WO2018219706A1

WO2018219706A1 - Lidar sensor

Info

Publication number: WO2018219706A1
Application number: PCT/EP2018/063301
Authority: WO
Inventors: Alexander Greiner
Original assignee: Robert Bosch Gmbh
Priority date: 2017-06-01
Filing date: 2018-05-22
Publication date: 2018-12-06
Also published as: DE102017209294A1

Abstract

The invention relates to a LiDAR sensor comprising a multibeam light source for emitting light beams; an optical receiving system for collecting incident light beams; a directional filter; and a light detector comprising at least one sensor which is paired with one of the light sources.

Description

description

title

Lidar sensor The invention relates to a LiDAR sensor. In particular, the invention relates to a multi-beam LiDAR sensor.

Background Art A LiDAR sensor includes a light source, a light detector, and a processing device. The light source emits light in a predetermined spatial area where an object can reflect the light toward the detector. The processing device determines a distance between the LiDAR sensor and the object on the basis of a signal propagation time (Time of Flight, TOF) or on the basis of a Frequency Modulated Continuous Wave (FMCW) signal. A single-beam system uses a laser as the light source, a multi-beam system includes a light source that emits multiple laser beams simultaneously. To cover large horizontal detection angles between 150 ° and 360 °, a mechanical laser scanner is generally used in which the propagation direction of the laser beams is changed by means of a movable mirror. In a rotating mirror laser scanner whose maximum detection angle is limited to about 150 °, only a motor-driven deflection mirror rotates. For larger detection ranges up to 360 °, all electro-optical components of the LiDAR sensor are mounted on a motor-driven turntable or rotor.

For imaging an incident laser beam onto the light detector, simple optics with few lenses are typically used, which typically have insufficient imaging property to be focused on the detector beam. side to generate a sufficient figure. In addition, the aperture of such a system is limited technically and due to the image, which is why an aperture of more than about 800 mm ^{2 is} hardly achievable.

An object underlying the present invention is to provide an improved LiDAR sensor. The invention achieves this object by means of the subject matter of the independent claim. Subclaims give preferred embodiments again.

Disclosure of the invention

A LiDAR sensor comprises a multi-beam light source for emitting light rays; a receiving optics for collecting incident light rays; a directional filter; and a light detector having at least one sensor associated with one of the light sources.

Usually, the light detector comprises a plurality of sensors, each sensor being associated with one of the light sources. Preferably, as many sensors as light sources are provided. The association between sensors and light sources can be bijective.

In particular, the receiving optics may have a large aperture in order to also receive a weak reflection of an emitted light beam on an object and to focus it in a focused manner onto the light detector. The aperture can be chosen freely over a wide range and in particular more than about 800 mm ² . As a result, the receiving optics can be designed to be bright, in order to reliably detect even a faint or distant reflection of a light beam. A detection range can thereby be increased. An accuracy of the LiDAR sensor, in particular with regard to its image sharpness or resolution, can be improved.

It is particularly preferred that the receiving optics comprise a reflective element. The reflective element may in particular comprise a mirror system with one or more mirrors, a prism or another element in which a total reflection of light takes place. In particular, the receiving optics may comprise a folded optics in which a light beam is deflected in such a way. is directed that an optical path through the receiving optics is significantly longer than their size.

A reflective receiving optics is usually limited in angle, so it may be poorly suited for a multi-beam LiDAR sensor, especially if this is to be used to cover a relatively large vertical angle range of up to about 8 ° or even more. In connection with the directional filter, however, despite the aberrations of the reflective element, it can be ensured that a light beam associated with a first sensor of the light detector does not fall, or falls only slightly, onto a second sensor which is adjacent to the first sensor. Losses in the light passing through the directional light amount can be compensated in particular by a large aperture of the receiving optics. Thus, an improved image sharpness or resolution can be realized. By a corresponding optical design of the receiving optics, the signal dynamics can be limited. The receiving optics can be realized compactly and with only a few elements. The reflective element can have a low temperature dependence, so that the receiving optics can be improved in terms of temperature stability. In a particularly preferred embodiment, the directional filter is integrated with the reflective element. As a result, a robust receiving optics, for example for use of the LiDAR sensor on a motor vehicle, can be provided. The directional filter may be formed, for example, on or in a prism or a concave mirror element.

In general, the directional filter may comprise a pinhole or a coating of a transparent element. Both variants can be easily integrated with the reflective element. For this purpose, the directional filter can be arranged, in particular when a light beam emerges from a more dense optical medium than air. The pinhole may, for example, comprise a plastic or metal part which carries as many recesses as light beams and sensors are provided. The recesses may be introduced, for example by means of punching. The position of each recess defines the direction of an incident light beam. Light that does not fall from the predetermined direction through the recess does not hit the sensor of the associated one

Light detector. The LiDAR sensor may further include imaging optics arranged to image the plane of the directional filter onto the light detector. In this case, an aperture of the imaging optics may be small, in particular substantially smaller than the aperture of the receiving optics, as a result of which the imaging optics can be realized inexpensively and arranged in a space-saving manner. In a preferred embodiment, the imaging optics have an imaging factor not equal to one. In other words, the imaging optics can be set up with little effort to realize an optical enlargement or reduction. The optics can be improved so adapted to a predetermined light detector, the number and arrangement of light sensors usually can not be changed. This can be a great variety of existing

Light sensors with the optics described can be used to provide an improved Lidarsensor.

It is particularly preferred that the imaging optics comprise a first and a second element, between which light beams can propagate. The division into two parts makes it possible to better control imaging properties of the imaging optics. In particular, the elements may be designed and arranged such that the light beams propagate between them substantially parallel to one another. In the area between the two elements of the imaging optics, an optical filter can then easily be arranged which, for example, keeps unwanted extraneous light away from the light detector. The optical filter may in particular be a narrow-band frequency filter. The interference immunity of the LiDAR sensor can thereby be improved.

Brief description of the figures

The invention will now be described in more detail with reference to the attached figures, in which:

1 shows a multi-beam lidar sensor in a first embodiment; FIG. 2 shows a multi-beam lidar sensor in a second embodiment; FIG. 3 shows a schematic representation of a lidar sensor with an imaging optics; and

4 shows exemplary directional filters for a multi-beam lidar sensor represents.

1 shows a multi-beam LiDAR sensor (or lidar sensor) 100 in a first embodiment. The LiDAR sensor 100 includes a multi-beam

A light source 105 adapted to emit a plurality of coherent light beams 110, a receiving optics 115 for collecting light beams 110 reflected at an object 120 (not shown), a directional filter 125, and a light detector 130 having a plurality of sensors 135 are preferred In addition, a processing device 140 is provided to determine the distance between the LiDAR sensor 100 and the object 120 based on emitted and received light.

The illustrated receiving optical system 1 15 is preferably designed as a folded optic and comprises in the illustrated embodiment one or more mirror elements 145 for collecting and directing the incident light. A folded optics is configured to make the length of an optical path along which light travels through the optics longer than the distance along the optical axis of the optic Typically, the folded optic comprises at least one reflective surface Frequently, the light is reflected multiple times within the optic, being able to cover part of the path through the optic in the opposite direction from the entrance to the exit of the optic, exemplified by a receiving optic 15 having a primary and a secondary mirror element 145 respectively For example, at least one of the mirror elements 145 may be spherical or parabolic, and incident light is reflected at the surface of the primary mirror element 145 and falls back onto the secondary mirror element 145 where it is reflected again. Both mirror elements 145 can bundle the incident light beams or direct the output side to a narrower area than an input area, through which they enter the optics.

In the beam path after the receiving optical system 1 15 is a directional filter 125, which is adapted to selectively forward incident light beams on the basis of their direction of arrival in each case only one of the sensors 135. Light that does not come from a predetermined direction is preferably absorbed or in one further embodiment completely or partially reflected. Preferably as many sensors 135 are provided on the light detector 130 as light beams 1 10 can be emitted simultaneously by the light source 105. The light detector 130 preferably has the same number of light sensors 135. The number of light sensors 135 can also be different from the number of light beams 110, in particular fewer light sensors 135 can be used, which is illuminated successively by means of different light beams 110. The arrangement of the light sensors 135 may correspond to the arrangement of the light rays emerging from the light source 105. This arrangement can be one or two-dimensional. The sensors 135 are usually called photosensitive

Semiconductor formed and can be configured to detect light of a predetermined wavelength range in which the wavelength emitted by the light source wavelength. The directional filter 125 can be used to compensate for an angle-related, relatively large error of the receiving optics 115. By retaining light which does not have a predetermined direction, the portions of the light which are due to an aberration of the receiving optical system 1 15 can be excluded from further processing. The attenuating effect of the directional filter 125 on the incident light can be compensated by selecting an aperture of the receiving optics 115 to be correspondingly large. As a result, it can nevertheless be ensured that sufficient light falls on the light sensors 135 in order to enable reliable detection.

Before the received light from the directional filter 125 falls on the light detector 130, it may pass through imaging optics 150 to enhance focusing of the light beams onto the light detector 130. The imaging optics can be made adjustable. Optionally, the imaging optics are arranged to enlarge or reduce an image of the light beams on the light detector 130. As will be explained in more detail below with reference to FIG. 3, the imaging optics 150 preferably comprises one or more refractive elements, in particular lenses.

Fig. 2 shows a multi-beam LiDAR sensor 100 in a second embodiment. In contrast to the embodiment shown in FIG. 1, hi the optical system 115 is preferably made in one piece. In particular, the optical system 1 15 may be formed in the manner of an inverted telescope and, for example, be made of glass or plastic. In this case, a material having a high refractive index can be used to make the optical system 115 and therefore the entire LiDAR system 100 more compact.

In a further variant, the directional filter 125 can be attached directly to or in the receiving optical system 1 15, integrated with it or designed as one piece with it. For example, the directional filter 125 may be formed as a coating of the material from which the receiving optical system 15 is formed. In a preferred embodiment, as will be described in more detail below with respect to FIG. 4, the directional filter 125 includes a pinhole attached to the receiving optics 115, such as by gluing, vapor deposition, or otherwise.

3 shows a schematic representation of a LiDAR sensor 100 in the manner of FIGS. 1 or 2, with imaging optics 150. The imaging optics 150 comprises at least one refractive element 205, which may be designed in particular as a lens. In the illustrated preferred embodiment, a first refractive element 205 and a second refractive element 210 are provided. The refractive elements 205, 210 are preferably designed and arranged against one another such that incident light beams 110 run substantially parallel to one another between them. It is further preferred that in the space between the refractive elements 205,

210, an optical filter 215 is provided so as to allow as far as possible to pass only light which was originally emitted by the light source 105. For this purpose, the optical filter can be designed in particular as a bandpass filter. The light emitted by the light source 105 ideally has a very narrow wavelength range. Accordingly, the optical filter 215 can be made very narrow-band in order to transmit only light whose wavelength corresponds to the wavelength of the emitted light.

4 shows exemplary directional filters 125 for a multi-beam LiDAR sensor 100. The illustrated directional filters 125 are designed as pinhole diaphragms. An embodiment a is for three light beams, an embodiment b for nine light beams, one embodiment c for sixteen light beams, and one embodiment d for twenty-five light beams. The directional filter 125 each includes an opaque material 405, such as a metal sheet, in which as many recesses 410 are provided as rays to be transmitted through the directional filter 125. A position of each recess

410 corresponds to a direction from which light may fall through the directional filter 125. Light incident on the material 405 from another direction is absorbed or reflected thereby.

Claims

claims

Lidar sensor (100) comprising:

- A multi-beam light source (105) for emitting light beams (1 10);

- Receiving optics (115) for collecting incident light beams (110);

a directional filter (125); and

- A light detector (130) with at least one sensor associated with one of the light sources (105).

The lidar sensor (100) of claim 1, wherein the receiving optic (115) comprises a reflective element.

The lidar sensor (100) of claim 2, wherein the directional filter (125) is integral with the reflective element.

The lidar sensor (100) of any one of the preceding claims, wherein the directional filter (125) comprises a pinhole.

The lidar sensor (100) of any one of the preceding claims, further comprising imaging optics (150) arranged to image the plane of the directional filter (125) onto the light detector (130).

The lidar sensor (100) of claim 5, wherein the imaging optics (150) has a non-unity imaging factor.

A lidar sensor (100) according to claim 5 or 6, wherein the imaging optics (150) comprises a first (205) and a second element (210) between which light rays (110) can propagate.

8. Lidarsensor (100) according to claim 7, wherein the light beams (1 10) between the two elements (205, 210) substantially parallel to each other propagate and in this area an optical filter (215) is arranged.