Method for determining a distance from an active optical sensor system and active optical sensor system

Abstract

To determine a distance, a light pulse (6a) is emitted by means of an emitter unit (22) of an active optical sensor system (2), and a sensor signal based on components (6b) reflected by an object (5) is generated by means of a detector unit (23) of the active optical sensor system (2). For at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b), a measured value is determined depending on an amplitude of the sensor signal, wherein a first measurement time window (9, 15a) has a predefined measurement duration, and the start time of a second measurement time window (10, 16a) lies after the start time of the first measurement time window (9, 15a) by a time difference that is smaller than the measurement duration.The light travel time of the reflected components (6b) of the light pulse (6a) is determined depending on the measured values ​​determined for the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) and the distance is calculated depending on the light travel time.

Description

[0001] The present invention relates to a method for determining a distance from an object using an active optical sensor system. The invention further relates to a method for at least partially automatically guiding a motor vehicle, which includes such a method for determining a distance, as well as a corresponding active optical sensor system. The invention also relates to an electronic vehicle guidance system with such an active optical sensor system and corresponding computer program products.

[0002] Active optical sensor systems, such as lidar sensor systems, are used for various driver assistance functions, autonomous driving, or other functions for the at least partially automatic control of a motor vehicle. Light or light pulses are emitted into the environment of the active optical sensor system, and reflected portions of the light or light pulses are detected by a detector unit of the active optical sensor system. Based on this, the distance can be calculated, for example, using a time-of-flight measurement.

[0003] Particularly in applications for at least partially automatic driving of a motor vehicle, it is desirable to cover a very large dynamic range with active optical sensor systems, since on the one hand distances from very weakly reflecting objects that are located far away from the active optical sensor system, as well as distances from highly reflecting objects, for example retroreflectors, that are comparatively close to the active optical sensor system, are important.

[0004] The appropriate tuning or adjustment of the optical detectors of the detector unit or the electronic components for signal processing can lead to saturation by the reflected portions of the light in the case of highly reflective objects and / or objects very close to the active optical sensor system, so that only a lower limit for the energy input of the reflected portions can be specified based on the sensor signal. In other words, no change in the amplitude as a function of time can be detected, or it can only be detected to a very limited extent. This leads to reduced temporal resolution and thus to reduced accuracy in measuring the distance of such objects.

[0005] For example, it is known to use weighting algorithms, such as fitting algorithms, depending on the temporal change in the amplitude of the sensor signal to effectively achieve more precise temporal resolution. However, in the case outlined above, when saturation occurs as described, this is not feasible due to the lack of or limited time dependence.

[0006] One possibility to increase the temporal resolution would be to reduce the measurement time duration of consecutive measurement windows, but this would increase the demands on electronic signal processing.

[0007] It is an object of the present invention to increase the accuracy for determining the distance when determining a distance of an object from an active optical sensor system, in particular without reducing the measuring time duration of successive measuring time windows.

[0008] This object is achieved by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

[0009] The invention is based on the concept of performing measurements for two or more measurement time windows, wherein a first measurement time window has a predefined measurement time duration and a start time of a second measurement time window lies after a start time of the first measurement time window by a time difference that is shorter than the measurement time duration, thus in particular also before an end time of the first measurement time window. In this way, the first measurement time window can be effectively subsampled without having to reduce the respective measurement time duration of the individual measurement time windows.

[0010] According to one aspect of the invention, a method for determining a distance of an object from an active optical sensor system is specified. By means of an emitter unit of the active optical sensor system, a light pulse is emitted into an environment of the active optical sensor system, and by means of a detector unit of the active optical sensor system, a sensor signal is generated based on portions of the light pulse reflected by the object. For at least two measurement time windows, in particular by means of at least one computing unit of the active optical sensor system, a measured value is determined in each case as a function of an amplitude of the sensor signal during the respective measurement time window, wherein a first measurement time window of the at least two measurement time windows has a predefined measurement time duration.A start time of a second measurement time window of the at least two measurement time windows lies after a start time of the first measurement time window by a time difference that is shorter than the measurement time duration. Depending on the measured values ​​determined for the at least two measurement time windows, in particular depending on all measured values ​​determined for all of the at least two measurement time windows, for example by means of the at least one computing unit, a light propagation time of the reflected portions of the light pulse is determined. The distance is calculated, in particular by means of the at least one computing unit, depending on the light propagation time.

[0011] An active optical sensor system, in particular the emitter unit, by definition comprises at least one light source for emitting light or light pulses. A light source can be configured, in particular, as a laser, in particular as a laser diode, for example, as an infrared laser. Furthermore, an active optical sensor system, in particular the detector unit, by definition comprises at least one optical detector for detecting reflected portions of the emitted light. The active optical sensor system is configured, in particular, to generate, process, or output one or more sensor signals based on the detected portions of the light.

[0012] Here and below, the term "light" can be understood to include electromagnetic waves in the visible range, the infrared range, and / or the ultraviolet range. Accordingly, the term "optical" can also be understood to refer to light in this sense. Preferably, particularly for automotive applications, the light pulse emitted by the emitter unit of the active optical sensor system according to the invention is a light pulse in the infrared range.

[0013] The described method steps of the method according to the invention refer to a single light pulse or the analysis and evaluation of the reflected components of this light pulse, unless otherwise stated. However, during operation of the active optical sensor system, for example, a plurality of light pulses are emitted into the environment, and corresponding reflected components are detected. The method steps described with respect to the light pulse can also be performed analogously for some or all of the other emitted light pulses.

[0014] Depending on the design of the active optical sensor system, the light pulse can be generated by a laser diode, as mentioned above. It is possible for a laser diode to be operated in a so-called burst mode, whereby a light pulse, also referred to in this context as a macropulse or burst, contains a multitude of rapidly successive micropulses. Successive macropulses are separated from one another by a period that is longer than the period between successive micropulses. In this case, the light pulse described in the context of the method according to the invention can be considered a macrolight pulse.

[0015] Depending on the design of the active optical sensor system, the detector unit can contain one or more optical detectors, which can be configured in different ways. In the case of lidar sensor systems, the detector unit typically contains several detector pixels, which can be arranged, for example, linearly or in a two-dimensional array. It is possible for each detector pixel to contain exactly one optical detector, for example an avalanche photodiode (APD), which is operated, for example, below its breakdown voltage. The detector pixel is then, for example, a radiation power-proportional photodetector, so that the sensor signal, which can be, for example, a current signal or a voltage signal, represents the radiation power of the reflected portions of the light pulse falling on the respective detector pixel, in particular is proportional or approximately proportional to it.However, this only applies if the radiant power does not exceed a saturation value of the corresponding detector pixel. Above the saturation value, the sensor signal is, for example, constantly equal to a maximum value or saturation value for the sensor signal.

[0016] It is also possible for a detector pixel to contain one or more single-photon detectors, in particular single-photon avalanche photodiodes (SPADs). If a photon falls onto a single-photon detector, this leads, for example, to a current pulse indicating the detection of the single photon. Accordingly, a single single-photon detector cannot distinguish between one photon and multiple photons falling onto the single-photon detector simultaneously or substantially simultaneously. Therefore, in some embodiments, multiple single-photon detectors are used per detector pixel to enable more precise measurement. For example, the sensor signal can be equal to or directly proportional to a number of detected photons, or the like.Here, too, saturation can occur, for example when all single-photon detectors of a detector pixel detect one or more photons simultaneously or essentially simultaneously.

[0017] In this case, the sensor signal corresponds to the sensor signal of a single detector pixel. A similar procedure can be used for the corresponding sensor signals of additional detector pixels in various embodiments of the method.

[0018] Aside from the described saturation effects of the optical detectors themselves, saturation effects can also occur due to the design and configuration of the electronic components for signal processing, for example, analog-to-digital converters, if used. In an example scenario in which a detector pixel itself is not saturated, for example, but saturation occurs due to signal processing, it may be that the sensor signal itself is below the corresponding saturation value for the sensor signal, but the respective corresponding measured value corresponds to a maximum measured value. On the other hand, if the detector pixel is already saturated and the sensor signal therefore corresponds to the saturation value, the corresponding measured value also assumes the maximum measured value.In the case of saturation, it is generally not possible to distinguish what is causing this saturation based on the corresponding measured value.

[0019] To determine the corresponding measured value based on the amplitude of the sensor signal, the amplitude of the sensor signal can be integrated over the corresponding measurement time window, for example. The measurement duration then corresponds, for example, to the corresponding integration time. It is also possible, especially when using single-photon detectors, to count peaks in the sensor signal over the measurement time window to determine the measured value. Other options for determining the measured value based on the amplitude of the sensor signal are also possible.

[0020] In addition to the first and second measurement time windows, the at least two measurement time windows can contain further measurement time windows, which, for example, have a start time that lies within the first measurement time window. The at least two measurement time windows can also contain further measurement time windows whose start time lies after the end time of the first measurement time window. For example, the at least two measurement time windows can contain one or more sequences of consecutive measurement time windows. The second measurement time window is then shifted by the time difference with respect to a sequence of measurement time windows that includes the first measurement time window. For example, the second measurement time window can also be part of a sequence of consecutive measurement time windows, and the two aforementioned sequences can, for example, be shifted from one another by the time difference.In other words, the shift in this case can also be interpreted as a phase shift between the sequences.

[0021] Depending on the measured values, the light transit time can be determined, for example, by a direct light transit time measurement or an indirect light transit time measurement.

[0022] By determining the measured values ​​as described and calculating the light transit time based on them, the temporal resolution in the event of saturation can be increased. For illustrative purposes, a modified method can be considered, for example, in which the at least two measurement time windows consist of a single sequence of consecutive and non-overlapping measurement time windows, each with the same measurement duration. If saturation now occurs, the light transit time can only be determined with an accuracy determined by the measurement duration. In particular, a fit to an ideal pulse shape or the like is not possible, since the measured values ​​during saturation are constantly equal to the maximum measured value.

[0023] In the method according to the invention, however, the measured values ​​are determined individually at least for the first measurement time window and the second measurement time window. If saturation occurs in the first measurement time window but not in the second measurement time window, it can be concluded that the reflected components were detected in a part of the first measurement time window that does not overlap with the second measurement time window, i.e., in particular, between the start time of the first measurement time window and the start time of the second measurement time window. Since the time difference is smaller than the measurement time duration, an increased temporal resolution is achieved.On the other hand, if saturation occurs in both the first measurement time window and the second measurement time window, it can be assumed that the reflected components were detected within the overlap area between the first measurement time window and the second measurement time window, i.e., in particular, not within the period between the start time of the first measurement time window and the start time of the second measurement time window. The accuracy of the time-of-flight measurement can be further increased by adjusting the measurement time duration of the second measurement time window, which can, for example, be the same as or different from the measurement time duration of the first measurement time window, and / or by providing additional measurement time windows shifted relative to the first and second measurement time windows, but whose start time still lies within the first measurement time window.

[0024] According to at least one embodiment, the amplitude of the sensor signal during the first measurement time window is equal to a predetermined saturation amplitude value and / or the measured value determined for the first measurement time window is equal to a predetermined saturation measured value.

[0025] In other words, in such embodiments, it is actively or positively determined that saturation exists during the first measurement time window. If the amplitude of the sensor signal during the first measurement time window is equal to the saturation amplitude value, the saturation is caused in particular by a corresponding optical detector of the detector unit itself. If the measured value determined for the first measurement time window is equal to the saturation measured value, this can also be due to saturation of the optical detector itself and / or the saturation can be caused by signal processing components. In other words, if the amplitude of the sensor signal during the first measurement time window is equal to the saturation amplitude value, it follows that the measured value determined for the first measurement time window is also equal to the saturation measured value, although the reverse is not necessarily the case.

[0026] For example, the evaluation of the at least two measurement time windows as described can only be performed if saturation has been positively determined. Otherwise, a time-of-flight measurement can be performed in a conventional manner. In this case, the analogous steps as described above can be performed, however, the at least two measurement time windows consist of a sequence of consecutive first measurement time windows with a constant measurement duration.

[0027] In this way, the effort in electronic signal processing can be reduced or only accepted if it is necessary or advantageous due to the detected saturation.

[0028] For example, in one or more measurement time windows prior to the first measurement time window, it can be determined that saturation is present, i.e. that the measured value corresponds to the saturation measured value or the value of the amplitude of the sensor signal corresponds to the saturation amplitude value, and only if this is the case, the measurement can be carried out in the manner described with the first and the second measurement time window in order to increase the resolution in terms of time.

[0029] On the other hand, however, it is also possible that saturation may not be positively determined before the above-mentioned and described steps regarding the first and second measurement time windows, etc. In this way, the complexity of the procedure can be limited.

[0030] According to at least one embodiment, two or more evaluation periods are determined, wherein in each evaluation period of the two or more evaluation periods, a number of overlapping measurement time windows of the at least two measurement time windows is constant and, in particular, is greater than or equal to one. An effective sensor signal is calculated, in particular by means of the at least one computing unit, by calculating a sum of the measured values ​​of the respective overlapping measurement time windows for each evaluation period of the two or more evaluation periods. The light propagation time is calculated as a function of the effective sensor signal.

[0031] The specific number, duration, and timing of the evaluation periods can vary depending on the design. In any case, within the first measurement period, there is an evaluation period that corresponds to the period between the start time of the first measurement window and the start time of the second measurement window, or an even shorter evaluation period.

[0032] The effective sensor signal therefore has a higher temporal resolution within the first measurement time window than that provided by the measurement duration. Accordingly, the effective sensor signal can be evaluated, for example, analogously to an actual sensor signal in a case where saturation is not present, to enable a corresponding determination of the light travel time. For example, fitting algorithms or weighting methods, etc., can be used to evaluate the effective sensor signal and calculate or estimate the light travel time based on it.

[0033] For illustration, assume that the at least two measurement time windows consist of the first measurement time window and the second measurement time window, and both have the same measurement time duration. In this case, three evaluation periods would result: an evaluation period between the start time of the first measurement time window and the start time of the second measurement time window, an evaluation period between the start time of the second measurement time window and the end time of the first measurement time window, and an evaluation period between the end time of the first measurement time window and the end time of the second measurement time window. Each of the evaluation periods would then be shorter than the measurement time duration.

[0034] Assuming that the at least two measurement time windows consist of exactly three measurement time windows, namely the first and the second measurement time window and a third measurement time window, the start time of which is twice the time difference after the start time of the first measurement time window, and that the three measurement time windows each have the same measurement time duration, this would result in five evaluation periods.In particular, this would result in an evaluation period between the start time of the first measurement time window and the start time of the second measurement time window, an evaluation period between the start time of the second measurement time window and the start time of the third measurement time window, an evaluation period between the start time of the third measurement time window and the end time of the first measurement time window, an evaluation period between the end time of the first measurement time window and the end time of the second measurement time window, and an evaluation period between the end time of the second measurement time window and the end time of the third measurement time window. This can be continued accordingly for further measurement time windows or sequences of measurement time windows.

[0035] According to at least one embodiment, a compensation curve is determined, in particular by means of the at least one computing unit, which approximates at least a part, in particular a temporal segment, of the effective sensor signal. The light propagation time is calculated depending on the compensation curve.

[0036] By constructing the effective sensor signal or the evaluation periods as described, the approximation by the compensation curve is made possible in a meaningful way in the case of saturation, since in contrast to a constant saturation measurement value, an evaluable time dependence is introduced by the effective sensor signal.

[0037] In particular, analogous or similar methods can be used to calculate the time of flight, and if necessary, the same methods can be used to determine the compensation curve, as is also possible in scenarios where saturation is not present. However, this would not be possible without the described steps of the method according to the invention.

[0038] According to at least one embodiment, the compensation curve is determined according to a predetermined ideal pulse shape. For example, the compensation curve can be determined as a Gaussian curve or part of a Gaussian curve. The ideal pulse shape then corresponds, for example, to the shape of the Gaussian curve or part of the Gaussian curve.

[0039] A Gaussian curve is given by f(t)=A exp(−12[t−t0s]2), where t0 corresponds to the center of the ideal impulse, s indicates its width, where s 2where Δ indicates the variance, and A is the maximum amplitude of the ideal pulse. A, s, and / or t0 can be used as variable parameters or fitting parameters to determine the fit curve.

[0040] In particular, it is assumed that the detection of the reflected portions would occur according to the ideal pulse shape if saturation did not occur. Assuming that the effective sensor signal at least partially and / or approximately reflects the actual pulse shape, a conclusive and accurate determination of the light propagation time can be achieved by evaluating the compensation curve.

[0041] According to at least one embodiment, the compensation curve is determined as a straight line or straight line segment.

[0042] In particular, a linear approximation of a portion of the effective sensor signal is performed. Especially with very strong radiation intensity, a linear approximation is a good approximation for a rising or falling edge of the actual pulse. The gradient and / or position of the line or line segment can therefore be used to determine the light propagation time with increased accuracy.

[0043] For example, in various embodiments, the light travel time can be calculated depending on the gradient of the straight line or straight line segment. Alternatively or additionally, in various embodiments, the light travel time can be calculated depending on a point in time at which the straight line or straight line segment assumes a predetermined value.

[0044] By evaluating the gradient, it is possible to estimate which portion of the detected pulse is approximated by the effective sensor signal, and based on this, the light travel time can be calculated. In the further variant mentioned, the value assumed by the straight line or straight line segment can, for example, correspond to a predefined zero line or a predefined noise level or another characteristic value, i.e., a horizontal line whose intersection with the straight line or straight line segment is calculated to determine the light travel time more precisely.

[0045] According to at least one embodiment, the second measurement time window has the predefined measurement time duration. For example, all measurement time windows of the at least two measurement time windows can have the predefined measurement time duration.

[0046] In other words, the end time of the second measurement window also lies after the end time of the first measurement window by the same time difference. In this case, the definition or generation of the second measurement window can be simplified, since it is identical to the first measurement window, shifted by the time difference.

[0047] According to at least one embodiment, the at least two measurement time windows include at least one further first measurement time window, wherein the first measurement time window and the at least one further first measurement time window form a first sequence of immediately consecutive measurement time windows. Each further first measurement time window of the at least one further first measurement time window has the predefined measurement time duration.

[0048] According to at least one embodiment, the at least two measurement time windows comprise at least one further second measurement time window, wherein the second measurement time window and the at least one further second measurement time window form a second sequence of immediately consecutive measurement time windows. Each further second measurement time window of the at least one further second measurement time window has the predefined measurement time duration.

[0049] In other words, the first and second sequences of measurement time windows are shifted relative to each other by a constant phase, which is determined by the time difference. This allows the temporal resolution to be easily increased for a larger overall period or permanently.

[0050] In particular, the number of the at least one further first measurement time window is equal to the number of the at least one further second measurement time window.

[0051] According to at least one embodiment, the at least two measurement time windows include a third measurement time window, wherein a start time of the third measurement time window lies after the start time of the second measurement time window. The start time of the third measurement time window lies after the start time of the first measurement time window by a further time difference that is shorter than the measurement time duration.

[0052] For example, the further time difference may be equal to twice the time difference, so that the shift of the third measurement time window with respect to the second measurement time window is equal to the shift of the second measurement time window with respect to the first measurement time window.

[0053] As already mentioned above, this effectively further increases the temporal resolution, in particular a larger number of relevant evaluation time windows can be defined and evaluated.

[0054] For example, the at least two measurement time windows comprise at least one further third measurement time window, wherein the third measurement time window and the at least one further third measurement time window form a third sequence of immediately consecutive measurement time windows. Each of the at least one further third measurement time window has the predefined measurement time duration.

[0055] In particular, three sequences are provided that are phase-shifted relative to each other and evaluated accordingly. This allows the resolution to be further increased over a longer period of time.

[0056] The aforementioned embodiments with two or three sequences of consecutive measurement time windows can be supplemented analogously by further sequences of measurement time windows in order to further increase the temporal resolution. The number of sequences is essentially limited by the measurement time duration and the respective time difference. If the measurement time duration is the same for all measurement time windows of the at least two measurement time windows and the respective time difference between consecutive sequences is constant, the maximum number of sequences results from the quotient of the measurement time duration and the time difference. In particular, N=⌊MZ⌋, where N denotes the maximum number of sequences, M the measurement time and Z the time difference.

[0057] According to a further aspect of the invention, a method for at least partially automatically driving a motor vehicle is provided. A method according to the invention is used to determine the distance of an object from an active optical sensor system. Depending on the distance, at least one control signal for at least partially automatically driving the motor vehicle is generated, in particular by means of the at least one computing unit.

[0058] The at least one control signal can be transmitted, for example, to one or more actuators of the motor vehicle, including, for example, at least one brake actuator, at least one steering actuator, and / or at least one drive motor of the motor vehicle. The one or more actuators of the motor vehicle can then influence a lateral control and / or longitudinal control of the motor vehicle depending on the at least one control signal in order to steer the motor vehicle at least partially automatically. Alternatively or additionally, the at least one computing unit can generate one or more user outputs depending on the at least one control signal and output them to a user of the motor vehicle in order to then assist the user in driving the motor vehicle.

[0059] The active optical sensor system can, in particular, be an active optical sensor system of the motor vehicle, i.e., mounted on the motor vehicle. However, it is also possible for the active optical sensor system to be part of an infrastructure facility and to be provided separately or externally to the motor vehicle.

[0060] Further embodiments of the method according to the invention for at least partially automatically driving a motor vehicle follow directly from the various embodiments of the method according to the invention for determining a distance, and vice versa. In particular, individual features and corresponding explanations as well as advantages relating to the various embodiments of the method according to the invention for determining the distance can be transferred analogously to corresponding embodiments of the method according to the invention for at least partially automatically driving a motor vehicle.

[0061] For use cases or application situations that may arise during the method and which are not explicitly described here, it may be provided that, in accordance with the method, an error message and / or a request to enter user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0062] According to a further aspect of the invention, an active optical sensor system is provided. The active optical sensor system comprises an emitter unit configured to emit a light pulse into an environment of the active optical sensor system, and a detector unit configured to generate a sensor signal based on portions of the light pulse reflected by an object in the environment.The active optical sensor system has at least one computing unit configured to determine a measured value for at least two measurement time windows depending on an amplitude of the sensor signal during the respective measurement time window, wherein a first measurement time window of the at least two measurement time windows has a predefined measurement time duration, and wherein a start time of the second measurement time window of the at least two measurement time windows lies after a start time of the first measurement time window by a time difference that is shorter than the measurement time duration. The at least one computing unit is configured to determine a light propagation time of the reflected portions of the light pulse depending on the measured values ​​determined for the at least two measurement time windows and to calculate the distance depending on the light propagation time.

[0063] A computing unit can be understood, in particular, as a data processing device that contains a processing circuit. The computing unit can therefore, in particular, process data to perform computing operations. This may also include operations for performing indexed access to a data structure, for example, a look-up table (LUT).

[0064] The computing unit may, in particular, contain one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example one or more application-specific integrated circuits (ASICs), one or more field-programmable gate arrays (FPGAs), and / or one or more single-chip systems (SoCs). The computing unit may also contain one or more processors, for example one or more microprocessors, one or more central processing units (CPUs), one or more graphics processing units (GPUs), and / or one or more signal processors, in particular one or more digital signal processors (DSPs). The computing unit may also include a physical or virtual network of computers or other of the aforementioned units.

[0065] In various embodiments, the computing unit includes one or more hardware and / or software interfaces and / or one or more memory units.

[0066] A memory unit can be a volatile data memory, for example a dynamic random access memory (DRAM) or a static random access memory (SRAM), or a non-volatile data memory, for example a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a flash memory or flash EEPROM, a ferroelectric random access memory (FRAM), a magnetoresistive random access memory,MRAM (magnetoresistive random access memory) or phase-change random access memory (PCRAM).

[0067] According to at least one embodiment, the active optical sensor system is designed as a lidar sensor system, for example as a laser scanner.

[0068] Further embodiments of the active optical sensor system according to the invention follow directly from the various embodiments of the methods according to the invention, and vice versa. In particular, individual features and corresponding explanations as well as advantages relating to the various embodiments of the methods according to the invention can be transferred analogously to corresponding embodiments of the active optical sensor system according to the invention. In particular, the optical sensor system according to the invention is designed or programmed to carry out a method according to the invention. In particular, the active optical sensor system according to the invention carries out a method according to the invention.

[0069] According to a further aspect of the invention, an electronic vehicle guidance system is provided, which comprises an active optical sensor system according to the invention. The at least one computing unit is configured to generate at least one control signal for at least partially automatically guiding a motor vehicle, depending on the distance.

[0070] An electronic vehicle guidance system can be understood as an electronic system designed to guide a vehicle fully automatically or autonomously, in particular without requiring driver intervention. The vehicle automatically performs all required functions, such as steering, braking, and / or acceleration maneuvers, monitoring and detecting road traffic, and corresponding reactions. In particular, the electronic vehicle guidance system can implement a fully automatic or fully autonomous driving mode of the motor vehicle according to level 5 of the SAE J3016 classification. An electronic vehicle guidance system can also be understood as an advanced driver assistance system (ADAS), which supports the driver in partially automated or semi-autonomous driving.In particular, the electronic vehicle guidance system can implement a partially automated or semi-autonomous driving mode according to levels 1 to 4 of the SAE J3016 classification. Here and below, "SAE J3016" refers to the corresponding standard in the April 2021 version.

[0071] The at least partially automated vehicle guidance may therefore include driving the vehicle according to a fully automated or fully autonomous driving mode of Level 5 according to SAE J3016. The at least partially automated vehicle guidance may also include driving the vehicle according to a partially automated or semi-autonomous driving mode according to Levels 1 to 4 according to SAE J3016.

[0072] According to a further aspect of the invention, a computer program is provided that has instructions. When the instructions are executed by an active optical sensor system according to the invention, in particular the at least one computing unit, the instructions cause the active optical sensor system to perform a method according to the invention for determining a distance.

[0073] The instructions can be provided, for example, as program code. The program code can be provided, for example, as binary code or assembly code and / or as source code of a programming language, for example, C, and / or as a program script, for example, Python.

[0074] According to a further aspect of the invention, a further computer program with further instructions is provided. Upon execution of the further instructions by an electronic vehicle guidance system according to the invention, in particular by the at least one computing unit, the further instructions cause the electronic vehicle guidance system to carry out a method according to the invention for at least partially automatically guiding a motor vehicle.

[0075] The additional instructions can be provided, for example, as program code. The program code can be provided, for example, as binary code or assembly code and / or as source code of a programming language, for example, C, and / or as a program script, for example, Python.

[0076] According to a further aspect of the invention, a computer-readable storage medium is provided which stores a computer program and / or another computer program according to the invention.

[0077] The computer program, the further computer program and the computer-readable storage medium according to the invention can be referred to as respective computer program products with the instructions or the further instructions.

[0078] Further features of the invention emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures can be encompassed by the invention not only in the respectively specified combination, but also in other combinations. In particular, the invention can also encompass embodiments and combinations of features that do not have all the features of an originally formulated claim. Furthermore, the invention can encompass embodiments and combinations of features that go beyond the combinations of features set out in the backreferences to the claims or deviate from them.

[0079] The invention is explained in more detail below using specific embodiments and associated schematic drawings. In the figures, identical or functionally equivalent elements may be provided with the same reference numerals. The description of identical or functionally equivalent elements may not necessarily be repeated for different figures.

[0080] The figures show: Fig. 1 a schematic representation of a motor vehicle with an exemplary embodiment of an electronic vehicle guidance system according to the invention; Fig. 2 a schematic block diagram of an exemplary embodiment of an active optical sensor system according to the invention; Fig. 3 a schematic representation of a measurement in which no saturation occurs; Fig. 4 a schematic representation of several measurement time windows in an exemplary embodiment of a method according to the invention for determining a distance; Fig. 5 shows a schematic representation of an effective sensor signal in a further exemplary embodiment of a method according to the invention for determining a distance; and Fig. 6 several measurement time windows and several effective sensor signals according to further exemplary embodiments of a method according to the invention for determining a distance.

[0081] In Fig. 1 schematically shows a motor vehicle 1 which has an exemplary embodiment of an electronic vehicle guidance system 3 according to the invention.

[0082] The electronic vehicle guidance system 3 contains an exemplary embodiment of an active optical sensor system 2 according to the invention and at least one computing unit 4. The at least one computing unit 4 or parts thereof can, in some embodiments, also be included in the active optical sensor system 2. The active optical sensor system 2 is configured to determine a distance of an object 5 in the surroundings of the motor vehicle, and the at least one computing unit 4 is configured to generate at least one control signal for at least partially automatically guiding the motor vehicle 1 depending on the distance.

[0083] Fig. 2 shows a schematic block diagram of an exemplary embodiment of an active optical sensor system 2 according to the invention, as it is used, for example, in the motor vehicle 1 of Fig. 1 can be used. In this example, the active optical sensor system 2 is designed as a lidar sensor system.

[0084] The active optical sensor system 2 has an emitter unit 22 with at least one light source, for example one or more laser diodes, by means of which a light pulse 6a can be emitted into the environment of the active optical sensor system 2. The active optical sensor system 2 also has a detector unit 23, which is configured to receive components 6b of the emitted light pulse 6a reflected in the environment, for example components 6b reflected by the object 5. The active optical sensor system 2 has, for example, a control and evaluation unit 24, which can control the at least one light source to generate the light pulse 6a and can receive a sensor signal from the detector unit 23, which the detector unit 23 generates based on the reflected components 6b of the light pulse 6a.

[0085] The control and evaluation unit 24 can determine a light propagation time of the reflected portions 6b of the light pulse 6a based on the sensor signal and calculate the distance between the object 5 and the active optical sensor system 2 based on the light propagation time. Depending on the distance and, if applicable, further distances of the object 5 or other objects in the vicinity of the active optical sensor system 2, the control and evaluation unit 24 and / or the at least one computing unit 4 can generate a point cloud, for example. The at least one computing unit 4 can generate the at least one control signal based, for example, on the point cloud.

[0086] In the example of Fig. 2, the active optical sensor system 2 is designed in particular as a laser scanner. The active optical sensor system 2 then has, for example, a deflection device with a mirror 25 rotatably mounted with respect to a rotation axis 26 oriented parallel to a z-axis. The mirror 25 can be controlled by the control and evaluation unit 24 and thus set in rotation, so that the surroundings in the xy-environment can be scanned by generating several consecutive light pulses. The azimuth angle, i.e. the corresponding angle in the xy-plane, can be determined based on the position of the corresponding optical detector of the detector unit 23, which detects the reflected portions 6b, and the associated current position of the mirror 25.A polar angle, i.e. a corresponding angle perpendicular to the xy-plane or with respect to the z-direction, can also be determined based on the position of the corresponding optical detector or detector pixel.

[0087] In Fig. Figure 3 shows a schematic scenario in which no saturation occurs. On the horizontal axis, Fig. 3 to Fig. 6 shows the time.

[0088] In Fig. 3 shows a plurality of consecutive measurement time windows with respective measurement time durations T. Within five of the measurement time windows, different amplitudes of the sensor signal are detected, so that corresponding measured values ​​7 can be determined. Since there is no saturation in the scenario shown, the measured values ​​7 are different and approximately represent the pulse shape of the reflected components 6b or of the radiant power or radiant energy incident on the corresponding optical detector. For example, the rising edge of the measured values ​​7 can be approximated by a straight line 8 in order to be able to determine the position of the measured pulse more precisely, in particular more precisely than the measurement time duration T. If saturation were present, the measured values ​​would be constant at the maximum measured value, so that such a linear approximation would not be meaningfully possible and, accordingly, no precise determination of the light propagation time would be possible.

[0089] In the method according to the invention, respective measured values ​​are determined for at least two measurement time windows depending on the amplitude of the sensor signal during the respective measurement time window. The light propagation time is determined depending on the measured values ​​determined for the at least two measurement time windows.

[0090] In Fig. 4 shows an example in which three measurement time windows 9, 10, 11 are shown, each having the same measurement time duration T, but offset from each other by a time difference t. A first measurement time window 9 is followed in particular by a second measurement time window 10, the start time of which lies by the time difference t after the start time of the first measurement time window 9. For example, a third measurement time window 11 can be provided, the start time of which also lies by the time difference t after the start time of the second measurement time window 10. As a result, the measurement time duration T is effectively undersampled. A possible resulting effective sensor signal 12 is shown in Fig. 5. The effective sensor signal 12 is calculated, for example, by comparing the measured values ​​for respective evaluation periods in which the number of overlapping measurement time windows of the measurement time windows 9, 10, 11 is constant. In the present example, it was assumed that the maximum measured value corresponding to saturation is measured in all three measurement time windows 9, 10, 11. This results in a gradual increase in the effective sensor signal from zero to a value that corresponds to three times the maximum measured value, whereby any standardizations that may have been performed are not taken into account.

[0091] In Fig. 4, only three individual measurement time windows 9, 10, 11 are shown. In fact, however, three or more sequences of directly consecutive measurement time windows can be provided, wherein a first sequence includes the first measurement time window 9 and subsequent further first measurement time windows, the second sequence includes the second measurement time window 10 and subsequent further measurement time windows, and the third sequence includes the third measurement time window 11 and subsequent further third measurement time windows. In the calculation of the effective sensor signal 12 in Fig. 5, it was assumed that saturation is only detected in the measurement time windows 9, 10, 11 and that no further detection occurs in the subsequent measurement time windows of the individual sequences. Therefore, the effective sensor signal 12 returns to zero in a step-like manner, symmetrical to the rise. It can therefore be assumed, for example, that the maximum of the actual reflected pulse lies in the range of the maximum value of the effective sensor signal 12. Alternatively or additionally, the rising edge of the effective sensor signal 12 can be approximated by a straight line 13, and this or its gradient and / or position can be determined analogously to the straight line 8 from Fig. 3 to calculate the light travel time.

[0092] Another example is in the Fig. 6 is shown schematically. This shows a first sequence of measurement time windows with first measurement time windows 15a, 15b, a second sequence of measurement time windows with consecutive second measurement time windows 16a, 16b, and a third sequence of measurement time windows with consecutive measurement time windows 17a, 17b. The measurement time windows 15a, 15b, 16a, 16b, 17a, 17b each have the same measurement time duration T. Possible additional measurement time windows for the individual sequences are not shown. The measurement time windows 16a, 16b of the second sequence are each shifted by the time difference t with respect to the measurement time windows 15a, 15b of the first sequence. Analogously, the measurement time windows 17a, 17b of the third sequence are each shifted by the time difference t with respect to the measurement time windows 16a, 16b of the second sequence.As a result, the overlapping areas of the measurement time windows 15a, 15b, 16a, 16b, 17a, 17b result in, for example, at least eight evaluation periods 21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h, each of which is shorter than the measurement time period T. In the present non-limiting example, the evaluation periods 21a, 21b, 21d, 21e, 21g, 21h each have a duration that corresponds to the time difference t and the remaining evaluation periods 21c, 21f have a duration that is given by T-2*t.

[0093] Three different scenarios are schematically shown, each of which detects a reflected pulse 14a, 14b, 14c. It should be noted that the exact position of the reflected pulses 14a, 14b, 14c is not known and is shown only for the sake of simplicity of explanation. Fig. 6. Furthermore, corresponding effective sensor signals 18, 19, 20 are shown. For the effective sensor signal 18, it was assumed that only the reflected pulse 14a is detected, for the effective sensor signal 19, it was assumed that only the reflected pulse 14b is detected, and for the effective sensor signal 20, it was assumed that only the reflected pulse 14c is detected.

[0094] The effective sensor signal 18, 19, 20 corresponds to the sum of the individual measured values ​​measured in the individual evaluation periods 21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h. Since the number of overlapping measurement time windows 15a, 15b, 16a, 16b, 17a, 17b in each evaluation period 21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h is a maximum of three, the effective sensor signal 18 assumes values ​​between zero and three times the maximum measured value, corresponding to saturation.

[0095] Considering the reflected pulse 14a and the corresponding effective sensor signal 18, the reflected pulse 14a is detected in the measurement time window 15a, in the measurement time window 16a, and in the measurement time window 17a, but not in the remaining measurement time windows 15b, 16b, and 17b. In units of the maximum measured value, the effective sensor signal 18 thus curves over the evaluation periods 21a, 21b, 21c, 21d, 21e, 21f, 21g, and 21h as 1, 2, 3, 2, 1, 0, 0, in that order.

[0096] Considering the reflected pulse 14b and the corresponding effective sensor signal 19, the reflected pulse 14b is detected in the measurement time window 16a, in the measurement time window 17a, and in the measurement time window 15b, but not in the remaining measurement time windows 15a, 16b, and 17b. In units of the maximum measured value, the effective sensor signal 19 thus curves over the evaluation periods 21a, 21b, 21c, 21d, 21e, 21f, 21g, and 21h as 0, 1, 2, 3, 2, 1, 0, 0, in that order.

[0097] Considering the reflected pulse 14c and the corresponding effective sensor signal 20, the reflected pulse 14c is detected in the measurement time window 17a, in the measurement time window 15b, and in the measurement time window 16b, but not in the remaining measurement time windows 15a, 16a, 17b. In units of the maximum measured value, the effective sensor signal 20 thus curves over the evaluation periods 21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h as 0, 0, 1, 2, 3, 2, 1, 0, in this order.

[0098] As from Fig. 6, the positions of the reflected pulses 14a, 14b, 14c can be localized with a higher accuracy than given by the measuring time T.

[0099] As described, in particular with regard to the figures, the invention thus enables a higher time resolution in the light transit time measurement and accordingly a higher accuracy in the distance measurement with an active optical sensor system, in particular without shortening the individual measurement times.

[0100] In various embodiments, it is possible to achieve a distance resolution just as high for highly reflective objects as for less reflective objects, regardless of whether the optical detectors and / or the signal processing are saturated.

[0101] For example, to improve the signal-to-noise ratio (SNR) of the measurements, multiple light pulses can be transmitted and received per distance measurement, and a histogram can be generated if necessary. The number of individual measurements per measurement point can be made dependent, for example, on the amplitude in the histogram. Furthermore, various embodiments can provide for data acquisition to precede data analysis.

Claims

[1] Method for determining a distance of an object (5) from an active optical sensor system (2), wherein - a light pulse (6a) is emitted into an environment of the active optical sensor system (2) by means of an emitter unit (22) of the active optical sensor system (2), and a sensor signal is generated by means of a detector unit (23) of the active optical sensor system (2) based on portions (6b) of the light pulse (6a) reflected by the object (5); - for at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) a measured value is determined in each case as a function of an amplitude of the sensor signal during the respective measurement time window (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b), wherein a first measurement time window (9, 15a) of the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) has a predefined measurement time duration; - a start time of a second measurement time window (10, 16a) of the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) lies after a start time of the first measurement time window (9, 15a) by a time difference which is shorter than the measurement time duration; - a light propagation time of the reflected portions (6b) of the light pulse (6a) is determined as a function of the measured values ​​determined for the at least two measuring time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b); and - the distance is calculated depending on the light travel time. [2] Method according to claim 1, wherein the amplitude of the sensor signal during the first measurement time window (9, 15a) is equal to a predetermined saturation amplitude value and / or the measured value determined for the first measurement time window (9, 15a) is equal to a predetermined saturation measured value. [3] Method according to one of the preceding claims, wherein - two or more evaluation periods (21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h) are determined, wherein in each evaluation period (21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h) of the two or more evaluation periods (21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h) a number of overlapping measurement time windows of the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) is constant; - an effective sensor signal (12, 18, 19, 20) is calculated by calculating a sum of the measured values ​​of the respective overlapping measurement time windows for each evaluation period (21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h) of the two or more evaluation periods (21a, 21b, 21c, 21d, 21e, 21f, 21g, 21h); and - the light travel time is calculated depending on the effective sensor signal (12, 18, 19, 20). [4] Method according to claim 3, wherein - a compensation curve (8) is determined which approximates at least a part of the effective sensor signal (12, 18, 19, 20); and - the light travel time is calculated depending on the compensation curve (8). [5] Method according to claim 4, wherein - the compensation curve (8) is determined according to a predetermined ideal pulse shape; or - the compensation curve (8) is determined as a Gaussian curve or part of a Gaussian curve. [6] Method according to claim 4, wherein the compensation curve (8) is determined as a straight line or as a straight line segment. [7] A method according to claim 6, wherein - the light travel time is calculated depending on the gradient of the straight line or the straight line segment; and / or - the light travel time is calculated depending on a point in time at which the straight line or the straight line segment takes on a given value. [8] Method according to one of the preceding claims, wherein the second measurement time window (10, 16a) has the predefined measurement time duration or wherein all measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) of the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) have the predefined measurement time duration. [9] Method according to one of the preceding claims, wherein - the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) have at least one further first measurement time window (15b), wherein the first measurement time window (9, 15a) and the at least one further first measurement time window (15b) form a first sequence of immediately consecutive measurement time windows; and - each of the at least one further first measurement time window (15b) has the predefined measurement time duration. [10] Method according to one of the preceding claims, wherein - the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) have at least one further second measurement time window (16b), wherein the second measurement time window (10, 16a) and the at least one further second measurement time window (16b) form a second sequence of immediately consecutive measurement time windows; and - each of the at least one further second measurement time window (16b) has the predefined measurement time duration. [11] Method according to one of the preceding claims, wherein - the at least two measurement time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) include a third measurement time window (11, 17a) and a start time of the third measurement time window (11, 17a) lies after the start time of the second measurement time window (10, 16a); - the start time of the third measurement time window (11, 17a) lies after the start time of the first measurement time window (9, 15a) by a further time difference which is smaller than the measurement time duration. [12] Method for at least partially automatically driving a motor vehicle (1), wherein a method according to one of the preceding claims is carried out and, depending on the distance, at least one control signal for at least partially automatically driving the motor vehicle (1) is generated. [13] Active optical sensor system (2) comprising an emitter unit (22) which is configured to emit a light pulse (6a) into an environment of the active optical sensor system (2), and a detector unit (23) which is configured to generate a sensor signal based on portions (6b) of the light pulse (6a) reflected by an object (5) in the environment, and at least one computing unit (4, 24) which is configured to - to determine a measured value for at least two measuring time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) in each case as a function of an amplitude of the sensor signal during the respective measuring time window, wherein a first measuring time window of the at least two measuring time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) has a predefined measuring time duration, and wherein a start time of a second measuring time window of the at least two measuring time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b) lies after a start time of the first measuring time window by a time difference which is shorter than the measuring time duration; - to determine a light propagation time of the reflected portions (6b) of the light pulse (6a) depending on the measured values ​​determined for the at least two measuring time windows (9, 10, 11, 15a, 15b, 16a, 16b, 17a, 17b); and - to calculate the distance depending on the light travel time. [14] Active optical sensor system (2) according to claim 13, which is designed as a lidar sensor system. [15] Electronic vehicle guidance system (3) comprising an active optical sensor system (2) according to one of claims 13 or 14, wherein the at least one computing unit (4, 24) is configured to generate at least one control signal for at least partially automatically guiding a motor vehicle (1) as a function of the distance. [16] Computer program product comprising - commands which, when executed by an active optical sensor system (2) according to one of claims 13 or 14, cause the active optical sensor system (2) to carry out a method according to one of claims 1 to 11; and / or - further commands which, when executed by an electronic vehicle guidance system (3) according to claim 15, cause the electronic vehicle guidance system (3) to carry out a method according to claim 12.

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