WO2016110442A1

WO2016110442A1 - 3d-lidar sensor

Info

Publication number: WO2016110442A1
Application number: PCT/EP2015/081450
Authority: WO
Inventors: Heiko Ridderbusch
Original assignee: Robert Bosch Gmbh
Priority date: 2015-01-09
Filing date: 2015-12-30
Publication date: 2016-07-14
Also published as: DE102015200224A1

Abstract

The invention relates to a 3D-LIDAR sensor, having a laser beam source (10), an optical receiver (14), and a scanning system for deflecting a laser beam (18) generated by the laser beam source in two scanning directions which are perpendicular to each other, characterized in that the scanning system has an oscillating mirror (12) for deflecting the laser beam (18) in one of the scanning directions and a rotation drive (32) for rotating the mirror (12) and the receiver (14) about an axis parallel to said scanning direction.

Description

description

title

3D LIDAR sensor

The invention relates to a 3D LIDAR sensor, in particular for motor vehicles, having a laser beam source, an optical receiver, and a scanning system for deflecting a laser beam generated by the laser beam source in two mutually perpendicular scanning directions.

PRIOR ART In LIDAR sensors, the laser beam source used is usually a pulse laser with a pulse duration of the order of magnitude of a few nanoseconds and a wavelength between 850 and 1500 nm or more. By deflecting the laser beam in two mutually perpendicular directions, a two-dimensional image is obtained. By additionally evaluating the transit time between the emission of a laser pulse and the reception of the light backscattered by an object, information about the distance of the object is obtained, so that a three-dimensional image of the environment can be constructed. In motor vehicles, such a 3D LIDAR sensor makes it possible to provide data about the traffic environment, which can then be stored in one or more driver assistance systems, for example in distance control systems, dead-angle warning systems, parking aids and the like.

Some conventional 3D LIDAR sensors have as a scanning system in a two-axis oscillating deflection mirror, which is formed for example by a MEMS (Micro-Electro-Mechanical System). Another known type of 3D LIDAR sensors are so-called Flash LIDARs, which work similarly to a digital camera with a two-dimensional optical detector array and a relatively wide-spread laser beam, so that no deflection of the laser beam is required.

Disclosure of the invention

The object of the invention is to provide a cost-effective and robust 3D LIDAR sensor which is particularly suitable for motor vehicles.

This object is achieved according to the invention in that the scanning system has an oscillating mirror for deflecting the laser beam in one of the scanning directions and a rotary drive for rotating the deflecting mirror and the receiver about an axis parallel to this scanning direction.

The scanning in the second scanning direction is thus achieved in that the entire sensor rotates about the axis parallel to the first scanning direction, so that the laser beam in the plane perpendicular to this axis sweeps over the entire angular range of 360 °. This has the advantage that in the second scanning direction, no reversal of the direction of movement of the mechanical components is required, but the entire system can rotate continuously in a single direction of rotation. This allows a high speed and a correspondingly high scanning speed in this direction and has the additional advantage that in principle an all-round view is made possible, for example, when the sensor is mounted on the roof of a motor vehicle. Another advantage is that due to the high (and constant) scanning speed a higher eye safety is achieved with unchanged intensity of the laser beam or vice versa given minimum requirements for eye safety higher laser power and thus a higher range is possible. For the first scanning direction (parallel to the axis of rotation), a low cost single axis MEMS scanner can be used.

Advantageous developments and refinements of the invention are specified in the subclaims.

In an advantageous embodiment, the deflection mirror, the receiver and the laser beam source form a rigid unit which is set in rotation by means of the rotary drive. In that case, the laser beam source can also be arranged in a position offset from the axis of rotation.

The optical receiver preferably has a detector array which includes a plurality of optical detector elements and extends in the direction parallel to the axis of rotation. Each detector element is then sensitive to backscattered laser light, which falls from a certain direction (in elevation, when the axis of rotation is vertically oriented) to a receiving optics of the receiver and then focused by this optics on the relevant sensor element. This allows a simple and fast signal evaluation in a plurality of parallel receiving channels.

In another embodiment, a frequency-modulated continuous wave laser can also be used as the laser beam source instead of a pulse laser. As is known per se, then obtained by mixing the emitted light with the reflected light, a beat signal whose frequency position of The speed of the frequency modulation as well as the signal transit time and thus the distance of the object and in moving objects also on the relative speed of the object is dependent. Optionally, it is also possible to use a laser beam source which can be switched over between pulse operation and continuous line operation.

A particularly high distance resolution in the near range can be achieved by an arrangement of the laser beam source and the receiver, which operates on the principle of the so-called "self-mixing interference". In this case, with the aid of a beam splitter, a part of the light reflected or backscattered by the object is directed back into the laser beam source so that a mixture of the emitted and reflected beams occurs directly in the laser cavity.

In the following embodiments are explained in detail with reference to the drawing.

Show it:

1 is a schematic front view of a LIDAR sensor according to a first embodiment;

FIG. 2 shows the LIDAR sensor according to FIG. 1 in a view from above; FIG.

Fig. 3 is a side view of the LIDAR sensor from the direction of the arrows

III-III in Fig. 1;

Fig. 4 is a side view from the direction of the arrows IV-IV in Fig. 3;

Fig. 5 is a front view of a LIDAR sensor according to another

Embodiment; 6 shows a side view of the LIDAR sensor according to FIG. 5 from the direction of the arrows V 1 -V 1 in FIG. 5;

7 shows a side view of a LIDAR sensor according to a further exemplary embodiment; and

Fig. 8 shows a modification of the embodiment of FIG. 7 in the

Top view.

The 3D LIDAR sensor shown in FIG. 1 comprises a laser beam source 10, an oscillating mirror 12, which is formed for example by a uniaxial MEMS scanner, and an optical receiver 14. The laser beam source 10 is mounted in the example shown on the underside of a rotatably driven disc 16 and generates a sharply focused laser beam 18 which falls through a hole 20 in the disc 16 vertically upwards on the mirror 12. The mirror 12 is tilted so that the laser beam 18 in Fig. 1 is reflected toward the viewer. The mirror 12 is mounted on a mirror support 22. The optical receiver 14 has a detector line 24 which extends vertically in the image plane of an optical lens 26. The detector row 24 and the mirror support 22 are mounted side by side on a common support plate 28 which projects perpendicularly from the disk 16.

Below the disc 16, a stationary base plate 30 is arranged, on which a rotary drive 32 for the disc 16 is mounted. The disc 16 is non-rotatably mounted on the free end of an output shaft 34 and is rotated at high speed, for example at 600 to 1200 min ^"1 , about a vertical axis A. The laser beam 18 (FIG. 2) deflected by the mirror 12 in a substantially horizontal direction thus scans the entire surroundings of the sensor over a full circle of 360 ° in each azimuth rotation of the disk 16. Since the lens 26 and the detector line 24, as well as the mirror 12 and the laser beam source 10 are rigidly secured to the disc 16, in each angular position of the disc 16, the light of the laser beam 18, which is reflected at a lying in the current direction of the laser beam object or backscattered (beam 18 'in FIG. 2), is focused and detected by the lens 26 on the detector line 24. Each time the disc 16 rotates, a horizontal picture line of a 360 ° panoramic picture is scanned at a line scanning frequency of 10 to 20 Hz.

At the same time, the mirror 12 is oscillated about a horizontal axis with the aid of the MEMS, so that the laser beam 18 also oscillates in a vertical scanning direction, as indicated by a double arrow B in FIG. The vertical scanning angle range can be 60 ° (± 30 °) and can be selectively increased by using an additional optics, not shown, for example, to 120 °. The reflected or backscattered beam 18 'from the object is focused by the lens 26 onto the detector array 24. The vertical position of the focus on the detector line 24 is, as indicated in Fig. 4, depending on the angle of incidence of the beam 18 ', which in turn is dependent on the current inclination of the mirror 12.

The oscillation frequency of the mirror 12 may be significantly higher than the determined by the rotation of the disc 16 Zeilenabtastfrequenz. In that case, the vertical scanning direction constitutes the main scanning direction. Depending on the application, however, an operation is possible in which the vertical scanning direction forms the (slow) sub-scanning direction. The detector row 24 has a multiplicity of optical detectors, for example PIN detectors or APD detectors made of silicon or indium / gallium arsenide. Each individual detector forms a receiving channel, to which a certain vertical position of the reflection source is assigned, from which the beam 18 'is received. The detectors of detector array 24 together thus provide at all times a set of electronic signals representing the image content of a pixel column in a two-dimensional image. Due to the rotation of the disc 16, the signals received at different times by the same detector element form one pixel row of that image.

The laser beam 18 generated by the laser beam source 10 has, for example, a wavelength between 850 and 1500 mm and is pulsed, with pulse durations on the order of a few nanoseconds. Due to the finite speed of light, the transit time between the emission of a pulse and the receipt of this pulse by the detector line 24 forms a measure of the distance of the object. Since this information is available for each pixel of the two-dimensional image, one obtains a total of a three-dimensional image of the environment of the sensor, on a full circle (360 °) in azimuth and in an angular range of 60 to 120 ° in elevation.

In practice, for example, the lens 26 has a diameter of the order of 20 to 30 mm, and the focal length of this lens is of the same order of magnitude. The mirror 12 may be a rectangular mirror with an edge length in the range of 1 to 3 mm. The brilliance of the laser beam source 10 is preferably in the range of 100 to 1000 kW / mm ² sr. This allows a range of the LIDAR sensor of more than 100 m to over 180 m. Figs. 5 and 6 show a modified embodiment. The reference numerals in Figs. 5 and 6 have the same meaning as in Figs. 1 to 4, but are each supplemented by an apostrophe. The mirror support 22 'and the optical receiver 14' are arranged one above the other here, so that the disk 16 'can have a smaller diameter.

This embodiment has the advantage that the unit-rotatable parts of the sensor have a smaller moment of inertia, thereby enabling higher speeds.

7 shows an exemplary embodiment in which a carrier 38 is arranged on a rotatably drivable disk 36, on which a laser beam source 40, a mirror 42 oscillatingly driven by means of a MEMS and a receiver 44 are arranged. The laser beam emitted from the laser beam source 40 is parallel to or coincides with the axis of rotation A and is then deflected by the mirror 42 in an approximately horizontal direction. By the oscillation of the mirror 42 takes place a deflection in the vertical.

In the beam path between the laser beam source 40 and the mirror 42, a beam splitter 46 is arranged in the form of a semitransparent mirror. The beam emitted by the laser beam source passes through the beam splitter and is then deflected by the mirror 42 onto the objects to be located. The light reflected or scattered on these objects travels in the same way back to the mirror 42 and is deflected by it again in the direction of the laser beam source 40. However, the beam splitter 46 leaves only a part of this

Light, for example 50%, again pass to the laser beam source 40, while the other part is directed to the receiver 44. The frequency of the laser beam emitted by the laser beam source 40 is modulated, for example in the form of rising and / or falling ramps. In the cavity of the laser beam source, there is an interference between the emitted light and the light emitted. back-scattered light (self-mixing interference) and thus to a beat in the signal received by the receiver 44, which is dependent on the frequency difference between transmitted and received light and thus the distance of the object. The evaluation of this signal allows a very high-resolution distance measurement, especially in the near range.

The reflectivity of the beam splitter 46 may vary depending on the application. If predominantly objects in the near range (e.g., <1 m) are to be located, it is expedient to design or adjust the steel divider so that the reflectivity is less than 50% in order to increase the interference in the laser beam source. On the other hand, if predominantly objects in the middle distance range are to be located, in the arrangement shown here, the intensity at the receiver 44 can be increased by increasing the reflectivity

Range can be increased. The reverse applies to an arrangement (not shown) in which the beam splitter reflects the light coming from the laser beam source and returning to it, and allows the beam traveling to the receiver to pass in transmission.

While in the embodiment shown in FIG. 7, the beam splitter 46, the receiver 44 and the laser beam source 40 rotate together with the mirror 42 and the disk 36, an arrangement is conceivable in which the laser beam source 40, the beam splitter 46 and the receiver 44 are stationary and only the mirror 42 rotates. 8 shows a further exemplary embodiment in which a laser beam source 40 ', a beam splitter 46', a receiver 44 'and a mirror 42' are arranged lying on the rotating disk 36. The oscillating movement of the mirror 42 'and thus the deflection of the laser beam takes place in this case in the direction perpendicular to the plane of the drawing.

Claims

claims

1 . A 3D LIDAR sensor comprising a laser beam source (10; 10 '; 40; 40'), an optical receiver (14; 14 '; 44; 44') and a scanning system for deflecting a laser beam (18) generated by the laser beam source two mutually perpendicular scanning directions, characterized in that the scanning system comprises an oscillating mirror (12; 42; 42 ') for deflecting the laser beam (18) in one of the scanning directions and a rotary drive (32; 32') for rotating the mirror (12; 42 ') and the receiver (14; 14'; 44; 44 ') around an axis (A) parallel to said scanning direction.

A sensor according to claim 1, wherein the laser beam source (10, 10 ', 40') is offset from the axis (A) and is disposed together with the mirror (12; 42; 42 ') and the receiver (14; 14'; 44 ') forms a rotatable unit.

3. Sensor according to claim 1 or 2, with a between the mirror (42; 42 ') and the laser beam source (40; 40') arranged beam splitter (46; 46 '), which covers a part of the backscattered from an object on the mirror laser beam and directs another part back into the laser beam source (40, 40 ').

A sensor according to claim 1 or 2, wherein the receiver (14; 14 ') has a detector array (24) extending parallel to the axis (A).

5. Sensor according to one of the preceding claims, wherein the mirror (12; 42 ') and the receiver (14; 44') side by side on a about the axis (A) rotatably driven disc (16; 36) are arranged.

6. Sensor according to one of claims 1 to 4, wherein the mirror (12; 42) and the receiver (14 '; 40) in the direction of the axis (A) are offset from one another.

7. driver assistance system for motor vehicles, with a 3D LIDAR sensor according to one of the preceding claims.