DE102022211841A1 - Procedure for operating a lidar system - Google Patents

Abstract

A method for operating a lidar system is described, wherein the lidar system has a plurality of lasers that can be individually controlled and emit laser light at different solid angles, and a plurality of detectors for detecting laser light. The method comprises the steps: a) activating all detectors; b) first emitting laser light by at least two lasers, each with a predefined power, at different solid angles; c) detecting reflected laser light by at least two detectors; d) comparing the detected laser light intensity with a predefined intensity threshold; e) second emitting laser light by at least one laser, wherein at least the laser whose associated detector has an intensity level above the intensity threshold is deactivated beforehand. Furthermore, a corresponding lidar system, computer program and machine-readable storage medium are described.

Description

The present invention is based on a method for operating a lidar system.

State of the art

Highly and fully automated vehicles (levels 3-5) will be increasingly found on our roads in the coming years. LiDAR systems in particular are playing an increasingly important role for autonomous driving systems.

The high point rates required by LiDAR systems make it necessary to measure several measuring points at the same time - this is called parallelization of the measurements. For example, the scene to be measured can be illuminated with a vertical laser strip and mapped onto a vertical detector array in the reception path, so that each detector pixel covers a measuring point in space. Such parallelization greatly shortens the measurement time, since a complete column of points is measured simultaneously. However, the LiDAR system is also more susceptible to crosstalk of the optical signal within a column (also known as blooming). This crosstalk is particularly strong for highly reflective targets, such as retroreflective targets (e.g. traffic signs), which can also trigger other measuring points in the column. In such a case, the object to be measured appears greatly enlarged in the point cloud and can even cover the entire vertical field of view. In this case, the LiDAR system would be blind in certain areas (e.g. under a retroreflective sign bridge). Therefore, it is necessary to develop LiDAR architectures that enable a high degree of parallelization while preventing blooming.

Disclosure of the invention

Advantages of the invention

A method for operating a lidar system with the features of the independent patent claim is disclosed.

The lidar system comprises several lasers that can be individually controlled and emit laser light at different solid angles, as well as several detectors for detecting laser light.

The procedure involves activating all detectors to detect laser light.

Laser light is first emitted by at least two lasers, each with a predefined power, in different solid angles.

The reflected laser light is then detected by at least two detectors. The laser light can be reflected by objects that are present in the area of the lidar system and reflect the laser light.

The detected laser light intensity is compared with a predefined intensity threshold to identify particularly highly reflective objects.

Then a second emission of laser light is carried out by at least one laser, whereby at least the laser whose associated detector has an intensity level above the intensity threshold is now deactivated. This can also mean that all lasers will emit in this step if no highly reflective objects were detected.

This is advantageous because it reduces the so-called "blooming effect", a crosstalk of the optical signal between the detectors or detector pixels. At the same time, the sensor advantageously retains the full range in all other detector pixels. Furthermore, the dynamic range of the detector is increased by this method because the brightness of the retroreflector can be determined precisely. Furthermore, the horizontal resolution is only reduced in the areas of the lidar system that make this necessary due to a highly reflective object.

Further advantageous embodiments of the present invention are the subject of the subclaims.

It is advisable to generate a data point cloud from intensity values of detectors whose assigned lasers are activated. This is advantageous because blooming effects in the data point cloud are also only taken into account to a lesser extent and downstream functions are therefore little or not at all influenced by them.

First intensity values that exceed the predefined intensity threshold are expediently classified as belonging to a highly reflective object. A first distance to the lidar system is determined for each of the classified intensity values. Furthermore, a second distance to the lidar system is determined for each of the second intensity values. In this case, second intensity values whose associated distance is in the range of the first distance up to a predefined distance are not taken into account when generating the data point cloud. det and whose laser assigned via the detector is different from the corresponding laser of the first intensity values. This is advantageous because it removes the crosstalk or blooming while preserving the highly reflective object in the data point cloud.

It is advisable to reactivate at least one deactivated laser after the second emission. This is advantageous because the horizontal resolution is retained as best as possible.

The lasers are expediently designed as a two-column laser array and the detectors as a two-column detector array, whereby, if the lasers were deactivated, the second column of the laser array is activated to emit laser light and the second column of the detector array is activated to detect laser light. This is advantageous because it closes gaps in the scanned field of view and thus enables gapless scanning of the field of view.

The invention further relates to a lidar system which comprises several lasers which can be individually controlled and can emit laser light at different solid angles. The system also has several detectors for detecting laser light and an electronic control unit which is set up to carry out all steps of the method according to the invention. This is advantageous because it achieves the advantages of the method described above.

The lasers expediently have at least one control unit and the detectors have at least one readout unit. The control unit and the readout unit are set up so that the comparison of the laser light intensity takes place on the readout unit and the readout unit directly controls the control unit to deactivate lasers and emit laser light. This is advantageous because it enables rapid control of the lasers by directly evaluating the laser light intensity and directly controlling the lasers.

The spatial laser detector calibration is conveniently stored directly on the readout unit. This is advantageous because the spatial laser detector assignment is stored directly on the readout unit and thus rapid control of the corresponding lasers is possible.

The lasers are expediently designed as a single-column laser array and the detectors as a single-column detector array. This is advantageous because it enables cost-effective implementation.

It is practical for the laser array to have two columns and the detector array to have two columns. This is advantageous because it closes gaps in the scanned field of view and thus enables the field of view to be scanned without gaps.

Short description of the drawings

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

• 1 ein Flussdiagramm des erfindungsgemäßen Verfahrens gemäß einer Ausführungsform;
• 2 eine erste schematische Darstellung der Ausführung des erfindungsgemäßen Verfahrens gemäß einer ersten Ausführungsform;
• 3 eine zweite schematische Darstellung der Ausführung des erfindungsgemäßen Verfahrens gemäß der ersten Ausführungsform;
• 4 eine dritte schematische Darstellung der Ausführung des erfindungsgemäßen Verfahrens gemäß einer zweiten Ausführungsform;
• 5 eine schematische Darstellung des erfindungsgemäßen LiDAR-Systems gemäß einer Ausführungsform.

Show it:

• 1 a flow chart of the method according to the invention according to one embodiment;
• 2 a first schematic representation of the execution of the method according to the invention according to a first embodiment;
• 3 a second schematic representation of the execution of the method according to the invention according to the first embodiment;
• 4 a third schematic representation of the execution of the method according to the invention according to a second embodiment;
• 5 a schematic representation of the LiDAR system according to the invention according to an embodiment.

Embodiments of the invention

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

1 shows a flow chart of the method according to the invention for operating a LiDAR system according to an embodiment. The LiDAR system comprises several lasers that can be individually controlled and emit laser light at different solid angles. The LiDAR system also comprises several detectors for detecting laser light.

In a first step S11, all detectors are activated. In a second step S12, laser light is first emitted by at least two lasers, each with a predefined laser power, in different solid angles.

In a third step S13, reflected laser light is detected by at least two detectors.

Subsequently, in a fourth step S14, the detected laser light intensity is compared with a predefined intensity threshold value.

In a fifth step S15, laser light is then emitted for the second time by at least one laser, with at least the laser whose associated detector has an intensity level above the intensity threshold being deactivated beforehand. The process can then continue with the first step S11.

If no detector has an intensity level above the intensity threshold, the process continues with the second step S12.

2 shows a first schematic representation of the execution of the method according to a first embodiment.

A LiDAR system 20 emits a laser strip 24 with full power using a laser array 21. The laser array 21 can regulate the power of each emitted laser beam individually. As can be seen from the 2 As can be seen, the laser light is emitted in different spatial directions. This is ensured by the lens 22.

In the far field, the laser strip 24 expands accordingly. As soon as the laser light hits a retroreflector 23, a portion of the laser light is reflected by the retroreflector 23 and received or detected by detectors of the LIDAR system 20, which are not shown here.

3 shows a second schematic representation of the execution of the method according to the first embodiment. It was determined that some laser light intensities detected by the detectors exceeded a predefined intensity threshold value. The lasers 31 correspondingly assigned to these detectors, whereby the assignment can take place, for example, by means of a characteristic map between lasers and detectors, are deactivated and the laser array 21 emits laser light a second time, whereby the correspondingly assigned lasers 31 are each deactivated.

Thus, no laser light hits the retroreflector 23, which prevents saturation of the corresponding detectors and thus crosstalk when the reflected laser light 32 is received again.

4 shows a third schematic representation of the implementation of the method according to the invention in accordance with a second embodiment. On the left side of the figure, an illumination situation of a street scene is shown, as it develops over time when illuminated with a column laser, i.e. an arrangement of several lasers in a column. Furthermore, the crosstalk 402 created by a highly reflective object in the lidar system is shown. For example, the scene is illuminated from left to right. First, the column laser emits a corresponding laser column 405 and then, in sequence, another laser column offset by a certain angle, and so on. The temporal synopsis then produces the image shown, with the resulting crosstalk 402 also shown here.

When a laser beam hits a highly reflective object 400, it is reflected by it and falls via a corresponding reception path of the lidar system onto one or more detectors of the lidar system. Crosstalk 402 can arise in the lidar system. The detectors thus register light even though no object has actually reflected it. The crosstalk can partially obscure objects that are actually present, for example object 401, so that they are not fully detected by the lidar system. However, the method according to the invention at least reduces the effects of the crosstalk. For example, object 401 is partially visible despite the presence of the highly reflective, crosstalk-generating object 400. This is because the corresponding lasers have been deactivated to prevent crosstalk. Line 403 represents the correspondingly deactivated lasers and line 404 represents the correspondingly active lasers. The lasers are then reactivated and crosstalk occurs again as a result.

On the right side of the 4 is a schematic representation of what the resulting data point cloud of the lidar system looks like. The highly reflective object 400 is represented by various data points 410. It is noticeable that there are larger distances between the data points 410. This is because the corresponding lasers were deactivated according to the method according to the invention. These gaps can be avoided if the laser array and the detector array are designed with two columns and the corresponding laser and detector column are switched on accordingly after emitting with deactivated lasers in the other column. The data points 411 represent the object 401 partially obscured by crosstalk.

The data points 412 represent the crosstalk generated by the highly reflective object 400 in the lidar system. The data points 413 represent the environment of the road. The data points 414 represent the road.

5 shows a schematic representation of the LiDAR system 50 according to the invention according to an embodiment. The LiDAR system 50 comprises a laser array 51 with several lasers 54 and a detector array 52 with several detector pixels 55. The system 50 also comprises an electronic control unit 53, which, for example, carries out a corresponding determination of the saturation of a detector pixel 55 and, for example, controls the process sequence. The electronic control unit 53 can be connected to the laser array 51 and the detector array 52, for example, by means of communication lines.

Claims (12)

Method for operating a lidar system (20, 50), wherein the lidar system (20, 50) has a plurality of lasers (31, 54) that can be individually controlled and emit laser light at different solid angles, and a plurality of detectors (55) for detecting laser light, comprising the steps: a) activating all detectors (55); b) first emitting laser light by at least two lasers (31, 54), each with a predefined power, at different solid angles; c) detecting reflected laser light by at least two detectors (55); d) comparing the detected laser light intensity with a predefined intensity threshold; e) second emitting laser light by at least one laser (31, 54), wherein at least the laser (31, 54) whose associated detector (55) has an intensity level above the intensity threshold is deactivated beforehand. Method according to the preceding claim, further comprising: f) generating a data point cloud from intensity values of detectors (55) whose associated lasers (31, 54) are activated. Method according to the preceding claim, wherein step f) comprises: g) classifying first intensity values that exceed the predefined intensity threshold as belonging to a highly reflective object; h) determining a first distance to the lidar system (20, 50) associated with each of the classified intensity values; i) determining a second distance to the lidar system (20, 50) associated with each of the second intensity values; wherein, in the generation of the data point cloud, second intensity values are not taken into account, the associated distance of which is in the range of the first distance up to a predefined distance interval and the laser (31, 54) of which is assigned via the detector (55) differs from the corresponding laser (31, 54) of the first intensity values. Method according to one of the preceding claims, wherein after the second emission the at least one deactivated laser (31, 54) is reactivated. Method according to one of the preceding claims, wherein the lasers (31, 54) are designed as a two-column laser array (21, 51) and the detectors (55) are designed as a two-column detector array (52), further comprising: j) If lasers (31, 54) were deactivated, activating the second column of the laser array (21, 51) to emit laser light and the second column of the detector array (52) to detect laser light. Lidar system (20, 50), comprising: - a plurality of lasers (31, 54) which are individually controllable and can emit laser light in different solid angles, - a plurality of detectors (55) for detecting laser light, - an electronic control unit (53) which is set up to carry out all steps of the method according to one of the Claims 1 until 5 to execute. Lidar system (20, 50) according to the preceding claim, wherein the lasers (31, 54) have at least one control unit and the detectors (55) have at least one readout unit, wherein the control unit and the readout unit are configured such that the comparison of the laser light intensity takes place on the readout unit and the readout unit directly controls the control unit for deactivating lasers (31, 54) and emitting laser light. Lidar system (20, 50) according to one of the Claims 6 or 7 , whereby the spatial laser detector calibration is stored directly on the readout unit. Lidar system (20, 50) according to one of the Claims 6 until 8th , wherein the lasers (31, 54) are designed as a single-column laser array (21, 51) and the detectors (55) are designed as a single-column detector array (52). Lidar system (20, 50) according to the preceding claim, wherein the laser array (21, 51) is designed with two columns and the detector array (52) is designed with two columns. Computer program comprising instructions that cause the lidar system (20, 50) to operate according to one of the Claims 6 until 10 all steps of the procedure according to one of the Claims 1 until 5 executes. Machine-readable storage medium on which the computer program is Claim 11 is stored.

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