Detection of functional limitations of a lidar sensor

Abstract

The invention relates to a method for detecting a functional limitation of a lidar sensor of a vehicle, wherein an intensity value of a backscattering from at least one scattering element arranged on the vehicle in the field of view of the lidar sensor is detected, wherein a functional limitation of the lidar sensor is determined based on a change in the intensity value of a backscattering and / or an undershoot of a specified threshold value of the intensity of a backscattering from the at least one scattering element.

Description

Fully automated or sensorless vehicles can handle many situations without driver intervention. They rely on fully functional sensors. In such a case, the sensor should independently identify the functional restriction and measures should be taken to further ensure traffic safety, however, in particular optical sensors such as lidar (laser scanner) are limited in their performance in the event of dirt, damage or poor weather conditions. In addition to automated cleaning, both takeover by an existing driver or a teleoperator is necessary. It can also be the transition to a safe operating state, e.g. an emergency stop. The basic problem currently consists in the secure detection of the restricted scope of functions by the sensor itself. Since almost all vehicles are automated only up to level 2, the vehicle operator is responsible here for monitoring the systems. However, with the continued spread of fully automated vehicles of stages 4 and 5, a clear and physically returnable methodology will be required.It is therefore an object of the invention to provide a simple and practicable methodology for reliably identifying the functional restriction. For this purpose, special scattering elements are used, which are mounted on the vehicle in the field of view of the lidar. The optical properties, especially the back scattering intensity, are known exactly and can be recorded by calibration processes under defined conditions (e.g. end-of-band test during production or in a workshop). Such materials, e.g. with retroreflective or specially absorbent properties, are simple to produce and are already used in the vehicle sector (trucks).The intensity value of the backscatter without disturbance I R,U is determined under defined conditions and permanently stored. If a fault occurs, for example due to contamination of the cover or due to environmental influences such as rain, snow or heavy fog, the current backscatter intensity I R,A will significantly reduce. If a threshold value dl R,S determined by systematic examinations is now undershot, this indicates a restricted mode of functioning of the sensor.When using highly reflective objects (retro-reflection), an overload of the channel may occur due to the short distance. This case should be avoided constructively or by using other materials. However, it is also possible for multiple detection to occur. Then, the target object is detected at twice or three times the distance. This effect can be exploited because multiple reflection reacts very strongly to contaminants.Alternatively, it is also possible to use objects with strong absorption. Then, the absence of the detection is an indication of a functional restriction occurring.Depending on the application, different activities are then possible after the recognition of a functional restriction:automatically cleaning the covertransferring control to operators in the vehicle / operator for remote interventionrisk minimizing maneuversA distinction between restriction of function caused by dirt and weather should be possible by the typical detection behavior. In the case of soiling, there is a permanent restriction, in the case of rainfall / snowfall only a temporary restriction which manifests itself in an oscillating behavior of the intensity. In the case of very heavy rain / snowfall, a reliable distinction is probably no longer possible. Here, however, the comparison with sensors in the vehicle (e.g. rain / light sensor) can enable reliable detection.In a simple embodiment of the method, it is not possible to distinguish whether the contamination is located on the sensor or on the reflector. Here, automatic cleaning mechanisms are to be established for both objects or the vehicle user is requested for manual cleaning of the soiled elements. However, structural measures can also be taken in order to avoid contamination of the reflector as far as possible.The use of defined scattering elements offers the advantage of the measurement traceability of the results. Other sensors, such as e.g. the rain / light sensor, are not suitable for this purpose on account of the measuring principle. Safety-critical situations can therefore not be managed automatically with such sensors. Such information can be provided by the invention, which can thus lead to an extension of the automated driving functions and an increase of the traffic safety.The invention also offers the advantage of making possible a simple check within the scope of the periodic main examination. Similar tests have already been carried out for retroreflective markings on commercial vehicles.It is also possible to use objects which are already present and have strong reflectance in the wavelength range of the excitation. Such objects are traffic signs or motor vehicle license plates. The methodology is less clear here, since the exact properties of the objects are not known. However, it can be derived from statistical investigations that certain weather conditions may have occurred. Particularly in the case of longer follow-up travel, the change in the measured intensity of the same license plate is only dependent on the environmental influences. Thus, a reliable detection of a wet roadway, for example, can be carried out. The brake path thus extending can thus be made available automatically to the distance control. Similar derivations are possible for traffic signs. Due to the only short detection time in each case, however, the relevance is less good compared to long-term license plate tracking. FIG. 1 : shows a possible arrangement of sensor and scattering elements in a typical vehicle constellation when the sensor system is installed on the roof, and FIG. 2 shows a basic measurement setup.List of reference characters1 Lidar 2 Scattering element 3 Visible area Front 4 Visible area Rear 5 Cover 6 Receiver 7 Transmitter 8 Reflected beam 9 Transmitted beam 10 Reflector

Claims

Method for detecting a functional restriction of a lidar sensor of a vehicle, wherein an intensity value of a back scattering is detected by at least one scattering element arranged on the vehicle in the field of view of the lidar sensor, wherein a functional restriction of the lidar sensor is determined on the basis of a change in the intensity value of a back scattering and / or a drop below a defined threshold value of the intensity of a back scattering by the at least one scattering element.

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