METHOD AND DEVICE FOR DETECTING CONTAMINATIONS ON A VIEWING WINDOW OF A LIDAR

Description

[0001] The invention relates to a method for detecting impurities on a viewing window of a lidar according to the preamble of claim 1.

[0002] The invention further relates to a device for detecting impurities on a viewing window of a lidar according to the preamble of claim 6.

[0003] Detecting contamination on a lidar's viewing window poses a particular challenge for automated vehicles, such as Level 3 or higher. Contamination leads to a degradation of sensor performance, thereby compromising the safety and availability of these systems. Lidars are active sensors and consist of a transmitter, such as one or more laser diodes, and a receiver, such as one or more avalanche photodiodes, especially single-photon avalanche diodes.

[0004] From DE 10 2017 222 618 A1 a method for detecting contamination in lidar systems is known, which comprises the following steps: Directed emission of electromagnetic radiation into the environment of the lidar system by a transmitting unit, wherein the electromagnetic radiation emitted by the transmitting unit is transmitted into the environment through an exit window which separates the lidar system from the environment at least in the direction of emission of the transmitting unit; detection of a portion of the electromagnetic radiation emitted by the transmitting unit that is backscattered into the lidar system from a surface of the exit window by a contamination sensor, wherein the contamination sensor is a single diode, a 1D array detector or a 2D array surface detector for the detection of electromagnetic radiation and / or the contamination sensor is integrated into the receiver unit; detection of contamination of the exit window by evaluating the detection of the contamination sensor.

[0005] From WO 2020 / 021914 A1, a method for detecting impurities in a distance measuring device is known. In this method, an exposure control unit controls the exposure of a light receiving unit caused by reflected light from a first distance; for light reflected from a second distance, the light receiving unit is not exposed. The reliability of the distance to an object determined by the distance measuring device is then determined by analyzing the light intensity data of the pixels of the light receiving unit.

[0006] The invention is based on the objective of providing a method and device for detecting impurities on a viewing window of a lidar that are improved compared to the prior art.

[0007] The problem is solved according to the invention by a method which has the features specified in claim 1 and by a device which has the features specified in claim 6.

[0008] Advantageous embodiments of the invention are the subject of the dependent claims.

[0009] A method is proposed for detecting contaminants on a viewing window of a lidar, for example a windshield, wherein A laser beam is emitted into a detection area by means of a transmitter of the lidar, and light present in the detection area is detected by means of a receiver of the lidar.

[0010] Furthermore, it is planned that An intensity image is generated as a grayscale image of laser reflection intensities from the light reflected and detected as a result of emitting the laser beam; a background light image is generated as a grayscale image of a background light from light detected without emitting a laser beam; the intensity image and the background light image are analyzed with regard to common features; and if a predetermined number of common features is not met, a contamination on the viewing window is concluded.

[0011] According to the invention, edges are detected in the intensity image and in the background light image using an edge detection algorithm.

[0012] Due to the active illumination from inside the sensor, the intensities of the reflections compared to the background light show different sensitivities to contamination of the viewing window, so that an assessment of the contamination is possible.

[0013] In one embodiment, the laser beam is emitted in pulses.

[0014] In one embodiment, the background light image is acquired shortly before the laser beam is emitted. A close temporal sequence for acquiring the background light image and the intensity image is particularly advantageous when using the method in a motor vehicle while driving, as this ensures that approximately the same scene is captured in both grayscale images.

[0015] In one embodiment, features of buildings and / or vehicles and / or windows are identified in the intensity image and the background image.

[0016] In one embodiment, edge distances and / or edge positions are determined as features based on detected edges.

[0017] According to one aspect of the present invention, a device for detecting contaminants on a viewing window of a lidar is proposed, comprising a data processing unit connected to the lidar and configured to perform the method described above.

[0018] Furthermore, a motor vehicle comprising such a device is proposed, in particular an automated vehicle, for example level 3 or higher.

[0019] Furthermore, the use of the method or device described above in a motor vehicle is proposed. Use in other autonomous platforms, such as trucks, buses, or robots that use LiDAR for navigation, is also possible.

[0020] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0021] This shows: Fig. 1 a schematic view of a grayscale image of the intensity of reflected laser radiation acquired by a lidar with a clean viewing window, Fig. 2 a schematic view of a grayscale image of background light acquired by the lidar with a clean viewing window, Fig. 3 a schematic view of a grayscale image of the intensity of reflected laser radiation acquired by the lidar with water droplets on the viewing window, and Fig. 4 a schematic view of a grayscale image of background light acquired by the lidar with water droplets on the viewing window.

[0022] Corresponding parts are marked with the same reference symbols in all figures.

[0023] The invention relates to a method for detecting contaminants on the viewing window of a lidar, for example, a windshield. A lidar is an active sensor and has at least one transmitter, for example, one or more laser diodes, and at least one receiver, for example, one or more avalanche photodiodes, in particular single-photon avalanche diodes. In the method according to the invention, the transmitter emits a pulsed laser beam, and the receiver detects reflections of the laser beam from objects within a detection range. With suitable receivers, in addition to distance information, further information such as the intensities of the reflections and the background light of the scene is also provided. This additional information exhibits varying sensitivities to contamination of the viewing window.The background light can be determined, for example, by having the receiver take a grayscale image without the transmitter emitting a laser beam, for example, shortly before the laser beam is emitted.

[0024] Figure 1 This is a schematic view of a grayscale image of the intensity of reflected laser radiation, hereinafter referred to as intensity image, captured by a lidar, with a clean viewing window. Figure 2 Figure 1 is a schematic view of a grayscale image of background light, hereinafter referred to as the background light image, acquired using lidar, with a clean viewing window. Visually, building B, vehicles V, and window W are recognizable in both images.

[0025] For a lidar system that provides this additional information, suitable features of the intensity image and the background light image are compared using image processing techniques. These features include edges, particularly road markings or the edges of windows in building walls. Edge detection algorithms known from the field of image processing can be used to extract edges from the background light image and the intensity image. Edge features, such as edge distances and positions, are then calculated for the two resulting edge images and subsequently compared. This comparison yields a measure of the similarity between the intensity image and the background light image. If the number of shared features exceeds a certain threshold, the images are interpreted as similar, and it is concluded that no contamination is present.

[0026] If few or no common features are found, as in the Figures 3 and 4 If the number of common features does not exceed the specified threshold, the images are interpreted as dissimilar and it is concluded that the viewing window is dirty.

[0027] Figure 3 is a schematic view of a grayscale image of the intensity of reflected laser radiation, hereinafter referred to as intensity image, captured by a lidar, on water droplets on the viewing window. Figure 4 This is a schematic view of a grayscale image of background light, hereinafter referred to as the background light image, captured by lidar, with water droplets on the viewing window. The background light image in Figure 4 The clearly identifiable building B, vehicles V and windows W are shown in the intensity image in Figure 3 difficult or impossible to recognize.

[0028] The threshold can be set specifically for each sensor. The method can be used for the entire detection range of the lidar or for a section of it for local contamination detection.

[0029] The proposed method for contamination detection may have limited effectiveness if there are few or no structures / edges within the lidar sensor's field of view, for example, when imaging a solid-colored wall or the sky. However, such scenarios are the exception in road traffic applications. A minimum number of features, particularly structures and / or edges, within the sensor's field of view, deemed necessary for contamination detection, can be defined on a sensor-specific basis. Reference symbol list

[0030] Building V Vehicle W Window

Claims

1. Method for detecting contaminants on a viewing window of a lidar, - a laser beam being emitted into an identification region by means of a transmitter of the lidar and - light present in the identification region being detected by means of a receiver of the lidar, - an intensity image being generated as a grayscale image of laser reflection intensities from the light reflected and detected as a result of the emission of the laser beam, - a background light image being generated as a grayscale image of background light from light detected without emission of a laser beam, - the intensity image and the background light image being analyzed with regard to common features and - if a predetermined number of common features is not reached, it being concluded that there is contamination on the viewing window, characterized in that edges in the intensity image and in the background light image are recognized by means of an edge detection algorithm.

2. Method according to claim 1, characterized in that the laser beam is emitted in pulses.

3. Method according to claim 1 or claim 2, characterized in that the background light image is determined shortly before the laser beam is emitted.

4. Method according to any of the preceding claims, characterized in that features of buildings (B) and / or vehicles (V) and / or windows (W) are determined in the intensity image and in the background light image.

5. Method according to claim 4, characterized in that edge distances and / or edge positions are determined as features based on recognized edges.

6. Apparatus for detecting contaminants on a viewing window of a lidar, comprising a data processing unit connected to the lidar and configured to carry out the method according to any of claims 1 to 5.

7. Motor vehicle comprising an apparatus according to claim 6.

8. Motor vehicle according to claim 7, configured as an automated vehicle.

9. Use of the method according to any of claims 1 to 5 or use of the apparatus according to claim 6 in a motor vehicle.