Double liquid telecentric lens

Abstract

The invention discloses a double liquid telecentric lens, which belongs to the technical field of optical design and is sequentially provided with an optical amplification group, an aperture diaphragm, a liquid lens and an imaging group along an optical path. Wherein the optical amplification group comprises three lenses, the first lens is a biconvex lens, the second lens is a biconvex lens, and the third lens is a biconcave lens in the direction of an optical path; the liquid lens comprises protective glass, optical liquid is packaged in the protective glass, and a magnetic field generator for adjusting the curvature of the liquid lens is arranged on the protective glass; the imaging group comprises three lenses, along the optical path direction, the fifth lens is a convex-concave lens, the sixth lens is a biconcave lens, and the seventh lens is a concave-convex lens. On the premise of keeping the magnification and resolution of the lens unchanged, the high-low fall detection accuracy and speed can be effectively improved, so that the high-low fall detection method plays a greater role in various precision detection fields.

Description

Technical Field

[0001] The invention belongs to the technical field of optical design, and in particular relates to a double liquid telecentric lens. Background Art

[0002] With the rapid development of the machine vision industry, practitioners have higher and higher requirements for the overall performance of the system. Most practitioners hope to have the highest possible visual accuracy and lens resolution, but this often conflicts with the height difference of the object to be tested. In the end, they can only give up high magnification and high resolution, or use machine means to change the relative position of the lens and the object to be tested, but this introduces new errors to the system. Liquid telecentric lenses can maintain the magnification and resolution of the lens while ensuring the accuracy and speed of height difference detection. As a special lens that can provide low distortion and low telecentricity imaging, telecentric lenses can greatly improve the accuracy of the system and are increasingly recognized by practitioners. However, in the face of more and more applications, the telecentric lens cannot change the working distance by adjusting the lens itself, which greatly limits the practitioners' pursuit of higher visual accuracy.

[0003] In practical applications, existing solutions generally choose to increase the depth of field by reducing the magnification, so as to accommodate the height difference within the imaging range, but this method will reduce the resolution of the lens and the visual accuracy of the overall system. Alternatively, the relative position of the lens and the object to be measured can be changed by using electric tracks or other methods to achieve imaging of different heights of the object to be measured, but this method is difficult to maintain accuracy and speed at the same time, and puts higher requirements on the design of the entire system. If it is a relatively old mechanism, it may not even be modified, and the only choice is to give up the use of high-magnification telecentric lenses. Summary of the invention

[0004] The present invention solves the technical problems existing in the known technology and provides a double liquid telecentric lens. The curvature of the liquid lens is adjusted by a magnetic field generator, so that the telecentric lens can adjust the corresponding working distance according to different needs. The realization of this technology means that the accuracy and speed of high and low drop detection can be effectively improved under the premise of keeping the magnification and resolution of the lens unchanged, thereby playing a greater role in various precision detection fields.

[0005] The object of the present invention is to provide a double liquid telecentric lens, which is provided with an optical magnification group, an aperture stop, a liquid lens and an imaging group in sequence along the optical path; wherein:

[0006] The optical magnification group includes three lenses. Along the light path direction, the first lens is a biconvex lens, the second lens is a biconvex lens, and the third lens is a biconcave lens;

[0007] The liquid lens comprises a protective glass, an optical liquid is encapsulated inside the protective glass, and a magnetic field generator for adjusting the curvature of the liquid lens is arranged on the protective glass;

[0008] The imaging group includes three lenses. Along the light path direction, the fifth lens is a convex-concave lens, the sixth lens is a biconcave lens, and the seventh lens is a concave-convex lens.

[0009] Preferably, the radius of curvature of the light incident surface of the first lens is 24±5%, and the radius of curvature of the light exit surface is -45±5%; the radius of curvature of the light incident surface of the second lens is 40±5%, and the radius of curvature of the light exit surface is -40±5%; the radius of curvature of the light incident surface of the third lens is -23±5%, and the radius of curvature of the light exit surface is 73±5%; the radius of curvature of the light incident surface of the fifth lens is 11±5%, and the radius of curvature of the light exit surface is 73±5%; the radius of curvature of the light incident surface of the sixth lens is -80±5%, and the radius of curvature of the light exit surface is 16±5%; the radius of curvature of the light incident surface of the seventh lens is -13±5%, and the radius of curvature of the light exit surface is -30±5%; the unit of the radius of curvature is millimeter.

[0010] Preferably, the center thickness of the first lens is 3±5%, the center thickness of the second lens is 3±5%, the center thickness of the third lens is 5±5%, the total thickness of the liquid lens is 5±5%, the center thickness of the fifth lens is 3±5%, the center thickness of the sixth lens is 2±5%, and the center thickness of the seventh lens is 2±5%, and the unit of the center thickness is millimeter.

[0011] Preferably, the distance between the object and the first lens on the optical axis is 67±5%; the distance between the first lens and the second lens on the optical axis is 5±5%; the distance between the second lens and the third lens on the optical axis is 1±5%; the distance between the third lens and the aperture stop on the optical axis is 1±5%; the distance between the aperture stop and the liquid lens on the optical axis is 14±5%; the distance between the liquid lens and the fifth lens on the optical axis is 37±5%; the distance between the fifth lens and the sixth lens on the optical axis is 1±5%; the distance between the sixth lens and the seventh lens on the optical axis is 4±5%. The unit of distance is millimeter.

[0012] Preferably, the refractive index of the first lens is 1.49±5%, and the Abbe number is 56±5%; the refractive index of the second lens is 1.53±5%, and the Abbe number is 58±5%; the refractive index of the third lens is 1.69±5%, and the Abbe number is 28±5%; the refractive index of the fifth lens is 1.57±5%, and the Abbe number is 35±5%; the refractive index of the sixth lens is 1.67±5%, and the Abbe number is 51±5%; the refractive index of the seventh lens is 1.67±5%, and the Abbe number is 51±5%.

[0013] Preferably, the magnetic field generator performs data exchange with a host computer via a single chip microcomputer.

[0014] Preferably, the working distance of the double liquid telecentric lens is 65 mm, and the working band is 450 nm to 700 nm.

[0015] The advantages and positive effects of the present invention are:

[0016] The technical solution of the present invention mainly includes six lenses, an aperture stop and a liquid lens made of multiple materials. Each lens has its own unique functional focus, so that each performance parameter of the lens is responsible for the corresponding lens, so that the performance parameters are more optimized. Among them, the parameters of the first lens determine the field of view size and the initial working distance of the lens, the second lens further shrinks the light to leave space for object telecentricity control, the third lens compensates for part of the aberration caused by the first lens and the second lens through a high refractive index, so that the light is input into the liquid lens more smoothly, and cooperates with the first lens and the second lens to control the object telecentricity, the liquid lens changes the overall focal length of the optical system by adjusting the curvature to achieve the change of the working distance, the fifth lens manages the edge field of view light and reduces the distortion and field curvature of the system, the sixth lens and the seventh lens cooperate to control the back focus of the lens, and the fifth and sixth lens combination is similar to the seventh lens in material, appearance and direction, so that the aberration can be eliminated as much as possible, and the seventh lens is also responsible for controlling the image size of the lens and the overall magnification.

[0017] In the present invention, each lens performs its own function and cooperates with each other, so that the lens formed by the combination can tolerate the aberration caused by different curvatures of the liquid lens and maintain the excellent performance of low telecentricity and distortion rate of the lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The optical path diagram of the preferred embodiment of the present invention;

[0019] Figure 2 The optical dispersion pattern of the preferred embodiment of the present invention;

[0020] Figure 3The modulation transfer function MTF diagram in the preferred embodiment of the present invention;

[0021] Figure 4 Field curvature and astigmatism diagrams of a preferred embodiment of the present invention; DETAILED DESCRIPTION

[0022] In order to further understand the content, features and effects of the present invention, the following embodiments are given as examples and described in detail with reference to the accompanying drawings:

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the technical solutions in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "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 invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0025] See also Figure 1 .

[0026] A double liquid telecentric lens mainly includes the following four parts: a first optical magnification group, an aperture stop, a liquid lens and an imaging group; wherein:

[0027] The optical magnification group mainly includes three lenses, along the optical path: the first lens L1 is a biconvex lens, the second lens L2 is a biconvex lens, and the third lens L3 is a biconcave lens; the aperture stop is placed afterwards; the liquid lens L4 mainly includes protective glass, optical liquid and a magnetic field generator, the optical liquid is encapsulated inside the protective glass, the magnetic field generator is controlled by a single-chip microcomputer, and the single-chip microcomputer can communicate with the host computer; the imaging group mainly includes three lenses, the fifth lens L5 is a convex-concave lens, the sixth lens L6 is a biconcave lens, and the seventh lens L7 is a concave-convex lens.

[0028] In order to more clearly understand the concept of the present invention, it is described in detail below:

[0029] Further explanation of the lenses that make up the optical path: Since the curvature of the liquid lens is variable and controlled by the circuit, in the design scheme, the liquid lens is not allowed to participate in the refraction, and the curvature is infinite. The curvature radius of the light-entering surface of the first lens L1 is 24±5%, and the curvature radius of the light-exiting surface is -45±5%; the curvature radius of the light-entering surface of the second lens L2 is 40±5%, and the curvature radius of the light-exiting surface is -40±5%; the curvature radius of the light-entering surface of the third lens L3 is -23±5%, and the curvature radius of the light-exiting surface is 73±5%; the curvature radius of the light-entering surface of the fifth lens L5 is 11±5%, and the curvature radius of the light-exiting surface is 73±5%; the curvature radius of the light-entering surface of the sixth lens L6 is -80±5%, and the curvature radius of the light-exiting surface is 16±5%; the curvature radius of the light-entering surface of the seventh lens L7 is -13±5%, and the curvature radius of the light-exiting surface is -30±5%. The units are all millimeters.

[0030] The center thickness of each lens constituting the double telecentric optical path is: the center thickness of the first lens L1 is 3±5%; the center thickness of the second lens L2 is 3±5%; the center thickness of the third lens L3 is 5±5%; the total thickness of the liquid lens is 5±5%; the center thickness of the fifth lens L5 is 3±5%; the center thickness of the sixth lens L6 is 2±5%; the center thickness of the seventh lens L7 is 2±5%. The units are all millimeters.

[0031] The distance between the object and the first lens L1 on the optical axis is 67±5%; the distance between the first lens L1 and the second lens L2 on the optical axis is 5±5%; the distance between the second lens L2 and the third lens L3 on the optical axis is 1±5%; the distance between the third lens L3 and the diaphragm on the optical axis is 1±5%; the distance between the diaphragm and the liquid lens on the optical axis is 14±5%; the distance between the liquid lens and the fifth lens L5 on the optical axis is 37±5%; the distance between the fifth lens L5 and the sixth lens L6 on the optical axis is 1±5%; the distance between the sixth lens L6 and the seventh lens L7 on the optical axis is 4±5%. The units are all millimeters.

[0032] The refractive index and Abbe number of each lens constituting the telecentric optical path are as follows: the refractive index of the first lens L1 is 1.49±5%, and the Abbe number is 56±5%; the refractive index of the second lens L2 is 1.53±5%, and the Abbe number is 58±5%; the refractive index of the third lens L3 is 1.69±5%, and the Abbe number is 28±5%; the refractive index of the fifth lens L5 is 1.57±5%, and the Abbe number is 35±5%; the refractive index of the sixth lens L6 is 1.67±5%, and the Abbe number is 51±5%; the refractive index of the seventh lens L7 is 1.67±5%, and the Abbe number is 51±5%.

[0033] In the patent of the present invention, when the liquid lens does not participate in refraction, the working distance of the double liquid telecentric lens is 65mm, and the working band is 450nm-700nm.

[0034] Depend on Figure 2 It can be seen that the RMS radius represents the root mean square radius of the diffuse spot, and the GEO radius represents the radius of the Airy disk, both in micrometers. As shown in the figure, in the central field of view, the root mean square radius is 8.732μm, and the Airy disk radius is 15.403μm; in the edge field of view, the root mean square radius is 8.865μm, and the Airy disk radius is 22.604μm. Most of them are within the radius of the Airy disk, and the energy concentration and aberration correction of the on-axis and off-axis points are very good, achieving the ideal resolution.

[0035] Depend on Figure 3 It can be seen that the horizontal axis is the spatial resolution, the unit is line pairs / mm, and the vertical axis is the contrast, the value range is 0-1. As shown in the figure, although the lens resolution is slightly lower due to the influence of various materials of the liquid lens, the overall lens contrast and resolution can meet the theoretical requirements of the lens parameters, and the performance of the full field of view is roughly the same.

[0036] Depend on Figure 4 It can be seen that the vertical axis is the field of view and the horizontal axis unit is millimeters.

[0037] From the distortion diagram, we can see that the ordinate is the field of view and the abscissa is the distortion value. As shown in the figure, the maximum distortion value of the lens is 0.0056%.

[0038] In summary: the contrast and resolution of the telecentric lens designed in the present invention meet the parameter theory standards and have lower telecentricity and distortion rate.

[0039] Some related concepts and definitions are explained:

[0040] Resolution: The measure of the optical system's capabilities, the minimum distance that can be distinguished.

[0041] Contrast: The contrast between black and white and light and dark lines.

[0042] Distortion: The change in the geometric shape of an object when viewed through a material.

[0043] Telecentricity: describes the angle at which the principal ray deviates from the optical axis.

[0044] Optical magnification: The ratio of the image size of an object on the focal plane through the lens group to the actual object size

[0045] Visual accuracy: The length of each pixel in machine vision imaging corresponds to the length in the real world.

[0046] Liquid lens: A lens encapsulated with optical liquid whose curvature can be controlled by circuits.

[0047] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A double liquid telecentric lens, characterized in that: An optical magnification group, an aperture stop, a liquid lens and an imaging group are arranged in sequence along the optical path; wherein: The optical magnification group includes three lenses. Along the light path direction, the first lens is a biconvex lens, the second lens is a biconvex lens, and the third lens is a biconcave lens; The liquid lens comprises a protective glass, an optical liquid is encapsulated inside the protective glass, and a magnetic field generator for adjusting the curvature of the liquid lens is arranged on the protective glass; The imaging group includes three lenses. Along the light path direction, the fifth lens is a convex-concave lens, the sixth lens is a biconcave lens, and the seventh lens is a concave-convex lens.

2. The double liquid telecentric lens according to claim 1, characterized in that: The radius of curvature of the light incident surface of the first lens is 24±5%, and the radius of curvature of the light exit surface is -45±5%; the radius of curvature of the light incident surface of the second lens is 40±5%, and the radius of curvature of the light exit surface is -40±5%; the radius of curvature of the light incident surface of the third lens is -23±5%, and the radius of curvature of the light exit surface is 73±5%; the radius of curvature of the light incident surface of the fifth lens is 11±5%, and the radius of curvature of the light exit surface is 73±5%; the radius of curvature of the light incident surface of the sixth lens is -80±5%, and the radius of curvature of the light exit surface is 16±5%; the radius of curvature of the light incident surface of the seventh lens is -13±5%, and the radius of curvature of the light exit surface is -30±5%; the unit of the radius of curvature is millimeter.

3. The double liquid telecentric lens according to claim 1, characterized in that: The center thickness of the first lens is 3±5%, the center thickness of the second lens is 3±5%, the center thickness of the third lens is 5±5%, the total thickness of the liquid lens is 5±5%, the center thickness of the fifth lens is 3±5%, the center thickness of the sixth lens is 2±5%, and the center thickness of the seventh lens is 2±5%, and the unit of the center thickness is millimeter.

4. The double liquid telecentric lens according to claim 1, characterized in that: The distance between the object and the first lens on the optical axis is 67±5%; the distance between the first lens and the second lens on the optical axis is 5±5%; the distance between the second lens and the third lens on the optical axis is 1±5%; the distance between the third lens and the aperture stop on the optical axis is 1±5%; the distance between the aperture stop and the liquid lens on the optical axis is 14±5%; the distance between the liquid lens and the fifth lens on the optical axis is 37±5%; the distance between the fifth lens and the sixth lens on the optical axis is 1±5%; the distance between the sixth lens and the seventh lens on the optical axis is 4±5%. The unit of distance is millimeter.

5. The double liquid telecentric lens according to claim 1, characterized in that: The refractive index of the first lens is 1.49±5%, and the Abbe number is 56±5%; the refractive index of the second lens is 1.53±5%, and the Abbe number is 58±5%; the refractive index of the third lens is 1.69±5%, and the Abbe number is 28±5%; the refractive index of the fifth lens is 1.57±5%, and the Abbe number is 35±5%; the refractive index of the sixth lens is 1.67±5%, and the Abbe number is 51±5%; the refractive index of the seventh lens is 1.67±5%, and the Abbe number is 51±5%.

6. The double liquid telecentric lens according to any one of claims 1 to 5, characterized in that: The magnetic field generator exchanges data with the host computer via the single chip microcomputer.

7. The double liquid telecentric lens according to claim 6, characterized in that: The working distance of the double liquid telecentric lens is 65mm, and the working band is 450nm~700nm.

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