Method for determining a change in the range of a lidar sensor

Abstract

The present invention relates to a method for determining a change in the range of a laser radar sensor (1) for a vehicle or a robot. According to the present invention, in a reference measurement using a reference target (RZ) located at a predetermined distance (d_0) from the laser radar sensor (1), a reference noise level (R_0) of infrared radiation (S) received by the laser radar sensor (1) and a signal-to-noise ratio of infrared radiation (S) reflected at the reference target (RZ) and received by the laser radar sensor (1) are determined. During the driving measurement, the current noise level (R_1, R_2) of infrared radiation (S) received by the laser radar sensor (1) is determined, and from the current noise level (R_1, R_2), a theoretical distance (d_1, d_2) to a position (P_1, P_2) where the reference target (RZ) should be located in the following situation is determined, i.e., at this time, at the current noise level (R_1, R_2), the same signal-to-noise ratio exists as in the reference measurement. In the range change calculation, a difference between a predetermined distance (d_0) and a target distance (d_1, d_2) is determined, wherein the difference corresponds to a change in the range of the lidar sensor (1) relative to its range during a reference measurement.

Description

Technical Field

[0001] The invention relates to a method for determining a change in the range of a lidar sensor for a vehicle or a robot. Background Art

[0002] DE 199 48 252 A1 discloses a method for state detection, in particular for detecting sensor contamination, in a system operating according to the lidar principle for automatic longitudinal and lateral control in a motor vehicle. State detection relies on two indicators consisting of the signals received and transmitted by the sensor. The indicators are weighted by weighting coefficients and associated with a unique probability. If the value exceeds or falls below a predetermined threshold for a predetermined period of time, a conclusion regarding sensor contamination is drawn from this probability. The time at low vehicle speed is selected to be greater than the time at high vehicle speed. The indicators used are object stability, which indicates the detection failure rate of target objects selected for the vehicle's longitudinal control, and the sum of all objects detected during the measurement.

[0003] Furthermore, DE 10 2020 115 252.3 describes a method and a device for detecting contamination on a protective plate of a lidar sensor. The detection area of ​​the lidar sensor is divided into a plurality of subareas, wherein it is determined for each subarea whether contamination is present on the protective plate within the respective subarea. To this end, a subarea background noise is determined in the respective subarea and a detection area background noise is determined within the remaining detection area or the entire detection area, wherein contamination is inferred in the subarea when the subarea background noise is significantly lower than the detection area background noise. Alternatively or additionally, the subarea background noise is determined in each subarea under different sensitivities of the receiver of the lidar sensor, wherein the presence of contamination in the respective subarea is inferred when the subarea background noise determined at a higher sensitivity is not significantly higher than the subarea background noise determined at a lower sensitivity. Summary of the Invention

[0004] The object of the present invention is to specify a novel method for determining the change in range of a lidar sensor for a vehicle or a robot.

[0005] According to the invention, this object is achieved by a method having the features of claim 1 .

[0006] Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0007] According to the present invention, in a method for determining the change in the range of a lidar sensor for a vehicle or robot, a reference noise level of infrared light received by the lidar sensor and a signal-to-noise ratio of infrared light reflected by the reference target and received by the lidar sensor are determined during a reference measurement using a reference target at a predetermined distance from the lidar sensor. During a driving measurement, the current noise level of infrared light received by the lidar sensor is determined while the vehicle or robot is driving, and from this current noise level, a theoretical distance from the reference target is determined, at which the signal-to-noise ratio should be the same as in the reference measurement. Furthermore, during the range change calculation, a difference between the predetermined distance and the theoretical distance is determined, wherein this difference corresponds to the change in the range of the lidar sensor relative to its range during the reference measurement.

[0008] For example, in automated, particularly highly automated or autonomous, vehicles or robots, the current sensor field of view, also known as sensor range or detection range, crucially determines driving parameters such as maximum speed or the minimum distance to other vehicles, robots, or objects. Therefore, reliable determination of the current sensor field of view is an important safety criterion for autonomous vehicles and robots. LiDAR sensors are particularly suitable as reference sensors for determining the range to objects.

[0009] With the help of the present invention, a reliable and trustworthy estimation of the sensor field of view can be achieved during the service life of the lidar sensor. As a result, the availability of systems using data collected by the lidar sensor can be significantly increased. In this case, a reliable and trustworthy estimation of the lidar sensor's range is achieved based on the noise measurement, and for this purpose, the presence of a target is not even required. In this case, the method is at least essentially independent of the exact type of object in the field of view, which is usually used for other types of estimation and is subject to strong fluctuations, such as dirty vehicles or traffic signs. For example, when a very bright road surface reflects more sunlight than a dark road surface (which is common in road repair areas), distance-related values ​​can also be determined when determining the overall noise curve. In addition, the distance estimation can be performed independently for the spatial angle, which provides additional information about system degradation.

[0010] In one possible embodiment of the method, the operating range is defined as the distance at which the signal-to-noise ratio corresponds to a predetermined threshold value. This allows a simple and precise determination of the operating range.

[0011] In another possible embodiment of the method, the distance-dependent attenuation of the lidar radiation is taken into account during the driving measurement when determining the target distance. This further increases the accuracy of the range determination.

[0012] In another possible embodiment of the method, the reference measurement is repeated after a specified time. This allows the reference noise level and the signal-to-noise ratio at the reference target determined in the reference measurement to be updated, so that, for example, aging effects of the lidar sensor can be taken into account.

[0013] In another possible embodiment of the method, changes in the intrinsic noise component of the lidar sensor are taken into account when determining the reference noise level in the reference measurement. Taking the intrinsic noise component into account allows the reference noise level to be reconstructed under controlled conditions during operation, and aging effects over the lifetime of the lidar sensor can be easily and reliably accounted for.

[0014] In another possible embodiment of the method, changes in the intrinsic noise component are taken into account by the computer in that the reference noise level and the signal-to-noise ratio at the reference target are corrected by the corresponding portion resulting from the intrinsic noise component. Thus, complex processing steps for taking into account changes in the intrinsic noise component can be omitted.

[0015] In another possible embodiment of the method, the intrinsic noise component is determined during a useless measurement time of the lidar sensor, during which the lidar sensor's receiver is shielded from external radiation. During this useless measurement time, a reference infrared signal is transmitted to the receiver using an infrared light source arranged within the lidar sensor, and the dark phase noise level is determined. This determination of the intrinsic noise component, performed using a defined reference infrared signal from the infrared light source and shielded from external radiation and / or light, according to a "dark measurement," allows for the precise reproduction / reconstruction / simulation of the reference noise level under controlled operating conditions, thereby reliably accounting for aging effects of the lidar sensor over its service life. The infrared light source is, for example, a power-controlled infrared light-emitting diode.

[0016] In another possible embodiment of the method, the dark phase noise level is determined as an average value of a plurality of dark phase noise levels. This allows fluctuations occurring during the process to be compensated.

[0017] In another possible embodiment of the method, the dark phase noise level is determined during travel of the vehicle or robot. Therefore, no additional determination of the dark phase noise level outside of travel is necessary. As a result, for example, additional visits to a repair shop to perform reference measurements can be omitted.

[0018] In another possible embodiment of the method, the reference measurement is carried out as an end-of-line check at the end of the manufacture of the vehicle or robot, wherein it can be easily integrated into the manufacturing process of the vehicle or robot. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The embodiments of the present invention will be explained in detail below with reference to the drawings, wherein:

[0020] Figure 1 Schematic illustration of the LiDAR reflection intensity determined in a reference measurement as a function of the distance to an object,

[0021] Figure 2 Schematically shows the difference between the Figure 1 The reference measurement of the lidar reflection intensity determined at night as a function of the distance to the object,

[0022] Figure 3 Schematically shows the difference between the Figure 2 The determination of the lidar reflection intensity at night of the reference measurement and the reference target position at a reduced noise level,

[0023] Figure 4 Schematically showing the Figure 1 The reference measurements of the LiDAR reflection intensity related to the distance to the object were compared to the determination of the reference target position under sunlight and at a higher noise level.

[0024] Figure 5 Schematic illustration of a comparison of the LiDAR reflection intensities determined in a reference measurement, a measurement performed at night and a measurement performed in sunlight as a function of the distance to an object,

[0025] Figure 6 schematically illustrates a lidar sensor in a first reflector state,

[0026] Figure 7 Schematic diagram showing the reflector in the second working state according to Figure 5 LiDAR sensor. DETAILED DESCRIPTION

[0027] Corresponding parts are provided with the same reference numerals in all the figures.

[0028] Figure 1 The values ​​determined in the reference measurement are shown by means of, for example, Figure 6 and Figure 7 The relationship between the intensity I of the lidar reflection LR received by the lidar sensor 1 and the distance d from the object O designed as a reference target RZ is shown in FIG. The object O is located at position P_0 here.

[0029] The environmental data measured by the lidar sensor 1 is used, for example, for the operation of a vehicle or robot that is operating autonomously, particularly highly autonomously or autonomously. For the vehicle or robot to operate reliably, it is necessary to know the range of the lidar sensor 1 in order to adjust the automated longitudinal and / or lateral control accordingly.

[0030] To determine the range, the lidar sensor 1 performs a measurement under predetermined conditions in a reference measurement, for example, on a production line in vehicle and robot manufacturing, such as a so-called end-of-line inspection station (EOL inspection station for short). For example, in this case, the range is determined for a reference target RZ having predetermined dimensions, such as 2 m×2 m, and a predetermined reflectivity, such as 10%, under a predetermined background light level of, for example, 50,000 lumens. At this range, a measurement point is obtained with a predetermined probability, such as 90%.

[0031] Here, the laser radar sensor 1 receives Figure 6 and 7 The reference noise level R_0 of the infrared radiation S, shown in detail in FIG, i.e. the strength of the received noise signal, is determined. The noise curve thus determined is shown here simply as a straight line. In addition, the intensity I_0 of the lidar reflection LR measured by the lidar sensor 1 is measured.

[0032] Furthermore, the signal-to-noise ratio (SNR) is determined, which occurs when infrared light S is reflected from a predetermined reference target RZ, which is located at a predetermined distance d_0 in front of the lidar sensor 1 and has a predetermined size and a predetermined reflectivity. The operating range of the lidar sensor 1 is defined as the distance d at which the SNR corresponds to a predetermined threshold value for the SNR.

[0033] Here, the signal-to-noise ratio of the reference-measured lidar reflection LR is obtained according to the following formula:

[0034]

[0035] The signal-to-noise ratio SNR_0 is then stored as a reference signal-to-noise ratio and the noise level R_0 is stored as a reference noise level R_0.

[0036] When the reference signal-to-noise ratio SNR_0 is equal to a predetermined threshold value of the signal-to-noise ratio, the distance d_0 corresponds to the operating range of the lidar sensor 1 .

[0037] When the reference signal-to-noise ratio SNR_0 is greater than a predetermined threshold value of the signal-to-noise ratio, that is, when the threshold value has not been reached, the operating range is greater than the distance d_0.

[0038] From the known attenuation of the lidar radiation with path length, based on the fact that the intensity of the lidar radiation decreases quadratically with path length, it is then possible to determine the path length by which the reference target RZ should be displaced backwards, thereby obtaining a signal-to-noise ratio equal to a predetermined threshold value of the signal-to-noise ratio.

[0039] The range can thus be determined from the distance d_0 and the reference signal-to-noise ratio SNR_0. This range can also be determined by moving the reference target RZ back step by step until the signal-to-noise ratio determined in each step corresponds to a signal-to-noise ratio threshold.

[0040] Figure 2 Shown compared to the Figure 1 The reference measurement of the intensity I of the lidar reflection LR as a function of the distance d_0 from the object O is determined at night.

[0041] During normal operation of the vehicle or robot, for example after delivery of the vehicle or robot to a customer, the noise level is measured again regularly during driving measurements.

[0042] At night, a noise level R_1 is determined to be lower than the reference noise level R_0.

[0043] like Figure 3 As shown, we now calculate the position P_1 where the reference target RZ should be in order to obtain the same value as that obtained in the case of the lower noise level R_1. Figure 1 The same signal-to-noise ratio as in the reference measurement.

[0044] If the signal-to-noise ratio SNR_1 determined in the driving measurement based on the intensity I_1 and the noise level R_1 is equal to the reference signal-to-noise ratio SNR_0 according to the following formula,

[0045]

[0046] Then we get

[0047] I_1=R_1·SNR_0 (3)

[0048] In this case, the value of the intensity I_1 is a value that can be measured in the presence of a noise level R_1 when the signal-to-noise ratio SNR_1 is equal to the reference signal-to-noise ratio SNR_0 .

[0049] From the intensity I_1 of the lidar radiation and the known distance-dependent attenuation, a theoretical distance d_1 from the position P_1 where the reference target RZ is to be located is determined in order to obtain the same signal-to-noise ratio SNR_1 = SNR_0 .

[0050] The lower noise level R_0 ensures that reference target RZ can be detected at the same signal-to-noise ratio as during the reference measurement, even at a greater distance. The distance d between distance d_0 and the target distance d_1 corresponds to the increase in the range of lidar sensor 1, which occurs when reference noise level R_0 decreases to noise level R_1. Therefore, the expected increase in the range of lidar sensor 1 is determined by the reduction in noise level R_1 relative to reference noise level R_0.

[0051] Similarly, the range of the lidar sensor 1 is determined when the measurement is performed under sunlight. Figure 4 is shown in .

[0052] Here, a noise level R_2 higher than the reference noise level R_0 is detected. In this case, the following position P_2 is calculated, that is, the reference target RZ should be located at this position when the signal-to-noise ratio SNR_2 that is the same as the reference signal-to-noise ratio SNR_2 should be obtained. Here, according to the following formula

[0053]

[0054] The intensity I_2 is obtained

[0055] I_2=R_2·SNR_0 (5)

[0056] In this case, the value of the intensity I_2 is a value that can be measured in the presence of a noise level R_2 when the signal-to-noise ratio SNR_2 is equal to the reference signal-to-noise ratio SNR_0 .

[0057] From the intensity I_2 of the lidar radiation and the known distance-dependent attenuation, the theoretical distance d_2 from the position P_2 is determined, at which the reference target RZ should be located in order to obtain the same signal-to-noise ratio SNR_2 = SNR_0.

[0058] A higher noise level R_2 means that reference target RZ can only be detected at shorter distances with the same signal-to-noise ratio as during the reference measurement. The distance d between distance d_0 and the target distance d_2 corresponds to the reduction in the range of lidar sensor 1, which occurs when reference noise level R_0 increases to noise level R_2. Therefore, the expected reduction in the range of lidar sensor 1 is determined by the increase in noise level R_2 relative to reference noise level R_0.

[0059] exist Figure 5 : shows a comparison of the intensity I of the lidar reflection LR determined as a function of the respective distance d_0 , d_1 , d_2 from the object O in a measurement performed in a reference measurement, a measurement performed at night and a measurement performed in sunlight.

[0060] Figure 6 shows the lidar sensor 1 in a first state, Figure 7 The lidar sensor is shown in a second state.

[0061] The laser radar sensor 1 includes a transmitter 2, a receiver 3, a reflector 4, a window 5 and an infrared light source 6 such as a power-controlled infrared light emitting diode.

[0062] Reference noise level R_0 includes the intrinsic noise component of LiDAR sensor 1. This intrinsic noise component can increase due to aging. This increase in the intrinsic noise component causes an increase in the noise level and reference noise level R_0. Because the signal-to-noise ratio is inversely proportional to the noise level, an increase in the noise level causes a decrease in the signal-to-noise ratio. When the signal-to-noise ratio decreases, the operating range of LiDAR sensor 1 also decreases. Therefore, the increase in the intrinsic noise component due to aging causes a decrease in the operating range of LiDAR sensor 1.

[0063] If a reference measurement was performed a long time ago and is to be performed again at the current moment, then under the same measurement conditions, new values ​​for the reference noise level R_0 and the reference signal-to-noise ratio and thus also for the range of the lidar sensor 1 appear due to the increase in the intrinsic noise component caused by aging.

[0064] In order to take into account aging-related changes in the range of lidar sensor 1 during the driving measurement, the stored initial values ​​of reference noise level R_0 and reference signal-to-noise ratio are updated to new values.

[0065] In principle, an update could be performed by repeating the reference measurement on an EOL inspection bench. However, this would require a visit to a repair shop.

[0066] To avoid this, one possible design implements the update via a computer. To this end, the increase in the intrinsic noise component, ΔRi, is first determined. The initial reference noise level R_0 and the initial reference signal-to-noise ratio SNR_0 are then corrected by the amount of change ΔRi that causes the intrinsic noise component. The result of this correction is an updated reference noise level R_0* and an updated reference signal-to-noise ratio SNR_0* according to the following equations:

[0067] R_0 ＊ =R_0+ΔRi (6)

[0068]

[0069] The infrared light S, shown as a dotted line, is a pulsed infrared laser beam generated by transmitter 2. The infrared light S is deflected through the environment to be scanned by means of a rotating reflector 4. The portion of the infrared light S reflected by an object O in the environment, the so-called infrared reflection R (shown as a solid line), is deflected by the rotating reflector toward a receiver 3, in particular a photodetector system. The distance d to the reflection location is then determined from the signal transit time.

[0070] Since the reflector 4 rotates, dark phases, so-called useless measurement times, are obtained, during which no infrared reflections R reach the receiver 3, e.g. Figure 7 As shown in detail.

[0071] During the useless measurement time of the lidar sensor 1, in which the receiver 3 is shielded from external radiation, the intrinsic noise portion is determined by transmitting a reference infrared signal RS to the receiver 3 during the useless measurement time with the aid of an infrared light source 6 arranged in a darkened area B within the lidar sensor 1 and determining the dark phase noise level.

[0072] During the dark phase, the receiver 3 receives only the reference infrared signal RS. During the reference measurement at the EOL inspection station, the noise level in the dark phase is determined and stored as the dark phase noise level. The dark phase noise level can also be the average value of the noise levels determined during multiple dark phases.

[0073] During normal operation of the vehicle or robot, the measurement is repeated regularly and the current dark phase noise level is determined. The difference between the current dark phase noise level and the stored dark phase noise level is then determined. The determined difference corresponds to the change ΔRi in the detected intrinsic noise component.

[0074] Reference Signs List

[0075] 1 LiDAR sensor

[0076] 2 Transmitters

[0077] 3 Receiver

[0078] 4 reflectors

[0079] 5 Windows

[0080] 6 Infrared light source

[0081] Area B

[0082] d distance

[0083] d_0 distance

[0084] d_1 distance

[0085] d_2 distance

[0086] I. Intensity

[0087] I_0 intensity

[0088] I_1 intensity

[0089] I_2 intensity

[0090] LR LiDAR Reflection

[0091] O Object

[0092] P_0 position

[0093] P_1 position

[0094] P_2 position

[0095] R Infrared reflectance

[0096] RS Reference Infrared Signal

[0097] RZ reference target

[0098] R_0 reference noise level

[0099] R_1 noise level

[0100] R_2 noise level

[0101] S Infrared

Claims

1. A method for determining a change in the range of a lidar sensor (1) for a vehicle or a robot, Its characteristics are: In a reference measurement using a reference target (RZ) located at a predetermined distance (d_0) from the lidar sensor (1), it is determined - a reference noise level (R_0) of infrared light (S) received by the laser radar sensor (1) and - the signal-to-noise ratio of the infrared radiation (S) reflected at the reference target (RZ) and received by the lidar sensor (1), During driving measurements of a vehicle or robot, - determining the current noise level (R_1, R_2) of the infrared radiation (S) received by means of the lidar sensor (1), - determining the value of the intensity (I_1, I_2) of the infrared radiation (S) by multiplying the determined current noise level (R_1, R_2) by the signal-to-noise ratio determined in the reference measurement, and - from the determined values ​​of the intensity (I_1, I_2) of the infrared radiation (S) and the known distance-dependent attenuation of the infrared radiation (S), the theoretical distance (d_1, d_2) to the position (P_1, P_2) at which the reference target (RZ) should be located when, at the current noise level (R_1, R_2), the same signal-to-noise ratio exists as in the reference measurement, and In the range change calculation, a difference between the predetermined distance (d_0) and the theoretical distance (d_1, d_2) is determined, wherein the difference corresponds to a change in the range of the lidar sensor (1) relative to its range during the reference measurement.

2. The method according to claim 1, wherein: The operating range is defined as the distance (d) at which the signal-to-noise ratio corresponds to a predetermined threshold.

3. The method according to claim 1 or 2, wherein: When determining the target distance (d_1, d_2) in the driving measurement, the distance-dependent attenuation of the lidar radiation is taken into account.

4. The method according to claim 1 or 2, wherein: The reference measurement is performed again after a specified time.

5. The method according to claim 1 or 2, wherein: When determining the reference noise level (R_0) in the reference measurement, variations in the intrinsic noise component of the lidar sensor (1) are taken into account.

6. The method according to claim 5, wherein: The variation of the intrinsic noise portion is taken into account by means of a computer in such a way that the reference noise level (R_0) and the signal-to-noise ratio at the reference target (RZ) are corrected by a corresponding portion resulting from the intrinsic noise portion.

7. The method according to claim 5, wherein: During the useless measurement time of the laser radar sensor (1) in which the receiver (3) of the laser radar sensor (1) is shielded from external radiation, the intrinsic noise portion is determined in the following manner: that is, during the useless measurement time, a reference infrared signal (RS) is transmitted to the receiver (3) by means of an infrared light source (6) arranged within the laser radar sensor (1) and a dark phase noise level is determined.

8. The method according to claim 7, wherein: The dark phase noise level is determined as an average of a plurality of dark phase noise levels.

9. The method according to claim 7 or 8, characterized in that: The dark phase noise level is determined during driving of the vehicle or robot.

10. The method according to claim 1 or 2, characterized in that: This reference measurement is performed at the end of vehicle or robot manufacturing as an end-of-line check.

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