Lidar system with interferer identification

Abstract

A laser radar system (1) with disturbance source detection, in particular for a vehicle, is described. A transmitter unit (2) and a detector unit are provided, whereby reflected light can be detected for scanning the surroundings. Through a window (4), light emitted by the transmitter unit (2) exits the housing and light reflected by the surroundings enters the housing. In the prior art, it is only difficult to ascertain disturbances in the window. According to the invention, at least one secondary detector (5) is provided, which is mounted on a coupling-out surface (6) of the window (4). The secondary detector (5) is provided for detecting scattered light which propagates in the window (4). The laser radar system (1) comprises a control unit, which is provided for evaluating the scattered light (SL) detected by the at least one secondary detector (5) in order to detect disturbances (7, 8) on or in the window (4).

Description

Technical Field

[0001] This invention relates to a lidar system for interference source identification, particularly for vehicles. The lidar system includes a transmitter unit comprising at least one light source and a detector unit comprising at least one main detector configured to detect reflected light from at least one light beam emitted by the transmitter unit for scanning the surrounding environment to detect objects in the environment. The system also includes a housing with a window through which light emitted by the transmitter unit exits and light reflected from the surrounding environment enters. Background Technology

[0002] LiDAR (Light Detection and Ranging) system li ght d etection a nd r "Light detection and ranging" (LDR) works by emitting a beam of light and detecting the portion of that light reflected by the surrounding environment. Typically, the transmitter and detector units are protected from environmental influences by a window (glass or any other optically textured material, with or without an additional coating). Interference sources on or within the window (e.g., scratches, dirt, or water droplets) can interfere with the optical path and degrade signal quality. This degradation is inherently difficult to distinguish from external influences on the signal-to-noise ratio (e.g., sunlight or ambient objects with low reflectivity). The window can be, for example, a glass or plastic panel, preferably substantially transparent at least for (near) infrared light.

[0003] The window is an optical element that refracts light, through which the signal light passes twice: once when it is emitted into the surrounding environment, and again on its return path to the detector unit. On dry and smooth surfaces, essentially all photons either pass through the window or are reflected back into the sensor. However, interference sources on or inside the window can locally reduce or block its permeability, and thus may severely interfere with the function of the lidar system.

[0004] In existing technologies, software-based estimations, such as those involving reduced field of view, are used; however, such estimations only allow for slow identification of contaminants (with delays of several minutes or longer). However, for highly automated vehicles operating at Level 4 or 5, identification is required within seconds or faster to react quickly enough to changing sensor availability.

[0005] A lidar system is known from US 2018 / 0143298, which proposes a software-based comparison scheme. Multiple sensors are used to monitor the surrounding environment around a portion of a vehicle. The outputs of these sensors are compared to determine if one of them is obstructed. This determination can be made by comparing the output of one sensor with the output of another sensor, determining whether the sensor output is within a pre-given threshold, or by comparing the characteristics of the outputs of multiple sensors. If a sensor is determined to be obstructed, the system can send a command to a cleaning system to automatically remove the obstruction. However, this solution requires a standardized surrounding environment, or at least a stationary vehicle, to enable direct comparability of sensor measurements with rapid identification of interference sources. During driving operations, direct comparison becomes difficult due to the constantly changing surrounding environment, and long-term measurements are often required to identify interference sources, for example, by averaging sensor data over time. Summary of the Invention

[0006] According to the present invention, a lidar system of the type mentioned at the beginning is provided, comprising at least one secondary detector mounted on the coupling output surface of a window, wherein the secondary detector is configured to detect scattered light propagating within the window, and wherein the lidar system includes a control unit configured to analyze and process the scattered light detected by the at least one secondary detector in order to detect interference sources on or within the window.

[0007] Advantages of the present invention

[0008] Unevenness, water droplets, or dirt on the window surface can cause light to scatter in multiple directions or reflect in unexpected directions. In the case of scratches (i.e., scattering occurs within the window's optical material) and water droplets (reflection at the water / air interface can cause reflection back into the material over a wide angular range), a portion of the light may have an angle relative to the (local) window surface smaller than the angle of total internal reflection. A portion of the scattered light from such permanent sources of interference (e.g., scratches, cracks) or temporary sources (e.g., water droplets, dirt) thus propagates laterally within the window in the main transmission direction and (partially after one or more internal total internal reflections) reaches the outer edge of the window. The main transmission direction here refers to the (local) direction perpendicular to the window surface, in which the emitted signal light substantially passes through the window.

[0009] In this configuration, this portion of the light remains within the window—which thus acts as a waveguide to some extent—and exits from the window at the coupling output surface. A detector mounted on this coupling output surface of the window is configured to detect the scattered light propagating within the window. Therefore, compared to existing technologies, the secondary detector is arranged such that it detects only light propagating substantially perpendicular to the main transmission direction within the window. Consequently, compared to a secondary detector oriented in the main transmission direction of the window, the secondary detector is able to detect a higher proportion of the scattered light relative to the useful light reflected back from the surrounding environment. The control unit then analyzes and processes the scattered light detected by the secondary detector to detect interference sources on or within the window.

[0010] The term "mounted on the coupling output surface of the window" should be understood here as meaning that at least one secondary detector is preferably mounted on a side surface or side edge of the window. However, the coupling output surface may also be arranged on the outside of the window in a manner opposite to the main transmission direction of the window and adjacent to the side surface or side edge of the window. In the latter case, if the secondary detector is located outside the area of ​​the window covered by the emitted laser, then practically only scattered light reaches the secondary detector.

[0011] Therefore, the coupling output surface itself can be arranged, for example, on the side edge of the window or in the outer edge region of the window. The coupling output surface can be a rough surface of the window. The secondary detector can be arranged in direct contact with the window surface, or it can be optically coupled in via a material arranged therebetween that has a refractive index adapted to the window material.

[0012] The window can, for example, have a flat cuboid shape, wherein at least one secondary detector is mounted on the coupling output surface; alternatively, multiple secondary detectors are mounted on multiple coupling output surfaces. However, the window can also have the shape of a thin cylindrical shell segment (see also...). Figure 3 In this configuration, at least one secondary detector is preferably mounted on a coupling output surface extending perpendicular to the polar direction (parallel to the rz plane in cylindrical coordinates). For lidar systems covering a large angular range (e.g., using a rotating mirror), the latter solution is preferred. If the lidar system only covers a limited angular range (e.g., as a more sensitive long-range detector interacting with other near-field detectors on the vehicle), the first solution may be preferred.

[0013] The scattered light arriving at at least one secondary detector on the coupling output surface of the window can have multiple sources. This scattered light can be coupled into the window either externally (sunlight, artificial light) or internally (the light source of a lidar system). In this application, the term "scattered light" should be understood as describing all light that has been deflected / reflected / refracted by interference sources in or on the window (e.g., light reflected at water droplets). While external light can theoretically be used for detecting interference sources, using an internal light source offers several advantages, which are further elaborated in the following embodiments.

[0014] By using a secondary detector, the lidar system according to the present invention can detect interference sources more effectively and faster, even while the lidar system is in operation (i.e., while driving a vehicle equipped with a lidar system). Compared with the prior art, interference source identification is particularly less dependent on the surrounding environment because it can primarily or solely use scattered light from an internal light source, and there is no need to use light reflected from the surrounding environment or other external light for interference source identification.

[0015] The control unit can be configured such that interference sources are only identified at a pre-given or adaptively readjusted minimum intensity of scattered light. This has the advantage of not identifying, for example, very minor dirt on the window surface, temporary dense external light sources, or strongly reflective surrounding objects (which may respectively cause a (partially temporary) increase in scattered light in the window) as problematic interference sources and triggering, for example, a false alarm (Fehlalarm).

[0016] In one embodiment, the lidar system includes at least partially wobbly beam optics configured to deflect at least one light beam emitted by a transmitter unit for scanning the surrounding environment in at least one direction and to deflect light reflected from the surrounding environment to a detector unit. The beam optics, through deflection, transmit at least one light beam through different segments of a window. A control unit is configured to correlate the instantaneous deflection position of the beam optics with the intensity of scattered light detected by a secondary detector to calculate the location of interference sources on or within the window. In lidar systems, wobbling / rotating elements of the lidar sensor itself or its beam optics to scan the surrounding environment for obstacles is generally significantly more economical and less expensive than providing separate lidar sensor transmitters and detectors for each angular segment. Here, the surrounding environment scanning is often performed using a time-of-flight (ToF) method, in which the time difference between light signal emission and detection is measured to determine the distance to objects in the surrounding environment. In this embodiment, the control unit is at least configured to perform one-dimensional location determination of the interference source (along the oscillation direction of the light beam). For the most accurate possible location determination of the interference source, the control unit is preferably calibrated in terms of the ratio of the deflection position of the beam optics to the expected intensity of the scattered light. For example, if the interference source is relatively close to the secondary detector, in the case of a single interference source, a higher intensity is expected at a greater distance from the same interference source; therefore, purely geometrically and due to multiple reflections of the scattered light, less scattered light reaches one or more secondary detectors.

[0017] Preferably, the lidar system includes at least two secondary detectors arranged at different positions on the coupling output surface of the window. The control unit is configured to calculate the location of an interference source on or within the window based on the intensity differences of the scattered light signals detected by the secondary detectors. If two or more secondary detectors are arranged at different positions along one or more coupling output surfaces, the closer the interference source is to the corresponding secondary detector, the higher the expected intensity of the scattered light. The control unit can then be configured to calculate the (one-dimensional or desired two-dimensional) location of the interference source from the different intensity signals of the secondary detectors. However, if multiple interference sources (e.g., a large number of raindrops) are present on the window simultaneously, location determination by simply comparing scattered light intensities becomes significantly difficult and even impossible. However, if the lidar system has at least partially wobbly beam optics, as in the previous embodiments, at least one-dimensional location determination of the interference source can be achieved in any case through correlation with the deflection angle of the light beam.

[0018] In a preferred embodiment, at least one light source emits within a limited wavelength range, particularly a laser emitting in the near-infrared region. A wavelength filter, especially a bandpass filter, is arranged between the coupling output surface and at least one secondary detector. This wavelength filter is permeable at least within the wavelength range of the light source. This embodiment allows for reduction of the influence of external light (e.g., sunlight, external light sources) not caused by interference sources on or within the window, and thus makes the identification of interference sources in the lidar system more accurate. The bandpass filter preferably has a half-width around the center wavelength (e.g., around the wavelength of the light source) of less than 50 nm, more preferably less than 25 nm, and particularly preferably less than 15 nm. Here, near-infrared should be understood as a wavelength range from 780 nm to 3 μm.

[0019] To distinguish between external and internal light, two criteria can be used. One criterion is the wavelength of the light. A bandpass filter with high transmittance within the wavelength of the lidar system, preceding the secondary detector, primarily allows the light emitted by the lidar system to pass through. The other criterion is timing (in lidar systems, this timing is based on propagation time measurements), since it is known when the emitted light pulse arrives at the window and how long it lasts.

[0020] It is preferred if at least one secondary detector is an avalanche photodiode, a single-photon avalanche diode, a gallium arsenide detector, or a gallium indium arsenide detector. These detector types have high sensitivity and therefore make it easy to identify even small interference sources that produce a small amount of scattered light. However, alternatively, especially if cost is low and the light intensity of the light source is high enough, common photodiodes can also be used, which produce sufficient scattered light even through the interference source. If the light source is a laser at a wavelength of 1550 nm, a gallium arsenide detector or an indium arsenide detector is particularly suitable, as this laser offers better eye safety, especially compared to shorter wavelength infrared lasers.

[0021] In one implementation, the control unit includes a database configured to store multiple time-displaced measurement results of scattered light measurements. The control unit is configured to distinguish between temporary and permanent interference sources by comparing these time-displaced measurement results. This allows, for example, a new measurement of the interference source to be performed after a restart of the lidar system and compared with the previously stored last measurement to determine whether a previously identified potential interference source has disappeared (e.g., because raindrops on the window have evaporated during this time).

[0022] Preferably, the lidar system includes a cleaning unit disposed on at least one outer side of the window to remove temporary sources of interference. The cleaning unit may include a liquid nozzle that can, for example, apply a cleaning liquid to the window. The cleaning unit may include one or more mechanical cleaning devices, such as windshield wipers. The control unit may be configured to activate the cleaning unit when a predefined amount of scattered light (depending on the deflection angle of the beam optics, if necessary) is detected by the secondary detector. Alternatively or additionally, the control unit may also provide a warning signal to a user (e.g., the driver of the vehicle) so that the user can initiate cleaning (e.g., by pressing a button or through a voice command).

[0023] In one implementation, the control unit is configured to perform interference source measurement after window cleaning is completed by the cleaning unit, and to compare the obtained measurement results with at least the last previously stored measurement results to distinguish between temporary and permanent interference sources. If the interference source disappears after cleaning, the control unit can assume it is a temporary interference source (e.g., dirt or water droplets).

[0024] In another embodiment, the control unit is configured to output a fault report (Fehlermeldung) when a permanent source of interference is identified, which notifies the user of the presence of the permanent source of interference. If the source of interference still exists after cleaning, the control unit may either initiate a re-cleaning process via the cleaning unit or notify the user of potential damage to the window (e.g., via optical and / or acoustic warning signals).

[0025] Preferably, the control unit is configured to calculate the size and / or type of an interference source on or within the window from the intensity of the detected scattered light. The intensity of the scattered light measured by the secondary detector depends not only on the distance between the interference source and the secondary detector, but also on the size (and type) of the interference source. If the distance to the interference source can be calculated (if the lidar system has at least partially wobbly beam optics and / or includes multiple secondary detectors), the control unit can calculate the size (and (possibly) type) of the interference source from the intensity of the scattered light. If the lidar system has a cleaning unit, as already described, to remove water from the surface, water droplets can be distinguished from surface defects. Shortly after the window dries, the remaining scattered light is more likely due to surface defects. Surface defects result in repeatable signals at the secondary detector, while the effects of water / dirt change over time (e.g., small water droplets may accumulate due to rain or fog, small water droplets may move on the surface, small water droplets may dry, and water / dirt may be removed by the cleaning unit).

[0026] Advantageous extensions of the invention are described below. Attached Figure Description

[0027] Embodiments of the invention are further illustrated with reference to the accompanying drawings and the following description. The drawings show:

[0028] Figure 1 A first embodiment of the lidar system according to the present invention is shown, in which there are no interference sources on or in the window;

[0029] Figure 2 A first embodiment is shown, with interference sources on and inside the window;

[0030] Figure 3 A second embodiment of the lidar system according to the present invention is shown, in which an interference source is present in the window;

[0031] Figure 4 A third embodiment of the lidar system according to the invention is shown, with interference sources on and in the window. Detailed Implementation

[0032] Figure 1 and Figure 2 A first embodiment of a lidar system 1 according to the present invention is shown, which has interference source identification capabilities and is particularly suitable for vehicles. The transmitter unit 2 includes at least one light source (e.g., a laser). The lidar system 1 also includes a detector unit (not shown) comprising at least one main detector configured to detect reflected light from at least one light beam 3 emitted by the transmitter unit 2 for scanning the surrounding environment to detect objects in the environment. The housing includes a window 4 through which light emitted by the transmitter unit exits the housing, and light reflected from the surrounding environment enters the housing.

[0033] The lidar system 1 includes at least one secondary detector 5, which is mounted on the coupling output surface (side edge) 6 of the window 4. The secondary detector 5 is configured to detect scattered light SL propagating within the window 4. Figure 1 on the contrary, Figure 2 The diagram illustrates a scenario where interference sources 7 and 8 are present on or within window 4, each generating scattered light SL. As shown, a portion of this scattered light SL reaches the secondary detector 5, for example, via internal total internal reflection.

[0034] The lidar system 1 also includes a control unit (not shown) configured to analyze and process the scattered light SL detected by at least one secondary detector 5 in order to detect interference sources 7, 8 on or within the window 4. Interference source 7 relates to scratches or cracks on the surface of the window 4, while interference source 8 relates to water droplets, i.e., temporary interference sources.

[0035] At least one light source emits within a limited wavelength range, and preferably is a laser, for example, emitting in the near-infrared region, which has proven advantageous in practice for lidar systems. A wavelength filter 9 (e.g., a bandpass filter) is arranged between the coupling output surface (side edge) 6 and at least one secondary detector 5, which is permeable at least within the wavelength range of the light source.

[0036] Figure 1 and Figure 2 The planar window 4 is shown only by way of example. It may be a cuboid, but other planar shapes, such as cylinders or elliptical cylinders, may also be conceived. One or more secondary detectors 5 are arranged along the coupling output surface (short side edge) 6 (here, the side edge extends parallel to the direction of passage of the light beam 3), so that they can detect scattered light propagating perpendicular to the direction of passage of the light beam 3.

[0037] Figure 3 A second embodiment of the lidar system 1 according to the invention is shown in top view, wherein corresponding elements are indicated by the same reference numerals. Here, the window 4 exemplarily has the shape of a semi-cylindrical housing, so that the lidar system 1 scans the surrounding environment at a range of slightly less than 180°. However, a larger or smaller angular range is also conceivable, wherein the window 4 can then accommodate a correspondingly larger or smaller polar angle range.

[0038] The lidar system 1 includes a wobbly beam optics 10, which is configured to deflect at least one light beam 3 emitted by a transmitter unit (not shown here, and arranged, for example, in a plane below or above the rotating mirror of the beam optics 10) for scanning the surrounding environment in different directions, and to deflect light reflected from the surrounding environment to the detector unit. Through the deflection of the beam optics 10, at least one light beam 3 is transmitted through different segments of the window 4 at different time points t = t1, t2, t3, t4, t5. The control unit is configured to correlate the instantaneous deflection position of the beam optics 10 with the intensity of the scattered light SL detected by the secondary detector 5 in order to calculate the position of the interference source 7 on or within the window 4. Therefore, the secondary detector 5 will detect an increase and subsequent decrease in the intensity of the scattered light SL before and after time point t = t4, which is not measurable at the remaining time points t = t1, t2, t3, t5. Therefore, the control unit can infer that the interference source 7 exists in the following section of window 4: this section corresponds to the swing angle of the beam optics 10 at time point t = t4. Then, the control unit can also additionally calculate the size of the interference source from the intensity of the scattered light SL (taking into account the correlation between the intensity of the scattered light SL and the distance between the interference source 7 and the secondary detector 5).

[0039] Figure 4 A third embodiment of the lidar system 1 according to the invention, similar to the first embodiment, is shown in a top view, wherein corresponding elements are indicated by the same reference numerals. However, here, with Figure 1 and Figure 2 Conversely, the coupling output surface 6 is arranged on the outside of window 4 in a manner opposite to the main transmission direction of the window and adjacent to the side or side edge of window 4. Here, although the secondary detector is arranged in a manner opposite to the main transmission direction of window 4, in practice only the scattered light reaches the secondary detector 5, because the secondary detector (as indicated) is outside the area of ​​window 4 covered by the emitted light beam 3.

[0040] Although the invention has been further described and illustrated in detail with reference to preferred embodiments, the invention is not limited to the disclosed examples, and other variations can be derived by those skilled in the art without departing from the scope of protection of the invention.

Claims

1. A lidar system (1), the lidar system (1) having interference source identification, the lidar system comprising: The emitter unit (2) includes at least one light source. A detector unit including at least one main detector, the at least one main detector being configured to detect reflected light from at least one light beam (3) emitted by the transmitter unit (2) for scanning the surrounding environment in order to detect objects in the surrounding environment. The housing includes a window (4), through which light emitted by the transmitter unit (2) exits and light reflected from the surrounding environment enters the housing. Its features are, The lidar system (1) includes at least one secondary detector (5) mounted on the coupling output surface (6) of the window (4). The coupling output surface (6) is located on the side surface or side edge of the window (4), or arranged on the outside of the window (4) in a manner opposite to the main transmission direction of the window (4) and adjacent to the side surface or side edge of the window (4). The secondary detector (5) is configured to detect scattered light propagating within the window (4). The lidar system (1) includes a control unit configured to analyze and process the scattered light (SL) detected by the at least one secondary detector (5) in order to detect interference sources (7, 8) on or in the window (4). The control unit is configured to calculate the size and / or type of the interference source (7, 8) on or in the window (4) based on the intensity of the detected scattered light.

2. The lidar system (1) according to claim 1, wherein the lidar system includes at least a partially wobbly beam optics (10), the beam optics being configured to deflect at least one light beam (3) emitted by the transmitter unit (2) for scanning the surrounding environment in different directions, and to deflect light reflected from the surrounding environment to the detector unit. in, Through the deflection of the beam optics (10), the at least one light beam (3) is transmitted through different sections of the window (4). The control unit is configured to associate the instantaneous deflection position of the beam optics (10) with the intensity of the scattered light (SL) detected by the secondary detector (5) in order to calculate the position of the interference source (7, 8) on or in the window (4).

3. The lidar system (1) according to claim 1 or 2, wherein the lidar system comprises at least two secondary detectors (5) arranged at different positions on the window (4) on the coupling output surface (6). in, The control unit is configured to calculate the position of the interference source (7, 8) on or in the window (4) based on the difference in the scattered light signal detected by the secondary detector (5).

4. The lidar system (1) according to claim 1 or 2, wherein, The at least one light source emits within a limited wavelength range, wherein a wavelength filter (9) is arranged between the coupling output surface (6) and the at least one secondary detector (5), the wavelength filter being permeable at least within the wavelength range of the light source.

5. The lidar system (1) according to claim 1 or 2, wherein, At least one secondary detector (5) is an avalanche photodiode, a single-photon avalanche diode, a gallium arsenide detector, or a gallium arsenide indium detector.

6. The lidar system (1) according to claim 1 or 2, wherein, The control unit includes a database configured to store multiple time-displaced measurement results of scattered light measurements, wherein the control unit is configured to distinguish between temporary interference sources (8) and permanent interference sources (7) by comparing the time-displaced measurement results.

7. The lidar system (1) according to claim 6, the lidar system includes a cleaning unit configured to clean at least one outer side of the window (4) in order to remove temporary interference sources (8).

8. The lidar system (1) according to claim 7, wherein, The control unit is configured to perform interference source measurement after window cleaning is completed by the cleaning unit, and to compare the obtained measurement results with at least the last measurement results previously stored, in order to distinguish between temporary interference sources (8) and permanent interference sources (7).

9. The lidar system (1) according to any one of claims 6 to 8, wherein, The control unit is configured to output a fault report when a permanent interference source (7) is identified, and the fault report notifies the user of the existence of the permanent interference source (7).

10. The lidar system (1) according to claim 1, wherein, The lidar system (1) is used in vehicles.

11. The lidar system (1) according to claim 4, wherein, The at least one light source is a laser that emits in the near-infrared.

12. The lidar system (1) according to claim 4, wherein, The wavelength filter (9) is a bandpass filter.

Images