Lidar system with interference source identification function

Abstract

To provide a lidar system with an interference source identification function.SOLUTION: A lidar system (1) with an interference source identification function specifically for a vehicle is described. An emitter unit (2) and a detector unit can detect a reflected light by scanning a surrounding environment. A light emitted from the emitter unit (2) is transmitted through a window (4) and is emitted from a housing. In addition, the reflected light from the surrounding environment is transmitted through the window (4) and is incident to the inside of the housing. An interference source inside the window is difficult to identify with prior arts. According to the present invention, at least one secondary detector (5) is mounted on an output coupling plane (6) of the window (4). The secondary detector (5) is configured so as to detect a stray light propagating in the inside of the window (4). The lidar system (1) comprises a control unit that is configured so as to evaluate the stray light (SL) detected by at least the one secondary detector (5), and to detect the interference source (7, 8) on the surface of or in the inside of the window (4).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a LiDAR system with interference source identification capability, particularly a LiDAR system for a vehicle, comprising an emitter unit including at least one light source, a detector unit including at least one primary detector configured to detect reflected light of at least one light beam emitted from the emitter unit to scan the surrounding environment and thereby detect surrounding objects, and a housing including a window portion that transmits light emitted from the emitter unit to the outside and transmits light reflected by the surrounding environment to the inside. [Background technology]

[0002] LiDAR (Light Detection and Ranging) systems operate by emitting light and detecting a portion of that light reflected by the surrounding environment. Typically, the emitter and detector units are protected from environmental influences by a window (made of glass or other optically high-quality material, with or without additional coatings). Interference sources on or within this window, such as scratches, dirt, or water droplets, can interfere with the optical path and degrade signal quality. In nature, this degradation cannot be easily distinguished from external factors that affect the signal-to-noise ratio (such as sunlight or surrounding objects with low reflectivity). The window, for example, is a glass or plastic sheet and is preferably substantially transparent at least to (near) infrared light.

[0003] The window is a refractive optical element through which the signal light passes twice: once as it is emitted into the surrounding environment and once as it returns to the detector unit. On a dry, smooth surface, nearly all photons are transmitted through the window or reflected back into the sensor. However, interference sources on the window surface or inside the window can locally reduce or block the window's transparency, severely interfering with the functioning of the lidar system.

[0004] Conventional techniques, for example, rely on software-based estimation of range reduction within the field of view, but this only allows for slow discrimination of clutter (with delays in the range of minutes or longer). However, highly automated vehicles at levels 4 and 5 require discrimination within a few seconds to respond quickly to changes in sensor usage.

[0005] U.S. Patent Application Publication No. 2018 / 0143298 discloses a lidar system that proposes such a software-based comparison solution. Multiple sensors are used to monitor a portion of a vehicle's environment. The outputs of the multiple sensors are compared to determine whether one of the sensors is obstructed. This determination can be made by comparing the output of one sensor with the output of another sensor, determining whether the output of a sensor is within a predetermined threshold, or comparing characteristics of the outputs of the multiple sensors with each other. If a sensor is determined to be obstructed, the system can send a command to a cleaning system to automatically remove the obstruction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 0143298 Summary of the Invention [Problem to be solved by the invention]

[0007] However, these solutions require a uniform environment or at least a stationary vehicle in order to directly compare measurements from multiple sensors and quickly identify interference sources. While driving, direct comparison is difficult due to the constantly changing environment, and identifying interference sources, for example by comparing averages of sensor data over time, typically requires long-term measurements. [Means for solving the problem]

[0008] According to the present invention, there is provided a LIDAR system of the type mentioned in the introduction, comprising at least one secondary detector attached to the out-coupling surface of the window, the secondary detector being configured to detect stray light propagating inside the window, and the LIDAR system including a control unit configured to evaluate the stray light detected by the at least one secondary detector to detect sources of interference on or inside the window. [Effects of the Invention]

[0009] Surface irregularities, water droplets, and dirt on the window can cause light to scatter in multiple directions or reflect in unintended directions. In the case of scratches (i.e., scattering within the optical material of the window) or water droplets (reflection at the water-air interface, resulting in back-reflection into the material over a wide range of angles), some of the light may have an angle relative to the (local) window surface that is smaller than the angle of total internal reflection. Stray light generated by such permanent interference sources (e.g., scratches or cracks) or temporary interference sources (e.g., water droplets or dirt) propagates from the interior of the window in a direction transverse to the primary transmission direction and reaches the outer edge of the window (after one or more total internal reflections). Here, the primary transmission direction refers to the direction (locally) perpendicular to the window surface through which the emitted signal light is approximately transmitted.

[0010] A portion of this light remains inside the window, which functions as a waveguide, and is emitted through the window at the out-coupling surface. A detector attached to the out-coupling surface of the window is configured to detect stray light propagating inside the window. That is, unlike the prior art, the secondary detector is configured to detect only light propagating inside the window substantially perpendicular to the main transmission direction. This allows the secondary detector to detect a greater proportion of stray light relative to useful light reflected back from the surrounding environment than if the secondary detector were positioned in the main transmission direction through the window. The control unit then evaluates the stray light detected by the secondary detector to detect interference sources on or inside the window.

[0011] The term "mounted on the out-coupling surface of the window" here means that the at least one secondary detector is preferably mounted on a side or edge of the window. However, the out-coupling surface may also be arranged outside the window with respect to the main transmission direction through the window and adjacent to the side or 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 light, then essentially only stray light reaches the secondary detector.

[0012] That is, the out-coupling surface itself may be located, for example, on a side edge of the window or on the outer periphery of the window. The out-coupling surface may be a roughened surface of the window. The secondary detector may be placed in direct contact with the window surface, or the light may be input through an intervening material with a refractive index matched to the window material.

[0013] The window may, for example, have a flat rectangular parallelepiped shape, with at least one secondary detector attached to the coupling-out surface, or with multiple secondary detectors attached to the coupling-out surfaces. However, the window may also have the shape of a thin cylindrical shell (see also FIG. 3), with at least one secondary detector preferably attached to the coupling-out surface extending perpendicular to the polar direction (parallel to the rz plane in cylindrical coordinates). The latter solution is preferred for lidar systems that cover a large angular range, for example using a rotating mirror. The first solution may be preferred if the lidar system only covers a limited angular range, for example as a more sensitive long-range detector interacting with other short-range detectors on the vehicle.

[0014] Stray light reaching the at least one secondary detector at the out-coupling surface of the window can have several sources. It can enter the window from the outside (sunlight, artificial light) or from the inside (light source of the LIDAR system). The term "stray light" is understood in this application to mean all light deflected / reflected / refracted by interference sources inside or on the surface of the window, i.e., light reflected by water droplets, for example. While external light can basically be used to detect interference sources, using an internal light source offers several advantages, which will be detailed in the following embodiments.

[0015] By using a secondary detector, the LIDAR system according to the present invention can more effectively and quickly detect interference sources even while the LIDAR system is in operation, i.e., while the vehicle equipped with the LIDAR system is moving. Furthermore, since stray light from internal light sources can be used primarily to identify interference sources, and reflected light from the surrounding environment or other external light is not required, identification of interference sources is less dependent on the surrounding environment than in conventional techniques.

[0016] The control unit can be configured to identify an interference source when a set, or later adaptively adjusted, minimum stray light intensity is reached, which has the advantage that, for example, very light dirt on the window surface, a temporary strong external light source, or a highly reflective surrounding object, each of which may (partially, temporarily) increase the stray light inside the window, will not be identified as a problematic interference source and will not, for example, trigger an error alarm.

[0017] In one embodiment, the lidar system includes at least partially steerable beam optics, the beam optics being at least configured to deflect at least one light beam emitted from the emitter unit and deflect light reflected by the environment toward the detector unit to scan the surrounding environment in multiple different directions, the at least one light beam passing through multiple different portions of the window as deflected by the beam optics, and the control unit being configured to calculate the location of an interference source on or within the window by correlating the instantaneous deflection position of the beam optics with the intensity of stray light detected by the secondary detector. In a lidar system, it is typically much more economical and less costly to swivel / rotate the lidar sensor itself or elements of the beam optics to scan around obstacles than to provide separate emitters and detectors for each angle of the lidar sensor. Here, scanning the surrounding environment is often performed using a time-of-flight (ToF) technique, which measures the time difference between the emission and detection of an optical signal to determine the distance to a surrounding object. In this embodiment, the control unit is configured to perform at least one-dimensional position determination of the interference source (along the direction of rotation of the optical beam). In order to determine the position of the interference source as accurately as possible, the control unit is preferably calibrated with respect to the state of the deflection position of the beam optics versus the expected intensity of the stray light, for example if an interference source is relatively close to the secondary detector, a higher intensity is expected at that source than if the same interference source were located further away, and therefore less stray light would reach the secondary detector, purely due to geometry and due to multiple reflections of the stray light.

[0018] Preferably, the lidar system includes at least two secondary detectors arranged on the out-coupling surface at different positions on the window, and the control unit is configured to calculate the location of an interference source on or inside the window from the difference in intensity of the stray light signals detected by the secondary detectors. When two or more secondary detectors are arranged at different positions along one or more out-coupling surfaces, the closer the interference source is to each secondary detector, the higher the stray light intensity is expected. The control unit may then be configured to calculate the (one-dimensional or two-dimensional) location of the interference source from the different intensity signals of the secondary detectors. However, when multiple interference sources (e.g., multiple raindrops) are simultaneously present on the window surface, it is quite difficult or even impossible to determine the location by comparing only the stray light intensity. However, when the lidar system has at least partially steerable beam optics, as in the above-described embodiment, the interference source can always be located at least one-dimensionally by correlation with the deflection angle of the light beam.

[0019] In a preferred embodiment, at least one light source emits light in a limited wavelength range, particularly a laser emitting light in the near-infrared range. A wavelength filter, particularly a bandpass filter, transmissive at least in the wavelength range of the light source is arranged between the output coupling surface and the at least one secondary detector. This embodiment reduces the influence of external light (e.g., sunlight, external light sources, etc.) that does not originate from interference sources on the window surface or inside the window, thereby enabling the LIDAR system to more accurately identify interference sources. The bandpass filter preferably has a half-width of 50 nm or less, more preferably 25 nm or less, and particularly preferably 15 nm or less, around its central wavelength (e.g., the wavelength of the light source). Near-infrared here can be understood to mean the wavelength range from 780 nm to 3 μm.

[0020] Two criteria can be used to distinguish between outdoor and indoor light. One is the wavelength of the light. Placing a bandpass filter with high transmittance at the wavelength of the lidar system in front of the secondary detector allows the light emitted by the lidar system to pass through. The other is timing (in the case of lidar systems based on time-of-flight measurements), which tells us when the emitted light pulse arrives at the window and how long it lasts.

[0021] Preferably, the at least one secondary detector is an avalanche photodiode, single-photon avalanche diode, gallium arsenide detector, or indium gallium arsenide detector. The high sensitivity of these detectors allows for easy identification of small interference sources with little stray light. Conventional photodiodes can also be used, particularly for low-cost applications, or when the light source is sufficiently intense to generate sufficient stray light from the interference source. Gallium arsenide and indium gallium arsenide detectors are particularly suitable, especially when the light source is a 1550 nm laser, which is more eye-safe than shorter-wavelength infrared lasers.

[0022] In one embodiment, the control unit includes a database configured to store multiple time-displaced measurements of the stray light measurement, and the control unit is configured to distinguish between transient and persistent sources of interference by comparing the multiple time-displaced measurements. For example, after a reboot of the lidar system, a new measurement of the interference source can be taken and compared with the last previously stored measurement to determine whether the previously determined source of interference has disappeared (e.g., because raindrops on the window have evaporated in the meantime).

[0023] Preferably, the lidar system includes a cleaning unit configured to clean at least the exterior of the window to remove transient interference sources. The cleaning unit may include, for example, a liquid nozzle capable of applying a cleaning liquid to the window. The cleaning unit may also include one or more mechanical cleaning means, such as wipers. The control unit may be configured to activate the cleaning unit when a predetermined amount of stray light (possibly dependent on the deflection angle of the beam optics) is detected by the secondary detector. Alternatively or additionally, the control unit may issue a warning signal to a user (e.g., a vehicle driver) so that the user can initiate cleaning using a button, voice command, or the like.

[0024] In one embodiment, the control unit is configured to perform interference source measurements after the cleaning unit has completed cleaning the window and compare the resulting measurements with at least the last previously stored measurements to distinguish between temporary and permanent interference sources, and if the interference source disappears after cleaning, the control unit can deduce that the interference source is temporary (e.g., dirt or water droplets).

[0025] In a further embodiment, the control unit is configured to, upon identification of a persistent source of interference, output an error message informing the user of the presence of the persistent source of interference. If the source of interference remains after cleaning, the control unit may initiate a new cleaning by the cleaning unit or may inform the user of possible window damage (e.g., via a visual and / or acoustic warning signal).

[0026] Preferably, the control unit is configured to calculate the size and / or type of interference source on or inside the window from the intensity of the detected stray light. The intensity of the stray light measured by the secondary detector depends not only on the distance from the interference source to 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 steerable 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 stray light. As mentioned above, if the lidar system has a cleaning unit that removes water from the surface, it can distinguish between water droplets and surface defects. Stray light remaining immediately after the window has dried is likely due to surface defects. Surface defects cause repeating signals in the secondary detector, while the effects of water / dirt change over time (e.g., droplets accumulate due to rain or splashes, droplets move on the surface, droplets dry, water / dirt is removed by the cleaning unit).

[0027] Advantageous refinements of the invention are set forth in the dependent claims and are described herein.

[0028] The embodiments of the present invention will now be described in detail with reference to the drawings and the following description. [Brief explanation of the drawings]

[0029] [Figure 1] 1 illustrates a first embodiment of a lidar system according to the present invention when there is no interference source on or inside the window. [Figure 2] 1A and 1B are diagrams illustrating a first embodiment in which there are interference sources on the surface of a window and inside the window. [Figure 3] FIG. 2 illustrates a second embodiment of a lidar system according to the present invention in the presence of an interference source inside a window. [Figure 4] FIG. 10 illustrates a third embodiment of a lidar system according to the present invention in the presence of interference sources on the surface of a window and inside the window. DETAILED DESCRIPTION OF THE INVENTION

[0030] 1 and 2 show a first embodiment of a LiDAR system 1 with interference source identification capability according to the present invention, particularly for a vehicle. The emitter unit 2 includes at least one light source (e.g., a laser). The LiDAR system 1 also includes a detector unit (not shown) including at least one primary detector configured to detect reflected light of at least one light beam 3 emitted from the emitter unit 2 to detect surrounding objects in order to scan the surrounding environment. The housing includes a window 4 that allows light emitted from the emitter unit to pass outward and light reflected by the surrounding area to pass inward.

[0031] The lidar system 1 includes at least one secondary detector 5 attached to the outcoupling surface (side edge) 6 of the window 4. The secondary detector 5 is configured to detect stray light SL propagating inside the window 4. Unlike FIG. 1, FIG. 2 shows interference sources 7 and 8 on the surface and inside the window 4, respectively, which generate stray light SL. Some of the stray light SL reaches the secondary detector 5, for example, by total internal reflection, as shown in the figure.

[0032] The lidar system 1 further includes a control unit (not shown) configured to evaluate the stray light SL detected by the at least one secondary detector 5 to detect interference sources 7, 8 on the surface of the window 4 or inside the window 4. The interference sources 7 are scratches or cracks on the surface of the window 4, while the interference sources 8 are water droplets, i.e., temporary interference sources.

[0033] It has been found that the at least one light source emits in a limited wavelength range, preferably a laser, for example emitting in the near infrared, which provides substantial advantages to the LIDAR system. Between the coupling-out surface (side edge) 6 and the at least one secondary detector 5, a wavelength filter 9, for example a bandpass filter, is arranged which is transparent at least in the wavelength range of the light source.

[0034] 1 and 2 show a planar window 4, which may be, for example, rectangular, although other planar shapes are also conceivable, such as a circular cylinder or an elliptical cylinder, and the secondary detectors 5 are each arranged along an exit face (short side edge) 6 (here parallel to the transmission direction of the light beam 3) so as to detect stray light propagating perpendicular to the transmission direction of the light beam 3.

[0035] 3 shows a plan view of a second embodiment of a lidar system 1 according to the present invention, in which corresponding components are given the same reference numerals. Here, the window 4 exemplarily has the shape of a semi-cylindrical shell, and the lidar system 1 scans a range of slightly less than 180° in the surrounding environment. However, larger or smaller angular ranges are also contemplated, and the window 4 may occupy a correspondingly larger or smaller polar angle range.

[0036] The lidar system 1 here includes a rotatable beam optics 10 configured to deflect at least one light beam 3 emitted from an emitter unit (not shown here, e.g., located in a plane below or above the illustrated rotating mirror of the beam optics 10) in multiple different directions to scan the surrounding environment and to deflect light reflected by the surrounding environment toward a detector unit. Due to the deflection in the beam optics 10, the at least one light beam 3 passes through multiple different portions of the window 4 at different times t=t1, t2, t3, t4, and t5. The control unit is configured to calculate the position of the interference source 7 on or within the window 4 by correlating the instantaneous deflection position in the beam optics 10 with the intensity of the stray light SL detected by the secondary detector 5. Therefore, around time t=t4, the secondary detector 5 detects an increase and subsequent decrease in the intensity of the stray light SL that cannot be measured at other times t=t1, t2, t3, and t5. From this, the control unit can deduce that at time t=t4, the interference source 7 is present in a part of the window 4 that corresponds to the rotation angle of the beam optics 10. Then, from the intensity of the stray light SL, the control unit can further calculate the size of the interference source (taking into account the dependence of the intensity of the stray light SL on the distance between the interference source 7 and the secondary detector 5).

[0037] 4 shows a third embodiment of a lidar system 1 according to the present invention in a plan view, similar to the first embodiment, with corresponding components having the same reference numerals. However, in contrast to FIGS. 1 and 2, the out-coupling surface 6 is now arranged outside the window 4 with respect to the main transmission direction through the window, adjacent to a side or side edge of the window 4. Again, the secondary detector 5 is (as shown) outside the region of the window 4 covered by the emitted light beam 3, so that substantially only stray light reaches the secondary detector 5, even though it is positioned with respect to the main transmission direction of the window 4.

[0038] Although the present invention has been illustrated and described in detail above by means of preferred embodiments, the present invention is not limited to the disclosed embodiments, and those skilled in the art may derive other modifications therefrom without departing from the scope of protection of the present invention.

Claims

1. A Lidar system (1) with interference source identification capability, particularly for vehicles, comprising: an emitter unit (2) including at least one light source; a detector unit including at least one primary detector configured to detect reflected light of at least one light beam (3) emitted from said emitter unit (2) to scan the surrounding environment and detect surrounding objects; a housing including one window (4) made of an optical material that transmits light emitted from the emitter unit (2) to the outside along a main transmission direction and transmits light reflected by the surrounding environment to the inside along the main transmission direction; Equipped with The lidar system (1) comprises at least one secondary detector (5) attached to an output coupling surface (6) of the window (4), the secondary detector (5) is configured to detect stray light propagating inside the window (4) by total internal reflection in a direction transverse to the main transmission direction from interference sources (7, 8) on the surface of or inside the window (4), the lidar system (1) has a control unit configured to evaluate stray light (SL) detected by the at least one secondary detector (5) to detect the interference source (7, 8) on the surface of or inside the window (4); A lidar system (1) characterized by:

2. Further comprising at least partially swivellable beam optics (10), the beam optics (10) is configured at least to deflect at least one light beam (3) emitted from the emitter unit (2) to scan the surrounding environment in a plurality of different directions and to deflect light reflected by the surrounding environment towards the detector unit; the at least one light beam (3) is transmitted through different portions of the window (4) by deflection of the beam optics (10); 2. The lidar system (1) of claim 1, wherein the control unit is configured to correlate the instantaneous deflection position of the beam optics (10) with the intensity of stray light (SL) detected by the secondary detector (5) to calculate the position of an interference source (7, 8) on the surface of or inside the window (4).

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

4. the at least one light source is a laser emitting in a limited wavelength range, in particular in the near infrared, 4. The lidar system (1) according to claim 1, wherein a wavelength filter (9), in particular a bandpass filter, which is transparent at least in the wavelength range of the light source, is arranged between the output coupling surface (6) and the at least one secondary detector (5).

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

6. the control unit includes a database configured to store a plurality of time-displaced measurement results of the stray light measurement; The control unit is configured to distinguish between temporary and permanent sources of interference (8) by comparing the results of multiple measurements offset in time. A lidar system (1) according to any one of claims 1 to 5.

7. 7. The lidar system (1) according to any one of claims 1 to 6, comprising a cleaning unit configured to clean at least the outside of the window (4) to remove transient interference sources (8).

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

9. 9. The lidar system (1) according to any one of claims 6 to 8, wherein the control unit is configured to, upon identification of a persistent source of interference (7), output an error message informing a user of the presence of the persistent source of interference (7).

10. 10. The lidar system (1) according to any one of claims 1 to 9, wherein the control unit is configured to calculate the size and / or type of the interference source (7, 8) on the surface of the window (4) or inside the window (4) from the intensity of the detected stray light.

Images