LASERSCANNER

Description

[0001] The present invention relates to a laser scanner for scanning, in particular airborne scanning, an environment.The laser scanner comprises a laser transmitter for emitting a transmitted beam, a laser receiver for receiving the transmitted beam reflected by the environment as a received beam, a beam deflection device arranged in the beam path of the transmitted and received beams in the form of a mirror pyramid rotatable about an axis of rotation with pyramid sides inclined relative to the axis of rotation, each forming a mirror facet, and a housing in which the laser transmitter, the laser receiver and the beam deflection device are arranged and which has a base and a cover surface, a casing connecting the base and cover surfaces, the clear width of which is less than the housing height between the base and cover surfaces, and a window for the transmitted and received beams, wherein the beam deflection device is adjacent to the window and its axis of rotation is aligned substantially parallel to the base surface.

[0002] Such a laser scanner is used in particular for mobile laser scanning and is mounted on or in a vehicle, in particular an aircraft, or in a specially designed, particularly motion-stabilizing platform, which in turn is attached to the vehicle. During scanning, the transmitted beam directed at the rotating beam deflection device is periodically swiveled over a scanning angle range and thus fanned out into a scanning fan, which scans the surroundings line by line in approximately parallel scan lines. Compared to laser scanners that refracted the transmitted beam into a scanning cone, e.g., using a rotating Risley prism, and thus scanned the surroundings in a spiral pattern during mobile use, such scanners allow for more uniform scanning of the surroundings.The same mirror facet of the beam deflection device that deflects the transmitted beam also deflects the received beam, which is reflected by the surroundings and arrives from the same direction, onto the laser receiver. From the transmission direction of the transmitted beam and the travel time until the received beam is received, the position of each scanned point in the surroundings relative to the laser scanner is determined, and from a multitude of such scanned points, for example, a 3D model of the surroundings is created. Laser scanners of this type are known, for example, from EP 3 182 159 A1 or WO 2019 / 064062 A1. The laser scanner of WO 2019 / 064062 A1 further has a deflection mirror that deflects the received beam from the beam deflection device to the laser receiver.

[0003] The housing facilitates installation in designated loading bays or on mounting brackets of different vehicles, as well as disassembly when changing vehicles. An aperture, e.g., an external wall hatch or similar, is provided in the outer wall of the vehicle or platform for the transmission and reception beams to pass through. On the one hand, the aperture should be small in order to minimize interference with the outer wall structure and the airflow above it. On the other hand, there is sometimes a need to allow other measuring and recording devices, e.g., cameras, etc., to use the same aperture to simultaneously measure the surroundings. These measuring devices then require additional space in the loading bay or on the mounting bracket alongside the laser scanner, without the aperture needing to be enlarged.

[0004] The invention aims to create a particularly compact laser scanner which enables a particularly small aperture and / or the arrangement of additional measuring devices at the same aperture.

[0005] This aim is achieved with a laser scanner of the type mentioned in the introduction, in which the window is located in the base area and the laser receiver is arranged closer to the cover than to the base area, wherein a deflecting mirror is arranged in the housing adjacent to the base area, which deflects the received beam from the beam deflection device to the laser receiver, wherein for focusing the received beam onto the laser receiver in the beam path between the beam deflection device and the laser receiver, a receiving optics is arranged in the housing between the beam deflection device and the laser receiver, which receiving optics is an optical lens with a decentralized optical axis, and wherein the deflecting mirror also deflects the transmitted beam from the laser transmitter to the beam deflection device and wherein the optical lens has a recess parallel to the mentioned optical axis and spaced therefrom for the passage of the transmitted beam.

[0006] Since this elongated laser scanner has its window in the base area rather than in the housing shell, it can be mounted upright behind the aperture. The beam deflection device and the deflection mirror together achieve a compact Z-shaped fold of the beam path. This folding enables optimization of the ratio between the base area of the housing and the area effective for receiving the received beam, i.e., the smaller of the two areas: the mirror facet area or the window area in the beam path, and thus maximizes the effective receiving area for a given base area, minimizes the base area for a given effective receiving area, or a combination thereof. Given that the axis of rotation of the beam deflection device is essentially parallel to the base area and the laser receiver is arranged closer to the cover surface, the deflection angle of the deflection mirror is approximately 90°, which enables a particularly small base area for the housing.This essentially depends solely on the beam deflection device and the deflection mirror. This allows the aperture in the vehicle's exterior wall to be kept small and / or allows space to be left next to or around the laser scanner for use by additional measuring or recording devices that measure the same environment through the aperture, synchronously with the laser scanner.

[0007] In the context of the laser scanner in question, "essentially parallel to the base surface" means, on the one hand, that the base surface could be flat only in sections, with the rotation axis being parallel to only one of the sections of the base surface, and, on the other hand, that the rotation axis can optionally have a slight inclination relative to the base surface or its sections in the order of a few angular degrees.

[0008] The receiving optics enable the use of a smaller light sensor for the laser receiver and promotes an overall smaller design of the laser scanner.

[0009] An optical lens is designed to be compact. Due to the decentralized optical axis, the laser receiver or its light sensor is not positioned centrally above the receiving optics or the deflection mirror, but rather along the optical axis, i.e., off-center, particularly near the outer surface of the housing, allowing for better utilization of the remaining space inside the housing.

[0010] Due to the transmission beam being guided parallel to the optical axis and the overall Z-shaped folding by means of the deflection mirror, the laser scanner, laser receiver, and beam path are combined in a particularly compact manner, enabling a particularly compact design of the laser scanner. This is especially true if the laser transmitter, as preferred, is located behind the laser receiver on the cover surface as seen from the deflection mirror, and the transmission beam is guided from the laser transmitter past the laser receiver to the recess using a fiber optic cable.

[0011] It is particularly advantageous if the transmitted beam hits the beam deflection device parallel to the rotation axis. This results in largely straight, parallel scan lines.

[0012] Preferably, the receiving optics are arranged between the deflection mirror and the laser receiver. Since the space between the deflection mirror and the beam deflection device remains free, the two can be arranged closer together, and the footprint of the housing can be further reduced.

[0013] In an advantageous variant of the laser scanner, the window, viewed in the direction of the axis of rotation, has the cross-section of a circular or elliptical arc or of an open polygonal line, within which the axis of rotation lies. The window therefore has a concave side on which the beam deflection device is arranged. In this variant, the mirror pyramid can protrude at least partially between the lateral legs of the polygonal line or the ends of the circular or elliptical arc. Even with a narrow laser scanner design, this leads to better utilization of the active mirror facet compared to a flat window, i.e. the mirror facet that is currently in the beam path of the transmit and receive beams, since the entire surface of this mirror facet can be used for the receive beam.

[0014] It is also advantageous if the mirror facets have different inclinations relative to the rotation axis. This allows the surroundings to be scanned in several approximately parallel scan lines.

[0015] To better dissipate any heat from the housing without increasing its footprint, the housing preferably has a heat sink on the outside of its cover surface. This allows, for example, accumulated heat in the top area of the housing to be reliably dissipated via the cover surface. The possibility of attaching additional sensors directly to the housing is not limited by excessive waste heat from the housing. Furthermore, if the laser transmitter is mounted on the cover surface, its waste heat can be dissipated directly.

[0016] The invention is explained in more detail below with reference to an embodiment illustrated in the accompanying drawings. In the drawings: Fig. 1 an embodiment of a laser scanner according to the invention in a longitudinal section in the plane of its transmission beam; and Fig. 2 a section of the laser scanner from Fig. 1 along a section line A - A.

[0017] Fig. 1 shows a laser scanner 1 for scanning an environment 2. The laser scanner 1 can be mounted either for stationary scanning on a scaffold or the like or for mobile scanning on a vehicle F, in particular for airborne scanning on an aircraft, e.g. in or behind an aperture P provided for this purpose, e.g. an external wall hatch or the like. If desired, the same aperture P can be used by other measuring and recording devices, e.g. a camera K etc., for simultaneous measurement of the environment.

[0018] The laser scanner 1 comprises a laser transmitter 3, which emits a pulsed or modulated transmission beam 4, which strikes the environment 2 at an impact point 5 and is at least partially reflected there, and a laser receiver 6, which receives the transmission beam 4 reflected by the environment 2 as a reception beam 7. A beam deflection device 8 of the laser scanner 1 is arranged in the beam path of the transmission and reception beams 4, 7. The beam deflection device 8 is a mirror pyramid, which is mounted on a shaft 9 for rotation about an axis of rotation D and has pyramid sides inclined relative to the axis of rotation D, each of which forms a mirror facet 10-12. In the example shown, the mirror pyramid has three mirror facets 10-12 or pyramid sides; alternatively, it can have four or more pyramid sides.Either all mirror facets have the same inclination relative to the rotation axis D or at least two - or all - of them have different inclinations relative to the rotation axis D.

[0019] It is understood that the mirror pyramid can have any pyramid shape with any polygonal base, both straight and "oblique", where the pyramid axis is not perpendicular to the base, regular or irregular, pointed or "blunt" ("truncated pyramid"), and can be cut at the top and / or base, as shown in the Fig. 1 and 2 shown pyramid, whose base is circularly cut to reduce air resistance as it rotates.

[0020] The shaft 9 of the mirror pyramid is driven by a motor 13, so that the transmitted beam 4 strikes an active mirror facet 10-12, i.e., the mirror facet 10-12 that is currently in the beam path of the transmitted and received beams 4, 7. In the example shown, the transmitted beam 4 strikes the active mirror facet 10-12 directly next to the outer edge of the mirror pyramid. The received beam 7 strikes the entire active mirror facet 10-12, namely from exactly the direction in which the transmitted beam 4 was emitted. Due to the rotational movement of the mirror pyramid, the transmitted beam 4 is periodically pivoted through a scanning angle α to form a scanning fan 14 ( Fig. 2 ). With the scanning fan 14, the environment 2 is scanned line by line, in particular point by point in lines.

[0021] An electronics unit 15 controls the laser scanner 3 and evaluates received signals from the laser receiver 6 to determine the travel time of the transmitted and received beams 4, 7. The electronics unit 15 also controls—optionally with the aid of a motor controller 16—the rotational movement of the motor 13 or the beam deflection device 8. From the determined travel time, the electronics unit 15 can determine the distance of the laser scanner 1 from the point of impact 5 of the transmitted beam 4 on the environment 2 and, from the position of the active mirror facet 10-12 during the transmission of the transmitted beam 4, the direction of the point of impact 5 from the perspective of the laser scanner 1, as is known in the art. From this, either the electronics unit 15 or a computing unit separate from the laser scanner 1 can calculate the position of the impact point 5 relative to the laser scanner 1 and optionally generate a 3D point cloud or a 3D model of the environment 2 from a plurality of impact points in a known manner.

[0022] The laser scanner 1 further comprises a housing 17 in which the laser transmitter 3, the laser receiver 6, the beam deflection device 8 and other components, e.g. the electronics unit 15, the motor 13, its optional motor control 16, etc., are arranged. The housing 17 is, for example, approximately cylindrical or prism-shaped with a base and a cover surface 18, 19 and a casing 20 connecting them, and is elongated such that the casing 20 has a smaller clear width W than the housing height H between the base and cover surfaces 18, 19. The elongated housing 17 is not necessarily completely regular in shape, but can, for example, have recesses, projections, etc. and additional openings - e.g. for ventilation.

[0023] In its base area 18, the housing 17 has a window 21 for the transmit and receive beams 4, 7. The beam deflection device 8 is arranged in the housing 17 adjacent to the window 21, in such a way that its axis of rotation D is aligned substantially parallel to the base area 18, ie that on the one hand the base area 18 could also be flat only in sections and the axis of rotation D could be parallel to one of the sections, and that on the other hand the axis of rotation D can optionally have a slight inclination with respect to the base area 18 or its sections in the order of a few angular degrees.

[0024] Adjacent to the base surface 18, a deflecting mirror 22 is also arranged in the housing 6. The deflecting mirror 22 deflects the received beam 7 coming from the beam deflection device 8 onto the laser receiver 6 arranged closer to the cover surface 19 than to the base surface 18 in the housing 17, i.e., in the direction of the cover surface 19, namely by an angle of approximately 90° in the illustrated embodiment, and by an angle between 70° and 110° in other embodiments. The interaction of the deflecting mirror 22 with the beam deflection device 8 causes a Z-shaped folding of the received beam 7 inside the housing 17, which favors a narrow housing shape.

[0025] The laser receiver 6 could in principle be of any type known in the art, for example a large-format photosensitive sensor, a CCD chip, etc. To focus the receiving beam 7 onto the laser receiver 6, a receiving optics 23 is arranged in the housing 17 in the beam path between the beam deflection device 8 and the laser receiver 6, either between the beam deflection device 8 and the deflection mirror 22 or - as in the example of the Fig. 1 - between deflecting mirror 22 and laser receiver 6. For this purpose, the laser receiver 6 has a light sensor 24, e.g., a photomultiplier or an avalanche photodiode, arranged at the focus of the receiving optics 23. The receiving optics 23 is an optical lens. This has a decentralized optical axis L, so that the received beam 7 is also focused decentrally, and the laser receiver 6 or its light sensor 24 is arranged decentrally in the housing 17 above the deflecting mirror 22.

[0026] According to Fig. 1 The transmitted beam 4 strikes the beam deflection device 8, i.e., the mirror facet 10 active here, parallel to the rotation axis D. This results in a largely straight scan line. Alternatively, the transmitted beam 4 can be at least slightly inclined relative to the rotation axis D.

[0027] The deflecting mirror 22 not only deflects the received beam 7 from the beam deflection device 8 to the laser receiver 6, but also the transmitted beam 4 from the laser transmitter 3 to the beam deflection device 8. The optical lens has a recess (here: a bore) 25 parallel to its optical axis L and spaced from the optical axis L for the unrefracted passage of the transmitted beam 4 parallel to the optical axis L, regardless of whether the receiving optics 23 are arranged upstream or downstream of the deflecting mirror.

[0028] In the example of Fig. 1 the laser transmitter 3 is arranged behind the laser receiver 6 as seen from the deflection mirror 22, specifically here directly on the cover surface 19 of the housing 17. The transmitted beam 4 is guided from the laser transmitter 3 with the aid of a light guide 26 past the laser receiver 6 to the recess 25. Optionally, a collimator lens 27 is arranged on the output side of the light guide. Instead of the light guide 26, the transmitted beam 4 could be guided past the laser receiver 6 to the recess 25 with the aid of, for example, one or more mirrors and / or the laser transmitter 3 could be arranged elsewhere in the housing 17, even in the received beam 7, e.g. if the laser transmitter 3 is a very small semiconductor laser.

[0029] Optionally, the housing 17 has a heat sink 28 on the outside of its cover surface 19. In the example of the Fig. 1 The housing 17 also carries an optional additional heat sink 29 for the electronics unit 15 on the outside of the casing 20.

[0030] As in Fig. 2As shown, the window 21 may not only be flat, but alternatively, viewed in the direction of the rotation axis D, may have the cross-section of a circular or elliptical arc or (in the illustrated case) an open polygonal arc 30. The rotation axis D lies in the interior of the polygonal arc 30, ie on its concave side, with at least part of the mirror pyramid protruding between the outer legs 30', 30" of the polygonal arc 30 or between the ends of the circular or elliptical arc.

[0031] The invention is not limited to the embodiments shown, but includes all variants, modifications and combinations thereof that fall within the scope of the appended claims.

Claims

1. Laser scanner for scanning, in particular airborne scanning, of an environment (2), comprising a laser transmitter (3) for transmitting a transmission beam (4), a laser receiver (6) for receiving the transmission beam (4) reflected on the environment (2) as a receive beam (7), a beam-deflection device (8) arranged in the beam path of the transmission and receive beams (4, 7) in the form of a mirror pyramid that is rotatable about a rotational axis (D) and has pyramid sides inclined relative to the rotational axis (D) that each form a mirror facet (10, 11, 12), and a housing (17), in which the laser transmitter (3), the laser receiver (6), and the beam-deflection device (8) are arranged and which comprises a bottom face and a top face (18, 19), a lateral shell (20) which connects the bottom face and top face (18, 19) and has an inner width (W) that is less than the housing height (H) between the bottom face and top face (18, 19), and a window (21) for the transmission and receive beams (4, 7), wherein the beam-deflection device (8) is adjacent to the window (21) and its rotational axis (D) is oriented substantially in parallel with the bottom face (18), and wherein a deflecting mirror (22) is arranged in the housing (17) deflecting the receive beam (7) from the beam-deflection device (8) onto the laser receiver (6), characterized in that the window (21) is in the bottom face (18), the laser receiver (6) is arranged closer to the top face than to the bottom face (19, 18) and the deflecting mirror (22) is arranged adjacent to the bottom face (18) in the housing (17), wherein, for focussing the receive beam (7) on the laser receiver (6), an optical receiving system (23) is arranged in the housing (17) in the beam path between the beam-deflection device (8) and the laser receiver (6), which optical receiving system (23) is an optical lens having a decentralized optical axis (L), and wherein the deflecting mirror (22) further deflects the transmission beam (4) from the laser transmitter (3) onto the beam-deflection device (8), the optical lens having a cut-out (25), which is in parallel with said optical axis (L) and spaced apart from said optical axis (L), for the transmission beam (4) to pass through.

2. Laser scanner according to claim 1, characterized in that the transmission beam (4) impinges on the beam-deflection device (8) in parallel with the rotational axis (D).

3. Laser scanner according to claim 1 or 2, characterized in that the optical receiving system (23) is arranged between the deflecting mirror (22) and the laser receiver (6).

4. Laser scanner according to any one of claims 1 to 3, characterized in that, when viewed from the deflecting mirror (22), the laser transmitter (3) is arranged behind the laser receiver (6) on the top face (19), wherein the transmission beam (4) is guided from the laser transmitter (3), past the laser receiver (6) and to the cut-out (25) by means of an optical waveguide (26).

5. Laser scanner according to any one of claims 1 to 4, characterized in that, when viewed in the direction of the rotational axis (D), the window (21) has the cross section of an arc of a circle or an arc of an ellipse, or of an open polygon (30), in the interior of which the rotational axis (D) is positioned.

6. Laser scanner according to any one of claims 1 to 5, characterized in that the mirror facets (10, 11, 12) each have inclinations relative to the rotational axis (D) that are different from one another.

7. Laser scanner according to any one of claims 1 to 6, characterized in that the housing (17) has a cooling body (28) on the outside of its top face (19).