Double telecentric imaging system

Abstract

The utility model relates to the technical field of optical instruments, in particular to a double telecentric imaging system which is formed by combining an imaging module and a projection module, and the imaging module is formed by sequentially arranging a first lens, a second lens, a first bonding lens, a beam splitter prism, a second bonding lens, a third lens and a fourth lens along an optical axis from left to right; the projection module is formed by sequentially arranging a first lens, a second lens, a first bonding lens, a beam splitter prism, a fifth lens, a sixth lens, a seventh lens and an eighth lens from left to right along an optical axis. The first lens, the second lens, the first balsaming lens and the beam splitter prism are common parts of the imaging module and the projection module to form a front objective lens group of the module, so that the imaging quality of the system reaches the diffraction limit, and the problem that a traditional imaging system is poor in imaging quality and measurement precision is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of optical instruments, in particular to a double telecentric imaging system. Background Art

[0002] With the rise of CCD cameras, optical imaging systems can transfer real-time images to televisions or monitors for direct observation, and can also be photographed by cameras. With the development of the digital industry and the computer industry, the functions of optical systems have also been improved through them, making them easier to operate. By the end of the 1990s, the development of the semiconductor industry and the wafer requirements could bring more coordinated functions, the combination of hardware and software, intelligence, and humanization, which enabled various imaging systems to have greater development in the industry. Video display and digital display are optical objective lenses that use television camera targets or photoelectric couplers as receiving elements, import the magnified image into a television or computer, and display it on the display screen for observation and analysis. The main advantage of this type of optical system is that it is easy to realize the automation of detection and information processing when used in conjunction with a computer, and is applied to occasions where a large amount of tedious detection work is required.

[0003] The objective lens is the most important optical component of the imaging system. It uses light to form the first image of the object under inspection, and thus directly affects the quality of the image and various optical technical parameters. Among the various technical parameters of the objective lens, the ability to distinguish details and the measurement accuracy are the primary criteria for measuring the quality of the optical system. The measurement accuracy is greatly related to the telecentricity of the system, especially the object-image double telecentric system has a special advantage. Therefore, improving the resolution and telecentricity of the system has always been the main direction of the development of the optical system for measurement.

[0004] When an optical system is not a telecentric system, when there is a difference in the measured object distance, it will bring about a large measurement error, which is unacceptable for precision measurement instruments; when the system is a telecentric optical path, a slight change in the measured object distance will not bring about a change in the system's magnification, that is, in theory, it will not affect the measurement accuracy. When the object and image are both double telecentric, the advantage will be more obvious. Of course, the telecentric optical system will bring about relatively large high-order aberrations due to the high projection height of the imaging beam on the lens, which will greatly increase the difficulty of system design.

[0005] Modern optical objective lenses for measurement have reached a high level of perfection. Their numerical aperture and telecentricity are close to the limit. The resolution at the center of the field of view is very close to the theoretical value. However, the possibility of increasing the field of view of the objective lens and improving the imaging quality at the edge of the field of view still exists. This research is still ongoing. The aberrations related to the wide beam are spherical aberration, coma, and position chromatic aberration; the aberrations related to the field of view are astigmatism, field curvature, distortion, and magnification chromatic aberration. Therefore, it is of great significance to match the various technical parameters of the entire optical system to achieve the highest performance and highest efficiency according to the specific conditions and requirements of actual use. Utility Model Content

[0006] The utility model aims to provide a dual telecentric imaging system, aiming to solve the problems of poor imaging quality and poor measurement accuracy of traditional imaging systems.

[0007] To achieve the above-mentioned purpose, the utility model provides a dual telecentric imaging system, including an imaging module and a projection module;

[0008] The imaging module includes a front objective lens group and a first rear objective lens group;

[0009] The projection module includes a front objective lens group and a second rear objective lens group;

[0010] The front objective lens group includes a first lens, a second lens, a first cemented lens and a beam splitter prism;

[0011] The first rear objective lens group includes a second cemented lens, a third lens, a fourth lens and a first system light barrier;

[0012] The second rear objective lens group includes a fifth lens, a sixth lens, a seventh lens, an eighth lens and a second system aperture;

[0013] The first lens, the second lens, the first cemented lens, the beam splitter prism, the second cemented lens, the third lens and the fourth lens included in the imaging module are arranged in sequence along the optical axis, and the first system light barrier is located between the beam splitter prism and the second cemented lens;

[0014] The first lens, the second lens, the first cemented lens, the beam splitter prism, the fifth lens, the sixth lens, the seventh lens and the eighth lens included in the projection module are arranged in sequence along the optical axis, and the second system light barrier is located between the beam splitter prism and the fifth lens;

[0015] Assume that the combined focal length of the first lens and the second lens is f1, the focal length of the first cemented lens is f2; the focal length of the second cemented lens is f3, and the combined focal length of the third lens and the fourth lens is f4, and they satisfy the following inequality:

[0016] 2.81<|f1 / f2|<3.52

[0017] 1.46<|f3 / f4|<1.53.

[0018] The first cemented lens is composed of a crown glass lens and a flint glass lens, wherein the crown glass lens is in front and has a positive focal length, and the flint glass lens is in the back and has a negative focal length.

[0019] The second cemented lens is composed of a flint glass lens and a crown glass lens, wherein the flint glass is in front and has a negative focal length, and the crown glass lens is in the back and has a positive focal length.

[0020] The concave surfaces of the fifth lens and the sixth lens are opposite and closely arranged. The fifth lens is a flint glass lens with a high refractive index, and the sixth lens is a crown glass lens with a low dispersion.

[0021] Wherein, the seventh lens and the eighth lens are both positive lenses, and the seventh lens is a positive meniscus lens, with the concave surface facing the direction of the beam splitter prism.

[0022] Wherein, the combined focal length of the fifth lens and the sixth lens is assumed to be f5; the combined focal length of the seventh lens and the eighth lens is f6, and the following inequality is satisfied between them: 9.15<|f5 / f6|<11.23.

[0023] The dual telecentric imaging system of the utility model is composed of an imaging module and a projection module, wherein the imaging module is composed of the first lens, the second lens, the first cemented lens, the dichroic prism, the second cemented lens, the third lens and the fourth lens arranged in sequence from left to right along the optical axis; the projection module is composed of the first lens, the second lens, the first cemented lens, the dichroic prism, the fifth lens, the sixth lens, the seventh lens and the eighth lens arranged in sequence from left to right along the optical axis. The first lens, the second lens, the first cemented lens and the dichroic prism are the common parts of the imaging module and the projection module, and constitute the front objective lens group of the module, so that the imaging quality of the system reaches the diffraction limit, thereby solving the problem of poor imaging quality and measurement accuracy of the traditional imaging system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, 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 utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is a diagram of an imaging optical system used for video display in the utility model;

[0026] Figure 2 It is a projection optical system diagram for video display of the utility model;

[0027] Figure 3 It is a wave aberration curve diagram of the double telecentric imaging optical system used for video display of the utility model;

[0028] Figure 4 It is a wave aberration curve diagram of the double telecentric projection optical system used for video display of the utility model;

[0029] Figure 5 It is the MTF curve diagram of the double telecentric imaging optical system used for video display of the utility model;

[0030] Figure 6 It is the MTF curve diagram of the double telecentric projection optical system used for video display of the utility model;

[0031] Figure 7 It is a field curvature and distortion curve diagram of the double telecentric imaging optical system used for video display of the utility model;

[0032] Figure 8 It is a field curvature and distortion curve diagram of the double telecentric projection optical system used for video display in the utility model;

[0033] Fig. 9 It is an overall diagram of a double telecentric optical system for video display of the utility model.

[0034] In the figure: E1-front objective lens group, E2-first rear objective lens group, E3-second rear objective lens group, U1-first lens, U2-second lens, J1-first cemented lens, P-beam splitter prism, J2-second cemented lens, U3-third lens, U4-fourth lens, U5-fifth lens, U6-sixth lens, U7-seventh lens, U8-eighth lens, STOP1-first system light barrier, STOP2-second system light barrier. DETAILED DESCRIPTION

[0035] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0036] See also Figures 1 to 9, the utility model provides a dual telecentric imaging system, including an imaging module and a projection module;

[0037] The imaging module comprises a front objective lens group (E1) and a first rear objective lens group (E2);

[0038] The projection module comprises a front objective lens group (E1) and a second rear objective lens group (E3);

[0039] The front objective lens group (E1) comprises a first lens (U1), a second lens (U2), a first cemented lens (J1) and a beam splitter prism (P);

[0040] The first rear objective lens group (E2) includes a second cemented lens (J2), a third lens (U3), a fourth lens (U4) and a first system light barrier (STOP1);

[0041] The second rear objective lens group (E3) includes a fifth lens (U5), a sixth lens (U6), a seventh lens (U7), an eighth lens (U8) and a second system light barrier (STOP2);

[0042] The imaging module comprises the first lens (U1), the second lens (U2), the first cemented lens (J1), the beam splitter prism (P), the second cemented lens (J2), the third lens (U3) and the fourth lens (U4), which are arranged in sequence along the optical axis, and the first system light barrier (STOP1) is located between the beam splitter prism (P) and the second cemented lens (J2);

[0043] The projection module comprises the first lens (U1), the second lens (U2), the first cemented lens (J1), the beam splitter prism (P), the fifth lens (U5), the sixth lens (U6), the seventh lens (U7) and the eighth lens (U8), which are arranged in sequence along the optical axis, and the second system light barrier (STOP2) is located between the beam splitter prism (P) and the fifth lens (U5).

[0044] Assuming that the combined focal length of the first lens (U1) and the second lens (U2) is f1, the focal length of the first cemented lens (J1) is f2; the focal length of the second cemented lens (J2) is f3, and the combined focal length of the third lens (U3) and the fourth lens (U4) is f4, they satisfy the following inequality:

[0045] 2.81<|f1 / f2|<3.52

[0046] 1.46<|f3 / f4|<1.53.

[0047] In this embodiment, for the imaging module, the light emitted from the object plane passes through the front objective lens and the first rear lens group to form an image on the CMOS surface. For the projection module, the light emitted by the DMD passes through the second rear lens group and the front objective lens to project an image on the object plane. The projected image is mainly used to assist image analysis. The imaging module and the projection module are connected together through a beam splitter prism. The first lens (U1), the second lens (U2), the third lens (U3), and the fourth lens (U4) are all single lenses, and the first cemented lens J1 and the second cemented lens J2 are both double cemented lenses. From the perspective of both sides of the first light barrier STOP1, the imaging optical system is approximately a symmetrical structure. For a symmetrical structure, the vertical axis aberration of the system has a very small residual amount due to the existence of the offset effect. The positional relationship between the positive and negative lenses in each cemented lens is: the first cemented lens (J1) is a positive-negative type, and the second cemented lens (J2) is a negative-positive type. The negative lenses of the two double cemented lenses are opposite, which can ensure that the incident angle of light on the cemented surface is small from the design point of view;

[0048] The ratio of the focal length of the second cemented lens (J2) of the first rear objective lens group (E2) to the combined focal length of the third lens (U3) and the fourth lens (U4) determines the overall performance of the optical system of this structural form. The focal length of the second cemented lens (J2) is f3, and the combined focal length of the third lens (U3) and the fourth lens (U4) is f4, and they satisfy the following inequality:

[0049] 1.46<|f3 / f4|<1.53.

[0050] If this range is exceeded, it will be difficult for system optimization to simultaneously ensure the image quality and the system image telecentricity (less than 0.05'). Such a structure is more beneficial to the aberration control of the entire system result.

[0051] The first cemented lens (J1) is cemented with a low-dispersion crown glass positive lens and a thick negative flint glass lens, with the crown glass lens in front. Its main function in the system is to correct the field curvature of the system to ensure that the image on the CMOS image plane is not bent.

[0052] Furthermore, the first cemented lens (J1) is composed of a crown glass lens and a flint glass lens, wherein the crown glass lens is in front and has a positive focal length, and the flint glass lens is in the back and has a negative focal length.

[0053] Furthermore, the second cemented lens (J2) is composed of a flint glass lens and a crown glass lens, wherein the flint glass lens is in front and has a negative focal length, and the crown glass lens is in the back and has a positive focal length.

[0054] Furthermore, the concave surfaces of the fifth lens (U5) and the sixth lens (U6) are opposite and closely arranged, the fifth lens (U5) is a flint glass lens with a high refractive index, and the sixth lens (U6) is a crown glass lens with a low dispersion.

[0055] Furthermore, the seventh lens (U7) and the eighth lens (U8) are both positive lenses, and the seventh lens (U7) is a meniscus positive lens with its concave surface facing the direction of the beam splitter prism (P).

[0056] Furthermore, the combined focal length of the fifth lens (U5) and the sixth lens (U6) is assumed to be f5; the combined focal length of the seventh lens (U7) and the eighth lens (U8) is assumed to be f6, and the following inequality is satisfied between the two: 9.15<|f1 / f2|<11.23.

[0057] In order to fully improve the uniformity of the image plane, the double telecentric optical system for video display of the utility model adopts a double telecentric solution for the object and the image, and the light barrier is located at the focal position of the front objective lens group E1, the first rear objective lens group E2, and the second rear objective lens group E3.

[0058] From the perspective of system adjustment, it is necessary to set up some effective and feasible adjustment mechanisms to compensate for processing and assembly errors. According to the tolerance analysis of the system, the third lens (U3) and the fourth lens (U4) are combined into an integral adjustment unit, and its axial left and right movement can well compensate for various axial errors of the system.

[0059] In order to further improve the imaging quality of the system, the aberration compensation relationship between the front objective lens group (E1) and the first rear objective lens group (E2) can be used to compensate and eliminate the respective residual aberrations to the maximum extent, thereby obtaining a high-performance double telecentric optical system.

[0060] The utility model discloses a dual telecentric optical system for video display. The light beam of the projection module needs to enter the system to provide a reference image on the object surface. Therefore, a beam splitter prism (P) is added between the front objective lens group (E1) and the first rear objective lens group (E2). The projection light beam enters the system from one side of the beam splitter prism (P), and illuminates the detection object surface after passing through the second rear objective lens group (E3). The detection object surface is then imaged onto a CMOS through an imaging objective lens system, i.e., the front objective lens group (E1) and the first rear objective lens group (E2).

[0061] The imaging performance curve of the system is shown in Figure 3 to Figure 8 As shown;

[0062] See also Figure 3, is a wave aberration curve diagram of the imaging part of the double telecentric optical system of the utility model. The maximum scale of the ordinate in the figure is 0.2wave. It can be seen that within the waveband range of 420nm-700nm, the wave aberration of each field of view and aperture is much smaller than a quarter wavelength.

[0063] See also Figure 4 , is a wavefront aberration curve diagram of the projection part of the double telecentric optical system of the utility model. The maximum scale of the ordinate in the figure is 0.5 wave. It can be seen that within the 420nm-700nm band, the wavefront aberration of each field of view and aperture is less than a quarter of a wavelength.

[0064] See also Figure 5 , Figure 6 This is the MTF curve of the diffraction transfer function of the double telecentric optical system of the utility model within the 420nm-700nm band. It can be seen that the system diffraction limit has been reached.

[0065] See also Figure 7 , Figure 8 It is a field curvature and distortion diagram of the double telecentric optical system of the utility model within the wavelength range of 420nm-700nm. It can be seen that the optical distortion in the maximum field of view is less than 0.01%.

[0066] See also Fig. 9 , is the general assembly diagram of the double telecentric optical system of the utility model, in which the horizontal part is the imaging optical system, which is connected to the projection optical system through a beam splitter prism (P), and the two share a common front objective lens group (E1).

[0067] The above disclosure is only a preferred embodiment of the dual telecentric imaging system of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope covered by the utility model.

Claims

1. A dual telecentric imaging system, characterized in that: including an imaging module and a projection module; The imaging module comprises a front objective lens group (E1) and a first rear objective lens group (E2); The projection module comprises a front objective lens group (E1) and a second rear objective lens group (E3); The front objective lens group (E1) comprises a first lens (U1), a second lens (U2), a first cemented lens (J1) and a beam splitter prism (P); The first rear objective lens group (E2) includes a second cemented lens (J2), a third lens (U3), a fourth lens (U4) and a first system light barrier (STOP1); The second rear objective lens group (E3) includes a fifth lens (U5), a sixth lens (U6), a seventh lens (U7), an eighth lens (U8) and a second system light barrier (STOP2); The imaging module comprises the first lens (U1), the second lens (U2), the first cemented lens (J1), the beam splitter prism (P), the second cemented lens (J2), the third lens (U3) and the fourth lens (U4), which are arranged in sequence along the optical axis, and the first system light barrier (STOP1) is located between the beam splitter prism (P) and the second cemented lens (J2); The projection module comprises the first lens (U1), the second lens (U2), the first cemented lens (J1), the beam splitter prism (P), the fifth lens (U5), the sixth lens (U6), the seventh lens (U7) and the eighth lens (U8), which are arranged in sequence along the optical axis, and the second system light barrier (STOP2) is located between the beam splitter prism (P) and the fifth lens (U5); Assuming that the combined focal length of the first lens (U1) and the second lens (U2) is f1, the focal length of the first cemented lens (J1) is f2; the focal length of the second cemented lens (J2) is f3, and the combined focal length of the third lens (U3) and the fourth lens (U4) is f4, they satisfy the following inequality: 2.81<|f1 / f2|<3.52 1.46<|f3 / f4|<1.

53.

2. The dual telecentric imaging system according to claim 1, characterized in that: The first cemented lens (J1) is composed of a crown glass lens and a flint glass lens, wherein the crown glass lens is in front and has a positive focal length, and the flint glass lens is in the back and has a negative focal length.

3. The dual telecentric imaging system according to claim 2, characterized in that: The second cemented lens (J2) is composed of a flint glass lens and a crown glass lens, wherein the flint glass is in front and has a negative focal length, and the crown glass lens is in the back and has a positive focal length.

4. The dual telecentric imaging system according to claim 3, characterized in that: The concave surfaces of the fifth lens (U5) and the sixth lens (U6) are opposite and closely arranged. The fifth lens (U5) is a flint glass lens with a high refractive index, and the sixth lens (U6) is a crown glass lens with a low dispersion.

5. The dual telecentric imaging system according to claim 4, characterized in that: The seventh lens (U7) and the eighth lens (U8) are both positive lenses. The seventh lens (U7) is a meniscus positive lens, with its concave surface facing the direction of the beam splitter prism (P).

6. The dual telecentric imaging system according to claim 5, characterized in that: Assume that the combined focal length of the fifth lens (U5) and the sixth lens (U6) is f5; the combined focal length of the seventh lens (U7) and the eighth lens (U8) is f6, and the following inequality is satisfied between the two: 9.15<|f5 / f6|<11.23.

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