METHOD FOR CONTROLLING SENSOR ELEMENTS OF A LIDAR MEASURING SYSTEM

Description

[0001] The invention relates to a method for controlling sensor elements of a LIDAR measuring system.

[0002] WO 2017 081 294 describes a LIDAR measuring system. It is statically configured and comprises a transmitting unit with a plurality of emitter elements and a receiving unit with a plurality of sensor elements. The emitter elements and the sensor elements are configured in a focal plane array configuration and arranged at a focal point of a respective transmitting optics and receiving optics. With respect to the receiving unit and the transmitting unit, a sensor element and a corresponding emitter element are assigned to a specific solid angle. The sensor element is thus assigned to a specific emitter element.

[0003] In a more advantageous design variant of the LIDAR measurement system, a sensor element is part of a macrocell, with the macrocell containing a plurality of sensor elements being assigned to an emitter element. This allows imaging errors caused, for example, by the optical elements or parallax errors to be compensated. However, the large number of sensor elements leads to excessive detection of ambient radiation. Since usually only a portion of the sensor elements are hit by a reflected laser light, it is advantageous to activate only those sensor elements that are also hit by the laser light.

[0004] US 2015 / 0285625 A1 discloses an apparatus and method for determining a distance to an object using a binary event-based image sensor.

[0005] DE 10 2009 029 372 A1 relates to a measuring device for measuring a distance between the measuring device and a target object using optical measuring radiation.

[0006] US 2016 / 0209498 A1 describes a system and a method for measuring a time delay experienced by an optical signal along a path with respect to photon-sensitive detectors and multiple optical pulse rates.

[0007] The task is therefore to provide a method to keep the ambient radiation detected by the sensor elements at the lowest possible level.

[0008] This object is achieved by the method according to the valid patent claim 1. Advantageous embodiments of the method are described in the dependent patent claims.

[0009] Such a method is particularly suitable for LIDAR measurement systems that operate according to the TCSPC (Time Correlated Single Photon Counting) method. This TCSPC method is explained in more detail below, especially in the description of the figures. The method is particularly designed for LIDAR measurement systems used in motor vehicles.

[0010] A suitable LIDAR measurement system for this purpose comprises sensor elements and emitter elements. An emitter element emits laser light and is implemented, for example, as a VCSEL (Vertical Cavity Surface Emitting Laser). The emitted laser light can be detected by the sensor element, which is implemented, for example, as a SPAD (Single Photon Avalanche Diode). The distance of the object from the LIDAR measurement system is determined from the time of flight of the laser light or laser pulse.

[0011] The emitter elements are preferably formed on a transmitting chip of a transmitting unit. The sensor elements are preferably formed on a receiving chip of a receiving unit. A transmitting optics and a receiving optics are assigned to the transmitting unit and the receiving unit, respectively. The light emitted by an emitter element is assigned to a solid angle by the transmitting optics. Likewise, a sensor element always observes the same solid angle via the receiving optics. Accordingly, one sensor element is assigned to one emitter element, or both are assigned to the same solid angle. The emitted laser light therefore always strikes the same sensor element after reflection in the far field.

[0012] The sensor elements and emitter elements are advantageously designed in a focal plane array (FPA) configuration. Here, the elements of a respective unit are arranged in one plane, for example, the sensor elements on one plane of the sensor chip. This plane is located in the focal plane of the respective optics, or the elements are arranged at the focal point of the respective optics.

[0013] The FPA configuration allows for a static design of the LIDAR measurement system and its transmitter and receiver units, meaning they contain no moving parts. Specifically, the LIDAR measurement system is mounted statically on a vehicle.

[0014] A plurality of sensor elements are advantageously assigned to an emitter element, which together form a macrocell composed of several sensor elements. This macrocell, or all sensor elements of the macrocell, are assigned to an emitter element. This allows imaging effects or aberrations, such as the parallax effect or lens misalignments, to be compensated.

[0015] Optical aberrations are static, whereas parallax has an influence that depends on the distance of the object from the LIDAR measurement system. For example, different sensor elements of the macrocell are illuminated for close objects than for objects in the medium or long range. Furthermore, by permanently activating all sensor elements of the macrocell, background radiation is detected more effectively than if only the required sensor elements are active.

[0016] A sensor element or a portion of the sensor elements is thus activated and / or deactivated during a measurement cycle to minimize detection of ambient radiation. This activation and deactivation of the sensor element occurs between the beginning and end of a measurement cycle, specifically between the first activation and the last deactivation of the sensor element or sensor elements with respect to the measurement cycle.

[0017] According to the invention, the sensor elements of the macrocell are divided into sensor groups for the various measuring ranges, so that a sensor group is assigned to each measuring range. The measuring range can, for example, be divided into a near range, a medium range, and a long range, with a different selection of the sensor elements of the macrocell being active in each of the ranges. For this purpose, the sensor elements of the macrocell can be activated and / or deactivated individually or at least together as a respective sensor group. The sensor elements of the sensor groups can partially or completely overlap, or they can have no overlap within the macrocell. This means that a sensor element can, for example, be a member of the sensor group for the medium range and the long range, or it can be assigned exclusively to a specific measuring range.

[0018] Accordingly, during a transition between the measuring ranges, one sensor group with all sensor elements may be deactivated and another non-overlapping sensor group may be activated. In another variant, some of the sensor elements may be deactivated, while some remain active. If necessary, additional, previously inactive sensor elements may also be activated in the latter variant.

[0019] Each of the active sensor elements contributes a portion to the background noise caused by the ambient radiation. Regarding the measurement process and a histogram determined using the TCSPC method, steps occur between the different measurement ranges, resulting from the detection of the ambient radiation by the changing number of active sensor elements. Each sensor element contributes to the background noise for its active period.

[0020] A measurement process comprises several measurement cycles. The histogram is the result of a measurement process. A measurement cycle contains at least the time required for the laser light to travel back and forth to an object at the maximum measurement distance. The histogram divides the measurement duration of a measurement cycle into time periods, also called bins. A bin corresponds to a specific time period of the total measurement duration.

[0021] If a sensor element is triggered by an incoming photon, the bin, which corresponds to the corresponding travel time starting from the emission of the laser pulse, is incremented by 1. During a measurement process, the measurement cycle is repeated multiple times so that the ambient radiation fills the bins essentially evenly. However, an object that reflects the laser light ensures that a specific bin is filled in each measurement cycle, which corresponds to the object's distance from the LIDAR measurement system. The majority of measurement cycles ensures that the bin is filled above the background noise where the object is located. The TCSPC method is explained in more detail in the figure description.

[0022] If the respective sensor groups are switched on at the same time in all measurement cycles of a measurement process, relative to the start of a different measurement range, steps will appear in the histogram. The detection of objects and their distance from the LIDAR measurement system is advantageously performed by detecting rising edges and / or local maxima. The step represents precisely such a steeply rising edge, although it merely switches from one sensor group to another.

[0023] It is proposed that, in a first measurement cycle, the sensor element be activated at a first point in time within the first measurement cycle, and in a second measurement cycle, the same sensor element be activated at a second point in time within the second measurement cycle. This is also referred to as the time interval.

[0024] According to the invention, the first time and the second time are different from one another. A sensor element is activated in particular when switching from one measuring range to another. Alternatively, the sensor elements of the respective sensor group can be activated instead of the sensor element. By activating the sensor elements with a time delay from measuring cycle to measuring cycle, the step is flattened into a rising line (see also the description of the figures). In this respect, object detection is significantly simplified. The times refer to a reference time, which is the time of light emission of a light pulse by an emitter element assigned to the sensor element.

[0025] The measurement cycle comprises at least the time it takes the light pulse to reach an object at the maximum measurement distance and back. The first and second times can be within a specified time range.

[0026] For example, a measurement process comprises X measurement cycles. In a first measurement cycle, the relevant sensor element or sensor group is activated at bin 100, in the second measurement cycle at bin 101, in the third measurement cycle at bin 102, and so on. In the last measurement cycle, activation occurs at bin 100 + X - 1. In particular, the background noise increases slowly and evenly. The time interval of a bin is chosen here as an example, as is the uniform step spacing between the times. In particular, the time interval between two measurement cycles for the activation of the sensor element or sensor group can be freely selected and can also be changed during a measurement process. The time interval can be positive or negative, i.e. the second time point can be after or before the first time point. In particular, the times are determined randomly or deterministically.

[0027] Activating sensor elements is analogous to deactivating sensor elements.

[0028] This can prevent a falling edge or step of the noise floor and instead achieve a smooth fall of the noise floor.

[0029] It is advantageous to apply the described time interval to a sensor group to be activated and a sensor group to be deactivated at essentially the same time. This results in a smooth transition between the noise levels of the different measuring ranges.

[0030] It is suggested that the first time point be before or after the second time point.

[0031] According to the invention, the first time and the second time lie within a predetermined time range.

[0032] This time range defines the time period during a measurement cycle within which switching between two measurement ranges takes place. If the entire time range is used evenly and completely by the multiple time points, the width determines the gradient of the rise or fall of the noise floor. The stepped rise of the noise floor is stretched over this time period, ensuring a flatter rise. According to the previous example, the width of the time range corresponds, for example, to the width of X bins.

[0033] Preferably, the first time point and the second time point of consecutive measurement cycles are chosen randomly.

[0034] This random or statistical selection of the time points for all measurement cycles is possible due to the statistical behavior of the system. On average, this results in a uniform increase in the background noise. In particular, the random selection is limited by the specified time range. This allows the range within which the background noise increases to be restricted. Alternatively, the time interval between two consecutive time points of consecutive measurement cycles for a measurement process can be identical, for example, a bin, as in the previous example.

[0035] In another variant, the first time point and the second time point of consecutive measurement cycles are chosen deterministically.

[0036] This can be achieved, for example, using a modulo counter, based on which the time points are selected with an increasing counter. For example, 10 bins are provided for the transition, so the times are selected so that activation or deactivation fills up bin by bin in correlation with the counter, particularly increasing over time. If necessary, the bins can also be filled multiple times, with the counter starting again at 1 after the value of 10. Alternatively, the first bin can be filled multiple times, followed by the next bin multiple times, and so on.

[0037] As already mentioned, the same time points can be used for multiple consecutive measurement cycles. This can be done directly one after the other or with several measurement cycles in between. This reduces the width of the time range.

[0038] It is useful if a point in time in a measuring cycle that has already been used to activate and / or deactivate a sensor element is eliminated for subsequent measuring cycles of the measuring process.

[0039] This also applies to sensor groups. In other words, a time point for activating or deactivating the same sensor element can only be used once. This is best combined with a time range. This ensures that every time point is used despite the random selection.

[0040] In another variant, a time point can be used for multiple measurement cycles. Especially with statistical selection, the time point can be used up after a certain number of uses. With deterministic selection, the number of uses of a time point is already predetermined.

[0041] For each point in time or bin, a different number of uses can be selected until the point in time is consumed.

[0042] For example, 200 measurement cycles with a period of 25 ns are selected, where 4 bins per ns correspond to 100 bins. Thus, each bin is used twice as the starting point.

[0043] In another example with 200 measurement cycles and a period of 30 ns, with 4 bins per ns, there are exactly 120 bins. With a deterministic pattern of 1, 2, 2, 1, 2, 2, 1, 2, 2, ..., 40 bins are used once and 120 bins are used twice as the starting time.

[0044] It is further proposed that if deactivation of one sensor element is associated with activation of another sensor element, the time offset between activation and deactivation of the sensor elements is identical or randomly distributed for all measuring cycles of the measuring process.

[0045] "Connection" here refers to the transition from one measuring range to another, i.e., in particular, when, with respect to the transition from one measuring range to another, one sensor group is activated and another sensor group is deactivated. This is temporally related in that the measuring ranges advantageously adjoin one another without gaps in order to detect all objects within the entire measuring range. According to the invention, during a transition from a first measuring range to a second measuring range, the sensor group assigned to the first measuring range is deactivated and the sensor group assigned to the second measuring range is activated.

[0046] This means that the activation of the sensor element to be activated is delayed from one measuring cycle to the next. The sensor element to be deactivated also experiences a delay from one measuring cycle to the next. A time offset corresponds to the time interval between the activation and deactivation of the sensor elements of the successive measuring ranges. The time offset can be positive, zero, or negative. If the time interval between the sensor elements to be activated and the time interval between the sensor elements to be deactivated are identical for two consecutive measuring cycles, the time offset also remains identical for these two measuring cycles. If the time intervals are different, the time offset changes from one measuring cycle to the next.

[0047] The time offset can therefore remain identical for two, more than two or all measuring cycles or can change from measuring cycle to measuring cycle, in particular deterministically or randomly, due to the random change in the time intervals.

[0048] It is advantageous if the time ranges of different sensor groups do not overlap, partially or completely.

[0049] This lack of overlap ensures particularly accurate measurements in the transition areas between the measurement sections. With this lack of overlap, two sensor groups are preferably active simultaneously.

[0050] During a measurement process, the time ranges for the points in time for the sensor elements to be activated are preferably exactly as large as the time ranges for the points in time for the sensor elements to be deactivated. In particular, the time ranges can be identical or different. A temporal shift between the time ranges is also possible.

[0051] If the time ranges overlap completely, i.e. if one time range fits completely into another or if they are identical, the background noise and also any useful signal present within the ramp are transferred slowly and evenly from one measuring range to the other, whereby part of the information about an object in the histogram is provided in part by two sensor groups.

[0052] The task is also solved by a LIDAR measuring system according to the invention.

[0053] The LIDAR measuring system is preferably designed according to one of the preceding embodiments. According to the invention, the LIDAR measuring system comprises a transmitting unit, a receiving unit, and a control unit for the time-controlled activation and deactivation of sensor elements of the receiving unit.

[0054] The control unit is part of the electronics. In particular, the control unit includes the timing unit. The timing unit is embodied, for example, by a timing controller or includes one. In particular, the timing unit controls the activation and deactivation of the individual elements of the measuring system, in particular the sensor elements and the emitter elements.

[0055] According to the invention, the timing unit is configured to perform the method described above. In particular, the timing unit controls the activation and deactivation of the sensor elements depending on the reference time corresponding to the emission of the light pulse. This time can be detected by a sensor or determined internally by the timing unit, for example, because the timing unit also controls the emission of the laser pulse.

[0056] Conveniently, the timing unit specifies the times for activating and deactivating the sensor elements for each measuring cycle according to the previous variants.

[0057] The procedure and the LIDAR measurement system are explained in detail below using several figures. They show: Fig. 1 a LIDAR measuring system in schematic representation; Fig. 2 a transmitting unit and a receiving unit of the LIDAR measuring system from Figur 1 in a front view; Fig. 3 a flow chart for a measuring cycle and an associated histogram; Fig. 4 a flow chart of a measuring process.

[0058] In the Figur 1 The structure of a LIDAR measuring system 10 is shown schematically. Such a measuring system 10 is intended for use on a motor vehicle. In particular, the measuring system 10 is statically mounted on the motor vehicle and, advantageously, is itself statically designed. This means that the measuring system 10, as well as its components and parts, do not and cannot perform any relative movement to one another.

[0059] The measuring system 10 comprises a LIDAR transmitting unit 12, a LIDAR receiving unit 14, a transmitting optics 16, a receiving optics 18 and an electronics 20.

[0060] The transmitting unit 12 forms a transmitting chip 22. This transmitting chip 22 has a plurality of emitter elements 24, which are schematically represented as squares for clarity. In contrast, the receiving unit 14 is formed by a receiving chip 26. The receiving chip 26 has a plurality of sensor elements 28. The sensor elements 28 are schematically represented by triangles. However, the actual shape of emitter elements 24 and sensor elements 28 may differ from the schematic representation. The emitter elements 24 are preferably formed by VCSELs (Vertical Cavity Surface Emitting Lasers). The sensor elements 28 are preferably formed by SPADs (Single Photon Avalanche Diodes).

[0061] The transmitting unit 12 and the receiving unit 14 are configured in a focal plane array (FPA) configuration. This means that the chip and the associated elements are arranged on one plane, in particular a flat plane. The respective plane is also arranged at the focal point or focal plane of an optical element 16, 18. Accordingly, the emitter elements 24 are arranged on one plane of the transmitting chip 22 and are located on the measuring system 10 within the focal plane of the transmitting optics 16. The same applies to the sensor elements 28 of the receiving chip 26 with respect to the receiving optics 18.

[0062] A transmitting optics system 16 is assigned to the transmitting unit 12, and a receiving optics system 18 is assigned to the receiving unit 14. A laser light emitted by the emitter element 24 or a light incident on a sensor element 28 passes through the respective optical element 16, 18. The transmitting optics system 16 assigns a specific solid angle to each emitter element 24. Likewise, the receiving optics system 18 assigns a specific solid angle to each sensor element 28.

[0063] A laser light emitted by the respective emitter element 24 is always radiated by the transmitting optics 16 into the same solid angle. Due to the receiving optics 18, the sensor elements 28 also always observe the same solid angle. Accordingly, a sensor element 28 is always assigned to the same emitter element 24. In particular, a sensor element 28 and an emitter element 24 observe the same solid angle. Fig. 1 a schematic representation shows the solid angle in the Fig. 1 not displayed correctly. In particular, the distance from the measuring system to the object is many times larger than the dimensions of the measuring system itself.

[0064] In this LIDAR measuring system 10, a single emitter element 24 is assigned a plurality of sensor elements 28, see Fig. 2 . The sensor elements 28 assigned to a common emitter element 24 are part of a macrocell 36, wherein the macrocell 36 is assigned to the emitter element 24.

[0065] At the beginning of a measurement cycle, an emitter element 28 emits laser light 30 in the form of a laser pulse 30. This laser pulse 30 passes through the transmitting optics 16 and is transmitted in the solid angle assigned to the emitter element 24. If an object 32 is located within this solid angle, at least a portion of the laser light 30 is reflected by it. The reflected laser pulse 30, coming from the corresponding solid angle, is guided through the receiving optics 18 to the associated sensor element 28 or the sensor elements 28 associated with a macrocell 36. The sensor elements 28 detect the incoming laser pulse 30, with the triggering of the sensor elements 28 being read out by a TDC 38 (time-to-digital converter) and written into a histogram. Using the time-of-flight method, the distance of the object 32 from the measuring system 10 can be determined from the travel time of the laser pulse 30.The determination of objects 32 and their distances is advantageously carried out using the TCSPC method, Time Correlated Single Photon Counting. The TCSPC method is described in more detail below.

[0066] The sequence of such a measuring cycle is controlled by the electronics 20, which can read at least the sensor elements 28. The electronics 20 is also connected or connectable to other electronic components of the motor vehicle via a connection 34, in particular for data exchange. The electronics 20 is shown here as a schematic modular system. However, further detailed explanations will not be given in this regard. It should be noted that the electronics 20 can be distributed across a plurality of components or assemblies of the measuring system 10. In this case, for example, a portion of the electronics 20 is formed on the receiving unit 14.

[0067] In the Figur 2 The transmitting chip 22 and the receiving chip 26 are shown schematically in a front view. Only a partial section is shown, with the remaining areas being essentially identical to those shown. The transmitting chip 22 has the previously described emitter elements 24, which are arranged in a column and row arrangement. However, this row and column arrangement is chosen only as an example. The columns are provided with capital Roman numerals, the rows with capital Latin letters.

[0068] The receiving chip 26 has a plurality of sensor elements 28. The number of sensor elements 28 is greater than the number of emitter elements 24. The sensor elements 28 are also configured in a row / column arrangement. This row / column arrangement is also chosen merely as an example. The columns are numbered with lowercase Roman numerals, and the rows with lowercase Latin letters. However, a row or column of the receiving chip 26 does not refer to the individual sensor elements 28, but rather to a macrocell 36, which has a plurality of sensor elements 28. The macrocells 36 are separated from one another by dashed lines for clarity. The sensor elements 28 of a macrocell 36 are all assigned to a single emitter element 24. Macrocell i, a is assigned, for example, to emitter element I, A.A laser light 30 emitted by an emitter element 24 images at least a part of the sensor elements 28 of the associated macrocell 36.

[0069] The sensor elements 28 can advantageously be activated and deactivated individually or at least in groups. This allows the relevant sensor elements 28 of a macrocell 36 to be activated and the irrelevant ones to be deactivated. This allows for the compensation of imaging errors. Such imaging errors can be, for example, static errors, such as imaging errors of the optical elements 16, 18, or parallax errors, which are explained by way of example in the following section.

[0070] Due to the parallax, for example, an emitted laser light 30 is directed at close range, i.e. at a short distance from the object 32, onto the Figur 2 imaged by the sensor elements 28 of the macrocell 36 arranged above. However, if the object is located further away from the measuring system 10, the reflected laser light 30 will strike a lower area of the macrocell 36 and thus the sensor elements 28 located below. The displacement of the incoming laser light due to parallax depends in particular on the arrangement of the units and the structural design of the measuring system 10.

[0071] The sensor elements 28 of a macrocell 36 are then activated and deactivated during a measurement cycle, so that unilluminated sensor elements are deactivated. Since each active sensor element detects the ambient radiation as background noise, the background noise of a measurement is kept low by deactivating the unilluminated sensor elements. Examples are shown in the Figur 2 Three sensor groups are shown on the receiving chip 26.

[0072] Sensor groups α, β, and γ are shown here as examples; they serve only to explain the method. Different sensor groups can also be selected in principle. Sensor group α comprises a single sensor element 28, which is used to detect a close range at the beginning of the measuring cycle. Sensor group β comprises a plurality of sensor elements 28 that are active at a medium measuring distance. Sensor group γ comprises several sensor elements 28 that are active in a long-range range. The number of sensor elements 28 in sensor group β is the largest, followed by sensor group γ.

[0073] The selection of the sensor elements 28 for the sensor groups α, β and γ is merely exemplary and may differ from those shown in a specific application, as may the design of the sensor elements 28 and the arrangement relative to the emitter elements 24.

[0074] Normally, only a small number of sensor elements 28 are active in the near field. For example, these sensor elements 28 may also differ in design from the other sensor elements 28 in order to accommodate specific requirements for the near field.

[0075] Sensor group γ is a partial section of sensor group β, but also has two sensor elements 28 that are exclusive to sensor group γ. For example, the different sensor groups can completely overlap, i.e., have a common number of sensor elements 28. However, all sensor elements 28 of a sensor group can also be exclusively assigned to this sensor group. It is also possible that only some of the sensor elements 28 are exclusive to a sensor group, with the remaining sensor elements 28 being part of multiple sensor groups.

[0076] During a transition from a first measuring range to a second measuring range, for example from the middle range to the long range, only a part of the sensor elements of the previously active sensor group are deactivated, with a part of the sensor elements remaining activated and, if necessary, a further number of sensor elements 28 being activated.

[0077] The sensor elements 28 are connected to a TDC 38, Time-to-Digital Converter. This TDC 38 is part of the electronics 20. A TDC 38 is formed on the receiving unit for each macrocell 36, which is connected to all sensor elements 28 of the macrocell 36. However, this design variant for the TDC 38 is exemplary.

[0078] A sensor element 28 designed as a SPAD, which is also active, can be triggered by an incoming photon. This triggering is read out by the TDC 38. The TDC 38 then enters this detection into a histogram of the measurement process. This histogram will be explained in more detail below. After a detection, the necessary bias voltage must first be built up again at the SPAD. During this time, the SPAD is blind and cannot be triggered by incoming photons. This time required for charging is also called dead time. In this regard, it should also be noted that an inactive SPAD requires a certain amount of time to build up the operating voltage.

[0079] The emitter elements 24 of the measuring system 10 emit their light pulses sequentially, for example, row by row or in a row. This prevents a row or column of emitter elements 24 from triggering the sensor elements 28 of the adjacent row or column of macrocells 36. In particular, only the sensor elements 28 of the macrocells 36 are active whose corresponding emitter elements 24 have emitted a laser light 30.

[0080] As already mentioned, the TCSPC method is provided for determining the distance between objects. This method is based on the Figur 3 explained. In the TCSPC, a measurement process is performed to determine any objects and their distance from the measuring system 10. A measurement process comprises several essentially identical measurement cycles that are repeated identically to provide a histogram.

[0081] This histogram is then evaluated to determine any objects and their distance. Figur 3 comprises several sub-figures a, b, c, d, e, f, g. Each of the figures has its own Y-axis, but they share a common X-axis on which the time is plotted. The Fig. 3a bis 3f show a single measurement cycle, where the Fig. 3g represents the result of an entire measurement process. A measurement process starts at the time t start and ends at the time t ende .

[0082] In the Figur 3a The activity of an emitter element 46 during a measurement cycle is shown. The emitter element is t 2 and shortly afterwards at the time t 2* deactivated, which emits a laser pulse.

[0083] Figures b, c and d show the activity phases of the sensor elements 28 of the sensor groups α, β and γ within a measurement cycle. The sensor element of the sensor group α is already activated before the laser pulse is emitted at the time t0 and is already at the time t 1 active. The times t 1 and t 2 can coincide in time or be offset from each other. Sensor group α is therefore active at the latest when laser pulse 30 is emitted. This corresponds to the near range.

[0084] The sensor elements of sensor group β are deactivated shortly before the deactivation of sensor group α at the time t 3 loaded and are at the time t 4 , where sensor group α is deactivated. Sensor group β, which covers the central area, remains active for a longer period of time until it is deactivated at the transition to the far area.

[0085] The activity of the sensor elements 28 of the sensor group γ is in the Figur 3d Since the sensor group γ is partly a subgroup of β, at the time t7, the overlapping sensor elements 28 are left active, whereas the remaining sensor elements 28 of the sensor group β are deactivated. The remaining sensor elements 28 of the sensor group γ are already deactivated in advance at the time t 6. The sensor group γ also remains active for a long period of time until it is t 8 can be deactivated. The time t 8 also corresponds to the end of the measurement cycle at the time t ende However, in other embodiments, the end of the measuring cycle does not have to be identical with the deactivation of the last active sensor group. The beginning of the measuring cycle 42 is determined by the time t start and the end of the measuring cycle 44 is determined by the time t ende defined.

[0086] The measuring cycle thus includes the emission of the laser pulse 46, the switching of the sensor groups and the detection of incoming light in the near range 48, the middle range 50 and the far range 52.

[0087] In the Figur 3e An object 32 is shown as an example, which is located in the central area. The representation corresponds to the reflection surface of the object 32. The laser pulse 30 reflected by the object 32 can be detected by the active sensor elements 28 of the sensor group β at the time t 5 can be detected.

[0088] In the Figur 3f a histogram 54 is shown, which represents an example filling of several measuring cycles. The histogram divides the entirety of the measuring cycle into individual time periods. Such a time period of a histogram 54 is also called bin 56. The TDC 38, which fills the histogram 54, reads the sensor elements 28. Only an active sensor element 28 can forward a detection to the TDC 38. If a SPAD is triggered by a photon, the TDC 38 fills the histogram, which is mapped, for example, by a memory, with a digital 1 or a detection 58. The TDC links this detection 58 to the current time and fills the corresponding bin 56 of the histogram 54 with the digital value.

[0089] Since there is only a single object 32 in the central area, only this single object 32 can be detected. Nevertheless, the histogram is filled with detections 58 throughout the entire measurement cycle. These detections 58 are generated by the background radiation. The photons of the background radiation can trigger the SPADs. The level of the resulting background noise thus depends on the number of active SPADs, i.e., the number of sensor elements 28 in a sensor group.

[0090] It can be seen that in the near field 48, only two bins 56 are filled with one detection each, while a third bin remains empty. This corresponds to the detected background radiation. The number of detections is very low, since only a single SPAD is active.

[0091] In the temporally subsequent middle range 50, the sensor group β is active, which has a multiple of active sensor elements 28. Accordingly, the detected background radiation is also larger, so that a bin is filled with an average of three detections 58, sometimes also 4 or 2 detections 58. In the area 32 in which the reflecting surface of the object 32 is located at the time t 5 of the measurement cycle, the number of detections 58 is significantly higher. Seven or eight detections 58 are recorded in the histogram 54.

[0092] There is no object that can be detected in the far range 52. Only the background radiation is shown here, with an average of one to two detections 58 per bin. The mean value of the background noise is accordingly lower than in the middle range 50, since the number of SPADS is also lower. However, the mean value of the detections 58 is higher than in the near range 48, since the near range 48 with sensor group α has only a fraction of the number of sensor elements 28 of sensor group γ.

[0093] As already mentioned, the histogram shown is filled only as an example. The number of bins and their filling can vary considerably during actual measurement cycles. Normally, no object 32 can be detected from a single measurement cycle or a few measurement cycles. Accordingly, the TCSPC method executes a large number of measurement cycles one after the other. Each measurement cycle fills the same histogram. Such a histogram, which has been filled by a large number of measurement cycles, is shown in the Fig. 3g shown.

[0094] The histogram of the Figur 3g is also formed by digitally filled bins. For a clearer view, however, this figure omits the representation of each bin and simply draws a line corresponding to the fill level of the bins.

[0095] In the near range 48, a low background noise is observed, while in the middle range 50, the highest background noise is observed, as this is where most of the sensor elements are active. In the far range 52, the measured background noise lies between that of the near range 48 and that of the middle range 50. Furthermore, in the middle range 50, the detection of the laser light 30 reflected by the object 32 can be seen in the form of a peak 33. The measured background radiation is statistically evenly distributed, providing an essentially straight line depending on the number of active sensor elements. However, the object and its reflective surface are always in the same position, and over the sum of the measurement cycles, peak 33 stands out above the background noise.

[0096] When determining the histogram according to the Figur 3g the measurement cycle of the Figur 3 repeated identically many times. In particular, all described actions always occur at the same times t 0 to t 8 carried out.

[0097] The histogram of the Figur 3g is now evaluated to identify objects and determine their distance. For detection, the slope, i.e. a steeply rising edge of the histogram curve, is usually evaluated. At the time interval at which the object 32 is located, the distance of the object can then be calculated using the speed of light. The problem arises with the histogram according to the Figur 3g especially when the object is at a distance that corresponds to the switching range between near and medium range and between medium and far range.

[0098] If one now specifies that no evaluation of possible objects takes place at the switching times, one would be blind in these transition areas. If one does not specify this, one would always detect a static object at the switching times, even if there is none there, or one would not be able to distinguish an actual signal from the edge of the switching time. This problem is solved by the following explanations for controlling the sensor elements. This procedure will be explained using the Figur 4 be explained in more detail.

[0099] The basic procedure of a measurement cycle is unchanged from that in Figur 3b However, each measurement cycle of the measurement process differs slightly from the other measurement cycles. Figur 4a, b, c, d, e , each show the same processes as the Figuren 3a, b , c , d, but for three different measuring cycles. For example, a first measuring cycle of the measuring process is represented by the solid line 60, a last measuring cycle of the measuring process by the dashed line 64, and an intermediate measuring cycle of the measuring process by the dotted line 62. With regard to the sub-figures a, b, c, d, the respective lines are supplemented by the suffix b, c, d.

[0100] In the following, only the times at which a sensor group and its sensor elements are activated and deactivated are described. If SPADs are involved, these must also be loaded. For the sake of simplicity, however, this loading phase is not described. The previous explanations in Fig. 3 to the measuring cycle and the measuring process also apply to the following statements, unless they contradict this.

[0101] At one point t a sensor group α is activated during measuring cycles 60, 62 and 64. This time t a remains unchanged for all measuring cycles of the measuring process.

[0102] The emitter element 24 is at the time t b activated and at the time t c deactivated, whereby the laser pulse 30 is emitted. The time t Q is before the time t b or both are identical.

[0103] The first sensor group α is measured in the measuring cycle 60 at the time t d deactivated, in which the sensor group β is activated. In a later measuring cycle 62 of the same measuring process, however, the first sensor group α is only activated at a later time t e deactivated. Likewise, in the measuring cycle 62, the sensor group β is only deactivated at the time t e And with regard to the later measurement cycle, the sensor group α and the sensor group β are only activated at a time t f deactivated or activated. In particular, the time t f after the time t e , which in turn depends on the time t d The length of the near range 48 and the length of the middle range 50 as well as their end and beginning are shifted in time over the number of measurement cycles. This compensates for the steep step increase, see also Fig. 4f , flattened. If the time intervals between the individual measurement cycles are identical, a uniform increase is achieved. For example, such a time interval can correspond to the duration of a bin. In principle, the time intervals can vary from measurement cycle to measurement cycle, although a uniform distribution of the time intervals is preferred.

[0104] The time difference between a single point in time in two measurement cycles is called the time difference.

[0105] The flat increase or decrease of the background noise results from the fact that the sensor group β in the measuring cycle 60 from the time t d However, in a measurement cycle of 62, a contribution to the background noise is only made from the time t e and in the measuring cycle 64 only from the time t f Accordingly, the noise floor rises slowly and steadily. Since the histogram divides the measurement duration of a measurement cycle into bins, the increase is essentially still step-like. However, the steps are so small that they are unproblematic when evaluating the histogram. In particular, the ramps are extended to a duration that is longer than the duration of the light pulse, in particular a multiple of the duration of the light pulse.

[0106] During subsequent evaluation of the histogram, an object can be easily detected at the transition between the different measurement ranges. This also eliminates the possibility of false detection.

[0107] The activation of sensor group α does not require such time intervals, since the laser pulse is always emitted at the same time and sensor group α is then already active.

[0108] The transition from sensor group β to sensor group γ behaves like the transition from sensor group α to sensor group β. For measuring cycle 60, this is the time t h , for the measuring cycle 62 the time t i and for the measuring cycle 64 the time t k . Accordingly, the histogram's decline from the mid-range noise floor 50 to the far-range noise floor 52 is flatter and more uniform.

[0109] Optionally, the remote area 52 can also be used at the times t l , t m and t n can be deactivated with a time delay.

[0110] The time points can be randomly selected from measurement cycle to measurement cycle. In particular, a time interval from measurement cycle to measurement cycle is randomly selected. This results in a statistically averaged, evenly increasing background noise. Here, a time range of 66 from t d until t f from which the time points are randomly selected. A further time range 68 extends from t h until t k .

[0111] Alternatively, the time points can also be selected deterministically, for example, using a predefined pattern. Preferably, the deterministic selection ensures a uniform distribution of the time points.

[0112] Optionally, a time within the time range 66, 68 that has already been used for activating or deactivating a sensor group can no longer be selected for further measurement cycles. For example, in a first measurement cycle, the time t e selected, it is no longer available for subsequent measurement cycles. This allows a random selection to be made while still using a predetermined set of time points. In particular, such statistical selection allows certain sources of error to be excluded.

[0113] According to the Fig. 4c und 4d Sensor group β is deactivated at the same time as sensor group γ is activated. Therefore, the time offset between the deactivation of the sensor elements of sensor group β and the activation of the sensor elements of sensor group γ is zero. This time offset is identical for all measurement cycles 60, 62, and 64 and does not change throughout the entire measurement process.

[0114] The time offset is the time interval between a time at which a sensor group is deactivated and a time at which a sensor group is activated within a single measurement cycle.

[0115] In an alternative embodiment, this time offset can be non-zero. For example, sensor group γ is activated, and sensor group β is deactivated only after the time offset has elapsed. This is also possible in the opposite direction. Such an identical time offset when switching between two sensor groups is advantageous when the sensor groups have overlapping sensor elements. This ensures a uniform increase or decrease in the background noise.

[0116] However, the time offset can also vary from measurement cycle to measurement cycle. This is possible, for example, if there is no overlap of the sensor elements between consecutive sensor groups.

[0117] Random selection is useful, for example, if the times for deactivating sensor group β and the times for activating sensor group γ are chosen randomly and independently of each other. However, as already mentioned, a deterministic selection is also possible.

[0118] To implement the method, the electronics 20 of the measuring system includes a timing unit. This timing unit specifies the time for the measuring system and also controls the chronological sequence of the elements. In particular, it specifies the time for the histogram and controls the activation and deactivation of the individual sensor elements and emitter elements. Furthermore, the timing unit enables the correct addition of the histograms. Likewise, the timing unit specifies the times for each measurement cycle at which the individual elements are activated and deactivated. Bezugszeichen

[0119] 10LIDAR measuring system 12LIDAR transmitter unit 14LIDAR receiver unit 16Transmitter optics 18Receiver optics 20Electronics 22Transmitter chip 24Emitter element 26Receiver chip 28Sensor element 30Laser light / laser pulse 32Object 33Peak 34Connection 36Macrocell 38TDC 40x-axis (time) 42Start of measurement cycle 44End of measurement cycle 46Emission of laser pulse 48Detection near range 50Detection mid-range 52Detection far range 54Histogram 56Bin 58Detection 60b,c,dLine, solid 62b,c,dLine, dashed 64b,c,dLine, dotted 66Time domain 68Time domain α,β,γSensor group I,II,...Column transmitting chip i,ii,...Column receiving chip A,B,...Row transmitting chip a,b,...Row receiving chip t start time t end time t 0 time t 1 time t 2 time t 2* time t 3 time t 4 time t 5 time t 6 time t 7 time t 8 time ta time tb time tc time td time te time tf time tg time th time ti time tk time tl time tm time tn time.

Claims

1. Method for controlling sensor elements (28) of a LIDAR measuring system (10), - wherein sensor elements of a macrocell for different measuring ranges are subdivided into sensor groups, so that a sensor group is assigned to a measuring range - wherein a sensor element (28) is activated and deactivated during a measuring cycle, - wherein a measuring process comprises several measuring cycles, characterized in that - in a first measuring cycle, the sensor element (28) is activated at a first point in time td within the first measuring cycle, and in a second measuring cycle, the same sensor element (28) is activated at a second point in time te within the second measuring cycle, - wherein the first point in time td and the second point in time te refer to a reference point in time, - wherein the reference point in time is the respective point in time at which a light pulse is emitted by means of an emitter element assigned to the sensor element, - wherein the first point in time td and the second point in time te are different, - wherein a measuring cycle comprises at least the duration of time that it takes for the light pulse to travel to an object at the maximum measuring distance and back, - wherein during a transition from a first measuring range to a second measuring range, the sensor group assigned to the first measuring range is deactivated and the sensor group assigned to the second measuring range is activated.

2. Method according to claim 1, characterized in that - in a first measuring cycle, the sensor element (28) is deactivated at a first point in time th within the first measuring cycle, and in a second measuring cycle, the same sensor element (28) is deactivated at a second point in time ti within the second measuring cycle, - wherein the first point in time and the second point in time refer to a reference point in time, - wherein the reference point in time is the respective point in time at which a light pulse is emitted by means of an emitter element assigned to the sensor element - wherein the first point in time th and the second point in time ti are different.

3. Method according to claim 1 or 2, characterized in that the first point in time is before or after the second point in time.

4. Method according to one of claims 1 to 3, characterized in that the first point in time and the second point in time are within a predetermined time range (66, 68), and5. Method according to one of claims 1 to 4, characterized in that the first point in time and the second point in time of successive measurement cycles are selected at random.

6. Method according to one of claims 1 to 5, characterized in that a point in time that has already been used in a measurement cycle to activate and / or deactivate a sensor element is excluded for subsequent measurement cycles of the measurement process.

7. Method according to one of claims 1 to 6, characterized in that, if a deactivation of a sensor element (28) is associated with an activation of another sensor element (28), the time offset between the activation and deactivation of the sensor elements (28) is identical or randomly distributed for all measurement cycles of the measurement process.

8. LIDAR measuring system with a transmitter unit, a receiver unit and a control unit for time-controlled activation and deactivation of sensor elements of the receiver unit, wherein the control unit comprises a time control unit, characterized in that the time control unit is configured to carry out a method according to one of claims 1 to 7.