OPTOELECTRONIC SENSOR FOR DETECTING AN OBJECT IN A SURVEILLANCE AREA

Description

[0001] The invention relates to an optoelectronic sensor for detecting an object in a surveillance area according to the preamble of claim 1.

[0002] Many optoelectronic sensors operate according to the scanning principle, in which a light beam is emitted into the monitored area and the light beam reflected by objects is received again, in order to then electronically evaluate the received signal. In addition to pure object detection, distance measuring systems also determine the distance to the object. Distance sensors based on the time-of-flight principle (Lidar) measure the time of flight of a light signal, which corresponds to the distance via the speed of light. A conventional distinction is made between pulse-based and phase-based measurements. In a pulse-time-of-flight method, a short light pulse is emitted and the time until a remission or reflection of the light pulse is received is measured. Alternatively, in a phase method, transmitted light is amplitude-modulated and a phase shift between transmitted and received light is determined, whereby the phase shift is also a measure of the light time of flight.

[0003] To expand the measuring range of a single-beam light sensor, the scanning beam can be moved, as is done in a laser scanner. A light beam generated by a laser periodically sweeps the monitored area with the aid of a deflection unit. In addition to the measured distance information, the angular position of the deflection unit is used to determine the angular position of the object, thus determining the location of an object in the monitored area in two-dimensional polar coordinates.

[0004] Another option for extending the measuring range and obtaining additional distance data is to simultaneously capture multiple measurement points with multiple scanning beams. This can also be combined with a laser scanner, which then captures not just one monitoring plane, but a three-dimensional spatial area across multiple monitoring planes. In most laser scanners, the scanning movement is achieved by a rotating mirror. However, especially when using multiple scanning beams, it is also known in the prior art to rotate the entire measuring head with light transmitters and light receivers instead, as described, for example, in DE 197 57 849 B4.

[0005] The choice of receiving element and the optical design of such a sensor have a significant impact on its performance. To detect even low reception intensities, avalanche photodiodes (APDs) are sometimes used. The incident light triggers a controlled avalanche breakdown (avalanche effect). This multiplies the charge carriers generated by the incident photons, creating a photocurrent that is proportional to the light reception intensity but significantly larger than that of a simple PIN diode.

[0006] Even greater sensitivity is achieved with avalanche photodiodes operated in so-called Geiger mode (SPAD, Single Photon Avalanche Diode, also SiPM, Silicon Photomultiplier). In this case, the avalanche photodiode is biased above the breakdown voltage, so that even a single charge carrier released by a single photon can trigger an uncontrolled avalanche, which then recruits all available charge carriers due to the high field strength. The avalanche photodiode thus counts individual events like the eponymous Geiger counter. Geiger-mode avalanche photodiodes are not only highly sensitive but also comparatively inexpensive. Furthermore, they can be integrated onto a circuit board with little effort.

[0007] However, the high sensitivity also brings with it disadvantages, as it is not limited to the transmission wavelength used in the sensor, but operates across a broad wavelength range, including ambient light. Due to the comparatively large detector area of ​​SPADs, their ambient light input is also high. The amount of ambient light, in turn, decisively determines the signal-to-noise ratio (SNR). Ambient light can be filtered out by using an optical bandpass filter tuned to the wavelength of the transmitted light. This significantly improves the signal-to-noise ratio, particularly with broadband ambient light such as sunlight. However, this alone often does not produce satisfactory results.

[0008] It is also possible to limit extraneous light by focusing the received light beam in the receive path and positioning an aperture at the position where the cross-section is smallest. However, such an aperture must be adjusted and fixed. Due to component tolerances and limited adjustment quality, the aperture is usually chosen larger than would be optimal, particularly for the most favorable signal-to-noise ratio. Signal losses due to received light components that cannot pass through an aperture that is too small or shifted relative to the received light beam would result in a disproportionate loss of quality. Extraneous light passing through the aperture next to the received light beam leads to random detection events, the influence of which contributes as shot noise according to a square root function.

[0009] If the losses caused by a suboptimal aperture are to be limited, low-tolerance components must be developed and manufactured, then adjusted with high precision and fixed with minimal distortion. This increases manufacturing costs due to component costs and complex and time-consuming processes that also lack flexibility. Furthermore, hazardous materials such as adhesives, soldering devices, and the like must be handled during production. In multi-beam systems, there is also the difficulty of aligning multiple transmit / receive pairs while still designing the apertures with high precision.

[0010] A conventional aperture insert is therefore of limited use due to the large mechanical tolerances and thus the aperture size. An alternative aperture at the chip level of the receiver element reduces the illuminated area, which, in a large-area SPAD receiver, also limits the useful light along with the extraneous light.

[0011] EP 3 432 023 B1 discloses a method for manufacturing an optoelectronic sensor with a diaphragm that is manufactured individually for each sensor using its own receiving optics. However, the diaphragm itself is not specified. DE 10 2020 109 596 A1 deals with an optoelectronic sensor with a diaphragm and a manufacturing method therefor. The diaphragm is formed as at least one diaphragm opening in an absorption layer of a multilayer substrate.

[0012] DE 10 2018 128 669 A1 discloses a method for manufacturing an optical system. First, a beam deflection element and a shielding element are fixed in a holder in a predetermined arrangement relative to each other. The shielding element is then processed using processing light beams to form a diaphragm element.

[0013] Due to the extreme sensitivity of SPADs, at least the light receiver is conventionally protected from electromagnetic interference (EMC, electromagnetic compatibility) by a metallic shield frame. However, this has nothing to do with the optical aperture function. On the contrary, the aperture and shield frame are spatially in each other's way.

[0014] DE 10 2020 216 043 A1 presents an optical sensor comprising a cylindrical shielding element made of a metal shield coated at least internally with a plastic material. A fastening element of the metal shield is connected to a printed circuit board housing, which has a ground contact, by means of an electrically conductive adhesive. DE 10 2020 214 584 A1 relates to a viewing window for a housing of a LiDAR sensor device.

[0015] In DE 20 2013 005 999 U1, an optical smoke detector operating according to the scattered light principle is protected against EMC radiation by means of a shielding device. A circuit board with a copper layer as a shielding layer is inserted into the shielding device. A photosensor is mounted on the inside of the circuit board, thus surrounded by the shielding device and shielding layer. A through-hole for the light to be detected is provided in the circuit board in the form of a circular hole through the circuit board. The through-hole also serves as an optical aperture that only allows light arriving from a scattering center of the smoke detector to pass through toward the photosensor.

[0016] DE 10 2020 214 584 A1 relates to a viewing window for a housing of a LiDAR sensor device.

[0017] DE 10 2018 202 925 A1 describes a sensor device whose receiving device is housed in a shielding box. A beam-permeable beam incidence area of ​​the shielding box is sealed with at least two electrically conductive grids arranged one behind the other in the beam direction.

[0018] It is therefore an object of the invention to further improve the light transit time measurement using a receiving optics with an aperture.

[0019] This object is achieved by an optoelectronic sensor for detecting an object in a monitored area according to claim 1. The sensor comprises a light transmitter for emitting transmitted light and a light receiver that receives the transmitted light remitted in the monitored area. The light transmitter can form a coaxial or biaxial arrangement with the light receiver. The sensor has a light receiver with a plurality of light receiving elements operable in Geiger mode. As explained in the introduction, such a SPAD or SiPM receiver is particularly sensitive and also has a fast response time. A plurality of light receiving elements offers an even larger detection area and also enables statistical evaluation.A control and evaluation unit is configured to evaluate a received signal from the light receiver to determine the distance between the objects based on the light propagation time between the emission of the transmitted light and the reception of the received light with the remitted transmitted light. The sensor thus implements the LIDAR measurement principle described above, based on SPADs or a SiPM.

[0020] A receiving optic with an aperture is arranged in front of the light receiver, for example a single lens, an objective with multiple lenses, or another arrangement of optical elements. The aperture is preferably arranged in a focal plane of the receiving optic, so that a received light beam generated by the receiving optic passes through the aperture opening of the aperture at the point of smallest constriction. Depending on the design, the focal plane may not be precisely reached due to tolerances; this is still referred to as an arrangement in the focal plane. The aperture can at least suppress the extraneous light component that reaches the receiving optic at near field or medium distances. The aperture opening is preferably located within the focal plane where the received light beam passes through the aperture, so that as little of the useful signal component as possible is lost in the aperture.The aperture comprises an aperture substrate with at least one metallic layer and an aperture opening. In principle, the aperture substrate can be metal, thus identical to the metallic layer. Due to better processing options, an aperture substrate such as glass, plastic, or a thin metallic carrier foil is preferably provided, which is then coated. In addition to the aforementioned at least one metallic layer, further layers for other functions are possible, as explained later.

[0021] The invention is based on the basic idea of ​​using the aperture as part of an EMC shield. For this purpose, a contact area of ​​the metallic layer is connected to another component of the sensor in a metallically conductive manner for potential equalization. The other component can be one of the components already mentioned, in particular the control and evaluation unit. Preferably, the other component is grounded, which then also grounds the metallic layer of the aperture. Preferably, two contact areas are provided on either side of the aperture opening, each electrically connected to the other component.

[0022] The invention has the advantage that the cover is not only compatible with EMC shielding, but even contributes to it in a dual function.

[0023] This preserves the optical function of the aperture, which is to allow only the remitted transmitted light to reach the light receiver, largely without any interfering ambient light. At the same time, very good EMC protection is achieved, which the very small aperture only minimally affects. Therefore, the sensor can measure with particularly good sensitivity, robustness, and accuracy.

[0024] The sensor preferably has a conductive shield, at least for the light receiver. The conductive shield provides EMC protection at the locations and in the directions where the aperture is not located. In other words, the conductive shield and the aperture, which is conductively connected to the other component, complement each other to provide EMC protection, preferably in all directions.

[0025] The contact area is preferably electrically connected to the shield. The shield is thus the other component to which the metallic layer is electrically connected for potential equalization. The shield, in turn, is preferably grounded.

[0026] The contact area is preferably electrically connected to an electronics board of the sensor, in particular an electronics board of the control and evaluation unit. The electronics board or printed circuit board provides a suitable potential for potential equalization, preferably a zero potential or ground. Thus, the electronics board is now the other component to which the metallic layer is electrically connected. Additional shielding can also be conductively connected to the electronics board, or the conductive connection can be made indirectly from the electronics board via the shielding to the metallic layer, or vice versa. The electronics board can be that of the control and evaluation unit, but also another electronics board of the light receiver, light transmitter, a power supply or interface of the sensor, or any other electronics board.

[0027] Preferably, a voltage can be applied to the metallic layer via the contact area in order to heat the metallic layer. This gives the panel an additional function as a heating element or particularly effective protection against condensation. For this purpose, a voltage source is preferably applied to two contact areas of the metallic layer. The voltage source can provide an adjustable or constant voltage, or it can be adjusted, for example by the control and evaluation unit, depending on the situation, application, operating phase, measured outside temperature or humidity, and the like. The power loss and thus heating can also be influenced via the electrical and thermal resistance, thus in particular by selecting the layer thickness and material composition.

[0028] According to the invention, a metallic layer facing the light receiver is at least partially exposed to reflect backscattered transmitted light back to the light receiver. The metallic layer acts as a concentrator or residual light amplifier. Stray light from the light receiver can thus still be detected, thereby increasing the efficiency of the measuring system. It should be noted that this stray light is light that has already passed through the aperture; it is therefore useful light and not extraneous light.

[0029] The exposed portion of the metallic layer is preferably structured to adjust reflection properties. The surface in the reflection region for backscattering remitted transmitted light to the light receiver thus has a structure or pattern that, for example, sets a preferred direction of reflection to reflect the light back to the light receiver particularly effectively.

[0030] The aperture is preferably multilayered with at least one of the following additional layers on a side facing the light receiver and / or a side facing away from the light receiver: an absorption layer, an anti-reflection layer, a filter layer. The metallic layer or layers are provided at any location in front of or in between, depending on the embodiment. If necessary, the contact areas are left exposed during a further coating or grown additively, or they are subsequently exposed again, for example by laser ablation. This creates a multilayer aperture with various additional functions. It is conceivable to structure the metallic layer, in particular by laser processing, so that it becomes diffuse or non-reflective.

[0031] An absorption layer ensures that incident light that does not pass through the aperture after remission in the monitored area does not reach the light receiver, even through multiple reflection, if possible. The absorption layer preferably has a metallic component, in particular black titanium or black chrome, a spray paint, and / or carbon nanotubes. Structured carbon nanotubes, for example, are known as VANTA. They exhibit particularly strong absorption. Structured inorganic layers such as Acktar MetalVelvet are conceivable as an intermediate form between a vapor-deposited absorption layer and carbon nanotubes. An anti-reflective layer is particularly advantageous when used in conjunction with glass or plastic as the aperture substrate. This suppresses stray light, especially at the exposed areas of the aperture.A filter layer, especially one with the filter characteristics of a bandpass filter, can further filter out extraneous light outside the spectrum of the useful light of the light transmitter. While the aperture ensures that extraneous light from the side is suppressed, extraneous light that is not affected by the aperture inevitably overlaps the core of the received light beam passing through the aperture. Here, wavelength selection further improves the signal-to-noise ratio.

[0032] The aperture is preferably manufactured using a laser, in particular a laser ablation process. Ultrashort laser pulses, i.e., pulses in the picosecond or even femtosecond range, are even more preferably used for this purpose. The aperture is particularly preferably manufactured individually using the receiving optics. The aperture, or its aperture, is therefore manufactured as an individual aperture using the receiving optics specifically for the receiving optics with which it is used in the optoelectronic sensor. The receiving optics can be involved in such a way that it is directly involved in the manufacturing process, or its properties determine the manufacturing of the aperture. The aperture thus optimally matches the receiving optics and the received light beam generated by the receiving optics. The individual manufacturing of the aperture replaces the adjustment or at least supplements it.Traditionally, however, an aperture would be purchased as a component for at least one entire batch of sensors, and the sensor would either have to accept the consequences of tolerances or compensate for this through complex adjustment.

[0033] Preferably, the aperture is produced with a laser whose beam path is guided through the receiving optics, in particular in a laser ablation process.

[0034] For this purpose, it is preferable not to measure the individual aperture in advance. Since the laser itself passes through the receiving optics, its beam path corresponds to that of the remitted transmitted light. To achieve this, the laser should ideally have comparable geometric beam properties, for example, it should be collimated to match light from infinity. Artificial defocusing or an additional optical element for the laser is conceivable to compensate for deviations in the beam path, for example, due to different wavelengths between the material processing laser and the later useful light.

[0035] Alternatively, the aperture can be produced using a laser whose beam path is not guided through the receiving optics but is focused onto the aperture layer, particularly in a laser ablation process. For this purpose, the position and shape of the individual aperture on the receiving side are measured in advance. Correction values ​​for the aperture position should also preferably be included. This method is particularly advantageous when there are multiple measurement positions. The remitted transmitted light beam is preferably measured in the mounting position of the receiving optics in order to obtain a property of the individual aperture to be produced. Relevant properties can be, for example, the beam cross-section at certain distances or its position in space. Without loss of generality, the direction of the optical axis of the receiving unit is referred to as the Z direction.

[0036] The custom aperture is preferably manufactured on the sensor's production line. This makes the production of a custom aperture an integral step within the standard manufacturing process. No parts need to be purchased, and no special process effort is required for the procurement and supply of the custom apertures.

[0037] The sensor is preferably designed as a laser scanner and has a movable deflection unit, with the aid of which the transmitted light is periodically guided through the monitored area. The laser scanner scans a plane with the transmitted light as the movable deflection unit moves. In a multi-beam measuring system, which will be presented shortly, each transmitted light beam scans a separate layer, creating a multi-layer scanner. Only its central layer at zero elevation, if present at all, is a plane in the mathematical sense; the remaining layers are curved like a nested hourglass. The deflection unit is preferably designed in the form of a rotatable scanning unit, which essentially forms a movable measuring head in which the light transmitter and / or light receiver and preferably also at least parts of the control and evaluation unit are housed. Alternatively, the deflection unit can be a rotating mirror.However, in a multi-layer scanner, this leads to further curvature of the layers and also to their mixing up, because the elevation angle of the scan then depends on the rotation position.

[0038] The light transmitter is preferably designed to emit several separate light beams, and the light receiver is designed to generate respective received signals from several remitted light beams. The sensor thus becomes a multi-beam sensor or multiple probe that scans several measuring points. Preferably, the control and evaluation unit measures a distance with each of the several beams based on the light travel time. The several measuring beams preferably share the same receiving optics. The aperture preferably has an aperture for each light beam.

[0039] The invention will be explained in more detail below with regard to further features and advantages, using exemplary embodiments and with reference to the accompanying drawings. The figures of the drawing show: Fig. 1 a schematic sectional view of an optoelectronic sensor; Fig. 2 a schematic sectional view of a layer system with a metallic layer from which a diaphragm is produced; Fig. 3 a sectional view according to Figure 2now with aperture; Fig. 4 a sectional view of a diaphragm in which a metallic layer is connected to a grounded component for potential equalization; Fig. 5 a sectional view of a diaphragm in which a metallic layer is connected to a voltage source for heating; Fig. 6 a sectional view with a schematic beam path at a light receiver, wherein backscattered light components from an exposed area of ​​a metallic layer of a diaphragm are reflected back to the light receiver; Fig. 7 a sectional view of a multi-layer diaphragm with a metallic layer; Fig. 8 a sectional view according to Figure 7 now with processing of the surface of the metallic layer at least in a partial area; and Fig. 9 shows a schematic sectional view of an optoelectronic sensor in an embodiment as a laser scanner.

[0040] Figure 1shows a block diagram of an optoelectronic sensor 10, which is embodied here as a light sensor, for example. The sensor 10 has a light transmitter 12, for example a laser diode, whose transmitted light 14 is collimated in a transmitting optics 16 and then emitted into a monitoring area 18. The light remitted by objects in the monitoring area 18 is guided as received light 20 by a receiving optics 22 through a diaphragm 24 to a light receiver 26. The light receiver 26 has a plurality of light receiving elements or pixels in the form of avalanche photodiodes, which are operated in Geiger mode for the highly sensitive detection of received light 20.

[0041] Furthermore, a control and evaluation unit 28 is provided, which is connected to the light transmitter 12 and the light receiver 26. The control and evaluation unit 28 detects objects in the monitoring area 18 based on the received signal from the light receiver 26. In one embodiment of the sensor 10 as a distance-measuring light sensor, the distance of the detected objects is also measured by emitting light pulses and determining the light propagation time until their reception. Via an interface 30, the control and evaluation unit 28 can output processed or raw sensor measurement data or, conversely, receive control and parameterization instructions.

[0042] The Figure 1The described embodiment of the sensor 10 is only an example. Distance measurement using the time-of-flight method is used in a larger family of optoelectronic sensors, for example in scanning or distance-measuring light grids, laser scanners, or solid-state LIDAR systems of various designs. These sensors 10 can differ significantly in their design from Figure 1 deviate, for example, transmit and receive channels via a common splitter mirror or operate passively and thus completely dispense with a transmit channel. A particularly advantageous embodiment as a multi-beam laser scanner or multi-layer scanner is finally described with reference to the Figure 9 presented.

[0043] The core of the invention relates to the aperture 24. It has a layered structure, which is explained in more detail below, wherein at least one metallic layer 32 is provided. Contact areas of the metallic layer 32 provide potential equalization or grounding through a conductive connection to a corresponding component of the sensor 10, which is at the desired potential. Shown in Figure 1 In this role, the control and evaluation unit 28 or its electronic card or circuit board is used.

[0044] Figure 2shows a schematic sectional view of a layer system from which the aperture 24 is produced by way of example. At this stage, the layer system is still unprocessed or a blank. As exemplary layers, a transparent substrate, for example a glass substrate 34, and the metallic layer 32 are shown. An absorption layer 36 is provided on the outside of the metallic layer 32 and a further absorption layer 38 is provided between the metallic layer 32 and the glass substrate 34. Instead of the glass substrate 34, a very thin foil, for example an aluminum foil or a similarly thin carrier material of, for example, 10 µm thickness, can be used. The metallic layer 32 can alternatively be arranged on the other side of the glass substrate 34, or further metallic layers can be provided on one side or on both sides.

[0045] The use of two absorption layers 36, 38 is to be understood as an example; the metallic layer 32 can already function as an absorption layer itself, only one absorption layer can be used, or additional absorption layers can be present on one side or both sides of the glass substrate 34. The absorption layers 36, 38 preferably have a high absorption coefficient over a broad wavelength range and a minimal hemispherical reflectance. The absorber material can be applied via a layer system with a metallic component, for example, black titanium or black chrome. Spray paints are also possible. For particularly high quality requirements, a structured carbon-based material can be used, for example, structured carbon nanotubes, which have a very high absorption coefficient and are non-glossy.Alternatively, structured inorganic coatings can be used, which technically fall between the two materials mentioned above, such as Acktar MetalVelvet. The absorber material is preferably applied as thinly and homogeneously as possible so that it can be removed by abrasion or ablation as homogeneously and residue-free as possible.

[0046] Additional layers on one or both sides of the glass substrate 34 are conceivable in virtually any arrangement of the layers. One example is an anti-reflective coating to transmit as much light as possible in the wavelength range of the useful light in the area of ​​the future apertures, preferably over a wide angle of incidence. Another example is a filter layer, preferably with the properties of an optical bandpass filter, which suppresses extraneous light outside the useful wavelength range of the light transmitter 12.

[0047] Figure 3 shows a sectional view according to Figure 2 now with aperture 40, which was created by targeted local ablation of the material of the absorption layer 36. A laser is preferably used for this purpose, even more preferably by structuring in an ablation process, in particular with an ultrashort pulse laser, i.e. a picosecond or femtosecond laser. This allows apertures 40 to be precisely created at any desired position. The process can be two-stage, in which reference holes are first introduced for optical alignment and then, after optical alignment, the apertures 40 are ablated. The reference holes can possibly already be created upon delivery of the blank according to Figure 2 be provided.

[0048] Figure 4shows a sectional view of a shutter 24 in which the metallic layer 32 is connected at contact regions 42 for potential equalization with a grounded component 44. The light receiving element 26 has a very high optical sensitivity, and this is accompanied by a high electrical sensitivity. To reduce electrical disturbances, grounded shields (not shown) are therefore preferably arranged at least around the light receiving element 26. The optical opening of this shield should remain as small as possible in order to minimally affect the shielding of electrical interference signals. Conventionally, this causes considerable difficulties because such an opening must still transmit the useful light taking into account all component tolerances. In contrast, according to the invention, the shutter 24 fulfills a dual function as an optical shutter and an electrical shield.

[0049] The metallic layer 32 is exposed at the contact areas 42. This can be taken into account during the coating process, or appropriate additive or subtractive processes, such as laser ablation, can be used to create the contact areas 42. The electrical connection to the grounded component 44 is established in any desired manner, for example, using spring contacts, soldering, welding, or other contact options. This grounds the panel 24 or its metallic layer 32, thus ensuring particularly efficient protection against electromagnetic interference (EMC, electromagnetic compatibility).

[0050] Figure 5 shows a sectional view of a diaphragm 24 in which a metallic layer is connected to a voltage source 46 for heating. Thus, while in the embodiment described with reference to Figure 4While the metallic layer was merely grounded in the described embodiment, another function is added here in addition to EMC shielding. By applying a voltage, power loss can be generated at the metallic layer 32, which heats the metallic layer and thus ensures effective protection against condensation. The electrical and thermal resistance can be adjusted via the layer thickness and the material system. This eliminates the need for conventional heating elements to prevent condensation or fogging of optical elements, in particular a windshield heater.

[0051] Figure 6shows a sectional view with a schematic beam path of the received light 20 at the light receiver 26. As is also preferably the case in the other embodiments, the aperture 24 is located in the immediate vicinity of the light receiver 26 to increase the aperture and shielding effect. The metallic layer 32 is additionally exposed here in a reflection region 48. As a result, light components of the received light 20 that were initially scattered back are reflected back onto the light receiver 26, as indicated by the arrows. This contributes to maximizing the photon yield and acts as a type of residual light amplifier, since initially lost light components can still be registered by the light receiving element 26. Especially in connection with SPADs or SiPMs, this has the additional advantage that the incoming radiation increases the probability of triggering additional SPAD cells and thus the signal quality.When exposing the reflection area 48, laser parameters can be set to further improve the reflection properties, for example, a preferred direction of reflection can be achieved via a hatching pattern.

[0052] Figure 7 shows again a sectional view of a multi-layer aperture 24 with a metallic layer 32. In Figure 8 This aperture 24 is laser-machined on the surface of the metallic layer 32, at least in a partial area 50. This can, for example, make the partial area 50 diffuse or no longer reflective.

[0053] Figure 9shows a schematic sectional view through an optoelectronic sensor 10 in an embodiment as a laser scanner. In this embodiment, the sensor 10 roughly comprises a movable scanning unit 52 and a base unit 54. The scanning unit 52 is the optical measuring head, while the base unit 54 houses additional elements such as a power supply, evaluation electronics, connections, and the like. During operation, the scanning unit 52 is set in a rotary motion about a rotation axis 58 with the aid of a drive 56 of the base unit 54 in order to periodically scan a monitoring area 18.

[0054] In the scanning unit 52 there is a rotating optoelectronic sensor similar to that of the Figure 1housed. However, this scanner is now designed with multiple beams, for example. This makes the laser scanner a multi-layer scanner. Alternatively, a laser scanner with only one beam or, conversely, a stationary multi-beam scanner would be conceivable. The light transmitter 12 thus generates multiple light beams as transmitted light 14 using multiple light sources 12a, here purely as an example four light sources 12a. Accordingly, multiple remitted light beams return to the sensor 10 as received light 20. The SPADs 26a of the light receiver 26 generate, individually or in groups, a received signal for each remitted light beam. Accordingly, an aperture 24 with multiple apertures 40 or multiple apertures 24 are provided for the different light beams.

[0055] Light transmitter 12 and light receiver 26 are in the Figure 9shown embodiment are arranged together on a circuit board 60, which lies on the rotation axis 58 and is connected to the shaft 62 of the drive 56. This is only an example; practically any number and arrangement of circuit boards is conceivable. A contactless supply and data interface 64 connects the movable scanning unit 52 to the stationary base unit 54. There is the control and evaluation unit 28, which can also be accommodated at least partially on the circuit board 60 or at another location in the scanning unit 52. In addition to the already Figure 1In addition to the functions explained, the drive 56 is also controlled and a signal from an angle measuring unit (not shown) is evaluated, which is generally known from laser scanners and determines the respective angular position of the scanning unit 52. From the distances to a scanned object measured using the time-of-flight method and the associated angular position, two-dimensional polar coordinates of all object points in a scanning plane are available after each scan period. The respective scanning plane is known from the identity of the respective light beam, so that a total three-dimensional spatial area is scanned through several planes. Strictly speaking, a plane is only scanned for a central light beam with an elevation angle of 0°; otherwise, they are conical surfaces, which, however, can also be viewed as scanning planes for simplicity.

[0056] The sensor 10 shown is a laser scanner with a rotating measuring head, namely the scanning unit 52. Not only can a single transmit / receive module rotate as shown here, but additional such modules with a height offset or an angular offset with respect to the rotational axis 58 are also conceivable. Alternatively, periodic deflection using a rotating mirror or a faceted mirror wheel is also conceivable. With multiple light beams, it should be noted that how the multiple light beams fall into the monitoring area 18 depends on the respective rotational position, because their arrangement rotates due to the rotating mirror, as known geometric considerations show. Another alternative embodiment pivots the scanning unit 52 back and forth, either instead of the rotational movement or additionally about a second axis perpendicular to the rotational movement, in order to also generate a scanning movement in elevation.

Claims

1. An optoelectronic sensor (10) for detecting an object in a monitored zone (18) that comprises a light transmitter (12) for transmitting transmitted light (14), a light receiver (26 for receiving transmitted light (20) remitted in the monitored zone (18), a reception optics (22) arranged upstream of the light receiver (26) and having a diaphragm (24), and a control and evaluation unit (28) that is configured to determine a distance from the object with reference to a received signal of the light receiver (26) from a time of flight between the transmission of the transmitted light (14) and the reception of the remitted received light (20), wherein the diaphragm (24) comprises a diaphragm substrate (34) having at least one metallic layer (32) and one diaphragm aperture (40), and a contact region (42) of the metallic layer (32) is electrically conductively connected to another component (44) of the sensor (10) for potential equalization, characterized in that the light receiver (26) has a plurality of light reception elements (26a) operable in Geiger mode; and in that the metallic layer (32) faces the light receiver (26 and is at least partly exposed (48) to reflect backscattered transmitted light (20) remitted by the light receiver (26) onto the light receiver (26) again.

2. A sensor (10) in accordance with claim 1, that has a conductive shield of at least the light receiver (26), with in particular the contact region (42) being electrically conductively connected to the shield.

3. A sensor (10) in accordance with claim 1 or claim 2, wherein the contact region (42) is electrically conductively connected to an expansion card of the sensor (10), in particular to an expansion card of the control and evaluation unit (28).

4. A sensor (10) in accordance with any one of the preceding claims, wherein a voltage (46) can be applied to the metallic layer (32) via the contact region (42) to heat the metallic layer (32).

5. A sensor (10) in accordance with any one of the preceding claims, wherein the exposed part (48) of the metallic layer (32) is structured to set reflection properties.

6. A sensor (10) in accordance with any one of the preceding claims, wherein the diaphragm (24) is configured as multilayer having at least one of the following additional layers on a side facing the light receiver (26) and / or remote from the light receiver (26): an absorption layer (36, 38), an anti-reflection layer, a filter layer.

7. A sensor (10) in accordance with any one of the preceding claims, wherein the diaphragm aperture (40) is manufactured by a laser, in particular by a laser ablation process, in particular individually using the reception optics (22).

8. A sensor (10) in accordance with any one of the preceding claims, that is configured as a laser scanner and has a movable deflection unit (52) with whose aid the transmitted light (14) is periodically guided through the monitored zone (18), wherein the deflection unit (52) is in particular configured in the form of a rotatable scanning unit in which the light transmitter (12) and / or the light receiver (26) is / are accommodated.

9. A sensor (10) in accordance with any one of the preceding claims, wherein the light transmitter (12) is configured to transmit a plurality of mutually separate light beams (14) and the light receiver (26) is configured to generate respective received signals from a plurality of remitted light beams (20), and wherein the diaphragm (24) in particular has one diaphragm aperture (40) per light beam (14, 20).