Calibrating a vehicle's environmental sensor unit using a reflector object subjected to the Doppler effect

Abstract

The invention relates to a method for calibrating an environment sensor unit (1) of a vehicle (3), comprising: operating (S1) an environment sensor unit (1); operating (S2) a reflector object (5) which virtually or physically reflects a signal emitted by the environment sensor unit (1) and thereby changes a frequency of the signal to simulate a Doppler effect; detecting (S3) the reflection generated at the reflector object (5); identifying (S4) the reflection based on the detected change in frequency; determining (S5) an orientation of the environment sensor unit (1) by means of the identified reflection; performing (S6) a calibration of the environment sensor unit (1).

Description

[0001] The invention relates to a method for calibrating and / or validating the orientation of an environmental sensor unit of a vehicle, and to a system for calibrating and / or validating the orientation of an environmental sensor unit of a vehicle.

[0002] Vehicles, such as passenger cars, equipped for automated driving typically feature a variety of environmental sensors to detect objects in the vehicle's vicinity and, if necessary, to monitor their condition. In this document, "automated driving" or automated vehicle control refers to driving with automated longitudinal and / or lateral guidance. Automated driving can, for example, involve extended periods of driving on the highway or time-limited driving during parking maneuvers. The term "automated driving" encompasses automated driving at any level of automation. Examples of automation levels include assisted, partially automated, conditionally automated, highly automated, and fully automated driving (each with an increasing degree of automation).The five automation levels mentioned above correspond to SAE Levels 1 to 5 of the SAE J3016 standard (SAE - Society of Automotive Engineering) as of April 30, 2021. In assisted driving (SAE Level 1), the system performs longitudinal or lateral control in certain driving situations. In partially automated driving (SAE Level 2), the system takes over longitudinal and lateral control in certain driving situations, but the driver must continuously monitor the system, as with assisted driving. In conditionally automated driving (SAE Level 3), the system takes over longitudinal and lateral control in certain driving situations without the driver needing to continuously monitor the system; however, the driver must be able to take over vehicle control within a certain timeframe if requested by the system.In highly automated driving (SAE Level 4), the system takes over vehicle control in certain driving situations, even if the driver does not respond to a request to intervene, thus eliminating the driver as a fallback option. In fully automated driving (SAE Level 5), the system can perform all aspects of the dynamic driving task under any road and environmental conditions that a human driver can also handle.

[0003] To achieve accurate and reliable operation of such environmental sensors, calibration is generally necessary, at least at the end of the vehicle's manufacturing process. Static calibration is a suitable method, in which the vehicle is positioned stationary relative to a calibration target and the calibration is performed. However, dynamic calibration methods are also known from the prior art. These are called dynamic because the vehicle moves along a calibration track, for example, on a factory site, on or near which one or more calibration targets are placed. Checking the orientation of an installed environmental sensor to ensure compliance with permissible angles can also be carried out at the end of the manufacturing process.

[0004] In this context, DE 10 2021 100 792 A1 relates to a method for calibrating a vehicle's environment sensor, comprising the following steps: determining uncalibrated measurement data using the environment sensor while maneuvering the vehicle on a predetermined calibration track, wherein the uncalibrated measurement data describe a reference object in the vehicle's environment; determining vehicle data describing the vehicle's current position and / or movement during the vehicle's maneuvering on the calibration track; determining correction data based on the uncalibrated measurement data and the vehicle data, and performing the calibration of the environment sensor based on the correction data; and determining the vehicle data using an external acquisition device located outside the vehicle, and transferring the determined vehicle data from the external acquisition device to the vehicle.

[0005] Driving the vehicle over a calibration track as described in DE 10 2021 100 792 A1 advantageously provides realistic boundary conditions for environmental perception; however, sensor calibration is generally also disadvantageously dependent on the vehicle's current speed on the calibration track and environmental conditions, such as contamination of the calibration target, wind, weather, temperature, sensor contamination, etc.; multiple reflections as well as reflections from unknown objects in the vehicle's vicinity further complicate calibration.

[0006] The object of the invention is to improve the calibration and / or validation of an environmental sensor of a vehicle.

[0007] The invention is defined by the features of the independent claims. Advantageous further developments and embodiments are the subject of the dependent claims.

[0008] A first aspect of the invention relates to a method for calibrating and / or validating an orientation of an environmental sensor unit of a vehicle, comprising the steps of: - Operating an environmental sensor unit mounted on the vehicle; - Operating a reflector object in the vicinity of the vehicle, which generates a simulated or physical reflection of a signal emitted by the environment sensor unit and thereby changes a frequency of the signal to replicate a Doppler effect that occurs when the distance between the vehicle and the reflector object changes, when a signal is emitted by the environment sensor unit; - Detection of the reflection simulated or physically generated at the reflector object by the environmental sensor unit; - Identifying the detected reflection as a reflection from the reflector object based on the detected change in the frequency of the reflected signal compared to an emitted signal; - Determining the orientation of the environment sensor unit by means of the identified reflection and based on a determined distance between the reflector object and the vehicle and based on a known height above ground of the reflector object; - Performing a calibration of the environmental sensor unit using the determined orientation and / or validating the determined orientation by comparison with a permissible orientation range.

[0009] The environmental sensor unit is located in or on the vehicle. The position of the environmental sensor unit relative to the vehicle body is static and known. However, the orientation of the environmental sensor unit determines where an object in the vehicle's vicinity appears in the sensor image. This orientation is described, for example, by Euler angles, specifically a pitch angle (also called elevation), a roll angle, and a yaw angle (also called azimuth). Not all three of these angles need to be considered when determining the orientation; in a simplified method, only the pitch angle and the roll angle can be considered, or only the pitch angle and the yaw angle, or only the pitch angle, or only the yaw angle.The basic procedure does not change the selection of the position angles, and the set of desired position angles is therefore simply referred to as "orientation" in the above and below.

[0010] Since the environmental sensor unit is an active sensor unit that actively emits a signal to detect and evaluate reflections of that signal in the vehicle's surroundings, its orientation is crucial insofar as it determines the main direction of radiation and the maximum amplitude of the emitted signal as it propagates into the environment. Therefore, this method is advantageously used to validate the orientation of the environmental sensor unit, i.e., to verify whether its installation position is sufficiently correct with respect to its angles, and / or to determine the orientation of the environmental sensor unit through software calibration and, if necessary, to compensate for any deviation from a nominal value.

[0011] The calibration or validation of the orientation itself is based on using pre-known data and comparing it with uncalibrated measurement data from the environmental sensor unit, which is determined by capturing the reflection of the reflector object. Since the distance between the vehicle and the reflector object is known at any given time, particularly through measurements by the environmental sensor unit itself (e.g., by measuring the time of flight of a transmitted signal and the captured reflection, or by using satellite-based positioning and a digital map), and especially since the position of the reflector object in the vicinity of the vehicle is fixed and known, this pre-known reference information can be used to compare it with the information measured by the environmental sensor unit and perform the calibration. Alternatively, it can be checked whether the installation position of the environmental sensor unit on the vehicle is sufficiently correct.These will be validated.

[0012] For example, the reference information contains the height of the reflector object above the ground. This means, in particular, that the pitch angle at which the reflector object appears in a sensor image from the environment sensor unit is known when the unit has a nominal orientation. A deviation from this pitch angle correlates with a different orientation of the environment sensor unit relative to the rest of the vehicle, which can be corrected mechanically and / or compensated for by calibrating software parameters.

[0013] To suppress—that is, filter out and discard—interfering reflections of a signal emitted by the environmental sensor unit in the vehicle's vicinity, the reflection, whether simulated or physical, is given a specific, recognizable characteristic so that it can be unambiguously identified by the environmental sensor unit as a reflection from the reflector object. This is advantageously achieved by imposing a frequency shift from the reflector object in the vehicle's environment to a signal from the environmental sensor unit. In the case of a physical reflection, this shift is also emitted by the environmental sensor unit; in the case of a simulated reflection, it may or may not be emitted. The resulting frequency shift should be within the narrowest possible frequency band to ensure the reliable assignment of this detected reflection to the corresponding reflector object.

[0014] The frequency change simulates the Doppler effect, which states that when two objects (sender and receiver) are moving relative to each other, a receiver perceives the signal emitted by the receiver at a different frequency than when both are stationary. As the objects move towards each other, the frequency increases; as they move away from each other, the frequency decreases. By replicating this effect with the reflector object, the vehicle, acting as the receiver, is given the impression that the reflector object is moving away from or towards the vehicle—in other words, that a relative velocity with a non-zero component exists between the vehicle and the reflector object.

[0015] This Doppler effect occurs naturally and inevitably during a natural reflection from an object moving towards the vehicle when a signal is emitted by the vehicle's environmental sensor unit. If it is simulated by a static reflector object, the reflection received by the environmental sensor unit is not an erroneous reflection; rather, such relative movement between the vehicle and the reflector object is simulated to allow the environmental sensor unit, acting as the receiver, to unambiguously identify the reflection. Advantageously, all other reflections from the vehicle's surroundings can thus be filtered out and discarded, and validation and calibration can be performed solely using the artificial reflection from the reflector object.It is also possible to consider only the virtual reflection and to discard a natural reflection without frequency change at the reflector object when a signal is emitted by the vehicle's environmental sensor unit.

[0016] This is particularly advantageous when the vehicle is moving along a test track and passes the reflector object. Using this method, such a reflector object can also be placed in a real, publicly accessible traffic situation, as the reflector object remains clearly identifiable. However, a static test can also be conducted in which the reflector object and the vehicle are stationary.

[0017] Operating the vehicle-mounted environmental sensor unit always results in the unit receiving a reflection, regardless of whether this reflection is simulated by a transmitter at the reflector object or occurs physically at the reflector element. If the reflection is physically generated at the reflector object, this requires the environmental sensor unit to actually transmit the signal. If the reflection is simulated at the reflector object, the environmental sensor unit may or may not actually transmit a signal; the simulated reflection is generated by a transmitter at the reflector object. Various methods can be used to generate the frequency change, which are implemented at the reflector object: According to an advantageous embodiment, when the environment sensor unit is operated, a signal is emitted by the environment sensor unit, which is physically reflected by the reflector object, wherein the change in the frequency of the reflected signal compared to the emitted signal is caused by a mechanically moved reflector element.

[0018] The mechanically moved reflector element is designed as a rotating reflector element, oriented such that a reflection of the signal emitted by the environmental sensor unit strikes a moving or trailing portion of the reflector element and is reflected there. This results in a physical reflection, and the Doppler effect occurs naturally because the reflection takes place at an object moving towards the vehicle. This allows for the advantageous construction of simple reflector elements and reduces costs. Furthermore, an amplifier can be arranged on the rotating reflector element to artificially amplify the amplitude of the reflections. This effectively increases the range between the vehicle and the reflector object, enabling calibration or validation of the environmental sensor unit based on sufficient signal strength measured at the sensor.

[0019] According to a further advantageous embodiment, a virtual reflection is generated by the reflector object, wherein the change in frequency is effected by means of a transmitter on the reflector object, which transmits a reflection with a changed frequency to the environment sensor unit, modeled on a signal emitted by the environment sensor unit.

[0020] Virtual reflection can be generated regardless of whether the environmental sensor unit actually emits a signal during operation. The environmental sensor unit can be in a calibration mode, receiving simulated reflected signals from the reflector object without actually transmitting a signal. Alternatively, the environmental sensor unit can emit a signal, which is then amplified as a reflection from the reflector object. In both cases, the reflection exhibits a frequency change compared to the frequency of a signal normally emitted by the environmental sensor unit. Simulated reflection at the reflector object requires a transmitter located on the reflector object, which artificially generates a reflection that can, however, be based on a real reflection.On the one hand, an artificial reflection signal can be emitted when a signal emitted by the environmental sensor unit is received. Through advantageously implemented phase alignment, a true-to-life reflection is thus generated. This reflection signal can also be amplified to any desired level to ensure sufficient amplitude and therefore intensity, thus guaranteeing a sufficient signal strength of the reflection as received by the environmental sensor unit.

[0021] According to another advantageous embodiment, the simulated reflection is emitted from the transmitter with increased amplitude compared to a physical reflection.

[0022] According to a further advantageous embodiment, several reflector objects are provided in the vicinity of the vehicle, which make different frequency changes at their respective reflections compared to a transmitted signal, wherein the reflections of the reflector objects are individually identified based on the respective frequency changes, so that reflections of the reflector objects are distinguishable, and wherein the calibration of the environment sensor unit is carried out using known positions of the reflector objects and known distances between the reflector objects and the vehicle.

[0023] Multiple reflector objects that are simultaneously within the detection range of the environmental sensor unit, or that are sequentially driven over by the vehicle while traveling a test route, advantageously allow for more comprehensive and reliable calibration and validation, as interfering secondary influences occurring at individual reflector objects can thus be averaged out.

[0024] The reflector objects, and especially their reflections, are individually identifiable, particularly if they each exhibit different frequency variations. Based on the intensity of the real or virtual Doppler effect measured in each case, a reflection can be assigned to a specific reflector object, and calibration or validation can be performed repeatedly accordingly.

[0025] According to a further advantageous embodiment, the calibration takes place only on the basis of one or more reflector objects and all other reflections in the vicinity of the vehicle of a signal emitted by the environment sensor unit are discarded.

[0026] This allows interfering reflections to be specifically ignored, and only the reflection for which reference information is available to be considered in order to successfully perform calibration or validation when a signal is emitted by the environmental sensor unit that is reflected in the environment.

[0027] According to another advantageous embodiment, the vehicle is driven while the environment sensor unit is being operated and while the reflector object is being operated.

[0028] The vehicle can be driven on a test track or in a publicly accessible traffic area. The test track offers the advantage that the positioning and design of the reflector objects can be carried out with greater freedom.

[0029] According to another advantageous embodiment, the environmental sensor unit is a radar sensor unit. If, in this case, the reflector object has a transmitter, this sensor is a so-called "radar target generator".

[0030] According to another advantageous embodiment, the environmental sensor unit is an ultrasonic sensor unit or a lidar sensor unit.

[0031] Additional active environmental sensor units can be used, i.e., environmental sensor units that each emit a signal with the aim of detecting and evaluating a reflection of the signal in the environment.

[0032] Another aspect of the invention relates to a system for calibrating an environmental sensor unit of a vehicle, comprising a vehicle with the environmental sensor unit arranged on the vehicle, wherein the environmental sensor unit is configured to send a signal into the environment in order to detect a reflection of the signal from the environment; a reflector object for the environment of the vehicle, which is configured to simulate or physically generate a reflection and thereby change a frequency of the reflection to replicate a Doppler effect that occurs when the distance of the vehicle to the reflector object changes; wherein the environmental sensor unit is configured to detect the reflection and to identify the reflection as a reflection from the reflector object based on the detected change in the frequency of the reflected signal compared to a transmitted signal;and comprising a calibration unit designed to determine the orientation of the environment sensor unit by means of the identified reflection and on the basis of a determined distance between the reflector object and the vehicle, as well as to perform a calibration of the environment sensor unit by means of the determined orientation and / or to validate the determined orientation by comparison with a permissible orientation range.

[0033] Advantages and preferred further developments of the proposed system result from an analogous and substantive transfer of the above statements made in connection with the proposed procedure.

[0034] Further advantages, features and details will become apparent from the following description, in which - possibly with reference to the drawing - at least one embodiment is described in detail.

[0035] They show: Fig. 1: An exemplary situation for the application of a system and a method for calibrating and / or validating an orientation of an environmental sensor unit according to an embodiment of the invention. Fig. 2: Schematic representation of a method for calibrating and / or validating the orientation of an environmental sensor unit according to an embodiment of the invention.

[0036] The representations in the figures are schematic and not to scale.

[0037] Fig. Figure 1 shows a situation in which a system for calibrating an environmental sensor unit 1 of a vehicle 3 is used, which employs a procedure as described in Fig. Figure 2 outlines the process. A vehicle 3, designed as a passenger car, has a radar environmental sensor unit 1. This unit emits a radar signal into the environment to detect reflections of the signal from the surroundings. The vehicle 3 is driven automatically or by a test driver along a dedicated track, along which several reflector objects 5 are arranged. While driving along the test track, each of the reflector objects 5 enters the detection range of the vehicle 3's environmental sensor unit 1 at a specific time and disappears from it after a certain speed-dependent period. The reflector objects 5 are statically positioned in the environment, particularly along the test track, and the distance between the vehicle 3 and each of the reflector objects 5 can be measured by the environmental sensor unit 1 using time-of-flight measurement.Thus, for each of the reflector objects 5 in the vehicle, it is known when and where it should appear in a sensor image of the environment sensor unit 1. The reflector objects 5 are designed to emit an artificial reflection at a specific frequency with very low error tolerance, which replaces a real reflection at the respective reflector object 5 of a signal emitted by the environment sensor unit 1. The frequency change simulates a Doppler effect that occurs when the vehicle 3 approaches or moves away from a particular reflector object 5, with the change in frequency generating an opposite increment for approach and distance. In this simplified case, only the approach of the vehicle 3 to a particular reflector object 5 is considered, due to the forward-facing detection range of the environment sensor unit 1.By using the modified frequency of the signal emitted by a transmitter at a respective reflector object 5, a so-called "radar target generator," a reflection detected by the environmental sensor unit 1, regardless of whether it is real or simulated at the reflector object 5, can be uniquely identified and assigned to that reflector object 5. Since reference information is available for each reflector object 5, unlike other arbitrary objects in the vicinity of the vehicle 3 that also reflect the signal emitted by the environmental sensor unit 1—in particular, the distance between the vehicle 3 and the respective reflector object 5—this reflection can be considered in isolation, and a reliable calibration or validation of the orientation of the environmental sensor unit 1 can be performed.

[0038] Fig.Figure 2 shows a method for calibrating and / or validating the orientation of an environmental sensor unit 1 of a vehicle 3, comprising the steps: - Operating S1 of an environment sensor unit 1 arranged on the vehicle 3, wherein the environment sensor unit 1 sends a signal into the environment to detect a reflection of the signal from the environment; - Operating S2 of a reflector object 5 in the vicinity of the vehicle 3, which simulates or physically reflects the signal emitted by the environment sensor unit 1 and thereby changes a frequency of the signal to replicate a Doppler effect that occurs when the distance of the vehicle 3 to the reflector object 5 changes and causes a frequency change between the signal emitted by the environment sensor unit 1 and its reflection at the reflector object 5; - Detection S3 of the reflection simulated or physically generated at the reflector object 5 by the environmental sensor unit 1; - Identify S4 of the reflection with changed frequency as a reflection of the reflector object 5 by the environment sensor unit 1 due to the detected change in the frequency of the reflected signal compared to the emitted signal; - Determine S5 an orientation of the environment sensor unit 1 by means of the identified reflection and on the basis of a known position of the reflector object 5 and a known distance between the reflector object 5 and the vehicle 3; - Performing S6 a calibration of the environmental sensor unit 1 using the determined orientation and / or validating the determined orientation by comparison with a permissible orientation range.

[0039] Although the invention has been further illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned as examples are truly only examples and are not to be understood in any way as limiting, for example, the scope of protection, the possible applications, or the configuration of the invention. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 100 792 A1 [0004, 0005]

Claims

[1] Method for calibrating and / or validating an orientation of an environment sensor unit (1) of a vehicle (3), comprising the steps: - Operation (S1) of an environmental sensor unit (1) arranged on the vehicle (3); - Operating (S2) a reflector object (5) in the vicinity of the vehicle (3) which generates a simulated or physical reflection of a signal emitted by the environment sensor unit (1) and thereby changes a frequency of the signal to replicate a Doppler effect that occurs when the distance of the vehicle (3) to the reflector object (5) changes when a signal is emitted by the environment sensor unit (1); - Detection (S3) of the reflection simulated or physically generated at the reflector object (5) by the environmental sensor unit (1); - Identifying (S4) the detected reflection as a reflection of the reflector object (5) based on the detected change in the frequency of the reflected signal compared to an emitted signal; - Determining (S5) an orientation of the environment sensor unit (1) by means of the identified reflection and on the basis of a determined distance between the reflector object (5) and the vehicle (3) and on the basis of a known height above ground of the reflector object (5); - Performing (S6) a calibration of the environment sensor unit (1) using the determined orientation and / or validating the determined orientation by comparison with an acceptable orientation range. [2] Method according to claim 1, wherein when operating the environment sensor unit (5) a signal is emitted by the environment sensor unit (1) which is physically reflected by the reflector object (5), wherein the change in the frequency of the reflected signal compared to the emitted signal is caused by a mechanically moved reflector element. [3] Method according to claim 1, wherein a simulated reflection is generated by the reflector object (5), wherein the change in frequency is effected by means of a transmitter on the reflector object (5) which transmits a reflection with a changed frequency to the environment sensor unit (1) that is modeled on a signal emitted by the environment sensor unit (1). [4] Method according to claim 3, wherein the simulated reflection is emitted from the transmitter with amplitude amplification compared to a physical reflection. [5] Method according to one of the preceding claims, wherein several reflector objects (5) are provided in the vicinity of the vehicle (3) which make different frequency changes at the respective reflection compared to a signal emitted by the environment sensor unit (1), wherein the reflections of the reflector objects (5) are individually identified on the basis of the respective frequency changes, so that reflections of the reflector objects (5) are distinguishable, and wherein the calibration of the environment sensor unit (1) is carried out using known positions of the reflector objects (5) and known distances between the reflector objects (5) and the vehicle (3). [6] Method according to one of the preceding claims, wherein the calibration takes place only on the basis of physical or simulated reflections of one or more reflector objects (5) and all other reflections in the vicinity of the vehicle (3) of a signal emitted by the environment sensor unit (1) are discarded. [7] Method according to one of the preceding claims, wherein the vehicle (3) is driven during the operation of the environment sensor unit (1) and during the operation of the reflector object (5). [8] Method according to any one of claims 1 to 7, wherein the environment sensor unit (1) is a radar sensor unit. [9] Method according to any one of claims 1 to 7, wherein the environmental sensor unit (1) is an ultrasonic sensor unit or a lidar sensor unit. [10] System for calibrating an environment sensor unit (1) of a vehicle (3), comprising a vehicle (3) with the environment sensor unit (1) arranged on the vehicle (3), wherein the environment sensor unit (1) is configured to send a signal into the environment in order to detect a reflection of the signal from the environment; a reflector object (5) for the environment of the vehicle (3), which is configured to generate a simulated or physical reflection and thereby change a frequency of the reflection to replicate a Doppler effect that occurs when the distance of the vehicle (3) to the reflector object (5) changes; wherein the environment sensor unit (1) is configured to detect the reflection generated at the reflector object (5) and to identify the reflection as a reflection of the reflector object (5) based on the detected change in the frequency of the reflected signal compared to a signal emitted by the environment sensor unit (1);and comprising a calibration unit designed to determine the orientation of the environment sensor unit (1) using the identified reflection and based on a determined distance between the reflector object (5) and the vehicle (3), as well as to perform a calibration of the environment sensor unit (1) using the determined orientation and / or to validate the determined orientation by comparison with a permissible orientation range.

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