WO2023280647A1

WO2023280647A1 - Method for correcting optical crosstalk between pixels of an optical detection device, and corresponding detection device

Info

Publication number: WO2023280647A1
Application number: PCT/EP2022/067823
Authority: WO
Inventors: Thorsten BEUTH; Christoph Parl
Original assignee: Valeo Schalter Und Sensoren Gmbh
Priority date: 2021-07-06
Filing date: 2022-06-29
Publication date: 2023-01-12
Also published as: DE102021117361A1

Abstract

A method for operating an optical detection device for determining at least distance variables that characterize distances of objects captured by the optical detection device is described. In the method, at least one electromagnetic scanning signal is generated and transmitted into a monitoring region. With at least some of pixels of an optical reception matrix, at least one electromagnetic echo signal is captured and converted into electrical reception signals. In at least one short measurement phase (MP_K), with at least some of the pixels, echo signals with at least one short integration duration (t_INT,K) are received and converted into electrical reception signals. For at least one pixel, at least one correction variable is determined by means of the at least one reception signal. In a long measurement phase (MPL), with at least some of the pixels, echo signals with a long integration duration (t_INT,L) are received and converted into reception signals. For at least some of the pixels, at least one distance variable is determined by means of at least one reception signal from a long measurement phase (MP_L) and at least one correction variable from a short measurement phase (MP_K).

Description

METHOD OF CORRECTING OPTICAL CROSSTALK BETWEEN PIXELS OF AN OPTICAL DETECTION DEVICE AND CORRESPONDING DETECTION DEVICE

technical field

The invention relates to a method for operating an optical detection device for determining at least distance variables which characterize distances from objects detected with the optical detection device, in which at least one electromagnetic scanning signal is generated and sent to a monitoring area of the detection device, with at least one part of pixels of an optical receiver matrix, at least one electromagnetic echo signal, which originates from at least one electromagnetic scanning signal reflected on an object, is detected and converted into corresponding electrical reception signals, and by means of at least a part of the reception signals at least one distance variable, which is a distance at least of a detected object to which characterizes at least one detection device is determined.

Furthermore, the invention relates to a detection device for determining at least distance variables which characterize distances from objects detected with the detection device, which has at least one transmission device with which at least one electromagnetic scanning signal can be generated and sent into at least one monitoring area of the detection device, and at least a receiving device with at least one optical receiver matrix with a plurality of pixels, with which electromagnetic echo signals, which stem from at least one electromagnetic scanning signal reflected on an object, can be detected and converted into corresponding electrical reception signals.

The invention also relates to a vehicle with at least one detection device for determining at least distance variables which characterize distances from objects detected with the detection device, wherein the at least one detection device has at least one transmission device, with which at least one electromagnetic scanning signal is generated and transmitted to at least one monitoring area of the Detection device can be sent, and at least one receiving device with at least one optical receiver matrix a plurality of pixels with which electromagnetic echo signals, which stem from at least one electromagnetic scanning signal reflected on an object, can be detected and converted into corresponding received electrical signals.

State of the art

A TOF (time-of-flight) distance sensor and a method for operating a TOF distance sensor are known from EP 2743724 B1. The TOF distance sensor comprises an electronic device for generating a modulation signal and for generating four correlation signals which are phase-shifted with respect to one another and have the same period length as the modulation signal; a radiation source for emitting radiation modulated with the modulation signal; a receiving device which is in a predetermined spatial relationship to the radiation source for receiving radiation reflected from the object; a correlation device for correlating the received radiation or a corresponding quantity with one of the four correlation signals to form four corresponding correlation values; a difference-forming device for forming two differential correlation values from the difference between two of the correlation values in each case; a calculation device which is designed to calculate the distance in a predetermined linear dependence on the two differential correlation values.

The invention is based on the object of designing a method, a detection device and a vehicle of the type mentioned at the outset, in which a determination of distance variables in scenes with objects that are reflective to different degrees with respect to the scanning signals can be improved.

Disclosure of Invention

The object is achieved according to the invention in the method in that optical crosstalk between pixels of the receiver matrix is corrected, with echo signals with at least a short integration period being received and converted into electrical reception signals in at least one short measurement phase with at least some of the pixels, for at least one pixel in which at least one amplitude of at least one received signal is greater than in at least one other pixel, at least one correction variable is determined by means of the at least one received signal is, in at least one long measurement phase with at least some of the pixels, echo signals with at least one long integration period, which is longer than the at least one short integration period, are received and converted into electrical reception signals, for at least some of the pixels at least one distance variable, which characterizes a distance of at least one detected object, is determined by means of at least one received signal from at least one long measurement phase and at least one correction variable from at least one short measurement phase.

According to the invention, echo signals are received with a short integration period in at least one short measurement phase. At least one correction value is determined for at least one pixel. The at least one correction variable is used to correct the effects of optical crosstalk between the pixels in at least one long measurement phase with at least one long integration period.

The at least one correction variable can advantageously be determined for at least one pixel in which at least one amplitude of at least one received signal is greater than in at least one other pixel. In this way, the correction variable can be determined for pixels that encounter strong echo signals that can lead to optical crosstalk.

With short integration times, optical crosstalk between the pixels is reduced. In this way, the pixels can be identified that are hit by echo signals from strongly reflecting objects. With correspondingly short integration times, only strongly reflecting objects provide sufficiently strong echo signals to be recognized by the pixels. With longer integration times, however, echo signals from strongly reflecting objects can lead to optical crosstalk between the pixels, so that received signals are overlaid by weaker echo signals originating from weaker reflecting objects.

At least one correction variable is determined using the received signals from the identified pixels. With the aid of the at least one correction variable, the optical crosstalk is reduced in the case of longer integration times, so that weaker reflecting objects can also be detected. Thus, through a combination of short measurement phases with shorter integration times, in which correction variables can be determined den, and long measurement phases with longer integration periods, which are corrected with the correction variable, the respective distance variables can also be determined in scenes with both strongly reflecting objects and weakly reflecting objects. For this purpose, no further, in particular active, change in intensity of the lighting device, in particular of the scanning signals, in particular with dynamic controllers, is required on the basis of a scene with objects reflecting to different degrees.

With the invention, strongly reflective objects, such as traffic signs with retroreflective properties, and less reflective objects, such as pedestrians, obstacles such as walls or the like, can be differentiated in scenes, especially in road traffic, and their respective distances can be determined more accurately. Without the invention, the signals of the distance measurement can be smeared across the receiver matrix due to internal reflections, in particular in the optical receiving path and/or due to optical crosstalk in the detection device. Without the invention, the echo signals from the highly reflective objects effectively overwhelm the echo signals from the weaker reflective objects, thus becoming the dominant information in the rest of the image - even when the weaker reflective objects are at a different distance from the more reflective objects. Without the correction according to the invention, distances from strongly reflecting objects whose echo signals dominate are incorrectly determined for all other objects as well. In a corresponding distance image, weaker reflecting objects are displayed as if they were all at the same distance.

At least distance variables, which characterize distances from objects, can be determined with the method and the detection device. In addition, further information about a monitoring area, in particular about objects, in particular directions and/or speeds of objects relative to the detection device and/or a vehicle with at least one detection device, can be determined with the method and the detection device.

Advantageously, the at least one detection device can work according to an indirect signal propagation time method. Optical detection devices working according to a signal transit time method can be used as time-of-flight (TOF), light-detection and ranging systems (LiDAR), laser detection and ranging systems (LaDAR), radar systems or the like designed and designated. In an indirect signal propagation time method, a phase shift of the received signal relative to the transmitted signal caused by the propagation time of the scanning signal and the corresponding echo signal can be determined. From the phase shift, the distance of an object can be determined from which the corresponding scanning signal is reflected.

Advantageously, optical scanning signals, in particular light signals, in particular laser signals, can be used as electromagnetic scanning signals. Objects can be detected without contact using electromagnetic scanning signals, in particular light signals. Correspondingly, the detection device can be an optical detection device.

The detection device can advantageously be designed as a laser-based distance measuring system. A laser-based distance measuring system can have at least one laser, in particular a diode laser, as the light source of a transmission device. In particular, pulsed light scanning signals can be sent with the at least one laser. The laser can be used to emit scanning signals in wavelength ranges that are visible or invisible to the human eye. Correspondingly, at least one receiver matrix can be implemented with at least one detector designed for the wavelength of the emitted light, in particular a CCD sensor, an active pixel sensor, in particular a CMOS sensor or the like. The laser-based distance measuring system can advantageously be a laser scanner. A monitoring area can be scanned with a laser scanner, in particular with a pulsed scanning signal.

The invention can advantageously be used in vehicles, in particular motor vehicles. The invention can advantageously be used in land vehicles, in particular passenger cars, trucks, buses, motorcycles or the like, aircraft, in particular drones, and/or water vehicles. The invention can also be used in vehicles that can be operated autonomously or at least partially autonomously. However, the invention is not limited to vehicles. It can also be used in stationary operation, in robotics and/or be used in machines, in particular construction or transport machines such as cranes, excavators or the like.

The detection device can advantageously be connected to at least one electronic control device of a vehicle or a machine, in particular a driver assistance system and/or chassis control and/or a driver information device and/or a parking assistance system and/or gesture recognition or the like, or be part of such being. In this way, at least some of the functions of the vehicle or machine can be operated autonomously or partially autonomously.

The detection device can be used to detect stationary or moving objects, in particular vehicles, people, animals, plants, debris, bumps in the road, in particular potholes or stones, road boundaries, traffic signs, open spaces, in particular parking spaces, precipitation or the like, and/or movements and /or gestures are used.

In an advantageous embodiment of the method, at least one correction variable for at least one pixel can be determined from at least one distance variable, which characterizes a distance of at least one detected object, and at least one correction parameter, with at least one correction parameter being determined in advance before the operation of the detection device and/or or at least one correction parameter is calculated from variables that are determined during operation of the detection device. In this way, optical crosstalk can be corrected even more precisely.

The method can be accelerated overall by using correction parameters determined in advance. The correction parameters can be determined in advance, in particular as part of a calibration of the detection device, in particular at the end of a production line, and stored in corresponding storage means of the detection device.

The calculation of correction parameters from variables that are determined during operation of the detection device enables a more individual adjustment of the correction correction parameters and thus an increase in the accuracy of the distance determination.

In a further advantageous embodiment of the method, at least one short measurement phase can be carried out before at least one long measurement phase and/or at least one short measurement phase can be carried out after at least one long measurement phase. Overall, the flexibility of the measurements can be improved in this way.

Advantageously, at least one short measurement phase can be carried out before at least one long measurement phase. In this way, the variables determined as part of the at least one short measurement phase are available more quickly for the at least one long measurement phase.

Alternatively or additionally, at least one short measurement phase can advantageously be carried out after at least one long measurement phase. In this way, it can already be determined from the results of the at least one long measurement phase whether a scene is present in which there is optical crosstalk between pixels. If this is not the case, the short measurement phase can be omitted. In this way, the measurement can be adjusted as required.

In a further advantageous embodiment of the method, at least one short integration period can be set in such a way that optical crosstalk in the optical receiver matrix is minimized. In this way, pixels that receive echo signals from highly reflective objects can be localized more precisely. Furthermore, the correspondingly strong echo signals can be detected more precisely.

In a further advantageous embodiment of the method, at least one long integration period can be set longer than at least one short integration period by a factor of approximately between 10 and 10,000. In this way, objects with correspondingly large differences in terms of their optical reflectivity can each be detected more precisely. Advantageously, at least one short integration period can have a length on the order of microseconds, in particular approximately between 0.5 ps and 2 ps. In this way it can be avoided that echo signals from strongly reflecting objects lead to oversteering and/or to optical crosstalk in neighboring pixels.

Advantageously, at least one long integration period can have a length of the order of 1000 ps, in particular between approximately 500 ps and 10000 ps. In this way, echo signals from weakly reflecting objects can also be detected.

In a further advantageous embodiment of the method, at least one electromagnetic scanning signal can be generated on the basis of at least one electrical transmission signal. In this way, the at least one electrical transmission signal can be generated with corresponding electrical signal generation means. At least one electrical transmission signal can be used to control at least one corresponding electro-optical signal source, in particular a light source, in particular a laser or the like, for emitting electro-optical scanning signals, in particular light signals, in particular laser pulses or the like.

In a further advantageous embodiment of the method, at least one modulated electromagnetic scanning signal can be generated from at least one modulated electrical transmission signal. An indirect propagation time determination can be carried out with modulated transmission signals and scanning signals and corresponding modulated echo signals and reception signals. In this way, phase shifts between the modulated transmission signals and corresponding reception envelope curves of the reception signals can be determined as distance variables. The phase shifts characterize the respective signal propagation time between the transmission of at least a sample signal and the reception of the corresponding echo signal. The distance of a reflecting object can be determined from the signal propagation time.

Advantageously, at least one transmission signal and thus at least one sampled signal can be amplitude-modulated over at least one modulation period. In this way, transmission signals can be efficiently defined on the transmitter side. corresponding Accordingly, reception envelope curves can be efficiently characterized on the receiver side using the reception variables determined with the pixels. The transmission signals and the reception envelope can be compared directly with one another.

At least one scanning signal is generated from at least one transmission signal. The transmission signals are modulated, in particular amplitude modulated. The transmission signals have a modulation period within which the at least one electrical transmission signal is modulated. A modulation period can be specified as a time interval or based on a circle function, in particular as 360° or 2p. Accordingly, the reception envelope is the envelope of the received signals that can be formed from the received echo signal.

Advantageously, at least one modulation period of at least one transmission signal can have a period of the order of magnitude of approximately 10 ms to 100 ms, in particular between 40 ms and 50 ms. With such periods, distances from objects in a few tens of meters to a few hundred meters can be detected.

In a further advantageous embodiment of the method, at least one signal section of at least one electromagnetic echo signal of at least one scanning signal reflected on at least one object can be detected in at least one defined recording time range with at least one pixel and converted into a corresponding electrical received signal. In this way, at least one interpolation point can be defined for a course of a reception envelope.

A recording time range can advantageously be defined by a defined starting point, an end point and/or a duration.

Advantageously, at least one duration of at least one recording time range can be defined by the integration period during which a corresponding pixel is activated in order to record the incident optical energy of an echo signal and convert it into an electrical reception signal. Advantageously, at least one recording time range can be related to at least one characteristic point of at least one electrical transmission signal and/or at least one scanning signal. In this way, the at least one acquisition time range can be assigned more simply and/or unambiguously.

Advantageously, at least one characteristic point of at least one transmission signal and/or at least one sampled signal, to which at least one recording time range can be related, can be a maximum, a minimum, a turning point, a zero crossing or the like, an edge of the at least one transmission signal and/or of the at least one sample signal. In this way, the characteristic point can be determined more precisely.

Advantageously, for at least one modulation period sequence, which comprises at least one modulation period of the at least one electrical transmission signal, for at least one modulation period of the at least one electrical transmission signal with at least two pixels in different defined recording time ranges, respective signal sections of the at least one echo signal can be recorded as electrical reception variables . The reception variables detected with the respective pixels can define respective support points with which a profile of a reception envelope can be approximated. The corresponding signal section of the received echo signal can be recorded in the at least two recording time ranges.

A modulation period sequence comprises at least one modulation period of the at least one electrical transmission signal. At least one modulation period sequence can advantageously include a plurality, in particular approximately 1000 or more, modulation periods. Advantageously, the electrical reception variables can be determined in the same modulation period sequence in the same way, in particular with the same activation of the reception areas.

At least one defined recording time range can advantageously be specified, which is shorter than a modulation period of the at least one electrical transmission signal. In this way, with the data recorded in the respective recording time th signal excerpts of the time course of the reception envelope within the period ode duration of a modulation period can be characterized. A phase shift of the reception envelope compared to the transmission signal can be determined from the recorded signal excerpts. The phase shift characterizes the signal propagation time between the transmission of the scanning signal and the reception of the echo signal. The distance of a reflecting object can be determined from the signal propagation time. The phase shift can thus be used as at least one distance quantity.

Advantageously, the time interval between at least two recording time ranges can be smaller than the duration of a modulation period of the at least one electrical transmission signal. In this way, two support points for at least one reception envelope can be realized within a modulation period.

Furthermore, the object is achieved according to the invention with the detection device in that the detection device has means for carrying out the method according to the invention. In this way, distances from objects with, with regard to the scanning signals, greatly differing reflectivities relative to the detection device can be determined.

Advantageously, the means for carrying out the method according to the invention can be implemented partially or entirely by means of at least one control and evaluation device, at least one transmitting device and/or at least one receiving device.

Advantageously, the detection device can have at least one control and evaluation device. The functions of the detection device can be controlled with the control and evaluation device. As an alternative or in addition, the control and evaluation device can be used to evaluate received signals which are detected with the detection device. Alternatively or additionally, information from the received signals determined with the control and evaluation device can be transmitted to other devices, in particular a driver assistance system. Advantageously, the detection device can have means for correcting optical crosstalk between pixels of the receiver matrix. Scenes with objects that reflect strongly differently can also be detected more precisely with the detection device.

In addition, the object is achieved according to the invention in the vehicle in that the vehicle has at least one detection device with means for carrying out the method according to the invention. In this way, distances of objects relative to the vehicle can be determined that have greatly differing reflectivities with respect to the scanning signals.

The vehicle can advantageously have at least one driver assistance system. With the driver assistance system, the vehicle can be operated autonomously or at least partially autonomously.

Advantageously, at least one detection device can be connected in terms of signals to at least one driver assistance system of the vehicle. In this way, information about the monitoring area, in particular distance variables and/or directional variables, which can be determined with the at least one detection device, can be transmitted to the at least one driver assistance system. With the at least one driver assistance system, the vehicle can be operated autonomously or at least partially autonomously, taking into account the information about the monitoring area.

Otherwise, the features and advantages shown in connection with the method according to the invention, the detection device according to the invention and the vehicle according to the invention and their respective advantageous configurations apply to one another and vice versa. The individual features and advantages can, of course, be combined with one another, which can result in further advantageous effects that go beyond the sum of the individual effects.

Brief description of the drawings

Further advantages, features and details of the invention result from the following description, in which exemplary embodiments of the invention are based on the drawings be explained in more detail. The person skilled in the art will expediently also consider the features disclosed in combination in the drawing, the description and the claims individually and combine them into useful further combinations.

It show schematic

FIG. 1 shows a front view of a vehicle with a driver assistance system and a LiDAR system for determining distances of objects from the vehicle;

FIG. 2 shows a functional representation of the vehicle with the driver assistance system and the LiDAR system from FIG. 1;

FIG. 3 shows a front view of a reception matrix of a reception device of the LiDAR system from FIGS. 1 and 2, the reception matrix having a multiplicity of linear reception areas, each of which consists of a multiplicity of pixels;

FIG. 4 shows a signal strength-time diagram with received quantities, which is determined from an electromagnetic echo signal of a reflected electromagnetic scanning signal of the LiDAR system from FIGS Received signals are determined from the echo signal;

FIG. 5 shows a signal strength-time diagram of an electromagnetic scanning signal of the LiDAR system from FIGS. 1 and 2;

FIG. 6 Signal strength-time diagrams of an electromagnetic echo signal, above, which can be received with the receiving device of the LiDAR system from FIGS. 1 and 2, of a first and a second shutter signal, in the middle and below, for determining a reception variable the electromagnetic echo signals;

FIG. 7 shows an amplitude-time diagram in which the composition of the respective and the four phase images DCS0 to DCS3 are shown, in which echo signals from retroreflective objects lead to optical crosstalk between pixels of the receiving matrix from FIG. 3;

FIG. 8 shows a diagram which shows a relationship between a correction factor Ci and a distance DR of a retroreflective object target, the correction factor Ci being used to correct an optical over- Speech between the pixels is used with a correction method according to a first embodiment;

FIG. 9 is a diagram showing a relationship between phase shifts and test factors used for a correction method for correcting optical crosstalk between pixels according to a second embodiment;

FIG. 10 shows a temporal control scheme for some reception areas of the reception matrix from FIG. 3, according to which the reception areas are controlled alternately with a short integration period and a long integration period.

The same components are provided with the same reference symbols in the figures.

embodiment(s) of the invention

FIG. 1 shows a front view of a vehicle 10 by way of example in the form of a passenger car. Figure 2 shows a functional representation of part of the vehicle 10.

The vehicle 10 has a detection device, for example in the form of a LiDAR system 12. The LiDAR system 12 is arranged in the front bumper of the vehicle 10, for example. With the LiDAR system 12, a monitoring area 14 in the direction of travel 16 in front of the vehicle 10 can be monitored for objects 18, or 18T and 18R. The LiDAR system 12 can also be arranged elsewhere on the vehicle 10 and oriented differently. The LiDAR system 12 can be used to determine object information, for example distances D, or DT and DR, directions and speeds of objects 18 relative to the vehicle 10 or to the LiDAR system 12 .

The objects 18 can be stationary or moving objects, for example other vehicles, people, animals, plants, obstacles, bumps in the road, for example potholes or stones, road boundaries, traffic signs, open spaces, for example parking spaces, precipitation or the like. By way of example, a retroreflective object 1 8R, for example in the form of a traffic sign, road markings or the like, is shown in Figure 2 at a distance DR and a less reflective object 1 8T, such as a pedestrian, a wall or the like, at a distance DT is indicated.

In the following, for the sake of simplicity of explanation, each object 18 is equated with a single object target. An object target is a location on an object 18 at which electromagnetic scanning signals 20 transmitted from the LiDAR system 12 into the surveillance area 14 may be reflected. Each object 18 usually has a number of such object targets.

The LiDAR system 12 is connected to a driver assistance system 22 . The vehicle 10 can be operated autonomously or partially autonomously with the driver assistance system 22 .

The LiDAR system 12 includes, for example, a transmitting device 24, a receiving device 26 and a control and evaluation device 28.

The functions of the control and evaluation device 28 can be implemented centrally or decentrally. Parts of the functions of the control and evaluation device 28 can also be integrated into the transmitting device 24 and/or the receiving device 26 .

The control and evaluation device 28 can be used to generate electrical transmission signals 30, such as a square-wave signal indicated by dashed lines in FIG.

The transmission device 24 can be controlled with the electrical transmission signals 30, so that it transmits corresponding electromagnetic, for example optical, scanning signals 20 in the form of light signals, for example light pulses, as shown by way of example in Figure 5 in the form of square-wave signals, into the monitoring area 14 . For the sake of clarity, FIG. 5 shows only one modulation period MP of the corresponding sampled signal 20 in a signal strength versus time diagram. FIG. 5 only shows the time profile of the corresponding electrical transmission signal 30 for comparison purposes, with the unit of the strength of the electrical transmission signal 30 differing from the signal strength P _s of the electromagnetic scanning signal 20 . The transmitting device 24 can have, for example, one or more lasers as a light source. In addition, the transmission device 24 can optionally have a scanning signal deflection device with which the electromagnetic scanning signals 20 can be correspondingly directed into the monitoring area 14 .

The electromagnetic scanning signals 20 reflected on an object 18 in the direction of the receiving device 26 as electromagnetic echo signals 34 can be received with the receiving device 26 . At the top of FIG. 6, an echo signal 34 is shown as an example, which belongs to the scanning signal 20 from FIG. Like the corresponding scanning signal 20, the echo signal 34 is a square-wave signal.

The receiving device 26 can optionally have an echo signal deflection device, with which the electromagnetic echo signals 34 are directed to a receiving matrix 36 of the receiving device 26 shown in the front view in FIG. The reception matrix 36 is implemented, for example, with an area sensor in the form of a CCD sensor with a large number of pixels 38 .

With the pixels 38 of the reception matrix 36, the components of the electromagnetic echo signal 34 which are incident in each case can be converted into corresponding electrical reception signals.

Each pixel 38 can be activated via suitable locking means for the detection of electromagnetic echo signals 34 for defined recording time ranges TB. For better differentiation, different recording time ranges TB can be provided with different indices, for example i, in the following, ie they can be referred to as recording time range TBi. By way of example, the pixels 38 can each be activated in four recording time ranges TB1, namely TB0, TB1, TB2 and TB3, for detecting received signals 34, which are labeled in FIG. 4, for example. Each recording time range TBi is defined by a start time and an integration period ΪINT. The integration periods ΪINT of the recording time ranges TBi are significantly shorter than a period tMOD of the modulation period MP of the transmission signal 30 and the electromagnetic scanning signal 20. The time intervals between two defined recording time ranges TBi are shorter than the period tMOD of the modulation period period MP. Several consecutive modulation periods MP can be seen below for better distinction with a respective index, for example k, ver, ie referred to as modulation period MPk.

During a recording time range TBi, portions of echo signals 34 striking the respective pixel 38 can be converted into corresponding received electrical signals. From the received signals, respective phase images DCSi (Differential Correlation Sample) and their amplitudes Ai can be determined, which characterize respective signal excerpts of the echo signal 34 in the respective recording time ranges TBi. The phase images DCSo, DCSi, DCS2 and DCS3 and their amplitudes Ao, A-i, A2 and A3 characterize the respective amount of light that is collected during the recording time ranges TBo, TBi, TB2 and TB3 with the correspondingly activated pixels 38 of the receiver 36.

For example, each pixel 38 can be activated and read out individually. The closure means can be implemented in software and/or hardware. Such closure means can be realized as a so-called “shutter”. By way of example, the pixels 38 can be driven with corresponding periodic recording control signals in the form of shutter signals 56-1 and 56-2. By way of example, the shutter signals 56-1 and 56-2 are shown in FIG. 6 in the middle and at the bottom, with which the respective receiver pixels 38 are controlled in order to determine the reception variable DCSo. The shutter signals 56-1 and 56-2 are square-wave signals with the same period as the transmission signals 30, the scanning signals 20 and the echo signals 34. The shutter signals 56-1 and 56-2 are transmitted via the electrical signals 30 or triggered together with these. Thus, the received electrical signals will be related to the transmitted electrical signals 30 . For example, the electrical transmission signals 30 can be triggered at a starting time ST, which is indicated in FIG. The receiver pixels 38 are triggered with the shutter signals 56-1 and 56-2, which are offset in time accordingly.

The pixels 38 are arranged areally in, for example, more than 100 receiver areas EBi in the form of lines, each with, for example, more than 100 pixels 38 . For example, the pixels 38 of a receiver area EBi are equal in a modulation period MPk activated early in the same recording time range TBi. The pixels 38 of adjacent receiver areas EBi can be activated in a modulation period MPk, for example, in different or identical recording time ranges TBi.

The receiving device 26 can optionally have optical elements, for example refractive elements, diffractive elements and/or reflective elements or the like, with which electromagnetic echo signals 34 coming from the monitoring area 14 are viewed in the direction of the receiving areas EBi depending on the direction from which they come are mapped onto respective pixels 38. The direction of an object 18 on which the scanning signal 38 is reflected can thus be determined from the position of the illuminated pixels 38 within a receiver area EBi. Viewed in the direction perpendicular to the receiver areas EBi, the echo signals 34 are imaged as uniformly as possible on the pixels 38 in the same column of all receiver areas EBi.

FIG. 4 shows a modulation period MP of a reception envelope curve 42 of the reception variables DCSo, DCSi, DCS2 and DCS3 in a common signal strength/time diagram.

The reception envelope curve 42 is offset in time with respect to the start time ST. The time offset in the form of a phase difference F characterizes the flight time between the transmission of the electromagnetic scanning signal 20 and the reception of the corresponding electromagnetic echo signal 34.

The distance D of the reflecting object 18 can be determined from the phase difference F. The phase shift F can therefore be used as a distance variable for distance D. The time of flight is known to be proportional to the distance D of the object 18 relative to the LiDAR system 12.

The period duration tMOD of the transmission signals 30 and the scanning signals 20 specifies the maximum distance that can still be clearly detected with the LiDAR system 12 . The period tMOD is greater than the flight time of the scanning signal 20 and the echo signal 34 in the case of reflections from objects 18 at the maximum distance of interest. The measurement duration of a measurement corresponds to the period duration tMOD. Exemplary the period duration tMOD can be of the order of about 40 ms to 50 ms. Distance measurements can be carried out continuously within the unambiguity range. Distances outside the maximum distance, which are not within the unambiguous range, can also be recorded by appropriate data processing, which is of no further interest here.

The reception envelope curve 42 can be approximated by four interpolation points in the form of the four phase images DCSo, DCSi, DCS2 and DCS3. Alternatively, the reception envelope curve 42 can also be approximated by more or fewer support points in the form of phase images.

The recording time ranges TBo, TB1, TB2 and TB3 are each started in relation to a start event, for example in the form of a trigger signal for the electrical transmission signal 30 . For example, the modulation period MPk of the transmission signal 30 and thus of the sampled signal 20 extends over 360°. The recording areas TBo, TB1, TB2 and TB3 each start at a distance of 90° relative to the modulation period MP.

A distance D of a detected object 18 can be calculated, for example, from the amplitudes Ao, Ai, A2 and A3 of the phase images DCSo, DCS1, DCS2 and DCS3 for a respective pixel 38 as follows:

Here, c is the speed of light and fs is the modulation frequency of the transmission signal 30. The term from the amplitudes Ao, A-i, A2 and A3 of the phase images DCSo, DCS1, DCS2 and DCS3 represents the phase shift F.

If there is a scene with objects 18 reflecting differently, as shown by way of example in FIG Strength of the echo signal 34 reflected from the less reflective object 18T. Depending on the integration Duration ΪINT, the echo signal 34 from the retroreflective object 18R can cause optical crosstalk between the pixels 38 that are directly hit by the echo signal 34 of the retroreflective object 18R and the neighboring pixels 38 that are hit by the echo signals 34 of the object 18T, for example , to lead. Depending on the integration period ΪINT, the measurement for the retroreflective object 18R itself can be overdriven. Consequently, the distances D of the object 18 cannot be determined or cannot be determined correctly.

Due to internal reflections, for example in an optical reception path and/or due to optical crosstalk in the reception matrix 36, the signal from the distance measurement can smear over large parts of the reception matrix 36. The echo signal 34 reflected from the retroreflective object 18R can effectively overlay the echo signals 34 from the other object 18T in the reception matrix 36 and form the dominant information in the rest of the image. The distance DR of the retroreflective object 18R is thus incorrectly assumed for the object 18T.

FIG. 7 shows an amplitude-time diagram for the respective amplitudes Ao, A-i, A2 and A3 of four phase images DCSo, DCS1, DCS2 and DCS3 in an exemplary distance measurement with an exemplary pixel 38, which is shown below for better differentiation referred to as the target pixel 38 for the object of interest 18T. The distance measurement took place in a measurement phase MP in the scene with the object 18T and the retroreflective object 18R shown as an example in FIG. The target pixel 38 is directly illuminated by the echo signal 34 coming from the object 18T. Furthermore, optical crosstalk from pixels 38, which are illuminated with the strong echo signal 34 coming from the retroreflective object 18R, affects the phase images DCSo, DCS1, DCS2 and DCS3 acquired with the target pixel 38 and their amplitudes Ao, A-i, A2 and A3 off.

Each amplitude Ak, where k is the index for the corresponding phase image DCSk, which is detected with the target pixel 38, is made up of a background noise N, in each case at the bottom in FIG. 7, and an amplitude component AAT,k, FIG. 7 in the middle , which originates from the echo signal 34 of the object 18T, and an amplitude component AAR,k, FIG. 7 above, which originates from the optical crosstalk of the echo signal 34 of the retroreflective object 18R. The background noise N is almost the same across all phase images DCSk.

The amplitude component AAT,k of the object 18T depends on the distance DT at which the object 1 8T is located and, accordingly, on the phase shift Ft . The following applies:

(G 2) AA _{T k} — A _{T k} sin(f _M0D t _INT + F _t )

In this case AT,k is an amplitude parameter of the phase image DCSk for the object 18T, fMOD is the modulation frequency of the transmission signal 30 and ΪINT is the integration period for the measurement.

The amplitude component AAR,k from the crosstalk effect of the retroreflective object 18R on the target pixel 38 is dependent on the distance DR at which the retroreflective object 18R is located and correspondingly on the phase shift OR. IT applies:

In this case, Ai,R,k are individual amplitude parameters of the phase image DCSk for the pixels 38 which are illuminated by the echo signal 34 of the retroreflective object 18R and from which optical crosstalk to neighboring pixels 38 emanates. The run parameter i designates the pixels 38, other than the target pixel 38, from which optical crosstalk originates.

For the amplitudes Ak, which are detected with the target pixel 38, the following applies:

Without the background noise N and the amplitude component AAR,k from the optical crosstalk effect, using the phase images DCSo, DCSi, DCS2 and DCS3 captured with the exemplary target pixel 38 according to the above equation G1, the corresponding distance DT of the object 18t can be determined from:

(G5)

The background noise N can easily be determined, for example by means of calibration measurements.

The amplitude component AAR.L from the optical crosstalk effect can be approximated as follows using a correction term KT.

For this purpose, at least one distance measurement (short distance measurement) in a short measurement phase in the form of a measurement period MPK with a short integration period tiNT.K and at least one distance measurement (long distance measurement) in a long measurement phase in the form of a measurement period MPL with a long -Integration time tiNT.L performed. The distance measurements can be carried out, for example, according to a control scheme that is explained further below in connection with FIG.

The length of the short integration period ΪINT,K is chosen such that the strong echo signals 34 from the retroreflective object 18R do not lead to an overload in the reception matrix 36 either. For example, the short integration time ΪINT,K can be about 1 ps. The phase shift OR for the retroreflective object 18R, which correlates with the distance DR, is determined from the amplitudes Ao, A-i, A2 and A3 of the phase images DCSo, DCS1, DCS2 and DCSa recorded during the short distance measurement.

The length of the long integration period tiNT.L is chosen such that weaker echo signals 34 from the object 18T can also be detected. For example, the long integration period tiNT.L can be about 1000 ps. For the sake of simplicity, it is assumed below that the echo signals 34 from the object 18T are only detected by one pixel 38 (target pixel 38) during the long-distance measurement.

The correction term KT is based on the phase shift OR from the short Distance measurement as follows:

(G6) KT — '' C _j sin(f _MOD t _{INT i} + F _b ) i

In this case, Ci is a respective correction factor for the pixels 38 as well as target pixels 38. As will be explained in more detail below, the correction factor Ci can be specified or determined from measured values of distance measurements. The longer the integration period ΪINT,L, the greater the correction term KT. Furthermore, the correction term KT becomes all the larger, the greater the number of pixels 38 that are detected as having been hit by echo signals 34 of the retroreflective object 18R in the short distance measurement.

From the amplitudes Ak recorded during the long distance measurement, namely Ao, Ai, A2 and A3, of the phase images DCSo, DCS1, DCS2 and DCS3, the background noise N and the correction term KT are determined as follows from the recorded amplitudes Ak, namely Ao , Ai, A2 and A3, and the corresponding corrected amplitudes Ak,corr , namely Ao,corr, Ai,corr, A2,corr and A3,corr , are determined!

so

In this way, the influence of the optical crosstalk through the retroreflective object 18R is reduced.

The distance DT of object 1 8T is determined from the corrected amplitudes Ao,corr, Ai, _Corr , A2,corr and A3,corr analogously to equation G5:

Two exemplary embodiments for methods for determining the correction term KT are explained below:

In a first exemplary embodiment for determining the correction term KT, the correction factor Ci is specified, for example, from model considerations. It is assumed that the individual amplitude parameters Ai,R,k of the phase image DCSk for the pixels 38 that are illuminated by the echo signal 34 of the retroreflective object 18R depend on the distance DR of the retroreflective object 18R from Equation G3. Correspondingly, the correction factor Ci is specified as a function of the distance DR. For example, there can be an exponential relationship between the correction factor Ci and the distance DR, as shown in FIG.

In a second exemplary embodiment for determining the correction term KT, the correction factor Ci is determined from measured values of distance measurements. Here, using Equation G8, for the pixels 38 that have a phase shift Fr close to the phase shift OR for the retroreflective object 18R, for different test factors TFi that are used instead of the correction factor Ci, the respective test phase shifts <t> test calculated. With good nutrition, the test phase shifts 0Test approach the phase shift Ft, which corresponds to the detected object 18T, with the corresponding test factor TFi.

The adjusted equation based on equation G8 is:

The relationship between the test phase shift Ft _q eί and the test factor TFi is shown in a diagram in FIG. There the test phase shifts Ftqeί for, for example, nine different test factors TFi.i to TFi,g shown.

The pairs of values for the test phase shifts Ftqeί for the first three test factors TFi,i to TFi,3, on the left in FIG. 9, all lie approximately on a first plateau 46 in the area of the phase shift Fh for the retroreflective object 18R.

The pairs of values for the test phase shifts Ftqeί for the last three test factors TFi,7 to TFi,9, on the right in FIG. 9, are all approximately on a second plateau 48 in the area of the phase shift Fh for the retroreflective object 18R plus 180°.

The pairs of values for the test phase shifts <t>Test for the mean test factors TFi,4 to TFi,6 lie approximately on a straight line 50, which extends between the pair of values for the test phase shifts <t>Test for the test factors TFi,3 and the pair of values for the test phase shift <t>Test for the test factor TFi,z , ie between the first plateau 46 and the second plateau 48 .

To determine the desired correction factor Ci, it is assumed that the actual phase shift Ft for the object 1 8T lies in the middle between the phase shift <t>R and the phase shift OR +180°. It can be seen from FIG. 9 that the pair of values with the phase shift Ft and the correction factor Ci lies on the straight line 50. The correction factor Ci sought can be determined, for example, by a numerical method, an iteration method or the like.

If the phase shift Ft is in the range of the phase shift Fh anyway, no major change in the phase shift is to be expected.

With the method according to the second exemplary embodiment, the correct range of the signal of the object 1 8T lying below the interference signal of the retroreflective object 1 8R can be calculated out. This method works very well when the spillover from the interference signal is very strong, since the two plateaus 46 and 48 differ greatly.

The two methods for determining the correction term KT according to the one explained above Exemplary embodiments can also be combined in different orders.

FIG. 10 shows a timing control scheme for an example of four reception areas EBn to EBn ₊₃ for measurement cycles each with four modulation periods MPi to MP, which can be used for the above-described method for correcting crosstalk. FIG. 10 shows an example of a complete measurement cycle with the modulation periods MPi to _MP4 and a section of another measurement cycle with the modulation periods MPi to MP3.

In each modulation period MPi, the reception areas EB _n to EB _n+3 are activated with different recording time areas TBo to TB3. The reception areas EBn to EBn ₊₃ cover all four phase images DCS0 to DCS3 in the modulation period MPi. For example, in the first modulation period MPi, the reception area EB _n is activated with the recording time range TBo, the reception area EB _n+i is activated with the recording time range TB1, the reception area EB _n +2 is activated with the recording time range TB2 and the reception area is activated EB _n+3 with the recording time range TB3.

As the modulation periods MP progress, the counter i for the respective recording time range TBi is incremented by one in the reception ranges EB _n to EBn ₊₃ . Thus, in four successive modulation periods MP, each of the reception areas EBn to EBn ₊₃ is controlled with a total of all four recording time areas TBo to TB3. For example, the reception area EB _n is activated in the four successive modulation periods MPi to MP ₄ in succession with the recording time areas TBo to TB3.

In each case in the second modulation period MP2 of a measurement cycle, the reception areas EBn to EBn ₊₃ are driven with the short integration period ΪINT,K, for example with 1 ps. A short distance measurement as described above is carried out in each case in the second modulation periods MP2. The second modulation periods MP2 form short measurement phases and are additionally provided with the index “K” in FIG. 10 for better differentiation. In the first modulation period MPi, the third modulation period MP3 and the fourth modulation period MP4, the reception areas EB _n to EB _n+3 are driven with the long integration period tiNT.L, for example with 1000 ps. The long-distance measurements described above are carried out in the modulation periods MPi, MP3 and MP4. The modulation periods MPi, MP3 and MP4 form the long measurement phases and are additionally provided with the index “L” in FIG. 10 for better differentiation.

In an embodiment that is not shown, the distance DR and/or the phase shift OR for the retroreflective object 18R can also be estimated instead of being determined using the short distance measurement. In this way, the repetition rate of distance measurements with the LiDAR system 12 can be increased.

In further exemplary embodiments that are not shown, different modulation frequencies fMOD can also be used for the transmission signal 30 in the short-distance measurement and the long-distance measurement. The modulation frequencies fMOD used can be offset against each other. In this way, the short distance measurement can be extended to determine an unambiguity in phase measurements.

Claims

Expectations

1. Method for operating an optical detection device (12) to determine at least distance variables (F) which characterize distances (D) from objects (18) detected with the optical detection device (12), in which at least one electromagnetic scanning signal (20 ) is generated and sent into a monitoring area (14) of the detection device (12), with at least some of the pixels (38) of an optical reception matrix (36) at least one electromagnetic echo signal (34) which is emitted by at least one on an object ( 18) reflected electromagnetic scanning signal (20), is detected and converted into corresponding received electrical signals, and by means of at least some of the received signals, at least one distance variable (F), which indicates a distance (D) of at least one detected object (18) from the at least Characterized a detection device (12), is determined, characterized in that optical Übers speech between pixels (38) of the reception matrix (36) is corrected, with echo signals (34) with at least one short integration period (ΪINT,K) being received with at least some of the pixels (38) in at least one short measurement phase (MPK) and are converted into electrical reception signals, at least one correction variable (KT) is determined for at least one pixel (38) by means of the at least one reception signal, in at least one long measurement phase (MPL) with at least some of the pixels (38) having echo signals (34). at least one long integration period (ΪINT,O, which is longer than the at least one short integration period (ΪINT,K), and converted into received electrical signals, for at least some of the pixels (38) by means of at least one received signal from at least one Long measurement phase (MPL) and at least one correction variable (KT) from at least one short measurement phase (MPK) at least one distance variable (F) is determined, which is a distance (D) little least one detected object (18) characterizes.

2. The method according to claim 1, characterized in that a correction variable (KT) for at least one pixel (38) from at least one distance variable (F), which characterizes a distance (D) of at least one detected object (18), and at least one correction parameter (C) is determined, with at least one correction parameter (C) being determined in advance before the operation of the detection device (12) and/or at least one correction parameter (C) is calculated from variables that are determined during operation of the detection device (12).

3. The method according to claim 1 or 2, characterized in that at least one short measurement phase (MPK) is carried out before at least one long measurement phase (MPL) and/or at least one short measurement phase (MPK) after at least one long -Measurement phase (MPL) is carried out.

4. The method as claimed in one of the preceding claims, characterized in that at least one short integration period (ΪINT,K) is set so that optical crosstalk in the optical receiving matrix (36) is minimized.

5. The method as claimed in one of the preceding claims, characterized in that at least one long integration period (tiNT.L) is set longer by a factor of approximately between 10 and 10,000 than at least one short integration period (ΪINT,K).

6. The method according to any one of the preceding claims, characterized in that at least one electromagnetic scanning signal (20) is generated on the basis of at least one electrical transmission signal (30).

7. The method as claimed in one of the preceding claims, characterized in that at least one modulated electromagnetic scanning signal (20) is generated from at least one modulated electrical transmission signal (30).

8. The method according to any one of the preceding claims, characterized in that with at least one pixel (38) at least one signal section of at least one electromagnetic echo signal (34) at least one of at least one object (18) reflected scanning signal (20) in at least one defined recording time rich (TB) is detected and converted into a corresponding electrical reception signal.

9. Detection device (12) for determining at least distance variables (F) which characterize distances (D) from objects (18) detected with the detection device (12), which has at least one transmission device (24) with which at least one electromagnetic cal Scanning signal (20) can be generated and sent into at least one monitoring area (14) of the detection device (12), and at least one receiving device (26) with at least one optical receiving matrix (36) with a plurality of pixels (38) with which electromagnetic Echo signals (34), which originate from at least one electromagnetic scanning signal (20) reflected on an object (18), can be detected and converted into corresponding electrical reception signals, characterized in that the detection device (12) has means for carrying out the method according to any of the preceding claims.

10. Vehicle (10) with at least one detection device (12) for determining at least distance variables (F) which characterize distances (D) from objects (18) detected with the detection device (12), the at least one detection device (12) has at least one transmitting device (24) with which at least one electromagnetic scanning signal (20) can be generated and sent into at least one monitoring area (14) of the detection device (12), and at least one receiving device (26) with at least one optical receiving matrix ( 36) with a plurality of pixels (38) with which electromagnetic echo signals (34) originating from at least one electromagnetic scanning signal (20) reflected on an object (18) can be detected and converted into corresponding electrical reception signals, characterized in that that the vehicle (10) has at least one detection device (12) means for carrying out ung of the method according to any one of claims 1 to 8.