An optical detection system for the inner wall of a cavity

Abstract

The application discloses a cavity inner wall optical detection system. The cavity inner wall optical detection system comprises a reflection module and a refraction module arranged in sequence from an object plane to an image plane; the reflection module comprises a mirror; the refraction module comprises an objective lens group and an eyepiece group arranged in sequence from one side of the object plane to the image plane, the objective lens group comprises a first lens with negative optical power and a second lens with positive optical power; the eyepiece group comprises a third lens with positive optical power and a fourth lens with negative optical power; and the reflection module and the refraction module are coaxially arranged. The reflection imaging technology of the reflection module and the refraction imaging technology of the refraction module are combined to realize the detection of the cavity inner wall, and the system has simple structure, high imaging resolution and high field of view utilization.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and more particularly to an optical detection system for the inner wall of a cavity. Background Technology

[0002] In machine vision systems, the most common optical system solutions for detecting the inner walls of cavities currently on the market mainly include two types: one is an endoscope-based solution based on fiber optic image bundles, and the other is an ultra-wide-angle macro imaging solution. The endoscope solution has low imaging resolution, and because the field of view is usually downwards along the cavity rather than perpendicular to the inner wall, its imaging field utilization and detection efficiency are both low. The ultra-wide-angle macro imaging solution has poor compatibility with the inner walls of cavities with small inner diameters, and the depth of the cavity that can be measured is limited by the lens's depth of field. Therefore, there is an urgent need to develop optical systems capable of detecting the inner walls of cavities with even smaller inner diameters and greater depths to meet application requirements. Summary of the Invention

[0003] This invention provides an optical detection system for the inner wall of a cavity, which improves the resolution of imaging of the inner wall of the cavity.

[0004] The present invention provides an optical detection system for the inner wall of a cavity, comprising: a reflection module and a refraction module arranged sequentially from the object plane to the image plane;

[0005] The reflection module includes a reflector;

[0006] The refractive module includes an objective lens group and an eyepiece group arranged sequentially along the object plane to the image plane. The objective lens group includes a first lens with negative optical power and a second lens with positive optical power. The eyepiece group includes a third lens with positive optical power and a fourth lens with negative optical power.

[0007] The reflection module and the refraction module are arranged coaxially.

[0008] Optionally, the reflector is a curved reflector, and the reflective surface of the reflector bulges toward the image plane.

[0009] Optionally, the reflecting surface of the mirror is spherical or aspherical.

[0010] Optionally, the reflective surface of the mirror is provided with a reflective film.

[0011] Optionally, the reflective module further includes an annular viewing window, which is arranged around the reflector, and the central axis of the annular viewing window is coaxial with the optical axis of the reflector.

[0012] Optionally, the surface of the annular viewing window is provided with an anti-reflective film.

[0013] Optionally, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the objective lens group is f0, and the focal length of the eyepiece group is fE, wherein:

[0014] 0.459≤f1 / fO≤0.538; -1.072≤f2 / fO≤-0.814; -0.565≤f3 / fE≤0.274; -0.426≤f4 / fE≤0.417.

[0015] Optionally, the first lens has a refractive index of Nd1 and an Abbe number of Vd1; the second lens has a refractive index of Nd2 and an Abbe number of Vd2; the third lens has a refractive index of Nd3 and an Abbe number of Vd3; and the fourth lens has a refractive index of Nd4 and an Abbe number of Vd4; wherein:

[0016] 1.670≤Nd1≤1.734, 51.494≤Vd1≤54.669; 1.800≤Nd2≤1.834, 34.972≤Vd2≤46.567; 1.567≤Nd3≤1.625, 35.713≤Vd3≤42.807; 1.693≤Nd4≤1.781, 35.020≤Vd4≤49.233.

[0017] Optionally, the first lens, the second lens, the third lens, and the fourth lens are all spherical lenses.

[0018] Optionally, the optical detection system on the inner wall of the cavity further includes an aperture stop, which is disposed in the optical path between the second lens and the third lens.

[0019] The technical solution of this invention includes an optical detection system for the inner wall of a cavity, comprising: a reflection module and a refraction module arranged sequentially from the object plane to the image plane; the reflection module includes a mirror; the refraction module includes an objective lens group and an eyepiece group arranged sequentially from the object plane to the image plane, the objective lens group including a first lens with negative optical power and a second lens with positive optical power; the eyepiece group including a third lens with positive optical power and a fourth lens with negative optical power; the reflection module and the refraction module are coaxially arranged. Based on the reflection imaging technology of the reflection module and the refraction imaging technology of the refraction module, the system has a simple structure, high imaging resolution and field of view utilization, and can detect the inner wall of a cavity with a smaller inner diameter and greater depth.

[0020] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of an integral optical detection system for the inner wall of a cavity, provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 1 of the present invention;

[0024] Figure 3 MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 1 of the present invention;

[0025] Figure 4 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 2 of the present invention;

[0026] Figure 5 This is an MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 2 of the present invention;

[0027] Figure 6 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 3 of the present invention;

[0028] Figure 7 MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 3 of the present invention;

[0029] Figure 8 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 4 of the present invention;

[0030] Figure 9 The MTF diagram is provided for an optical detection system on the inner wall of a cavity according to Embodiment 4 of the present invention. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0032] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0033] Example 1

[0034] Figure 1 This is a schematic diagram of the structure of an integral optical detection system for the inner wall of a cavity, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 1 of the present invention, as shown below. Figure 1 and Figure 2 As shown, the optical detection system on the inner wall of the cavity includes: a reflection module M1 and a refraction module M2 arranged sequentially along the object plane OBJ to the image plane IMA; the reflection module M1 includes a reflecting mirror R; the refraction module M2 includes an objective lens group GO and an eyepiece group GE arranged sequentially along the object plane OBJ to the image plane IMA, the objective lens group GO includes a first lens G1 with negative optical power and a second lens G2 with positive optical power; the eyepiece group GE includes a third lens G3 with positive optical power and a fourth lens G4 with negative optical power; the reflection module M1 and the refraction module M2 are coaxially arranged.

[0035] The system comprises a reflection module M1 and a refraction module M2 arranged sequentially from the object plane OBJ to the image plane IMA. The reflection module M1 includes a reflector R. Detection light is reflected by the reflector R in the reflection module M1 and then incident on the objective lens group GO in the refraction module M2. After being adjusted by the first lens G1 and the second lens G2 in the objective lens group GO, the light is again incident on the eyepiece group GE in the refraction module M2. After being adjusted by the third lens G3 and the fourth lens G4 in the eyepiece group GE, the light is imaged on the image plane IMA side. By combining reflection imaging technology and refraction imaging technology, the internal wall of the cavity is imaged. The distance between the object plane OBJ and the optical axis X of the reflector R affects the range of the detected cavity inner diameter. The greater the distance between the object plane OBJ and the optical axis X of the reflector R, the larger the range of the detected cavity inner diameter. Therefore, appropriately setting the distance between the object plane OBJ and the optical axis X of the reflector R ensures the detection effect of the cavity inner wall. For the lens in the refractive module M2, the optical power is equal to the difference between the image-side beam convergence and the object-side beam convergence, which characterizes the optical system's ability to deflect light. The larger the absolute value of the optical power, the stronger the bending ability of light; the smaller the absolute value, the weaker the bending ability. When the optical power is positive, the refraction of light is converging; when the optical power is negative, the refraction of light is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., one surface of the lens), a single lens, or a system formed by multiple lenses (i.e., a lens group). In this embodiment, the imaging lens module M2 is sequentially provided with an objective lens group GO and an eyepiece group GE. The objective lens group GO includes a first lens G1 with negative optical power and a second lens G2 with positive optical power. The first lens G1 and the second lens G2 are combined to form a cemented lens, effectively reducing the air gap between the first lens G1 and the second lens G2, thereby reducing the overall length of the lens. Furthermore, cemented lenses can be used to minimize or eliminate chromatic aberration, allowing various aberrations in the optical inspection system to be fully corrected. While maintaining a compact structure, they can improve resolution and optimize optical performance such as distortion. They can also reduce light energy loss caused by inter-lens reflections, increasing illumination and thus improving image quality and image sharpness. The eyepiece group GE includes a third lens G3 with positive optical power and a fourth lens G4 with negative optical power. The optical power of the entire refractive module M2 is distributed in a certain proportion, ensuring consistent imaging quality across all fields of view and guaranteeing overall imaging performance. Focusing on the inner walls of cavities with different inner diameters can be achieved by adjusting the distance between the fourth lens G4 in the refractive module M2 and the image plane IMA, i.e., the optical back intercept (BFL).

[0036] In this embodiment of the invention, a reflection module and a refraction module are coaxially arranged. The reflection module includes a reflector; the refraction module includes an objective lens group and an eyepiece group arranged sequentially along the object plane to the image plane. The objective lens group includes a first lens with negative optical power and a second lens with positive optical power; the eyepiece group includes a third lens with positive optical power and a fourth lens with negative optical power. Based on the reflection imaging technology of the reflection module and the refraction imaging technology of the refraction module, it is possible to achieve a cavity with a smaller inner diameter and greater depth, a simple cavity inner wall system structure, and at the same time, the optical detection system has high imaging resolution and field of view utilization.

[0037] Optionally, the reflector R is a curved reflector, and the reflecting surface of the reflector R protrudes towards the image plane IMA.

[0038] The reflection module M1 includes a reflector R, which can be made of glass or metal. The specific material can be chosen according to actual design requirements, and this embodiment of the invention does not impose specific limitations. The reflective surface of the reflector R protrudes towards the image plane IMA, so that the incident detection light rays from the object plane OBJ side are received by the reflector R and reflected to the refraction module M2, ensuring the normal transmission of light and thus ensuring the normal operation of the optical detection system.

[0039] Optionally, the reflecting surface of the mirror R can be spherical or aspherical.

[0040] The reflecting surface of the mirror R can be spherical or aspherical, such as... Figure 2 As shown, the reflecting surface of mirror R is spherical; as Figure 4 As shown, the reflecting surface of the reflector R is aspherical. Compared with the reflector R with a spherical reflecting surface, the imaging resolution of the optical detection system composed of the reflector R with an aspherical reflecting surface can be further improved, the imaging is clearer, and the optical detection length of the inner wall of the cavity is also further improved, thereby ensuring the effectiveness of the optical detection system.

[0041] Optionally, the reflective surface of the reflector R is provided with a reflective film.

[0042] To further ensure the reflection effect of the reflector R on the incident detection light, a reflective film can be provided on the reflective surface of the reflector R. The reflective film increases the reflectivity of the optical surface, ensuring that the detection light changes its propagation direction after passing through the reflector R, so that the detection light is incident on the refraction module M2, and finally realizes the normal operation of the optical detection system.

[0043] Optionally, the reflective module M1 also includes an annular viewing window P, which is set around the reflector R, and the central axis of the annular viewing window P is coaxial with the optical axis of the reflector R.

[0044] The reflective module M1 also includes a ring-shaped viewing window P, which serves both light transmission and dust protection. The ring-shaped viewing window P is made of highly transparent glass or plastic; the specific material can be chosen based on actual design requirements, and this embodiment of the invention does not impose specific limitations. The ring-shaped viewing window P is positioned around the reflector R. Figure 2 The required annular viewing window P is only schematically shown in the diagram. The central axis of the annular viewing window P is coaxial with the optical axis of the reflector R to ensure the normal transmission of the detection light, thereby ensuring the optical detection effect on the inner wall of the cavity.

[0045] Optionally, the surface of the annular viewing window P is provided with an anti-reflective film.

[0046] Since the annular viewing window P is made of a light-transmitting material, in order to ensure that the detection light can smoothly reach the reflective surface of the reflector R through the annular viewing window P and reduce the light loss of the detection light, anti-reflection films can be set on both the inner and outer surfaces of the annular viewing window P to reduce the reflection loss of the surface of the annular viewing window P, thereby increasing the intensity of the transmitted light and making the optical detection system image clearer.

[0047] Optionally, the focal length of the first lens G1 is f1, the focal length of the second lens G2 is f2, the focal length of the third lens G3 is f3, the focal length of the fourth lens G4 is f4, the focal length of the objective lens group GO is fO, and the focal length of the eyepiece group GE is fE, where: 0.459≤f1 / fO≤0.538; -1.072≤f2 / fO≤-0.814; -0.565≤f3 / fE≤0.274; -0.426≤f4 / fE≤0.417. By rationally allocating the focal lengths of each lens, aberration correction is facilitated, ensuring that the optical detection system has high resolving power.

[0048] Optionally, the first lens G1 has a refractive index of Nd1 and an Abbe number of Vd1; the second lens G2 has a refractive index of Nd2 and an Abbe number of Vd2; the third lens G3 has a refractive index of Nd3 and an Abbe number of Vd3; and the fourth lens G4 has a refractive index of Nd4 and an Abbe number of Vd4; wherein: 1.670≤Nd1≤1.734, 51.494≤Vd1≤54.669; 1.800≤Nd2≤1.834, 34.972≤Vd2≤46.567; 1.567≤Nd3≤1.625, 35.713≤Vd3≤42.807; 1.693≤Nd4≤1.781, 35.020≤Vd4≤49.233.

[0049] The refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium, primarily used to describe a material's ability to refract light; different materials have different refractive indices. The Abbe number is an index used to represent the dispersion ability of a transparent medium; the more severe the dispersion, the smaller the Abbe number; conversely, the less severe the dispersion, the larger the Abbe number. Thus, by carefully configuring the refractive indices and Abbe numbers of the lenses in the refractive module M2, the balance of the incident angles between the front and rear lens groups is ensured, reducing the sensitivity of the optical inspection system and improving production feasibility.

[0050] Optionally, the first lens G1, the second lens G2, the third lens G3, and the fourth lens G4 are all spherical lenses.

[0051] Among them, the first lens G1, the second lens G2, the third lens G3 and the fourth lens G4 are all spherical lenses, and the materials can be various types of glass known to those skilled in the art, which can effectively improve the imaging quality.

[0052] Optionally, the optical detection system on the inner wall of the cavity also includes an aperture S, which is disposed in the optical path between the second lens G2 and the third lens G3.

[0053] By placing the aperture stop S in the optical path between the second lens G2 and the third lens G3, the propagation direction of the light beam can be adjusted, and the incident angle of the light can be adjusted, which is beneficial to further improve the imaging quality.

[0054] As a feasible implementation method, the curvature radius, thickness and material of each lens surface in the refractive module M2 are described below.

[0055] Table 1 Design values ​​for the radius of curvature, thickness, and materials of the imaging lens module.

[0056]

[0057] Continue to refer to Figure 2 The refractive module M2 provided in Embodiment 1 of the present invention includes a first lens G1, a second lens G2, a third lens G3, and a fourth lens G4 arranged sequentially from the object plane OBJ to the image plane IMA. Table 1 shows the optical physical parameters such as the radius of curvature, thickness, and material of each lens in the refractive module M2 provided in the embodiment. The surface number is determined according to the surface order of each lens; for example, "1" represents the object plane surface of the first lens G1, "2" represents the image plane surface of the first lens G1, "6" represents the object plane surface of the third lens G3, "7" represents the image plane surface of the third lens G3, and so on. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. The thickness represents the central axial distance from the current surface to the next surface. The units for both the radius of curvature and the thickness are millimeters (mm).

[0058] like Figure 2 As shown, in this embodiment, the distance h1 between the object plane OBJ and the optical axis X of the reflector R is 25-100mm, that is, the inner diameter range of the measurable cavity inner wall in this embodiment is 25-100mm; the focusing imaging of the cavity inner wall with different inner diameters is achieved by adjusting the back intercept BFL of the refraction module M2.

[0059] like Figure 2 As shown, in this embodiment of the invention, the maximum lower half-field of view α1 = 35° and the maximum upper half-field of view β1 = 55° in the optical detection system, enabling a 90° side viewing angle to be obtained in a single imaging. Simultaneously, the reflecting surface of the mirror R is spherical with a radius of curvature of 10.162 mm; the annular viewing window P has a thickness of 1 mm and an outer diameter of 20 mm, enabling optical detection of the inner wall of the cavity with the corresponding inner diameter.

[0060] Based on the above implementation, optionally, the first lens G1, the second lens G2, the third lens G3, and the fourth lens G4 are all glass spherical lenses. The refractive module M2 provided in Embodiment 1 of the present invention also includes an aperture stop (STO). By adding the aperture stop S, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. The aperture stop S is located in the optical path between the second lens G2 and the third lens G3. The above design parameters ensure that the optical detection system has high imaging resolution.

[0061] Furthermore, Figure 3 The MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 1 of the present invention is shown below. Figure 3 As shown, the transfer function in the MTF curve is generally above 0.3 when there are 60 line pairs / mm, which can meet the requirements of high resolution.

[0062] Example 2

[0063] Figure 4 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 2 of the present invention, as shown below. Figure 4 and Figure 1 As shown, the optical detection system on the inner wall of the cavity includes: a reflection module M1 and a refraction module M2 arranged sequentially along the object plane OBJ to the image plane IMA; the reflection module M1 includes a reflecting mirror R; the refraction module M2 includes an objective lens group GO and an eyepiece group GE arranged sequentially along the object plane OBJ to the image plane IMA, the objective lens group GO includes a first lens G1 with negative optical power and a second lens G2 with positive optical power; the eyepiece group GE includes a third lens G3 with positive optical power and a fourth lens G4 with negative optical power; the reflection module M1 and the refraction module M2 are coaxially arranged.

[0064] In the reflection module M1, the reflecting surface of the mirror R is aspherical. The optical power, focal length, refractive index, Abbe number, surface shape, material, and aperture position of each lens in the refraction module M2 are the same as in Embodiment 1, and will not be repeated here.

[0065] Table 2 Design values ​​for the radius of curvature, thickness, and materials of the imaging lens module.

[0066]

[0067] Continue to refer to Figure 4 The refractive module M2 provided in Embodiment 2 of the present invention includes a first lens G1, a second lens G2, a third lens G3, and a fourth lens G4 arranged sequentially from the object plane OBJ to the image plane IMA. Table 2 shows the optical physical parameters such as the radius of curvature, thickness, and material of each lens in the refractive module M2 provided in the embodiment. The surface number is determined according to the surface order of each lens; for example, "1" represents the object plane surface of the first lens G1, "2" represents the image plane surface of the first lens G1, "6" represents the object plane surface of the third lens G3, "7" represents the image plane surface of the third lens G3, and so on. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. The thickness represents the central axial distance from the current surface to the next surface. The units for both the radius of curvature and the thickness are millimeters (mm).

[0068] Based on the above implementation, optionally, the first lens G1, the second lens G2, the third lens G3, and the fourth lens G4 are all glass spherical lenses. The refractive module M2 provided in Embodiment 2 of this invention also includes an aperture stop (STO). By adding the aperture stop S, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. The aperture stop S is located in the optical path between the second lens G2 and the third lens G3. The above design parameters ensure that the optical detection system has high imaging resolution. Meanwhile, the reflecting surface of the mirror R is aspherical, and its aspherical surface shape equation Z satisfies:

[0069]

[0070] Where Z(h) is the distance vector from the vertex of the aspherical surface at a height of h along the optical axis, c = 1 / r, r represents the radius of curvature of the aspherical mirror, k is the conic coefficient, and A, B, C, D, and E are the higher-order coefficients of the aspherical surface.

[0071] Table 3 Aspheric coefficients of the reflecting mirror

[0072] r k A B C D E 10.194 <![CDATA[7.4×10 -2 ]]> <![CDATA[4.45×10 -3 ]]> <![CDATA[-9.65×10 -3 ]]> <![CDATA[3.81×10 -3 ]]> <![CDATA[-4.66×10 -3 ]]> <![CDATA[3.23×10 -5 ]]>

[0073] Among them, 4.45×10 -3The coefficient A of the aspherical equation representing the mirror R is 4.45 × 10⁻⁶. -3 .

[0074] like Figure 4 As shown, in this embodiment, the distance h2 between the object plane OBJ and the optical axis X of the reflector R is 25-100mm, that is, the measurable cavity inner diameter range corresponding to this embodiment is 25-100mm; the focusing imaging of the inner wall of the cavity with different inner diameters is achieved by adjusting the back intercept of the refraction module M2.

[0075] like Figure 4 As shown, in this embodiment, the corresponding maximum lower half-field of view α2 = 35°, and the corresponding maximum upper half-field of view β2 = 55°, and a side viewing angle of 90° can be obtained in a single imaging. The thickness of the annular viewing window P is 1mm, and the outer diameter is 20mm, so as to realize optical detection of the inner wall of the cavity with the corresponding inner diameter.

[0076] Furthermore, Figure 5 This is an MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 2 of the present invention, as shown below. Figure 5 As shown, the transfer function at 65 line pairs / mm in the MTF curve is generally above 0.3, which can meet the requirements of high resolution. Furthermore, the MTF curve is superior to that of Embodiment 1 based on the spherical reflector R, further improving the system's imaging resolution.

[0077] Example 3

[0078] Figure 6 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 3 of the present invention, as shown below. Figure 6 and Figure 1 As shown, the optical detection system on the inner wall of the cavity includes: a reflection module M1 and a refraction module M2 arranged sequentially along the object plane OBJ to the image plane IMA; the reflection module M1 includes a reflecting mirror R; the refraction module M2 includes an objective lens group GO and an eyepiece group GE arranged sequentially along the object plane OBJ to the image plane IMA, the objective lens group GO includes a first lens G1 with negative optical power and a second lens G2 with positive optical power; the eyepiece group GE includes a third lens G3 with positive optical power and a fourth lens G4 with negative optical power; the reflection module M1 and the refraction module M2 are coaxially arranged.

[0079] In the reflection module M1, the reflecting surface of the mirror R is spherical. The optical power, focal length, refractive index, Abbe number, surface shape, material, and aperture position of each lens in the refraction module M2 are the same as in Embodiment 1, and will not be repeated here.

[0080] Table 4 Design values ​​for the radius of curvature, thickness, and materials of the imaging lens module

[0081]

[0082] Continue to refer to Figure 6 The refractive module M2 provided in Embodiment 3 of the present invention includes a first lens G1, a second lens G2, a third lens G3, and a fourth lens G4 arranged sequentially from the object plane OBJ to the image plane IMA. Table 2 shows the optical physical parameters such as the radius of curvature, thickness, and material of each lens in the refractive module M2 provided in the embodiment. The surface number is determined according to the surface order of each lens; for example, "1" represents the object plane surface of the first lens G1, "2" represents the image plane surface of the first lens G1, "6" represents the object plane surface of the third lens G3, "7" represents the image plane surface of the third lens G3, and so on. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. The thickness represents the central axial distance from the current surface to the next surface. The units for both the radius of curvature and the thickness are millimeters (mm).

[0083] like Figure 6 As shown, in this embodiment, the distance h3 between the object plane OBJ and the optical axis X of the reflector R is 5-25mm, that is, the measurable cavity inner diameter range corresponding to this embodiment is 5-25mm; the focusing imaging of the inner wall of the cavity with different inner diameters is achieved by adjusting the back intercept of the refraction module M2.

[0084] like Figure 6 As shown, in the optical detection system of Embodiment 3 of the present invention, the maximum lower half field of view α3 = 25° and the maximum upper half field of view β3 = 55° are correspondingly obtained, and a side viewing angle of 80° can be obtained in a single imaging. Meanwhile, the reflecting surface of the mirror R is spherical with a radius of curvature of 1.656 mm; the thickness of the annular viewing window P is 0.5 mm and the outer diameter is 4 mm, to achieve optical detection of the inner wall of the cavity with the corresponding inner diameter.

[0085] Based on the above implementation, optionally, the first lens G1, the second lens G2, the third lens G3, and the fourth lens G4 are all glass spherical lenses. The refractive module M2 provided in Embodiment 3 of the present invention also includes an aperture stop (STO). By adding the aperture stop S, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. The aperture stop S is located in the optical path between the second lens G2 and the third lens G3. The above design parameters ensure that the optical detection system has high imaging resolution.

[0086] Furthermore, Figure 7 The MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 3 of the present invention is shown below. Figure 7 As shown, the transfer function of the MTF curve at 25 line pairs / mm is generally above 0.3, which can meet the requirements of high resolution.

[0087] Example 4

[0088] Figure 8 This is a schematic diagram of the structure of an optical detection system on the inner wall of a cavity according to Embodiment 4 of the present invention, as shown below. Figure 8 and Figure 1 As shown, the optical detection system on the inner wall of the cavity includes: a reflection module M1 and a refraction module M2 arranged sequentially along the object plane OBJ to the image plane IMA; the reflection module M1 includes a reflecting mirror R; the refraction module M2 includes an objective lens group GO and an eyepiece group GE arranged sequentially along the object plane OBJ to the image plane IMA, the objective lens group GO includes a first lens G1 with negative optical power and a second lens G2 with positive optical power; the eyepiece group GE includes a third lens G3 with positive optical power and a fourth lens G4 with negative optical power; the reflection module M1 and the refraction module M2 are coaxially arranged.

[0089] In the reflection module M1, the reflecting surface of the mirror R is aspherical. The optical power, focal length, refractive index, Abbe number, surface shape, material, and aperture position of each lens in the refraction module M2 are the same as in Embodiment 1, and will not be repeated here.

[0090] Table 5 Design values ​​for the radius of curvature, thickness, and materials of the imaging lens module.

[0091]

[0092] Continue to refer to Figure 8 The refractive module M2 provided in Embodiment 4 of the present invention includes a first lens G1, a second lens G2, a third lens G3, and a fourth lens G4 arranged sequentially from the object plane OBJ to the image plane IMA. Table 2 shows the optical physical parameters such as the radius of curvature, thickness, and material of each lens in the refractive module M2 provided in the embodiment. The surface number is determined according to the surface order of each lens; for example, "1" represents the object plane surface of the first lens G1, "2" represents the image plane surface of the first lens G1, "6" represents the object plane surface of the third lens G3, "7" represents the image plane surface of the third lens G3, and so on. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. The thickness represents the central axial distance from the current surface to the next surface. The units for both the radius of curvature and the thickness are millimeters (mm).

[0093] Based on the above implementation, optionally, the first lens G1, the second lens G2, the third lens G3, and the fourth lens G4 are all glass spherical lenses. The refraction module M2 provided in Embodiment 4 of this invention also includes an aperture stop (STO). By adding the aperture stop S, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. The aperture stop S is located in the optical path between the second lens G2 and the third lens G3. The above design parameters ensure that the optical detection system has high imaging resolution. Meanwhile, the reflecting surface of the mirror R is aspherical, and its aspherical surface shape equation Z satisfies:

[0094]

[0095] Where Z(h) is the distance vector from the vertex of the aspherical surface at a height of h along the optical axis, c = 1 / r, r represents the radius of curvature of the aspherical mirror, k is the conic coefficient, and A, B, C, D, and E are the higher-order coefficients of the aspherical surface.

[0096] Table 6 Aspheric coefficients of the reflecting mirrors

[0097] r k A B C D E 1.789 <![CDATA[2.7×10 -1 ]]> <![CDATA[2.19×10 -2 ]]> <![CDATA[-2.78×10 -2 ]]> <![CDATA[7.21×10 -3 ]]> <![CDATA[-1.43×10 -3 ]]> <![CDATA[2.81×10 -4 ]]>

[0098] Among them, 2.19×10 -2 The coefficient A of the aspherical equation representing the mirror R is 2.19 × 10⁻⁶. -2 .

[0099] like Figure 8 As shown, in this embodiment, the distance h4 between the object plane OBJ and the optical axis X of the reflector R is 5 to 25 mm, that is, the measurable cavity inner diameter range corresponding to this embodiment is 5 to 25 mm; the focusing imaging of the inner wall of the cavity with different inner diameters is achieved by adjusting the back intercept of the refraction module M2.

[0100] like Figure 8 As shown, in this embodiment, the maximum lower half-field of view α4 = 25°, and the maximum upper half-field of view β4 = 55°, allowing for an 80° side viewing angle in a single imaging session. The annular viewing window P has a thickness of 0.5 mm and an outer diameter of 4 mm to enable optical detection of the inner wall of the cavity with the corresponding inner diameter.

[0101] Furthermore, Figure 9 The MTF diagram of an optical detection system for the inner wall of a cavity provided in Embodiment 4 of the present invention is shown below. Figure 9 As shown, the transfer function in the MTF curve at 30 line pairs / mm is generally above 0.3, which can meet the requirements of high resolution. Furthermore, the MTF curve is superior to that of Embodiment 3 based on the spherical reflector R, further improving the system's imaging resolution.

[0102] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An optical detection system for the inner wall of a cavity, characterized in that, include: Reflection and refraction modules are arranged sequentially from the object plane to the image plane; The reflection module includes a reflector; The refractive module includes an objective lens group and an eyepiece group arranged sequentially along the object plane to the image plane. The objective lens group includes a first lens with positive optical power and a second lens with negative optical power. The eyepiece group includes a third lens with negative optical power and a fourth lens with positive optical power. The reflection module and the refraction module are coaxially arranged; The first lens and the second lens are combined to form a cemented lens to reduce the air gap between the first lens and the second lens and reduce the overall length of the lens. Wherein, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, the focal length of the objective lens group is f0, and the focal length of the eyepiece group is fE, wherein: 0.459≤f1 / fO≤0.538; -1.072≤f2 / fO≤-0.814; -0.565≤f3 / fE≤0.274; -0.426≤f4 / fE≤0.

417.

2. The optical detection system for the inner wall of the cavity according to claim 1, characterized in that, The reflector is a curved reflector, and the reflective surface of the reflector bulges toward the image plane.

3. The optical detection system for the inner wall of the cavity according to claim 2, characterized in that, The reflecting surface of the mirror is either spherical or aspherical.

4. The optical detection system for the inner wall of the cavity according to claim 3, characterized in that, The reflective surface of the mirror is provided with a reflective film.

5. The optical detection system for the inner wall of the cavity according to claim 2, characterized in that, The reflective module also includes an annular viewing window, which is arranged around the reflector, and the central axis of the annular viewing window is coaxial with the optical axis of the reflector.

6. The optical detection system for the inner wall of the cavity according to claim 5, characterized in that, The surface of each annular viewing window is provided with an anti-reflective film.

7. The optical detection system for the inner wall of the cavity according to claim 1, characterized in that, The first lens has a refractive index of Nd1 and an Abbe number of Vd1; the second lens has a refractive index of Nd2 and an Abbe number of Vd2; the third lens has a refractive index of Nd3 and an Abbe number of Vd3; the fourth lens has a refractive index of Nd4 and an Abbe number of Vd4; wherein: 1.670≤Nd1≤1.734, 51.494≤Vd1≤54.669; 1.800≤Nd2≤1.834, 34.972≤Vd2≤46.567; 1.567≤Nd3≤1.625, 35.713≤Vd3≤42.807; 1.693≤Nd4≤1.781, 35.020≤Vd4≤49.

233.

8. The optical detection system for the inner wall of the cavity according to claim 1, characterized in that, include: The first lens, the second lens, the third lens, and the fourth lens are all spherical lenses.

9. The optical detection system for the inner wall of the cavity according to claim 1, characterized in that, The optical detection system on the inner wall of the cavity also includes an aperture stop, which is disposed in the optical path between the second lens and the third lens.

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