DE102017200691A1 - Projection apparatus and method for scanning a solid angle area with a laser beam - Google Patents

Abstract

The invention relates to a projection device for scanning a solid angle range by means of a laser beam (6), comprising a laser light source (1) for generating the laser beam (4), a micromirror (2) deflectable about two axes for deflecting the laser beam and an expansion optics (3) Expanding the scannable angular range, with an optical axis (8) along which the laser beam (6) deflected by the micromirror (2) is emitted in a basic position of the micromirror, a lens system of the expansion optics (3) being designed such that an exit angle ( β), below which the laser beam (6) leaves the expansion optics (3), is larger than a deflection angle (a), by the laser beam (6) deflected by the micromirror (2) in front of the expansion optics (3) by a deflection of the micromirror (2) is deflected out of the optical axis (8).

Description

The invention is in the field of optics and laser scanning and relates to a projection apparatus, a detection system and a method for scanning a solid angle range with a laser beam.

Projection devices with a laser light source and a deflection device about two axes are known from the prior art. The deflection device is often realized by a 2D MEMS scanner. An advantage of scanning laser projection with 2D MEMS scanners is that no lens is required for projection. This is due to the fact that a laser beam passing through an objective is influenced in its geometric properties such as divergence, beam waist and Rayleigh range. Without a lens, beam quality and associated accuracy are essentially defined only by the characteristics of the laser.

The EP 2 514 211 B1 shows, for example, a projection apparatus comprising a deflection device and a laser light source for projecting Lissajous figures onto an observation field. A deflection unit oscillates about a first and a second axis.

A field of application for such optical devices are room monitoring and distance measuring systems in the field of vehicle safety, in particular for driver assistance systems and systems for autonomous driving. For this purpose, optical systems are needed, with the help of which a wide solid angle range can be monitored with sufficient accuracy.

In known systems, the scannable solid angle range is determined by a maximum deflection angle of the 2D MEMS scanner. In the course of ongoing developments, especially in the field of autonomous driving, however, requirements are made with regard to the scannable solid angle, the known MEMS scanners can not meet or not sufficiently due to their limited maximum deflection angle. To a certain extent, it is possible to develop special scanners, which open up a larger angular range by means of corresponding torsional vibrations. However, unlike traditional 2D MEMS scanners, these scanners are very sensitive to external mechanical disturbances such as shock or vibration and therefore unsuitable for many applications.

The present invention is therefore based on the object to provide a comparable optical system, which is able to cover or monitor the widest possible solid angle range.

The object is achieved by a projection device with the features of independent claim 1 and by a detection system according to claim 7. Advantageous embodiments and developments of the invention will become apparent with the features of the subclaims.

Accordingly, the invention relates to a projection apparatus for scanning a solid angle range by means of a laser beam. The projection device comprises a laser light source for generating the laser beam, a micromirror deflectable about two axes for deflecting the laser beam, and an expansion optics for expanding the scannable angular range. The expansion optics has an optical axis, along which the laser beam deflected by the micromirror is radiated in a basic position of the micromirror. A lens system of the expansion optics is designed such that an exit angle at which the laser beam exits the expansion optics is greater than a deflection angle by which the laser beam deflected by the micromirror is deflected out of the optical axis by the deflection of the micromirror before the expansion optics.

The laser light source preferably generates the laser beam in the form of pulses. The duration and intensity of the pulses can be adjustable and adjusted depending on the application. The laser light source may, for example, also be adjustable such that it only generates laser beams if the micromirror is deflected in such a way that the laser beam falls into the expansion optics. Preferably, the micromirror has a pivot point. The pivot point of the micromirror preferably lies on the optical axis of the expansion optics and the micromirror is deflectable about two axes, which are preferably orthogonal to one another, in order to enable a spatial scanning. The micromirror can be deflected by oscillations of the micromirror about the two axes in order to realize, for example, Lissajous projections for scanning the solid angle range. For a detailed explanation of the spatial sampling in the form of Lissajous figures is on EP 2 514 211 B1 directed. The expansion optics include a lens system with an optical axis. The optical axis is generally known as the line of symmetry in an optical structure passing through the centers of curvature of the lenses of the lens system. As a basic position, a position of the micromirror is referred to, in which the laser beam is emitted by the micromirror along the optical axis. The exit angle describes the angle at which the laser beam leaves the expansion optics, and lies between the optical axis and a deflected by deflection of the micromirror from the optical axis, the expansion optics leaving laser beam. The deflection angle describes the angle between the optical axis and a deflected by deflection of the micromirror from the optical axis laser beam in front of the expansion optics.

The scanned by the laser beam angle range is therefore typically more than twice as large as a deflection range of the micromirror. With the proposed features thus results in a very large scannable solid angle range. Preferably, the scannable solid angle range includes all possible exit angles of up to 60 °, possibly even up to 70 °, 80 ° or 90 °.

In one possible embodiment, the micromirror may be part of a MEMS device, preferably part of a 2D MEMS. Micromirror actuators that can be used belong to the class of MEMS (Micro Eletro Mechanical System) or MOEMS (Micro Opto Electro Mechanical System) components and are advantageous because of their very small construction, since they are produced on the one hand in large quantities at low cost can be because of their small embodiment and resonant frequencies up to 50 kHz and beyond. The micromirror may have a diameter of e.g. at least 0.5 mm, preferably at least 1 mm, and / or have a diameter of up to 2.5 mm, preferably at most 2 mm. The micromirror of the MEMS device can be driven electrostatically, piezoelectrically, magnetically, mechanically or in another way.

In another possible embodiment, the lens system may be a so-called fisheye optic. Fisheye lenses are well known, for example, from photography. However, the laser light beam generated by the laser light source passes through the fisheye optics counter to the direction of a light beam using a fisheye lens in the photograph. It is advantageous in the presently described embodiment, a widening part of the fish-eye lens. Preferably, the fish-eye optics may comprise three lenses, more preferably a plano-concave, a convex-concave and another plano-concave lens, arranged along the optical axis. The expanding properties of the fisheye optics can enable a scannable solid angle of at least 160 ° in the direction of the laser beam deflected by the micromirror through the fisheye optics.

The expansion optics can expand the laser beam as it passes through the expansion optics. After leaving the expansion optics, this can lead to spot sizes and spot shapes of the laser beam, which have distortions and lead to measurement inaccuracies, depending on the exit angle. In a further embodiment, a beam-shaping optical system can therefore be arranged between the laser light source and the micromirror such that the laser beam generated by the laser light source passes through the beam-shaping optical system before being deflected by the micromirror. The beam shaping optics can influence geometric beam parameters of the laser beam, in particular a divergence, a Rayleigh length and a waist diameter, by means of successively lined lenses in such a way that a beam quality of the laser beam, in particular after leaving the expansion optics, can be improved. Thus, it can be achieved that the spot sizes and shapes of the laser beam as a function of the deflection angle is substantially constant.

In another possible embodiment, the expansion optics may comprise a first collecting lens group or lens and a second dispersive lens group. The first collecting lens group or lens may be disposed between the micromirror and the second dispersive lens group. The first collecting lens group or lens may be formed such that a beam path of the laser beam deflected by the micromirror is parallel to the optical axis independent of the deflection angle between the first collecting lens group or lens and the second dispersive lens group. The first collecting lens group or lens may thus be a collimator. This has the advantage that in a region in which the laser beam is parallel to the optical axis, further optical components such as beam splitters and / or polarizing filters can be installed.

An advantageous detection system may comprise a projection device of the type described and a detector for detecting detection light produced by scattering of the laser beam on a surface of an obstacle within the scanned solid angle range. To a good approximation, it can be assumed for many scattering surfaces that the detection light distribution is a cosine distribution (Lambert distribution). Thus, a surface located in the solid angle range can be detectable with the detector. Using pulsed lasers, it is possible, for example, to use a time-of-flight method (TOF) or a phase detection method by means of which the distance of the reflecting or scattering surface from the detector can be determined. The independent measurement of the angular position of the micromirror and thus the exit angle of the laser beam in Connection with the distance determination allows the localization of the surface in the solid angle range.

Furthermore, the detection system may have optics for the detector, which is designed such that the detection light falls on a point of the detector which is independent of a direction of the laser beam leaving the expansion optics and / or of a location of the obstacle. This may allow a compact design of the detection system because detector arrays can be avoided and a single detector is sufficient.

The optics for the detector may in particular comprise a collimator for focusing the detection light onto the detector. The focal point of the collimator may lie in the detector plane and thus ensure that the detection light falls on only one point of the detector. Furthermore, a diaphragm can be arranged, for example, between the detector and the collimator, so that a maximum detection angle of the detection light can be defined.

In a further embodiment, the detection system can have a beam splitter for decoupling the detection light within the expansion optics or between the micromirror and the expansion optics. Particularly advantageous may be an arrangement of the beam splitter between the first, collecting lens group or lens and the second, dispersing lens group, since a beam path of the deflected laser beam is parallel to the optical axis here. Thus, part of the detection light entering the expansion optics can be deflected by the beam splitter onto the detector. Typically, the beam splitter is a polarizing beam splitter. The polarizing beam splitter can pass a portion of the passing laser beams and deflect another part. Deflected beams can leave the polarizing beam splitter and then be absorbed, for example.

Advantageously, a polarization filter can furthermore be arranged in a beam path between the laser light source and the beam splitter. The polarization filter can be designed in such a way that it transmits only or predominantly a polarized portion of the laser beam that is not reflected by the polarizing beam splitter, so that stray light in the beam splitter can be avoidable. This has the advantage that in the detector only or primarily detection light can be directed and a measurement accuracy can be increased.

To further increase the measurement accuracy and the avoidance of stray light, further optical components, for example an edge filter or an interference filter, can be installed in the beam path in front of the detector. To suppress daylight, it is also possible to exploit the time structure of the laser.

In an advantageous embodiment, the detection system may include an evaluation device, which may be set up to allocate a current output signal of the detector to the instantaneous deflection of the micromirror and to determine a current direction of the laser beam leaving the expansion optics. Thus, an obstacle scattering the laser beam in the solid angle region can be located on an angular straight line which lies along the instantaneous direction of the laser beam leaving the expansion optics. In order to determine a distance of the obstacle along the angular straight line, the evaluation device can also assign a time of a transmission of the laser beam by the laser light source to a current input signal of the detector.

In another embodiment, optical materials, such as CaF 2 or MgF 2, that are translucent in the near infrared (NIR) range may be used for the lenses and detectors. In this way, illumination of surfaces in the NIR wavelength range, e.g. between 0.8 μm -4 μm, be possible. In this wavelength range, the detection of many organic materials is possible.

In the described detection system with the expansion optics and the laser light source typically configured to emit laser pulses, it can be e.g. to trade a LIDAR system. LIDAR systems emit laser pulses and detect backscattered light. LIDAR systems can be advantageous in a variety of applications, for example, in driver assistance systems for sensors in autonomous driving, speed measurements of vehicles or the detection of cloud or dust particles in the air, since they generate accurate measurement results. A detection system with the structure according to the invention and an embodiment as LIDAR system is particularly advantageous because of the wide, scannable solid angle range, a high measurement accuracy of the LIDAR and yet compact design.

For scanning a relatively large solid angle range, a method performed with a projection device or a detection system of the type described above, in which the laser beam is generated by the laser light source, is directed to the micromirror, and after reflection by the laser Micromirror falls through the expansion optics, the micromirror oscillating is excited, so that the solid angle range is scanned by the laser beam leaving the expansion optics.

This method is suitable e.g. for detecting and locating obstacles within said solid angle range and / or for analyzing surfaces of such obstacles when performed with the described detection device and detecting detection light caused by scattering of the preferably pulsed laser beam at a surface within the scanned solid angle range by the detector and an output signal of the detector is detected by detecting a momentary displacement of the micromirror respectively of a current direction of the laser beam leaving the expansion optics and used for determining a distance to the surface by a transit time or phase measurement.

• 1 eine schematische Darstellung einer Projektionsvorrichtung mit optionaler Strahlformungsoptik,
• 2 eine schematische Darstellung der Projektionsvorrichtung mit der Strahlformungsoptik und einer ersten, sammelnden Linsengruppe,
• 3 eine perspektivische Ansicht der Projektionsvorrichtung mit der Strahlformungsoptik und der ersten, sammelnden Linsengruppe und einem Strahlteiler,
• 4 eine schematische Darstellung der Projektionsvorrichtung mit der Strahlformungsoptik, der ersten, sammelnden Linsengruppe und dem Strahlteiler,
• 5 eine schematische Darstellung der Projektionsvorrichtung mit der Strahlformungsoptik, der ersten, sammelnden Linsengruppe, einem polarisierenden Strahlteiler und einem Polarisationsfilter,
• 6 eine schematische Darstellung eines Detektionssystems mit einer Strahlformungsoptik, einer ersten, sammelnden Linsengruppe, einem Strahlteiler, einer Optik für den Detektor und einem Detektor und
• 7 einen vergrößert dargestellten Ausschnitt des Detektionssystems aus 6.

Embodiments of the invention are illustrated in the figures and are explained in more detail in the following description. Show it:

• 1 a schematic representation of a projection device with optional beam shaping optics,
• 2 1 is a schematic representation of the projection device with the beam-shaping optical system and a first, collecting lens group,
• 3 3 is a perspective view of the projection apparatus with the beam shaping optics and the first collecting lens group and a beam splitter,
• 4 a schematic representation of the projection device with the beam shaping optics, the first, collecting lens group and the beam splitter,
• 5 a schematic representation of the projection device with the beam shaping optics, the first, collecting lens group, a polarizing beam splitter and a polarizing filter,
• 6 a schematic representation of a detection system with a beam shaping optics, a first, collecting lens group, a beam splitter, an optic for the detector and a detector and
• 7 an enlarged section of the detection system from 6 ,

In 1 schematically is a projection device with a laser light source 1, a micromirror 2 , and an expansion optics 3 shown. The laser light source 1 generates a laser beam 4 by a beam shaping optics 5 on the micromirror 2 meets. The 1 shows an exemplary beam path of the laser beam 4 , after a deflection by the micromirror 2 with the reference number 6 is marked. The beam shaping optics 5 is a lens system, the geometrical parameters of the laser beam 4 For example, a Rayleigh length, a waist diameter and a divergence of the laser beam 4 , Are defined. The micromirror 2 is deflectable about two axes and part of a 2D MEMS. In this embodiment, the micromirror oscillates about the two torsion axes. The laser beam 6 is with a beam direction at a deflection of the micromirror 2 with a maximum deflection angle α, in which the laser beam 6 still through the expansion optics 3 is shown, shown. A laser beam 7 shows an example of a further beam path at a deflection of the micromirror 2 in which the laser beam 7 still through the expansion optics 3 is steered. The micromirror directs the laser beam 6 respectively. 7 So from an optical axis 8th the expansion optics 3 out. The optical axis 8th forms a symmetry line of the expansion optics 3 , The expansion optics 3 includes a lens system 9 which in this example consists of three lenses. Im in 1 As shown, the three lenses are two plano-concave and one convex-concave, but the lens system may also have a different lens combination and number. The laser beam 6 leaves the expansion optics with an exit angle β. The exit angle β is greater than the deflection angle α. In the illustrated embodiment, the exit angle β, for example, 60 degrees, while the deflection angle α is 10 degrees. In the example shown, the laser beam has 6 at an exit angle of 60 ° and at a distance of 10 m from the exit point of the optical axis from the expansion optics a diameter of 5 cm, at an exit angle of 0 °, the diameter is 1 cm. An overall length of the projection device along the optical axis is for example about 7 cm.

2 shows the projection device 1 with a first collecting lens group 10 , Recurring features are provided with identical reference numerals. The first, collecting lens group 10 is between the micromirror 2 and a second dispersive lens group 11 arranged. The first, collecting lens group is a collimator, so that a beam path of the micromirror 2 deflected laser steel 6 regardless of the angle of deflection between the first collecting lens group 10 and the second dispersive lens group 11 parallel to the optical axis 8th runs. Im in 2 In the example shown, an overall length of the projection device along the optical axis is opposite to that in FIG 1 shortened. An overall length is here for example about 6 cm.

3 illustrates the schematic in 2 shown projection device in one perspective view, extended by a beam splitter 12 , The beam splitter 12 is between the first, collecting lens group 10 and the second dispersive lens group 11 arranged. In this area, a beam path runs parallel to the optical axis 8th (in 3 not shown) of the expansion optics 3 , The beam splitter is formed in this example as a beam splitter cube, but may also be other shape. In 4 is the projection device off 3 shown in a schematic representation.

5 shows the projection device 4 also in a schematic representation, extended by a polarizing filter 13 , The polarizing filter 13 is between the first collecting lens group 10 and the beam splitter 12, so that the polarizing filter 13 as well as the beam splitter 12 is arranged in the area in which the beam path of the laser beam 6 parallel to the optical axis 8th runs. Both the beam splitter 12 as well as the polarization filter 13 can also be elsewhere in the expansion optics 3 to get integrated. The beam splitter 12 is a polarizing beam splitter cube in the example shown. The polarization filter 13 avoids that stray light in the beam splitter 12 passes by the polarizing filter 13 only or predominantly a polarized portion of the laser beam 6 transmits, which is not reflected by the polarizing beam splitter. Since the installation of a polarizing filter has no effect on a direction or geometry of the laser beam 6 has the direction and geometry of the laser beam 6 corresponds to those of the 4 ,

In 6 a detection system is shown. This detection system, which is a LIDAR system, includes a projection device with a laser light source 1 , a beam shaping optics 5 a micromirror 2 , a first, gathering lens group 10 and a second dispersive lens group 11 , The laser light source 1 generates a laser beam 4 by a beam shaping optics 5 on the micromirror 2 meets. After a deflection by the micromirror 2 is the laser beam by the reference numeral 6 Mistake. The laser beam 6 is with a beam direction at a deflection of the micromirror 2 with a maximum deflection angle in which the laser beam 6 still through the expansion optics 3 is shown, shown. The detection system further comprises a beam splitter 12 that is between the first, collecting lens group 10 and the second dispersive lens group 11 is arranged such that by scattering the laser beam 6 on a surface 14 Detection light generated within the scanned solid angle 15 from the beam splitter through optics 16 is deflected to a detector 17. The laser beam 6 is from the micromirror 2 thus first by the first, collecting lens group 10 following through the beam splitter 12 and then into the second, dispersing lens group 11 directed. While the laser beam is the beam splitter 12 passes through, becomes a part of the laser light at the surfaces of the beam splitter 12 reflects and forms stray light 19 , This stray light 19 can be absorbed by an additional optical component or greatly reduced, for example, by an upstream polarizing filter as in 5 is shown.

In the example shown, the laser beam hits 6 after the expansion optics on the obstacle 14 at which the vice beam 6 is scattered, so proof light 15 in the expansion optics 3 falls. The proof light 15 radiates through the second, dispersing lens group 11 in the laser beam 6 opposite direction and is from the beam splitter 12 through an optic 16 bundled for the detector. Then the proof light hits 15 regardless of a direction of the laser beam leaving the expansion optics 6 and / or from a place of obstacles 14 to one point of the detector 17 , Due to the beam splitter 12 only about 50 percent of the light 15 reaches the detector 17 , The proof light 15 is in 6 represented as two bands of rays, in the beam splitter cube in each case to a part through the collimator 16 be focused on the detector and to another part of the beam splitter 12 shine through without distraction. A panel 18 between the detector 17 and the optics 16 is arranged, improves the signal-to-noise behavior of detection light 15 to the underground.

The detection system in 6 also includes an evaluation, which is not shown. The evaluation device orders a momentary output signal of the detector 17 a momentary mirror deflection of the micromirror 2 to give a momentary direction of the expansion optics 3 leaving laser beam 6 to investigate. The evaluation device also assigns the current direction of the expansion optics 3 leaving laser beam 6 a timing of generating the laser beam 4 and thus determines a laser light time which describes a time interval between a transmission of the laser beam 4 through the laser light source 1 and a detection of resulting detection light 15 on the detector 17 passes. From this information, by means of an algorithm, a distance of the obstacle along the direction of the expansion optics 3 leaving laser beam 6 be determined. Thus, the evaluation locates the obstacle 14 ,

In 7 is an enlarged section of the detection system 6 shown. The laser light source 1 , the beam shaping optics 5 , the micromirror 2 and the first collecting lens group 10 are not shown for clarity. In addition, only one beam path of the detection light 15 drawn, but not the laser beam 4 respectively 6 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2514211 B1 [0003, 0009]

Claims (16)

Projection device for scanning a solid angle range by means of a laser beam (6), comprising a laser light source (1) for generating the laser beam (4) and a micromirror (2) deflectable about two axes for deflecting the laser beam, characterized by an expansion optics (3) for expanding the laser beam Scannable angle range with an optical axis (8), along which the laser beam (6) deflected by the micromirror (2) is emitted in a basic position of the micromirror, wherein a lens system of the expansion optics (3) is designed so that an exit angle (β), below which the laser beam (6) leaves the expansion optics (3) is greater than a deflection angle (a), by which the laser beam (6) deflected by the micromirror (2) in front of the expansion optics (3) by a deflection of the micromirror (2) is deflected out of the optical axis (8). Projection device according to Claim 1 , characterized in that the micromirror (2) is part of a MEMS. Projection device according to one of Claims 1 or 2 , characterized in that the lens system is a fisheye optic. Projection device according to one of Claims 1 to 3 , characterized in that between the laser light source (1) and the micromirror (2) a beam shaping optics (5) for increasing the beam quality is arranged such that the laser beam generated by the laser light source (1) (4) before deflecting by the micromirror ( 2) passes through the beam shaping optics (5). Projection device according to one of Claims 1 to 4 , characterized in that the expansion optics (3) comprises a first, collecting lens group (10) or lens, which is arranged between the micromirror (2) and a second, dispersing lens group (11) of the expansion optics. Projection device according to Claim 5 , characterized in that the first, collecting lens group (10) or lens and the second, dispersing lens group (11) are designed so that a beam path of the micromirror (2) deflected laser beam (6) regardless of the deflection angle (a) between the first collecting lens group (10) or lens and the second dispersive lens group (11) are parallel to the optical axis (8). A detection system comprising a projection apparatus according to any one of Claims 1 to 6 and a detector (17) for detecting detection light (15) formed by scattering the laser beam (6) on a surface (14) within the scanned solid angle range. Detection system after Claim 7 characterized in that it comprises an optical system (16) for the detector, which is designed such that the detection light (15) falls on a position of the detector (17) which is incident from a direction of the laser beam (6) leaving the expansion optics or independent of a location of the surface (14). Detection system after Claim 8 , characterized in that the optics (16) for the detector (17) comprises a collimator for focusing the detection light (15) on the detector (17). Detection system according to one of Claims 7 to 9 , characterized in that within the widening optics (3) or between the micromirror (2) and the widening optics (3) a beam splitter (12) for decoupling the detection light (15) is arranged. Detection system after Claim 10 , characterized in that the beam splitter (12) between the first lens group (10) or lens and the second lens group (11) is arranged. Detection system according to one of Claims 10 or 11 , characterized in that in a beam path between the laser light source (1) and the beam splitter (12), a polarization filter (13) is arranged, which only or predominantly transmits a polarized portion of the laser beam to avoid interference light (19), of the polarizing Beam splitter is not reflected. Detection system according to one of Claims 7 to 12 , characterized by an evaluation device, arranged for assigning a current output signal of the detector (17) to the instantaneous deflection of the micromirror (2) for determining a current direction of the laser beam (6) leaving the expansion optics (3). Detection system according to one of Claims 7 to 13 , characterized in that it is a LIDAR system. Method for scanning a solid angle range with a laser beam (6) by means of a projection device according to one of Claims 1 to 6 or a detection system according to one of Claims 7 to 14 in which the laser beam (6) is generated by the laser light source (1), is directed onto the micromirror (2) and, after being reflected by the micromirror (2), passes through the expansion optics (3), the micromirror (2) for Swinging is excited, so that the solid angle range through which the expansion optics (3) leaving laser beam (6) is scanned. Method according to Claim 15 , provided that one of the Claims 7 to 14 is referenced, characterized in that by scattering of the laser beam (6) on a surface (14) within the scanned solid angle range caused detection light (15) by the detector (17) is detected, wherein an output signal of the detector (17) by detecting a current Deflection of the micromirror (2) each associated with a current direction of the expansion optics (3) leaving the laser beam (6) and used to determine a distance to the surface (14) by a transit time or phase measurement.

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