, and the MTF of 100lp / mm is greater than 0.4.

[0101] Figure 8 As shown in the focal shift curve of Example 2, the focal shift difference of the three colors of light is about 41um, which achieves a smaller axial chromatic aberration and meets the use requirements of the telecentric lens.

[0102] Fig. 9 This is the vertical axis chromatic aberration diagram of Example 2. The maximum vertical axis chromatic aberration is about 2.2um, which is smaller than 1 pixel of the camera used, thus avoiding the phenomenon such as purple fringing caused by vertical axis chromatic aberration.

[0103] Fig.10 The field curvature diagram and distortion diagram of Example 2 show that the distortion is about 0.035%, which is basically distortion-free and meets industrial detection requirements.

[0104] Embodiment three:

[0105] like Fig.11 As shown, the object-side telecentric lens system data of implementation three is as follows:

[0106]

[0107]

[0108] The total length of the optical system of the object side telecentric lens is TTL=177.63, the vertical axis magnification is 0.287X, and its field of view can reach a maximum of 61.3mm.

[0109] Refractive index and Abbe number of the second lens L2 of the first lens group G1:

[0110] nd L2 =1.5

[0111] vd L2 =81.6

[0112] Refractive index and Abbe number of the third lens L3 of the first lens group G1:

[0113] nd L3 =1.8

[0114] vd L3 =23.8

[0115] Fig.12 This is the MTF diagram of Example 1. It can be seen that the curve is close to the diffraction limit, and the MTF of 100lp / mm is greater than 0.4.

[0116] Fig.13 As shown in the focal shift curve of Example 3, the focal shift difference of the three colors of light is about 40um, which achieves a smaller axial chromatic aberration and meets the use requirements of the telecentric lens.

[0117] Fig.14 This is the vertical axis chromatic aberration diagram of Example 3. The maximum vertical axis chromatic aberration is about 2um, which is smaller than 1 pixel of the camera used, thus avoiding the phenomenon such as purple fringing caused by vertical axis chromatic aberration.

[0118] Fig.15 The field curvature diagram and distortion diagram of Example 3 show that the distortion is about 0.035%, which is basically distortion-free and meets industrial detection requirements.

[0119] From the above three embodiments, it can be seen that the curves in the above three embodiments are close to the diffraction limit, the MTF of 100lp / mm is greater than 0.4, the focal shift difference of the three colors of light is within 50um, the vertical axis chromatic aberration is less than 2.5um, which is less than 1 pixel of the camera used, and the distortion is less than 0.05%, which is basically distortion-free. The three embodiments all have lower distortion and smaller chromatic aberration, and the field of view is more than 60mm, with a larger field of view.

[0120] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An object-side telecentric lens, characterized in that: The object-side telecentric lens comprises a first lens group, an aperture, and a second lens group arranged in sequence from the object side to the image side, the first lens group has a positive focal power, the first lens group comprises a plurality of positive focal power lenses, and the second lens group has a positive focal power; The object-side telecentric lens satisfies the following conditional formula: 0.2≤PMAG≤0.3 PMAG is the vertical axis magnification of the object-side telecentric lens.

2. The object-side telecentric lens according to claim 1, wherein: The first lens group includes a first lens, a second lens, a third lens and a fourth lens in order from the object side to the image side. The first lens, the second lens and the fourth lens are all positive power lenses, the third lens is a negative power lens, and the second lens and the third lens form a doublet lens.

3. The object-side telecentric lens according to claim 2, wherein: The shape of the first lens on the object side is convex toward the object surface, the shape of the second lens from the object side to the image side is convex toward the object surface and concave toward the object surface, the shape of the third lens from the object side to the image side is concave toward the object surface and convex toward the object surface, and the shape of the fourth lens from the object side to the image side is convex toward the object surface and convex toward the object surface.

4. The object-side telecentric lens according to any one of claims 1 to 3, characterized in that: The second lens group includes a fifth lens, a sixth lens and a seventh lens in order from the object side to the image side. The fifth lens is a negative power lens, and the sixth lens and the seventh lens are positive power lenses.

5. The object-side telecentric lens according to claim 4, wherein: The shapes of the fifth lens from the object side to the image side are concave toward the object surface and concave toward the object surface, respectively; the shapes of the sixth lens from the object side to the image side are concave toward the object surface and concave toward the object surface, respectively; and the shapes of the seventh lens from the object side to the image side are convex toward the object surface and concave toward the object surface, respectively.

6. The object-side telecentric lens according to any one of claims 1 to 3, characterized in that: The object-side telecentric lens meets the following conditions: 1.65≤f L01 / f G1 ≤2.75 where f L01 is the focal length of the first lens from the object side to the image side, f G1 is the focal length of the first lens group.

7. The object-side telecentric lens according to claim 2 or 3, characterized in that: The refractive index and Abbe number of the second lens and the third lens satisfy the following relationship: 1.40≤nd L2 ≤1.63 60.0≤vd L2 ≤98.0 1.70≤nd L3 ≤1.95 20.0≤vd L3 ≤35.0 Among them, n L2 represents the refractive index of the second lens, vd L2 represents the Abbe number of the second lens, nd L3 represents the refractive index of the third lens, vd L3 represents the Abbe number of the third lens.

8. The object-side telecentric lens according to claim 2 or 3, characterized in that: The object-side telecentric lens satisfies the following conditional formula: 0.2≤T L01-L2 / L≤0.4 Where T L01-L2 is the air space between the first lens and the second lens of the object side telecentric lens, and L is the total optical length of the object side telecentric lens.

9. The object-side telecentric lens according to any one of claims 1 to 3, characterized in that: The object-side telecentric lens satisfies the following conditional formula: Angle 物方 ≤0.1° Where Angle 物方 It is the object telecentricity of the object telecentric lens.

10. A machine vision system, characterized in that: The invention comprises the object-side telecentric lens as described in any one of claims 1 to 9.

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