A scanning prism and a prism scanning device

Abstract

This invention relates to a scanning prism and a prism scanning device. The prism has a rotation axis and two parallel top and bottom surfaces. The rotation axis passes through the top and bottom surfaces and is perpendicular to them. The top and bottom surfaces are polygons, with the number of sides of the top surface being the same as that of the bottom surface, and the sides of the top and bottom surfaces are arranged parallel to each other. The plane formed by connecting adjacent vertices of the top and bottom surfaces serves as the working surface of the prism. The angle β between the working surface and the rotation axis ranges from 0° to 90°. Compared to tower mirror scanning, the scanning prism provided by this invention has a smaller volume, weight, and moment of inertia, and lower power consumption, while maintaining the same working surface area. The laser footprint trajectory projected onto the target by the scanning prism is parabolic, making it easier to acquire point cloud data of vertical surfaces. Furthermore, this prism has a larger field of view than tower mirrors, which improves acquisition efficiency.

Description

Technical Field

[0001] This invention relates to the field of lidar scanning technology, and more specifically to a scanning prism and a prism scanning device. Background Technology

[0002] Line-scan lidar typically has a 360° field of view. When applied to airborne scenarios for mapping strip targets such as pipeline inspections, corridor mapping, or power line inspections, the detection target is only located in a fan-shaped area to the side or below the lidar, resulting in wasted scan lines and sparse scan lines in the target area. To address this, various lidar scanning methods adapted for airborne applications have been proposed in recent years. These methods aim to compress the lidar's scanning field of view from 360 degrees to a suitable angle, thereby increasing the number of scan lines in the central field of view and improving the scanning efficiency and point cloud density of the target area. Among existing technologies, the tower-view scanning scheme is the most widely used.

[0003] The technical principle of the tower mirror scanning scheme is as follows: Figure 1 The tower mirror rotates at high speed driven by a motor, and its working surface consists of several oblique facets distributed along the circumference. The emitted laser is reflected on the working surface, and the light path is deflected and points towards the target. After a complete working surface sweeps across the emitted light, the laser's tracking point on the target forms a straight line perpendicular to the direction of travel. However, the tower mirror scanning scheme has the following problems: First, because the tower mirror has multiple working surfaces, and there are angles between its working surfaces and the mounting surface and the rotation axis, it is an irregular structure, which makes the tower mirror difficult to manufacture and increases the manufacturing cost. Second, with the same aperture, the tower mirror has a larger volume, weight, and moment of inertia, thus increasing the overall volume, weight, and power consumption of the lidar unit. Third, the tower mirror has a relatively small scanning field of view, resulting in lower scanning efficiency. Figure 2 Taking the four-faced tower mirror shown as an example, when one of the working faces completely sweeps across the outgoing light, the computer simulation shows that the field of view of the tower mirror scanning is 83.6°. Summary of the Invention

[0004] This invention addresses the technical problems existing in the prior art by providing a scanning prism and a prism scanning device. Compared with the tower mirror scanning method, when the working surface area is the same, the volume, weight and moment of inertia of the scanning prism in this solution are smaller, and the overall size, weight and power consumption of the product are better. The laser footprint trajectory projected onto the target by the scanning prism presents a parabola, making it easier for this scanning method to acquire point cloud data of vertical surfaces. In addition, this prism has a larger field of view than the tower mirror, which can improve the acquisition efficiency.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] As a first aspect of the present invention, the present invention provides a scanning prism, the prism having a rotation axis and a top surface and a bottom surface that are parallel to each other, the rotation axis passing through the top surface and the bottom surface and being perpendicular to the top surface and the bottom surface respectively; the top surface and the bottom surface are both polygons, the number of sides of the top surface is the same as the number of sides of the bottom surface, and the sides of the top surface and the sides of the bottom surface are arranged in parallel and correspond one-to-one; the plane formed by connecting adjacent vertices between the top surface and the bottom surface serves as the working surface of the prism, and the angle β between the working surface and the rotation axis is in the range of 0° < β < 90°.

[0007] Based on the above technical solution, the present invention can be further improved as follows.

[0008] Preferably, the rotation axis passes through the geometric center of the top and bottom surfaces.

[0009] Preferably, the longer side of the top surface is parallel to the shorter side of the bottom surface, the shorter side of the top surface is parallel to the longer side of the bottom surface, and the working surface is trapezoidal.

[0010] Preferably, the top surface and the bottom surface are both rectangles, the long side of the top surface is equal to the long side of the bottom surface, and the short side of the top surface is equal to the short side of the bottom surface.

[0011] Preferably, the number of working surfaces n ≥ 4.

[0012] Preferably, a reflective film is provided on the working surface.

[0013] As a third aspect of the present invention, the present invention also provides a prism scanning device, including the scanning prism described above, and further including a light source, a drive motor and a mounting base. The light source and the drive motor are respectively fixedly mounted on the mounting base. The rotation axis of the prism is coaxially arranged and fixedly connected to the rotor of the drive motor. The light source is arranged facing the working surface of the prism, and the angle α between the optical axis of the light source and the rotation axis is in the range of 0°≤α≤90°.

[0014] As a third aspect of the present invention, the present invention also provides a prism scanning device, including the scanning prism described above, and further including a light source, a drive motor, a reflector, and a mounting base. The light source, the reflector, and the drive motor are respectively fixedly mounted on the mounting base. The rotation axis of the prism is coaxially arranged and fixedly connected to the rotor of the drive motor. The reflecting surface of the reflector is arranged facing the light source and the working surface of the prism. The emitted light from the light source is reflected by the reflector and points to the working surface of the prism. The angle α between the optical axis of the light source and the rotation axis is in the range of 0°≤α≤90°.

[0015] The beneficial effects of this invention are: 1. In the solution of this invention, the trajectory of the laser footprint projected onto the target by the scanning prism is a parabola, making it easier to acquire point cloud data of the vertical surface; 2. Compared with the tower mirror scanning solution, with the same working surface area, the scanning prism of this solution has a smaller volume, weight, and moment of inertia, and the overall volume, weight, and power consumption of the scanning device are better; 3. While ensuring the optimal volume and weight of the scanning components, the scanning prism of this solution has a larger field of view, which can improve the acquisition efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the tower mirror scanning structure.

[0017] Figure 2 This is a schematic diagram of the field of view for tower mirror scanning;

[0018] Figure 3 This is a schematic diagram of the scanning prism structure of the present invention, wherein (a) is a front view and (b) is a perspective view;

[0019] Figure 4 This is a schematic diagram of the specialized scanning prism structure of the present invention, wherein (a) is a front view and (b) is a perspective view;

[0020] Figure 5 This is a schematic diagram of the two sets of symmetrical working surfaces of the specialized scanning prism of the present invention.

[0021] Figure 6 This is the light path emitted from working surfaces A and B when the angle between the rotation axis and the optical axis is 45° in this invention.

[0022] Figure 7 This is the light path emitted from working surfaces C and D when the angle between the rotation axis and the optical axis is 45° in this invention.

[0023] Figure 8 This is the trajectory line of the laser foot point when the angle between the rotation axis and the optical axis is 45° in this invention;

[0024] Figure 9 This is the light path emitted from working surfaces A and B when the angle between the rotation axis and the optical axis is 90° in this invention.

[0025] Figure 10 This is the light path emitted from working surfaces C and D when the angle between the rotation axis and the optical axis is 90° in this invention;

[0026] Figure 11 This is the trajectory line of the laser foot point when the angle between the rotation axis and the optical axis is 90° in this invention;

[0027] Figure 12 This refers to the field of view of working surfaces A and B when the angle between the rotation axis and the optical axis is 45° in this invention.

[0028] Figure 13 This refers to the field of view of working surfaces C and D when the angle between the rotation axis and the optical axis is 45° in this invention.

[0029] Figure 14 This is a schematic diagram of the field of view achieved by the prism rotation when the angle between the rotation axis and the optical axis is 90° in this invention.

[0030] Figure 15 This is a schematic diagram of the irregular hexagonal prism structure in Embodiment 2 of the present invention;

[0031] Figure 16 This is a schematic diagram of the light path emitted by the prism when the angle between the rotation axis and the optical axis is 0° in Embodiment 4 of the present invention.

[0032] The attached diagram lists the components represented by each number as follows:

[0033] 1. Target object, 2. Prism, 3. Working surface, 4. Rotation axis, 5. System base, 6. Light source, 7. Reflector. Detailed Implementation

[0034] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0035] Example 1:

[0036] like Figure 3 As shown, this embodiment provides a scanning prism. The prism has a rotation axis and two parallel top and bottom surfaces. The rotation axis passes through the top and bottom surfaces and is perpendicular to both. The top and bottom surfaces are polygons, with the number of sides of the top surface being the same as that of the bottom surface, and the sides of the top and bottom surfaces are arranged in parallel and correspond one-to-one. The plane formed by connecting adjacent vertices of the top and bottom surfaces serves as the working surface of the prism. The angle β between the working surface and the rotation axis ranges from 0° to 90°. The angle β between the working surface and the rotation axis can be adjusted by adjusting the ratio of the side lengths of the top and bottom surfaces.

[0037] When scanning using the prism of this embodiment, the laser emitted by the light source is directed toward the working surface of the prism. The prism rotates at high speed around the rotation axis. Through the reflection effect of the working surface, the laser is reflected onto the target object. The photodetector of the scanning device receives the reflected light from the target object, thereby realizing the scanning of the target object.

[0038] As a preferred embodiment, the rotation axis passes through the geometric center of the top and bottom surfaces. Of course, the rotation axis may not be located at the geometric center of the top and bottom surfaces. When this prism is used for scanning, having the rotation axis at the geometric center of the top and bottom surfaces allows the prism to have a smaller moment of inertia and run more smoothly during rotation.

[0039] Preferably, the longer side of the top surface is parallel to the shorter side of the bottom surface, and the shorter side of the top surface is parallel to the longer side of the bottom surface, making the working surface trapezoidal. The edges of the top and bottom surfaces are parallel to each other, forming a plane for reflecting the scanning laser; this plane serves as the working surface. Because the dimensions of the parallel edges on the top and bottom surfaces are different, the resulting working surface is trapezoidal. To enhance the prism's reflection of the laser, a reflective film is provided on the working surface.

[0040] The structural form of the prism in this embodiment, its working state at various angles, and the principle of its field of view analysis are now explained with reference to the accompanying drawings.

[0041] I. Structural Morphology of Prisms

[0042] The scanning prism structure of this embodiment is shown in [reference needed]. Figure 3 Figure (a) shows the front view of the prism, and Figure (b) shows the three-dimensional view of the prism. The scanning prism is an irregularly shaped quadrangular prism with rectangular top and bottom faces that are parallel to each other. Its four sides together form four continuous trapezoidal working surfaces. The short side of the top rectangle is a1, and the long side is b1; the short side of the bottom rectangle is a2, and the long side is b2. The short side a1 of the top surface is parallel to the long side b2 of the bottom surface, and the long side b1 of the top surface is parallel to the short side a2 of the bottom surface. c is the rotation axis of the scanning prism.

[0043] For the convenience of the discussion and calculations below, the structure and size of the scanning prism will be further specialized here, let:

[0044] 1. The long side b1 of the top rectangle of the scanning prism is equal in size to the long side b2 of the bottom rectangle;

[0045] 2. The short side a1 of the top rectangle of the scanning prism has the same dimensions as the short side a2 of the bottom rectangle;

[0046] 3. The geometric centers (intersection of the diagonals) of the top and bottom rectangles are both located on the rotation axis c.

[0047] The morphology of the scanning prism after special processing is shown in the figure. Figure 4 Figure (a) is a front view of the prism, and Figure (b) is a three-dimensional view of the prism.

[0048] Under the above dimensional constraints, such as Figure 5 As shown, the four working surfaces of the scanning prism consist of two sets of mutually symmetrical surfaces. Figure 5 (a) and Figure 5 As shown in (b), surface A and surface B are a set of symmetrical surfaces, surface C and surface D are a set of symmetrical surfaces, and the angle β between each working surface of the prism and the axis of rotation is equal, let this angle be 5°.

[0049] II. Angle Analysis Between the Optical Axis and the Prism Rotation Axis

[0050] In this embodiment, the angle α between the optical axis of the laser output from the light source and the rotation axis c of the prism can be in the range of 0°≤α≤90°. The following sections use 45° and 90° as examples to introduce the layout relationship between the light emitted from the light source and the prism, as well as the scanning foot trajectory under this layout relationship.

[0051] 1. The angle between the scanning prism rotation axis and the output optical axis is 45°.

[0052] When the angle between the rotation axis of the scanning prism and the output light axis is 45°, the output light path is as follows: Figure 6 and Figure 7 ,in Figure 6 This is the output optical path between working surfaces A and B. Figure 7 This is the light path exiting from the working surfaces C and D. 1 represents the target object; 2 represents the scanning prism assembly; 3 represents the working surface of the prism; 4 represents the prism rotation axis; 5 represents the system base, which is the rigid support structure for the system's optical components; and 6 represents the light source. The laser emitted by the light source is reflected by the working surface of the scanning prism and leaves the system, pointing towards the target being measured.

[0053] Computer simulations show that when the angle between the optical axis and the rotation axis of the scanning prism is 45°, the laser's trajectory on the planar target after one rotation of the scanning prism is two parabolic curves. Each parabola is symmetrical and evenly distributed. (See...) Figure 8 When the equipment moves with a carrier (such as a drone), this scanning method is more likely to acquire point cloud data of the vertical facade than tower-mounted scanning schemes, and the trajectory effect is suitable as airborne laser point cloud data.

[0054] Figure 8 The coordinate system is defined as follows: the emission direction of the light source coincides with the negative Y-axis, and point "O" is the projection of the intersection of the optical axis and the rotation axis onto the target plane. For ease of display, the trajectory points have been thinned out; a sampling point is provided every 5° of scanning prism rotation, with ±35° as the boundary. The parabolas of the two trajectory points are placed in the same coordinate system, and the coordinates of the trajectory points are given.

[0055] Assuming the distance from the light source to the target plane is 100 meters, Table 1 gives the X and Y coordinates of the trajectory points of the working surfaces A and B, and C and D of the prism.

[0056] Table 1

[0057]

[0058] 2. The angle between the scanning prism rotation axis and the output optical axis is 90°.

[0059] When the angle between the rotation axis of the scanning prism and the output light axis is 90°, the output light paths from working surfaces A and B are shown below. Figure 9 The light paths emitted from the C and D working surfaces are shown. Figure 10 In this system, 1 represents the target object; 2 represents the scanning prism assembly; 3 represents the working surface of the scanning prism; 4 represents the rotation axis of the scanning prism; 5 represents the system base, which is the rigid support structure for the system's optical components; and 6 represents the light source, whose laser light, after being reflected by the working surface of the scanning prism, leaves the system and points towards the target being measured.

[0060] Computer simulations show that when the angle between the scanning prism's rotation axis and the output light axis is 90°, the laser's trajectory on the ground after one rotation of the prism is two symmetrical parabolas with opposite opening directions. The two parabolas are symmetrical left and right and evenly distributed, as shown in the figure. Figure 11 .

[0061] Figure 11 The coordinate system is defined as follows: the light source is perpendicular to the XY plane, the rotation axis of the scanning prism coincides with the Y-axis, and point "O" is the intersection of the optical axis and the target plane. For ease of display, the trajectory points have been thinned out; a sampling point is provided every 5° of scanning prism rotation, with ±30° as the boundary. The parabolas of the two trajectory points are placed below the origin of the same coordinate system, and the coordinate values ​​of the trajectory points are given.

[0062] Assuming the distance from the light source to the target plane is 100 meters, Table 2 gives the X and Y coordinates of the trajectory points on working surfaces A and B, and working surfaces C and D.

[0063] Table 2

[0064]

[0065] III. Field Angle Analysis of Scanning Prism

[0066] The preceding section introduced the trajectory of the laser on a planar target when the angle between the rotation axis of the scanning prism and the optical axis is 45° and 90°. The following section analyzes the scanning field of view under these two conditions.

[0067] When the angle between the rotation axis of the scanning prism and the output light axis is 45°, when the output light from the light source is tangent to the left and right edges of the same working surface of the scanning prism, two reflected beams appear sequentially after reflection by the prism. The angle between the two reflected beams when viewed directly from the direction of the output light is the field of view. Figure 12 and 13 As shown. Among them, Figure 12 Let A and B be the field of view angles of the working surfaces. Figure 13 Let be the field of view angles of working surfaces C and D. When the angle between the rotation axis of the scanning prism and the output optical axis is 90°, the field of view angle is as follows: Figure 14 As shown.

[0068] Depend on Figure 12 and Figure 13It can be seen that when the angle between the rotation axis of the scanning prism and the output optical axis is 45°, the field of view is 96° and 117.4°. From... Figure 14 It can be seen that when the angle between the scanning prism's rotation axis and the output optical axis is 90°, the field of view is 151.6°. (Comparison) Figure 2 As can be seen from the scanning field of view of the tower mirror, under the same number of working surfaces, the scanning prism of this scheme has a larger field of view than the tower mirror scanning scheme.

[0069] In summary, this solution has the following main advantages compared to the tower mirror scanning solution:

[0070] 1. The laser footprint trajectory projected onto the target by the scanning prism presents a parabola, making it easier for this scanning method to acquire point cloud data of the vertical facade.

[0071] 2. With the same working surface area, the scanning prism of this solution has a smaller volume, weight and moment of inertia, and the overall product has a better volume, weight and power consumption.

[0072] 3. While ensuring optimal size and weight of the scanning components, the scanning prism in this solution has a larger field of view, which can improve acquisition efficiency.

[0073] Example 2:

[0074] In this embodiment, as Figure 15 The prism structure shown in (a) and (b) in this embodiment is an irregular hexagonal prism structure. The top and bottom surfaces are both hexagonal, and at least one hexagon is irregular. The six sides of the top surface correspond to the six sides of the bottom surface and are parallel to each other. The six side planes together form six continuous trapezoidal working surfaces. Compared with the tower mirror scanning scheme with six working surfaces, this embodiment also has the following advantages: the laser footprint trajectory projected onto the target is parabolic. Since the angle β between each working surface and the rotation axis may be different, the laser footprint trajectory projected onto the target by working surfaces with different angles β presents parabolas with different curvatures. Compared with the straight footprint trajectory presented by the tower mirror, the scanning method of this scheme is more likely to acquire point cloud data of the vertical surface; when the working surface area is the same, the volume, weight and moment of inertia of the scanning prism in this scheme are small, and the overall volume, weight and power consumption of the product are better; the scanning prism has a larger field of view, which can improve the acquisition efficiency.

[0075] Similarly, as a further extension, the working face of the prism can be set to other numbers, such as five, seven, etc.

[0076] Example 3:

[0077] Based on the prism structure and principle of Embodiment 1 or Embodiment 2, this embodiment provides a prism scanning device, including the scanning prism described above, and also including a light source, a drive motor and a mounting base. The light source and the drive motor are respectively fixedly mounted on the mounting base. The rotation axis of the prism is coaxially arranged and fixedly connected to the rotor of the drive motor. The light source is arranged facing the working surface of the prism, and the angle α between the optical axis of the light source and the rotation axis is in the range of 0°≤α≤90°.

[0078] The light source provides the scanning laser, the drive motor drives the prism to rotate at high speed, and the mounting base provides mechanical support for the light source and drive motor.

[0079] Example 4:

[0080] Based on Embodiment 3, this embodiment also provides another prism scanning device, including the aforementioned scanning prism, and further including a light source, a drive motor, a reflector, and a mounting base. The light source, reflector, and drive motor are respectively fixedly mounted on the mounting base. The rotation axis of the prism is coaxially arranged with the rotor of the drive motor and fixedly connected through the system base. The reflecting surface of the reflector faces the light source and the working surface of the prism. The emitted light (pulsed laser) from the light source is reflected by the reflector and points towards the working surface of the prism. After being reflected again by the scanning prism, it reaches the target object being measured. The angle α between the optical axis and the rotation axis of the light source is in the range of 0°≤α≤90°. Figure 16 The image shows an example of a usage scenario for this scanning device. Figure 16 In the diagram, 1 represents the target object; 2 represents the scanning prism assembly; 3 represents the working surface of the prism; 4 represents the prism rotation axis; 5 represents the system base, which is a rigid support structure for the system's optical components (prisms), used to mount the prisms onto the rotor of the drive motor; 6 represents the light source, used to provide the pulsed laser for scanning; and 7 represents the reflector, where the laser emitted by the light source 6 is reflected by the reflector 7 onto the working surface of the scanning prism, and after being reflected by the working surface of the prism, it leaves the system and points towards the target object 1 being measured.

[0081] In this embodiment, as Figure 16 As shown, the scanning prism's rotation axis can be arranged parallel to the output optical axis, i.e., the angle between the prism's rotation axis and the optical axis is set to 0°. A reflector is placed in front of the light source. The pulsed laser emitted from the light source passes through the reflector to reach the scanning prism, and is reflected again by the scanning prism before reaching the target object. The reflector can be used to further adjust the angle α between the optical axis of the light source and the prism's rotation axis, for example, extending the angle α to 0°. The reflector also allows for flexible adjustment of the incident angle between the laser optical axis and the working surface without changing the inherent structure of the laser scanning system.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A scanning prism, characterized in that, The prism has a rotation axis and two parallel top and bottom surfaces. The rotation axis passes through the top and bottom surfaces and is perpendicular to them. The top and bottom surfaces are polygons, with the number of sides of the top surface being the same as that of the bottom surface, and the sides of the top and bottom surfaces are arranged in parallel and corresponding order. The longer side of the top surface is parallel to the shorter side of the bottom surface, and the shorter side of the top surface is parallel to the longer side of the bottom surface. The working surface is trapezoidal and has a reflective film. The plane formed by connecting adjacent vertices of the top and bottom surfaces serves as the working surface of the prism. The angle β between the working surface and the rotation axis is in the range of 0° < β < 90°.

2. The scanning prism according to claim 1, characterized in that, The axis of rotation passes through the geometric center of the top and bottom surfaces.

3. A scanning prism according to claim 2, characterized in that, The top and bottom surfaces are both rectangles, with the long side of the top surface being equal to the long side of the bottom surface, and the short side of the top surface being equal to the short side of the bottom surface.

4. A scanning prism according to claim 1 or 2, characterized in that, The number of working faces, n, is ≥ 4.

5. A prism scanning device, characterized in that, The scanning prism according to any one of claims 1 to 4 further includes a light source, a drive motor, and a mounting base. The light source and the drive motor are respectively fixedly mounted on the mounting base. The rotation axis of the prism is coaxially arranged and fixedly connected to the rotor of the drive motor. The light source is arranged facing the working surface of the prism, and the angle α between the optical axis of the light source and the rotation axis is in the range of 0°≤α≤90°.

6. A prism scanning device, characterized in that, The scanning prism according to any one of claims 1 to 4 further includes a light source, a drive motor, a reflector, and a mounting base. The light source, the reflector, and the drive motor are respectively fixedly mounted on the mounting base. The rotation axis of the prism is coaxially arranged and fixedly connected to the rotor of the drive motor. The reflecting surface of the reflector faces the light source and the working surface of the prism. The emitted light from the light source is reflected by the reflector and points towards the working surface of the prism. The angle α between the optical axis of the light source and the rotation axis is in the range of 0°≤α≤90°.

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