Optical receiving unit for a lidar system, lidar system for a vehicle, and method for operating a lidar system

Abstract

The invention relates to an optical receiving unit (14) for a lidar system (10) for a vehicle (100). The optical receiving unit (14) has: a receiving sensor (16) which is designed to receive received light (22) on a receiving path; and a lens element (24) which is arranged in the receiving path, an optical receiving plane (17) of the receiving sensor (16) being inclined relative to an optical plane (25) of the lens element (24) in such way that any multiple reflection of the received light (22) between the receiving sensor (16) and the lens element (24) strikes the receiving plane (17) outside the receiving path. The invention also relates to: a lidar system (10) comprising such an optical receiving unit (14); a vehicle (100) comprising such a lidar system (10); and a method for operating a lidar system (10) in the vehicle (100).

Description

[0001] OPTICAL RECEPTION UNIT FOR A LIDAR SYSTEM, LIDAR SYSTEM FOR A VEHICLE AND METHOD FOR OPERATING A LIDAR SYSTEM

[0002] Technical area

[0003] The application relates to an optical receiving unit for a lidar system for a vehicle, a lidar system for a vehicle and a method for operating such a lidar system in a vehicle.

[0004] background

[0005] Modern vehicles (cars, vans, trucks, motorcycles, etc.) are equipped with a multitude of sensor systems whose data is used to inform the driver and / or provide it to driver assistance systems. These sensor systems monitor the vehicle's surroundings and other road users. Based on the recorded data, a model of the vehicle's environment can be created, and changes in this environment can be responded to.

[0006] An important sensor principle for detecting the environment, e.g., of vehicles, is Lidar technology (Light Detection and Ranging). A Lidar system has an optical transmitter unit and an optical receiver unit. The transmitter unit can emit transmitted light, which can be pulsed. In a Lidar system, laser beams in the ultraviolet, visible, or infrared range can be used. The receiver unit can receive the transmitted light as received light after it has been reflected from an object in a detection area in the vicinity of the Lidar system. The received light can be evaluated using the transmitted signal by a processing unit of the Lidar system using a time-of-flight method, and the spatial position and distance of the objects from which the reflection occurred can be determined. It is also possible to determine a relative speed.In this context, reflection or reflected light refers to any light that is returned and is intended to include, in particular, light that is returned by scattering or absorption / emission. Time-of-Flight (TOF) systems can be used, in particular, to determine the distance to objects.

[0007] The lidar system can be designed as a system that operates with light flashes, a so-called flash lidar. In this case, an area of ​​the environment can be illuminated with a flash of light, and the signals reflected from any objects can be recorded by the receiver.

[0008] Scanning lidar systems emit light beams that move in a scanning direction. Point scanners illuminate areas of the surrounding area point by point. Line scanners illuminate areas of the surrounding area line by line.

[0009] Receiving sensors of lidar systems can have multiple receiving elements, so-called pixels, and the pixels can be configured to receive received light from different receiving angles.

[0010] Lidar systems are constantly being developed for various functions, such as capturing environmental information in the near and far range of vehicles such as passenger cars or commercial vehicles. Lidar systems can also serve as sensor systems for driver assistance systems, particularly assistance systems for autonomous or semi-autonomous vehicle control. They can be used, in particular, to detect obstacles and / or other road users in the front, rear, or blind spot area of ​​a vehicle.

[0011] DE102020130492A1 describes a lidar system for a vehicle. The receiver includes one or more light intensity sensors; and one or more lens assemblies configured with respect to the one or more light intensity sensors such that at least one sensor plane of the one or more light intensity sensors is tilted to form a non-zero angle with at least one equivalent lens plane of the one or more lens assemblies, wherein the sensor focal plane is translated to align with the main light illumination direction of the lidar system's light source and is consistent with the vehicle's direction of travel. Overview

[0012] An optical receiving unit for a vehicle lidar system comprises a receiving sensor configured to receive received light along a receiving path. The receiving unit further comprises a lens element arranged in the receiving path. An optical receiving plane of the receiving sensor is inclined relative to an optical plane of the lens element such that a multiple reflection of the received light between the receiving sensor and the lens element impinges on the receiving plane outside the receiving path.

[0013] The receiving sensor is configured to convert incident light into an electrical signal. The lens element comprises optical elements such as one or more lenses and / or one or more optical filters, in particular an optical bandpass filter. The optical plane is the (virtual) plane in which the receiving sensor is arranged. It extends beyond the receiving sensor. It can also be referred to as the image plane.

[0014] The received light is received by the optical receiving unit on the receiving path. The received light is directed, for example, by the lens element on the receiving path, e.g., onto the receiving sensor, and then focused on the receiving sensor.

[0015] The described optical receiving unit can reduce blooming. Blooming is also referred to as optical crosstalk. Blooming can produce undesirable optical effects caused by reflections between the receiving sensor and the lens element, particularly a bandpass filter. The described inclination can direct the reflections out of the receiving path, thus reducing blooming, such as local overexposure, within the receiving path.

[0016] The inclination is selected such that the reflections generated by the receiving sensor itself are not reflected back into the receiving path via the lens element, but intersect the image plane outside the receiving path. In one embodiment, the receiving plane of the receiving sensor is inclined relative to the optical plane of the lens element such that a multiple reflection of the received light between the receiving sensor and the lens element strikes the receiving plane outside the receiving sensor. This can cause the reflections generated by the receiving sensor itself to not be reflected back onto the receiving sensor, but to intersect the image plane outside the receiving sensor.

[0017] However, this can be difficult to achieve with planar receiving sensors, as the spatial extent of the receiving sensor can lead to unfeasible tilt angles. In embodiments, the receiving sensor therefore has multiple receiving elements that can be activated to receive received light, with the receiving path for receiving received light having at least one activated receiving element. The receiving elements, also called pixels, can be configured to receive received light from different receiving angles.

[0018] Activating a receiving element can, for example, involve switching the receiving element from a non-receiving state to a receiving state, e.g., by changing a bias voltage. Deactivation can accordingly occur through targeted control and / or, after a certain period of time, through automatic shutdown, for example.

[0019] In embodiments, the receiving elements are arranged in rows and can be assigned to the receiving path line by line. This can correspond to a line-by-line assignment to a corresponding, e.g., line-like, area in the detection range of the lidar system. The assignment to the receiving path through the corresponding activation of the receiving elements can correspond to a targeted illumination of the corresponding, e.g., line-like, area in the detection range by transmitted light from the lidar system.

[0020] In this case, the lines can run longitudinally, particularly parallel, to the receiving plane and / or the optical plane of the lens element. This allows two advantages to be combined: a focal plane of the lidar system that is inclined relative to the ground in front of the vehicle and a deflection of multiple reflections onto non-activated receiving elements of the receiving sensor.

[0021] In one embodiment of the optical receiving unit, the receiving plane is inclined relative to the optical plane of the lens element such that multiple reflections of the received light between the receiving sensor and the lens element impinge on non-activated receiving elements of the receiving sensor. The optical plane of the lens element corresponds to its lens plane, with the lens plane forming the plane through the center of the lens element, perpendicular to the optical axis.

[0022] The inclination of the image plane relative to the lens element preferably follows the Scheimpflug principle. This means that a focal plane of the lidar system is also inclined relative to the lens element. The receiving plane, the optical plane of the lens element, and a focal plane of the receiving unit intersect in a straight line.

[0023] A focal plane is the plane in the object space of the lens element whose points are sharply imaged by the lens element as points on the image plane, i.e. the reception plane, in the image space of the lens element.

[0024] The application further relates to a lidar system with one of the optical receiver units described above. The object space lies within the lidar system's detection range.

[0025] The lidar system can also include an optical transmission unit with a transmission light source for emitting transmitted light and a transmission lens element. The transmission lens element is arranged in a transmission path of the transmitted light. A transmission plane, which runs vertically to the transmission direction of the transmitted light, is inclined relative to an optical plane of the transmission lens element. The optical plane of the transmission lens element corresponds to its lens plane, with the lens plane forming the plane through the center of the transmission lens element, perpendicular to the optical axis. The inclination of the optical plane of the transmission lens element relative to the transmission plane can also correspond to the Scheimpflug principle.The optical receiving unit and the optical transmitting unit of such a lidar system can be designed such that in the receiving unit the angle of inclination between the receiving plane and the optical plane of the lens element essentially corresponds to the angle of inclination between the direction of the transmitted light and the optical plane of the transmitted lens element in the transmitting unit.

[0026] The transmitting plane and the receiving plane can run longitudinally, in particular parallel, to each other, so that the lens element and the transmitting lens element can have the same inclination.

[0027] The lidar system can further comprise a processing unit configured to activate the receiving elements of the receiving sensor in the receiving path depending on the transmitted light. This allows the receiving elements located in the transmitted light path to be specifically activated, based on the angle of inclination between the receiving sensor and the lens element. Receiving elements outside the transmitted light path can be deactivated or left deactivated if necessary, so that multiple reflections hit non-activated receiving elements, i.e., outside the receiving path, the receiving plane.

[0028] In embodiments, the computing unit of the lidar system can activate the receiving elements row by row.

[0029] A vehicle may have one or more of the lidar systems described above. The lidar system(s) may be coupled to one or more of the vehicle's control systems. The control systems may be connected to, for example, the propulsion system, the steering system, the braking system, and may control various vehicle functions, such as lane keeping, collision warning, and others, using information received from the lidar system.

[0030] In a method for operating such a lidar system in the vehicle, the processing unit activates the receiving elements in the receiving path depending on the transmitted light.

[0031] In the following, embodiments of this application are further explained and described with reference to the figures.

[0032] Fig. 1 schematically shows a vehicle with Lidar system,

[0033] Fig. 2 schematically shows an inclination from the receiving plane to the optical plane of the lens element and

[0034] Fig. 3 shows a schematic representation of a receiving sensor with sensor elements.

[0035] The same reference numerals are used throughout the figures to refer to identical or similar elements. Representations in the figures may not be to scale.

[0036] Flower description

[0037] Figure 1 schematically illustrates a vehicle 100, for example, a passenger car, with a lidar system 10. The lidar system 10 has an optical transmitting device 12 and an optical receiving device 14 with a receiving sensor 16. The optical transmitting device 12 has a transmitted light source 19, e.g., a laser or LED, which generates the transmitted light 20. The lidar system shown has a transmitting optical path, also called the transmit path, and a receiving optical path, also called the receive path. The transmitted light 20 propagates along the transmit path. The received light 22 propagates along the receive path.

[0038] The transmitting lens element 21 is located in the transmission path and is designed to influence the optical properties, e.g., its direction, of the transmitted light 20 after it has been emitted by the transmitted light source 19. For this purpose, the transmitting lens element 21 can, for example, comprise one or more lenses and / or optical filters, in particular a bandpass filter.

[0039] Before being received by the receiving sensor 16, the received light 22 is influenced in its optical properties by the lens element 24, which is located in the receiving path, and is focused, for example, onto the receiving sensor 16. For this purpose, the lens element 24 can, for example, comprise one or more lenses and / or optical filters.

[0040] A controller can monitor and control the transmission of transmitted light 20 and the reception of received light 22 in the receiving unit 14. The controller can evaluate transmitted light 20 and received light 22 for the detection, distance determination, and / or speed determination of an object 0 located in the detection area 30. The controller can be arranged, for example, on a computing unit 18 with a processor and memory of the lidar system 10 and can be implemented there, for example, as software.

[0041] In the illustrated example, the lidar system 10 is arranged in a front area of ​​the vehicle 100. The detection area 30 is located in front of the front area of ​​the vehicle 100. This allows an area in the direction of travel in front of the vehicle 100 to be monitored in the illustrated example. It is also possible to arrange the lidar system 10 in other areas of the vehicle 100, for example, in the rear area and / or in the side areas. It is also possible to arrange multiple lidar systems 10 on the vehicle 100, in particular in corner areas of the vehicle 100.

[0042] In a scanning lidar system 10, the detection area 30 is successively scanned by the transmitted light 20, e.g., point-by-point, line-by-line, or region-by-region. In a flash lidar, the detection area 30 can be illuminated simultaneously in whole or in part.

[0043] With the lidar system 10, stationary or moving objects O, in particular vehicles, people, animals, plants, obstacles, road surface irregularities, in particular potholes or stones, road markings, traffic signs, open spaces, in particular parking spaces, precipitation or the like, can be detected, i.e. recorded, in the detection area 30. By evaluating the transmitted light 20 and the received light 22 by the control of the computing unit 18, the distance to the object O and / or the direction in which the object O is located can be determined, for example. Alternatively or additionally, a relative speed to the object O and / or properties of the object O can be determined. Information about properties of the object O can be obtained, for example, by determining the phase shift of the received light 22 compared to the transmitted light 20. To determine the phase shift, for example,Modulation methods such as AMCW (AMCW: Amplitude Modulated Continuous Wave) or FMCW (FMCW: Frequency Modulated Continuous Wave) are used.

[0044] The lidar system 10 can, for example, also be configured as a TOF system for distance determination. A TOF system uses the time of light travel to determine a distance. It can thus be used as a distance measuring device for measuring the distance to an object 0. A configuration as a direct TOF system (dTOF) or an indirect TOF system (iTOF) is conceivable. A direct TOF system uses a direct measurement of the time of light travel to determine the distance to an object 0. An indirect TOF system uses a measure derived from the time of light travel, e.g., a phase difference between transmitted light 20 and received light 22, to determine the distance.

[0045] Reception paths via which the receiving sensor 16 can receive received light 22 can also be referred to as the FOV (field of view) of the receiving sensor. By actively controlling the receiving sensor 16, the FOV of the receiving sensor 16 can be changed, e.g., by specifically activating and / or deactivating receiving elements Px of the receiving sensor 16. The activation of the receiving elements Px can be performed, for example, by the processing unit 18.

[0046] The optical transmission unit 12 is configured to adapt the emitted transmitted light 20 to the field of view of the receiving sensor 16. This means, for example, that the transmitted light 20 is radiated into those areas of the detection area 30 that can currently be received by the receiving sensor 16. Such control of the field of view of the receiving sensor 16 and the corresponding adaptation of the transmitted light 20 can be performed, for example, by the computing unit 18.

[0047] The totality of the reception paths via which the receiving sensor 16 can receive received light 22 can correspond to the detection range 30 of the lidar system 10 and is also referred to as the FOV (field of view) of the lidar system 10. Figure 2 schematically shows the tilt of the optical plane 25 of the lens element 24 relative to the optical reception plane 17 of the receiving sensor 16. The optical plane 25 of the lens element 24 is inclined by an angle 38 relative to the optical reception plane. The tilt occurs, for example, in the vertical direction as viewed from the vehicle 100, so that the plane of focus 32, also called the focal plane, of the lidar system 10 is inclined toward the road as viewed from the vehicle 100. Figure 2 shows further planes of focus 34, 36 of the lidar system 10.

[0048] The tilting by angle 38 follows the Scheimpflug principle. This principle states that the optical plane 25 of the lens element 24 and the sensor plane 17 intersect at a straight line 28 with the plane from which a sharp image is possible on the receiving sensor 16. This applies, for example, to the focal planes 32, 34, 36 shown. The focal planes 32, 34, 36 are located at the focus of the optical arrangement and are therefore also called focal planes.

[0049] Such an inclination of the focal planes 32, 34, 36 is very well suited to an application in the vehicle 100, where ground conditions can play a significant role. Furthermore, a sharper image can be achieved at close range, which can be advantageous for near-field lidar systems, for example.

[0050] Due to the proposed inclination by angle 38, received light 22, which is reflected by the receiving sensor 16 and reflected back by the receiving lens 24 toward the receiving plane 17, strikes the receiving plane 17 at a different location than received light 22 on the receiving path, which strikes the receiving sensor 16 directly. The inclination angle 38 can now be selected, for example, such that the multiply reflected light no longer strikes the receiving sensor 16 at all. This is possible, for example, with receiving sensors 16 with a small spatial extent.

[0051] With flat receiving sensors 16, it can be difficult to select the inclination with the angle 38 so large that multiply reflected light no longer hits the receiving sensor 16.

[0052] For this purpose, a further embodiment is proposed, which is explained in more detail below with reference to Figure 3. The light-sensitive receiving elements Px of the receiving sensor 16 can in particular be designed as CMOS chips. Further embodiments of the receiving elements Px are conceivable, for example as avalanche photodiodes (APDs) or as so-called single photon avalanche diodes (SPADs). The receiving elements Px can be controlled with regard to their readiness to receive. In particular, the readiness to receive can be specifically switched on and, if necessary, switched off again, for example by the computing unit 18. This corresponds to activation and, if necessary, deactivation. Independent deactivation of the pixels a certain time after activation is also conceivable.

[0053] Individual receiving elements Px of the receiving sensor 16, also called pixels, can have different FOVs. For example, individual receiving elements Px can receive received light 22 from different directions.

[0054] The activation of the receiving elements Px of the receiving sensor 16 occurs in sections. The scanning, comprising the capture of light and its conversion into electrical signals, by the receiving sensor 16 thus occurs in sections corresponding to the respectively activated receiving elements Px. Activated receiving elements Px are represented in Figure 3 by checkered hatching.

[0055] Figure 3 shows an embodiment in which the activated sections are aligned horizontally line by line. The activated receiving elements Px are each located in the currently activated receiving path. The angle 38 is selected such that reflections at the receiving sensor 16 and back reflections at the lens element 24 outside the activated section, vertically offset in the specific embodiment, strike the receiving sensor 16. This non-activated section is not ready to receive and therefore does not produce any disruptive effects. The vertical deviation depends on the inclination of the lens element 24 in the direction of the horizontal, see Figure 2. The vertical inclination therefore has two advantageous effects on the lidar system 10. Firstly, an inclination of the focal planes 32, 34, 36 relative to the ground, and secondly, a deflection of the multiple reflections into the vertical.

[0056] The angle of inclination 38 between the receiving plane 17 and the lens element 24 is selected such that a reflection at the receiving sensor 16 of the received light 22 arriving on the receiving path is reflected back at the lens element 24 from one (activated) receiving element 42 into another (deactivated) receiving element 40. This is illustrated in Figure 3 with a solid line for the activated receiving element 42 and a dashed line for the inactive receiving element 40. It is also possible to activate the pixels of the horizontal sections individually or in groups in a horizontal direction.

[0057] Blooming artifacts can be prevented or at least reduced by the proposed optical receiving unit 14. Optical crosstalk in the form of blooming due to reflections from the receiving sensor 16 and the lens element 24 can be reduced. Falsification of measured values ​​caused by this optical crosstalk, e.g., by falsification of phase information in indirect measurements such as FMCW and AMCW, can be reduced, or false positive results can be better avoided. It is also possible to better avoid false positive results in direct TOF measurements.

[0058] In addition to the inclination of the lens element 24, it can be provided to incline the transmitting lens element 21 relative to the transmitted light source 19 by an angle, preferably by an angle equal to the angle 38. Both angles can be selected such that they satisfy the Scheimpflug principle. The inclination of the transmitting lens element 21 is determined relative to a transmission plane that is perpendicular to the transmitted light 20 at the transmitted light source 19. The transmission plane can be selected such that it runs parallel to the receiving plane 17.

Claims

CLAIMS 1. An optical receiving unit (14) for a lidar system (10) for a vehicle (100), comprising a receiving sensor (16) which is designed to receive received light (22) on a receiving path, and a lens element (24) which is arranged in the receiving path, wherein an optical receiving plane (17) of the receiving sensor (16) is inclined with respect to an optical plane (25) of the lens element (24) such that a multiple reflection of the received light (22) between the receiving sensor (16) and the lens element (24) strikes the receiving plane (17) outside the receiving path.

2. Optical receiving unit according to claim 1, wherein the receiving plane (17) of the receiving sensor (16) is inclined relative to the optical plane (25) of the lens element (24) such that a multiple reflection of the received light (22) between the receiving sensor (16) and the lens element (24) strikes the receiving plane (17) outside the receiving sensor (16).

3. Optical receiving unit according to claim 1, wherein the receiving sensor (16) has receiving elements (Px) which can be activated to receive received light (22), wherein the receiving path for receiving received light (22) has at least one activated receiving element (Px).

4. Optical receiving unit according to claim 3, wherein the receiving elements (Px) are arranged in rows and can be assigned to the receiving path row by row.

5. Optical receiving unit according to claim 4, wherein the lines run longitudinally, in particular parallel, to the receiving plane (17) and / or the optical plane (25) of the lens element (24).

6. Optical receiving unit according to one of claims 3 to 5, wherein the receiving plane (17) is inclined relative to the optical plane (25) of the lens element (24) such that a multiple reflection of the received light (22) between the receiving sensor (16) and the lens element (24) strikes non-activated receiving elements (Px) of the receiving sensor (16).

7. Optical receiving unit according to one of the preceding claims, wherein the angle of inclination (38) between the receiving plane (17) and the optical plane (25) of the lens element (24) is selected such that the receiving plane (17), the optical plane (25) of the lens element (24) and a focal plane (32, 34, 36) of the receiving unit (14) intersect in a straight line (28).

8. Lidar system (10) with an optical receiving unit (14) according to one of the preceding claims.

9. Lidar system according to claim 8, comprising an optical transmission unit (12) with a transmission light source (19) for emitting transmission light (20) and a transmission lens element (21) which is arranged in a transmission path of the transmission light (20), wherein a transmission plane which runs vertically to the transmission direction of the transmission light (20) is inclined with respect to an optical plane of the transmission lens element (21).

10. Lidar system according to claim 9, wherein the angle of inclination (38) between the receiving plane (17) and the optical plane (25) of the lens element (24) substantially corresponds to the angle of inclination between the direction of the transmitted light (20) and the optical plane of the transmitted lens element (21).

11. Lidar system according to claim 9 or 10, wherein the transmitting plane and the receiving plane (17) run parallel to each other.

12. Lidar system according to one of claims 8 to 11, further comprising a computing unit (18) which is configured to activate the receiving elements (Px) of the receiving sensor (16) in the receiving path as a function of the transmitted light (20).

13. Lidar system according to claim 12, wherein the computing unit is configured to activate receiving elements (Px) line by line.

14. Vehicle (100) with a lidar system (10) according to one of claims 8 to 13.

15. Method for operating a lidar system (10) according to one of claims 12 or 13 in a vehicle (100), wherein the computing unit (18) activates the receiving elements (Px) in the receiving path as a function of the transmitted light (20).

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