Optical reception unit for lidar system, lidar system for vehicle, and method for operating lidar system

Abstract

The invention relates to an optical receiving unit (14) for a lidar system (10) of a vehicle (100). The optical receiving unit (14) has: a receiving sensor (16) which is designed to receive receiving light (22) on a receiving path; and a lens element (24) which is arranged in the receiving path, in which 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 multiple reflections of the receiving light (22) between the receiving sensor (16) and the lens element (24) reach the receiving plane (17) outside the receiving path. The invention further relates to a lidar system (10) having such an optical receiving unit (14), to a vehicle (100) having such a lidar system (10), and to a method for operating a lidar system (10) in a vehicle (100).

Description

TECHNICAL FIELD

[0001] The present application relates to an optical receiving unit for a laser radar system for a vehicle, to a laser radar system for a vehicle and to a method for operating such a laser radar system in a vehicle. BACKGROUND

[0002] Modern vehicles (cars, transporters, trucks, motorcycles, etc.) are equipped with a large number of sensor systems, the data of which are used for driver information and / or are provided to driver assistance systems. The vehicle environment and other traffic participants are acquired by means of the sensor systems. On the basis of the acquired data, a vehicle environment model can be generated and changes in the vehicle environment can be responded to.

[0003] An important sensor principle for acquiring an environment, for example a vehicle environment, is the laser radar technology (Lidar, English: Light Detection and Ranging). A laser radar system has an optical transmitting unit and an optical receiving unit. The transmitting unit can emit a transmitting light, which can be pulsed. In a laser radar system, in particular laser beams in the ultraviolet, visible or infrared range can be used. By means of the receiving unit, the transmitting light can be received as receiving light after reflection on objects in a detection area of the laser radar system environment. The receiving light can be evaluated by means of a computing unit of the laser radar system using the transmitting signal according to the time-of-flight method and the spatial position and distance of the object on which the reflection took place can be determined. In addition, the relative speed can be determined. In this context, reflection or reflected light is understood as any light reflected back and should in particular include light reflected back by scattering or absorption-emission. In order to determine the distance to the object, in particular so-called time-of-flight (English: Time-of-Flight, abbreviation TOF) systems can be used.

[0004] The laser radar system can be designed as a system that works with light pulses, i.e. as a so-called flash laser radar (Flash-Lidar). Here, an area of the environment can be illuminated with one light pulse (English: Flash) and the receiving signal reflected on objects possibly present can be acquired with a receiving device.

[0005] Scanning laser radar systems emit a light beam that moves in a scanning direction. Point scanners illuminate the environmental area point by point. Line scanners illuminate the environmental area line by line.

[0006] The receiving sensor of a laser radar system can have a plurality of receiving elements, so-called pixels, and these pixels can be provided for receiving the receiving light from respectively different reception angles.

[0007] Laser radar systems are continuously being developed for various functions, for example for acquiring environmental information in the near and far range of a vehicle, such as a passenger car or a commercial vehicle. Laser radar systems can also be used as sensor systems for driver assistance systems, in particular for assistance systems for autonomous or partially autonomous vehicle control. These laser radar systems can be used, among other things, to identify obstacles and / or other road users in the front, rear or blind spot area of a vehicle.

[0008] DE 102020130492 A1 describes a laser radar system for a vehicle. The receiver comprises one or more light intensity sensors; and one or more lens assemblies configured relative 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 such that it forms a non-zero angle with at least one equivalent lens plane of the one or more lens assemblies, wherein the sensor focal plane is shifted such that it is aligned with a main illumination direction of a light source of the laser radar system and coincides with a direction of motion of the vehicle. SUMMARY

[0009] The optical receiving unit of the laser radar system for a vehicle has a receiving sensor, which is designed to receive receiving light on a receiving path. The receiving unit also has a lens element, which is arranged in the receiving path. The optical receiving plane of the receiving sensor is tilted relative to the optical plane of the lens element, so that multiple reflections of the receiving light between the receiving sensor and the lens element reach the receiving plane outside the receiving path.

[0010] The receiving sensor is provided to convert the 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 optical bandpass filters. The optical plane is the (virtual) plane in which the receiving sensor is arranged. The optical plane extends beyond the receiving sensor as a plane. The optical plane can also be referred to as the image plane.

[0011] The receiving light is received by the optical receiving unit on the receiving path. The receiving light is, for example, directed to the receiving sensor and, for example, focused on the receiving sensor by the lens element on the receiving path.

[0012] With the described optical receiving unit a reduction of high blooming can be achieved. High blooming is also referred to as optical cross-talk. High blooming can produce unwanted optical effects, which can be caused by reflections between the receiving sensor and the lens element, in particular the bandpass filter. By the described tilting, reflections can be directed out of the receiving path, so that high blooming, i.e. for example local overexposure, within the receiving path can be reduced.

[0013] The tilt is here chosen such that reflections by the receiving sensor itself are not reflected back into the receiving path by the lens element, but outside the receiving path and intersecting the image plane.

[0014] In an embodiment, the receiving plane of the receiving sensor is tilted with respect to the optical plane of the lens element such that multiple reflections of the received light between the receiving sensor and the lens element reach the receiving plane outside the receiving sensor. This can cause that reflections by the receiving sensor itself are not reflected back into the receiving sensor, but outside the receiving sensor and intersecting the image plane.

[0015] But for a planar receiving sensor, this can be difficult to achieve, as the spatial extent of the receiving sensor can lead to unachievable tilt angles. In some embodiments, the receiving sensor thus has a plurality of receiving elements activatable for receiving the received light, wherein the receiving path has at least one activated receiving element for receiving the received light. The receiving elements, also referred to as pixels, can be arranged for receiving the received light from respectively different receiving angles.

[0016] Activating the receiving elements here can for example comprise placing the receiving elements from a non-receiving ready state, for example by changing a bias, into a receiving ready state. Deactivating can correspondingly be achieved by targeted control and / or by being switched off, for example autonomously, after a certain time duration.

[0017] In some embodiments, the receiving elements are arranged in rows and can be assigned to the receiving path row by row. This can correspond to a row-by-row assignment of respective, for example line-shaped, regions in the detection area of the lidar system. Assigning the receiving elements to the receiving path by corresponding activation can correspond to a targeted illumination of respective, for example line-shaped, regions in the detection area by the transmitted light of the lidar system.

[0018] Herein, the rows can extend longitudinally, in particular parallel, with respect to the receiving plane and / or the optical plane of the lens element. This can achieve the combination of two advantages: a tilted focal plane of the lidar system with respect to the ground in front of the vehicle, and a deflection of the multiple reflections onto non-activated receiving elements of the receiving sensor.

[0019] In an embodiment of the optical receiving unit, the receiving plane is tilted with respect to the optical plane of the lens element such that multiple reflections of the received light between the receiving sensor and the lens element reach non-activated receiving elements of the receiving sensor. The optical plane of the lens element corresponds to a lens plane of the lens element, wherein the lens plane is a plane through the center of the lens element, perpendicular to the optical axis.

[0020] The inclination of the image plane with respect to the lens element preferably follows the Scheimpflug law. This means that the focal plane of the lidar system is also inclined with respect to the lens element. The receiving plane, the optical plane of the lens element and the focal plane of the receiving unit intersect in a straight line.

[0021] The focal plane is that 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 receiving plane, in the image space of the lens element.

[0022] The application also relates to a lidar system having one of the aforementioned optical receiving units. For the lidar system, the object space is located in its detection region.

[0023] The lidar system can also have an optical transmitting unit having a transmitting light source for transmitting the transmitting light and a transmitting lens element. The transmitting lens element is arranged in the transmitting path of the transmitting light. A transmitting plane extending perpendicular to the direction of the transmitting light is inclined with respect to the optical plane of the transmitting lens element. The optical plane of the transmitting lens element corresponds to the lens plane of the transmitting lens element, wherein the lens plane is the plane through the center of the transmitting lens element perpendicular to the optical axis. The inclination of the optical plane of the transmitting lens element with respect to the transmitting plane can likewise comply with the Scheimpflug law.

[0024] The optical receiving unit and the optical transmitting unit of such a lidar system can be designed such that the angle of inclination between the receiving plane and the optical plane of the lens element in the receiving unit substantially corresponds to the angle of inclination between the direction of the transmitting light and the optical plane of the transmitting lens element in the transmitting unit.

[0025] The transmitting plane and the receiving plane can extend longitudinally, in particular parallel, to one another, so that the lens element and the transmitting lens element can have the same inclination.

[0026] The lidar system can also have a computing unit which is set up to activate the receiving elements of the receiving sensor in the receiving path by the transmitting light. By knowing the angle of inclination between the receiving sensor and the lens element, those receiving elements which are located in the transmitting light path can be activated in a targeted manner. The receiving elements outside the transmitting light path can be deactivated or remain inactive if necessary, so that multiple reflections reach the inactive receiving elements, i.e. the receiving plane outside the receiving path.

[0027] In some embodiments, the computing unit of the lidar system can activate the receiving elements line by line.

[0028] A vehicle can have one or more of the aforementioned lidar systems. The one or more lidar systems can be coupled with one or more control systems of the vehicle. The control systems can for example be connected with a drive system, a steering system, a brake system and control various vehicle functions, such as lane keeping, collision warning and other functions, using information received from the lidar system.

[0029] In a method for operating such a lidar system in the vehicle, the computing unit activates the receiving elements in the receiving path in dependence on the transmitted light. BRIEF DESCRIPTION OF DRAWINGS

[0030] Embodiments of the present application will be further explained and described below with the help of the drawings. In the drawings

[0031] Figure 1 A vehicle with a lidar system is schematically shown,

[0032] Figure 2 The inclination of the receiving plane relative to the optical plane of the lens element is schematically shown, and

[0033] Figure 3 A receiving sensor with sensor elements is schematically shown.

[0034] In the drawings, identical reference numerals are used for identical or similar elements. The representations in the drawings can not be to scale. BRIEF DESCRIPTION OF DRAWINGS

[0035] In Figure 1 A vehicle 100, for example a passenger car, is schematically shown in which the vehicle has 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 transmitting light source 19, for example a laser or an LED, through which a transmitting light 20 is generated. The shown lidar system has a transmitting optical path, also called transmitting path, and a receiving optical path, also called receiving path. The transmitting light 20 here propagates through the transmitting path. The receiving light 22 here propagates through the receiving path.

[0036] A transmitting lens element 21 is located in the transmitting path and is designed to influence the optical properties of the transmitting light 20, for example the direction of the transmitting light, after it has been transmitted by the transmitting light source 19. The transmitting lens element 21 can for this purpose have for example one or more lenses and / or optical filters, in particular bandpass filters.

[0037] The receiving light 22 is influenced in its optical properties by a lens element 24 located in the receiving path before it is received by the receiving sensor 16 and for example focused onto the receiving sensor 16. The lens element 24 can for this purpose have for example one or more lenses and / or optical filters.

[0038] The sending process of the sending light 20 and the receiving process of the receiving light 22 in the receiving unit 14 can be monitored and controlled by a controller. The sending light 20 and the receiving light 22 can be evaluated by the controller in order to perform detection, distance determination and / or speed determination with respect to an object O located in the detection area 30. The controller can be arranged, for example, on a computing unit 18 of the lidar system 10 having a processor and a memory and implemented, for example, as software on the computing unit.

[0039] In the example shown, the lidar system 10 is arranged in a front region of the vehicle 100. The detection area 30 is located in front of the front region of the vehicle 100. Thereby, in the example shown, the area in front of the vehicle 100 in driving direction can be monitored. The lidar system 10 can also be arranged in other different regions of the vehicle 100, for example, in a rear region and / or in a side region. A plurality of lidar systems 10 can also be arranged on the vehicle 100, in particular also in corner regions of the vehicle 100.

[0040] For a scanning lidar system 10, the detection area 30 is scanned stepwise, for example, point by point, line by line or region by region, by the sending light 20. For a flash lidar, the detection area 30 can be illuminated in whole or in part simultaneously.

[0041] With the lidar system 10, stationary or moving objects O in the detection area 30 can be detected, i.e., acquired, in particular vehicles, persons, animals, plants, obstacles, road unevenness, in particular potholes or stones, lane boundaries, traffic signs, free space, in particular parking spaces, precipitation, etc. By evaluating the sending light 20 and the receiving light 22 by the controller of the computing unit 18, it can be possible, for example, to determine the distance with respect to the object O and / or the direction in which the object O is located. Alternatively or additionally, it can be possible to determine the relative speed with respect to the object O and / or the properties of the object O. Information about the properties of the object O can be obtained, for example, by determining the phase shift of the receiving light 22 with respect to the sending light 20. In order to determine the phase shift, for example, a modulation method can be used, such as AMCW (AMCW: amplitude modulated continuous wave) or FMCW (FMCW: frequency modulated continuous wave).

[0042] The lidar system 10 can also be configured, for example, as a TOF system for distance determination. A TOF system uses the light run time to determine the distance. Thus, a TOF system can be used as a range finder for measuring the distance with respect to the object O. Here, a design as a direct TOF system, dTOF, or an indirect TOF system, iTOF, can be considered. A direct TOF system uses a direct measurement of the light run time to determine the distance with respect to the object O. An indirect TOF system uses a measure derived from the light run time, for example, the phase difference between the sending light 20 and the receiving light 22, for distance determination.

[0043] The receiving sensor 16 can receive the reception light 22 through a plurality of receiving paths, which can also be referred to as a field of view (FOV) of the receiving sensor. By actively controlling the receiving sensor 16, it is possible to change the FOV of the receiving sensor 16, for example by selectively 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 computing unit 18.

[0044] The optical transmitting unit 12 is provided for adjusting the transmitted transmission light 20 accordingly to adapt to the FOV of the receiving sensor 16. This means, for example, that the transmission light 20 is radiated into those areas of the detection area 30 which are currently receivable by the receiving sensor 16. This control of the FOV of the receiving sensor 16 and the corresponding adjustment of the transmission light 20 can be performed, for example, by the computing unit 18.

[0045] The receiving sensor 16 can receive the reception light 22 through a plurality of receiving paths, the totality of which can correspond to the detection area 30 of the lidar system 10 and also be referred to as the field of view (FOV) of the lidar system 10.

[0046] In Figure 2 The inclination of the optical plane 25 of the lens element 24 relative to the optical receiving plane 17 of the receiving sensor 16 is schematically shown in Fig. 1. The optical plane 25 of the lens element 24 is inclined by an angle 38 relative to the optical receiving plane. Here, the inclination is performed in a vertical direction as viewed from the vehicle 100, so that the focal plane 32, also referred to as the focal point plane, of the lidar system 10 is inclined towards the road as viewed from the vehicle 100. Figure 2 Further focal planes 34, 36 of the lidar system 10 are also shown in Fig. 1.

[0047] The inclination by the angle 38 here follows the Scheimpflug principle. This principle states that the optical plane 25 of the lens element 24, the sensor plane 17 intersect a plane from which a sharp image can be formed onto the receiving sensor 16 in a straight line 28. This applies, for example, to the shown focal planes 32, 34, 36. The focal planes 32, 34, 36 are located at the focal points of the optical arrangement and are therefore also referred to as focal point planes.

[0048] This inclination of the focal planes 32, 34, 36 is very suitable for applications in vehicles 100, in which ground relationships can play an important role. Furthermore, a sharper imaging can be achieved in the short-range region, which can be advantageous, for example, for near-field lidar systems.

[0049] By tilting at angle 38, the position of the received light 22 reflected off the receiving sensor 16 and then reflected back towards the receiving plane 17 by the receiving lens 24 on the receiving plane 17 differs from the position of the received light 22 that directly reaches the receiving sensor 16 along the receiving path. The tilt angle 38 can now be selected, for example, so that the light that has been reflected multiple times does not reach the receiving sensor 16 at all. This is possible, for example, for a receiving sensor 16 with a small spatial range.

[0050] For a planar receiving sensor 16, it may be difficult to select a tilt angle of 38 so large that the light reflected multiple times no longer reaches the receiving sensor 16.

[0051] Therefore, an alternative implementation method is proposed below, using... Figure 3 This implementation method will be explained in detail.

[0052] The photosensitive receiving element Px of the receiving sensor 16 can be designed as a CMOS chip. Other designs for the receiving element Px are possible, such as an avalanche photodiode (APD) or a so-called single-photon avalanche diode (SPAD). The receiving element Px can be controlled regarding its reception readiness. In particular, reception readiness can be selectively turned on and off again when necessary, for example, via the computing unit 18. This corresponds to activation and deactivation when necessary. It is also possible for the pixel to autonomously deactivate after a certain period of time following activation.

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

[0054] The activation of the receiving element Px of the receiving sensor 16 is performed segmentally. Therefore, the scanning process performed by the receiving sensor 16, including capturing light and converting it into an electrical signal, is performed segmentally, with each segment corresponding to a separately activated receiving element Px. The activated receiving element Px... Figure 3 The text is represented by a grid of shaded lines.

[0055] Figure 3 One embodiment is shown, in which the active segments are horizontally oriented row by row. The active receiving elements Px are located in the currently active receiving path. Angle 38 is chosen such that reflections at the receiving sensor 16 and back reflections (German: Rückreflexion) at the lens element 24 arrive at the receiving sensor 16 outside the active segments, in this specific embodiment, with a vertical offset. Inactive segments are not receiving-ready and therefore do not produce interference effects. The vertical offset here depends on the tilt of the lens element 24 toward the horizontal line, see [reference]. Figure 2Thus, the vertical tilting has two advantageous effects on the laser radar system 10. On the one hand, the tilting of the focal planes 32, 34, 36 relative to the ground, and on the other hand, the deflection of multiple reflections to the vertical.

[0056] The angle of inclination 38 between the receiving plane 17 and the lens element 24 is chosen such that the received light 22 arriving on the receiving path in the reflection of the receiving sensor 16 reaches from the (active) receiving element 42 to a different (inactive) receiving element 40 via the counter-reflection on the lens element 24. This is illustrated in Figure 3 The active receiving elements 42 are illustrated in solid lines and the inactive receiving elements 40 in dashed lines. Furthermore, the individual pixels of the horizontal section can also be activated one after the other or in groups in the horizontal direction.

[0057] By means of the proposed optical receiving unit 14, blooming artefacts can be prevented or at least reduced. Optical crosstalk in the form of blooming due to the reflection of the receiving sensor 16 and the lens element 24 can be reduced. Distortion of the measurement values due to this optical crosstalk, for example due to a distortion of the phase information in indirect measurements, such as FMCW and AMCW, can be reduced or false positive results can be better avoided. Likewise, false positive results in direct TOF measurements can be better avoided.

[0058] In addition to the tilting of the lens element 24, it can be provided that the transmitting lens element 21 is tilted relative to the transmitting light source 19 by an angle, preferably by an angle of the same size as the angle 38. Both angles can be chosen such that the Scheimpflug law is fulfilled. The tilting of the transmitting lens element 21 is here determined relative to a transmitting plane, which is perpendicular to the transmitting light 20 at the transmitting light source 19. The transmitting plane can be chosen such that it extends parallel to the receiving plane 17.

Claims

1. An optical receiving unit (14) for a laser radar system (10) of a vehicle (100), comprising a receiving sensor (16) designed to receive receiving light (22) on a receiving path; and a lens element (24) arranged in the receiving path, an optical receiving plane (17) of the receiving sensor (16) is tilted relative to an optical plane (25) of the lens element (24) such that multiple reflections of the receiving light (22) between the receiving sensor (16) and the lens element (24) reach the receiving plane (17) outside the receiving path. an optical receiving plane (17) of the receiving sensor (16) is tilted relative to an optical plane (25) of the lens element (24) such that multiple reflections of the receiving light (22) between the receiving sensor (16) and the lens element (24) reach the receiving plane (17) outside the receiving path. the receiving sensor (16) has receiving elements (Px) which can be activated in order to receive receiving light (22), wherein the receiving path has at least one activated receiving element (Px) in order to receive receiving light (22). wherein the receiving elements (Px) are arranged in rows and can be assigned to the receiving path row by row.

2. The optical receiving unit according to claim 1, wherein, the rows extend in a longitudinal direction, in particular parallel, relative to the receiving plane (17) and / or the optical plane (25) of the lens element (24).

3. The optical receiving unit according to claim 1, wherein, the receiving plane (17) is tilted relative to the optical plane (25) of the lens element (24) such that multiple reflections of the receiving light (22) between the receiving sensor (16) and the lens element (24) reach non-activated receiving elements (Px) of the receiving sensor (16).

4. The optical receiving unit according to claim 3, wherein an 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).

5. The optical receiving unit according to claim 4, wherein 8. A laser radar system (10) having an optical receiving unit (14) according to any one of the preceding claims.

6. The optical receiving unit according to any one of claims 3 to 5, wherein, 9. The laser radar system according to claim 8, having an optical transmitting unit (12) with a transmitting light source (19) for transmitting transmitting light (20) and a transmitting lens element (21) arranged in a transmitting path of the transmitting light (20), a transmitting plane extending perpendicular to a transmitting direction of the transmitting light (20) is tilted relative to an optical plane of the transmitting lens element (21).

7. The optical receiving unit according to any of the preceding claims, wherein, an angle of inclination (38) between the receiving plane (17) and the optical plane (25) of the lens element (24) substantially corresponds to an angle of inclination between the direction of the transmitting light (20) and the optical plane of the transmitting lens element (21). the transmitting plane and the receiving plane (17) extend parallel to one another. ​ ​ wherein ​ 10. The lidar system of claim 9, wherein, ​ 11. The lidar system of claim 9 or 10, wherein, ​ 12. The lidar system according to any one of claims 8 to 11, further having a computing unit (18) which is set up to activate the receiving elements (Px) in the receiving path of the receiving sensor (16) in dependence on the transmitted light (20).

13. The lidar system of claim 12, wherein, The computing unit is set up to activate the receiving elements (Px) line by line.

14. A vehicle (100) having a lidar system (10) according to any one of claims 8 to 13.

15. A method for operating a lidar system (10) according to claim 12 or 13 in a vehicle (100), wherein, The computing unit (18) activates the receiving elements (Px) in the receiving path in dependence on the transmitted light (20).

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