Photoelectric sensor and method for operating a photoelectric sensor

Abstract

The invention relates to a photoelectric sensor, comprising: a laser assembly (2) having a plurality of individually activatable laser sources (3a-3j), a receiving unit (11) and an analyzing unit (7), wherein the laser assembly (2) addresses a partial area of ​​pixels of a field of view with respect to an object (21) by means of the individually activatable laser sources (3a-3j) with the aid of a sequence of distinguishable illumination patterns (1a, 1b), the receiving unit (11) being configured to receive reflections and / or scatterings of the illumination patterns (1a, 1b), and the analyzing unit (7) being configured to create a complete object image based on the received illumination patterns (1a, 1b) of the partial area of ​​the field of view.

Description

Technical Field

[0001] The invention relates to an optoelectronic sensor, in particular a lidar sensor, and to a method for operating an optoelectronic sensor. Background Art

[0002] There are two basic concepts for operating lidar systems. On the one hand, flash systems are known, in which the entire scene or the entire field of view of the system is illuminated, wherein parallel detection then takes place. On the other hand, scanning systems are known, in which the scene or the field of view is scanned by a single laser beam.

[0003] Conventional flash systems include a two-dimensional detector that records a complete image of the scene in a coded manner over time. An alternative for detection is the so-called "compressed sensing (CS) laser radar", which is also known from various publications under the term "photon counting laser radar".

[0004] Semiconductor lasers (VCSELs) implemented as surface emitters can be individually controlled in a simple manner. An addressable VCSEL array consists of, for example, 8×32 emitters. In addition, such a VCSEL array can be scaled to more emitters. In combination with imaging optics connected downstream, the laser beam of the emitter can be imaged to a distance.

[0005] For this purpose, DE 10 2007 004609 A1 discloses a VCSEL array laser scanner in which laser emitters can be activated sequentially.

[0006] DE 20 2013 012622 U1 discloses a principle of addressable field illumination in conjunction with a lidar system, wherein a light modulator, in particular a spatial light modulator (SLM) is disclosed. However, it is disadvantageous that the field of view can only be scanned very slowly with an SLM.

[0007] Flash-based systems require corresponding two-dimensional detectors, which are very expensive due to demanding electronic requirements (eg, high readout times in the microsecond range and high sensitivity). The low efficiency of these detectors limits the range or requires high power of the beam source.

[0008] Compressed sensing approaches, on the other hand, use relatively cost-effective components suitable for the mass market, wherein complex imaging optics can be dispensed with. Furthermore, due to the lack of imaging optics, these approaches are not subject to imaging errors. However, a disadvantage here is that relatively many individual images are required to reconstruct the scene accordingly. Furthermore, common technical implementations of compressed sensing approaches are susceptible to spatial fluctuations of the light source.

[0009] Conventional compressed sensing systems include three components. The first component is a light source, while the second component is an element for structuring light. The third component is a one-dimensional detector. For structuring light, a commercially available "digital light modulator" (DLM) is usually used. In a typical variant of a CS system, the DLM is connected downstream of the light source, wherein the scene is illuminated in a structured manner. Then, the backscattered light is received with the aid of a converging lens and measured by a one-dimensional photodetector. Photodetectors mostly involve "avalanche photodiodes" (APD), which allow high sensitivity at fast measurement times. However, a complete set of structuring is required to illuminate the scene. In addition, disadvantageously, the illumination pattern is transmitted on the transmitting side by a digital micro-mirror device (DMD), wherein 50% of the light efficiency is usually lost due to the occlusion of individual pixels, because the pattern is usually composed of 50% dark pixels. Summary of the invention

[0010] According to a first aspect, the invention relates to a photoelectric sensor, which can be arranged on a vehicle, for example. A "photoelectric sensor" can include, in particular, a lidar sensor or other laser-operated sensors. The photoelectric sensor according to the invention includes a laser ensemble with a plurality of individually activatable laser sources. Such a "laser ensemble" can include, in particular, a VCSEL array. The laser ensemble according to the invention includes a plurality of individually activatable laser sources, wherein, due to the activation of a plurality of individually activatable laser sources, any pattern can be generated in the laser ensemble. In other words, the laser sources can be addressed individually and / or in any combination in order to send a laser beam. In addition, the photoelectric sensor according to the invention includes a receiving unit, in particular a lidar detector, and an evaluation unit, in particular a CPU and / or a microcontroller and / or an electronic control unit and / or a graphics processor. The laser ensemble can address a partial area of ​​a pixel of a field of view (which is assigned to the photoelectric sensor with respect to an object to be measured) for each illumination pattern by means of a sequence of distinguishable illumination patterns (in particular a time sequence) by means of individually activatable or addressable laser sources. The illumination pattern is reflected and / or scattered at the corresponding position of the object and is received by means of a receiving unit and assigned to the field of view. In other words, a portion of the total number of pixels of the field of view is addressed for each illumination pattern. By transmitting the distinguishable illumination patterns according to the invention, a portion (e.g. 5% to 50%) of the following measurements can be performed to obtain a sufficient image of the object, which is theoretically necessary to address each pixel of the field of view individually. The receiving unit can especially convey the detected illumination pattern to the evaluation unit. With the aid of the evaluation unit, a complete object image can be created based on the illumination pattern received with respect to the partial area of ​​the field of view. In other words, an extrapolation of the following recording is performed: the recording is associated with the addressed partial area of ​​the pixels of the field of view in order to create a complete image. In other words, the photoelectric sensor according to the invention can be operated, for example, by means of a compressed sensing method - when the laser sources of the laser assembly can be individually addressed or activated in order to generate the illumination pattern required for the compressed sensing method. In the compressed sensing method, the scene to be acquired is illuminated in particular with a plurality of different spatial illumination patterns. In such an illumination situation, the illumination patterns are preferably orthogonal. From the multiple measurements, the scene can be reconstructed, in particular based on the orthogonality of the patterns, by multiplying the measured values ​​of the respective pattern with the associated pattern and adding them—which corresponds, for example, to a linear combination of orthogonal bases.

[0011] The photoelectric sensor according to the invention thus makes it possible to generate a fast sequence of illumination patterns which exceeds the illumination speed of conventional DMD-based compressed sensing systems by many times. In addition, the individual illumination patterns and the temporal course of the illumination patterns can be freely selected based on the laser assembly. Eye safety can be further improved by optimizing the sequence of illumination patterns, wherein higher transmission powers can be achieved. Thus, better sensor statistics and sensor ranges can also be achieved according to the invention. In addition, the photoelectric sensor according to the invention has the following advantages: compared to the conventional compressed sensing systems described above, power losses are significantly reduced, since essentially all transmitted photons are used for object detection, whereas in known compressed sensing methods, photons are absorbed to generate patterns. Accordingly, higher transmission powers can be used with the aid of the photoelectric sensor according to the invention.

[0012] The dependent claims reveal preferred embodiments of the invention.

[0013] According to an advantageous embodiment of the photosensor according to the invention, when individual measurements are performed for each pixel of the field of view, the addressed field of view can be imaged in a sufficient manner with the aid of a portion of the pattern required for complete reconstruction of 5% to 50%, in particular 20% to 30% (generally about 25%). In this case, each measurement performed according to the invention has a pattern that can be distinguished from other measurements, for example. In other words, the number of distinguishable illumination patterns of the sequence as a percentage of the theoretical number of measurements required to individually address each pixel of the field of view is 5% to 50%. Thus, in order to produce a complete image of the object, much less data is generated from the received illumination pattern than is the case with conventional (flash) systems. In this case, in the event that the addressed partial pattern falls below 5%, the accuracy of the object imaging can be adversely affected.

[0014] According to another advantageous embodiment of the photoelectric sensor according to the invention, the receiving unit has a one-dimensional detector. In this case, the detector can be, but not necessarily, an avalanche photodiode (APD). Thus, the mode of operation of the photoelectric sensor according to the invention advantageously allows the use of a cost-effective detector.

[0015] According to another advantageous embodiment of the photoelectric sensor according to the invention, at least one laser light source of the plurality of laser light sources has a rectangular shape. In particular, half or all of the laser light sources of the plurality of laser light sources may also have a rectangular shape.

[0016] The distinguishable illumination patterns measured according to the invention can in particular be such that after the measurement no gaps remain in the addressed field of view. In other words, each pixel in the field of view can be addressed at least once by a sequence of distinguishable illumination patterns.

[0017] According to an advantageous embodiment of the invention, the laser aggregate according to the invention can comprise a VCSEL array and / or a plurality of edge emitters. Furthermore, any semiconductor laser known to the person skilled in the art is also suitable for use with the laser aggregate.

[0018] According to an advantageous embodiment, the distinguishable illumination patterns can be generated by the evaluation unit using a Hadamard matrix and / or a Walsh matrix. These matrices have the advantage, in particular, that they form a complete orthogonal basis and thus allow complete object imaging based on the received illumination patterns.

[0019] According to another advantageous embodiment of the optoelectronic sensor according to the invention, the laser assembly can include an optical imaging unit, which is configured to direct an illumination pattern onto an object at an emission angle predefined by the arrangement of the imaging unit. In this way, a precise imaging of an illumination pattern originating from the individually activated laser sources of the laser assembly onto an object can be achieved. The optical imaging unit can in particular include a microlens arrangement and a lens (e.g. a projection lens). In accordance with the microlens arrangement and the lens, the beam sent onto the object can be expanded or reduced or collimated.

[0020] The following aspects of the invention accordingly have the advantageous embodiments and refinements, which have the above-mentioned features, and the general advantages of the photoelectric sensor according to the invention, which are omitted in order to avoid repetition.

[0021] According to a second aspect, the invention relates to a method for operating a photoelectric sensor according to the first aspect of the invention. The method is in particular a compressed sensing method. The method according to the invention comprises the following steps: a sequence of distinguishable illumination patterns is sent by means of the above-mentioned laser assembly in order to address pixels of a field of view with respect to an object, wherein the illumination patterns respectively address partial areas of the pixels of the field of view. In response thereto, a corresponding reflected and / or scattered illumination pattern is received, which is backscattered and / or reflected by the object. Based on the addressed partial areas of the field of view or based on the received corresponding reflected and / or scattered illumination pattern, a complete object imaging is created, for example in an analysis unit.

[0022] The distinguishable illumination patterns are in particular orthogonal to one another. In this way, a power-efficient (ie laser power-saving) and time-efficient measurement can be performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The accompanying drawings show:

[0024] Figure 1 A flow chart showing a variant of the method according to the invention;

[0025] Figure 2 A diagram showing a sequence of lighting patterns according to the present invention;

[0026] Figure 3 A variant of the transmitting unit of the photoelectric sensor according to the present invention is shown;

[0027] Figure 4 A variation of the laser assembly of the photoelectric sensor according to the present invention is shown;

[0028] Figure 5 A variant of the photoelectric sensor according to the invention is shown. DETAILED DESCRIPTION

[0029] Figure 1 A flow chart of a variant of the method according to the invention is shown. In a first step 100, a sequence of distinguishable illumination patterns 1a, 1b is transmitted by means of a laser assembly 2, which comprises a plurality of individually addressable or activatable laser sources 3a to 3j. By transmitting according to the first step 100, in particular each illumination pattern of a sub-region of pixels of a field of view is addressed, wherein the field of view is associated with an object 21. In particular, three distinguishable illumination patterns are transmitted, and all pixels of the field of view are addressed at least once. In a second step 200, a reflected or scattered illumination pattern corresponding to the transmitted illumination patterns 1a, 1b is received, for example, by means of a receiving unit 11. In a third step 300, the field of view imaged with respect to the object is completed. In other words, an image is generated by addressing pixels of 25% of the pixels of the field of view according to the addressed sub-region of the field of view. This can be done, for example, by means of an evaluation unit 7, for example by means of a graphics processor.

[0030] Figure 2 An object 21 in the form of a bust is shown. In the first figure part I, the object 21 is illuminated by means of a first illumination pattern 1a. In the second figure part II, the object 21 is illuminated by means of a second illumination pattern 1b, wherein black stripes not detected by the first illumination pattern 1a are covered by the second illumination pattern 1b to a reduced black stripe which represents a non-addressed partial area of ​​the field of view. Figure 2Part II of the figure shows in particular the superposition of the first illumination pattern 1a and the second illumination pattern 1b in order to show the composition of the illumination patterns 1a, 1b according to which the imaging of the object is completed. Figure 2 , non-addressed pixels are shown by black stripes in the illumination patterns 1a, 1b of FIG. 11. However, a complete image of the object can be generated from imaging as shown in FIG. part II.

[0031] Figure 3 A variant of a transmission unit 10 of an assembly 40 according to the invention is shown. The transmission unit 10 has a laser assembly 2 with a plurality of individually addressable or activatable laser sources 3a to 3j. Any illumination pattern comprising the first to third light beams 4a to 4c can be projected onto the object by the individually addressable laser sources 3a to 3j and the lens 6, so that a sequence of patterns is received by the above-mentioned reflections of the light beams 4a to 4c, from which the imaging of the object 21 can be completed.

[0032] Figure 4 A variant of a laser assembly 2 of an assembly 40 according to the invention is shown, which has a plurality of laser sources 3a to 3c. Obviously, in addition to the first to third laser sources 3a to 3c, all other points of the laser assembly 2 (here VCSEL array) shown in the diagram 4 can be addressed arbitrarily and individually in order to generate the desired illumination pattern 1a, 1b.

[0033] Figure 5 A lidar sensor 20 according to the invention is shown. The lidar sensor 20 comprises a transmitting unit 10 and a receiving unit 11. In addition, an evaluation unit 7 is provided, which is connected to the receiving unit 11 and the transmitting unit 10. The evaluation unit 7 can generate illumination patterns 1a, 1b in particular, and the received illumination patterns 1a, 1b reflected or scattered relative to the field of view can be completed into an object image.

Claims

1. A photoelectric sensor, the photoelectric sensor include: A laser assembly (2) having a plurality of individually activatable laser sources (3a-3j); Receiving unit (11); Analysis and processing unit (7); The laser assembly (2) is configured to address a partial area of ​​pixels of a field of view of an object (21) for each distinguishable illumination pattern (1a, 1b) by means of the individually activatable laser sources (3a-3j) with the aid of a sequence of distinguishable illumination patterns (1a, 1b), and the receiving unit (11) is configured to receive reflections and / or scatterings of the distinguishable illumination patterns (1a, 1b), and the analyzing unit (7) is configured to create a complete object image based on the received illumination patterns (1a, 1b), the received illumination patterns (1a, 1b) addressing partial areas of pixels of the field of view, Therein, the percentage of the number of illumination patterns (1a, 1b) distinguishable in the sequence relative to the number of measurements required to individually address each pixel of the field of view is between 5% and 50%.

2. The photoelectric sensor according to claim 1, in, The percentage of the number of illumination patterns (1a, 1b) that can be distinguished in the sequence relative to the number of measurements required to address each pixel of the field of view individually is between 20% and 30%.

3. The photoelectric sensor according to claim 1, in, The percentage of the number of illumination patterns (1a, 1b) that can be distinguished in the sequence relative to the number of measurements required to address each pixel of the field of view individually is 25%.

4. The photoelectric sensor according to any one of the preceding claims, in, Based on the sequence of distinguishable illumination patterns (1a, 1b), each pixel in the field of view can be addressed at least once.

5. The photoelectric sensor according to any one of the preceding claims, in, The receiving unit (11) comprises a one-dimensional detector.

6. The photoelectric sensor according to any one of the preceding claims, in, At least one surface of a laser source among the plurality of laser light sources (3a-3j) from which laser light can be emitted has a rectangular shape.

7. A photoelectric sensor according to any one of the preceding claims, in, The laser assembly (2) comprises a VCSEL array and / or a plurality of edge emitters.

8. The photoelectric sensor according to any one of the preceding claims, in, The distinguishable illumination patterns (1a, 1b) can each be generated with the aid of a Hadamard matrix and / or a Walsh matrix.

9. The photoelectric sensor according to any one of the preceding claims, in, An optical imaging unit is arranged behind the laser assembly (2), wherein the optical imaging unit is configured to direct the illumination pattern (1a, 1b) onto the object (21) at an emission angle predefined by the arrangement of the imaging unit.

10. A method for operating a photoelectric sensor according to any one of claims 1 to 9, the method The following steps are involved: A sequence of distinguishable illumination patterns (1a, 1b) is sent (100) by means of a laser assembly (2) having a plurality of individually activatable laser sources (3a-3j) in order to address pixels of a field of view, wherein for each illumination pattern (1a, 1b) a partial region of the pixels of the field of view is addressed; and in response thereto, receiving (200) a corresponding reflected and / or scattered illumination pattern (1a, 1b), A complete object imaging is created (300) from the received corresponding reflected and / or scattered illumination patterns (1a, 1b).

11. The method according to claim 10, in, The distinguishable illumination patterns (1a, 1b) are orthogonal to each other.

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