DEVICE FOR SURVEYING AN ENVIRONMENT

Description

[0001] The present invention relates to a device for measuring an environment moving relative to the device in a direction of movement at a relative velocity by measuring the time of flight of laser beams reflected therefrom in a coordinate system, comprising a first scan unit for emitting a first laser beam over a first sequence of deflection periods with a respective deflection period duration, which first laser beam passes through a first scan fan in each deflection period and scans the environment along a first scan line that is not parallel to the direction of movement, wherein the first scan lines form a first set of scan lines, and for receiving the associated laser beam reflected from the environment.

[0002] Devices of this type are described, for example, in EP 3 182 159 B1 and are carried, for instance, by an aircraft or ship to survey environments such as the ground or seabed. It is also possible to mount such a device on a land vehicle to survey, for example, building facades, street canyons, or tunnels as it drives by. The device can also be set up in a stationary position, for example, above a conveyor belt, to survey objects moving on it, etc.

[0003] The scanning unit emits a laser beam, e.g., pulsed or modulated, at various angles within the scan area for each deflection period of the sequence. This beam is directed at numerous target points ("scanning points") on the scan line in the surrounding area. Time-of-flight measurements of the target reflections are used to determine the target distances and, based on the scan unit's position and the respective emission angle, to create a point model ("3D point cloud") of the environment. In mobile, vehicle-based devices, the scan area defined by the laser beam is moved across the environment by the vehicle's movement, allowing the scan line to be scanned one by one. In stationary devices, the environment to be measured is moved relative to the scan area, for example, to measure objects on conveyor belts.

[0004] Ideally, the 3D point cloud should be generated as quickly and with the highest possible spatial resolution. However, there are limits to the resolution of the point cloud. On the one hand, the deflection period cannot be shortened arbitrarily due to the inertia of the scanning unit's deflection mechanism. Therefore, for a given relative speed, the distance between two consecutive scan lines in the scan array, the "step size," is limited. On the other hand, with a shorter deflection period and a constant laser pulse repetition rate, fewer sample points fall within a deflection period, which reduces the resolution within a scan line and thus the resolution of the 3D point cloud.The pulse repetition rate cannot be increased arbitrarily: at high pulse repetition rates or greater target distances, for example, the next laser pulse is emitted even before the reflected first transmitted pulse is received, so that the incoming received pulses can no longer be uniquely assigned to their respective transmitted pulses. This is known as the multiple time-around (MTA) problem. The maximum size dmax of a uniquely measurable distance range, a so-called MTA zone, is calculated from the pulse repetition rate (PRR) and the speed of light c as dmax = c / (2·PRR).

[0005] Additionally, due to the design, so-called "blind ranges" occur at the edges of each MTA zone because the receiving electronics become saturated or overloaded by near reflections of an emitted laser pulse from, for example, the housing or mounting parts of the device, and are thus "blind" to receiving a reflected laser pulse. Large MTA zones are therefore desirable to minimize the number of "blind ranges" across the entire distance range to be measured. However, this in turn limits the pulse repetition rate and consequently the number of sampling points, thus reducing the resolution of the 3D point cloud.

[0006] Simply increasing the number of scan points in the 3D point cloud, as achieved in DE 10 2004 050 682 A1 by using multiple scan units, does not necessarily increase its spatial resolution. For example, some target points could be scanned multiple times. d.h. Local clusters of sample points may form, while other areas of the environment contain too few sample points, meaning the desired resolution of the 3D point cloud is not achieved across the entire environment. Therefore, a distribution of sample points across the environment that is as uniform as possible is essential to obtaining a high-quality 3D point cloud.

[0007] The invention aims to create a laser scanning device that enables the particularly rapid and informative creation of a 3D point cloud of the environment.

[0008] This objective is achieved with a device of the type mentioned in the introduction, comprising at least one further scanning unit for emitting a further laser beam over a further sequence of deflection periods with the same respective deflection period duration, which further laser beam passes through a further scan fan in each deflection period and scans the environment along a further scan line non-parallel to the direction of movement, wherein the further scan lines form a further set of scan lines, and for receiving the associated laser beam reflected from the environment, wherein all scan fans substantially overlap in the direction of movement and the direction of all sets of scan lines are substantially parallel from the device, wherein the device is configured to emit two or more scan fans simultaneously by means of the first scanning unit and the at least one further scanning unit.and a control device connected to at least one further scanning unit, which is designed to offset the set of scan lines of each further scanning unit relative to the set of scan lines of a neighboring scanning unit in a given sequence of scanning units in the direction of movement by a spatial offset dependent on the relative speed and the deflection period duration, such that the said further scan lines do not coincide with the said first scan lines.

[0009] The laser scanning device of the invention, by virtue of its multiple scanning units, can simultaneously emit two or more scan fields, thereby enabling at least twice as many sampling points of the environment to be generated for the point cloud in the same amount of time. Due to the relative movement between the device and the environment, in the overlapping area of ​​the scan fields, a region of the environment already scanned by a scan field located ahead (in the direction of movement) can be rescanned by a scan field located behind it (in the direction of movement).

[0010] The term "scan direction" refers to a direction normal to all scan lines of the respective scan line set as seen from the device. Parallel scan directions of all scan units, as seen from the device, result in parallel scan lines of different scan line sets. The offsetting of parallel scan line sets in the direction of movement, as described in the invention, prevents the laser beam of the rear scan unit from potentially hitting the sampling points of the area already scanned by the front scan unit again, i.e., from the scan lines of the front and rear scan units coinciding. This ensures that the environment is indeed measured with a higher resolution.

[0011] Relative velocity and deflection period can be fixed for a specific surveying task or change during the survey. The inventive dependence of the positional offset on the relative velocity and deflection period enables the control unit to operate automatically adapted to these conditions. The control unit can, for example, measure these values ​​itself or receive them from a measuring unit or a position transmitter, which the measurement technician then uses to set these values ​​during operation.

[0012] Finally, each scanning unit receives only its own laser beam reflected from the environment, thus geometrically separating the laser beams emitted by different scanning units at the receiver. This allows, for example, the number of processed laser pulses per unit of time to be multiplied according to the number of scanning units, without reducing the size of the MTA zones.

[0013] As a result, the device of the invention achieves a particularly fast, high-quality and meaningful measurement of the environment.

[0014] As briefly discussed earlier, a preferred application of the device of the invention is that it is mounted on a vehicle, preferably an aircraft. This allows large-area environments such as entire landscapes to be surveyed quickly and flexibly, e.g. from a helicopter, a drone, an airplane, etc.

[0015] In a preferred embodiment, the control unit is configured to specify the deflection period and / or the relative velocity depending on at least one past distance measurement of the environment. This allows the scan line step size of each scan unit and / or the sampling point spacing within each scan line to be standardized. For example, the device could be mounted on an aircraft, and the control unit could specify the deflection period and the relative velocity depending on the altitude, such that a higher altitude corresponds to longer deflection periods and lower relative velocity, and a lower altitude to shorter deflection periods and higher relative velocity, in order to achieve, at a constant pulse repetition rate, as uniform as possible sampling point spacing within the scan compartments and scan line spacing across the entire area to be measured.

[0016] It is particularly advantageous if the control device is designed to offset the scan line array of each subsequent scan unit relative to the scan line array of an adjacent scan unit in a predefined sequence, such that the scan lines are arranged at regular intervals in the direction of movement. The regular intervals of all scan lines can be defined, for example, from the device's perspective in a top view of the environment, in a predefined tangent plane to the environment, or—especially when using past distance measurements—in scanned surfaces of the environment itself. This regular arrangement of the scan lines prevents the potential overlap of scanning points from different scan areas in the environment and thereby increases the resolution of the 3D point cloud.

[0017] In particular, it is advantageous if the spatial offset between the sets of scan lines of each pair of adjacent scan units in the sequence, increased by a displacement in the direction of movement, which would be caused by the relative movement without this spatial offset between these two sets of scan lines, corresponds to the distance in the direction of movement between two successive scan lines of a scan unit in the direction of movement, divided by the number of all scan units.

[0018] For example, to achieve a regular arrangement of scan lines, the spatial offset between the sets of scan lines of each pair of adjacent scan units in the sequence could be chosen as Δ S k , k − 1 = ν ⋅ T AP K − D k , k − 1 + h ⋅ tanα k − tanα k − 1 mod ν ⋅ T AP with Kn Number of scan units, ΔS k,k-1 Positional offset of the k-th scan line set relative to the (k-1)-th scan line set, v Relative velocity, TAP Deflection period duration, D k,k-1 Distance between vertices of the k-th and (k-1)-th scan compartments along the direction of movement, expected normal distance between device and environment, α k Angle from an expected normal to the environment to the k-th scan compartment in a plane spanned by the direction of movement and the expected normal, and mod Modulo operator.

[0019] In a particularly preferred embodiment, all scan compartments are essentially parallel. This allows the spatial offset required for aligning the scan lines to be determined independently of the surrounding topography, and thus particularly easily. Furthermore, the use of parallel scan compartments maximizes the overlap area of ​​the scan compartments and thus the width of the scan strip in which the environment can be scanned at the improved resolution. For example, this eliminates the need to determine the aforementioned tangent plane to the environment and the hardware or software elements that perform this determination.

[0020] In particular, with essentially parallel scan trays, the spatial offset between the scan line sets of each pair of adjacent scan units in the sequence can be selected as Δ S k , k − 1 = ν ⋅ T AP K − D k , k − 1 mod ν ⋅ T AP with Knumber scan units, ΔSk,k-1 positional offset of the k-th scan line set relative to the (k-1)-th scan line set, vrelative velocity, TAP deflection period duration, Dk,k-1 distance between the k-th and (k-1)-th scan fan along the direction of movement, and mod modulo operator.

[0021] As can be seen from equation (2), only values ​​independent of the environment are used in the determination of the positional offset with the deflection period duration, the relative velocity and the number of scan compartments or scan units, which significantly simplifies the effort required to determine the positional offset.

[0022] In a preferred embodiment, the positional offset of the scan line array(s) is achieved optically by means of a control device configured to displace the scan line array of the aforementioned at least one further scan unit by controlling optical elements in the beam path of its laser beam. The use of controlled optical elements, e.g., electro-optic elements, pivotable or rotatable mirrors, prisms, etc., in the beam path allows the associated scan array to be moved and / or pivoted in the direction of movement in order to displace the associated scan line array.

[0023] In this embodiment, the deflection periods of different scan units can be shifted relative to each other in time by means of a control device designed to offset the scan line set of the aforementioned at least one further scan unit by controlling a time offset of the respective sequence. This allows existing oscillating or rotating mirrors of the scan unit to be controlled with a time offset, e.g., by delay elements, or with a phase offset by actuators, and thus used simultaneously for generating and offsetting the scan lines.

[0024] The scanning units of the device can be configured for laser beam deflection using, for example, oscillating mirror, rotating mirror, Palmer scanners, or the like. In a particularly preferred device configuration, each scanning unit comprises a deflection device with a mirror prism rotatable about its prism axis, the lateral surfaces of which each form a mirror surface, and a laser transmitter for emitting the respective laser beam in a specific direction onto the deflection device. With such a rotating mirror prism, a constant angular velocity can be achieved within each deflection period as the scan area is traversed, followed by a return to the beginning of the scan area in the next deflection period. This allows for high-speed, line-by-line scanning of the surroundings with constant out-of-transmission angle spacing within each scan line.If the deflection mechanisms of all scan units are formed by one and the same deflection mechanism, the scan units can be designed in a particularly compact manner, and separate drives for each mirror prism are no longer necessary. Additionally, the transmission directions of different laser transmitters can be easily aligned by referencing them to the single common mirror prism. Furthermore, by design, a single mirror prism results in the same deflection period for all scan units, eliminating the need for separate synchronization.

[0025] In the aforementioned preferred apparatus setup of the invention, three advantageous variants for shifting the scan lines can be provided, which can optionally be combined with each other.

[0026] In a first variant, the laser transmitter has an adjustable deflecting mirror located in the laser beam path, and the control unit is designed to shift the scan line array of at least one additional scan unit by adjusting the associated deflecting mirror. The deflecting mirror defines the respective transmission direction by its position and can be adjusted, for example, by an actuator connected to the control unit. A lightweight deflecting mirror, due to its low inertia, can be adjusted particularly quickly, for example, pivoted or shifted, so that a change in the positional offset, necessary due to a change in the deflection period or the relative velocity, can be implemented rapidly. Furthermore, a deflecting mirror can be adjusted over a large angular range, thus enabling large changes in the transmission direction and the positional offset.

[0027] In a second variant, the laser transmitter is mounted in an adjustable position relative to the deflection device, and the control unit is designed to shift the scan line array of at least one further scanning unit by controlling the position of the associated laser transmitter. In this variant, the laser transmitters are adjusted by actuators connected to the control unit, e.g., pivoted or moved, so that large positional offsets can be achieved even without deflection mirrors.

[0028] In the first and second variants, to receive the laser pulses from pivoted or shifted scan compartments, the receiving aperture of the laser receiver of each additional scan unit could be enlarged so that the reflected laser pulses, even from the pivoted or shifted associated scan compartment, still lie within this receiving aperture. Alternatively, the laser receivers of the additional scan units can maintain their receiving aperture if the viewing direction of the laser receivers is pivoted or shifted along with the associated scan compartment, for example, by having adjustable optical elements in the beam path of the reflected laser pulses or by controlling the position of the laser receivers themselves.

[0029] In a third variant, the control unit is designed to shift the scan line array of at least one additional scan unit by controlling the phase of the rotational movement of the associated mirror prism. This allows the existing mirror prisms to be used for scan line shifting – for example, by appropriately controlling their rotation axis drives – thus eliminating the need for additional optical elements.

[0030] In particular, in the third variant, with essentially parallel scan trays, the regular arrangement of the scan lines of all scan units can be achieved by selecting the phase relationship between the rotational movements of the mirror prisms of each pair of adjacent scan units in the sequence as Δ φ k , k − 1 = 360 ° K ⋅ J − D k , k − 1 ⋅ 360 ° J ⋅ ν ⋅ T AP with Knumber scan units, Jnumber mirror surfaces, Δφ k,k-1 phase position of the mirror prism of the k-th scan unit relative to the mirror prism of the (k-1)-th scan unit, v relative velocity, TAP deflection period, D k,k-1 distance between the k-th and (k-1)-th scan fan along the direction of motion and mod modulo operator.

[0031] As can be seen from equation (3), only the deflection velocity, the number of scan units and their mirror surfaces are taken into account in the determination of the phase position, so that the position offset is independent of the topography of the environment to be measured.

[0032] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the accompanying drawings. The drawings show: Fig. 1 a laser scanning device mounted on an aircraft and one of its scanning units sending out its scan fan to measure an environment in a schematic perspective view; Fig. 2 a transmitting and receiving channel of the device from Fig. 1 in a block diagram with schematically drawn beam paths; the Fig. 3a - 3c Three different embodiments of the laser scanning device, each mounted on an aircraft, are shown in a schematic perspective view when measuring an environment using three scan units, each emitting a scan fan and each forming a transmit and receive channel of the device. Fig. 3a und 3b ) or in a side view ( Fig. 3c ); Fig. 4 Exemplary phase / time diagrams of the deflection devices of the scan units of the Fig. 3a - 3c each for a sequence of distraction periods; Fig. 5 An exemplary distribution of scan line sets on a section of the environment, as seen with the scan trays of the Fig. 3a - 3c , however without the inventive spatial offset for the phase positions of Fig. 4 would be obtained in a top view; Fig. 6 An exemplary distribution of regularly arranged scan line sets on a section of the environment, as achieved with the scan trays of Fig. 3a - 3c and the offsetting of the scan line sets according to the invention, in a top view; Fig. 7 a possible constructive design of the laser scanning device Fig. 3a - 3c when performing three variants for offsetting the scan line sets in a perspective side view with schematically drawn beam paths; Fig. 8 Phase / time diagrams of the deflection devices of the scan units of the Fig. 3a - 3c for time-shifted sequences of distraction periods, which are used in a variant for offsetting the scan line sets; and Fig. 9 a further constructive design of the laser scanning devices of the Fig. 3a - 3c when executing one of the variants of Fig. 7 and 8 in a block diagram with schematically drawn beam paths.

[0033] In Fig. 1 A device 1 for measuring an environment 2 from a vehicle 3 is shown. The environment 2 to be measured can be, for example, a landscape (terrain), but also the road surface and the facades along a street, the interior surface of a hall, tunnel or mine, or the sea surface or seabed, etc. The vehicle 3 can be a land, air or water vehicle, manned or unmanned. Alternatively, the device 1 could also be stationary and measure an environment 2 that is moving relative to the device 1, e.g., objects moving on a conveyor belt, workpieces, etc.

[0034] The device 1 scans the surroundings for measurement purposes using an emitted laser beam 4. For this purpose, the laser beam 4 is deflected by a scanning unit 5 with a deflection period AP (see later). Fig. 4 ) swivels back and forth. As a result, the laser beam 4 passes through a scan fan 6 within each deflection period AP at an angular velocity ω L, along whose intersection line 7 with the environment 2, whose "scan line", laser pulses 8 n (n = 1, 2, ...) of the laser beam 4 scan the environment 2 at associated sampling points P n.

[0035] Additionally, the device 1 is moved forward in the direction of motion R of the vehicle 3 at a relative velocity v in order to travel over a sequence F ( Fig. 4 The system uses successive deflection periods AP with the same deflection period duration TAP to scan the environment 2 with multiple scan lines 7 in a scan strip 9. The distance SW between two successive scan lines 7, the "step size," is given by SW = v · TAP for a flat environment 2 parallel to the direction of movement R, or in a top view of the environment 2. The scan lines 7 of all deflection periods AP form a set of scan lines 10, whose direction SR is normal to each scan line 7 and tangential to the environment 2, i.e., tangential to its scanned surface ("topography").

[0036] If the vehicle 3 is, for example, an aircraft, the direction of motion R is the aircraft's primary flight direction, for which it is designed. The direction of motion R is not in the plane of the scan fan 6; that is, the scan lines 7 are not parallel to the direction of motion R, and the strip direction 10 is not normal to the direction of motion R. In the case shown, the direction of motion R is normal to the plane of the scan fan 6, so the scan fan 6 lies in the nadir direction of the vehicle 3 and points downwards towards the surroundings 2. However, the scan fan 6 can also be rotated about, for example, a vertical axis g of the vehicle 3, so that the scan lines 7 in the scan strip 9 are oblique to the projected direction of motion R. Similarly, the scan fan 6 could be rotated about a pitch axis p and / or roll axis r of the vehicle 3.

[0037] Each laser pulse 8n is emitted by the device 1 in a corresponding scan direction Rn towards the environment 2, reflected back to the device 1 at the respective scanning point ("target point") Pn of the environment 2, and received by the scan unit 5. Distance measurements dn from the current position posn of the device 1 to the respective scanning point Pn of the environment 2 can be calculated from a time-of-flight measurement of the laser pulses 8n using the known relationship. d n = c ⋅ ΔT n / 2 = c ⋅ t E , n − t S , n / 2 with ts,n transmission time of the laser pulse 5 n , t E,n reception time of the laser pulse 5 n and c speed of light.

[0038] Knowing the respective position pos n of the device 1 at the time the laser pulse 8 n is emitted in a local or global x / y / z coordinate system 11 of the environment 2, the respective orientation ori n of the device 1 in the coordinate system 11, specified, for example, by the pitch, roll, and yaw angles of the vehicle 3 about its transverse, longitudinal, and vertical axes p, r, g, and the respective angular position ang n of the laser pulse 8 n in the direction of point P n relative to the vehicle 3, the position of the scanning point P n in the coordinate system 11 can then be calculated from the respective distance measurement dn. A multitude of such measured and calculated scanning points P n represent the environment 2, more precisely its scanned surface, in the form of a "3D point cloud" in the coordinate system 11.

[0039] Fig. 2 The time-of-flight measurement principle of device 1 is shown in a transmit / receive channel of device 1, which is used for the in Fig. 1 The scan compartment 6 of the scan unit 5 is responsible for the example shown.

[0040] According to Fig. 2 The laser pulses 8 n in each transmit / receive channel of the device 1 are emitted by a laser transmitter 12 via a deflecting mirror 13 and a deflection device 14. Fig. 2 The deflection device 14 is a mirror prism 16 rotating about its prism axis 15 at an angular velocity ω, each of whose lateral surfaces forms a mirror surface 17j (j = 1, 2, ..., J), and around whose prism axis 15 the scan fan 6 is fanned out. The current angular position of the mirror prism 16 within a deflection period AP, the "phase" of the deflection device 14, is denoted by φ. The constant or variable angular velocity ω and the number J of mirror surfaces 17j determine the aforementioned deflection angular velocity ωL and the deflection period TAP according to the formulas ωL = 2·ω and TAP = 360° / (ωd·J), where ωd denotes the average angular velocity ω. Alternatively, the deflection device 14 could be implemented by any other deflection device known in the prior art, e.g. as a oscillating mirror, rotating mirror pyramid, etc.

[0041] The emitted laser pulses 8n are reflected at the respective ambient point Pn and received back via the deflection device 14 along the same path, arriving at a laser receiver 18. This means that the current viewing direction of the laser receiver 18 is equal to the current scan direction Rn. The transmission times tS,n of the laser pulses 8n and the reception times tE,n of the reflected laser pulses 8n are fed to a distance calculator 19, which calculates the respective distance dn using equation (4).

[0042] The pulse repetition rate (PRR) of the laser pulses 8 n is constant or can be modulated, for example, to resolve MTA (multiple time around) ambiguities within a deflection period AP, in order to facilitate the assignment of sent and received laser pulses 8 n to each other, as is known in the art.

[0043] Alternatively, for time-of-flight measurement and assignment of the sent and received laser beam 4, this could also be non-pulsed, e.g. modulated or continuous ("continuous wave"), as is known in the prior art.

[0044] Optionally, the angular velocity ω and thus the deflection period T AP of the deflection device 14 and / or the relative velocity v can be adapted to a measured or expected distance dn, e.g. to obtain regular intervals of the sampling points P n within each scan line 7 and a regular step size SW between successive scan lines 7 over an environment 2 with highly variable topography.

[0045] In the Fig. 1 und 2 To explain the measurement principle, only the scan compartment 6 of a scan unit 5 of the device 1 or the associated transmit / receive channel was shown. Fig. 3a - 3c In contrast, the laser scanning device 1 carried on aircraft 3 shows several (here: three) as in connection with the Fig. 1 und 2 The described scan units 5k (k = 1, 2, ..., K; here K = 3), i.e., in a predetermined sequence of a "first", "second", and "third" scan unit 51, 52, 53. It is understood that the device 1 can have any number K > 1 of scan units 5k.

[0046] Each of the three scan units 5 k sends its respective laser beam 4 k with laser pulses 8 k,n via a sequence F k ( Fig. 4 ) of deflection periods AP k, where the deflection period duration T AP is the same for all scan units 5 k. For each deflection period AP k, each laser beam 4 k fans out an associated scan fan 6 k to scan the environment 2 along associated scan lines 7 k that are not parallel to the direction of movement R, forming a set of scan lines 10 k for each scan unit 5 k.

[0047] In the embodiment of Fig. 3a The scan compartments 6k are essentially parallel and their vertices 20k are spaced apart from each other in the direction of movement R by mutual distances Dk,k-1. In the embodiment of Fig. 3b The scan compartments 6k are not parallel and their vertices 20k coincide. In the embodiment of Fig. 3c The vertices 20k of the scan fans 6k in the direction of motion R are set at mutual distances Dk,k-1 from each other, and the scan fans 6k are arranged at different angles α1, α2, α3 to a normal N to the environment 2 approximated as a plane in a plane E spanned by the direction of motion R and the normal N.

[0048] In each of the embodiments of the Fig. 3a - 3c The scan line directions SR k of the scan line sets 10 k are essentially parallel in a top view of the environment 2, i.e., as seen from the device 1, and the scan compartments 6 k overlap each other substantially in a common overlap area 21 (hatched) when viewed in the direction of movement R, in which the scanning points P k, n of several scan compartments 6 k thus lie when viewed in the direction of movement R. As a result, a trailing scan compartment 6 k, viewed in the direction of movement R, follows a leading scan compartment 6 k, viewed in this direction, due to the relative movement between the device 1 and the environment 2, and rescans the already measured portion of the common scan strip 9 of the leading scan compartment 6 k. For example, the trailing scan compartment 6 1 can rescan the scan lines 7 2, 7 3 of its two leading scan compartments 6 2, 6 3, and the trailing scan compartment 6 2 can rescan the scan lines 7 3 of its leading scan compartment 6 3.Due to the essentially parallel scanning directions SR k, the scan lines 7 k of the rear scan trays 6 k are essentially parallel to the already scanned scan lines 7 k of a front scan tray 6 k when the rear scan trays 6 k catch up with these.

[0049] The 6k scan trays are not necessarily flat. For example, in the Fig. 3b und 3c The scan compartments 61, 63, inclined forwards and backwards in the direction of movement F – e.g., due to the deflection mechanism of the laser pulses 8k,n – lie on slightly curved conical surfaces. This can be disregarded for the purposes of the present invention; thus, in the present disclosure, "essentially parallel" scan compartments, scan lines, or scan line arrays are also understood to include those which, for example, are slightly differently curved or are only largely parallel in their central regions.

[0050] Instead of as in the Fig. 3a - 3c The scan compartments 6k could also be positioned in any other orientation relative to each other, as long as they overlap each other at least in pairs within an overlap area 21 and the direction SRk of their scan lines 7k are essentially parallel.

[0051] The Fig. 4 und 5 This illustrates a mutually uncoordinated deflection of the laser beams 4k of the individual scan units 5k, i.e., without taking the other scan units 5k into account. This is shown in Fig. 4 The phase φk of the deflection device 14k of each scan unit 5k is plotted against time t for their respective sequence Fk of deflection periods APk,p (p = 1, 2, ...). Fig. 5 The resulting sets of 10 k scan lines 7 k,p of scan units 5 k for several deflection periods AP k,p are shown.

[0052] The deflection devices 14k deflect their laser beams 4k in the example shown synchronously with the same deflection period TAP, the same angular velocity ω, and the same phase φk(t), i.e., their sequences Fk of deflection periods APk,p are identical. Depending on the magnitude of the deflection period TAP, the relative velocity v, and the position of the scan compartments 6k, different distributions of the scan lines 7k,p on the environment 2 result, as simplified below using a planar environment 2. Fig. 5 shown.

[0053] If a simultaneous distance A k,k-1 , i.e. a distance between two simultaneously measured scan lines 7 k,p , 7 k-1,p of different scan compartments 6 k , 6 k-1 , is a multiple of the step size SW , i.e. A k,k-1 = m · SW (m ... a natural number ), the scan lines 7 k,p , 7 k-1,q (q ≠ p) of different scan compartments 6 k , 6 k-1 do indeed occur one after the other in time due to the relative movement in the direction R, but are spatially in the same place . This allows, for example, the scanning points P1,n (represented as diamonds) and P2,n (represented as circles) of the rear scan trays 61, 62 to coincide with the already scanned scanning points P3,n (represented as triangles) of the front scan tray 63, i.e., the scan line sets 10k coincide—except for the initial and final phases of scanning. As shown in Fig. 3c As can be seen, the simultaneous distance A k,k-1 can be determined by determining or specifying a normal distance h between device 1 and environment 2 and the angle α k , α k-1 of the respective scan compartments 6 k , 6 k-1 as A k,k-1 = D k,k-1 + h · (tan(α k ) - tan(α k-1 )).

[0054] If the simultaneous spacing Ak,k-1 is not a multiple of the step size SW, i.e., Ak,k-1 ≠ m · SW ("coprimality"), the scan lines 7k, 7k-1 of different scan units 5k, 5k-1 do not coincide, but rather their scan line sets 10k are spaced apart from each other by a mutual shift Sk,k-1. This generally results in an irregular alignment of the scan lines 7k of all scan units 5k, as in Fig. 5 shown.

[0055] The Fig. 6 - 9 illustrate how such a coincidence or irregular juxtaposition of scan lines 7 k,p from different scan units 5 k can be prevented and how the scan lines 7 k,p can be distributed more evenly over the environment 2.

[0056] This is done, as in Fig. 6 The scan line set 10 2 of the second scan unit 5 2 is shown offset relative to the scan line set 10 1 of the adjacent first scan unit 5 1, and the scan line set 10 3 of the third scan unit 5 3 is offset relative to the scan line set 10 2 of the adjacent second scan unit 5 2, each by a positional offset ΔS 2,1 and ΔS 3,2, respectively, in the direction of movement R. It should be noted that the sequence of the scan units 5 k is arbitrary; that is, which of the scan units 5 k is designated as "first," "second," "third," etc., is arbitrary. Accordingly, the term "adjacent" scan unit 5 k is not to be understood in a spatial sense but in a numerical sense within this arbitrarily defined sequence.

[0057] For example, with three scan units 5 1 , 5 2 , 5 3, the positional offsets ΔS 2,1 and ΔS 3,2 are chosen such that, when added to the corresponding displacement S k,k-1 caused by the coprimality of step size SW and simultaneous distance A k,k-1, they correspond to one third of the step size SW, whereby the scan lines 7 k of all scan compartments 6 k, when they have passed through one and the same area of ​​the scan strip 9, lie there at regular intervals S r = SW / 3. In particular, the positional offset ΔS k,k-1 of two scan line sets 10 k , 10 k-1 , increased by the displacement S k,k-1 between these two scan line sets 10 k , 10 k-1 , each corresponds to the step size SW between two scan lines 7 k,p , 7 k,p+1 successively scanned by a scan fan 6 k divided by the number K of all scan units 5 k .

[0058] If, optionally, the pulse repetition rate PRR is additionally selected as dependent on a measured or expected distance dk,n to the environment 2 and changed within the deflection period AP k,p, the sampling points P k,n can be as in Fig. 5 and 6 The scan lines 7 k,p are also shown to be arranged regularly.

[0059] The Fig. 7 - 9 Three possible variants for offsetting the scan line sets 10k to the in Fig. 6 described manner. For each of these variants, the device 1 has a control unit 22 that controls optical elements in the beam path of the associated laser beams 4k, e.g. electro-optical elements, mirrors, prisms, etc., in order to displace the scan line sets 10k.

[0060] In a first variant ( Fig. 7 The control unit 22 contains a controlled actuator 23k for each scan unit 5k, which can adjust the position of its deflecting mirror 13k, i.e., its position and / or orientation. This shifts or tilts the respective transmission direction ϑk onto the respective mirror prism 16k and thus the associated scan fan 6k, depending on the required spatial offset ΔS k,k-1, i.e., changes the angle αk between scan fan 6k and normal N and / or the distance Dk,k-1 between scan fan vertices 20k.

[0061] In a second variant ( Fig. 7 ) the laser transmitters 12 k are adjustable and the control unit 22 controls actuators 24 k which can change the position and / or orientation, i.e. the position, of the respective laser transmitter 12 k relative to a common or (here:) respective mirror prism 16 k and thus the transmission direction ϑ k and adjust the spatial offset ΔS k,k-1.

[0062] It is understood that, for time-of-flight measurement, the laser pulses 8k,n from the displaced or tilted scan compartments 6k must also be received by the associated laser receivers 18k in the first and second variants. For this purpose, these laser receivers 18k have, in one embodiment, a receiving aperture large enough to allow the reflected laser pulses 8k,n to pass through despite the displacement or tilting of the associated scan compartment 6k. In an alternative embodiment, these laser receivers 18k retain their, for example, optimally adapted receiving aperture, and the viewing directions of these laser receivers 18k are shifted or tilted along with the associated scan compartment 6k. For this tilting or shifting, the control unit 22 could—as described for the transmitting channel in the first and second variants—have adjustable optical elements in the receiving channel by means of actuators or control the position of these laser receivers 18k themselves.

[0063] In a third, in the Fig. 7 - 9 In the variant shown, the control unit 22 controls actuators 26k mounted on a common drive shaft 25 of the mirror prisms 16k, with which the mirror prisms 16k can each be individually rotated relative to the drive shaft 25 in order to adjust the phase angle Δφ k,k-1 = φ k - φ k-1 between two mirror prisms 16k, 16k-1. By adjusting the phase angle Δφ k,k-1, a change is effected, as it were, in Fig. 8 The shown temporal shift of the sequences F k of sampling periods AP k,p by a corresponding temporal offset ΔV k,k-1 = Δφ k,k-1 / ω.

[0064] That such control of the phase positions Δφ k,k-1 or the sequences F k also leads to a positional offset ΔS k,k-1 of the respective scan line set 10 k in the direction of motion R is evident from Fig. 6 This is evident: For example, a scan line 7' 2,2 , as it would be without shifting the phase position Δφ 2,1 ( Fig. 5 ), by delaying the associated deflection period AP 2,2 by the time offset ΔV 2,1 , during which the scan unit 5 k covers the distance and thus the position offset ΔS 2,1 = v · ΔV 2,1 due to its relative movement in the direction of movement R, actually generating as scan line 7 2,2 shifted by the position offset ΔS 2,1.

[0065] Fig. 9 shows a block diagram of an electronic implementation of this third variant in a three-channel device 1 according to the embodiments of Fig. 3a - 3c Each scan unit 5 k comprises a laser transmitter 12 k and an associated laser receiver 18 k, each equipped with a deflection device 14 k - as in Fig. 2 shown for one channel - interact and are connected to a common distance calculator 19, which calculates the respective distances dk,n to the sampling points P k,n. A clock generator 27 generates a control pulse train 28 for the laser transmitters 12 k, which generate the laser pulses 8 k,n from it. The control device 22 delays the associated deflection device 14 k relative to the deflection device 14 k-1 of a neighboring scan unit 5 k-1 in the sequence of scan units 5 k by the time offset ΔV k,k-1 and thus the associated sequence F k of deflection periods AP k,p , see Fig. 8 . In order to delay the sequences F k by the respective time offset ΔV k,k-1, the control unit 22 can, as mentioned, control the actuators 26 k or alternatively offset control signals of the deflection devices 14 k, e.g. in the case of deflection devices with oscillating mirrors, by the time offsets ΔV k,k-1.

[0066] In each of the aforementioned variants, the applicable spatial offset ΔS k,k-1, the temporal offset ΔV k,k-1, or the phase angle Δφ k,k-1 can be determined by the control unit 22. For this purpose, the control unit 22 receives, for example, the current deflection period T AP from a first sensor 29 and the relative velocity v from a second sensor 30, and determines the respective values ​​accordingly.

[0067] The control unit 22 can be implemented together with the distance calculator 19 in a processor system 31, either in hardware and / or software.

[0068] In all the aforementioned embodiments and variants, the control device 22 thus displaces the scan line sets 10k in the direction of movement R, specifically the second scan line set 102 relative to the first scan line set 101 by the positional offset ΔS 2.1 and the third scan line set 103 relative to the second scan line set 102 by the positional offset ΔS 3.2. For example, ΔS k,k-1 = ΔV k,k-1 · v could be used to displace the scan line sets 10k, which appear uniform in a top view of the environment 2. Fig. 6 to obtain.

[0069] In particular, the control device 22 can determine the spatial offsets ΔS k,k-1, the phase positions Δφ k,k-1 and / or the temporal offsets ΔV k,k-1 for the embodiment of Fig. 3a and the scan line equalization of Fig. 6 according to one of the formulas Δ S k , k − 1 = ν ⋅ T AP K − D k , k − 1 mod ν ⋅ T AP Δ φ k , k − 1 = 360 ° K ⋅ J − D k , k − 1 ⋅ 360 ° J ⋅ ν ⋅ T AP Δ V k , k − 1 = T AP K − D k , k − 1 ν Δ V k , k − 1 = T AP K − 1 ν D k , k − 1 mod ν ⋅ T AP adjust, with Kn Number of scan units 5 k , Jn Number of mirror surfaces 17 j , ΔS k,k-1 Positional offset of the k-th scan line set 10 k relative to the (k-1)-th scan line set 10 k-1 ; Δφ k,k-1 Phase position of the mirror prism 16 of the k-th scan unit 5 k relative to the mirror prism 16 of the (k-1)-th scan unit 5 k-1 , ΔV k,k-1 Time offset of the sequence F k of the k-th scan unit 5 k relative to the sequence F k-1 of the (k-1)-th scan unit 5 k-1 , v Relative velocity, AP Deflection period, D k,k-1 Distance between the k-th and (k-1)-th scan fan 6 k along the direction of motion R and mod Modulo operator.

[0070] Optionally, the control unit 22 can determine the spatial offset ΔS k,k-1, the phase positions Δφ k,k-1 and / or the time offsets ΔV k,k-1 also depending on other values, e.g. the angles α k, the normal distance h, etc. The regular intervals S r of Fig. 6 from the control unit 22, e.g. for the embodiment of the Fig. 3c , can be achieved according to Δ S k , k − 1 = ν ⋅ T AP K − D k , k − 1 + h ⋅ tanα k − tanα k − 1 mod ν ⋅ T AP Δ φ k , k − 1 = 360 ° K ⋅ J − 360 ° ν ⋅ T AP ⋅ J D k , k − 1 + h ⋅ tanα k − tanα k − 1 mod ν ⋅ T AP Δ V k , k − 1 = T AP K − 1 ν D k , k − 1 + h ⋅ tanα k − tanα k − 1 mod ν ⋅ T AP with KNumber of scan units 5 k , ΔS k,k-1 Positional offset of the k-th scan line set 10 k relative to the (k-1)-th scan line set 10 k-1 ; Δφ k,k-1 Phase position of the mirror prism 16 of the k-th scan unit 5 k relative to the mirror prism 16 of the (k-1)-th scan unit 5 k-1 , ΔV k,k-1 Time offset of the sequence F k of the k-th scan unit 5 k relative to the sequence F k-1 of the (k-1)-th scan unit 5 k-1 , v Relative velocity, T AP Deflection period duration, D k,k-1 Distance between the vertices 20 k of the k-th and (k-1)-th scan compartments 6 k along the direction of motion R, h ...... expected normal distance between device 1 and environment 2, α k Angle from the expected normal N to the environment 2 to the k-th scan compartment 6 k in the plane E spanned by the direction of motion R and the expected normal N and mod modulo operator.

[0071] For this purpose, the normal N, the normal distance h, and the angles αk, αk-1 can be estimated or expected, e.g., determined from past sampling points Pk,n and the position of the device 1. In the case of a non-planar environment 2, a top view of the environment 2 can be used, or the environment 2 can be approximated, e.g., by a plane, in particular a tangent plane to its surface (topography).

[0072] Of course, in other variants, further optical elements upstream or downstream of the deflection device 14 may also be present in the beam path of the laser beams 4 k, which can be controlled by the control device 22 to shift the scan line sets 10 k.

Claims

1. An apparatus for surveying an environment (2), which is moving relative to the apparatus (1) in a direction of movement (R) at a relative speed (v), by time-of-flight measurement of laser beams (4) reflected from the environment in a coordinate system (11), comprising a first scanning unit (51) for transmitting a first laser beam (41) over a first series (F1) of deflection periods (AP1,p) with a respective deflection period duration (TAP), the first laser beam, in each deflection period (AP1,p), passing through a first scanning fan (61) and scanning the environment (2) along a first scan line (71,p) which is non-parallel to the direction of movement (R), wherein the first scan lines (71,p) form a first scan line group (101), and for receiving the corresponding laser beam (41) reflected from the environment (2), at least one further scanning unit (5k) for transmitting a further laser beam (4k) over a further series (Fk) of deflection periods (APk,p) with the same respective deflection period duration (TAP), the further laser beam, in each deflection period (APk,p), passing through a further scanning fan (6k) and scanning the environment (2) along a further scan line (7k,p) non-parallel to the direction of movement (R), wherein the further scan lines (7k,p) form a further scan line group (10k), and for receiving the corresponding laser beam (4k) reflected from the environment (2), wherein all scanning fans (6k), seen in the direction of movement (R), substantially overlap and the grouping directions (SRk) of all scan line groups (10k) are substantially parallel as seen from the apparatus (1), characterised in that the apparatus (1) is configured to, by means of the first scanning unit (51) and the at least one further scanning unit (5i), simultaneously transmit two or more scanning fans (61, 6k), and comprises a control device (22) connected to the at least one further scanning unit (5k) and configured to offset the scan line group (10k) of each further scanning unit (5k) with respect to the scan line group (10k) of a scanning unit (5k-1), that is respectively adjacent in a predetermined sequence of the scanning units (5k), in the direction of movement (R) by a position offset (ΔSk,k-1) which is dependent on the relative speed (v) and the deflection period duration (TAP), in such a way that said further scan lines (7k,p) do not coincide with said first scan lines (7k,p).

2. The apparatus according to claim 1, characterised in that it is mounted on a vehicle (3), preferably on an aircraft.

3. Apparatus according to any one of claims 1 or 2, characterised in that the control device (22) is configured to predetermine the deflection period duration (TAP) and / or the relative speed (v) depending on at least one past distance measurement value (dk,n) of the environment (2).

4. The apparatus according to any one of claims 1 to 3, characterised in that the control device (22) is configured to offset the scan line group (10k) of each further scanning unit (5k) with respect to the scan line group (10k-1) of a scanning unit (5k-1) that is respectively adjacent in a predetermined sequence of the scanning units (5k), in such a way that the scan lines (7k) are arranged at regular intervals (Sr) in the direction of movement (R).

5. The apparatus according to any one of claims 1 to 4, characterised in that the position offset (ΔSk,k-1) between the scan line groups (10k, 10k-1) of each two scanning units (5k, 5k-1) adjacent to one another in the sequence, increased by a displacement (Sk,k-1) between these two scan line groups (10k, 10k-1) in the direction of movement (R) caused by the relative movement without this position offset (ΔSk,k-1), corresponds to the distance (SW) between two successive scan lines (7k,p, 7k,p+1) of a scanning unit (5k) in the direction of movement (R), divided by the number (K) of all scanning units (5k).

6. The apparatus according to any one of claims 1 to 5, characterised in that the position offset (ΔSk,k-1) between the scan line groups (10k, 10k-1) of each two scanning units (5k, 5k-1) adjacent to one another in the sequence is chosen as Δ S k , k − 1 = ν ⋅ T AP K − D k , k − 1 + h ⋅ tanα k − tanα k − 1 mod ν ⋅ T AP with K number of scanning units (5k), ΔSk,k-1 position offset of the k-th scan line group (10k) with respect to the (k-1)-th scan line group (10k-1) , v relative speed, TAP deflection period duration, Dk,k-1 distance between vertices (20k) of the k-th and (k-1)-th scanning fans (6k, 6k-1) along the direction of movement (R), h expected normal distance between apparatus (1) and environment (2), αk angle between an expected normal (N) on the environment (2) and the k-th scanning fan (6k) in a plane (E) spanned by the direction of movement (R) and the expected normal (N), and mod modulo operator.

7. The apparatus according to any one of claims 1 to 6, characterised in that all scanning fans (6k) are substantially parallel.

8. The apparatus according to claim 7, characterised in that the position offset (ΔSk,k-1) between the scan line groups (10k, 10k-1) of each two scanning units (5k, 5k-1) adjacent to one another in the sequence is chosen as Δ S k , k − 1 = ν ⋅ T AP K − D k , k − 1 mod ν ⋅ T AP with K number of scanning units (5k), ΔSk,k-1 position offset of the k-th scan line group (10k) with respect to the (k-1)-th scan line group (10k-1), v relative speed, TAP deflection period duration, Dk,k-1 distance between the k-th and (k-1)-th scanning fans (6k, 6k-1) along the direction of movement (R), and mod modulo operator.

9. The apparatus according to any one of claims 1 to 8, characterised in that the control device (22) is configured to offset the scan line group (10k) of said at least one further scanning unit (5k) by controlling optical elements in the beam path of its laser beam (4k).

10. The apparatus according to claim 9, characterised in that the control device (22) is configured to offset the scan line group (10k) of said at least one further scanning unit (5k) by controlling a time offset (ΔVk,k-1) of the respective series (Fk).

11. The apparatus according to any one of claims 1 to 10, characterised in that each scanning unit (5k) comprises: a deflection device (14) with a mirror prism (16k) rotatable about its prism axis (15k), the lateral sides of which mirror prism each form a mirror face (17j), and a laser transmitter (12k) for transmitting the respective laser beam in a respective transmission direction (ϑk) to the deflection device (14).

12. The apparatus according to claim 11, characterised in that the laser transmitter (12k) further comprises an adjustable deflection mirror (13k) arranged in the beam path of the laser beam (4k), and the control device (22) is configured to offset the scan line group (10k) of said at least one further scanning unit (5k) by adjusting the corresponding deflection mirror (13k).

13. The apparatus according to claim 11 or 12, characterised in that the laser transmitter (12k) is arranged adjustably relative to the deflection device (14), and the control device (22) is configured to offset the scan line group (10k) of said at least one further scanning unit (5k) by adjusting the arrangement of the corresponding laser transmitter (12k).

14. The apparatus according to any one of claims 11 to 13, characterised in that the control device (22) is configured to offset the scan line group (10k) of said at least one further scanning unit (5k) by controlling the phase shift (Δφk,k-1) of the rotational movement of the corresponding mirror prism (16k).

15. The apparatus according to claim 14 in conjunction with claim 7, characterised in that the phase shift (Δφk,k-1) between the rotational movements of the mirror prisms (16k, 16k-1) of each two scanning units (5k, 5k-1) adjacent to one another in the sequence is chosen as Δ φ k , k − 1 = 360 ° K ⋅ J − D k , k − 1 ⋅ 360 ° J ⋅ ν ⋅ T AP with K number of scanning units (5k), J number of mirror faces (17j), Δφk,k-1 phase shift of the mirror prism (16k) of the k-th scanning unit (5k) with respect to the mirror prism (16k-1) of the (k-1)-th scanning unit (5k-1), v relative speed, TAP deflection period duration, Dk,k-1 distance between the k-th and (k-1)-th scanning fans along the direction of movement, and mod modulo operator.