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EP-4063900-B1 - DEVICE FOR MEASURING AN ENVIRONMENT

EP4063900B1EP 4063900 B1EP4063900 B1EP 4063900B1EP-4063900-B1

Inventors

  • RIEGER, PETER

Dates

Publication Date
20260513
Application Date
20210325

Claims (15)

  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 (5 1 ) for transmitting a first laser beam (4 1 ) over a first series (F 1 ) of deflection periods (AP 1,p ) with a respective deflection period duration (T AP ), the first laser beam, in each deflection period (AP 1,p ), passing through a first scanning fan (6 1 ) and scanning the environment (2) along a first scan line (7 1,p ) which is non-parallel to the direction of movement (R), wherein the first scan lines (7 1,p ) form a first scan line group (10 1 ), and for receiving the corresponding laser beam (4 1 ) reflected from the environment (2), at least one further scanning unit (5 k ) for transmitting a further laser beam (4 k ) over a further series (F k ) of deflection periods (AP k,p ) with the same respective deflection period duration (T AP ), the further laser beam, in each deflection period (AP k,p ), passing through a further scanning fan (6 k ) and scanning the environment (2) along a further scan line (7 k,p ) non-parallel to the direction of movement (R), wherein the further scan lines (7 k,p ) form a further scan line group (10 k ), and for receiving the corresponding laser beam (4 k ) reflected from the environment (2), wherein all scanning fans (6 k ), seen in the direction of movement (R), substantially overlap and the grouping directions (SR k ) of all scan line groups (10 k ) 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 (5 1 ) and the at least one further scanning unit (5 i ), simultaneously transmit two or more scanning fans (6 1 , 6 k ), and comprises a control device (22) connected to the at least one further scanning unit (5 k ) and configured to offset the scan line group (10 k ) of each further scanning unit (5 k ) with respect to the scan line group (10 k ) of a scanning unit (5 k-1 ), that is respectively adjacent in a predetermined sequence of the scanning units (5 k ), in the direction of movement (R) by a position offset (ΔS k,k-1 ) which is dependent on the relative speed (v) and the deflection period duration (T AP ), in such a way that said further scan lines (7 k,p ) do not coincide with said first scan lines (7 k,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 (T AP ) and/or the relative speed (v) depending on at least one past distance measurement value (d k,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 (10 k ) of each further scanning unit (5 k ) with respect to the scan line group (10 k-1 ) of a scanning unit (5 k-1 ) that is respectively adjacent in a predetermined sequence of the scanning units (5 k ), in such a way that the scan lines (7 k ) are arranged at regular intervals (S r ) in the direction of movement (R).
  5. The apparatus according to any one of claims 1 to 4, characterised in that the position offset (ΔS k,k-1 ) between the scan line groups (10 k , 10 k-1 ) of each two scanning units (5 k , 5 k-1 ) adjacent to one another in the sequence, increased by a displacement (S k,k-1 ) between these two scan line groups (10 k , 10 k-1 ) in the direction of movement (R) caused by the relative movement without this position offset (ΔS k,k-1 ), corresponds to the distance (SW) between two successive scan lines (7 k,p , 7 k,p+1 ) of a scanning unit (5 k ) in the direction of movement (R), divided by the number (K) of all scanning units (5 k ).
  6. The apparatus according to any one of claims 1 to 5, characterised in that the position offset (ΔS k,k-1 ) between the scan line groups (10 k , 10 k-1 ) of each two scanning units (5 k , 5 k-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 (5 k ), ΔS k,k-1 position offset of the k-th scan line group (10 k ) with respect to the (k-1)-th scan line group (10 k-1 ) , v relative speed, T AP deflection period duration, D k,k-1 distance between vertices (20 k ) of the k-th and (k-1)-th scanning fans (6 k , 6 k-1 ) along the direction of movement (R), h expected normal distance between apparatus (1) and environment (2), α k angle between an expected normal (N) on the environment (2) and the k-th scanning fan (6 k ) 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 (6 k ) are substantially parallel.
  8. The apparatus according to claim 7, characterised in that the position offset (ΔS k,k-1 ) between the scan line groups (10 k , 10 k-1 ) of each two scanning units (5 k , 5 k-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 (5 k ), ΔS k,k-1 position offset of the k-th scan line group (10 k ) with respect to the (k-1)-th scan line group (10 k-1 ), v relative speed, T AP deflection period duration, D k,k-1 distance between the k-th and (k-1)-th scanning fans (6 k , 6 k-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 (10 k ) of said at least one further scanning unit (5 k ) by controlling optical elements in the beam path of its laser beam (4 k ).
  10. The apparatus according to claim 9, characterised in that the control device (22) is configured to offset the scan line group (10 k ) of said at least one further scanning unit (5 k ) by controlling a time offset (ΔV k,k-1 ) of the respective series (F k ).
  11. The apparatus according to any one of claims 1 to 10, characterised in that each scanning unit (5 k ) comprises: a deflection device (14) with a mirror prism (16 k ) rotatable about its prism axis (15 k ), the lateral sides of which mirror prism each form a mirror face (17j), and a laser transmitter (12 k ) for transmitting the respective laser beam in a respective transmission direction (ϑ k ) to the deflection device (14).
  12. The apparatus according to claim 11, characterised in that the laser transmitter (12 k ) further comprises an adjustable deflection mirror (13 k ) arranged in the beam path of the laser beam (4 k ), and the control device (22) is configured to offset the scan line group (10 k ) of said at least one further scanning unit (5 k ) by adjusting the corresponding deflection mirror (13 k ).
  13. The apparatus according to claim 11 or 12, characterised in that the laser transmitter (12 k ) is arranged adjustably relative to the deflection device (14), and the control device (22) is configured to offset the scan line group (10 k ) of said at least one further scanning unit (5 k ) by adjusting the arrangement of the corresponding laser transmitter (12 k ).
  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 (10 k ) of said at least one further scanning unit (5 k ) by controlling the phase shift (Δφ k,k-1 ) of the rotational movement of the corresponding mirror prism (16 k ).
  15. The apparatus according to claim 14 in conjunction with claim 7, characterised in that the phase shift (Δφ k,k-1 ) between the rotational movements of the mirror prisms (16 k , 16 k-1 ) of each two scanning units (5 k , 5 k-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 (5 k ), J number of mirror faces (17 j ), Δφ k,k-1 phase shift of the mirror prism (16 k ) of the k-th scanning unit (5 k ) with respect to the mirror prism (16 k-1 ) of the (k-1)-th scanning unit (5 k-1 ), v relative speed, T AP deflection period duration, D k,k-1 distance between the k-th and (k-1)-th scanning fans along the direction of movement, and mod modulo operator.

Description

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. Devices of this type are used, for example, in the EP 3 182 159 B1 These devices are described and are carried, for example, by an aircraft or ship to topographically 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 measure objects moving on it, etc. The scanning unit emits a laser beam, e.g., pulsed or modulated, at various angles within the scan field, targeting numerous points ("scanning points") of the scan line in the surrounding area during each deflection period. From time-of-flight measurements of the target reflections, the target distances are determined, and from these distances—knowing the position of the scanning unit and the respective emission angle—a point model ("3D point cloud") of the environment is created. In mobile, vehicle-based devices, the scan field defined by the laser beam is moved across the environment by the vehicle's movement, scanning each scan line individually. In stationary devices, the environment to be measured is moved relative to the scan fan, e.g. for measuring objects on conveyor belts. 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 a deflection mechanism in the scanning unit. Therefore, for a given relative velocity, 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, reducing the resolution within a scan line and thus the resolution of the 3D point cloud. The pulse repetition rate also cannot be increased arbitrarily: at a high pulse repetition rate or greater target distance, the next laser pulse is emitted before the reflected first transmitted pulse is received, so 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 d max of a uniquely measurable distance range, a so-called MTA zone, is derived from the pulse repetition rate PRR and the speed of light c as d max = c/(2·PRR). 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 in order 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 and therefore the resolution of the 3D point cloud. Simply increasing the number of sampling points in the 3D point cloud, as in the DE 10 2004 050 682 A1 Using multiple scanning units can increase the spatial resolution, but this doesn't necessarily mean it's higher. For example, some target points might be scanned multiple times, resulting in local clusters of scan points, while other areas of the environment might contain too few scan points, meaning the desired resolution of the 3D point cloud isn't achieved across the entire area. Therefore, a uniform distribution of scan points across the environment is essential for obtaining a high-quality 3D point cloud. 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. 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