A telecentric lens

Abstract

The present invention relates to the field of lens technology, and in particular to a telecentric lens, comprising a front lens group and a first rear lens group; the front lens group comprises a first lens group with a positive focal length, the first lens group comprises a first lens and a second lens arranged in sequence from the object side to the first image side; the first rear lens group comprises a first diaphragm, a second lens group with a negative focal length, a third lens group with a negative focal length, and a fourth lens group with a positive focal length, arranged in sequence from the object side to the first image side. The telecentric lens provided by the present invention adopts a large-aperture front lens group to expand the field of view, and then through the position focal length setting of the first diaphragm, the obtained image has better clarity, thereby improving the accuracy of telecentric lens detection.

Description

Technical Field

[0001] The invention relates to the technical field of lenses, and in particular to a telecentric lens. Background Art

[0002] Telecentric lens is a high-end machine vision lens. Its characteristic is to eliminate the problem of different magnifications caused by the inconsistent distance between the measured object (or CCD chip) and the lens. Due to the unique technical advantages of telecentric lens, it is currently used in the demand for high-precision detection such as mechanical parts measurement, plastic parts measurement, glass products and medical parts measurement, electronic components measurement, etc., and is particularly suitable for precision measurement occasions.

[0003] At present, the market demand for telecentric lenses is increasing, and at the same time, the imaging requirements for lenses are becoming more stringent, requiring a wide field of view as well as high detection accuracy. This poses a great challenge to the selection of lenses. In many cases, the lens has a wide field of view, but the image obtained is inevitably not clear enough, resulting in inaccurate measurement results. Summary of the invention

[0004] In view of the problems of the prior art, the present invention provides a telecentric lens which has a large field of view and accurate detection results.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solution: a telecentric lens, comprising a front lens group and a first rear lens group; the front lens group comprises a first lens group with a positive focal length, the first lens group comprises a first lens and a second lens arranged in sequence from an object side to a first image side;

[0006] The first rear lens group includes a first aperture, a second lens group with a negative focal length, a third lens group with a negative focal length, and a fourth lens group with a positive focal length, which are arranged in sequence from the object side to the first image side.

[0007] Preferably, a reflector is provided between the front lens group and the first rear lens group, and the light beam of the front lens group passes through the first rear lens group after being reflected by the reflector.

[0008] Preferably, the first lens is a plano-convex lens, and the second lens is a meniscus-convex lens.

[0009] Preferably, the focal length of the first lens is set to f5, and the focal length of the second lens is set to f6, and the focal length f5 and the focal length f6 should satisfy: |f5 / f6-1|≤10%.

[0010] Preferably, the second lens group includes a third lens and a fourth lens arranged in sequence from the object side to the first image side, the third lens is a meniscus convex lens, the fourth lens is a meniscus concave lens, and the third lens and the fourth lens are glued together;

[0011] The third lens group includes a fifth lens and a sixth lens arranged in sequence from the object side to the first image side, the fifth lens is a concave lens of a meniscus type, the sixth lens is a meniscus convex lens, and the fifth lens and the sixth lens are cemented together;

[0012] The fourth lens group includes a seventh lens, an eighth lens and a first plane mirror which are arranged in sequence from the object side to the first image side. The seventh lens is a biconvex lens, and the eighth lens is a biconvex lens.

[0013] Preferably, the focal length of the front lens group is set to f, and the focal length of the first rear lens group is set to f1, then the focal lengths f and f1 satisfy 180 mm. <f<280mm,|(f1 / f-0.16) / 0.16|≤10%。

[0014] Preferably, the back focus of the front lens group is set to fbl, then |(fbl-f) / f|≤10%.

[0015] Preferably, the front lens group and the first rear lens group are both made of optical glass with a refractive index nd>1.6.

[0016] Beneficial effects of the present invention:

[0017] A telecentric lens provided by the present invention adopts a large-aperture front lens group to expand the field of view, and then through the position focal length setting of the first aperture, the obtained image has better clarity, thereby improving the accuracy of telecentric lens detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of embodiment 1 of the present invention.

[0019] Figure 2 This is a schematic diagram of the structure of Example 2 of the present invention.

[0020] exist Figure 1 to Figure 2 Reference numerals in the drawings include:

[0021] 1-front end lens group, 11-first lens group, 111-first lens, 112-second lens, 2-first rear end lens group, 21-first aperture, 22-second lens group, 221-third lens, 222-fourth lens, 23-third lens group, 231-fifth lens, 232-sixth lens, 24-fourth lens group, 241-seventh lens, 242-eighth lens, 243-first plane mirror, 3-reflecting mirror. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with the embodiments and drawings, and the contents mentioned in the embodiments are not intended to limit the present invention. The present invention is described in detail below in conjunction with the drawings.

[0023] Embodiment 1:

[0024] This embodiment provides a telecentric lens, such as Figure 1 , including a front lens group 1 and a first rear lens group 2; the front lens group 1 includes a first lens group 11 with a positive focal length, the first lens group 11 includes a first lens 111 and a second lens 112 arranged in sequence from the object side to the first image side; the first rear lens group 2 includes a first aperture 21, a second lens group 22 with a negative focal length, a third lens group 23 with a negative focal length, and a fourth lens group 24 with a positive focal length, which are arranged in sequence from the object side to the first image side.

[0025] The first lens 111 is a plano-convex lens, the second lens 112 is a concave-convex convex lens, the focal length of the first lens 111 is set to f5, and the focal length of the second lens 112 is set to f6, then the focal length f5 and the focal length f6 should satisfy the error condition of |f5 / f6-1|≤10%, so as to ensure that the front lens group 1 can obtain a larger field of view;

[0026] The specific structure of the first rear lens group 2 is as follows: the second lens group 22 includes a third lens 221 and a fourth lens 222 arranged in sequence from the object side to the first image side, the third lens 221 is a concave-convex convex lens, the fourth lens 222 is a concave-convex concave lens, and the third lens 221 and the fourth lens 222 are glued together; the third lens group 23 includes a fifth lens 231 and a sixth lens 232 arranged in sequence from the object side to the first image side, the fifth lens 231 is a concave-convex concave lens, the sixth lens 232 is a concave-convex convex lens, and the fifth lens 231 and the sixth lens 232 are glued together; the use of double glued lenses can effectively eliminate chromatic aberration and amplify monochromatic aberration. The fourth lens group 24 includes a seventh lens 241, an eighth lens 242 and a first plane mirror 243 arranged in sequence from the object side to the first image side, the seventh lens 241 is a biconvex lens, and the eighth lens 242 is a biconvex lens.

[0027] Specifically, the focal length f of the front lens group 1 and the focal length f1 of the first rear lens group 2 in this embodiment preferably satisfy f1 / f = 0.16, and |(f1 / f - 0.16) / 0.16| ≤ 10%. Through experiments, this accuracy range can reduce the deviation of the acquired image, improve the detection accuracy. Moreover, the focal length range of the front lens group 1 is 180mm < f < 280mm, further improving the detection accuracy.

[0028] Regarding the position setting of the first aperture 21, the back intercept of the front lens group is fbl, such that |(fbl - f) / f| ≤ 10%, thereby restricting the position of the first aperture 21, and further ensuring that under the conditions of large field of view and high-precision measurement, the acquired field of view has uniform illuminance and good brightness.

[0029] In addition, the front lens group 1, the first rear lens group 2, and the second rear lens group 3 all adopt optical glass materials with a refractive index nd > 1.6, which can ensure that the lens has better telecentricity.

[0030] The telecentric lens provided in this embodiment uses a front lens group 1 with a large aperture to expand the field of view, and then through the position and focal length setting of the first aperture 21, the obtained image has better clarity, thereby improving the accuracy of the telecentric lens detection.

[0031] Embodiment 2:

[0032] The telecentric lens provided in this embodiment, as Figure 2 , the difference between Embodiment 2 and Embodiment 1 is that a reflector 3 is provided between the front lens group 1 and the first rear lens group 2, and the light beam of the front lens group 1 passes through the first rear lens group 2 after being reflected by the reflector 3.

[0033] Specifically, the path of the reflected light beam is bent, so that the detection image can be obtained from the side of the telecentric lens. The reflector 3 can also be set at other positions in the first rear lens group 2 to bend the light beam, so that the length of the bent light path is different, and the user can set according to actual needs, so as to be applicable to more product detection occasions.

[0034] The above are only preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention is disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, when making some changes or modifications using the above-disclosed technical content as equivalent change equivalent embodiments, but as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical meaning of the present invention all fall within the scope of the technical solution of the present invention.

Claims

1. A telecentric lens, characterized in that: It includes a front lens group and a first rear lens group; the telecentric lens includes nine lenses in total; the front lens group includes a first lens group with a positive focal length, and the first lens group includes a first lens and a second lens arranged in sequence from the object side to the first image side; The first rear lens group includes a first aperture, a second lens group with a negative focal length, a third lens group with a negative focal length, and a fourth lens group with a positive focal length, which are arranged in sequence from the object side to the first image side; A reflector is provided between the front lens group and the first rear lens group, and the light beam of the front lens group passes through the first rear lens group after being reflected by the reflector; The first lens is a plano-convex lens, and the second lens is a concave-convex convex lens; The focal length of the first lens is set to f5, and the focal length of the second lens is set to f6. Then the focal length f5 and the focal length f6 should satisfy: ; The second lens group includes a third lens and a fourth lens arranged in sequence from the object side to the first image side, the third lens is a meniscus convex lens, the fourth lens is a meniscus concave lens, and the third lens and the fourth lens are glued together; The third lens group includes a fifth lens and a sixth lens arranged in sequence from the object side to the first image side, the fifth lens is a concave lens of a meniscus type, the sixth lens is a meniscus convex lens, and the fifth lens and the sixth lens are cemented together; The fourth lens group includes a seventh lens, an eighth lens and a first plane mirror arranged in sequence from the object side to the first image side, the seventh lens is a biconvex lens, and the eighth lens is a biconvex lens; The focal length of the front lens group is set to f, and the focal length of the first rear lens group is set to f1, then the focal lengths f and f1 satisfy 180mm <f<280mm, .

2. A telecentric lens according to claim 1, characterized in that: The back focus of the front lens group is set to fbl, then .

3. A telecentric lens according to claim 1, characterized in that: The front lens group and the first rear lens group are both made of optical glass with a refractive index nd>1.6.

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