A 360-degree scanning laser radar optical system and a design method thereof

Abstract

The application relates to a 360-degree scanning laser radar optical system and a design method thereof, the system comprising a laser, a converging module, a MEMS mirror, a detector and a free-form surface lens, the free-form surface lens comprising a refractive surface, a first reflecting surface and a second reflecting surface; a light beam emitted by the laser is incident to the MEMS mirror through the converging module, and is reflected to the refractive surface through the MEMS mirror, the second reflecting surface and the first reflecting surface in sequence, and after being refracted through the refractive surface, the light beam forms a parallel light beam to be incident to a target object to be diffusely reflected, part of light rays in the diffusely reflected light rays return to the detector along the original path, the detector receives the light beam and obtains the position of the target object; the MEMS mirror rotates around the central axis of the free-form surface lens by 360 degrees to scan the target object by 360 degrees. The system adopts a solid free-form surface lens, is compact in size, has few optical system elements, is simple in structure, convenient to assemble and adjust and light in weight; the application has good collimation of an outgoing light beam and high radar resolution.

Description

Technical Field

[0001] This invention relates to the field of lidar technology, and in particular to a 360-degree scanning lidar optical system and its design method. Background Technology

[0002] LiDAR (Light Detection and Ranging) measures the position, velocity, and other information of a target object by emitting a laser beam towards it and receiving the beam reflected back from the target. It has wide applications in fields such as autonomous driving and robot navigation. Achieving a large field of view is crucial for LiDAR, especially those capable of 360-degree scanning.

[0003] Existing mechanical scanning lidar systems suffer from several drawbacks due to the need for rotating optical components to achieve scanning, such as slow scanning speed, short lifespan, and large size. Therefore, the development of semi-solid-state or solid-state 360-degree scanning lidar is of great significance. Examples include MEMS-based 360-degree lidar and flash-type 360-degree lidar. However, existing semi-solid-state or solid-state lidar systems suffer from a large number of optical system components, complex system structure, difficult assembly and adjustment, and significant weight when achieving 360-degree panoramic scanning. Therefore, a compact 360-degree scanning lidar optical system is urgently needed. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a 360-degree scanning lidar optical system and its design method. This system employs a solid-state freeform lens, effectively solving the problems of existing solid-state or semi-solid-state lidar optical systems having a large number of components, complex system structure, difficult assembly and adjustment, and heavy weight.

[0005] Specifically, the following technical solutions are included:

[0006] On one hand, the present invention provides a 360-degree scanning lidar optical system, comprising:

[0007] A laser is used to emit a beam of light;

[0008] A convergence module is disposed on the emission optical path of the laser;

[0009] MEMS reflectors are disposed on the outgoing light path of the converging module;

[0010] A detector is positioned on the side of the laser away from the focusing module; and

[0011] A freeform lens is disposed between the converging module and the MEMS mirror. The freeform lens includes a refractive surface, a first reflective surface, and a second reflective surface. The refractive surface, the first reflective surface, and the second reflective surface are configured as arc-shaped surfaces that rotate around the central axis of the freeform lens.

[0012] The laser beam emitted by the laser is incident on the MEMS mirror through the converging module, and then reflected sequentially through the MEMS mirror, the second reflecting surface, and the first reflecting surface to the refractive surface. After being refracted by the refractive surface, it forms a parallel beam that is incident on the target object and undergoes diffuse reflection. Part of the diffusely reflected light returns along its original path and is incident on the detector. The detector receives the beam and obtains the position of the target object. The MEMS mirror rotates 360 degrees around the central axis of the freeform lens to perform a 360-degree scan of the target object.

[0013] In some embodiments, the MEMS mirror is located on the central axis of the freeform lens, and the MEMS mirror is tilted and the angle between the MEMS mirror and the central axis of the freeform lens is adjustable.

[0014] In some embodiments, the freeform lens further includes a first bottom surface connected to the refractive surface and a second bottom surface connected to the second reflective surface.

[0015] In some embodiments, the first and second bottom surfaces are planes, spheres, aspherical surfaces, or freeform surfaces.

[0016] In some embodiments, the first bottom surface, the refractive surface, the first reflective surface, the second reflective surface, and the second bottom surface are connected in sequence by a connecting surface, which is a smooth curved surface.

[0017] In some embodiments, the converging module is an independent lens, which can be a spherical lens or an aspherical lens, and the first bottom surface and the second bottom surface of the freeform lens are both planar.

[0018] In some embodiments, the converging module is a first bottom surface, a second bottom surface, or a combination of a first bottom surface and a second bottom surface of a freeform lens, wherein one of the first bottom surface and the second bottom surface is a spherical or aspherical surface, or both the first bottom surface and the second bottom surface are spherical or aspherical surfaces.

[0019] In some embodiments, the laser includes a fiber laser or a semiconductor laser.

[0020] On the other hand, the present invention provides a design method based on the aforementioned 360-degree scanning lidar optical system, comprising:

[0021] Step 101: Set initial points A1, B1, C1 and virtual image points I1, I2, I3; calculate the curve of the refractive surface; a set of parallel rays are used as sampling rays, assuming there are k sampling rays, the aperture is D, the distance between adjacent rays is h, the direction vector of any ray can be obtained and represented as In=[0,0,1]; the first ray is called r1, which is refracted at point A1 and enters point I1; the refracted ray A1I1 is the outgoing ray from the refractive surface 41, and its direction vector is also known. The incident ray from point A1 and the The direction vectors of the outgoing rays are known. According to the vector formula for refraction, the normal vector NA1 passing through point A1 is also known. Thus, the tangent line passing through point A1 can be calculated. The intersection of ray r2 and the tangent line passing through point A1 gives point A2. Once point A2 is known, the incident ray, the outgoing ray vector, and the normal vector can all be determined. The intersection of the third ray and the tangent line passing through A2 gives point A3. Based on this rule, the coordinates of all sampling points on the curve of the refracting surface can be calculated using the recursive relationship between adjacent points.

[0022] Step 102: Calculate the curve of the first reflecting surface; the light rays emitted from the refracting surface can be used as the incident light rays to the first reflecting surface. Based on the incident light ray vector, the initial point B1 of the curve of the first reflecting surface and the virtual image point I2, the coordinates of all sampling points on the curve of the first reflecting surface can be calculated.

[0023] Step 103: Calculate the coordinates of all sampling points on the curve of the second reflecting surface using the same method as in steps 101 and 102;

[0024] Step 104: Connect all the sampling points on the curve of the refractive surface in Step 101, all the sampling points on the curve of the first reflective surface in Step 102, and all the sampling points on the curve of the second reflective surface in Step 103 with connecting lines, which can be straight lines or splines.

[0025] Step 105: Rotate the connecting line from step 104 around the central axis of the freeform lens by 360 degrees to form a freeform lens.

[0026] In some embodiments, the detector, laser, lens, and MEMS mirror are arranged on the central axis of the freeform lens.

[0027] Based on the above technical solution, an embodiment of the 360-degree scanning lidar optical system of the present invention employs a solid-state freeform lens including a refractive surface, a first reflecting surface, and a second reflecting surface. The refractive surface, the first reflecting surface, and the second reflecting surface are configured as an arc-shaped surface that rotates one revolution around the central axis of the freeform lens. The laser beam emitted by the laser is incident on the MEMS mirror through the lens, and is reflected sequentially through the MEMS mirror, the second reflecting surface, and the first reflecting surface to the refractive surface. After refraction by the refractive surface, a parallel beam is formed and incident on the target object, resulting in diffuse reflection. Part of the diffusely reflected light returns along its original path and is incident on the detector. The detector receives the beam and obtains the position of the target object. The present invention only requires rotating the MEMS mirror 360 degrees around the central axis of the freeform lens to form a 360-degree scan. It is compact, has few optical system components, a simple system structure, is easy to assemble and adjust, and is lightweight. The beam of the present invention can scan 360 degrees around the perimeter, and the output beam has good collimation, thus resulting in high radar resolution. Attached Figure Description

[0028] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0029] Figure 1 This is a schematic diagram of an embodiment of the 360-degree scanning lidar optical system of the present invention.

[0030] Figure 2 This is a schematic diagram of the imaging of the 360-degree scanning lidar optical system of the present invention.

[0031] Figure 3 This is a schematic diagram of another embodiment of the 360-degree scanning lidar optical system of the present invention.

[0032] Figure 4 This is a schematic diagram of the freeform lens design for the 360-degree scanning lidar optical system of the present invention.

[0033] Figure 5 This is a simulation diagram of the main viewpoint generated by optical simulation software in the 360-degree scanning lidar optical system of this invention.

[0034] Figure 6 This is a simulation image of a top-down view generated by optical simulation software in the 360-degree scanning lidar optical system of this invention.

[0035] Explanation of reference numerals in the attached figures: 1. Detector; 2. Laser; 3. Lens; 4. Freeform lens; 41. Refractive surface; 42. First reflecting surface; 43. Second reflecting surface; 44. First bottom surface; 45. Second bottom surface; 5. MEMS mirror. Detailed Implementation

[0036] The invention is described in detail below. In the following paragraphs, different aspects of the embodiments are defined in more detail. The aspects so defined may be combined with any other aspect or aspects unless explicitly stated otherwise. In particular, any feature considered preferred or advantageous may be combined with one or more other features considered preferred or advantageous.

[0037] The terms "first" and "second" used in this invention are merely for ease of description and to distinguish different components with the same name, and do not indicate a sequential or primary / secondary relationship.

[0038] Furthermore, when an element is referred to as being "on" another element, the element may be directly on the other element, or it may be indirectly on the other element with one or more intermediate elements inserted between them. Additionally, when an element is referred to as being "connected" to another element, the element may be directly connected to the other element, or it may be indirectly connected to the other element with one or more intermediate elements inserted between them. In the following drawings, the same reference numerals denote the same elements.

[0039] The present invention uses terms such as "upper", "lower", "top", "bottom", "front", "rear", "inner" and "outer" to indicate orientation or positional relationships. This is only for the convenience of describing the present invention and is not intended to indicate or imply that the device referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the scope of protection of the present invention.

[0040] like Figure 1-6 As shown, the present invention provides a 360-degree scanning lidar optical system, which in some embodiments includes:

[0041] Laser 2, used to emit a beam;

[0042] A convergence module is disposed on the emission optical path of the laser 2;

[0043] MEMS reflector 5 is disposed on the outgoing light path of the converging module;

[0044] Detector 1 is positioned on the side of laser 2 away from the focusing module; and

[0045] A freeform lens 4 is disposed between the converging module and the MEMS mirror 5. The freeform lens 4 includes a refractive surface 41, a first reflective surface 42 and a second reflective surface 43 from top to bottom. The refractive surface 41, the first reflective surface 42 and the second reflective surface 43 are configured as arc-shaped surfaces that rotate around the central axis of the freeform lens 4.

[0046] The laser beam emitted by the laser 2 is incident on the MEMS mirror 5 through the converging module, and is reflected sequentially through the MEMS mirror 5, the second reflecting surface 43 and the first reflecting surface 42 to the refractive surface 41. After being refracted by the refractive surface 41, it forms a parallel beam that is incident on the target object and undergoes diffuse reflection. Part of the diffusely reflected light returns along the original path and is incident on the detector 1. The detector 1 receives the beam and obtains the position of the target object. The MEMS mirror 5 rotates 360 degrees around the central axis of the freeform lens 4 to perform a 360-degree scan of the target object.

[0047] Optionally, in some embodiments, the MEMS mirror 5 is located on the central axis of the freeform lens 4, and the MEMS mirror 5 is tilted with an adjustable angle to the central axis of the freeform lens 4. The adjustable angle between the MEMS mirror and the horizontal plane ultimately enables 360-degree horizontal scanning and -30 to +30-degree vertical scanning, allowing the light beam to scan the surrounding objects.

[0048] This embodiment of the invention employs a solid-state freeform lens comprising a refractive surface 41, a first reflecting surface 42, and a second reflecting surface 43. The refractive surface 41, the first reflecting surface 42, and the second reflecting surface 43 are configured as an arc-shaped surface that rotates one revolution around the central axis of the freeform lens 4. The laser beam emitted by the laser 2 passes through the lens 3 and is incident on the MEMS mirror 5. It is then reflected sequentially by the MEMS mirror 5, the second reflecting surface 43, and the first reflecting surface 42 to the refractive surface 41. After refraction by the refractive surface 41, a parallel beam is formed and incident on the target object, resulting in diffuse reflection. A portion of the diffusely reflected light returns along its original path and is incident on the detector 1. The detector 1 receives the beam and obtains the position of the target object. This invention only requires rotating the MEMS mirror 5 360 degrees around the central axis of the freeform lens 4 to form a 360-degree scan. It is compact, has few optical system components, a simple system structure, is easy to assemble and adjust, and is lightweight.

[0049] Optionally, in some embodiments, the freeform lens 4 further includes a first bottom surface 44 connected to the refractive surface 41 and a second bottom surface 45 connected to the second reflective surface 43. The first bottom surface 44 and the second bottom surface 45 are planes, spheres, aspherical surfaces, or freeform surfaces. The first bottom surface 44, the refractive surface 41, the first reflective surface 42, the second reflective surface 43, and the second bottom surface 45 are connected in sequence by a connecting surface, which is a smooth curved surface.

[0050] Alternatively, in some embodiments, such as Figure 1 As shown, the converging module is an independent lens 3, which can be a spherical lens or an aspherical lens. The first bottom surface 44 and the second bottom surface 45 of the freeform lens 4 are both planar.

[0051] Alternatively, in some embodiments, such as Figure 3 As shown, the converging function can be achieved without using a separate lens 3 by setting the first bottom surface 44 or the second bottom surface 45 of the freeform lens 4 as a spherical or aspherical surface. That is, the converging module is the first bottom surface 44, the second bottom surface 45, or a combination of the first bottom surface 44 and the second bottom surface 45 of the freeform lens 4, where one of the first bottom surface 44 and the second bottom surface 45 is a spherical or aspherical surface, or both the first bottom surface 44 and the second bottom surface 45 are spherical or aspherical surfaces.

[0052] Optionally, in some embodiments, the laser 2 includes a fiber laser or a semiconductor laser.

[0053] Finally, as Figure 4 As shown, the present invention also provides a design method for a 360-degree scanning lidar optical system based on the above embodiment; the freeform lens 4 is formed by rotating 360 degrees around its central axis, therefore, only the central axis needs to be calculated to form the freeform lens 4. Since the optical path is reversible, parallel light can be used as the incident light. Figure 2 As shown, initial points A1, B1, C1 and virtual image points I1, I2, I3 are set; in some embodiments, the design method includes:

[0054] Step 101: Calculate the curve of the refractive surface 41; a set of parallel rays are used as sampling rays. Assume there are k sampling rays, the aperture is D, and the distance between adjacent rays is h. The direction vector of any ray can be obtained and represented as In = [0, 0, 1]; the first ray is called r1, which is refracted at point A1 and enters point I1; the refracted ray A1I1 is the outgoing ray from the refractive surface 41, and its direction vector is also known. The direction vectors of the incident and outgoing rays from point A1 are known. According to the vector formula for refraction, the normal vector N passing through point A1 is... A1 We also know that the tangent at point A1 can be calculated, and the intersection of ray r2 and the tangent at point A1 can be used to obtain point A2. Once point A2 is known, the incident ray, the outgoing ray vector, and the normal vector can all be obtained. The intersection of the third ray and the tangent at A2 can be used to obtain point A3. Based on this rule, the coordinates of all sampling points on the curve of the refracting surface 41 can be calculated using the recursive relationship between adjacent points.

[0055] Step 102: Calculate the curve of the first reflecting surface 42; the light rays emitted from the refracting surface 41 can be used as incident light rays on the first reflecting surface 42. Based on the incident light ray vector, the initial point B1 of the curve of the first reflecting surface 42 and the virtual image point I2, the coordinates of all sampling points on the curve of the first reflecting surface 42 can be calculated.

[0056] Step 103: Calculate the coordinates of all sampling points on the curve of the second reflecting surface 43 using the same method as in steps 101 and 102;

[0057] Step 104: Connect all the sampling points on the curve of the refractive surface 41 in step 101, all the sampling points on the curve of the first reflective surface 42 in step 102, and all the sampling points on the curve of the second reflective surface 43 in step 103 with connecting lines respectively. The connecting lines are straight lines or splines. These connected areas are not effective working areas, and only need to be smooth and easy to process.

[0058] Step 105: Rotate the connecting line from step 104 around the central axis of the freeform lens 4 by 360 degrees to form the freeform lens 4.

[0059] The detector 1, laser 2, lens 3, and MEMS reflector 5 are arranged on the central axis of the freeform lens 4, thereby realizing the design and assembly of the entire 360-degree scanning lidar optical system.

[0060] like Figure 5 and 6 As shown, Figure 5 and 6 The simulation diagram generated by the optical simulation software in the 360-degree scanning lidar optical system of this invention shows that when the MEMS mirror reflects 360 degrees, the beam can scan 360 degrees around it, and the collimation of the emitted beam is very good, so the resolution of the radar will also be very high.

[0061] This article uses specific embodiments to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A design method for a 360-degree scanning lidar optical system, characterized in that, The 360-degree scanning lidar optical system includes: A laser is used to emit a beam of light; A convergence module is disposed on the emission optical path of the laser; MEMS reflectors are disposed on the outgoing light path of the converging module; A detector is positioned on the side of the laser away from the focusing module; and A freeform lens is disposed between the converging module and the MEMS mirror. The freeform lens includes a refractive surface, a first reflective surface, and a second reflective surface. The refractive surface, the first reflective surface, and the second reflective surface are configured as arc-shaped surfaces that rotate around the central axis of the freeform lens. The laser beam emitted by the laser is focused by a converging module and incident on a MEMS mirror. It is then reflected sequentially by the MEMS mirror, a second reflecting surface, and a first reflecting surface before reaching a refractive surface. After refraction by the refractive surface, a parallel beam is formed and incident on the target object, causing diffuse reflection. A portion of the diffusely reflected light returns along its original path and is incident on a detector. The detector receives the beam and acquires the position of the target object. The MEMS mirror rotates 360 degrees around the central axis of the freeform lens to perform a 360-degree scan of the target object. The design method includes: Step 101: Set initial points A1, B1, C1 and virtual image points I1, I2, I3; calculate the curve of the refractive surface; a set of parallel rays are used as sampling rays, assuming there are k sampling rays, the aperture is D, the distance between adjacent rays is h, and the direction vector of any ray can be obtained and represented as In=[0,0,1]; the first ray is called r1, which is refracted at point A1 and enters point I1; the refracted ray A1I1 is the outgoing ray from the refractive surface 41, and its direction vector is also known. The direction vectors of the incident ray and the outgoing ray from point A1 are known. According to the vector formula for refraction, the normal vector N passing through point A1 is... A1 We also know that the tangent at point A1 can be calculated, and the intersection of ray r2 and the tangent at point A1 can be used to obtain point A2. Once point A2 is known, the incident ray, the outgoing ray vector, and the normal vector can all be obtained. The intersection of the third ray and the tangent at A2 can be used to obtain point A3. Based on this rule, the coordinates of all sampling points on the curve of the refracting surface can be calculated using the recursive relationship between adjacent points. Step 102: Calculate the curve of the first reflecting surface; the light rays emitted from the refracting surface can be used as the incident light rays to the first reflecting surface. Based on the incident light ray vector, the initial point B1 of the curve of the first reflecting surface and the virtual image point I2, the coordinates of all sampling points on the curve of the first reflecting surface can be calculated. Step 103: Calculate the coordinates of all sampling points on the curve of the second reflecting surface using the same method as in steps 101 and 102; Step 104: Connect all the sampling points on the curve of the refractive surface in Step 101, all the sampling points on the curve of the first reflective surface in Step 102, and all the sampling points on the curve of the second reflective surface in Step 103 with connecting lines, which can be straight lines or splines. Step 105: Rotate the connecting line from step 104 around the central axis of the freeform lens by 360 degrees to form a freeform lens.

2. The design method of the 360-degree scanning lidar optical system according to claim 1, characterized in that, The MEMS mirror is located on the central axis of the freeform lens, and the MEMS mirror is tilted and the angle between the MEMS mirror and the central axis of the freeform lens can be adjusted.

3. The design method of the 360-degree scanning lidar optical system according to claim 1, characterized in that, The freeform lens also includes a first bottom surface connected to the refractive surface and a second bottom surface connected to the second reflective surface.

4. The design method of the 360-degree scanning lidar optical system according to claim 3, characterized in that, The first and second bottom surfaces are planes, spheres, aspherical surfaces, or freeform surfaces.

5. The design method of the 360-degree scanning lidar optical system according to claim 4, characterized in that, The first bottom surface, the refractive surface, the first reflective surface, the second reflective surface, and the second bottom surface are connected in sequence by a connecting surface, which is a smooth curved surface.

6. The design method of the 360-degree scanning lidar optical system according to claim 5, characterized in that, The converging module is an independent lens, which can be a spherical lens or an aspherical lens. The first bottom surface and the second bottom surface of the freeform lens are both planes.

7. The design method of the 360-degree scanning lidar optical system according to claim 5, characterized in that, The converging module is a first bottom surface, a second bottom surface, or a combination of the first bottom surface and the second bottom surface of a freeform lens. One of the first bottom surface and the second bottom surface is a spherical or aspherical surface, or both the first bottom surface and the second bottom surface are spherical or aspherical surfaces.

8. The design method of the 360-degree scanning lidar optical system according to claim 1, characterized in that, The laser includes a fiber laser or a semiconductor laser.

9. The design method of the 360-degree scanning lidar optical system according to claim 1, characterized in that, The detector, laser, and lens are arranged on the central axis of the freeform lens.

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