DE102009021764A1 - Laser scanner i.e. three dimensional laser scanner, for use in three dimensional area to detect distance of object i.e. unpilot aerial vehicle, to another object, has mirror arranged such that laser rays are reflected in scanning areas - Google Patents

Abstract

The invention relates to a laser scanner with a laser beam emission device (1), which is designed to emit at least one laser beam (2, 2a) by means of a laser beam emission source in an emission region (3, 11, 11a, 11b), wherein the emission region (3 , 11, 11a, 11b) comprises a scanning area (5, 12, 12a, 12b). In this case, the laser scanner has at least one mirror (6) which is arranged at least partially in the emission region (3, 11, 11a, 11b) and outside the scan region (5, 12, 12a, 12b) such that the laser beams (2, 2a ) are reflected in the scanning area (5, 12, 12a, 12b).

Description

The The invention relates to a laser scanner with a laser beam emission device, for emitting at least one laser beam by means of a laser beam emission source is formed in an emission range, wherein the emission range includes a scan area.

The The field of application of modern laser scanner systems is diverse today. They are especially used for distances detect other objects, for obstacle detection, object recognition and to capture a three-dimensional mapping of the spatial Surroundings. Especially in the three-dimensional presentation offer Laserscannerysteme compared to the stereo cameras using two captured fields a three-dimensional image of the scene generate the big advantage that the depth data very much accurate and precise. This is especially true for safety critical Applications particularly relevant, such. B. in the control of unmanned aerial vehicles (UAV - Unpilot Aerial Vehicle), where a visually based environmental perception is required becomes.

Laser scanner systems, which work both in 2D and in 3D, are mostly based on one of two techniques. In the first variant is a Light source or a laser used, the light or laser beams via mechanically moving mirrors and / or joints in the surrounding space be scattered. So z. B. in a two-dimensional laser scanner, in which the laser beam using a single laser beam emission source is generated, the laser beam deflected in a line, so that this from one side to an opposite another Page pivots and so a two-dimensional emission range or Spans scan area. Objects that are within the spanned two-dimensional scan surfaces are thereby from detected by the laser scanner. Objects that are outside the two-dimensional scan area, z. B. above or below this area, are not being used by the laser scanner system captured, so that two-dimensional laser scanner system for safety-critical applications usually only partially suitable. Your scope is therefore limited to the determination of distances as well as the monitoring defined danger area, the of persons or cars, for example be allowed to.

at The second variant, several light sources or lasers mounted on an axle, so basically with a two-dimensional Scan no pivoting or scattering of the laser light required becomes. On the one hand, this has the great advantage of being This increases the scanning speed, but the decisive one Disadvantage that the technique is very complicated, expensive and too big, which is particularly negative in the field of unmanned aerial vehicles effect. To get a three-dimensional picture, it is there still possible, the laser beam emission source mounted on the axle to pivot along the solder of this axis, resulting in the so-called "fan-beam".

In addition to these three-dimensional laser scanner systems, which are based on more than one light source or laser source, there is the possibility to extend the widespread 2D line laser scanners, which are based on a single light source, with additional mirrors or joints so that the creation of Three-dimensional scanned images is possible. The use of 2D line laser scanner for creating a 3D scan image has the decisive advantage that due to the low weight and the acceptable size and the relatively low cost compared to the pure 3D laser scanners, the applications are significantly expanded, so that such systems z. B. in an unmanned aerial vehicle (UAV) for the purpose of environmental perception can apply. So z. In " Whalley, N .; et al.: Aerospace Dynamics Directorate (AMRDEC) US Army Research, Development & Engineering Command Ames Research Center, San Jose State Foundation Ames Research Center, Perot Systems Government Services Ames Research Center, Feb. 2008 "Describes an unmanned helicopter, which can perform a three-dimensional scan by means of a rotating 2D line laser scanner.

In order to obtain a three-dimensional scan from a 2D line laser scanner, there are basically two variants for expanding the two-dimensional emission range into the third dimension. In the first variant, as in " Wulf, O .; Wagner, B .: Fast 3D scanning methods for laser measurement systems in International Conference on Control and Computer Science, volume 14, July 2003 Is described, the entire laser head or the laser beam emitting device is moved so that the laser beam is emitted in a three-dimensional scan area. So there is z. Example, the possibility to hang the laser head on the x-axis of the laser beam such that it carries out a Mitbewegung and thus transforms the two-dimensional line scan in the third dimension (Pitching Scan, Variant A). Another possibility is to continuously rotate the laser or laser beam emitting device, so that results in a hemispherical or spherical 3D scan area (Roling Scan, Variant B). In the so-called Roling Scan, the 3D scan area depends on which axis the laser head is suspended in rotation.

The second variant, in order to obtain a 3D scan from a 2D line laser scanner, consists of having the emitted laser beams reflected on a multi-sided rotating polygon mirror so that the 2D line scan is transformed into the third dimension. Such a combination of 2D line laser scanner and rotating polygon mirror is described in TC Ng. Development of a 3D Ladar system for autonomous vehicle guidance, Technical report SIMTech, 2005 "Described accordingly. The great advantage of the second variant is that only the polygon mirror is rotated, which applies a fraction of the weight of the entire laser scanner and thereby much lower torques are generated, which is crucial especially when using small UAVs. This is precisely the main disadvantage of the first variant, in which complete line scanner is nodded or rotated, which leads to corresponding force and torque due to this movement of the scanner. Especially with small UAVs, this can lead to problematic flight behavior. Another disadvantage of the first variant and the so-called Roling scan consists in the fact that between the actual line scanner and the evaluation no cable connection is used, so that the necessary data must be transmitted via slip rings. This can lead to contact problems in the slip rings and thus to data loss, especially at higher rotational speeds, which is an exclusion criterion in the area of safety-critical application.

One Another disadvantage of the second variant, in which a 2D line laser scanner combined with a rotating polygon mirror is to that only a certain part of the emitted laser beams for The 3D scan can be used because of the rigid design of the polygon mirror a not insignificant part of the emitted Laser beams are emitted past the polygon mirror. These Laser beams are then no longer available to the scanner.

In all variants, however, the significant disadvantage over a stereo camera is that the total scan time per 3D image or per 3D scan is relatively high. For example, a stereo camera needs around 0.04 seconds per shot, while a rotating 2D line scanner needs around 2.39 seconds per 3D scan. In the so-called pitching scan configuration, there are still 1.2 seconds, while in the variant with the polygon mirror still about 0.8 seconds per 3D scan are required (at a selected resolution of 1 °). If the resolution is adjusted to a maximum of 0.25 °, the time required per scan will increase sixfold. The following table once again shows in the entirety the comparison. table Resolution 1 ° Resolution 0.25 ° Resolution 0.16 ° Laser scanner rotating (scan field 180 ° × 180 °) 2,3 s 38.33 s - Laser scanner -nickend- (scan field 180 ° × 90 °) 1.2 s 19.2 s - Laser scanner -polygon mirror- (scan field 90 ° × 60 °) 0.8 s 12.8 s - Stereo camera (field of view 50 ° × 40 °) - - 0.04 s

The measured data are based on the SICK laser scanner LMS 201 and a digital Firewire camera that operates at a frame rate of 25 fps and a resolution of 320 × 240 pixels works.

Just in safety-critical areas, such as B. in the UAV area, are the required scanning times of the laser scanner too long to to ensure a corresponding real-time operation. there is an approximation of the scanning times to the stereo camera only at the expense of angular resolution or vice versa possible.

It is therefore an object of the present invention, an improved Specify a laser scanner that clearly displays the scan time or frame rates elevated.

The The object is achieved by the laser scanner of the type mentioned in the present invention solved that the laser scanner at least one mirror which is at least partially in the emission area and outside of the scanning area is arranged such that the laser beams be reflected in the scan area.

As a result, is at least partially within the emission range in which Laser beams can be sent out, but outside of the scan area used for the result of the scan is exclusively relevant, at least one mirror such arranged on the laser scanner that in the emission area but laser beams emitted outside the scan area be reflected in the scan area. Thus, it becomes possible that the laser beams that miss the scan area are in the scan area be reflected back.

With Look at the conventional 2D line laser scanners, at which the 2D scan due to a continuous deflection of a Laser beam takes place, now also those laser beams contribute to the actual scanning process that misses the scan area. By using those laser beams that are at the actual Scanning process are not involved, since they are not within the Scanning area can be emitted, the sampling rate of the scanning Environment can be increased accordingly. Thus lets reduce the corresponding total scan time, which laser scanner applicable for use in the safety-critical area power.

In order to even conventional 2D scanners perform a 3D scan can, points, the laser scanner according to the invention a corresponding deflection device which is set up in this way is that of the laser scanner normally emitted 2D emission range extended accordingly into the third dimension. The laser beams, which are emitted by the laser scanner are doing so deflected or deflected so that a three-dimensional scan is created. In other words, the 2D scan range within the 2D emission range is moved to a 3D scanning area by means of the laser beam deflection device extended.

there For example, the laser beam deflecting device may be a rotating polygon mirror which is arranged in the plane of the 2D scan area such that the laser beams emit within this 2D scan area are so deflected due to the rotation of the polygon mirror be redirected to a 3D scan area.

by virtue of the fixed shape of the polygon mirror, which is in the plane of the 2D scan area is arranged, the 2D emission range is larger as the 2D scan area. In other words, some of the laser beams, which are emitted by the laser beam emitting device are emitted outside the scan area and thus miss the polygon mirror, so they do not for the 3D scan To be available. According to the invention the laser scanner next to the polygon mirror in the plane of the 2D emission range at least one such mirror on which the laser beams, the miss the polygon mirror, reflect on the polygon mirror, so that these laser beams are now used for the 3D scan To be available.

A such a constellation arises z. B. in that the original opening angle the 2D line laser scanner spanning a 2D emission area, 180 °. When using a polygon mirror, to transform the 2D scan area into the third dimension, due to the specified design only a range of about 90 ° is clamped, depending on the distance and size of the polygon mirror. Both 45 ° on one side and 45 ° on the other side of the polygon mirror remain unused and can not be used for scanning.

The However, laser beam deflection device can also be set up in this way be that the laser beam emitting device rotates or a Pitching motion to that of the laser beam emission device transformed 2D emission range in the 3D scan area to transform. So For example, when rotating the laser beam emitting device a hemispherical 3D scan area spanned or a spherical, depending on which axis the rotation is suspended.

Advantageously, the mirrors which reflect the laser beam which misses the scanning region are then suspended on the rotating or nodding axis, so that there is likewise an increase in the frame rate or sampling rate. In other words, the mirrors are arranged on the laser beam emission device or on a laser scanner in such a way that they participate in rotational movement or the pitch movement, respectively. Compared to the original emission range of the scan area is of course smaller when using the mirror than the original emission range, but this z. B. in the UAV area is not critical, since the scanners are usually aligned anyway in the flight direction. By increasing the frame rate or sampling rate again this disadvantage is corrected accordingly.

It But it is also conceivable that the mirror on the laser scanner in such a way be arranged that they are firmly connected to the laser scanner are and opposite the laser beam emission device do not make a nodding or rotating movement. So is For example, it is particularly advantageous if in a rotating Movement of the laser beam emission device of the mirrors annular Rotationally fixed about the rotating laser beam emission device is arranged to miss the scan area in any rotational position Reflect laser beams back into the scan area. Such a mirror can, for. B. have the shape of a conical ring, wherein the arrangement takes place in the emission area, the diameter of the ring decreases towards the laser source. This device has it the advantage of no additional weights on the laser beam emission device must be arranged so that less accordingly Rotational and force moments occur.

Of Furthermore, it is also conceivable that with a nodding suspension the laser beam emitting device, the mirror fixed to the Laser scanners are arranged, d. H. she did not hang in the pitch axis are and thus the movement of the laser beam emission device not with perform. The mirrors can do that also be arranged on the side so that they have the appropriate Laser beams that miss the scan area reflect back into them. The mirrors can also be ring-shaped with conical Inner circumferential surface or planar with sufficient size, to cover the pitch range of the scanner, be configured.

Conceivable But it is also that the laser scanner from the outset a 3D laser scanner system which is for sending a three-dimensional scan area is set up (so-called "fan-beam"), where Here too, in the emission area, the mirrors are arranged in such a way that that they are reflected back in the scan area. Consequently can be achieved that the emitted laser beams, which miss the actual scan area, reflected back into the scan area become, so that among other things the dissolution increases.

there It has been recognized that the mirrors are advantageously at an angle with respect to the laser source of a quarter or a Sixth of the original opening angle arranged become. This results in the arrangement of the mirror at an angle from a quarter of the original opening angle a doubling of the scan rate, while at an angle from one sixth of the original opening angle a tripling of the scan rate can be achieved.

Based The accompanying drawings illustrate the invention by way of example explained. Show it:

1a) . 1b) schematic representation of the principle of a 2D line laser scanner;

2a) - 2d) schematic representation of 3D scans using 2D line laser scanners;

3 schematic representation of the mirror assembly;

4a) . 4b) . 4c) schematic representation of the emission and scan area.

1a) shows a plan view of a known from the prior art 2D line laser scanner. The laser scanner has a laser beam emitting device for this purpose 1 on that a laser beam 2 in the emission area 3 sending out. The laser beam 2 is suspended on the y-axis (not shown) and has an opening angle of 180 ° or 90 ° in both directions from the perpendicular (z-axis). 1b) shows this principle again in a three-dimensional representation.

The schematically illustrated 2D line laser scanner in 1a) works in such a way that the laser beam 2 on a circular path from one side of the emission area 3 on the opposite side of the emission area 3 is pivoted, so in this embodiment, the laser beam 2 a path of 180 ° travels, wherein the laser beam is bound to a rotation angle of 180 ° in the housing. During such a scan, no laser beams are emitted in the other regions of the emission area.

The following explanations show the extension of a 2D line laser scanner to a 3D scanner, in which the laser beams in the 2D emission area by means of a deflection device in the third dimension to be transformed.

2a) shows the schematic representation of a line laser scanner, by means of a servo device (motor with drive control), with the laser beam emission device 1 coupled, the laser beams 2 send out in a 3D emission area. For this purpose, the laser head or the laser beam emission device performs 1 a corresponding pitching motion while the laser beam 2 , as in 1 shown, continues to be deflected two-dimensionally, so that the laser beam 2 Overall, a three-dimensional distraction learns.

2 B) schematically shows the principle that the laser head 1 around an axis, here in this example the z-axis, rotates. In this case, a hemispherical or a spherical emission region would be clamped.

2c) shows the schematic representation of a 2D line scanner using a polygon mirror 4 can do a 3D scan. The polygon mirror 4 is located in the plane of the two-dimensional scan area 5 such that the laser beams 2 be deflected into the third dimension and thus a three-dimensional scan area 5a span. In this arrangement has the particular advantage that only the polygon mirror 4 moved and thus the resulting forces and torques are very low, which allows the use of such laser scanner systems in the UAV area.

2d) shows again a plan view of the 2D line laser scanner with a laser beam emission device 1 and a polygon mirror 4 , Due to the solid shape and fixed size of the polygon mirror 4 Only one scan area is detected, which corresponds to approximately 90 ° of the opening angle. In the lateral emission areas 3a and 3b but miss the laser beams 2 the polygon mirror 4 so that they remain unused for the 3D scan. During this time, in which the laser beam emission device the laser beam 2 within the lateral emission range 3b sends, no active 3D scanning can be done.

3 shows schematically the representation of a possible mirror arrangement according to the teaching of the present invention. It will be in the emission area 3a . 3b one mirror each 6 arranged, which the laser beams 2a that are in the emission area 3a . 3b outside the scan area, into the scan area 5 . 5a reflected. This leaves the laser beams 2 that in the lateral emission areas 3a . 3b are sent out, no longer idle, but are also used for scanning, resulting in a corresponding higher scan rate.

It is particularly advantageous if the mirror 6 be arranged at an angle of one quarter of the original opening angle in the emission region, which in this embodiment results in an angle of 45 ° with respect to the z-axis. This leads to a doubling of the scan rate. With an angular arrangement of one sixth of the original opening angle, which in this embodiment is 30 °, this leads to a tripling of the scan rate, resulting in a maximum scanning range of 60 °.

4a) shows schematically the representation of the emission range 11 and the scan area 12 as generated by a 2D line laser scanner. Starting from the z-axis results in a first scan area 12a with an opening angle of 0 ° to 45 ° and a second scan area 12b with an opening angle of 0 ° to -45 °. To the first scan area 12a Furthermore, the unused emission area closes 11a on, which has the opening angle of 45 ° to 90 °. On the opposite side closes at the second scan area 12b another unused emission area 11b with an opening angle of -45 ° to -90 °.

According to the teachings of the present invention, the unused emission regions become 11a and 11b due to the mirror arrangement in the scan area 12 reflected back, which is schematically in 4b) is shown. The scan area now includes the original scan areas 12a and 12b , as well as the areas reflected back in the scan area 11a and 11b , Specifically, this means that the laser beams in the unused emission area 11a be sent out, in the scan area 12a be reflected while the laser beams in the emission area 11b be sent out, in the scan area 12b be reflected so that each scan scan remains unused each of the laser beams. In this embodiment, the mirrors are arranged at an angle of 45 ° or a quarter of the original opening angle, this arrangement leading to a doubling of the scan rate.

4c) shows the schematic representation of the emission and scan area at an angle Order the mirror of 30 ° or one sixth of the original opening angle. In doing so, the unused laser beams that are in the emission area 11a be sent out in the complete scan area 12 ( 12a and 12b ) and the laser beams in the unused emission area 11b be sent out, also in the complete scan area 12 ( 12a and 12b ) reflected back.

Each scanning pass thus becomes the scan area 12 scanned three times, ie twice each of the reflected laser beams in the emission areas 11a and 11b as well as the laser beams going directly into the scan area 12 to be sent out. This arrangement resulted in a tripling of the scan rate at a scanning angle of 60 °.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Whalley, N .; et al.: Aerospace Dynamics Directorate (AMRDEC) US Army Research, Development & Engineering Command Ames Research Center, San Jose State Foundation Ames Research Center, Perot Systems Government Services Ames Research Center, Feb. 2008 [0005]
• - Wulf, O .; Wagner, B .: Fast 3D Scanning Methods for Laser Measurement Systems in International Conference on Control and Computer Science, volume 14, July 2003 [0006]
• - TC Ng. Development of a 3D Ladar system for autonomous vehicle guidance, Technical Report SIMTech, 2005 [0007]

Claims (9)

Laser scanner with a laser beam emission device, which is capable of emitting at least one laser beam ( 2 . 2a ) by means of a laser beam emission source in an emission region ( 3 . 3a . 3b . 11 . 11a . 11b ), the emission range ( 3 . 3a . 3b . 11 . 11a . 11b ) a scan area ( 5 . 12 . 12a . 12b ), characterized in that the laser scanner comprises at least one mirror ( 6 ), which at least partially in the emission area ( 3 . 3a . 3b . 11 . 11a . 11b ) and outside the scan area ( 5 . 12 . 12a . 12b ) is arranged such that the laser beams ( 2 . 2a ) in the scan area ( 5 . 12 . 12a . 12b ) are reflected. Laser scanner according to claim 1, characterized in that the laser beam emission device ( 1 ) for emitting the laser beam ( 2 . 2a ) into a 2D emission range ( 3 . 3a . 3b . 11 . 11a . 11b ) is set up and the laser scanner a laser beam deflection device ( 4 ), which for deflecting the laser beam ( 2 . 2a ) from the 2D scan area ( 12 . 12a . 12b ) within the 2D emission range ( 3 ) is set up in a 3D scan area. Laser scanner according to claim 2, characterized in that the laser beam deflection device is a rotating polygon mirror ( 4 ), which is in the plane of the 2D scan area ( 5 . 12 . 12a . 12b ) is arranged such that the laser beams ( 2 . 2a ) into the 3D scan area ( 5a ), wherein the at least one mirror ( 6 ) in the plane of the 2D emission range ( 3 . 11 ) is arranged such that the laser beams ( 2 . 2a ) on the polygon mirror ( 4 ) are reflected. Laser scanner according to claim 2, characterized in that the laser beam deflection device for rotating and / or nodding the laser beam emission device ( 1 ) is formed around an axis (x, y, z) such that the laser beams ( 2 . 2a ) into the 3D scan area ( 5a ) are emitted. Laser scanner according to claim 4, characterized in that the at least one mirror ( 6 ) with the rotating and / or nodding laser beam emission device ( 1 ) and in the plane of the 2D emission range ( 3 . 3a . 3b . 11 . 11a . 11b ) is arranged such that the laser beams in the 3D scan area ( 5a ) are reflected. Laser scanner according to claim 4, characterized in that the at least one mirror ( 6 ) annularly around the rotating laser beam emitting device ( 1 Rotationally fixed to the laser scanner is arranged such that the laser beams in the 3D scan area ( 5a ) are reflected. Laser scanner according to claim 4, characterized in that the at least one mirror ( 6 ) fixed against the laser beam emission device ( 1 ) is arranged on the laser scanner such that the laser beams ( 2 . 2a ) into the 3D scan area ( 5a ) are reflected. Laser scanner according to claim 1, characterized in that the laser beam emission device ( 1 ) for emitting the laser beam ( 2 . 2a ) is set up in a 3D emission area. Laser scanner according to one of the preceding claims, characterized in that the at least one mirror ( 6 ) at an angle with respect to the laser source (z-axis) of a quarter or a sixth of the opening angle of the emission region ( 3 . 11 ) is arranged.