Three-dimensional imaging optical system for civil small unmanned aerial vehicle

Abstract

The invention is applicable to the technical field of optical imaging, and provides a three-dimensional imaging optical system for a civil small unmanned aerial vehicle, which consists of a spherical positive lens, two groups of doublet spherical lenses, a diaphragm, a convex spherical reflector and a concave parabolic reflector, the two groups of doublet spherical lenses comprise a first doublet spherical lens and a second doublet spherical lens; according to the invention, high-resolution imaging can be realized under multiple wavelengths, rich spectral information is provided for a user, and more accurate analysis and judgment of a target area are facilitated. The compact design enables the system to be small in size and light in weight, is very suitable for being mounted on a low-altitude civil small unmanned aerial vehicle, and expands the application range and operation capability of the civil unmanned aerial vehicle. The three-dimensional imaging function can obtain three-dimensional information of a target area, has important application value in the fields of geographic surveying and mapping, urban planning and the like, and can provide more comprehensive and accurate data compared with a traditional imaging mode.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a stereoscopic imaging optical system for small civilian unmanned aerial vehicles. Background Art

[0002] Existing civilian small drone imaging technology is limited by the long focal length, large size, and large distortion of wide-field-of-view stereo imaging. It is difficult to achieve high-resolution, wide-area, and miniaturized stereo imaging capabilities. The following specific technical deficiencies exist, covering key indicators such as ground pixel resolution, optical distortion, volume, and the spectral range of stereo imaging: The challenge of balancing high ground pixel resolution (GSD) with wide-area imaging: The resolution of small civilian drones is primarily related to the focal length of the optical system, the pixel size of the camera sensor, and the flight altitude. Given a certain focal length and pixel size, ground pixel resolution is inversely proportional to flight altitude, so resolution can be improved by lowering the flight altitude. For example, the DJI Phantom 4 Multispectral Edition drone has a GSD of 9.52 cm / pixel at an altitude of 180 meters. Professional surveying and mapping requires a GSD of ≤5 cm / pixel. To achieve 3 cm / pixel, the flight altitude must be lowered to approximately 60 meters. To maintain the same observation range, the system's field of view must be tripled. Otherwise, work efficiency will be significantly reduced and flight risks will increase. Therefore, how to maintain high resolution while meeting the observation range of a large area is a challenge currently faced by drone imaging technology.

[0003] Limited distortion control capabilities of wide-field optical lenses: Existing civilian small drones generally use wide-angle lenses to expand their field of view, but barrel distortion is a significant issue. For example, in 4K resolution mode, the DJI Phantom 4 series experiences distortion rates of 5%-8% in the peripheral areas, causing straight objects to appear noticeably curved. Although some models (such as the Phantom 4 RTK) have factory-calibrated units to reduce distortion, residual distortion in high-resolution modes still requires post-processing with software, increasing data processing complexity. Furthermore, distortion performance varies significantly between different resolution modes. For example, distortion rates in 2.7K and 1080P modes are typically less than 3%, while in 4K mode, they can double.

[0004] The contradiction between size and ground pixel resolution is prominent: In civilian drone design, the conflict between ground pixel resolution and drone size is essentially a game between optical physics limitations and engineering constraints. In civilian drone design, higher GSD (i.e., the ability to capture finer ground details) requires a larger optical system, while miniaturization demands a smaller sensor and lens. This contradiction permeates the design of all drone categories, from consumer to professional.

[0005] Limitations of the stereoscopic imaging spectral range: The stereoscopic imaging spectral range of traditional civilian small drone cameras is mainly full-color, while color imaging mostly uses Bayer array imaging mode, such as the DJI Mavic 3 series. Multispectral imaging technology is rarely used for image registration and synthesis. In addition, traditional small-scale stereoscopic multispectral imaging technology often relies on external dual-lens modules, which are mechanically fixed for strapdown applications, such as the Trimble UX5 HP multispectral aerial survey system. This will significantly increase the payload weight and volume, and the optical axis calibration is complex, making it difficult to meet the mounting application scenarios of civilian light and small drones.

[0006] Overall, existing technologies face multiple bottlenecks. In terms of size, existing large-field-of-view, high-resolution UAV payloads are generally large due to the requirements for aberration compensation parameters and dual-line arrays, making them difficult to adapt to the application scenarios of lightweight and small UAVs. In terms of functionality, existing stereo UAV payloads are mostly based on panchromatic imaging, with few offering multispectral stereo imaging capabilities, making them difficult to meet the requirements for detecting spectral information of ground objects. In terms of performance, existing UAV payloads generally have a limited optical field of view when the resolution reaches 2cm@200m. While payloads with large-field-of-view imaging capabilities generally have lower resolutions and significant optical distortion, which significantly reduces the accuracy of 3D reconstruction. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the purpose of the present invention is to propose a stereoscopic imaging optical system for small civilian drones, aiming to solve the technical problems raised in the background technology.

[0008] A stereoscopic imaging optical system for small civilian drones, comprising a spherical positive lens, two groups of double-cemented spherical lenses, an aperture, a convex spherical reflector, and a concave parabolic reflector, wherein the two groups of double-cemented spherical lenses include a first double-cemented spherical lens and a second double-cemented spherical lens; The system takes the optical axis as the axis and the direction of incident light as the arrangement direction. The order of the optical components is: spherical positive lens, the first double-cemented spherical lens, the aperture, the second double-cemented spherical lens, the concave parabolic reflector and the convex spherical reflector; the light is incident toward the detector through the positive lens, and passes through the spherical positive lens, the first double-cemented spherical lens, the aperture, the second double-cemented spherical lens, the convex spherical reflector and the concave parabolic reflector in sequence, and finally guides the light to the detector for imaging.

[0009] Preferably, the focal length of the optical system is 45.9865 mm, the total length of the lens is 50.0021 mm, the system aperture value is 5, the longitudinal semi-field of view range is plus or minus 13.5-16.5 degrees, the vertical field of view is 60 degrees, and the working spectrum includes: full-color 0.45μm-0.72μm, multi-spectral 0.45μm, 0.52μm, 0.65μm, and 0.75μm.

[0010] Preferably, the spherical positive lens is made of material H-ZPK5, which has a thickness of 5.502 mm.

[0011] Preferably, the first double-cemented spherical lens is made of glass H-FK71 and H-LAF53, with thicknesses of 3.648 mm and 1.761 mm respectively; the second double-cemented spherical lens is made of glass H-ZF88 and D-LAF50, with thicknesses of 1.828 mm and 1.352 mm respectively; the convex spherical reflector and the concave parabolic reflector have thicknesses of -12.004 mm and 17.6599 mm respectively, and are used to reflect light so that the light is finally imaged on the detector.

[0012] Preferably, the air gap between the spherical positive lens and the first double-cemented spherical lens is 8.614 mm, the air gap between the first double-cemented spherical lens and the aperture is 3.462 mm, the air gap between the aperture and the second double-cemented spherical lens is 0.168 mm, and the air gap between the second double-cemented spherical lens and the reflector group is 18.012 mm, and the reflector group consists of a convex spherical reflector and a concave parabolic reflector.

[0013] Beneficial effects achieved by the present invention: This invention enables high-resolution imaging at multiple wavelengths, providing users with rich spectral information and enabling more accurate analysis and assessment of target areas. The compact design makes the system small and lightweight, making it ideal for mounting on small, low-altitude civilian drones, expanding the application and operational capabilities of civilian drones. The stereoscopic imaging function, which can capture three-dimensional information about target areas, has significant application value in fields such as geographic surveying and urban planning, providing more comprehensive and accurate data than traditional imaging methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of a stereoscopic imaging optical system for small civilian drones.

[0015] Figure 2 This is the MTF curve of a stereo imaging optical system for small civilian drones.

[0016] Figure 3 This is a distortion curve of a stereo imaging optical system for small civilian drones.

[0017] Figure 4 This is a point diagram of a stereoscopic imaging optical system for small civilian drones.

[0018] Notes on reference numerals: 1 - spherical positive lens, 2 - first double cemented spherical lens, 3 - aperture, 4 - second double cemented spherical lens, 5 - concave parabolic reflector, 6 - convex spherical reflector. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0021] This invention enables high-resolution imaging at multiple wavelengths, providing users with rich spectral information and enabling more accurate analysis and assessment of target areas. The compact design makes the system small and lightweight, making it ideal for mounting on small, low-altitude civilian drones, expanding the application and operational capabilities of civilian drones. The stereoscopic imaging function, which can capture three-dimensional information about target areas, has significant application value in fields such as geographic surveying and urban planning, providing more comprehensive and accurate data than traditional imaging methods.

[0022] The design parameters are as follows: 1. Detector parameters: resolution - 16556 pixels (H) × 9200 pixels (V); pixel size 3.2 μm; 2. Flight altitude: 200m; 3. Ground pixel resolution: better than 2cm; 4. Field of view: not less than 60°; 5. Distortion: better than 0.2% in vertical direction; 6. Focal length: 45.9865mm; 7.F / # :5.00096; See also Figure 1The embodiment of the present invention provides a stereoscopic imaging optical system for small civilian drones. The system is composed of a spherical positive lens 1, two groups of double-cemented spherical lenses, an aperture 3, a convex spherical reflector 6, and a concave parabolic reflector 5. The two groups of double-cemented spherical lenses include a first double-cemented spherical lens 2 and a second double-cemented spherical lens 4. The system takes the optical axis as the axis and the direction of incidence of light as the arrangement direction. The order of the optical components is: spherical positive lens 1, the first double-cemented spherical lens 2, the aperture 3, the second double-cemented spherical lens 4, the concave parabolic reflector 5 and the convex spherical reflector 6; the light is incident toward the detector through the positive lens, and passes through the spherical positive lens 1, the first double-cemented spherical lens 2, the aperture 3, the second double-cemented spherical lens 4, the convex spherical reflector 6 and the concave parabolic reflector 5 in sequence, and finally guides the light to the detector for imaging.

[0023] In this embodiment, the focal length of the optical system is 45.9865 mm, the total length of the lens is 50.0021 mm, the system aperture value is 5, the longitudinal semi-field of view range is plus or minus 13.5-16.5 degrees, the vertical field of view is 60 degrees, and the working spectrum includes: full-color 0.45μm-0.72μm, multi-spectral 0.45μm, 0.52μm, 0.65μm, and 0.75μm.

[0024] In this embodiment, the spherical positive lens 1 is made of H-ZPK5 material, which has specific optical properties. Its thickness is 5.502 mm, which is calculated based on the initial convergence requirements of light and the overall optical performance of the system.

[0025] In this embodiment, the first double-cemented spherical lens 2 is made of glass H-FK71 and H-LAF53, with thicknesses of 3.648 mm and 1.761 mm, respectively. The combination of the two materials effectively corrects aberrations; the second double-cemented spherical lens 4 is made of glass H-ZF88 and D-LAF50, with thicknesses of 1.828 mm and 1.352 mm, respectively, further optimizing the focusing and aberration correction of light; the convex spherical reflector 6 and the concave parabolic reflector 5 have thicknesses of -12.004 mm and 17.6599 mm, respectively, and are used to reflect light so that the light is ultimately imaged on the detector.

[0026] In this embodiment, the air gap between the spherical positive lens 1 and the first double-cemented spherical lens 2 is 8.614 mm, the air gap between the first double-cemented spherical lens 2 and the aperture 3 is 3.462 mm, the air gap between the aperture 3 and the second double-cemented spherical lens 4 is 0.168 mm, and the air gap between the second double-cemented spherical lens 4 and the reflector group is 18.012 mm. The reflector group consists of a convex spherical reflector 6 and a concave parabolic reflector 5. This precise air gap design ensures the propagation path and interaction of light between the optical elements, thereby achieving precise control of light and imaging optimization.

[0027] Image quality: (1) MTF: MTF is the most important way to describe the performance of an optical system. It is used to describe the ability of an optical system to transmit target contrast at different spatial frequencies. The weight of the optical system of the present invention is biased towards the average MTF of visible light (MTF@156lp / mm>0.2), which can meet the requirements of clear imaging for earth observation. Figure 2 ; (2) Distortion: Distortion is a type of geometric aberration in an optical system, which is defined as a nonlinear deformation of the image geometry that does not affect the clarity but changes the object proportions. The distortion of the optical system of the present invention meets the requirement of better than 0.2% within the 60° vertical field of view. Figure 3 .

[0028] (3) Spot diagram: Optical system spot diagram reference Figure 4 The distribution of different points in the point diagram can be considered as the diffuse spot energy distribution, and the imaging quality of the optical system can be judged by the compactness of the diffuse spot energy distribution. It can be seen from the figure that the spot size is uniform and round, which can meet the imaging requirements of the high-resolution wide-area multi-spectral stereo imaging optical system for low-altitude perception.

[0029] The multispectral stereo images acquired by this method clearly reveal detailed information about buildings and roads on the ground. In multispectral images, different features exhibit distinct characteristics at different wavelengths, facilitating the classification and analysis of land use types. In stereo imaging, image processing can construct a three-dimensional model of the ground, accurately measuring information such as building heights and road slopes.

[0030] It should be noted that, in this document, the term "comprises" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article, or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0031] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the description of the present invention, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A stereoscopic imaging optical system for small civilian drones, characterized in that: The system is composed of a spherical positive lens (1), two groups of double-cemented spherical lenses, an aperture (3), a convex spherical reflector (6), and a concave parabolic reflector (5), wherein the two groups of double-cemented spherical lenses include a first double-cemented spherical lens (2) and a second double-cemented spherical lens (4); The system takes the optical axis as the axis and the light incident direction as the arrangement direction, and the order of the optical components is: spherical positive lens (1), the first double-cemented spherical lens (2), the aperture (3), the second double-cemented spherical lens (4), the concave parabolic reflector (5) and the convex spherical reflector (6); the light is incident on the detector from the positive lens, and passes through the spherical positive lens (1), the first double-cemented spherical lens (2), the aperture (3), the second double-cemented spherical lens (4), the convex spherical reflector (6) and the concave parabolic reflector (5) in sequence, and finally guides the light to the detector for imaging.

2. The stereoscopic imaging optical system for a small civilian UAV according to claim 1, characterized in that: The focal length of the optical system is 45.9865mm, the total length of the lens is 50.0021mm, the system aperture value is 5, the longitudinal track half field of view range is plus or minus 13.5-16.5 degrees, the vertical track field of view is 60 degrees, and the working spectrum includes: panchromatic 0.45μm-0.72μm, multispectral 0.45μm, 0.52μm, 0.65μm, 0.75μm.

3. The stereoscopic imaging optical system for a small civilian UAV according to claim 1, characterized in that: The spherical positive lens (1) is made of H-ZPK5 material, and its thickness is 5.502 mm.

4. The stereoscopic imaging optical system for a small civilian UAV according to claim 3, characterized in that: The first double-cemented spherical lens (2) is made of glass H-FK71 and H-LAF53, with thicknesses of 3.648 mm and 1.761 mm respectively; the second double-cemented spherical lens (4) is made of glass H-ZF88 and D-LAF50, with thicknesses of 1.828 mm and 1.352 mm respectively; the convex spherical reflector (6) and the concave parabolic reflector (5) are -12.004 mm and 17.6599 mm respectively, and are used to reflect light so that the light is finally imaged on the detector.

5. The stereoscopic imaging optical system for a small civilian UAV according to claim 1, characterized in that: The air gap between the spherical positive lens (1) and the first double-cemented spherical lens (2) is 8.614 mm, the air gap between the first double-cemented spherical lens (2) and the aperture (3) is 3.462 mm, the air gap between the aperture (3) and the second double-cemented spherical lens (4) is 0.168 mm, and the air gap between the second double-cemented spherical lens (4) and the reflector group is 18.012 mm. The reflector group consists of a convex spherical reflector (6) and a concave parabolic reflector (5).

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