A multi-faceted receiving mirror for laser radar

Abstract

The present invention discloses a multi-faceted receiving mirror for laser radar, wherein one end face of the receiving mirror along the optical axis direction is a plane, and the other end face is a composite curved surface; the composite curved surface includes multiple curved surface areas, and a certain curved surface area and its projection area on the plane end of the receiving mirror are framed to form a lens area corresponding to the curved surface area, and different lens areas have different focal lengths. The multi-faceted receiving mirror uses lens areas with different focal lengths to receive reflected light with different reflection angles, so that the receiving mirror can converge the reflected light of the target to be measured at a very close distance to the detector, effectively reducing the measurement blind area of ​​the laser radar.

Description

Technical Field

[0001] The present invention relates to the technical field of laser radar, and in particular to a multi-faceted receiving mirror for laser radar. Background Art

[0002] Scanning LiDAR can provide real-time and accurate scene distance information, and has the inherent advantage of environmental perception. It has the advantages of large ranging range and high accuracy, and is widely used in unmanned driving, security monitoring, surveying and exploration, etc.; usually, the information obtained by LiDAR after scanning the target obstacle is presented in the form of point cloud. The principle is: a laser pulse is sent at each sampling to complete the measurement of the object to be detected. Ideally, the laser pulse irradiates the surface of the object and appears as a light spot, but because the actual laser pulse has a certain divergence angle, it irradiates the object as a surface, and this surface will increase with the increase of distance.

[0003] In order to effectively receive the reflected or scattered echo laser from the target object irradiated by the laser, the radar receiving field of view and the transmitting field of view should be effectively matched, that is, the receiving field of view angle is close to or equal to the transmitting field of view angle. The receiving field of view is mainly determined by the focal length of the receiving mirror and the size of the photosensitive surface of the detector, neither of which is a variable (the corresponding focal length and photosensitive surface size are determined by selecting the specifications of the receiving mirror and the detector). In the actual implementation of the radar, it is necessary to take into account the measurement of different target objects at different distances, and a single receiving field of view will inevitably limit the measurement range. When the target is very close to the radar, the reflected and scattered light in the area illuminated by the laser emission spot is received by the receiving mirror. Due to the large angle, it exceeds the receiving field of view angle and cannot be converged on the photosensitive surface of the detector, thus forming a near-end ranging blind area. Factors such as the mechanical structure of the transmitting lens barrel, the receiving lens barrel, and the axial spacing between the transmitting optical axis and the receiving optical axis further increase the blind area.

[0004] The radar cannot receive or receives very weak echo signals from the target in the blind spot, resulting in the phenomenon of no detection or inaccurate measurement. This greatly limits the application of radar in measuring the distance of close-range objects, such as deformation and loss of target contour when measuring large-sized targets at close range; and failure of obstacle avoidance caused by the inability to detect the sudden appearance of extremely close targets. Summary of the invention

[0005] The object of the present invention is to provide a multi-faceted receiving mirror for laser radar so as to reduce the detection blind area of ​​the laser radar.

[0006] To solve the above technical problems, the present invention provides a technical solution: a multi-faceted receiving mirror for a laser radar, wherein one end face of the receiving mirror along the optical axis direction is a plane, and the other end face is a composite curved surface; the composite curved surface includes multiple curved surface areas, and a curved surface area and its projection area on the plane end of the receiving mirror frame a lens area corresponding to the curved surface area, and different lens areas have different focal lengths.

[0007] According to the above solution, the composite curved surface includes a first curved surface area and a second curved surface area, and the lens areas corresponding to the first curved surface area and the second curved surface area are respectively the first lens area and the second lens area.

[0008] According to the above solution, the projection areas of the first curved surface area and the second curved surface area on the plane end of the receiving mirror are arcuate shapes with unequal areas.

[0009] According to the above solution, the projection area of ​​the first curved surface area on the plane end of the receiving mirror is a circle with the position of the optical axis as the center, and the projection area of ​​the second curved surface area on the plane end of the receiving mirror is a ring surrounding the circle.

[0010] A laser radar provided with the above-mentioned multi-faceted receiving mirror comprises a transmitter and a transmitting mirror arranged in sequence along a transmitting light path, and a receiving mirror and a detector arranged in sequence along a receiving light path.

[0011] According to the above scheme, the transmitting light path and the receiving light path are parallel to each other and do not overlap.

[0012] According to the above scheme, the emitting light path is coaxial with the receiving light path, and the center of the receiving mirror is a hollow area for the receiving light path to pass through; the projection area of ​​each curved surface area on the plane end of the receiving mirror is in a ring shape surrounding the emitting light path or the receiving light path.

[0013] According to the above scheme, the distance between the lens area used for converging the returned light from the target at a closer distance and the emitted light path is farther, and the distance between the lens area used for converging the returned light from the target at a farther distance and the emitted light path is closer.

[0014] According to the above scheme, the proportion of the lens area used for converging the light returned by the target at a closer distance is smaller than the proportion of the lens area used for converging the light returned by the target at a farther distance.

[0015] The beneficial effect of the present invention is that by arranging multiple lens areas with different focal lengths on the receiving mirror of the laser radar, light beams of a specific angle will be converged to different focal planes when passing through the receiving mirror, thereby increasing the probability that the laser radar detector receives the converged echo light, expanding the receiving field of view of the laser radar, and improving the measurement range and measurement accuracy of the near-end target.

[0016] Furthermore, in the echo light of the extremely close target, the small-angle light in the receiving field of view corresponding to the lens area used to converge the light returned by the target at a farther distance will be blocked, while the large-angle light in the receiving field of view corresponding to the lens area used to converge the light returned by the target at a closer distance can be received, and because the target to be measured is extremely close to the laser radar, even if the format of the lens area used to converge the light returned by the target at a closer distance is small, it can ensure that the detector can receive a sufficiently strong echo signal to achieve accurate identification of the laser radar. Based on the above characteristics, by making the lens area on the receiving mirror used to converge the target at a farther distance have a larger proportion in the laser radar, the receiving mirror can take into account the measurement needs within the full range. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic structural diagram of a double-sided receiving mirror according to a first embodiment of the present invention;

[0018] Figure 2 is a schematic structural diagram of a double-sided receiving mirror according to a second embodiment of the present invention;

[0019] Figure 3 Schematic diagram of the laser radar transceiver structure of the third embodiment of the present invention;

[0020] Figure 4 It is a schematic diagram of the laser radar transceiver structure of embodiment 4 of the present invention.

[0021] In the figure: 1-emitter, 2-emitter mirror, 3-detector, 4-area A, 5-area B, 6-first curved surface area, 7-second curved surface area. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0023] Embodiment 1:

[0024] See also Figure 1 This embodiment provides a double-sided receiving mirror structure, whose composite curved surface includes a first curved surface area 6 and a second curved surface area 7. The surface parameters of the first curved surface area 6 and the second curved surface area 7 are different. Accordingly, the focal lengths of the first lens area and the second lens area respectively framed by the first curved surface area 6 and the second curved surface area 7 are different. The cross-sectional shape of the first lens area is circular, the cross-sectional shape of the second lens area is annular, and the first lens area is nested in the second lens area.

[0025] Embodiment 2:

[0026] See also Figure 2 This embodiment provides a double-sided receiving mirror structure, whose composite curved surface includes a first curved surface area 6 and a second curved surface area 7. The surface parameters of the first curved surface area 6 and the second curved surface area 7 are different. Accordingly, the focal lengths of the first lens area and the second lens area respectively framed by the first curved surface area 6 and the second curved surface area 7 are different. The cross-sectional shapes of the first lens area and the second lens area are both arcuate, and the two are spliced ​​into a complete circular lens.

[0027] For the double-sided receiving mirror in the first or second embodiment, since there are two areas with different optical characteristics (focal length) on the receiving mirror, the receiving mirror is placed in the receiving optical path of the radar, that is, two (or more) different receiving fields of view are formed. For the near-end target to be measured, the echo light with a large field of view received by the detector 3 is the main echo signal; for the far-end target to be measured, the echo light with a small field of view received by the detector 3 is the main echo signal. The subsequent signal processing system of the radar performs distance calculation based on the main echo signal. When measuring the near-end target to be measured, the detector 3 can also receive the echo signal with a small field of view; when measuring the far-end target to be measured, the detector 3 can also receive the echo signal with a large field of view, but such signals do not carry the distance information of the target to be measured, and need to be suppressed or filtered out as interference items in the signal processing stage.

[0028] Embodiment three:

[0029] See also Figure 3 This embodiment provides a transceiver structure of a laser radar, including a transmitter 1 and a transmitting mirror 2 arranged in sequence along a transmitting optical path, and a receiving mirror and a detector 3 arranged in sequence along a receiving optical path, and the transmitting optical path and the receiving optical path are parallel to each other and do not overlap. The structural form of the receiving mirror in the transceiver structure is the same as that in the first embodiment, the B region 5 converges the approximately parallel echo laser of the medium and long distance onto the detector 3, and the A region 4 converges the echo laser of the short distance and large angle onto the detector 3, the A region 4 is arranged at the outer circle of the receiving mirror, and the B region 5 is arranged at the center of the receiving mirror.

[0030] In other embodiments of the present invention, the positions of region A 4 and region B 5 can be interchanged by changing the surface configuration of the receiving mirror, that is, region A 4 is set at the center of the receiving mirror, and region B 5 is set at the outer circle of the receiving mirror.

[0031] Embodiment 4:

[0032] See also Figure 4This embodiment provides a transceiver structure of a laser radar, including a transmitter 1 and a transmitting mirror 2 arranged in sequence along a transmitting optical path, and a receiving mirror and a detector 3 arranged in sequence along a receiving optical path, wherein the transmitting optical path is coaxial with the receiving optical path, and the center of the receiving mirror is a hollow area for the receiving optical path to pass through. The structural form of the receiving mirror in the transceiver structure is the same as that in the first embodiment, and the region B 5 converges the approximately parallel echo laser of the medium and long distance onto the detector 3, and the region A 4 converges the echo laser of the short distance and large angle onto the detector 3, and the region A 4 is arranged at the outer circle of the receiving mirror, and the region B 5 is arranged at the center of the receiving mirror.

[0033] In other embodiments of the present invention, the positions of region A 4 and region B 5 can be interchanged by changing the surface configuration of the receiving mirror, that is, region A 4 is set at the center of the receiving mirror, and region B 5 is set at the outer circle of the receiving mirror.

[0034] Embodiment 3 and Embodiment 4 provide a laser radar transceiver structure using the double-sided receiving mirror in Embodiment 1. The double-sided receiving mirror in Embodiment 3 or Embodiment 4 can be replaced with a multi-sided receiving mirror having more than two lens areas and the lens areas are arranged in a "circular manner" similar to that in Embodiment 1. The double-sided receiving mirror in Embodiment 3 can also be replaced with the double-sided receiving mirror in Embodiment 2. The double-sided receiving mirror in Embodiment 3 can also be replaced with a multi-sided receiving mirror having more than two lens areas and the lens areas are arranged in a "horizontal manner" similar to that in Embodiment 2. The number of lens areas, the focal length parameters of the lens areas, and the position setting method of different lens areas can be set according to actual needs, so that the proportion of effective echo light and noise light of the object being measured at different positions near and far received by the detector 3 meets certain requirements. Based on the above replacement method, multiple embodiments can be derived, which will not be repeated here.

[0035] It should be noted that:

[0036] When the lens area of ​​the multi-faceted receiving mirror is in a "horizontal arrangement mode" and the transmitting light path and the receiving light path in the laser radar are parallel but not coaxial, if the lens area used to converge the light returned by the target at a farther distance is closer to the transmitting light path, the focal length value between different lens areas can be reduced to achieve a better effect of reducing the blind spot. When the lens area of ​​the multi-faceted receiving mirror is in a "circular arrangement mode" and the transmitting light path and the receiving light path in the laser radar are parallel but not coaxial, for a certain lens area of ​​the receiving mirror, it has both an area close to the transmitting light path and an area far from the transmitting light path. The focal length difference between different lens areas is designed based on the area far from the transmitting light path to achieve a better effect of reducing the blind spot.

[0037] The mirror ratio of different lens areas should be adjusted according to actual needs. Usually, in order to take into account the measurement needs of the full range, the lens area used to converge the reflected light of targets at a farther distance has a larger mirror ratio (for example, the mirror ratio of area B 5 in embodiments three and four is much larger than that of area A 4. When measuring extremely close targets, the reflected large-angle light is collected by area A 4 for echo, which ensures the detection of extremely close objects and reduces the detection blind spot of the laser radar. The reflected light collected by the corresponding field of view of area B 5 is used as the background interference light noise of the echo signal; when measuring distant objects, the reflected small-angle light is collected by area B 5 for echo, and the reflected light collected by the corresponding field of view of area A 4 is used as the background interference light noise of the echo signal. Since area A 4 has a small ratio, it is beneficial to subsequent optical noise reduction).

[0038] The transition area between different lens areas should be as small as possible to avoid introducing too much stray light into the detector 3 from the transition area.

[0039] The present invention realizes the expansion of the receiving field of view based on the partition design of the receiving mirror, thereby ensuring that the large-angle echo laser returned by the near-end measured target is effectively received by the detector 3, effectively reducing the near-end measurement blind area of ​​the radar system, and improving the radar's measurement range and measurement accuracy for the near-end measured target. Since the partition design of the receiving mirror reduces the blind area, other means of reducing the blind area (such as reducing the distance between the optical axes of the transmitting optical path and the receiving optical path) can be appropriately relaxed, thereby providing greater flexibility for the optical-mechanical structure design of the system.

[0040] The above descriptions are merely 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 contents of the present invention specification and drawings, 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 multi-faceted receiving mirror for laser radar, characterized in that: One side end face of the receiving mirror along the optical axis direction is a plane, and the other side end face is a composite curved surface; the composite curved surface includes multiple curved surface areas, a curved surface area and its projection area on the plane end of the receiving mirror are framed to form a lens area corresponding to the curved surface area, and different lens areas have different focal lengths; the composite curved surface includes a first curved surface area and a second curved surface area, and the lens areas corresponding to the first curved surface area and the second curved surface area are respectively the first lens area and the second lens area; the projection areas of the first curved surface area and the second curved surface area on the plane end of the receiving mirror are arcs of unequal areas; the distance between the lens area used for converging the light returned by a closer target and the emission light path is farther, and the distance between the lens area used for converging the light returned by a farther target and the emission light path is closer.

2. A laser radar provided with the multi-faceted receiving mirror according to claim 1, characterized in that: It includes a transmitter and a transmitting mirror arranged in sequence along a transmitting light path, and a receiving mirror and a detector arranged in sequence along a receiving light path; the transmitting light path and the receiving light path are parallel to each other and do not overlap.

3. The laser radar according to claim 2, characterized in that: The percentage of the lens area used to focus light returned from closer targets is smaller than the percentage of the lens area used to focus light returned from farther targets.

Images