WO2020065015A1

WO2020065015A1 - Lidar measurement system and method for a lidar measurement system

Info

Publication number: WO2020065015A1
Application number: PCT/EP2019/076194
Authority: WO
Inventors: Günther Scharnagel
Original assignee: Zf Friedrichshafen Ag; Ibeo Automotive Systems GmbH
Priority date: 2018-09-28
Filing date: 2019-09-27
Publication date: 2020-04-02
Also published as: DE102018216705A1

Abstract

The present invention relates to a LIDAR measurement system comprising a LIDAR sensor with an adjustable angle of view. The LIDAR measurement system comprises, furthermore, a stationary element to which a code which provides information about the angle of view of the LIDAR sensor is applied so that reflections of light emitted by the LIDAR sensor at the code are received by a receiving unit of the LIDAR sensor. The LIDAR measurement system comprises, in addition, an evaluation element which is designed to determine the angle of view of the LIDAR sensor based on information, provided by the LIDAR sensor, about the received reflections.

Description

LIDAR measuring system and method for a LIDAR measuring system

The present invention relates to LIDAR (Light Detection And Ran ging) measuring systems for detecting the environment, e.g. of a vehicle. The invention further relates to a method for a LIDAR measuring system.

A LIDAR measuring system can have one or more LIDAR sensors. Each LIDAR sensor preferably comprises a LIDAR transmitter unit and a LIDAR receiver unit.

A LIDAR sensor resolves a spatial area with a predetermined resolution at a given viewing angle. In order to recognize small objects even at large distances (for example a tire with a height of approx. 20 cm at a distance of 100 m), a higher resolution of the LIDAR image is sometimes required. The same LIDAR sensor can be used for this if its viewing angle is reduced by appropriate optics and thus its resolution is increased with the same number of pixels. So that the LIDAR sensor can cover the same image area with a narrowed viewing angle as before, the viewing angle of the LIDAR sensor is deflected (i.e. varies). This can be done, for example, by tilting the sensor (e.g. by ± 5 °) or by tilting a mirror or prism (e.g. by ± 10 °).

To derive the reaction of a system processing the LIDAR measurements (e.g. a vehicle), the viewing angle of the LIDAR sensor, i.e. the angle of the tilt can be sensed very precisely (e.g. with an accuracy of ± 0.05 °). A rotation angle sensor is usually used for sensing.

The high safety requirements for the LIDAR sensors also apply to the rotation angle sensor. To monitor the LIDAR sensor, therefore, a rotation angle sensor with high accuracy must be used. Rotation angle sensors that offer the required accuracy are hardly available on the market or are very expensive. For the calibration of a stereo camera system in a vehicle, the publication DE 10 2017 005 056 A1 suggests arranging a hologram on the windshield in the field of view of the two camera units in order to calibrate the stereo camera system with the aid of the hologram. In contrast to optical cameras, LIDAR sensors do not deliver optical images in the classic sense. Rather, a LIDAR sensor provides information such as a distance, a speed or an elevation angle relative to an object illuminated by the LIDAR sensor. In addition, the method proposed in the publication DE 10 2017 005 056 A1 relates only to the calibration of two cameras relative to one another. The absolute orientation of a camera cannot be determined using this method.

Against this background, it is an object of the present invention to provide an improved and more cost-effective way of determining the viewing angle of a LIDAR sensor.

The object of the invention is achieved by a LIDAR measuring system and a method for a LIDAR measuring system according to the independent claims. Further aspects and developments of the invention are described in the dependent claims, the following description and in the figures.

According to a first aspect, the invention relates to a LIDAR measuring system comprising at least one LIDAR sensor with an adjustable viewing angle. For example, the entire LIDAR sensor can be tilted about a tilt axis in order to adjust the viewing angle of the LIDAR sensor depending on a tilt of the LIDAR sensor. Likewise, the LIDAR sensor can comprise an optical element (for example a mirror or a prism) which can be tilted about a tilt axis in order to set a viewing angle of the LIDAR sensor depending on a tilt of the optical element. In other words: By adjusting the tilt angle of the LIDAR sensor or the optical element in relation to the respective tilt axis, the viewing angle of the LIDAR sensor can be changed. Accordingly, the LIDAR sensor can scan different areas of the room. In addition, the LIDAR measuring system comprises a stationary element, to which a coding is applied, which describes information about the viewing angle of the LIDAR sensor, so that reflections of a light emitted by the LIDAR sensor are received at the coding by the receiving unit. The coding on the stationary element can be understood as a reference which is scanned by the LIDAR sensor in order to code information about the viewing angle of the LIDAR sensor in the information provided by the LIDAR sensor. The coding can be, for example, a bar code, a point code, or some other code that describes one or more possible viewing angles of the LIDAR sensor. For evaluation, the LIDAR measuring system includes an evaluation element which is set up to determine the viewing angle of the LIDAR sensor based on information provided by the LIDAR sensor about the received reflections.

For example, the code can consist of several points arranged along a spatial direction, the viewing angle of the LIDAR sensor being changeable along this spatial direction. The distance between two directly successive points is chosen differently in order to characterize the different possible viewing angles of the LIDAR sensor. The light emitted by the LIDAR sensor is reflected back from the points within the current viewing angle of the LIDAR sensor to the receiving unit, so that information about the characteristic reflections is contained in the output information provided by the LIDAR sensor. The evaluation element can now recognize or detect the information about the characteristic reflections in the output information provided by the LIDAR sensor and infer the current viewing angle of the LIDAR sensor. It goes without saying that the preceding coding example is chosen purely by way of example to explain the concept according to the invention and that any other coding (e.g. bar code, text code etc.) can be used to display the viewing angle information.

The scanning of a reference code according to the invention can thus determine the viewing angle of a LIDAR sensor without the use of a rotation angle. enable kelsensors. In other words: The solution according to the invention can make it possible to save the rotation angle sensor. The evaluation element can, for example, be a programmable hardware component already present in the LIDAR measuring system, such as a processor, a processor core, an application-specific integrated circuit (ASIC = Application-Specific Integrated Circuit) or an integrated circuit (IC = Integrated) Circuit) on which software for the control of the LIDAR measuring system runs. Accordingly, the determination of the viewing angle of the LIDAR sensor can be integrated into the existing software with only one effort. No additional hardware is then required. In addition to the simplified structure of the LIDAR measuring system, this also results in a cost advantage.

Depending on the type of part of the LIDAR measuring system that can be tilted to adjust the viewing direction, the stationary element can e.g. be stationary relative to the entire LIDAR sensor or the optical element.

According to some embodiments, the stationary element can e.g. be a front window of the LIDAR measuring system. The front screen of the LIDAR measuring system is fixed in relation to the tiltable parts of the LIDAR measuring system and is therefore a simple and inexpensive way to provide the coding. For example, the coding can be steamed onto the windscreen of the LIDAR measuring system.

Alternatively, the fixed element can e.g. be permanently connected to a vehicle in which the LIDAR measuring system is installed. In other words, an (at least partially transparent) additional part can be provided in the vehicle in order to provide the reference for determining the viewing angle by means of the coding.

In a further aspect, the present invention also relates to a method for a LIDAR measuring system comprising a LIDAR sensor with an adjustable viewing angle. The method comprises receiving by the receiving unit of the LIDAR sensor of reflections of a light emitted by the LIDAR sensor at a coding which is applied to a stationary element and which describes information about the perspective of the LIDAR sensor. Furthermore, the method comprises determining the viewing angle of the LIDAR sensor based on information provided by the LIDAR sensor about the received reflections.

As already described above in connection with the LIDAR measuring system according to the invention, the method according to the invention can also enable an improved and more cost-effective determination of the viewing angle of a LIDAR sensor.

Possible further refinements of the method are described above in connection with the LIDAR measuring system according to the invention.

Exemplary embodiments of the present invention are explained in more detail below, with reference to the attached figures. Show it:

1 schematically shows an embodiment of a LIDAR measuring system;

FIG. 2 schematically shows a section through the LIDAR sensor shown in FIG. 1;

FIG. 3 shows schematically different viewing angles of the LIDAR measuring system shown in FIG. 1;

Fig. 4 exemplary encodings; and

5 schematically shows an embodiment of a further LIDAR measuring system.

1 shows a LIDAR measuring system 100 with a first LIDAR sensor 110 and a second LIDAR sensor 120, which are arranged in a housing 140 of the LIDAR measuring system 100. A sectional view of the first LIDAR sensor 110 is shown in FIG. 2. The second LIDAR sensor 120 can be configured like the first LIDAR sensor 110. The basic structure of the LIDAR measuring system 100 is in accordance with the statements relating to the prior art (WO 2017/081294 A1). The second LIDAR sensor 120 is immobile, ie its viewing angle is fixed. The second LIDAR sensor 120 comprises a LI DAR transmission unit and a LIDAR reception unit.

The first LIDAR sensor 110 comprises a LIDAR transmission unit and a LIDAR reception unit. Together with the LIDAR transmission unit, the reception optics 1 13, the transmission optics 114 and a mirror 116 that can be tilted about a tilt axis 1 15, the LIDAR reception unit 1 12 forms a movable LIDAR unit with a viewing angle that can be changed by tilting the mirror 1 16.

The LIDAR receiving unit and / or the LIDAR transmitting unit are advantageously designed in a focal plane array configuration, as indicated in FIG. 2. The elements of the respective unit are essentially arranged in one plane, more favorably on a chip. The respective unit is arranged on the LIDAR sensor 110, preferably in a focal point of a corresponding optical system - transmitting optical system 114 or receiving optical system 113. In particular, the sensor elements 11 1 and the emitter elements 1 12 are arranged in the focal point of the receiving optics 1 13 and the sensor de optics 1 14. Such optics can be formed, for example, by an optical lens system.

The LIDAR receiver unit has a plurality of sensor elements 1 1 1, which are preferably designed as SPAD, single photon avalanche diode. The LIDAR transmitter unit has several emitter elements 1 12 for sending e.g. Laser light, conveniently laser pulses. The emitter elements 112 are advantageously designed as VCSELs, vertical cavity surface emitting lasers.

The transmitter unit has emitter elements 1 12 which are distributed over an area of the sensor chip. The receiving unit has sensor elements 11, which are distributed over an area of the receiving chip. A transmission optics 1 14 is assigned to the transmission chip and the reception optics 1 13 is assigned to the reception chip. The optics represent a light arriving from a room area on the respective chip. The spatial area corresponds to the viewing area of the measuring system 100, which is examined or sensed for objects. The spatial area of the transmitting unit and the receiving unit are essentially identical. The transmission optics 1 14 images an emitter element 1 12 to a solid angle, which represents a partial area of the spatial area. The emitter element 1 12 accordingly emits laser light into this solid angle. The emitter elements 1 12 together cover the entire room area.

The receiving optics 1 13 images a sensor element 1 1 1 to a solid angle, which represents a partial area of the spatial area. The number of all sensor elements 1 1 1 covers the entire room area. Emitter elements 1 12 and sensor elements 1 1 1, which consider the same solid angle, map to one another and are assigned to one another accordingly. A laser light from an emitter element 1 12 normally maps onto the associated sensor element 1 1 1. If necessary, a plurality of sensor elements 1 1 1 are arranged within the solid angle of an emitter element 1 12.

To determine objects within the spatial area, the measuring system 100 carries out a measuring process. Such a measuring process comprises one or more measuring cycles, depending on the design of the measuring system 100 and its electronics.

The Time Correlated Single Photon Counting method, TCSPC, is preferably used. Here, individual incoming photons are detected, in particular by SPAD, and the time at which sensor element 1 1 1 is triggered, including the time of detection, is stored in a memory element. The time of detection is related to a reference time at which the laser light is emitted. The transit time of the laser light can be determined from the difference, from which the distance of the object can be determined.

A sensor element 1 1 1 can be triggered on the one hand by the laser light and on the other hand by the ambient radiation. A laser light always arrives at the same time at a certain distance from the object, whereas the ambient radiation always provides the same probability of a sensor element 1 1 1 being designed. to solve. If a measurement is carried out several times, in particular several measurement cycles, the triggering of the sensor element at the time of detection that corresponds to the duration of the laser light with respect to the distance of the object add up, whereas the triggering by the ambient radiation is distributed uniformly over the measuring duration of a measuring cycle . A measurement corresponds to the emission and subsequent detection of the laser light. The data of the individual measurement cycles of a measurement process stored in the memory element enable the multiple times of detection to be evaluated in order to infer the distance of the object.

A sensor element 1 1 1 is advantageously connected to a time to digital converter, TDC, which stores the point in time at which the sensor unit is triggered in the memory element. Such a memory element can be designed, for example, as a short-term memory or as a long-term memory. For a measurement process, the TDC fills a storage element with the times at which the sensor elements 1 1 1 detected an incoming photon. This can be graphically represented by a histogram, which is based on the data of the storage element. In the case of a histogram, the duration of a measurement cycle is divided into short periods of time, so-called bins. If a sensor element 1 1 1 is triggered, the TDC increases the value of a bin by one. The bin that corresponds to the transit time of the laser pulse, that is the difference between the detection time and the reference time, is filled.

A side view of part of the LIDAR measurement system 100 is shown in FIG. 3. From Fig. 3 it can be seen that for different tilt angles (eg 40 °, 45 ° or 50 °) of the mirror 1 16 with respect to the tilt axis 1 15 different spatial areas in the environment of the LIDAR measuring system 100 by the first LIDAR sensor 1 10 can be sensed on objects. In other words: The viewing angle of the first LIDAR sensor 1 10 is determined by the tilting of the mirror 1 16 based on the tilt axis 115.

The coding, which is scanned by the first LIDAR sensor 110, is applied to the front pane 150 in order to then use the evaluation element 130 to look at the viewing angle from the measurement data of the first LIDAR sensor 110 of the first LIDAR sensor 1 10 to close. From the determined viewing angle of the first LIDAR sensor 1 10, the tilt angle of the mirror 1 16 based on the tilt axis can then also be determined (calculated).

FIG. 4 shows an example of a room area 400 to be covered by the first LIDAR sensor 110. In order to be able to cover the entire space 400, the mirror 116 is tilted about the tilt axis 115. The current Blickwin angle 410 of the first LIDAR sensor 1 10 then always covers an adjustable part of the entire area 400 to be covered. In order to be able to determine the viewing angle of the first LIDAR sensor 110, for example, an element with a coding 420 can be provided at the edge of the resolved spatial area, so that the coding 420 is reliably scanned by the first LIDAR sensor 420. As already indicated above, the specific implementation of the coding 420 can be done in a variety of ways. In addition to bar codes, text codes or other graphic codes, e.g. a point code 430 can be used, as shown in the right part of FIG. 4 next to the area 400 to be covered.

The point code 430 has a plurality of points which follow one another along a spatial direction. The viewing angle of the first LIDAR sensor 110 can be changed along this spatial direction. In the example shown in FIG. 4, the points are arranged along the vertical, since the viewing angle of the first LIDAR sensor 110 is variable in the vertical direction. In other embodiments, the points can e.g. also be arranged along the horizontal and the viewing angle of the first LIDAR sensor 110 can be varied in the horizontal direction. Detection of the viewing direction is therefore possible vertically and horizontally.

The distance between directly successive points varies so that the viewing angle can be determined by scanning two of the points. For example, a first pair of points may have a distance x from one another that is smaller by a value y in each subsequent pair. The initial distance x should be selected so that at least two points are in the field of view of the first LIDAR sensor 1 10. The value y should be chosen so that y can be resolved safely, ie the LIDAR sensor 110 has a better resolution than y.

Based on the received reflections of the light emitted by the first LIDAR sensor 110 at the point code 430 (and further received reflections of the light on other objects in the field of view of the first LIDAR sensor 110), the first LIDAR sensor can e.g. create a distance map. The extremely short distance of the points of the point code 430 is characteristic of the coding of the viewing angle. From the distances of these characteristic distances in the distance map, the evaluation element can conclude the viewing angle of the first LI DAR sensor 110, since each viewing angle is coded with a certain distance between the points.

Instead of the mirror 116, the entire LIDAR sensor can alternatively also be tilted about a tilt axis, as shown in FIG. 5. FIG. 5 shows a further LIDAR measuring system 500. The LIDAR sensor 510 in turn comprises a transmitting unit, a receiving unit, a receiving optics 513 and a transmitting optics 514, only the receiving optics 513 and the transmitting optics 514 due to the illustration selected in FIG. 5 are indicated. The transmitting unit as well as the receiving unit are arranged inside the housing of the LIDAR sensor 510 shown in FIG. 5 behind the respective optics (as shown in FIG. 2).

The LIDAR sensor 510 is held on a holder 520 and is the

Tilt axis 515 can be tilted in order to set the viewing angle of the LIDAR sensor 515 depending on a tilt of the LIDAR sensor 510 with respect to the tilt axis 515.

On a mirror for adjusting the viewing angle of the LIDAR sensor, as shown in Figs. 1 and 3, the embodiment of FIG. 5 can be dispensed with due to the tiltability of the LIDAR sensor 510. By means of the scanning of the coding according to the invention on the stationary element 550, the viewing angle of the LIDAR sensor 510 can again be inferred directly. Out For the sake of clarity, the evaluation element which determines the viewing angle of the LIDAR sensor 510 is not shown.

Reference LI DAR measuring system

first LI DAR sensor

Sensor element

Emitter element

Receiving optics

Transmission optics

Tilt axis

mirror

second LI DAR sensor

Evaluation element

casing

Windscreen

Room area to be covered

current perspective

Coding

Point coding

LI DAR measuring system

LIDAR sensor

Receiving optics

Transmission optics

Tilt axis

bracket

stationary element

Claims

1. LIDAR measuring system (100, 500) comprising a LIDAR sensor (1 10, 510) with an adjustable viewing angle,

characterized in that:

the LIDAR measuring system (100, 500) further comprises a stationary element (150, 550), onto which a coding (420) is applied, which describes information about the viewing angle of the LIDAR sensor (1 10, 510), so that from a receiving unit of the LIDAR sensor (1 10, 510) reflections of a light emitted by the LIDAR sensor (1 10, 510) are received at the coding; and

the LIDAR measuring system (100, 500) further comprises an evaluation element (130), which is set up to adjust the viewing angle of the LIDAR sensor (1 10, 510) based on information provided by the LIDAR sensor (1 10, 510) to determine received reflections.

2. LIDAR measuring system according to claim 1, characterized in that the stationary element (150, 550) is a front window of the LIDAR measuring system (100, 500).

3. LIDAR measuring system according to claim 1, characterized in that the stationary element (150, 550) is firmly connected to a vehicle in which the LIDAR measuring system (100, 500) is installed.

4. LIDAR measuring system according to one of claims 1 to 3, characterized in that the LIDAR measuring system (100) further comprises an optical element (1 16) which can be tilted about a tilt axis (1 15) in order to depend on a tilt of the optical element (1 16) adjust the viewing angle of the LIDAR sensor (1 10).

5. LIDAR measuring system according to one of claims 1 to 3, characterized in that the LIDAR sensor (510) can be tilted about a tilt axis (515) in order to depend on a tilt of the LIDAR sensor (510) the viewing angle of the LIDAR Sensor (510).

6. Method for a LIDAR measuring system (100) comprising a LIDAR sensor (1 10) with an adjustable viewing angle, characterized by:

Receiving by a receiving unit (1 1 1) of the LIDAR sensor (1 10) of refle xions of a light emitted by the LIDAR sensor (1 10) at a coding (320), which is applied to a stationary element and information about describes the viewing angle of the LIDAR sensor (1 10); and

Determining the viewing angle of the LIDAR sensor (1 10) based on information provided by the LI DAR sensor (1 10) about the received reflections.

7. The method according to claim 6, characterized in that the fixed element (150, 550) is a front window of the LIDAR measuring system (100, 500).

8. The method according to claim 6, characterized in that the fixed element (150, 550) is fixedly connected to a vehicle in which the LIDAR measuring system (100, 500) is installed.

9. The method according to any one of claims 6 to 8, characterized in that the LIDAR measuring system (100) further comprises an optical element (1 16) which can be tilted about a tilt axis (1 15) in order to depend on a tilt of the optical element ( 1 16) adjust the viewing angle of the LIDAR sensor (1 10).

10. The method according to any one of claims 6 to 8, characterized in that the LIDAR sensor (510) can be tilted about a tilt axis (515) in order to, depending on a tilt of the LIDAR sensor (510), the viewing angle of the LIDAR sensor ( 510) to be set.