Lidar device and method for operating a lidar device

Abstract

The present invention relates to a method for operating a lidar device of a vehicle which has a plurality of lidar sensors (12), wherein in the course of the method: laser light is emitted from the lidar sensors (12) into an environment, and Laser light reflected from the environment is received by the lidar sensors (12) and converted into electrical signals by at least one detector of the lidar device, wherein a central time management is applied which determines transmission times (t0, t1, t2) for each lidar sensor (12) at which this lidar sensor (12) emits at least one laser light pulse train (18, 20, 22). The present invention further relates to a lidar device which is configured to carry out such a method.

Description

[0001] The present invention relates to a method for operating a lidar device according to claim 1 and a lidar device according to claim 11.

[0002] Known methods for operating a lidar device serve to scan the area surrounding a vehicle. Lidar devices emit laser beams (for example, pulsed) and receive laser light reflected from the environment, which is then converted into electrical signals by a detector. In the time-of-flight (TOF) measurement method, the distance between the lidar device and an object in the environment is calculated from the travel time of the light pulses. Detected reflection points are compiled into a lidar point cloud, which is stored as a representation of the environment and continuously updated by a cyclical scanning process of the lidar device.

[0003] Lidar devices of this type have a plurality of lidar sensors for emitting laser light into the environment and for receiving laser light reflected from the environment, as well as at least one detector designed to convert received laser light into electrical signals.

[0004] When multiple lidar sensors are installed on a vehicle, the total available aperture, and therefore the intensity of light that can be received, is increased. This is an important factor that improves the maximum range of the lidar system. This is particularly relevant when multiple lidar sensors are mounted in positions where each sensor's detection range extends forward in the direction of travel. Furthermore, installing multiple lidar sensors in positions around the vehicle enables 360° coverage of the area surrounding the vehicle. Vertical coverage, covering 180° of the positive hemisphere above the vehicle, is also important. Here, arranging the sensors vertically is usually advantageous, as different viewing heights are typically used to achieve the most complete coverage possible.

[0005] When operating more than one lidar sensor on a vehicle using known methods for such lidar devices, interference can occur due to the permanently fixed alignment of the lidar sensors relative to each other. This can lead to reduced detection quality and, in the worst case, false detections. For example, it may be erroneously assumed that no object is in the vicinity of the vehicle, even though such an object is present. Conversely, objects that are not actually present may also be detected.

[0006] When multiple lidar sensors are operated on a single vehicle, they are spatially aligned relative to each other at a constant rate, and their detection ranges can partially overlap. Furthermore, the lidar sensors can be temporally coupled, albeit unintentionally. As a result, interference or beat frequencies can develop, and because these disturbances are constant over time, such effects can occur continuously.

[0007] Known methods attempt to prevent interference from other lidar sensors. However, such known measures are only aimed at interference from lidar sensors in other vehicles.

[0008] It is therefore the object of the present invention to provide a method for operating a lidar device in which these problems are solved.

[0009] This problem is solved by a method for operating a lidar device of a vehicle according to claim 1, and by a lidar device according to claim 11.

[0010] A method according to the invention serves to operate a lidar device comprising a plurality of lidar sensors. In the course of the method, laser light is emitted from the lidar sensors into an environment. Laser light reflected from the environment is received by the lidar sensors and converted into electrical signals by at least one detector of the lidar device. According to the invention, a central timing system is used, which defines transmission times for each lidar sensor at which that sensor emits at least one laser light pulse train.

[0011] The method according to the invention offers the advantage that it specifies at which transmission time or in which time slice each lidar sensor emits laser light. This allows for consideration of situations where, for example, lidar sensors that could interfere with each other do not emit laser light simultaneously. It is not yet specified which of the lidar sensors receives laser light in the corresponding time slice. In principle, laser light emitted by a first lidar sensor can be received by the same lidar sensor, but also by others if the detection ranges of the sensors overlap. Advantageously, however, the method according to the invention is designed such that no lidar sensors emit laser light pulse trains simultaneously when their detection ranges overlap, thus avoiding beat frequencies and interference.

[0012] A lidar device according to the invention is configured to apply a central timing management system that defines transmission times for each lidar sensor, at which each lidar sensor emits at least one laser light pulse train. With a lidar device according to the invention, it is therefore possible to prevent lidar sensors with overlapping detection ranges from simultaneously emitting laser light and causing interference or beat frequencies.

[0013] Preferred embodiments of the present invention are set forth in the dependent claims.

[0014] Preferably, the central time management defines active listening periods (AL) for each lidar sensor, within which the lidar sensor receives laser light that it has emitted itself as a laser light pulse train and that has been reflected by the environment.

[0015] Furthermore, the central time management for each lidar sensor advantageously defines passive listening periods (PL), within which the lidar sensor receives laser light that another lidar sensor has emitted as a laser light pulse train and which has also been reflected by the environment.

[0016] According to a further embodiment of the present invention, the active and passive reception periods each begin with or after a transmission time and end before the following transmission time.

[0017] These embodiments of the invention thus offer the possibility for the central time management system to determine which lidar sensor transmits within which time slot. Such a lidar sensor can receive its "own" laser light again after reflection from its surroundings. Lidar sensors with an overlapping detection range (i.e., particularly neighboring lidar sensors), to which this reflected laser light also reaches, can receive and process it. However, it is advantageously possible to avoid lidar sensors that could influence each other and generate interference or beat frequency from transmitting simultaneously in the same time slot.

[0018] This avoids disruptive interference or beat frequencies that can lead to false detections.

[0019] Advantageously, in a method according to the invention, the duration of the active and passive reception periods AL and PL is at least as long as the maximum travel time of a laser light pulse train from the lidar device to an object within the maximum range of the lidar device and from there back to the lidar device. It should be taken into account that typical laser light pulse trains have a time-of-flight (ToF) of 2 ns to 10 ns, typically 5 ns. For example, at a distance of 200 m from an object in the vicinity, the distance traveled by the laser light from the lidar device to the object and back is 400 m, resulting in a typical travel time of approximately 1.33 µs.Naturally, in the method according to the invention, one should wait until laser light pulse trains that are reflected within the range of the lidar device could still be received by all lidar sensors with a corresponding spatial orientation before the active or passive reception period of the respective lidar sensor ends.

[0020] In a further particularly preferred embodiment of the method according to the invention, the timing is configured such that different lidar sensors are only assigned a common transmission time and emit laser light simultaneously if their detection ranges do not overlap. This means that a lidar sensor with a detection range oriented forward in the direction of travel and another lidar sensor with a detection range oriented backward in the opposite direction of travel can actually emit laser light pulse trains simultaneously, since, due to their different orientations and corresponding detection ranges, the laser light pulse trains of these two lidar sensors cannot interfere with each other and / or produce beat frequencies.This approach offers the advantage that, on the one hand, the problems of known methods mentioned at the beginning are avoided, and on the other hand, multiple lidar sensors can still actively emit laser light, thus allowing the emission of laser light to occur not only sequentially but also partially in parallel. This enables a lidar point cloud, acquired by the lidar device, to be refreshed more quickly.

[0021] Accordingly, according to the invention, it is also preferably provided that different lidar sensors are assigned different transmission times when their detection ranges overlap. For example, it can be provided that three adjacent lidar sensors with at least partially overlapping detection ranges only ever emit laser light pulse trains alternately in order to avoid interference and beat frequencies.

[0022] In a further embodiment of the present method, the lidar device includes a lidar central unit for controlling the lidar sensors and for evaluating signals generated from the received laser light. Such a lidar central unit can, for example, also control a scanning unit in the lidar sensors and thus regulate the cyclical scanning of the environment. Electrical signals, which are acquired by the detection of the laser light, for example, in the lidar sensors themselves, can also be further processed in the lidar central unit and, for example, processed into a complete image in the form of a lidar point cloud as a representation of the environment.

[0023] Preferably, the central time management system communicates the different transmission times to the various lidar sensors and / or the lidar central processing unit (CPU) via a system clock. A currently used pseudo-noise code, and preferably the number of laser light pulse trains and / or the number of pulses per laser light pulse train, can also be transmitted. The use of pseudo-noise codes, also known as "pseudo-jitter," offers the advantage of further suppressing mutual interference between lidar sensors. It can be implemented that the time intervals between the laser light pulses of a laser light pulse train and / or the duration of the laser light pulses are changed as a function of time. Such a change can be made, for example, for each image or for each frame.

[0024] In a further method according to the invention as described in one of the preceding claims, the central time management system continuously defines successive time slices and, for each time slice, at least one first lidar sensor which actively emits first laser light within this time slice and receives components reflected from this first laser light. The central time management system further defines at least one additional lidar sensor for this time slice which does not actively emit laser light but passively receives components reflected from the first laser light. For successive time slices, it is again defined which lidar sensor(s) actively transmit and receive (AL) and which only passively receive (PL).

[0025] In a preferred embodiment of a lidar device according to the invention, the lidar device has a system clock which is configured to communicate the different transmission times to the various lidar sensors and / or a lidar central unit.

[0026] The invention will be explained in more detail below using the figures as examples.

[0027] This shows: Fig. 1: a vehicle equipped with a lidar device; Fig. 2: vehicle 10 of the Fig. 1 in a schematic view from above; Fig. 3 the temporal sequence of the method according to the present invention, and Fig. 4 shows another aspect of the procedure of Fig. 3.

[0028] Fig. Figure 1 shows a vehicle 10 according to the present invention. The vehicle 10 is equipped with a lidar device comprising a plurality of lidar sensors 12. These lidar sensors 12 are arranged at installation positions located at different vertical and horizontal positions on the vehicle 10.

[0029] In the schematic representation of the Fig. Figure 2 shows a top view of vehicle 10. The lidar sensors 12 are not only arranged at different heights, but also all around vehicle 10, including the front and rear of the vehicle 10 as well as the sides. Fig. 1 and Fig. Figure 2 further shows a lidar central unit 14, which can be located at any point within the vehicle body of the vehicle 10. At least one connection 16 for exchanging signals and / or data is provided between the lidar sensors 12 and the lidar central unit 14. The detection ranges of the lidar sensors 12 of the vehicle 10 partially overlap.

[0030] The various lidar sensors 12 of the vehicle 10 can all emit laser light. All lidar sensors 12 can also receive reflected laser light, not only that which they themselves have emitted, but also laser light originally emitted by another, for example, neighboring lidar sensor 12. Due to the overlapping detection ranges of the various lidar sensors 12, the detection range of the entire lidar system extends 360° around the vehicle 10. Redundancies also arise if, for example, a particular lidar sensor 12 is covered by contamination to such an extent that it may still be able to emit laser light, but can no longer receive the significantly weaker intensity of reflected laser light.

[0031] Fig. Figure 3 schematically shows the temporal sequence of the inventive method for operating the lidar device. On a horizontal time axis, the system time of a system clock, as is customary referred to as the "system clock," is shown with different transmission times t0, t1, and t2 from lidar sensors 1, 2, and 3. These lidar sensors 1, 2, and 3 of the Fig. 3 are an exemplary selection of such lidar sensors 12 of the Fig. 1 and Fig. 2, where their detection areas overlap.

[0032] Each lidar sensor 1, 2, and 3 emits laser light pulse trains at different times, of which only a single laser light pulse train 18 is shown for simplicity. In reality, several such laser light pulse trains can be arranged sequentially. A corresponding transmission period S is shown schematically. For each lidar sensor 1, 2, and 3, the transmission times t0, t1, and t2 are fixed, at which the lidar sensors 1, 2, and 3 emit the laser light pulse train 18. The time offset between the transmissions ensures that several of the lidar sensors 1, 2, and 3 do not transmit simultaneously, which could cause the interferences described above.

[0033] Within the time slices (or periods) between t0 and t1, t1 and t2, and the subsequent time slice after t2, active and passive receive periods AL and PL are defined, during which the lidar sensors 1, 2, and 3 receive laser light reflected from the environment. Corresponding arrows indicate the assignment of transmitting lidar sensors to passively receiving lidar sensors. The received laser light is converted into electrical signals by at least one detector of the lidar device and transformed into a lidar point cloud—a representation of the environment—by the lidar device or downstream electronic processes.

[0034] The essential aspect of the invention is that within each time slice or reception period AL and PL, both the transmitting lidar sensor actively receives reflected laser light (AL) and the other lidar sensors passively receive it (PL). Passive reception or "passive listening" PL means that laser light is received from a lidar sensor without that lidar sensor emitting any laser light during the period under consideration.

[0035] The role of lidar sensors 1, 2, and 3 now changes over time as shown in the Fig. Figure 3 is shown. After the first reception periods AL and PL have elapsed, the central time management system initiates another transmission time t1, at which point the lidar sensor 2 takes over the active role, i.e., it emits the laser light pulse train 18 shown. In contrast, lidar sensor 1 and lidar sensor 3 do not emit laser light, but passively (PL) receive reflected laser light, which was previously emitted into the environment by lidar sensor 2. Passively receiving lidar sensors are, in particular, those that do not actively emit laser light, but whose detection range overlaps with the detection range of the emitting, active lidar sensor at least to the extent that they can detect a sufficient intensity of reflected laser light pulse trains in a usable manner. After the second reception periods AL and PL have elapsed, respectively...In addition to the second time slice, which was started at time t1, a third time slice, beginning at time t2, is schematically shown, within which the lidar sensor 3 now takes over the active part, i.e. emits at least one laser light pulse train 18.

[0036] In summary, a central time management system is provided for the operation of multiple lidar sensors 12 in a vehicle, and in particular a central system clock is used to define multiple time scales. This offers the advantage that the effects of mutual interference between the different lidar sensors 12 are prevented, and at the same time, multiple lidar sensors 12 can be used on the receiving side to receive a signal from a transmitting lidar sensor 12. The transmission times t0, t1, and t2 for each lidar sensor 12 are centrally coordinated and can be defined according to a fixed sequence or at least a sequence regulated by the system itself.

[0037] The Fig. Figure 4 shows a more detailed aspect of the procedure. Fig. 3. How the Fig. Figure 4 shows that the central time management for the various lidar sensors 12 and / or a lidar central unit 14 not only determines the different transmission times t0, t1 and t2, but also a currently used pseudo-noise code for different laser light pulse trains 18, 20 and 22 that a lidar sensor 12 emits, as well as optionally the number of pulses per laser light pulse train 18, 20 and 22.

[0038] As already shown from the Fig. As explained in section 4, the system clock sets the transmission time t0, triggering the emission of at least one laser light pulse train 18 by a relevant lidar sensor 12 (number 1 in the Fig. 3) After the image of Fig. After lidar sensors 2 and 3 have emitted corresponding laser light pulse trains 18 at times t2 and t3, this sequence is restarted, and at a second transmission time t0, lidar sensor 12, numbered 1, again emits a laser light pulse train 20. As shown schematically, the temporal sequence of laser light pulse train 20 differs slightly from the temporal sequence of laser light pulse train 18. After the sequence t0 to t2 has been repeated, Fig. 3 The lidar sensor 1 sends another laser light pulse train 22. This process is continued continuously (indicated by the dotted line).

[0039] The timing of the laser light pulse trains 18, 20, and 22 emitted by a specific lidar sensor 12 changes continuously, resulting in a so-called clock jitter or pseudo jitter. This continuous change in pulse intervals and / or pulse widths is thus modified as a function of time, for example, as in the Fig. 4 is shown with each frame or individual image captured within a single reception period AL or PL. Mutual interference between the lidar sensors 12 of an Ego vehicle is thus further suppressed. The current pseudo-jitter pattern is transmitted to all actively or passively receiving lidar sensors 12 so that they can apply the appropriate filter to filter the received reflected laser light pulse trains during further processing.

[0040] The corresponding clock jitter or pseudo-jitter of the laser light pulse trains 18, 20, and 22 can be identical at the corresponding start times t0, t1, and t2 from each lidar sensor 1, 2, and 3. Alternatively, a different pseudo-jitter pattern can be used when lidar sensor 2 subsequently transmits at start time t1. In any case, the method offers the advantage that for each received laser light pulse train from each receiving lidar sensor 12 (whether AL or PL), it can be determined whether the corresponding laser light pulse train originates from the first transmission at the first time t0 (laser light pulse train 18) or from the second or third transmission of the laser light pulse train 20 or 22. If different pseudo-grids are used for different lidar sensors, each receiving lidar sensor 12 can detect which lidar sensor 10 emitted the light.This offers the advantage that interferences, beat frequencies and other mutual influences of the lidar sensors 12 can be further suppressed. Reference symbol list 10 vehicles 12 Lidar sensors 14 Lidar central unit 16 connections 18 first impulse move Lidar 1 20 second impulse train Lidar 1 22 third impulse train Lidar 1 Send AL “active listening” PL “passive listening” t0, t1, t2: Transmission times of the lidar sensors

Claims

[1] Method for operating a lidar device of a vehicle, wherein the lidar device comprises a plurality of lidar sensors (12), and in the course of the method: laser light is emitted from the lidar sensors (12) into an environment, and Laser light reflected from the environment is received by the lidar sensors (12) and converted into electrical signals by at least one detector of the lidar device, wherein a central time management is applied which determines transmission times (t0, t1, t2) for each lidar sensor (12) at which this lidar sensor (12) emits at least one laser light pulse train (18, 20, 22). [2] Method according to claim 1, wherein the central time management defines active reception periods (AL) for each lidar sensor (12) within which the lidar sensor (12) receives such laser light which it has emitted as a laser light pulse train (18) itself and which has been reflected by the environment. [3] Method according to one of the preceding claims, wherein the central time management for each lidar sensor (12) defines passive reception periods (PL) within which the lidar sensor (12) receives such laser light which another lidar sensor has emitted as a laser light pulse train (18) and which has been reflected by the environment. [4] Method according to one of the preceding claims 2 and 3, wherein the active and passive receiving periods (AL, PL) each begin with or after a transmission time (t0) and end before the subsequent transmission time (t1). [5] Method according to any one of claims 2 to 4, wherein the duration of the active and passive reception periods (AL, PL) is at least as long as the maximum travel time of a laser light pulse train (18, 20, 22) from the lidar device to an object within a maximum range of the lidar device and from there back to the lidar device. [6] Method according to one of the preceding claims, wherein the central time management is designed such that different lidar sensors (12) are only assigned a common transmission time (t0, t1, t2) and emit laser light simultaneously if their detection areas do not overlap. [7] Method according to one of the preceding claims, wherein the central time management is designed such that different transmission times (t0, t1, t2) are assigned to different lidar sensors (12) when their detection ranges overlap. [8] Method according to one of the preceding claims, wherein the lidar device comprises a lidar central unit (14) for controlling the lidar sensors (12) and for evaluating signals generated from the received laser light. [9] Method according to one of the preceding claims, wherein the central time management communicates the different transmission times (t0, t1, t2) to the various lidar sensors (12) and / or a lidar central unit (14), as well as a currently used pseudo-noise code and preferably the number of laser light pulse trains (18, 20, 22) and / or the number of pulses per laser light pulse train (18, 20, 22). [10] Method according to any of the preceding claims, wherein the central time management: a. defines continuously successive time slices, b. defines at least one first lidar sensor (12) for each time slice which actively emits first laser light within this time slice and receives components reflected from this first laser light (AL), c. specifies at least one further lidar sensor (12) for this time slice which does not actively emit laser light but passively receives components reflected from the first laser light (PL), d. where, for successive time slices, it is determined again which lidar sensors (12) actively transmit and receive (AL) and which only passively receive (PL). [11] Lidar device for a vehicle, wherein the lidar device comprises a plurality of lidar sensors (12) which are designed to emit laser light into an environment of the vehicle and to receive laser light reflected from the environment, and at least one detector which is designed to convert received laser light into electrical signals, characterized by , that the lidar device is designed to apply a central time management which specifies transmission times (t0, t1, t2) for each lidar sensor (12) at which this lidar sensor (12) emits at least one laser light pulse train (18, 20, 22). [12] Lidar device according to claim 11, characterized by , that the lidar device has a system clock which is designed to communicate the different transmission times (t0, t1, t2) to the various lidar sensors (12) and / or a lidar central unit.

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