Multi-plane scanner and method of detecting object

Abstract

The invention relates to a multi-plane scanner and a method for detecting an object. A multi-plane scanner is presented comprising: a light emitter that emits a light beam toward a monitored area; a light receiver that receives a light beam reflected by an object in the monitored area; an evaluation unit that evaluates a reception signal of the optical receiver; and a polygonal mirror wheel rotatable about a first axis of rotation to periodically deflect the light beam, the polygonal mirror wheel having a plurality of mirror surfaces arranged in a ring shape and at least partially inclined to each other with respect to the first axis of rotation to scan a plurality of angular sections of the monitoring area at different heights, i.e., a plurality of superimposed scanning planes, the light beam deflection unit is arranged between the light emitter and the polygonal reflector wheel as a monitoring area for each turn of the polygonal reflector wheel so as to adjust the incident angle of the light beam to the mirror surface. The control unit is arranged to receive a target trajectory of the light beam in the monitoring area and to control the polygonal mirror wheel and the light beam deflection unit such that the light beam scans the monitoring area along the target trajectory.

Description

[0001] The invention relates to a multiplane scanner and a method for detecting objects in a surveillance area having a plurality of superimposed planes according to the preambles of claims 1 and 11 .

[0002] Scanners are used for various monitoring and measuring tasks. For this purpose, a light beam scans an area and the reflected light is evaluated. In order to also obtain information about the distance, contour or profile of an object, it is often necessary not only to determine the presence of an object but also its distance at the same time. Such distance-measuring laser scanners or LiDAR (Light Detection And Ranging) scanners operate according to the light time-of-flight principle, in which the flight time from the scanner into the scene and back again is measured and the distance data is calculated based on the speed of light.

[0003] Two types of time-of-flight methods are widely used. In phase-based methods, a light transmitter modulates a light beam and the phase between a reference and received beam is determined. In pulse-based methods, a significant pattern (e.g., a narrow pulse of only a few nanoseconds duration) is imparted to the light beam and the time of reception of the pattern is determined. In a generalized method called pulse averaging, multiple pulses or a train of pulses are emitted and the received pulses are statistically evaluated.

[0004] Furthermore, frequency modulated continuous wave (FMCW)-LiDAR scanners are also referred to as range-finding laser scanners. The basis of FMCW-LiDAR technology is described, for example, in the scientific publication “Linear FMCW Laser Radar for Precision Range and Vector Velocity Measurements” (Pierrottet, D., Amzajerdian, F., Petway, L., Barnes, B., Lockard, G., & Rubio, M. (2008). Linear FMCW Laser Radar for Precision Range and Vector Velocity Measurements. MRS Proceedings, 1076, 1076-K04-06. doi: 10.1557 / PROC-1076-K04-06) or the doctoral thesis “Realization of Integrated Coherent LiDAR” (T. Kim, University of California, Berkeley, 2019. https: / / escholarship.org / uc / item / 1d67v62p).

[0005] Unlike LiDAR scanners or laser rangefinders based on the light time-of-flight measurement of laser pulses, FMCW-LiDAR scanners do not emit a pulsed emission beam into the monitoring area, but rather a continuous emission beam which has a specified frequency modulation (i.e. the change in the wavelength of the emission light over time) during the measurement period (i.e. during the time-discrete scanning of the measurement points in the monitoring area). Here, the measurement frequency of the total frame consisting of 100,000 or more measurement points is usually in the range of 10 Hz to 30 Hz. The frequency modulation can, for example, be designed as a periodic up and down modulation. Compared to the radiated emission light, the emission light reflected by the measurement point in the monitoring area has a time shift corresponding to the light flight time, which depends on the distance of the measurement point from the sensor and is accompanied by a frequency shift caused by the frequency modulation. In the FMCW-LiDAR scanner, the radiated emission light and the reflected emission light are coherently superimposed, wherein the distance of the measurement point from the sensor can be determined from the superimposed signal. Compared to pulsed or amplitude-modulated incoherent LiDAR measurement principles, the measuring principle of coherent superposition has the advantage of being better protected against extraneous light, for example from other optical sensors / sensor systems or the sun.

[0006] Known laser scanners have a rotating mirror or polygon wheel that rotates about an axis of rotation in order to periodically scan a monitoring plane or a section of a two-dimensional monitoring plane. However, in many applications, it is desirable to detect the surroundings in more than one plane. This is particularly true in mobile applications, such as unguided vehicles (AGV, Automated Guided Vehicle), where it is necessary to detect floors with edges and steps, as well as objects that protrude into the driving area at different heights. Another application is the monitoring and classification of vehicles, for example on highways or at automatic inspection points.

[0007] Three-dimensional scanners are known from the prior art, in which the sensor as a whole or a rotating mirror is additionally tilted periodically. However, this requires a very complex structure. It is usually sufficient to monitor only a few planes stacked on top of each other rather than the entire spatial area.

[0008] Methods for achieving such multi-plane scanning include using a mirror wheel instead of a simple polygon wheel as a beam deflection unit, the mirror surface of which has different inclinations or tilt angles relative to the rotation axis of the polygon wheel. Although the scanning angle range is usually reduced to less than 100° by using a polygon wheel, the monitoring area can be scanned multiple times at different heights per rotation by means of the tilted mirror surface. In this case, the light beam extends on a trajectory that generates superimposed scanning planes at different heights of the monitoring area.

[0009] However, a disadvantage of these mirror wheels is that, if the feed angle is chosen to be greater than 0° (i.e. not directly from the front), the scan plane will be distorted during the rotational movement due to the different angles of incidence of the scanning beam on the mirror, which is almost always the case. Figure 5 This is illustrated in Figure 1, where the vertical offsets of several planes are plotted over the rotation angle of the grating mirror wheel. In other words, the scan line displayed on the target plane of the monitored area is generated by several differently tilted mirrors.

[0010] from Figure 5 As can be seen in Figure 1, only the center line of the non-tilted mirror is straight. Now, it is OK that the other lines are curved. This is because, strictly speaking, a multiplane scanner does not detect multiple planes, but rather a cone surface. Therefore, when the mirror is tilted, the scan lines projected onto the target plane are curved radially. So far, this difference in planes is not relevant because the tilt angle is small and the cone angle is very large.

[0011] Even more disturbing is that when the rotational position is 0°, the scan line is not symmetrical with respect to the center line. Therefore, the vertical angular resolution at positive rotational position is better than that at negative rotational position, which means that the detection area belonging to the face is no longer flat even when viewing in polar coordinates on the surface of the cone. The vertical resolution is linked to the angular position of the grating mirror wheel in an undesirable way.

[0012] As a result, tilted mirrors lead to distorted parabolic beam deflections, especially in the long-range area, which makes equidistant scanning in the long-range area more difficult. If the parabolic curves extend too far from each other, the edge areas may be outside the region of interest (ROI). In extreme cases, the beam extends outside the monitoring area and wastes measurement time without producing any meaningful output results. In addition, the point density in the monitoring area ROI is reduced.

[0013] DE 36 02 008 A1 discloses an optical scanning device with a mirror wheel. The mirror surfaces of the mirror wheel have different curvatures. As a specific example, a mirror wheel with six mirror surfaces is given, wherein each pair of mirror surfaces facing each other radially is respectively configured to be flat, concave and convex. The scanning device includes an evaluation electronic device, which evaluates the sharpness of the received light spot. reacts and only evaluates the signal from the sharpest scanning spot.

[0014] US2013 / 0076852 A1 relates to a scanning system that uses a light beam to generate parallel scan lines on an image plane. For this purpose, a raster polygonal reflector is provided, and its mirror surfaces have different inclination angles. In order to compensate for the curvature of the scan line generated by the mirror surface, a lens system consisting of five single lenses is used in a specific example to compensate for the distortion.

[0015] EP 1 965 225 A2 discloses various variants which additionally tilt a rotating mirror of a laser scanner in order to change the scanning plane and thus expand the field of view.

[0016] It is known from EP 2 983 030 A2 to compensate for the above-mentioned distortion of the scanning plane in various ways. On the one hand, by static measures, for example, shaping the mirror surface as a free-form surface with a compensation profile, or shaping as a front screen with a plurality of segments corresponding to the scanning plane, which are superimposed on each other and have a compensation profile. In addition, dynamic correction schemes are mentioned, such as dynamic tilting of the mirror surface synchronized with the rotation of the mirror wheel or displacement of the light transmitter and / or light receiver. The purpose is in particular to achieve a constant vertical angle resolution on different scanning planes. This means that the above-mentioned scanning lines on the target plane generated by the differently tilted mirror surfaces are preferably designed to be parallel.

[0017] In general, the known techniques aim to achieve a scanning of the monitoring area that is as uniform as possible. However, in many cases, the scanning of the monitoring area needs to be flexible and application-dependent, such as the number, density and position of scanning planes or scanning lines as well as the shape and inclination. Therefore, the light beam should be guided on a trajectory that is as flexible as possible in the monitoring area.

[0018] It is therefore an object of the present invention to improve the monitoring of a 3-dimensional monitoring area by means of a multi-plane scanner.

[0019] This object is achieved by a multiplane scanner and a method for detecting objects in a surveillance area having a plurality of superimposed planes according to claims 1 and 11 .

[0020] Like the known LiDAR or FMCW-LiDAR scanners with polygonal reflectors, the multiplane scanner comprises a light transmitter for emitting a light beam to the monitored area, a light receiver for receiving the light beam reflected by an object in the monitored area, an evaluation unit for evaluating the received signal of the light receiver, and a polygonal reflector wheel (Polygonspiegelrad) rotatable about a first rotation axis, the polygonal reflector wheel having a plurality of mirror surfaces arranged in a ring. The mirror surfaces are at least partially tilted relative to the first rotation axis, so that the multiplane scanner can scan an angular section of the monitored area multiple times at different heights when the reflector unit rotates once. A beam deflection unit is arranged between the light transmitter and the polygonal reflector wheel for adjusting the angle of incidence of the light beam on the mirror surface.

[0021] The basic idea of ​​the present invention is that the control unit is configured to receive a target trajectory of a light beam in a monitoring area and control the polygonal mirror wheel and the light beam deflection unit so that the light beam scans the monitoring area along the target trajectory.

[0022] The invention has the advantage that a multiplane scanner or multi-layer scanner with freely assignable scanning planes can be created, wherein the light beam can scan the monitoring area along a substantially freely assignable trajectory. "Substantially" here means that the possibility of specifying the trajectory is only limited by boundary conditions, such as the number and size of the mirrors and the maximum possible beam deflection in time and space by the beam deflection unit. The invention thus differs from the prior art, in which the scanning planes are fixedly defined by the system structure and optimized, for example, for a constant angular resolution.

[0023] Preferably, the control unit is configured to determine control parameters of the polygon mirror wheel and the beam deflection unit based on the received target trajectory, thereby enabling a particularly precise scanning of the monitoring area along the target trajectory.

[0024] Preferably, the control unit can be arranged to receive a target trajectory of the light beam in the monitoring area by means of a user input. For example, the user can define a target trajectory in the monitoring area on an input unit, which transmits this information to the control unit. For example, the user can make such an input when the sensor is commissioned. Alternatively or additionally, the target trajectory can also be adjusted depending on the situation, for example based on the distance of the multiplane scanner from the detected object. The terms "control unit" and "input unit" are to be understood here as functional blocks which can be implemented individually or together as hardware or can, for example, also be components of a superior control and evaluation unit of the sensor.

[0025] In particular, the target trajectory can be input by specifying a scanning plane in the monitoring area or a scanning line on an imaginary target plane in the monitoring area. Preferably, the imaginary target plane can be a plane aligned parallel to the rotation axis of the polygonal mirror wheel and arranged at a defined distance from the multi-plane scanner.

[0026] For example, after the multiplane scanner has been installed, the alignment of the monitored area can be corrected by specifying the target trajectory. This saves the need for mechanical realignment of the scanner. This is particularly advantageous if the scanner is fixed in a difficult-to-access location (e.g. on a crane, mast or in a deep well) or if the installation position of the scanner changes over time.

[0027] For example, target trajectories can be specified for beams in the surveillance area, eliminating the reference Figure 5 The described asymmetries make it possible to create multiplane scanners or multi-layer scanners with a constant angular offset. In polar coordinate observation, the additional planes can also have a constant deviation relative to the middle plane that is independent of the rotational position. In this case, a complete compensation does not necessarily have to be achieved, since the reduction of the asymmetry already improves the multiplane scanner. However, at least at the measuring distance (i.e. at a defined distance from the sensor), a complete compensation is possible. Reference Figure 5 In particular, parallel scan lines can be generated on the target plane in the monitoring area. Here, the beam deflection unit deflects the beam onto the mirror surface, thereby compensating the influence of the change in the incident angle of the beam onto the mirror surface during the rotational movement, that is, the beam in the monitoring area scans the specified target trajectory.

[0028] The beam deflection unit can be designed as a rotating mirror (e.g., a galvanometer) rotatable about a second rotation axis, wherein the second rotation axis is not aligned parallel to the first rotation axis of the polygonal mirror wheel, but is preferably aligned perpendicularly to the first rotation axis of the polygonal mirror wheel. As a result, a vertical deflection is generated in the monitoring area, i.e., a deflection perpendicular to the deflection of the light beam by the polygonal mirror wheel. Alternatively, the deflection element can be designed as a MEMS mirror or a so-called phase array, i.e., the light beam is deflected by phase modulation.

[0029] In addition to the incident angle of the light beam, the light beam deflection unit can also be configured to adjust the incident position of the light beam on the mirror surface, thereby making it possible to better adapt the light beam trajectory in the monitoring area to the specified target trajectory.

[0030] Preferably, the control unit can be configured to determine control parameters of the polygonal mirror wheel and the beam deflection unit based on a model, wherein a calculation model can be stored in the control unit, with which the optical path of the light beam in the monitoring area can be calculated or simulated as a function of the rotation angle of the polygonal mirror wheel. Starting from the received target trajectory, control parameters of the light beam deflection by the beam deflection unit, such as the setting position of the galvanometer, can then be determined, which control parameters are necessary for the light beam to scan the monitoring area along the target trajectory.

[0031] The calculation model can be based on known geometrical optics methods, such as ray tracing, and in addition to the beam deflection by the polygonal mirror wheel and the beam deflection unit, can also specifically take into account the influence of the transmitting optics and / or receiving optics of the multiplane scanner on the optical path of the beam.

[0032] The control parameters can be calculated recursively by symbolic / algebraic calculations starting from an assumed object in the monitoring area or the above-mentioned target plane. Alternatively or additionally, a forward calculation can also be performed, in which the light path to the polygon mirror wheel and further to the assumed object or target plane in the monitoring area is calculated starting from the variable deflection of the light beam through the beam deflection unit. An iterative search algorithm can systematically analyze different deflections of the light beam by the beam deflection unit and numerically approximate the target trajectory. The advantage of using a calculation model is that the control parameters can be calculated at runtime, wherein the control unit can preferably have a real-time computer for calculating the control parameters at runtime. This allows the beam deflection to be specified arbitrarily subsequently. If only one or some situations (Konstellation) are specified, it is also possible to perform the calculation in advance and create a lookup table, which is used when the multiplane scanner is running.

[0033] Preferably, the control of the polygonal mirror wheel and the beam deflection unit can be carried out by a cascade control system having a regulator of the polygonal mirror wheel and the beam deflection unit, wherein the control unit can preferably be configured to adjust the rotation speed of the polygonal mirror wheel, in particular independently of the control of other components of the multiplane scanner. The beam deflection unit obtains its control parameters from the above-mentioned calculation model, which receives the position of the polygonal mirror wheel and calculates the control parameters of the beam deflection unit using the target trajectory. As a result, the beam deflection unit is always synchronized with the position of the polygonal mirror wheel. The position of the polygonal mirror wheel can be provided, for example, by a first encoder, which detects the angular position and / or angular velocity or the rotational position and / or rotational speed of the polygonal mirror wheel. If the beam deflection unit is designed as a rotating mirror, the second encoder can detect the rotational position of the rotating mirror.

[0034] Preferably, the regulator of the beam deflection unit is designed to be faster than the regulator of the polygon mirror wheel. This ensures synchronization of the polygon mirror wheel and the beam deflection unit. The time delays of the control loop of the beam deflection unit can be taken into account in the calculation model, for example by a physical model of the beam deflection unit and its control loop. In particular, other measured variables can also be taken into account here, such as control errors, currents and voltages at the galvanometer or acceleration sensors on the multiplane scanner (disturbance feedforward). ) data.

[0035] Preferably, the control unit can be configured to receive the distance between the multi-plane scanner and the target area in the monitoring area, and use the distance between the multi-plane scanner and the target area in the monitoring area to control the polygonal mirror wheel and the beam deflection unit, thereby further compensating for the distance-related trajectory distortion.

[0036] The multiplane scanner may have an acceleration sensor, wherein the control unit is configured to receive data from the acceleration sensor and use the data from the acceleration sensor to control the polygon mirror wheel and the beam deflection unit. For example, by taking into account the data from the acceleration sensor, deviations of the trajectory caused by the rotation of the multiplane scanner itself can be reduced.

[0037] The control unit can be configured to determine intermediate values ​​of encoder signals of the polygon mirror wheel and / or of the deflection element by temporal interpolation and to generate uniform control parameters for the deflection element, for example to set the movement of the rotatable mirror.

[0038] Preferably, the evaluation unit is configured to correct a reception signal of the optical receiver using a position error of the polygon mirror wheel and / or of the beam deflecting unit.

[0039] Preferably, the polygonal mirror wheel can be controlled by the control unit so that the polygonal mirror wheel rotates around the first rotation axis at a constant speed, thereby generating a temporally uniform horizontal deflection of the light beam in the monitoring area.

[0040] In another embodiment of the invention, the polygonal mirror wheel may have at least one tilting element to change the inclination of at least one mirror surface relative to the rotation axis of the polygonal mirror wheel. This can further expand the vertical scanning range of the scanner. In one embodiment of this embodiment, the inclination of the mirror surface can be changed synchronously with the rotation movement of the polygonal mirror wheel. This provides greater freedom for influencing the trajectory of the light beam in the monitoring area.

[0041] The light emitter of the multi-plane scanner can be designed to emit a plurality of light beams spaced apart from each other, so that the monitoring area can be scanned more quickly or more intensively. Since only one of the plurality of light beams can scan the monitoring area along the target track, the control unit can be configured to control the polygonal mirror wheel and the beam deflection unit so that the average deviation of the light beam from the target track is minimized.

[0042] The sensor according to the invention can be used in various systems and applications, for example in the above-mentioned unguided vehicles (AGV - automatic guided vehicle) or in the monitoring and classification of vehicles, for example on highways or at automatic detection points (toll bridges). Other fields of application can be, for example, the detection of aircraft on the apron of an airport or the detection of ships and / or their cargo in a port. When ships and their cargo are detected in a port, the monitoring area can be specially adapted to the (tide-related) water level by means of a solution for specifying the target trajectory.

[0043] The method according to the invention can be further developed in a similar manner and simultaneously exhibits similar advantages. Such advantageous features are described exemplarily but not exhaustively in the dependent claims which are dependent on the independent claim. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other features and advantages of the present invention will be described in more detail below based on exemplary embodiments and with reference to the accompanying drawings. In the accompanying drawings:

[0045] Figure 1 A block diagram showing an embodiment of a multi-plane scanner according to the present invention;

[0046] Figure 2 A schematic diagram showing an exemplary adjustment of a multi-plane scanner according to the present invention;

[0047] Figure 3 shows an exemplary trajectory that can be scanned on a target plane using a multi-plane scanner according to the present invention;

[0048] Figure 4 A schematic diagram showing the use of a multi-plane scanner according to the present invention to detect a ship is shown;

[0049] Figure 5 The asymmetric distribution of the vertical offset of the scan lines depending on the rotation angle in a conventional multi-plane scanner is shown.

[0050] Figure 1A block diagram of a multiplane scanner 10 is shown. A light emitter 12 (e.g. a laser diode or an LED) generates a light beam 16 by means of a transmission optics 14, which is deflected for a first time via a beam deflection unit 18 and for a second time via a polygonal mirror wheel 20 rotating about a first rotation axis 19 and then emitted into a monitoring area 22.

[0051] If the light beam 16 falls on the object in the monitoring area 22, the reflected light beam 24 returns to the multi-plane scanner, and the light beam is deflected again on the polygon mirror wheel 20 and the beam deflection unit 18, and then imaged onto the light receiver 28 via the beam splitter 25 and the receiving optical device 26. Here, the language does not distinguish between reflection on the object and the more common diffuse reflection. The beam splitter 25 is designed as a beam splitter or a perforated mirror. A two-axis design is also possible. Then, the light beam 16 and the received light 24 are arranged substantially parallel to each other at a small distance in the direction of the rotation axis of the polygon mirror wheel 20.

[0052] The reception signal generated by the light receiver 28 is transmitted to the evaluation unit 30. For example, it is recognized in the evaluation unit whether an object is scanned and when an object is detected the distance to the object is determined preferably using a light time-of-flight method or an FMCW method.

[0053] The polygonal mirror wheel 20 is an example of a rotatable mirror unit having a plurality of mirror surfaces 32 on its outer circumference. The number of mirror surfaces 32 corresponds to the scanning angle range, and the fewer mirror surfaces 32 are provided, the greater the scanning angle range. Therefore, the number of eight mirror surfaces 32 is not fixed, but more or fewer mirror surfaces 32 may also be provided. The base surface also does not have to be a regular polygon, but in principle mirror surfaces 32 of different lengths may also be provided.

[0054] Despite Figure 1, but the mirror surfaces 32 are tilted relative to each other. This does not refer to a tilt in the horizontal direction (which is determined by the nature of the polygon), but rather to an additional separate tilt in the vertical direction. Therefore, the surfaces of the mirror surfaces 32 are not aligned parallel to the central axis of the polygonal mirror wheel 20 (which also forms the first rotation axis 19 in the embodiment shown), but are tilted individually by at least a few degrees. Therefore, depending on the horizontal tilt with which the light beams 16 of the light emitter 12 each fall on the mirror surface 32, different planes are scanned in an angular range corresponding to the horizontal range of the mirror surface 32, and thus a multi-plane scan (represented by the trajectories 40a, 40b of the light beams 16) is generated, which will be generated in the monitoring area 22 on a target plane perpendicular to the drawing plane, which represents the target area 23 in the monitoring area, which target area is located at a distance D from the multi-plane scanner 10. Preferably, the inclination of the mirror surfaces is individual, but it is also conceivable that a plurality of mirror surfaces 32 have the same inclination, so that the corresponding plane is scanned multiple times per rotation of the polygonal mirror wheel 20.

[0055] The evaluation unit 30 detects the corresponding rotational position of the polygon mirror wheel 20, for example, via a first encoder The first encoder is the same as the drive for rotation. Figure 1 The rotational position of the polygonal mirror wheel 20 is not shown and is known per se. It contains not only information about the horizontal angle directly, but also indirectly about the vertical angle when the inclination of the mirror surface 32 relative to the first rotation axis 19 is saved. The evaluation unit 30 also knows the vertical angle at which the light beam 16 leaves the beam deflection unit 18 in the direction of the polygonal mirror wheel 20. In the present embodiment, the beam deflection unit 18 is designed as a rotating mirror 36 (e.g., a galvanometer), whose rotation axis 34 is aligned perpendicular to the first rotation axis 19 of the polygonal mirror wheel 20. The angle at which the light beam 16 leaves the beam deflection unit 18 in the direction of the polygonal mirror wheel 20 is generated by the rotation position θ of the rotating mirror 36, which is also detected by a second encoder (not shown). Therefore, when the rotation position θ of the polygonal mirror wheel 20 is known, the rotation position θ of the light beam 16 is detected by a second encoder (not shown). When the rotation position θ of the rotating reflective mirror 36 is φ, the position of the object or the contour of the object can be detected in three-dimensional spherical coordinates using the distance measured by the light flight time method.

[0056] The polygon mirror wheel 20 and the beam deflection unit 18 are controlled by a control unit 38. The control unit 38 is configured to receive a target trajectory 40a of the light beam 16 in the monitoring area 22, for example by a user input via an input unit 42.

[0057] As referenced in the introduction Figure 5As explained, only one mirror 32 generates a true scanning plane (which is called the middle plane or horizontal plane, regardless of its actual position) without any vertical inclination (inclination=0°) relative to the first rotation axis 19. Strictly speaking, the other planes, although designated as planes here, are not planes in the geometric sense, which results in a distorted trajectory 40b of the light beam 16 in the monitoring area 22 that deviates from the designated target trajectory 40a.

[0058] In order to compensate for this influence, the control unit 38 is configured to control the polygon mirror wheel 20 and the beam deflection unit 18 such that the light beam scans the monitoring area along the target trajectory 40 a.

[0059] To this end, the control unit 38 can first adjust the rotation speed of the polygonal mirror wheel 20 and keep it constant. Then, the control unit 38 is also designed to adjust the rotation speed of the polygonal mirror wheel 20 based on the rotation position of the polygonal mirror wheel 20. The calculation model is used to determine the rotation position θ of the rotating mirror 36 (which is necessary to scan the target track 40a), and the rotating mirror 36 is controlled accordingly. Thus, the rotating mirror 36 is always synchronized with the polygon mirror wheel 20 and causes the light beam to scan the target track 40a.

[0060] according to Figure 1 The basic structure of the multiplane scanner 10 is to be understood only as an example. For example, the transmission path and the reception path can also differ from the beam splitter 25 shown, or the polygon mirror wheel 20 can be arranged and oriented differently relative to the transmission path and the reception path.

[0061] Figure 2 A schematic diagram of an exemplary regulation 50 of the multiplane scanner 10 by the control unit 38 is shown. A first regulator 52 is provided for regulating the rotational speed of the polygon mirror wheel 20 in a first step and for keeping it constant. The rotational speed is derived from a specified value for the speed at which the light beam 16 should scan the monitoring area 22. A first encoder 54 determines the rotational position of the polygon mirror wheel 20. The rotational position is transmitted to the first regulator 52, and the first regulator 52 can adjust the rotational position based on the measured rotational position. To stabilize the rotation speed of the polygonal mirror wheel 20.

[0062] In addition, the rotation position of the polygonal mirror wheel 20 is also transmitted to the calculation model 56, which uses the rotational position of the polygonal mirror wheel 20 The incident angle of the light beam 16 onto the mirror 32 is calculated by using the specified target trajectory 40a, and the control parameters of the deflection unit 18 are calculated accordingly, that is, the target rotation position θ of the rotating mirror 36 in this example. S . Target rotation position θS is transmitted to the second regulator 58, which adjusts the deflection unit 18 or the rotating mirror 36 accordingly. As a result, the deflection unit 18 or the rotating mirror 36 is synchronized with the polygon mirror wheel 20. The second encoder 60 determines the actual rotational position θ of the rotating mirror 36. I and returns it to the second regulator 58, which is based on the measured actual rotational position θ I To correct the target rotation position θ of the rotating mirror 36 S deviation.

[0063] The second controller 58 of the deflection unit 18 or the rotating mirror 36 must be designed to be faster than the first controller 52 of the polygon mirror wheel 20 in order to ensure synchronization. The time delay of the control of the deflection unit 18 must be taken into account in the calculation model 56 as a function of the controller speed. For this purpose, a physical model of the deflection unit 18 and its controller 58 can be incorporated. Other measured variables can also be taken into account here, such as control errors, currents and voltages on the rotating mirror 36 or data from acceleration sensors (disturbance feedforward) on the multiplane scanner 10.

[0064] Figure 3 Various exemplary trajectories that can be scanned on a target plane 23 in a monitoring area 22 using the multiplane scanner 10 according to the present invention are shown. Since the trajectories can be adjusted substantially freely, taking into account the monotonically progressive rotational position of the polygonal mirror wheel 20, All trajectory shapes are theoretically possible.

[0065] In a), substantially parallel horizontal tracks 70 are shown, the density of which increases in the upper region. Thus, scan lines with locally different densities can be generated.

[0066] As shown in b), an inclined trajectory 72 is also possible, which allows, for example, an alignment correction in the case of an inclined multiplane scanner, which can also correct the alignment of its monitoring area at any time after installation.

[0067] In c), a freely definable trajectory 74 is shown, which can exclude certain areas of the monitoring area (eg light-sensitive areas or areas where data acquisition is not required) from the light beam.

[0068] Figure 4 A schematic diagram of the application of a multiplane scanner 80 according to the present invention is shown, which is arranged at a quay 82 of a port. In a), a light beam 84 emitted by the multiplane scanner 80 detects a ship 86 at a first water level 88.1 of a water surface 90 moored at the quay 82.

[0069] If the water surface 90 sinks to the second water level 88 . 2 as shown in b) (eg due to tidal differences), the light beams 84 emitted by the multiplane scanner 80 will miss the vessel 86 and in particular can no longer be reliably detected in the area near the quay 82 .

[0070] By adjusting the target trajectory, as shown in c), the light beam 84 emitted by the multi-plane scanner 80 can be fanned out so that the vessel 86 can be detected without mechanically changing the alignment of the multi-plane scanner 80. The fanning out of the light beam 84 also has the advantage that objects (not shown) far from the pier 82 can still be detected, whereas without the fanning out of the light beam 84, mechanically tilting the entire multi-plane scanner 80 would only allow detection of the vicinity of the pier 82.

Claims

1. A multi-plane scanner (10), comprising: A light transmitter (12) for transmitting a light beam (16) to a monitoring area (22); a light receiver (28) for receiving the light beam (24) reflected by an object in the monitoring area (22); an evaluation unit (30) for evaluating a received signal of the light receiver (28); and a polygonal reflector wheel (20) which is rotatable about a first rotation axis (19) to periodically deflect light beams (16, 24), the polygonal reflector wheel having a plurality of mirror surfaces (32) which are annular and at least partially arranged to be tilted relative to the first rotation axis (19) so as to scan angular sections of the monitoring area (22) multiple times at different heights, i.e., a plurality of superimposed scanning planes as the monitoring area (22) per rotation of the polygonal reflector wheel (20), wherein a light beam deflection unit (18) is arranged between the light emitter (12) and the polygonal reflector wheel (20) for adjusting the incident angle of the light beam (16) onto the mirror surface (32), It is characterized in that The control unit (38) is configured to receive a target trajectory (40a) of the light beam (16) in the monitoring area (22), and control the polygonal mirror wheel (20) and the light beam deflection unit (18) so that the light beam (16) scans the monitoring area (22) along the target trajectory (40a).

2. The multi-plane scanner (10) according to claim 1, wherein: The control unit is configured to determine control parameters of the polygonal mirror wheel (20) and the beam deflection unit (18) based on the received target trajectory (40a).

3. The multi-plane scanner (10) according to claim 1 or 2, wherein: The multi-plane scanner (10) has an input unit (42) for inputting the target trajectory (40a), and the control unit (38) is configured to receive the target trajectory (40a) from the input unit (42).

4. The multi-plane scanner (10) according to claim 2 or 3, wherein: The control unit (38) is configured to determine control parameters of the polygon mirror wheel (20) and the beam deflection unit (18) based on a model.

5. The multiplane scanner (10) according to any one of the preceding claims, wherein: The multi-plane scanner (10) has a first regulator (52) for adjusting the polygonal mirror wheel (20) and a second regulator (58) for adjusting the beam deflection unit (18).

6. The multi-plane scanner (10) according to claim 5, wherein: The second regulator (58) is designed to be faster than the first regulator (52).

7. The multiplane scanner (10) according to any one of the preceding claims, wherein: The control unit (38) is configured to receive a distance (D) between the multi-plane scanner (10) and a target area (23) in the monitoring area (22), and to control the polygonal reflector wheel (20) and the beam deflection unit (18) using the distance (D) between the multi-plane scanner (10) and the target area (23) in the monitoring area (22).

8. The multiplane scanner (10) according to any one of the preceding claims, characterized in that The multi-plane scanner (10) has an acceleration sensor, and the control unit (38) is configured to receive data from the acceleration sensor and control the polygon mirror wheel (20) and the beam deflection unit (18) using the data from the acceleration sensor.

9. The multiplane scanner (10) according to any one of the preceding claims, wherein: The beam deflection unit (18) is a rotating mirror (36), in particular a galvanometer mirror, which is rotatable about a second rotation axis (34), wherein the second rotation axis (34) is aligned non-parallel to the first rotation axis (19).

10. The multiplane scanner (10) according to any one of the preceding claims, wherein: At least one mirror surface (32) has a tilting element in order to adjustably tilt the mirror surface (32) relative to the first rotation axis (19), and the control unit (38) is configured to control the tilting element.

11. A method for detecting an object using a multi-plane scanner (10), wherein: A light beam (16) is emitted to a monitoring area (22) and after reflection on an object in the monitoring area (22) is received again and evaluated, wherein the monitoring area (22) is scanned cyclically by deflecting the light beam (16) at a polygonal mirror wheel (20) so that, per one revolution of the mirror unit (20), an angular segment, i.e., a plurality of superimposed planes, is scanned multiple times at different heights of the monitoring area (22), the polygonal mirror wheel (20) being rotatable about a first rotation axis (19) and having a plurality of mirror surfaces (32) arranged in an annular shape and at least partially tilted relative to one another, wherein a light beam deflection unit (18) arranged between the light transmitter (12) and the polygonal mirror wheel (20) adjusts the angle of incidence of the light beam (16) on the mirror surface (32), It is characterized in that The control unit (38) receives a target trajectory (40a) of the light beam (16) in the monitoring area (22), and controls the polygonal mirror wheel (20) and the light beam deflection unit (18) so that the light beam (16) scans the monitoring area (22) along the target trajectory (40a).

12. The method according to claim 11, wherein: The control unit (38) uses the target trajectory (40a) to determine control parameters of the polygonal mirror wheel (20) and the beam deflection unit (18).

13. The method according to claim 12, wherein: The control unit (38) controls the rotation position of the polygonal reflector wheel (20) To calculate the optical path of the light beam (16) in the monitoring area (22).

14. The method according to claim 12, wherein: The beam deflection unit (18) has a rotating reflector (36) which adjusts the incident angle of the beam (16) onto the mirror surface (32), and the control unit (38) adjusts the incident angle of the beam (16) onto the mirror surface (32) according to the rotation position of the polygonal reflector wheel (20). The rotation position (θ) of the rotating reflector (36) is calculated.

15. The method according to claim 12, wherein: The control unit (38) uses the distance (D) between the multi-plane scanner (10) and a target area (23) in the monitoring area (22) to determine control parameters of the polygonal mirror wheel (20) and the beam deflection unit (18).

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