A large-surface continuously variable-magnification telecentric lens

Abstract

The present invention discloses a large-target-surface continuously variable-magnification telecentric lens, wherein the telecentric lens includes, from the object plane to the image plane, a first lens group with positive refractive index optical focal power, a second lens group with positive refractive index optical focal power, a third lens group with positive refractive index optical focal power, and a fourth lens group with positive refractive index optical focal power; wherein the first lens group and the fourth lens group are fixed groups, and the second lens group and the third lens group are movable groups, and when the variable-magnification telecentric lens changes from low magnification to high magnification, the second lens group approaches the first lens group, and the third lens group approaches the first lens group. The large-target-surface continuously variable-magnification telecentric lens provided by the present invention can match a 4 / 3-inch image sensor, with a telecentricity of less than 0.05°, an optical distortion of less than 0.02%, and a magnification of 0.5x‑1x.

Description

Technical Field

[0001] The invention belongs to the technical field of optical lenses, and in particular relates to a large-target-surface continuously variable-magnification telecentric lens. Background Art

[0002] The machine vision system uses machines to replace human eyes for measurement and judgment. Optical lenses are an important part of the machine vision system. Compared with ordinary imaging lenses, telecentric lenses can effectively correct the parallax of ordinary imaging lenses due to their unique optical path structure, thereby ensuring that the imaging magnification remains unchanged within a certain object distance range. Therefore, they are widely used in various machine vision inspection systems.

[0003] Currently, there are mainly the following types of telecentric lenses used in machine vision inspection systems on the market:

[0004] The first type is a telecentric lens with a constant magnification. Fixed-magnification telecentric lenses can be designed to match sensors with large target surfaces, so they have a larger field of view and can ensure the accuracy of detection. However, due to the fixed magnification, different magnification lenses need to be replaced to detect different objects, which limits the use of scenarios.

[0005] The second type of continuously zooming telecentric lens. In order to achieve the purpose of zooming, the continuously zooming telecentric lenses currently on the market are designed with a smaller sensor target surface and a smaller observation field of view. At the same time, due to the poor telecentricity, when measuring within the depth of field of the lens, there are differences in the measured values, and the measurement results are not accurate enough. For example, a Chinese patent with publication number CN204188874U discloses a zoom telecentric lens, which involves optical technology. From the object plane to the image plane, it includes: a first lens group with positive refractive index optical power, a second lens group with positive refractive index optical power, a third lens group with negative refractive index optical power, a fourth lens group with positive refractive index optical power, and a fifth lens group with positive refractive index optical power; wherein the first lens group, the third lens group and the fifth lens group are fixed groups, and the second lens group and the fourth lens group are mobile groups. When the zoom telecentric lens changes from low magnification to high magnification, the second lens group approaches the first lens group, and the fourth lens group approaches the third lens group. For example, a Chinese patent with publication number CN109471244A discloses a large-field-of-view bi-telecentric lens based on machine vision, comprising: a first group of lenses, a second group of lenses, a third group of lenses, a fourth group of lenses and a fifth group of lenses, which are arranged in sequence from left to right in the incident direction of the light path; wherein the first group of lenses is a plano-convex lens with positive focal power; the second group of lenses is a convex-concave lens with positive focal power; the third group of lenses is a biconcave lens with negative focal power; the fourth group of lenses is a double-cemented lens; the fifth group of lenses is a biconvex lens with positive focal power; and an aperture stop is provided between the third group of lenses and the fourth group of lenses.

[0006] It can be seen that there are almost no zoom telecentric lenses on the market that can match 4 / 3-inch image sensors, have a telecentricity of less than 0.05°, an optical distortion of less than 0.02%, and a magnification of 0.5x-1x. Therefore, it is urgent to develop a zoom telecentric lens that matches 4 / 3-inch image sensors, has a telecentricity of less than 0.05°, an optical distortion of less than 0.02%, and a magnification of 0.5x-1x to fill the market gap. Summary of the invention

[0007] The object of the present invention is to provide a large-target-surface continuously variable-magnification telecentric lens, which can match a 4 / 3-inch image sensor, has a telecentricity of less than 0.05°, an optical distortion of less than 0.02%, and a magnification of 0.5x-1x.

[0008] The technical solution adopted by the present invention is:

[0009] A large target surface continuously variable magnification telecentric lens, characterized in that the telecentric lens comprises, from the object plane to the image plane, a first lens group with positive refractive index optical focal power, a second lens group with positive refractive index optical focal power, a third lens group with positive refractive index optical focal power and a fourth lens group with positive refractive index optical focal power; wherein the first lens group and the fourth lens group are fixed groups, and the second lens group and the third lens group are movable groups, and when the variable magnification telecentric lens changes from low magnification to high magnification, the second lens group approaches the first lens group, and the third lens group approaches the first lens group.

[0010] Furthermore, the first lens group, the second lens group, the third lens group, and the fourth lens group satisfy the relationship:

[0011] 0.15<|f s2 / f s1 |<0.9

[0012] 0.1<|f s3 / f s1 |<0.85

[0013] 0.75<|f s4 / f s1 |<1.25

[0014] Among them, f s1 is the combined focal length of the first lens group, f s2 is the combined focal length of the second lens group, f s3 is the combined focal length of the third lens group, f s4 is the combined focal length of the fourth lens group.

[0015] Furthermore, the first lens group S1 includes a biconvex first lens G1 with positive power, a meniscus second lens G2 with positive power, a plano-convex third lens G3 with positive power, and a biconcave fourth lens G4 with negative power, which are arranged in sequence from the object side to the image side; wherein the third lens G3 and the fourth lens G4 are cemented together to form a first cemented lens group U1 with negative power, and the focal length of the first cemented lens group is f U1 , and satisfy the relationship:

[0016] 0.1<|f U1 / f s1 |<0.3.

[0017] Furthermore, the second lens group S2 includes a fifth meniscus lens G5 with negative power, a sixth plano-convex lens G6 with positive power, and a seventh meniscus lens G7 with positive power, which are arranged in sequence from the object side to the image side; wherein the fifth lens G5 and the sixth lens G6 are cemented together to form a second cemented lens group U2 with positive power, and the focal length of the second cemented lens group is f U2 , and satisfy the relationship:

[0018] 1.0<|f U2 / f s2 |<1.8.

[0019] Furthermore, the third lens group S3 includes a meniscus eighth lens G8 with positive focal power, a plano-convex ninth lens G9 with positive focal power, and a plano-concave tenth lens G10 with negative focal power, which are arranged in sequence from the object side to the image side. The ninth lens G9 and the tenth lens G10 are cemented together to form a third cemented lens group U3 with positive focal power. The focal length of the second cemented lens group is f U3 , and satisfy the relationship:

[0020] 3<|f U3 / f s3 |<4.5.

[0021] Furthermore, the telecentric lens further includes an aperture, and the aperture is arranged between the eighth lens G8 and the third cemented lens group U3.

[0022] Furthermore, the aperture is circular, moves with the third lens group S3 and keeps a constant diameter.

[0023] Furthermore, the fourth lens group S4 includes a biconcave eleventh lens G11 with negative power, a plano-convex twelfth lens G12 with positive power, and a plano-convex thirteenth lens G13 with positive power, which are arranged in sequence from the object side to the image side.

[0024] Preferably, the first lens group, the second lens group, the third lens group and the fourth lens group are all spherical lenses. That is, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6, the seventh lens G7, the eighth lens G8, the ninth lens G9, the tenth lens G10, the eleventh lens G11, the twelfth lens G12 and the thirteenth lens G13 are all spherical lenses.

[0025] Preferably, the air interval between the first lens group S1 and the second lens group S2 is D1, the air interval between the second lens group S2 and the third lens group S3 is D2, and the air interval between the third lens group S3 and the fourth lens group S4 is D3, and D1, D2 and D3 satisfy the relationship:

[0026] 0.3<|D 1 / D 2 |<7.5

[0027] 0.25<|D 1 / D 3 |<7.5

[0028] 0.15<|D 2 / D 3 |<4.25.

[0029] The beneficial effect of the present invention is that it adopts a simple four-component structure, and realizes the change of lens magnification through the cooperation of the moving group and the zoom group. The large target surface continuous zoom telecentric lens provided by the present invention realizes a zoom range of 0.5x-1x, and the image can be clearly imaged without re-adjusting the object distance and image distance during the zoom process; it can match the maximum target surface 4 / 3 inch sensor, and the observable field of view is larger; the object space telecentricity is less than 0.05°, ensuring the accuracy of the measurement data and the repeatability of the measurement data within the depth of field; the optical distortion is less than 0.02% under all magnification conditions, and the shape of the measured object is truly restored; it has ultra-high object space resolution, and the maximum object space resolution reaches 4.9μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the optical system of the large target surface continuously variable magnification telecentric lens in Example 1;

[0031] Figure 2 This is a comparison chart of the large target surface continuously variable magnification telecentric lens from low magnification to high magnification in Example 1;

[0032] Figure 3 This is the MTF curve of the large-target-surface continuously zooming telecentric lens at low magnification in Example 1;

[0033] Figure 4This is the MTF curve of the large-target-surface continuously zooming telecentric lens at high magnification in Example 1;

[0034] Figure 5 is a distortion curve diagram of the large target surface continuously variable magnification telecentric lens at low magnification in Example 1;

[0035] Figure 6 is a distortion curve diagram of the large target surface continuously variable magnification telecentric lens at high magnification in Example 1;

[0036] Figure 7 This is the point diagram of the large target surface continuously variable magnification telecentric lens at low magnification in Example 1;

[0037] Figure 8 This is the point diagram of the large target surface continuously variable magnification telecentric lens at high magnification in Example 1;

[0038] Fig. 9 Schematic diagram of the optical system of the large target surface continuously variable magnification telecentric lens in Example 2;

[0039] Fig.10 Schematic diagram of the optical system of the large target surface continuously variable magnification telecentric lens in Example 3. DETAILED DESCRIPTION

[0040] In order to make the above features and advantages of the present invention more clearly understood, embodiments are given below with reference to the accompanying drawings for detailed description.

[0041] like Figure 1 As shown, the large target surface continuously variable magnification telecentric lens provided by the present invention includes, from the object plane to the image plane, the following components in sequence:

[0042] The first lens group S1 with positive refractive index power includes a biconvex first lens G1 with positive power, a meniscus second lens G2 with positive power, a plano-convex third lens G3 with positive power, and a biconcave fourth lens G4 with negative power, which are arranged in sequence from the object side to the image side; wherein the third lens G3 and the fourth lens G4 are cemented to form a first cemented lens group U1 with negative power, and the focal length of the first cemented lens group is f U1 , and satisfy the relationship:

[0043] 0.1<|f U1 / f s1 |<0.3;

[0044] The second lens group with positive refractive index power includes a fifth meniscus lens G5 with negative power, a sixth plano-convex lens G6 with positive power, and a seventh meniscus lens G7 with positive power, which are arranged in sequence from the object side to the image side; wherein the fifth lens G5 and the sixth lens G6 are cemented to form a second cemented lens group U2 with positive power, and the focal length of the second cemented lens group is fU2 , and satisfy the relationship:

[0045] 1.0<|f U2 / f s2 |<1.8;

[0046] The third lens group with positive refractive index power includes a meniscus eighth lens G8 with positive power, a plano-convex ninth lens G9 with positive power, and a plano-concave tenth lens G10 with negative power, which are arranged in sequence from the object side to the image side; wherein the ninth lens G9 and the tenth lens G10 are cemented to form a third cemented lens group U3 with positive power, and the focal length of the second cemented lens group is f U3 , and satisfy the relationship:

[0047] 3<|f U3 / f s3 |<4.5;

[0048] A diaphragm is arranged between the eighth lens G8 and the third cemented lens group U3. The diaphragm is circular and moves with the third lens group S3 with its diameter remaining unchanged.

[0049] The fourth lens group having positive refractive index power includes a biconcave eleventh lens G11 having negative power, a plano-convex twelfth lens G12 having positive power, and a plano-convex thirteenth lens G13 having positive power, which are arranged in sequence from the object side to the image side.

[0050] Among them, the first lens group S1 and the fourth lens group S4 are fixed groups, and the second lens group S2 and the third lens group S3 are movable groups. When the zoom telecentric lens changes from low magnification to high magnification, the second lens group S2 approaches the first lens group S1, and the third lens group S3 approaches the first lens group S1.

[0051] The first lens group S1, the second lens group S2, the third lens group S3, and the fourth lens group S4 satisfy the relationship:

[0052] 0.15<|f s2 / f s1 |<0.9

[0053] 0.1<|f s3 / f s1 |<0.85

[0054] 0.75<|f s4 / f s1 |<1.25

[0055] Among them, f s1 is the combined focal length of the first lens group S1, f s2 is the combined focal length of the second lens group S2, f s3is the combined focal length of the third lens group S3, f s4 is the combined focal length of the fourth lens group S4.

[0056] Among them, the air gap between the first lens group S1 and the second lens group S2 is D1, the air gap between the second lens group S2 and the third lens group S3 is D2, and the air gap between the third lens group S3 and the fourth lens group S4 is D3, satisfying the relationship:

[0057] 0.3<|D 1 / D 2 |<7.5

[0058] 0.25<|D 1 / D 3 |<7.5

[0059] 0.15<|D 2 / D 3 |<4.25.

[0060] In the present invention, the optical system structure composed of the above lenses achieves the following optical indicators:

[0061] Magnification: 0.5x-1.0x;

[0062] Working distance: 80mm;

[0063] Target size: 4 / 3 inch;

[0064] Object telecentricity: less than 0.05°;

[0065] Optical distortion: less than 0.02%;

[0066] Maximum resolution: 4.9μm;

[0067] Applicable spectral range: 450-700nm.

[0068] Embodiment 1:

[0069] The optical system of the large-target-surface continuously variable-magnification telecentric lens provided in this embodiment is as follows: Figure 2 As shown, the parameters of the first lens to the thirteenth lens are shown in the following table:

[0070]

[0071]

[0072] Wherein, R is the central radius of the lens surface, D is the distance from the corresponding optical surface to the next optical surface and the optical axis, nd corresponds to the refractive index of d light (wavelength 587nm); S1 and S2 are the object surface and image surface of the first lens, S3 and S4 are the object surface and image surface of the second lens, S5 and S6 are the object surface and image surface of the third lens, S6 and S7 are the object surface and image surface of the fourth lens, S8 and S9 are the object surface and image surface of the fifth lens, S9 and S10 are the object surface of the sixth lens and image side surfaces, S11 and S12 are the object surface and image side surfaces of the seventh lens, S13 and S14 are the object surface and image side surfaces of the eighth lens, Stop is the aperture stop surface, S15 and S16 are the object surface and image side surfaces of the ninth lens, S16 and S17 are the object surface and image side surfaces of the tenth lens, S18 and S19 are the object surface and image side surfaces of the eleventh lens, S20 and S21 are the object surface and image side surfaces of the twelfth lens, and S22 and S23 are the object surface and image side surfaces of the thirteenth lens.

[0073] Figure 2 A comparison chart of the lens provided in this embodiment (large target area continuously zooming telecentric lens) from low magnification to high magnification. When the zooming telecentric lens changes magnification from low magnification to high magnification, the second lens group approaches the first lens group, and the third lens group approaches the first lens group.

[0074] Figure 3 The MTF curve diagram of the lens at low magnification provided in this embodiment. Figure 3 It can be seen that the MTF curve of the lens is close to the diffraction limit at low magnification, and the MTF value is greater than 0.3 at 100lp / mm.

[0075] Figure 4 This is the MTF curve of the lens at high magnification provided in this embodiment. Figure 4 It can be seen that the MTF curve of the lens is close to the diffraction limit at high magnification, and the MTF value is greater than 0.2 at 100lp / mm.

[0076] Figure 5 This is a distortion curve diagram of the lens provided in this embodiment at low magnification. Figure 5 It can be seen that the optical distortion of the lens is less than 0.02% at low magnification.

[0077] Figure 6 This is a distortion curve diagram of the lens provided in this embodiment under high magnification conditions. Figure 6 It can be seen that the optical distortion of the lens is less than 0.02% at high magnification.

[0078] Figure 7 This is a spot diagram of the lens provided in this embodiment at low magnification. Figure 7It can be seen that at low magnification, the spot diagram of the lens is less than 6.5μm in the entire field of view.

[0079] Figure 8 This is a spot diagram of the lens provided in this embodiment at high magnification. Figure 8 It can be seen that at high magnification, the spot diagram of the lens is less than 7μm in the entire field of view.

[0080] Example 2

[0081] The optical system of the large-target-surface continuously variable-magnification telecentric lens provided in this embodiment is as follows: Fig. 9 As shown, the parameters of the first lens to the thirteenth lens are shown in the following table:

[0082]

[0083]

[0084] Wherein, R is the central radius of the lens surface, D is the distance from the corresponding optical surface to the next optical surface on the optical axis, nd corresponds to the refractive index of d light (wavelength 587nm); S1 and S2 are the object surface and image surface of the first lens, S3 and S4 are the object surface and image surface of the second lens, S5 and S6 are the object surface and image surface of the third lens, S6 and S7 are the object surface and image surface of the fourth lens, S8 and S9 are the object surface and image surface of the fifth lens, S9 and S10 are the object surface of the sixth lens and image side surfaces, S11 and S12 are the object surface and image side surfaces of the seventh lens, S13 and S14 are the object surface and image side surfaces of the eighth lens, Stop is the aperture stop surface, S15 and S16 are the object surface and image side surfaces of the ninth lens, S16 and S17 are the object surface and image side surfaces of the tenth lens, S18 and S19 are the object surface and image side surfaces of the eleventh lens, S20 and S21 are the object surface and image side surfaces of the twelfth lens, and S22 and S23 are the object surface and image side surfaces of the thirteenth lens.

[0085] The lens provided in this embodiment has an MTF curve close to the diffraction limit at low magnification, and the MTF value is greater than 0.2 at 100lp / mm; the MTF curve close to the diffraction limit at high magnification, and the MTF value is greater than 0.15 at 100lp / mm. The optical distortion of the lens is less than 0.1% at low magnification; the optical distortion of the lens is less than 0.1% at high magnification.

[0086] Example 3

[0087] The optical system of the large-target-surface continuously variable-magnification telecentric lens provided in this embodiment is as follows: Fig.10 As shown, the parameters of the first lens to the thirteenth lens are shown in the following table:

[0088]

[0089] Wherein, R is the central radius of the lens surface, D is the distance from the corresponding optical surface to the next optical surface on the optical axis, nd corresponds to the refractive index of d light (wavelength 587nm); S1 and S2 are the object surface and image surface of the first lens, S3 and S4 are the object surface and image surface of the second lens, S5 and S6 are the object surface and image surface of the third lens, S6 and S7 are the object surface and image surface of the fourth lens, S8 and S9 are the object surface and image surface of the fifth lens, S9 and S10 are the object surface of the sixth lens and image side surfaces, S11 and S12 are the object surface and image side surfaces of the seventh lens, S13 and S14 are the object surface and image side surfaces of the eighth lens, Stop is the aperture stop surface, S15 and S16 are the object surface and image side surfaces of the ninth lens, S16 and S17 are the object surface and image side surfaces of the tenth lens, S18 and S19 are the object surface and image side surfaces of the eleventh lens, S20 and S21 are the object surface and image side surfaces of the twelfth lens, and S22 and S23 are the object surface and image side surfaces of the thirteenth lens.

[0090] The lens provided in this embodiment has an MTF curve close to the diffraction limit at low magnification, and the MTF value is greater than 0.3 at 100lp / mm; the MTF curve close to the diffraction limit at high magnification, and the MTF value is greater than 0.17 at 100lp / mm. The optical distortion of the lens is less than 0.1% at low magnification; the optical distortion of the lens is less than 0.1% at high magnification.

Claims

1. A large-target-surface continuously variable-magnification telecentric lens, characterized in that: The telecentric lens includes, from the object plane to the image plane, a first lens group with positive refractive index power, a second lens group with positive refractive index power, a third lens group with positive refractive index power, and a fourth lens group with positive refractive index power; The first lens group and the fourth lens group are fixed groups, and the second lens group and the third lens group are movable groups. When the zoom telecentric lens changes from low magnification to high magnification, the second lens group moves closer to the first lens group, and the third lens group moves closer to the first lens group. The first lens group, the second lens group, the third lens group, and the fourth lens group satisfy the relationship: 0.15<|f s2 / f s1 |<0.9 0.1<|f s3 / f s1 |<0.85 0.75<|f s4 / f s1 |<1.25 Among them, f s1 is the combined focal length of the first lens group, f s2 is the combined focal length of the second lens group, f s3 is the combined focal length of the third lens group, f s4 is the combined focal length of the fourth lens group; The first lens group S1 includes a biconvex first lens G1 with positive focal power, a meniscus second lens G2 with positive focal power, a plano-convex third lens G3 with positive focal power, and a biconcave fourth lens G4 with negative focal power, which are arranged in sequence from the object side to the image side; wherein the third lens G3 and the fourth lens G4 are cemented to form a first cemented lens group U1 with negative focal power, and the focal length of the first cemented lens group is f U1 , and satisfy the relationship: 0.1<|f U1 / f s1 |<0.3; The second lens group S2 includes a fifth meniscus lens G5 with negative power, a sixth plano-convex lens G6 with positive power, and a seventh meniscus lens G7 with positive power, which are arranged in sequence from the object side to the image side; wherein the fifth lens G5 and the sixth lens G6 are cemented together to form a second cemented lens group U2 with positive power, and the focal length of the second cemented lens group is f U2 , and satisfy the relationship: 1.0<|f U2 / f s2 |<1.8; The third lens group S3 includes a meniscus eighth lens G8 with positive focal power, a plano-convex ninth lens G9 with positive focal power, and a plano-concave tenth lens G10 with negative focal power, which are arranged in sequence from the object side to the image side; wherein the ninth lens G9 and the tenth lens G10 are cemented together to form a third cemented lens group U3 with positive focal power, and the focal length of the third cemented lens group is f U3 , and satisfy the relationship: 3<|f U3 / f s3 |<4.5; The fourth lens group S4 includes a biconcave eleventh lens G11 with negative power, a plano-convex twelfth lens G12 with positive power, and a plano-convex thirteenth lens G13 with positive power, which are arranged in sequence from the object side to the image side.

2. The large-target-area continuously variable-magnification telecentric lens according to claim 1, characterized in that: The telecentric lens further includes an aperture, which is disposed between the eighth lens G8 and the third cemented lens group U3.

3. The large-target-surface continuously variable-magnification telecentric lens according to claim 2, characterized in that: The aperture stop is circular, moves with the third lens group S3 and has a constant diameter.

4. The large-target-area continuously variable-magnification telecentric lens according to claim 1, characterized in that: The first lens group, the second lens group, the third lens group and the fourth lens group are all spherical lenses.

5. The large-target-area continuously variable-magnification telecentric lens according to claim 1, characterized in that: The air interval between the first lens group S1 and the second lens group S2 is D1, the air interval between the second lens group S2 and the third lens group S3 is D2, and the air interval between the third lens group S3 and the fourth lens group S4 is D3. D1, D2 and D3 satisfy the relationship: 0.3<|D1 / D2|<7.5 0.25<|D1 / D3|<7.5 0.15<|D2 / D3|<4.25.

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