DE102020206813A1 - LiDAR system - Google Patents

Abstract

A LiDAR system (2) is disclosed which is set up to scan an environment with a laser pulse, the LiDAR system (2) having a laser source (4) to generate the laser pulse and a micromirror arrangement (5) to emit the laser pulse into the environment. The micromirror arrangement (5) has two or more micromirrors (6a, b) and the LiDAR system (2) is set up to split the laser pulse between the two or more micromirrors (6a, b) in order to communicate with different areas of the environment to scan split laser pulse.

Description

The present invention relates to a LiDAR system which is set up to scan an environment with a laser pulse, the LiDAR system having a laser source in order to generate the laser pulse and having a micromirror arrangement in order to emit the laser pulse into the environment.

State of the art

Two types of LiDAR systems are known, one with a combined receive and transmit beam path that is split up in front of the transmit / receive source (coaxial), and one with everything in parallel. The former have several advantages, mainly that the required field of view, which is taken into account at any point in time, can be significantly smaller, which in turn has great advantages in terms of the signal-to-noise ratio. However, it requires a directional mirror and other complexities in the signal path, which leads to losses and other challenges due to the vastly different transmit and receive signal power.

It is known to direct a laser pulse in a LiDAR system onto a micromirror arrangement which has a single micromirror. The micromirror-based prior art usually uses a single micromirror, which only allows the measurement of a small field of view or requires a high degree of optimization of the field of view and a mirror speed in order to scan large parts of or the entire environment. It is also known to duplicate the entire receiving beam path / transmitting beam path in a LiDAR system.

the DE 10 2017 222 654 A1 discloses a LiDAR system with micromirrors. The micromirrors simultaneously direct radiation emitted by the radiation source and radiation emitted by a light source into an environment. Different wavelengths are used for the two radiations so that there is no crosstalk with regard to the two radiations.

the DE 10 2016 122 712 B3 shows and describes a light receiver which can have micromirrors and comprises a row with a plurality of light receiving elements, a manipulation unit being provided for shifting or deforming a light spot transversely to the row. Crosstalk is named as a problem and proposed as a solution is to keep a space free between light receiving elements.

From the EP 2 955 545 A1 and the WO 2014 084 973 A1 a LiDAR system for a wind turbine installation is known in each case, in which a single laser pulse is split into two beams, the first beam being emitted in the opposite direction of the second beam. A digital micromirror arrangement (DVD) can be used in the receiving beam path.

the WO 2019 041 274 A1 and the WO 2019 041 268 A1 each teach a LiDAR system in which a single laser pulse can be emitted into an environment via a 2D micromirror system in order to expand the laser pulse and thus scan a large field of view.

the WO 2018 075 291 A2 discloses a LiDAR system with a single laser pulse source. The laser output can be expanded using an optical beam splitter or a fan-out component so that several points in the far field can be scanned in parallel with just a single laser source.

"3D Imaging Using Resonant Large-Aperture MEMS Mirror Arrays and Laser Distance Measurement" by Andner, T., Wildenhain, M., Klose, T., Schenk, H., Schwarzer, S., Hinkov, V., Höfler, H ., Wölfelschneider, H. in IEEE / LEOS International Conference on Optical MEMS and Nanophotonics, OPTMEMS, 4607837, pp.78-79 (2008) suggests a single-channel system with a directional mirror as the transmitting mirror.

Automotive LiDAR systems with a large viewing angle must address a large number of “pixels” in the environment, also known as “scenes”, quickly enough. The speed of addressing each point in a scene is important. It is particularly desirable to have a large micromirror field of view and high speed. The availability and price of micromirrors must be taken into account. Limitations in compromising the design must not be disregarded.

Disclosure of the invention

According to the invention, a LiDAR system is provided in which the micromirror arrangement has two or more micromirrors and the LiDAR system is set up to split the laser pulse between the two or more micromirrors in order to scan different areas of the environment with the split laser pulse.

Advantages of the invention

The LiDAR system has the advantage that the laser pulse emitted by the laser source is divided into several “copies”, with each copy being directed onto a corresponding micromirror. So the number of laser sources can be reduced and a large field of view can be scanned at the same time. Laser sources are expensive and demanding, so it is better to use a few better than many poor laser sources. In addition, only part of the field of view is lost if one of the micromirrors should suffer a defect, so that redundancy is provided. Cost savings are also possible because simpler and / or more readily available components can be used, such as, for example, larger micromirrors than in the prior art, which are easier to hit and can possibly withstand higher laser power. The copies of the original laser pulse can also have a higher degree of correspondence with one another than different laser pulses from several laser sources. Fewer laser pulses are also required per frame because more scanning points are scanned per pulse so that, for example, energy consumption can be reduced. The laser pulses can be longer, which can improve the signal and simplify the design of the receiving beam path. Furthermore, eye safety can be improved. The speed of the multiple micromirrors can be slower than the speed of a single micromirror in the prior art, making the system easier to synchronize and control.

In embodiments it is provided that each of the micromirrors is assigned a predetermined area of the environment for scanning, which area differs from the predetermined areas of the other micromirrors. In this way, a large field of view can be scanned without overlapping the areas to be scanned. In this way, the field of view can be maximized in relation to the existing micromirrors. It is particularly preferred that the two or more micromirrors are set up to scan a contiguous area of the environment, so that gap-free scanning without overlapping is made possible.

Some embodiments provide that each of the micromirrors is assigned a predetermined area of the environment for scanning in that each micromirror is arranged at a reflection angle in the micromirror arrangement which differs from the reflection angles of the other micromirrors. It can thus be ensured in a particularly reliable manner that the two or more micromirrors do not produce any overlaps in the field of vision in the environment.

The two or more micromirrors are preferably set up so that they can be controlled in a synchronized manner. Thus, with each of the micromirrors, a scan of the environment can be generated which, compared to the other micromirrors, follows an identical pattern. It is preferred that the micromirrors can be controlled two-dimensionally, that is to say can be tilted in exactly one direction. If the mirrors are synchronized, the transmitted laser pulse will always have a known angular offset from one another. This means that after a known distance, only one of the laser pulses has to be taken into account. There is preferably a linear relationship between a normalized distance and an angular offset. It is particularly preferred that the angular offset is 2 ° at a standardized distance of approximately 0.06. It is further preferred that the angular offset is at a standardized distance of approximately 0.29 8 °. It is again preferred that the angular offset runs linearly between these two normalized distance values. The distance is preferably a standardized distance from an emitter to a focal point of an adjacent mirror, depending on their angular offset. The normalized distance is preferably normalized to the distance between the emitter plane and the mirror. The normalized distance is particularly preferably between an emitter and the focal point, which corresponds to the light transmitted through an adjacent mirror with a constant angular offset.

In embodiments, the two or more micromirrors are arranged to scan the respectively assigned areas of the environment in parallel lines of scanning points. This can particularly well enable the environment to be scanned as completely as possible. Gapless can mean that the distance between two adjacent scanning points is not greater than the diameter of a scanning point, it being particularly preferred that two adjacent scanning points directly abut one another. The scanning points of each micromirror are each preferably located in an m × n scanning matrix of m rows and n columns, wherein, particularly preferably, one row is first completely scanned before a change is made to the next row. It is preferred that when changing the line to the scanning point of the next line, which is arranged immediately below the last scanning point of the line just scanned, a change is made. This is preferably continued until all lines have been scanned, after which the scanning can be repeated, particularly preferably. In some embodiments, however, it is provided that when changing the line to the scanning point of the next line, which is arranged immediately below the first scanning point of the line just scanned, a change is made. The scanning preferably begins at a scanning point in an upper right corner or an upper left corner of the respective scanning matrix. Preferably each are micromirrors 15th Scanning points are provided, which are arranged in 3 lines of 5 scanning points each. It is particularly preferred that each scanning matrix in the scanned environment adjoins further scanning matrices of further micromirrors, preferably in an o × p matrix, wherein the o × p fields of this matrix can be equal to the number of micromirrors in the micromirror arrangement. Preferred is that sampling points in each of the sampling matrices that correspond to one another are sampled at the same time, so for example all sampling points that are located in the upper right corners of the sampling matrices are sampled simultaneously and so on line by line. The environment can therefore be scanned in a simple manner with synchronized firing via several micromirrors, preferably with a single laser source.

Embodiments of the LiDAR system have exactly one laser source. The LiDAR system allows the number of laser sources to be reduced to a minimum, but nevertheless, due to the two or more micromirrors to which the laser pulse from the laser source is divided, a relatively large field of view in the environment can be scanned. However, embodiments are conceivable which have two or more laser sources, each of which is assigned micromirror arrangements with two or more micromirrors. The described receiving beam path / transmitting beam path can therefore be duplicated or even multiplied. As a result, the field of view can be multiplied in size depending on the number of laser sources.

The LiDAR system preferably has a beam splitter which is arranged in the beam path between the laser source and the micromirror arrangement in order to split the laser pulse between the two or more micromirrors of the micromirror arrangement. Accordingly, the beam splitter preferably has a beam splitter input for the laser pulse incident from the laser source and two or more emitters which are beam splitter outputs, each emitter being assigned to one of the two or more micromirrors and directing the split beam onto the assigned micromirror. Generally speaking, the beam splitter preferably has o × p emitters if the micromirror arrangement has o × p mirrors. If the micromirror arrangement, as provided in embodiments, has two micromirrors in two columns each, that is to say a total of four micromirrors, then four emitters are preferably also provided in a matching arrangement. The emitters are preferably arranged in a common emitter plane.

The LiDAR system is preferably set up to make crosstalk between individual partial beams of the split laser pulse usable as a useful signal. It is desirable to be able to use any number of transmit / receive channels with minimal crosstalk between the channels. In this way, the need for optical conditioning of the signal can be reduced and optically directional mirrors become superfluous, which can further simplify the beam path. This can be particularly beneficial in applications where performance, cost, and / or size are important, such as automotive LiDAR. A higher signal-to-noise ratio can also be achieved in this way.

The LiDAR system preferably has one or more crosstalk receivers in a receiving beam path, which are each assigned to one of the micromirrors in order to receive portions of partial beams that pass through a different micromirror than the micromirror assigned to the crosstalk receiver when emitted into the environment to have. In embodiments, the LiDAR system has additional receiving beam paths in order to make the crosstalk usable. The returning light will likely impinge on all of the micromirrors in the micromirror array. This means that not only one image will be realized on the emitter level of the beam splitter. The best signals are likely to be found on the nearest neighboring micromirrors of the micromirror in question (both above and below), but an additional degree of receiver diversity can be achieved by adding a receive beam path comprising one or more of the crosstalk receivers to more than the nearest micromirror will. This means that the next micromirror above / below it will also reflect a signal back to the emitter level, which can be intercepted by another receiving channel. This signal will have a larger offset than that of the nearest neighbor because the angular offset between the respective micromirrors is larger. With respect to the present LiDAR system with two or more micromirrors in the micromirror array, the returning laser pulse will be centered around its transmitting micromirror. However, due to beam dispersion, it will also hit neighboring micromirrors. Assuming that the angular movement of the micromirrors is negligible during the flight time of the laser pulse, light reflected away from the transmitting micromirror will be reflected back to its source (or to a directional mirror, in coaxial systems). Two neighboring micromirrors with only one vertical offset (so that they are at the same distance from the emitter plane) will have a fixed angular offset in the vertical direction. In this case, when the reflected beam hits an adjacent mirror, it is reflected back towards the emitter plane, but with an offset which depends on the angular offset between the micromirrors. The point at which the returning light hits the emitter plane is determined by simple geometry and will always be in the same place, provided that noise and similar errors are negligible because the micromirrors are at the same distance from the plane and the angular offset between the micromirrors is the same . The crosstalk receiver or receivers can then preferably be placed at this location, which then preferably has a similar performance to that of one coaxial system without the directional mirror.

In some embodiments, the LiDAR system has additional mirrors in order to make the crosstalk usable. This can in particular be additional micromirrors that can be arranged around one of the above-discussed transmission micromirrors and that can be synchronized with its operation. In this way, the amount of light returning to a receiver associated with the transmitting micromirror can be increased. The additional micromirrors can of course be adapted to the desired aperture for better focusing. The additional micromirrors can be arranged in the emitter plane, preferably alternating with the emitters.

A vehicle is preferably also made available which has a LiDAR system mentioned at the beginning. It is preferred that the LiDAR system is operatively connected to a battery of the vehicle in order to operate the LiDAR system. The LiDAR system preferably has the micromirror arrangement which has two or more micromirrors and is set up to split the laser pulse between the two or more micromirrors in order to scan different areas of the environment with the split laser pulse.

The vehicle can be a motor vehicle, in particular a road-bound motor vehicle, for example a passenger car or a truck or a two-wheeled vehicle.

Further embodiments and their advantages follow mutatis mutandis from the above explanations of embodiments of the LiDAR system, so that repetitions are dispensed with at this point.

Advantageous further developments of the invention are given in the subclaims and described in the description.

Figure list

• 1 ein Fahrzeug mit einem LiDAR-System nach der Erfindung in einer ersten beispielhaften Ausführungsform,
• 2 ein LiDAR-System nach der Erfindung in der Ausführungsform nach 1 und
• 3 ein LiDAR-System nach der Erfindung in einer zweiten beispielhaften Ausführungsform.

Exemplary embodiments of the invention are explained in more detail with reference to the drawings and the following description. Show it:

• 1 a vehicle with a LiDAR system according to the invention in a first exemplary embodiment,
• 2 a LiDAR system according to the invention in the embodiment according to 1 and
• 3 a LiDAR system according to the invention in a second exemplary embodiment.

Embodiments of the invention

In the 1 is a vehicle 1 shown that a LiDAR system 2 in one embodiment according to the invention. The LiDAR system 2 is with a battery 3 of the vehicle 1 connected to the LiDAR system 2 to operate. The vehicle 1 is a road-bound motor vehicle, here specifically an autonomously driving passenger vehicle.

In 2 is the LiDAR system 2 the end 1 illustrated in a simplified plan view. The LiDAR system 2 is set up to scan an environment with a laser pulse. The LiDAR system 2 has a laser source 4th on, namely in this embodiment exactly one laser source 4th to generate the laser pulse. The LiDAR system 2 further comprises a micromirror assembly 5 to emit the laser pulse into the environment.

The micromirror array 5 has two or more micromirrors 6a , b, only two of a large number being shown in the first exemplary embodiment for the sake of clarity, and the LiDAR system 2 is set up to apply the laser pulse to the two or more micromirrors 6a to split b in order to scan different areas of the environment with the split laser pulse. In the first embodiment according to 1 instructs the LiDAR system 2 a beam splitter for this purpose 7th in the beam path between the laser source 4th and the micromirror array 5 is arranged to apply the laser pulse to the two or more micromirrors 6a , b the micromirror array 5 to split up. In 2 are four emitters 8a , b, c, d of the beam splitter 7th shown, each emitter 8a , b, c, d is set up to direct the split laser beam onto an associated micromirror 6a to direct b. The emitters 8a , b, c, d are on a common emitter level 9 arranged.

Every micromirror 6a , b is assigned to a predetermined area of the environment for scanning, which area differs from the predetermined areas of the other micromirrors 6a , b differs. As a result, no area of the environment is scanned twice. Each of the micromirrors 6a , b is assigned to a predetermined area of the environment for scanning, more precisely in that, as in 1 can be seen every micromirror 6a , b at a reflection angle in the micromirror arrangement 5 is arranged, which differs from the reflection angles of the other micromirrors 6a , b differs. In addition, the two or more are micromirrors 6a , b arranged to scan the respectively assigned areas of the environment in parallel lines of scanning points.

In other words shows 2 the operation of the LiDAR system 2 where the laser source 4th produces a laser pulse which is nxm parallel laser pulses using the beam splitter 7th is divided. Each of the split laser pulses comes from one of the emitters 8a , b, c, d on a specific one of the micromirrors 6a , b steered. The micromirrors 6a , b are oriented at precise angles in two dimensions to focus their field of view on a portion of the scene to be scanned. Thus, each emitter micromirror channel corresponds to a part of the total field of view, each of which is scanned simultaneously. For example, the entire field of view is quartered so that four points are scanned at the same time.

3 shows a LiDAR system 2 according to a second embodiment, which alternatively in the vehicle 1 the end 1 can be built in. This LiDAR system too 2 exhibits the micromirror assembly 5 on that two or more micromirrors 6a , b, and is set up to direct the laser pulse onto the two or more micromirrors 6a to split b in order to scan different areas of the environment with the split laser pulse. In this embodiment there are two emitters 8a , b of the beam splitter 7th shown enlarged, the split laser pulse on a respectively assigned micromirror 6a , b, which in this case are semi-transparent micromirrors.

In the second embodiment from 3 it is provided that the two or more micromirrors 6a , b are set up so that they can be controlled in a synchronized manner. So can deflection angles of the micromirrors 6a , b can be adjusted synchronized. Next is the LiDAR system 2 in the second embodiment set up to make crosstalk between two individual partial beams of the split laser pulse usable as a useful signal. The LiDAR system 2 for this purpose has one or more crosstalk receivers in a receiving beam path 10a , b on, each one of the micromirrors 6a , b are assigned to receive portions of partial beams that, when emitted into the environment, reach a different micromirror 6a , b as the micromirror 6a , b, the crosstalk receiver 10a , b is assigned. The micromirror 6a is the crosstalk receiver 10a assigned. The micromirror 6b is the crosstalk receiver 10b assigned. The crosstalk receivers 10a , b are adjacent to the respective emitters 8a , b arranged, alternating with these in the emitter level 9 . The crosstalk receivers 10a , b is in the embodiment shown in each case a beam shaping lens in the beam path 11a , b upstream. Next are between the emitters 8a , b absorbent elements 12a , b provided to avoid crosstalk between neighboring crosstalk receivers 10a to prevent b. The absorption elements 12a , b are designed as walls. Every crosstalk receiver 10a , b is an emitter on one side 8a , b and on the other side an absorption element 12a , b adjacent. Any beam shaping lens 11a , b is also an emitter on one side 8a , b and on the other side an absorption element 12a , b adjacent.

As in 3 As illustrated, not all portions of the split light pulse, when reflected off a distant object in the environment, pass through the micromirror again 6a , b into the LiDAR system 2 one that removes them from the LiDAR system 2 have been submitted. For example, a portion of the occurs from a first emitter 8a emitted first partial beam, which is shown as a dashed line, through the micromirror 6b back into the LiDAR system, the micromirror 6a is adjacent, through which the light pulse from the LiDAR system 2 has left. Mutatis mutandis, the same applies to that of a second emitter 8b emitted second partial beam, which is shown as a continuous line. This phenomenon is referred to as crosstalk in the context of this application. The receiving beam path for the portion of the first partial beam that passes through the neighboring micromirror 6b when the crosstalk light pulse re-enters is due to the deflection angle of the neighboring micromirror 6b set. The crosstalk receiver can accordingly 10b be arranged at a position at which the crosstalk light pulse emitted by the first emitter 8a through the micromirror 6a is output and through the neighboring micromirror 6b back into the LiDAR system 2 occurs, as expected, at the emitter level 9 will hit. The crosstalking light pulse can be received as a useful signal and then evaluated. A receiver for an adjacent channel could also be placed next to each emitter. Any number of receivers (corresponding to further channels) can be placed between the emitters.

The receiver of the LiDAR system 2 with several transmission beam paths must be designed carefully in order to reduce crosstalk. This becomes an increasing challenge, the more "channels" the LiDAR system 2 having. As illustrated, the present invention, in some embodiments, allows returning signals to be focused on their respective receivers with minimal crosstalk. The LiDAR system proposed here 2 further allows greater freedom for compromises in the design of the LiDAR system 2 what allows from a larger basic set of micromirrors 6a to choose b, especially for applications with a large field of view or high-speed applications such as automotive LiDAR. Because laser sources 4th The LiDAR system allows this to be expensive and demanding 2 , fewer, but better laser sources 4th to use, for example, only a single, instead of a large number of comparatively poor laser sources 4th to use. As with Automotive LiDAR - Applications with a large field of view often require a large number of scanning points in the environment to be scanned sufficiently quickly. In embodiments, the invention also allows laser distance measurement applications in particular, such as LiDAR, to be implemented with a larger field of view using a plurality of simpler micromirrors 6a , 6b instead of using a single micromirror for the entire field of view, which can also be particularly useful for automotive applications. The invention can be useful for any application in which a laser or other optical signal must be received simultaneously from different angles. It can be particularly useful for applications with a large field of view, such as automotive LiDAR or projection applications.

Although the invention has been illustrated and described in more detail by means of preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102017222654 A1 [0004]
• DE 102016122712 B3 [0005]
• EP 2955545 A1 [0006]
• WO 2014084973 A1 [0006]
• WO 2019041274 A1 [0007]
• WO 2019041268 A1 [0007]
• WO 2018075291 A2 [0008]

Claims (9)

LiDAR system (2) which is set up to scan an environment with a laser pulse, wherein the LiDAR system (2) has a laser source (4) to generate the laser pulse and a micromirror arrangement (5) to the Emitting laser pulse into the environment, characterized in that the micromirror arrangement (5) has two or more micromirrors (6a, b) and the LiDAR system (2) is set up to apply the laser pulse to the two or more micromirrors (6a, b) split in order to scan different areas of the environment with the split laser pulse. LiDAR system (2) Claim 1 wherein each of the micromirrors (6a, b) is assigned a predetermined area of the environment for scanning which differs from the predetermined areas of the other micromirrors (6a, b). LiDAR system (2) Claim 2 , wherein each of the micromirrors (6a, b) is assigned a predetermined area of the environment for scanning in that each micromirror (6a, b) is arranged at a reflection angle in the micromirror arrangement (5) which differs from the reflection angles of the other micromirrors (6a , b) differs. LiDAR system (2) according to one of the preceding claims, wherein the two or more micromirrors (6a, b) are set up so that they can be controlled in a synchronized manner. LiDAR system (2) according to one of the Claims 2 until 4th , wherein the two or more micromirrors (6a, b) are arranged to scan the respectively assigned areas of the environment in parallel lines of scanning points. LiDAR system (2) according to one of the preceding claims, wherein the LiDAR system (2) has exactly one laser source (4). LiDAR system (2) according to one of the preceding claims, wherein the LiDAR system (2) has a beam splitter (7) which is arranged in the beam path between the laser source (4) and the micromirror arrangement (5) in order to generate the laser pulse (4 ) to be divided between the two or more micromirrors (6a, b) of the micromirror arrangement (5). LiDAR system (2) according to one of the preceding claims, wherein the LiDAR system (2) is set up to make crosstalk between individual partial beams of the split laser pulse usable as a useful signal. LiDAR system (2) according to any one of the preceding claims, wherein the LiDAR system (2) has one or more crosstalk receivers (10a, b) in a receiving beam path, each of which is assigned to one of the micromirrors (6a, b) in order to convert portions of To receive partial beams which, when released into the environment, have passed through a different micromirror (6a, b) than the micromirror (6a, b) which is assigned to the crosstalk receiver (10a, b).

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