Automatic calibration of vehicle radar sensors

Abstract

A method for calibrating a radar sensor (34) of a vehicle (14), the method comprising: attaching the vehicle (14) to a transport device (16); moving the vehicle (14) along a route past a reflector (28) for radar waves (30) by means of the transport device; illuminating the reflector (28) with radar waves and receiving the reflected radar waves (36) with the radar sensor while the vehicle (14) moves along the route; determining a position and / or orientation of the radar sensor (34) relative to the reflector (28) multiple times from the reflected radar waves (36); and spatially calibrating the radar sensor (34) by determining a position and / or orientation of the radar sensor (34) relative to the vehicle (14) based on the determined position and orientation relative to the reflector (28).

Description

Technical Field

[0001] The invention relates to a method and a system for calibrating a radar sensor of a vehicle. Background Art

[0002] In vehicles, radar systems can be used as basic elements for environmental detection. Radar waves, i.e. electromagnetic waves (so-called primary signals), are emitted and reflected by objects. The reflected part of the radar waves (so-called secondary signals) is evaluated according to different criteria in order to determine information (e.g. the distance or size of an object).

[0003] For use in a vehicle, the radar system must be adjusted or calibrated. This can be done by manual fine-tuning, or the radar system can be used to perform an automatic calibration. The manual adjustment is done by aligning one or more radar sensors of the radar system exactly with the geometric axis of travel of the vehicle (e.g., the rear axle). This can be done with the aid of a laser beam that is projected onto a mirror of the sensor housing and irradiates a defined position on the measuring plate.

[0004] Certain radar systems can perform automatic calibration during driving. Here, the radar system automatically finds a reference point, based on which the geometrical axes of travel and the installation position can be identified and coordinated with each other. Summary of the invention

[0005] The object of the present invention is to automate and simplify the calibration of a radar sensor of a vehicle.

[0006] The above object is achieved by the technical solution according to the present invention. Other embodiments of the present invention are apparent from the description and the drawings.

[0007] One aspect of the invention relates to a method for calibrating a radar sensor of a vehicle. The radar sensor or radar head can be part of a radar system integrated into the vehicle, but the radar sensor and radar head can also be part of an external system, which is sometimes mechanically connected to the vehicle in order to control the vehicle autonomously, for example. The vehicle can be a car, a road vehicle (for example a car, a truck, a bus or a motorcycle) or a commercial vehicle. The method can be used for the automated operation of a vehicle, for example a shuttle for transporting people or goods in factories, airports, construction sites and exhibition venues, etc.

[0008] According to one embodiment of the present invention, the method comprises: fixing the vehicle on the transport device. The vehicle can be fixed on the transport device by fastening and / or placing on the transport device or driving on the transport device.

[0009] According to one embodiment of the invention, the method further comprises: moving the vehicle along a route passing by a reflector for radar waves by means of a transport device. Typically, the reflector can be implemented for reflecting radar waves. For example, the reflector can have a flat and / or metallic surface. The route along which the vehicle is guided can be a straight route. This can simplify the calculation of the calibration value (see below).

[0010] According to one embodiment of the present invention, the method further comprises: during the movement of the vehicle along the route, irradiating a reflector with radar waves and receiving the reflected radar waves with the radar sensor. The radar waves may be generated by the radar sensor and / or radiated into the surroundings, so that the radar waves are irradiated onto the reflector and also reflected by the reflector back to the radar sensor.

[0011] According to one embodiment of the invention, the method further comprises: during the transport of the vehicle along the route, the position and / or orientation of the radar sensor relative to the reflector is determined multiple times from the reflected radar waves. The distance of the radar sensor to the reflector and / or the direction to the reflector can be determined from the reflected radar waves. As a result, the relative position and / or orientation of the radar sensor to the reflector can be determined. During the transport of the vehicle along the route, multiple positions and / or orientations of the radar sensor relative to the reflector at different times or at different positions of the vehicle can be determined in this way.

[0012] According to one embodiment of the present invention, the method further comprises: spatially calibrating the radar sensor by determining the position and / or orientation of the radar sensor relative to the vehicle based on the determined position and / or orientation relative to the reflector. From the relative position and / or orientation of the radar sensor relative to the reflector at different times or at different positions of transportation along the route, it is possible to determine by geometric calculation how the radar sensor is positioned relative to the route. If the route is a straight line, the geometric determination can be particularly simple. Then, the position and / or orientation of the radar sensor relative to the vehicle can be determined from the position of the vehicle relative to the transport device. For example, the center axis can be arranged centered relative to the transport device and / or parallel to the transport route.

[0013] According to one embodiment of the invention, during the spatial calibration of the radar sensor, a lateral displacement of the radar sensor relative to the center axis of the vehicle is determined. This can be achieved, for example, by determining the vertical distance of the reflector from the transport path of the radar sensor. The lateral displacement can then be derived from the difference in distance from the center axis of the vehicle to the reflector (the center axis can be known by correspondingly fixing the vehicle on a transport device).

[0014] According to one specific embodiment of the invention, during the spatial calibration of the radar sensor, a deviation in the orientation of the radar sensor relative to the center axis of the vehicle is determined. From the determined orientation of the radar sensor relative to the reflector, it can be determined how the radar sensor is oriented relative to the center axis of the vehicle. The orientation can generally be defined by an angle relative to a predetermined direction, such as a transport direction, a direction defined by a transport route, and / or a center axis of the vehicle.

[0015] According to one embodiment of the invention, the vehicle is fixed to the transport device in such a way that the center axis of the vehicle points in a predetermined direction and / or the center axis is at a predetermined distance from the reflector. This can be achieved, for example, by markings on the transport device, predefined fixing points and / or by fixing the vehicle to the transport device in a defined manner (for example by means of rails).

[0016] According to one embodiment of the invention, the center axis of the vehicle is oriented relative to the transport device by means of a track. The vehicle can be driven into the track, which forces the vehicle to a defined position relative to the transport device. The track can guide the vehicle to or onto the transport device. For example, the vehicle can be centered on a conveyor belt.

[0017] According to one embodiment of the present invention, the method further comprises: fixing an external vehicle control system on the vehicle, the vehicle control system comprising a radar sensor; after the radar sensor has been calibrated and the vehicle has left the transport device, autonomously guiding the vehicle to the destination by the vehicle control system based on the measurements by the radar sensor. For example, the external vehicle control system can be fixed on the vehicle and electrically connected to the control system of the vehicle. For example, the vehicle can be equipped with an external vehicle control system at the end of a production line, so that the vehicle control system autonomously controls the vehicle to a loading point.

[0018] The method may be used to calibrate a system for automated driving of a vehicle on a bounded area, such as a factory area, for example.

[0019] According to one embodiment of the present invention, the vehicle control system is fixed on the vehicle during the transportation of the vehicle by means of the transport device. For example, after the vehicle has been driven onto the conveyor belt, the technician can fix the vehicle control system on the vehicle.

[0020] According to one embodiment of the invention, the transport device is a conveyor belt. For the purpose of fixing, the vehicle can be driven onto the conveyor belt. The conveyor belt can then transport the vehicle past the reflector, wherein at the same time the position of the radar sensor relative to the reflector is measured.

[0021] According to one embodiment of the present invention, based on the spatial calibration of the radar sensor, other sensors rigidly connected to the radar sensor are spatially calibrated. Corresponding calibration data for the other sensors can also be generated from the relative positions and / or orientations of the other sensors. The other sensors may include GPS sensors, laser radar sensors, single cameras, stereo cameras and / or ultrasonic sensors.

[0022] According to one embodiment of the present invention, the reflector is a trihedral corner reflector. A trihedral corner reflector may include three surfaces arranged perpendicular to each other. As is common in reflectors, these surfaces may be implemented for reflecting radar waves. These surfaces may have a metal surface.

[0023] Another aspect of the invention relates to a system for calibrating a radar sensor of a vehicle, wherein the system is implemented for performing the method as described herein. It should be understood that features of the method, as described above and as described below, may also be features of the device, and vice versa.

[0024] According to one embodiment of the invention, the system comprises an analysis unit for determining the position and / or orientation of the radar sensor relative to the reflector and for spatially calibrating the radar sensor. For example, the analysis unit can be installed in the vehicle or be part of an external vehicle control system.

[0025] According to one embodiment of the present invention, the system comprises a transport device for transporting the vehicle, such as a conveyor belt, a transport track or a transport slide.

[0026] According to one embodiment of the present invention, the system includes a reflector mounted near the transportation device, such as a trihedral corner reflector. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Figure 1 Schematically shows a site in which a calibration system according to an embodiment of the present invention can be used;

[0029] Figure 2 A schematically illustrated calibration system according to an embodiment of the present invention;

[0030] Figure 3 Schematically illustrating an external vehicle control system for the calibration system according to an embodiment of the present invention;

[0031] Figure 4Schematically showing a trihedral corner reflector used in the calibration system according to one embodiment of the present invention;

[0032] Figure 5 It shows how a lateral displacement of a radar sensor can be determined in a calibration method according to one specific embodiment of the present invention;

[0033] Figure 6 It is shown how the orientation of a radar sensor can be determined in a calibration method according to one specific embodiment of the present invention.

[0034] In principle, identical or similar parts are provided with the same reference symbols. DETAILED DESCRIPTION

[0035] Figure 1 A factory site 10 is schematically shown in which the calibration system and the calibration method can be used. The factory site 10 comprises a factory hall 12 in which vehicles 14 are manufactured and transported by means of a conveyor belt or transport device 16 to a driving area 18 through which the vehicles are driven to a transfer area 20 in which the vehicles are loaded into a loading station 22 (for example onto a truck or a train).

[0036] For so-called “end-of-line automation” (ELA), a newly manufactured vehicle 14 should already be capable of driving in the vehicle manufacturer's factory hall 12 automatically and therefore without passengers from the end of a conveyor belt 16 in the factory hall 12 to a transfer area 20 or a loading station 22. For automated driving, no onboard sensors should be used.

[0037] Therefore, in order to enable the vehicle 14 to be used for automated driving, an external vehicle control system 24 is attached to the vehicle 14 (e.g. while the vehicle is still on the conveyor belt 16), which has its own sensors (e.g. radar sensors) and is connected to the internal vehicle control system of the vehicle 14. After the vehicle 14 has been equipped with the external vehicle control system 24, it can be connected to a fleet management system and information about the destination (e.g. the handover area 20 or the loading station 22) can be received by the external vehicle control system.

[0038] Since the external vehicle control system 24 may be manually secured to the vehicle 14 by factory personnel, it may not be known exactly where the external vehicle control system 24 is mounted. For this reason, adjustment or calibration of the external vehicle control system 24 may be performed as described herein.

[0039] In this case, an automated calibration during operation of the vehicle 14 may be disadvantageous, since the external vehicle control system 24 should already be available without restriction at the end of the conveyor belt 16, and the calibration process is generally uneconomical. Manual calibration may also be disadvantageous, since the vehicle 14 is located in the last section on the moving conveyor belt, and static adjustments may be time-consuming and therefore also uneconomical.

[0040] It should be understood that the calibration system and the calibration method can also be used elsewhere, such as in a shuttle vehicle for passenger transportation as described above.

[0041] Figure 2 A calibration system 26 is schematically shown, which comprises a transport device 16 in the form of a conveyor belt and a reflector 28 for radar waves 30 which is fixed next to the transport device 16 . Figure 2 A calibration method is also shown.

[0042] In step S10, the vehicle 14 is fixed to the transport device 16 in such a way that the center axis 32 of the vehicle 14 points in a predetermined direction and / or the center axis 32 is at a predetermined distance from the reflector 28. For example, the center axis 32 of the vehicle 14 can be oriented relative to the transport device 16 by means of rails 33. It should be understood that in the case of a conveyor belt or a transport slide, the vehicle 14 can be fixed by simply placing it on the conveyor belt or the transport slide.

[0043] By positioning the vehicle 14 on the transport device 16 in a targeted manner, it can be ensured that the vehicle position on the transport device 16 is known. This vehicle position can be used to determine the relative position of the external vehicle control system 24 and the vehicle 14. For example, the rail 33 can be used as a contour that forces the tires of the vehicle 14 to enter a certain lane and / or as it is used in a car wash.

[0044] For example, in step S20 , when the vehicle 14 has been fixed on the transport device 16 , the external vehicle control system 24 is fixed on the vehicle 14 (eg, on the windshield) by a factory worker.

[0045] Figure 3 An external vehicle control system 24 is schematically shown, which can be fastened to the windshield, for example, by means of a suction cup.

[0046] The vehicle control system 24 includes a plurality of sensors, such as a radar sensor 34, a GPS sensor 35 and a camera 38. As mentioned above, the vehicle control system may also include other sensors, such as a lidar, a monocular camera, a stereo camera and / or an ultrasonic sensor. These sensors are connected to each other with the housing of the vehicle control system 24, in which an analysis unit 40 may also be included, which may perform calibration of the radar sensor 34 and / or implement autonomous control of the vehicle 14 based on the signals of the sensor. For this purpose, the external vehicle control system 24 may be connected to the internal vehicle control system 42 of the vehicle 14 by means of a cable.

[0047] The external vehicle control system 24 can, for example, take over GPS tracking, vehicle regulation, communication with a fleet management system, and / or safety functions during autonomous driving. To ensure safe driving on the plant site 10, other road users as well as persons and other objects on the roadway must be detected. The radar sensor 34 can, for example, be a component of a safety system of the external vehicle control system 24 that can take over these tasks.

[0048] Refer again Figure 2 At the end of step S12 , the external vehicle control system 24 is activated so that at this moment, the radar sensor emits electromagnetic waves or radar waves 30 .

[0049] Vehicle 14 is now moved by means of transport device 16 along a route that passes by reflector 28. Reflector 28 is illuminated by radar sensor 34 with radar waves 30, which results in reflected radar waves 36 that can be detected by radar sensor 34.

[0050] Figure 4 The reflector 28 is schematically shown, which is implemented as a trihedral corner reflector 28. As shown in the figure, the trihedral corner reflector 28 includes three faces 44 arranged perpendicular to each other, which causes the radar wave 30 incident in one direction to be reflected back in the same direction after two reflections. Through the strong reflection generated in this way, the external vehicle control system 24 can uniquely and clearly identify the trihedral corner reflector 28.

[0051] Refer again Figure 2 In step S14 , while the vehicle 14 is moved along the route by the conveying device 16 , the radar sensor 34 receives the radar wave 36 reflected by the reflector 28 .

[0052] In this case, evaluation unit 40 determines the position and / or orientation of radar sensor 34 relative to reflector 28 multiple times from reflected radar waves 36. From the properties of reflected radar waves 36, a uniquely definite relative position and orientation of radar sensor 34 relative to reflector 28 can be calculated.

[0053] If sufficient measurements have been performed and / or the end of the transport route is reached, evaluation unit 40 performs a spatial calibration of radar sensor 34. Evaluation unit 40 calculates the position and / or orientation of radar sensor 34 relative to vehicle 14 from a plurality of ascertained positions and orientations relative to reflector 28.

[0054] Since vehicle 14 itself is moved by means of transport device 16 or external vehicle control system 24 is moved together with vehicle 14 , a nearly continuous calculation of the position and orientation of radar sensor 34 or a calculation based on a large number of measurement points can be performed. This can lead to a robust estimate.

[0055] For each point in time at which the position and orientation of radar sensor 34 relative to reflector 28 have been determined, the position of the vehicle can also be determined (for example, using the speed of transport device 16). Thus, the position and / or orientation of radar sensor 34 relative to vehicle 14 can be calculated from the known position of reflector 28 in the vicinity of transport device 16, or the absolute position and orientation of radar sensor 34 can be determined.

[0056] Calibration can also be used for other sensors, such as sensors 35, 38, which are fixedly connected to radar sensor 34. This can be achieved, for example, if there is a rigid connection and a known distance and / or orientation between radar sensor 34 and the other sensors.

[0057] like Figure 5 and Figure 6 As shown, in step S12, the installation of the external vehicle control system 24 on the vehicle 14 by the factory staff may basically lead to two errors. Figure 5 As shown, the system may be mounted with a lateral offset. Figure 6 As shown, another error may occur when orienting the external vehicle control system 24.

[0058] Both installation errors can be compensated by the described method. For example, by the centering described in step S10, the position of the center axis 32 of the vehicle can be known, for example. Therefore, the deviation b can be calculated. In this case, when the radar sensor 34 is spatially calibrated, the lateral displacement b of the radar sensor 34 relative to the center axis 32 of the vehicle 14 can be determined.

[0059] This orientation error α (i.e., the angle between the viewing direction of radar sensor 34 and central axis 32) can be determined based on the direction of the back-radiated or reflected radar wave 36. In this case, when performing a spatial calibration of radar sensor 34, the deviation of the orientation of radar sensor 34 relative to central axis 32 of vehicle 14 can be determined.

[0060] The method allows for rapid provisioning of the external vehicle control system. Furthermore, automated calibration allows for different installation positions of the external vehicle control system, thereby increasing the availability of the external vehicle control system and making it easier for plant personnel to install the external vehicle control system. Continuous calculation of the radar position at different positions of the vehicle 14 transported by the transport device 16 allows for an exact determination of the position of the radar sensor, thereby, for example, achieving a higher quality than in the case of manual calibration.

[0061] The external vehicle control system 24 can then autonomously guide the vehicle 14 to the destination (eg, the handover area 20 or the loading station 22). This can be done based on measurements by the radar sensor 34 after the radar sensor 34 has been calibrated and the vehicle 14 has left the transport 16.

[0062] In summary, a method for calibrating a radar sensor 34 or an external vehicle control system 24 of a vehicle 14 that is fixed to a transport device or parked on a movable surface is described. With the aid of a trihedral corner reflector 28, the position and / or orientation of the radar sensor 34 can be determined from the reflected radar waves 36 of the radar sensor 34 and based on an algorithm implemented in the external vehicle control system 24. The method allows fully automated calibration of the radar sensor 34 and can make complex manual adjustments or calibrations superfluous.

[0063] It is additionally pointed out that "comprising" does not exclude the existence of other elements or steps, and "one" does not exclude the existence of multiple elements. It should also be pointed out that the features or steps described with reference to any one of the above embodiments can be used in combination with other features or steps of other above embodiments.

Claims

1. A method for calibrating a radar sensor (34) of a vehicle (14), the method comprising: securing the vehicle (14) to a transport device (16); Using the transport device (16), the vehicle (14) is moved along a path that passes by a reflector (28) for radar waves (30); While the vehicle (14) is moving along the route, the reflector (28) is illuminated by the radar wave (30), and the reflected radar wave (36) is received by the radar sensor; determining a position and / or an orientation of the radar sensor (34) relative to the reflector (28) multiple times from the reflected radar waves (36); wherein, for each point in time at which the position and orientation of the radar sensor (34) relative to the reflector (28) has been ascertained, the position of the vehicle (14) relative to the transport device (16) is ascertained, Based on the determined position and orientation relative to the reflector (28), the radar sensor (34) is spatially calibrated by determining the position and / or orientation of the radar sensor (34) relative to the vehicle (14) from the position of the vehicle (14) relative to the transport device (16), wherein the relative position and / or orientation of the radar sensor (34) relative to the reflector (28) at different times or at different positions of transportation along the route is determined by geometric calculations to determine how the radar sensor (34) is positioned relative to the route.

2. The method according to claim 1, in, When spatially calibrating the radar sensor (34), a lateral displacement of the radar sensor (34) relative to a center axis (32) of the vehicle (14) is determined; and / or In the process of spatially calibrating the radar sensor (34), a deviation of the orientation of the radar sensor (34) relative to a center axis (32) of the vehicle (14) is ascertained.

3. The method according to claim 1 or 2, in, The vehicle (14) is fastened to the transport device (16) in such a way that a center axis (32) of the vehicle (14) points in a predetermined direction and / or the center axis (32) is at a predetermined distance from the reflector (28).

4. The method according to any one of the preceding claims, in, A central axis (32) of the vehicle (14) is aligned relative to the transport device (16) by means of a rail (33).

5. The method according to any one of the preceding claims, further comprising: securing an external vehicle control system (24) to the vehicle (14), the external vehicle control system including the radar sensor; After the radar sensor (34) has been calibrated and the vehicle (14) has left the transport device (16), the vehicle (14) is autonomously guided to a destination (20, 22) by the external vehicle control system (24) based on measurements by the radar sensor (34).

6. The method according to claim 5, in, The vehicle control system (24) is fixed to the vehicle (14) while the vehicle (14) is being transported by means of the transport device (16).

7. The method according to any one of the preceding claims, in, The transport device (16) is a conveyor belt.

8. The method according to any one of the preceding claims, in, Based on the spatial calibration of the radar sensor (34), other sensors rigidly connected to the radar sensor (34) are spatially calibrated.

9. The method according to any one of the preceding claims, in, The reflector (28) is a trihedral corner reflector.

10. A system (26) for calibrating a radar sensor of a vehicle (14), wherein: The system (26) is implemented for executing the method according to any of the above claims, and the system (26) includes an analysis unit (40) for determining the position and / or orientation of the radar sensor (34) relative to the reflector (28) and for spatially calibrating the radar sensor (34).

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