DE102021202234A1 - LiDAR system for determining the distance of objects - Google Patents

Abstract

A LiDAR system (10) for determining the distance of objects is described, comprising a transmitter module (15) for emitting a light beam, a receiver module (16) for receiving a light beam and a mirror (12) rotatable about an axis of rotation (19), wherein the LiDAR system (10) further comprises a photodiode (14) which is rotatable about the axis of rotation (19).

Description

The present invention is based on a LiDAR system according to the independent patent claim.

State of the art

Highly and fully automated vehicles (level 3-5) will be found more and more on our roads in the next few years. There are various concepts of how such an automated vehicle can be implemented. All of these approaches require a wide variety of sensors (e.g. video cameras, LiDAR, radar, ultrasonic sensors), with LiDAR sensors in particular playing an increasingly important role - optical sensors that use laser light to generate 3D point clouds of the environment.

One type of LiDAR sensors are rotating mirror LiDAR sensors. The transmitter and receiver modules are permanently installed on the stator and the laser light is deflected in different spatial directions by a rotating mirror. The mirror rotation covers one spatial direction, while the second scanning direction is covered by attaching multiple laser sources or by using a line flash and multiple detectors in the receiving module.

The precise measuring directions of the laser radiation depend on the rotor position and are determined in a calibration step during the manufacture of the LiDAR sensor (angle calibration). During normal operation, the current rotor angle is determined by an encoder. However, the determination of the angle of the rotating mirror can become incorrect over time. In such cases, a recalibration or a reset of the angles becomes necessary. It can be of high safety relevance that the automated vehicle automatically recognizes such a miscalibration situation and accordingly requests a recalibration. However, a workshop visit for a recalibration is expensive. It would therefore be desirable to develop a method to automatically recalibrate LiDAR sensors on the road (also called online calibration).

The pamphlet DE 69836766 T2 describes laser scanner systems for imaging three-dimensional features of objects in a scene. A horizontal position in an image is adjusted using an optical encoder that accurately measures the angle through which a first rotating mirror has rotated. The greater the number of counts for a given rotation, the smaller the spacing between measured points at a given distance.

The pamphlet EP 3171201 B1 describes an optoelectronic distance meter and in particular a laser distance meter, as well as a distance measuring method. In particular due to a temperature dependency of an emission power of laser diodes, a driver stage can contain a control circuit for maintaining a desired optical transmission power, which is monitored with a monitor photodiode, for example. The laser driver stage or its control can also be designed to comply with safety requirements, such as eye safety guidelines.

Disclosure of Invention

Advantages of the Invention

A LiDAR system with the characterizing features of the independent patent claim is disclosed.

The LiDAR system includes a transmitter module for emitting a light beam, a receiving module for receiving a light beam and a mirror that can be rotated about an axis of rotation, the LiDAR system also including a photodiode that can be rotated about the axis of rotation. This is advantageous in order to be able to use the photodiode to monitor and calibrate the LiDAR system for correct angles even during operation.

Further advantageous embodiments of the present invention are the subject matter of the dependent claims.

The LiDAR system expediently comprises a further rotatable mirror, with the photodiode being arranged between the mirrors. This is advantageous in order to achieve a compact design of the LiDAR system.

The two mirrors are expediently arranged in parallel. This is advantageous in order to be able to cover a large angular range. Another advantage is that parallel mirrors ensure a constant time difference between consecutive frames (e.g. 100ms each). If the mirrors were arranged at an angle to each other, the time differences would be different (e.g. 90ms and 110ms).

The LiDAR system is expediently set up to determine an angular position of the rotatable mirror using the photodiode. This is advantageous for obtaining a compact LiDAR system in which the LiDAR system integrally performs angle calibration.

The LiDAR system is expediently set up to carry out an angular calibration of the rotatable mirror using the determined angular position of the rotatable mirror. This is advantageous because the LiDAR system can thus be automatically calibrated during operation with regard to the angle of rotation.

The LiDAR system is expediently set up to detect a defect in the LiDAR system when angle calibrations are repeated within a predefined period of time. This is advantageous for detecting a defective LiDAR system in good time and, if necessary, for repairing or replacing it.

The LiDAR system is expediently set up to use the photodiode to determine the light output of the light beam emitted by the transmission module and to reduce the light output if a predefined light output limit value is exceeded. This is beneficial to ensure eye safety when using the LiDAR system.

Conveniently, an attenuating optical filter is placed in front of the photodiode to attenuate an intensity of light incident on the photodiode. This is advantageous in order to avoid saturation of the photodiode and thus increase the operational readiness of the LiDAR system.

character list

Advantageous embodiments of the invention are shown in the figures and explained in more detail in the following description.

• 1 eine schematische Darstellung der Draufsicht eines erfindungsgemäßen LiDAR-Systems gemäß einer ersten Ausführungsform;
• 2 eine schematische Darstellung einer Seitenansicht des erfindungsgemäßen LiDAR-Systems gemäß der ersten Ausführungsform; und
• 3 eine schematische Darstellung einer Seitenansicht eine erfindungsgemäßen LiDAR-Systems gemäß einer zweiten Ausführungsform.

Show it:

• 1 a schematic representation of the plan view of an inventive LiDAR system according to a first embodiment;
• 2 a schematic representation of a side view of the LiDAR system according to the invention according to the first embodiment; and
• 3 a schematic representation of a side view of an inventive LiDAR system according to a second embodiment.

Embodiments of the invention

The same reference symbols designate the same device components or the same method steps in all figures.

1 shows a schematic representation of the plan view of an inventive LiDAR system 10 according to a first embodiment. The LiDAR system 10 has a transmitter module 15 for emitting a light beam and a receiver module 16 for receiving a light beam. Furthermore, the LiDAR system 10 comprises a housing 18 in which a mirror 12 rotatable about an axis of rotation 19 is arranged.

Furthermore, the LiDAR system 10 has a photodiode 14 which is arranged such that it can rotate about the axis of rotation 19 . Furthermore, the LiDAR system 10 has a further rotatable mirror 13 which can also be rotated about the axis of rotation 19 . The photodiode 14 is arranged between the mirrors 12, 13.

The mirrors 12, 13 are preferably arranged parallel to one another. As soon as the transmission module 15 emits a corresponding light beam, it is reflected by one of the mirrors 12, 13 and directed outwards from the housing 18 through a correspondingly transmissive optical window 17. A light beam reflected by an object enters the housing 18 through the optical window 17 and is directed through one of the mirrors 12, 13 onto a receiving module 16, where it is registered accordingly.

At the in 1 In the angular position shown, the photodiode 14 can be used in order to carry out an angular calibration of the rotatable mirror 12 and/or of the further rotatable mirror 13. For example, the in 1 The angle calibration shown can always be identified with a 0° angle position. If there are deviations in different measurements of this angular position, these deviations can be used for the angle calibration, for example by subtracting a corresponding angle offset from the angle determined by an angle encoder.

2 shows a schematic representation of a side view of the LiDAR system 10 according to the invention according to the first embodiment. In this case, the transmission module 15 is arranged above the reception module 16 . Furthermore, it can be seen that the photodiode 14 is arranged at the height of the transmission module 15 in order to be able to optimally register an emitted light beam.

3 shows a schematic representation of a side view of an inventive LiDAR system according to a second embodiment. The in 2 elements described are present. In addition, an attenuating optical filter 20 is arranged in front of the photodiode 14 . Due to the spatial proximity of the photodiode 14 to the transmission module 15, a high-intensity light beam that impinges on the photodiode 14 can be expected. The filter 20 thus serves to prevent the photodiode 14 from being saturated.

In all of the described embodiments, the pot diode 14 can also be used to determine the light output of the light beam emitted by the transmission module 15 . For this purpose, the LiDAR system 14 can be set up to reduce the light output of the light beam emitted by the transmission module 15 when a predefined light output limit value is exceeded in order in particular to comply with prescribed limit values and to ensure the eye safety of a human observer.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 69836766 T2 [0005]
• EP 3171201 B1 [0006]

Claims (8)

LiDAR system (10) for determining the distance of objects, comprising a transmitter module (15) for emitting a light beam, a receiver module (16) for receiving a light beam and a mirror (12) rotatable about an axis of rotation (19), characterized in that the LiDAR system (10) further comprises a photodiode (14) which is rotatable about the axis of rotation (19). LiDAR system (10) according to claim 1 , further comprising a further rotatable mirror (13), wherein the photodiode (14) is arranged between the mirrors (12, 13). LiDAR system (10) according to the preceding claim, wherein the two mirrors (12, 13) are arranged in parallel. LiDAR system (10) according to one of the preceding claims, wherein the LiDAR system (10) is set up to determine an angular position of the rotatable mirror (12, 13) by means of the photodiode (14). Lidar system (10) according to the preceding claim, wherein the LiDAR system (10) is set up to carry out an angular calibration of the rotatable mirror (12, 13) using the determined angular position of the rotatable mirror (12, 13). LiDAR system (10) according to the preceding claim, wherein the LiDAR system (10) is set up to detect a defect in the LiDAR system (10) during repeated angle calibrations within a predefined period of time. LiDAR system (10) according to one of the preceding claims, wherein the LiDAR system (10) is set up to use the photodiode (14) to determine the light output of the light beam emitted by the transmitter module (15) and to increase the light output when a predefined light output limit value is exceeded to reduce. A LiDAR system (10) according to any one of the preceding claims, wherein an attenuating optical filter (20) is placed in front of the photodiode (14) to attenuate an intensity of light incident on the photodiode (14).

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