Optical system comprising a contamination detection system

Abstract

Optical system (1) comprising a primary optical sensor (3) which is protected against environmental influences by an optically transparent protective cover (2), wherein the optical system (1) comprises a contamination detection system (4), wherein the contamination detection system (4) comprises at least one optical transmitting unit (5, 6) and at least one optical receiving unit (7, 8), wherein a first transmitting unit (5) is configured to couple a first light signal into the protective cover (2) in such a way that the first light signal propagates in a directed manner with at least one total internal reflection within the protective cover (2) on a first propagation path (9), wherein a first receiver unit (7) is configured to couple out and receive the first light signal from the protective cover (2) at one end of the first propagation path (9), wherein the contamination detection system (4) is configured to detect contamination (11) on a surface of the protective cover (2) along the first propagation path (9) by comparing the first light signal received by the first receiver unit (7) with an expected first light signal, wherein the optical system (1) is configured such that by rotating and / or shifting the contamination detection system (4) the first propagation path (9) within the protective cover (2) is shifted and / or rotated so that the contamination detection system (4) detects contamination (11) along the surface of the protective cover (2) swept by the first propagation path (9); characterized by the fact that the contamination detection system (4) comprises a second optical transmitting unit (6) and a second optical receiving unit (8) which, according to the first propagation path (9), form a second propagation path (10) through the protective cover (2) by means of a second light signal, wherein the second propagation path (10) differs from the first propagation path (9).

Description

[0001] The present invention relates to an optical system, in particular a LiDAR (Light Detection and Ranging) system, comprising a primary optical sensor which is protected against environmental influences by an optically transparent protective cover, wherein the optical system comprises a contamination detection system, wherein the contamination detection system comprises at least one optical transmitter unit and at least one optical receiver unit, wherein a first transmitter unit is configured to couple a first light signal into the protective cover such that the first light signal propagates directionally with at least one total internal reflection within the protective cover on a first propagation path, wherein a first receiver unit is configured to couple the first light signal out of the protective cover at one end of the first propagation path and to receive it. State of the art

[0002] Many sensors, such as those used in driver assistance systems in automobiles like cameras, radar, or LiDAR sensors, are protected from external environmental influences by a transparent cover. The information transmitted by the respective sensor (for example, the propagation of light) passes through this cover. If this cover becomes contaminated with substances such as water or dirt, the information flow is disrupted, and the sensors' functionality is impaired. To overcome this limitation, cleaning systems are often installed on the outside of the cover. Examples include windshield wipers or spray nozzles. However, these cleaning systems cannot operate continuously due to wear and tear and the consumption of cleaning agents.

[0003] For example, patent DE102013211738A1 is known from the prior art. This patent describes the detection of moisture on a glass pane (especially a vehicle windshield) using total internal reflection (TIR). The radiation is thus totally reflected one or more times within the glass pane. The moisture detection system consists of an electromagnetic radiation transmitter, an input element for coupling the radiation into a cover glass, an output element, and a detector. The principle is based on the propagation of the radiation within the glass pane via TIR and the detection of deviations from the expected output radiation signal. Alternatively, a surround-view camera can also be used to monitor the windshield.

[0004] WO2014 / 005585A1 describes the detection of moisture on a disc (especially a windshield) using a camera whose main task is independent of moisture detection, such as the detection of objects external to the vehicle (e.g., other vehicles or obstacles).

[0005] In the prior art, it is generally known to use TIR in a pane of glass to detect moisture on the glass surface. Current systems primarily consist of rain sensors for detecting moisture on a windshield. These rain sensors detect raindrops only on a small area of ​​the windshield and use this information to control the cleaning of the glass, for example, by means of windshield wipers. However, if contaminants (particles, water, snow, ice, oils; solid, liquid, transparent, and opaque contaminants, etc.) come into contact with another area of ​​the windshield, the contamination is not detected by the conventional rain sensor. For some applications (for example, a protective cover for a LiDAR system), this is insufficient, as any contamination of the protective cover can negatively affect the measurement data.

[0006] Camera sensors for monitoring the glass surface / protective cover, on the other hand, are very dependent on the ambient lighting.

[0007] A detector-independent, automatic, regular cleaning of the protective cover is problematic because, depending on the interval length, this either results in very high cleaning agent and water consumption / high wear and tear and / or longer periods of soiling of the protective cover and thus faulty measurement data of the optical system.

[0008] From DE 10 2014 107 353 A1, an optoelectronic sensor for detecting objects in a monitoring area, in particular a laser scanner, is disclosed, comprising a light transmitter for emitting a transmitting light beam, a light receiver for generating a received signal from the light remitted by objects in the monitoring area, a base unit with a circumferential front window, a scanning unit movable relative to the base unit for periodically scanning the monitoring area, and an evaluation unit for recording information about objects in the monitoring area based on the received signal, wherein the scanning unit has a first optical data transmission unit and the base unit has a second optical data transmission unit to exchange data between the base unit and the scanning unit via an optical signal.The data transmission units are designed for data exchange via a fiber optic cable that is located on the windshield. Disclosure of the invention

[0009] According to the invention, an optical system of the type mentioned at the outset is provided, characterized in that the contamination detection system is configured to detect contamination on a surface of the protective cover along the first propagation path by comparing the first light signal received by the first receiver unit with an expected first light signal, wherein the optical system is configured such that by rotating and / or displacing the contamination detection system the first propagation path within the protective cover is displaced and / or rotated, so that the contamination detection system detects contamination along the surface of the protective cover swept by the first propagation path. Advantages of the invention

[0010] The invention enables the detection and / or cleaning of contaminants on the protective cover of an optical sensor, for example, a LiDAR sensor, a camera, or a combination of a camera and a LiDAR sensor behind a common protective cover. The optically transparent protective cover can be, for example, a glass or plastic sheet.

[0011] The basic concept involves the use of one or more optical transmitter units and one or more optical receiver units that rotate or move along the protective cover. A significant advantage of the invention is the at least one-dimensional, and preferably two-dimensional, spatially resolved detection of contaminants on the surface of the protective cover. This precise location of contaminants allows for more efficient use of resources (e.g., spray water, cleaning agents) through targeted cleaning. For example, only a section of the protective cover where contamination has been detected can be cleaned by a connected cleaning device.

[0012] In addition, the data measured by the primary sensor (e.g., distance measurements) can be interpreted more reliably, as any false detections can be attributed to contamination. Thus, software can determine which measurement data is reliable and / or at least partially correct for artifacts caused by contamination until cleaning is possible. Since the contamination detection system according to the invention can, in principle, monitor all relevant internal and external surfaces of the protective cover, it can be ensured that contamination is detected quickly and reliably. At the same time, the consumption of cleaning agents / water is reduced, thereby extending the maintenance cycle of the optical system.

[0013] A negative impact of the contamination detection system on the primary sensor of the optical system itself can be avoided by using a different wavelength. Additionally, any impact on the primary sensor can be avoided by always orienting the transmitter unit(s) and receiver unit(s) in a different direction than the primary sensor.

[0014] The system according to the invention has the advantage over passive, purely camera-based systems that it delivers equally good results even in poor lighting conditions.

[0015] In cross-sectional views, a propagation path within the protective cover runs in a zigzag pattern between the total internal reflections. However, in top view, projections of the propagation paths perpendicular to a surface of the protective cover are essentially straight, although some scattering and angular deviations are unavoidable. Even in curved protective covers (for example, cylindrical protective covers), the propagation paths only approximate a linear projection onto the curved surface.

[0016] "Light" here is not necessarily limited to visible light, but can also include, for example, infrared light or UV radiation. In the following, light and radiation are sometimes used synonymously.

[0017] A propagation path, viewed from above the surface of the protective cover, can have a certain extent in the lateral direction. Simultaneously, a propagation path in the thickness direction of the protective cover can have an extent of the same order of magnitude as the thickness of the protective cover. This ensures that a substantial portion (or the entirety) of the inner and outer surface of the protective cover can be scanned.

[0018] The optical system is equipped with one or more transmitter and receiver units, which are located, for example, on the opposite side, or alternatively above or below the actual primary sensor.

[0019] Two, three, four, five, six, or more propagation paths can be used to determine the location of contaminants as precisely as possible. Within each propagation path, one or more light signals can be used to detect contaminants. The light signals can differ in their geometric path through the protective cover and / or in their signal characteristics (wavelength, wavelength range, etc.). Multiple light signals can be provided by the same transmitter and receiver units.

[0020] The contamination detection system underlying the invention is based on one or more optical transmitting units (for example, an LED or a laser, etc.) and one or more optical receiver units (for example, a photodiode, a CCD, etc.).

[0021] According to the invention, the contamination detection system comprises a second optical transmitter unit and a second optical receiver unit, which, corresponding to the first propagation path, establish a second propagation path through the protective cover by means of a second light signal, wherein the second propagation path differs from the first propagation path. The second transmitter unit is thus configured to couple a second light signal into the protective cover in such a way that the second light signal propagates directionally with at least one total internal reflection within the protective cover along a second propagation path, wherein the second receiver unit is configured to couple the second light signal out of the protective cover at one end of the first propagation path and receive it. The use of two different propagation paths allows for a more precise localization of contamination on one of the surfaces of the protective cover.

[0022] In one embodiment, at least two propagation paths run at a relative angle within the protective cover, and the contamination detection system is configured to determine a two-dimensional position and / or extent of the contamination on the surface of the protective cover by comparing two detected one-dimensional positions of the contamination detected by means of the two corresponding light signals. By comparing the two time points at which contamination is detected in the first propagation path and in the second propagation path, respectively, a two-dimensional position of the contamination on a surface of the protective cover can then be reconstructed. This allows for more economical use of any cleaning device and also enables a more precise determination of signal interference from the primary sensor caused by the contamination.

[0023] In one embodiment, at least one propagation path is configured such that substantially complete strips of an inner surface and an outer surface of the protective cover are scanned along this propagation path. A strip is understood to be a two-dimensional section, for example in the form of a rectangle or parallelogram, on the inner surface or the outer surface of the protective cover, respectively. In this embodiment, the dimensions of the light signal are advantageously designed such that substantially the entire inner and outer surface of the protective cover (preferably exactly) comes into contact with the light signal once along the strip.

[0024] It is preferred if at least one propagation path is configured such that only a portion of an inner surface of the protective cover and only a portion of an outer surface of the protective cover are scanned along this propagation path. This embodiment makes it possible to distinguish, when using multiple light signals, whether contamination is present on the inner or the outer surface of the protective cover.

[0025] In a further preferred embodiment, at least two propagation paths run essentially parallel and each scans different parts of the inner surface and different parts of the outer surface, wherein at least a third propagation path runs at a relative angle to the other two propagation paths. The contamination detection system is configured to determine, by identifying in which two of the three propagation paths a detected contamination was detected, whether the contamination is present on the inner surface or the outer surface of the protective cover. In the case of a cylindrical protective cover, the parallel light signals can, for example, alternately scan one cylindrical ring of the inner surface and then, offset vertically, one cylindrical ring of the outer surface.Here, "parallel" refers only to a two-dimensional projection of the propagation paths onto the outer or inner surface of the protective cover. Together, the two parallel light signals scan an essentially complete strip of the inner and outer surfaces at any given time, with specific height segments on the cylindrical surface being assigned to each of the two light signals. Together with a third light signal traveling at a relative angle, the two-dimensional position of a detected contamination can then be determined. Knowing which of the two parallel light signals, together with the third light signal, indicates contamination, it is then possible to determine whether the contamination is located on the inner or outer surface of the protective cover.

[0026] Preferably, at least one light signal is coupled into and / or coupled out of the protective cover via optical components or through at least one light-receiving area of ​​the protective cover. The optical components can include beam splitters, light guides, prisms, lenses, collimating lenses, or holograms. A light-receiving area of ​​the protective cover can, for example, be a beveled edge of the protective cover. In principle, a light-receiving area is configured to guide a light signal striking the protective cover onto a propagation path within the protective cover. This can be achieved through a suitable geometric design of the protective cover in the light-receiving area.

[0027] It is preferred that the contamination detection system be configured to vary at least one signal parameter of a light signal to determine the properties of a detected contaminant. A signal parameter can be, for example, a wavelength or wavelength range, or the width of the propagation path in the scanning direction (i.e., the direction of movement of the propagation path during rotation and / or translation). A change in wavelength or wavelength range generally causes a change in the proportion of the light signal that is absorbed by the contamination, depending on the type of contamination (e.g., particles, water, snow, ice, oils; solid, liquid, transparent, and opaque contaminants).For certain types of soiling, it may be sufficient to use a cleaning mechanism without cleaning fluid for removal, while for other types of soiling it may be useful to apply a cleaning fluid to the protective cover in addition to mechanical cleaning.

[0028] In one embodiment, the at least one transmitting unit and the at least one receiving unit are arranged such that, during operation of the optical system, they rotate together with the primary optical sensor around a common axis of rotation, with the at least one propagation path sweeping across the surfaces of the protective cover for contamination detection. Rotating the primary sensor often allows for a larger field of view. Simultaneously, the existing rotation of the primary sensor then serves the contamination detection system to detect contamination by scanning the protective cover.

[0029] In one embodiment, the contamination detection system comprises its own movement mechanism, configured such that rotation and / or displacement of at least one transmitter unit and at least one receiver unit shifts and / or rotates at least one propagation path within the protective cover, enabling the contamination detection system to detect contamination along the surface of the protective cover swept by this propagation path. This embodiment is particularly suitable for optical systems with a static primary sensor. The contamination detection system then, in effect, provides the necessary relative movement between the protective cover and the transmitter or receiver unit for scanning the surfaces of the protective cover.

[0030] Advantageous embodiments of the invention are specified in the dependent claims and described in the description. Drawings

[0031] Exemplary embodiments of the invention are explained in more detail with reference to the drawings and the following description. The drawings show: Fig. 1 a schematic representation of an embodiment of an optical system according to the invention, Fig. 2 a schematic representation of an embodiment of an optical system according to the invention, Fig. 3 a schematic representation of an embodiment of a contamination detection system according to the invention, Fig. 4 a schematic representation of a further embodiment of a contamination detection system according to the invention, and Fig. 5 a schematic representation of total internal reflection in the protective cover. Embodiments of the invention

[0032] Fig. Figure 1 shows a schematic sectional view through an optical system 1 according to the invention (for example, a LiDAR sensor system as a driver assistance system), which is surrounded by a protective cover 2. The protective cover is optically transparent and, in the present embodiment, cylindrical. The optical system 1 comprises a primary sensor 3, which can be, for example, a LiDAR sensor or a camera, and a contamination detection system 4. In this embodiment, the primary sensor 3 and the contamination detection system 4 rotate together about an axis.

[0033] For optical systems 1 with a rotating primary sensor 3 and a cylindrical protective cover 2, the contamination detection system 4 according to the invention can be most easily integrated, since the operational rotation of the primary sensor 3 can then also be used to scan the protective cover 2 by the contamination detection system 4.

[0034] Optical system 1 is additionally equipped with one or more transmitter units and receiver units (see in particular Fig. 2), which, for example, are on the opposite side ( Fig. 1), alternatively also arranged above or below the primary sensor 3.

[0035] Fig. Figure 2 shows a schematic representation of an embodiment of an optical system 1 according to the invention, wherein all components except the contamination detection system 4 and the protective cover 2 are not shown for the sake of clarity.

[0036] The contamination detection system 4 comprises two optical transmitters 5, 6 and two optical receivers 7, 8. A first transmitter 5 is configured to couple a first light signal into the protective cover 2 such that the first light signal propagates directionally with at least one total internal reflection within the protective cover 2 along a first propagation path 9. A first receiver 7 is configured to couple the first light signal out of the protective cover 2 at one end of the first propagation path 9 and receive it. Correspondingly, a second transmitter 6 is configured to couple a second light signal into the protective cover 2 such that the second light signal propagates directionally with at least one total internal reflection within the protective cover 2 along a second propagation path 10.A second receiver unit 8 is designed to extract and receive the second light signal from the protective cover 2 at one end of the second propagation path 9.

[0037] The coupling of the light signals into and / or out of the protective cover 11 can be effected via optical components or by at least one light-receiving area of ​​the protective cover 11 (see also Fig. 5).

[0038] A light-receiving area of ​​the protective cover 11 can, for example, be a beveled edge of the protective cover 11. In principle, a light-receiving area is designed to direct a light signal striking the protective cover 11 onto a propagation path 9, 10 within the protective cover 11. This can be achieved by a suitable geometric design of the protective cover 11 in the light-receiving area.

[0039] The contamination detection system 4 is configured to detect contamination on a surface of the protective cover 2 along the propagation paths 9, 10 by comparing the light signal received by the receiver units 7, 8 with expected light signals. The optical system 1 is configured as described such that (here) by rotating (and / or shifting) the contamination detection system 4, the propagation paths 9, 10 within the protective cover 2 are (shifted and / or) rotated, enabling the contamination detection system 4 to detect contamination along the surface of the protective cover 2 swept by the propagation paths 9, 10. The propagation paths migrate counterclockwise across the protective cover 2.

[0040] The transmitting and receiving units 5, 6, 7, 8 can (as in Fig. 1 indicated) for example on the opposite side, or alternatively above and below the primary sensor 3.

[0041] The optical transmitter(s) 5, 6 can be, for example, LEDs, lasers, or IR laser diodes with or without collimation optics. The optical receiver(s) can be, for example, (Si) photodiodes, cameras, or CCDs with or without collimation optics. Electromagnetic radiation is coupled into the top or bottom surface of the protective cover 2 by the transmitter(s) 5, 6, so that the light is reflected within the protective cover 2 by total internal reflection (see Fig. 5) propagated to the opposite side and coupled out there at the receiver unit 7, 8.

[0042] A cylindrical plate made of plastic or glass can be used as protective cover 2. The refractive index of the material defines the reflection properties of the system, which must be taken into account when implementing the coupling.

[0043] In the case shown, Fig. In Figure 2, both transmitting units 5, 6 and receiving units 7, 8 are coupled to the system's rotational axis. The points where the radiation couples in and out remain constant relative to each other. The positions of the contaminants can be determined via the current rotation angle (see Figure 2). Fig. 3 and Fig. 4).

[0044] The coupling in and out can be achieved using various elements (for example, prisms, mirrors, holograms, etc.). If contaminants are present on the surface of the protective cover 2, total internal reflection is prevented at the corresponding points if the coupling angle is appropriately chosen, and the light signal decreases. This is primarily due to a different refractive index at the contaminated areas compared to clean areas of the surface of the protective cover 2, which interrupts or at least reduces total internal reflection along the respective propagation path (for example, due to partial absorption and / or scattering of the light signal).

[0045] The light signal strength can thus be considered a measure of the degree of contamination. In simplified terms, only one-dimensional propagation paths on the protective cover 2 are monitored, where the electromagnetic radiation couples in and out. The rotation of the sensor causes a shift in the coupling plane, so that essentially the entire surface of the protective cover 2 is scanned. "Essentially" here means that, depending on the type of coupling, the (here upper and lower) edges of the protective cover 2 are not scanned. However, this can be unproblematic, since the primary sensor 3 does not necessarily use the entire protective cover 2 for its field of view. Furthermore, part of the edges of the protective cover 2 may also be covered by connection areas of a housing of the optical system 1.

[0046] The embodiments differ in particular in the coupling of the radiation into and out of the protective cover, the transmitter units 5, 7 and receiver units 8, 9 used, optics for beam shaping and deflection, or in the shape and material of the protective cover. The coupling in and out can be achieved, for example, by chamfering the upper and lower edges of the protective cover 2, respectively. Alternatively, optical elements such as prism structures or holograms can be applied to the surface of the protective cover 2 to minimize coupling losses.

[0047] The Fig. 3 and Fig. Figure 4 shows two embodiments of the optical system 1 and the principle of the contamination detection according to the invention. The protective cover 2 can, for example, be cylindrical or rectangular in the two embodiments shown. According to the embodiment of the Fig. 1 and Fig. Figure 2 shows the protective cover "unrolled" from left to right, i.e., along a rotation around the cylinder's axis of rotation. However, the optical system 1 also functions with, for example, a rectangular protective cover 2, in which case the contamination detection system 4 preferably includes its own movement mechanism. In the following, such an embodiment is described without specifying a rotationally symmetrical protective cover in order to illustrate the operating principle.

[0048] In Fig. 3 The contamination detection system 4 comprises an optical transmitter unit 5 and an optical receiver unit 7, which generate a propagation path 9 through the protective cover 2. If there is no contamination on the protective cover 2, the light signal is the same for all angles of rotation (or all positions of displacement). If there is contamination on the surface, the signal decreases at the corresponding locations. By reading the current angular setting (or the spatial position) of the propagation path 9, a one-dimensional contamination position 12 of the contamination 11 on the corresponding vertical (see Fig. 3 below) are determined and, for example, passed on to a cleaning system.

[0049] In Fig. 4 The contamination detection system 4 comprises two optical transmitter units 5, 6 and two optical receiver units 7, 8. To ensure that contamination 11 is detected at every position on the vertical, the radiation entering the protective cover 2 must be directed so that every point on the vertical is irradiated at least once.

[0050] As in Fig. 3 shown, contamination can occur in the embodiment of the Fig. 4 on the corresponding vertical of the protective cover (the internal total reflections are perpendicular to the image plane and are therefore not visible, see also Fig. 5) The pollution detection system 4 is then horizontally spatially resolved (by rotation or translation). To add vertical spatial resolution to the pollution detection system 4, it is extended by at least one further propagation path 10. For each propagation path 9, 10, the pollutions 11 can then be detected on the corresponding verticals (or slopes, if the planes are rotated). From the times or horizontal coordinates of each pollution 11, which are determined by means of one of the propagation paths 9, 10, it is then generally possible (with a limited number of pollutions 11) to determine both a horizontal and a vertical coordinate for a two-dimensional pollution position 13 of each pollution 11. Fig. 4. The two propagation paths determine the first contamination from the left almost simultaneously, from which a vertically centered position can be calculated. The second contamination 11 from the left is located very far down, which can be determined from the fact that it affects propagation path 10 significantly earlier (during a rotation "to the right") than propagation path 9.

[0051] To realize the crossed propagation paths 9, 10, several transmitter units 5, 6 (with optional optics, etc.) and several receiver units 7, 8 (with optional optics) can be used. Alternatively, the light from a single transmitter unit 5 can be split into several propagation paths 9, 10 via optical elements (e.g., beam splitters), thus requiring fewer components. The transmitter units 5, 6 (e.g., LEDs) can also be configured to introduce multiple light signals into the protective cover 11 at different angles, so that these signals propagate at different angles (divergently) along the propagation path 9, 10. Similarly, the receiver units 7, 8 can be configured to receive and distinguish multiple light signals from the same propagation path 9, 10 (e.g., by their geometric arrival area in the receiver unit, their wavelength, or their wavelength range, etc.).).

[0052] Fig. Figure 5 shows the propagation of light / radiation by means of total internal reflection through a protective cover 2 between transmitter unit 5, 6 and receiver unit 7, 8. The in Fig. 3 and Fig. The four planes shown are perpendicular to the image plane, so the reflections are not visible there. The protective cover 2 is scanned by a relative movement of transmitter unit 5, 6 and receiver unit 7, 8. The vertical (or diagonal, Fig. 4), on which there is a pollution 11, provides a reduced light signal.

[0053] The percentage of emitted radiation upon impact with a contaminant 11 depends on the propagation angle of the propagation path 9, the refractive indices of the protective cover 2, and the extent and severity of the contaminant 11 (and thus on the wavelength of the radiation), as well as on the polarization of the radiation. By appropriately selecting the parameters, the degree of attenuation of the radiation can also be interpreted as a measure of the degree of contaminant 11. Varying the parameters allows conclusions to be drawn about the type of contaminant (for example, refractive index).

[0054] Multiple light signals at different angles can propagate through the same propagation path 9. This allows the light signals to "scan," for example, different sections of the surface of the protective cover 2 along the propagation path 9. This improves the spatial resolution of the contamination detection system 4. The light signals can differ, for example, in a signal property (wavelength, wavelength range, etc.) and simultaneously allow for an analysis of the type of contamination 11.

[0055] By increasing the number of propagation paths 9, 10, it is possible to distinguish whether the contamination is located on the inside or outside of the protective cover 2. Two, three, four, five, six, or more propagation paths can be used to determine the position of the contamination 11. For this purpose, the different paths can be defined such that they illuminate different areas (no longer every position on the protective cover 2 for each propagation path 9, 10) along a propagation direction. Depending on which areas are illuminated, and considering different propagation paths 9, 10, it can be deduced whether the contamination is located on the inner surface of the outer surface of the protective cover 2. This generally requires three propagation paths 9, 10, at least two of which must differ in their relative angles in the plane of the protective cover (see Fig. 4).

[0056] In this case, at least two propagation paths 9, 10 run essentially parallel and each scans different parts of the inner surface and different parts of the outer surface. At least a third propagation path 9, 10 runs at a relative angle to the other two propagation paths 9, 10. The contamination detection system can then be configured to determine, by identifying in which two of the three light signals a detected contamination 11 was detected, whether the contamination 11 is present on the inner surface or the outer surface of the protective cover 2.

[0057] In the case of a cylindrical protective cover 2, the parallel light signals can, for example, alternately scan a cylindrical ring of the inner surface and then, offset in the vertical direction, a cylindrical ring of the outer surface (compare Fig. 2) Here, "parallel" refers only to a two-dimensional projection of the propagation paths 9, 10 onto the outer or inner surface of the protective cover 2. Together, the two parallel light signals scan an essentially complete strip of the inner and outer surfaces at any given time, with specific height segments on the cylindrical surface being assignable to each of the two light signals. Together with a third light signal traveling at a relative angle, the two-dimensional position of a detected contamination 11 can then be determined. Knowing which of the two parallel light signals, together with the third light signal, indicates a contamination 11, it is then also possible to determine whether the contamination 11 is located on the inner or outer surface of the protective cover 2.

[0058] Fig. Figure 5 shows the coupling of the radiation into the protective cover 2 over a specific width, such that successive reflections in the protective cover 2 strike the entire surface of the protective cover. The coupling is shown via edges angled at 45°, so the necessary beam width trivially corresponds exactly to the edge length. For larger propagation angles or edge angles, additional considerations are necessary to achieve the required beam width.

[0059] For a defined propagation angle of the propagation paths 9, 10, the incoming radiation can be spread out so that successive reflections illuminate the entire area of ​​the sensor cover 2. Alternatively, one of the transmitting units 5, 6 can be configured to alternately transmit only one propagation path 9 at a time, with half the "width" (half the "width" of the propagation path 9 in Fig.5) Half of the surfaces are scanned at a time (for example, divided into alternating cylindrical rings), and the scanning of the surfaces is performed twice in succession, each time using one of the "half" propagation paths 9, 10. This allows it to be determined whether contamination 11 is present on the outer or inner surface. It is also possible to propagate two, three, or more light signals at different angles through the same propagation path 9, 10. In this way, the light signals "scan," for example, different sections of the surfaces of the protective cover 2 along the propagation path 9.

[0060] The coupling of radiation at the end of the protective cover 2 can, in principle, be avoided by using several receiver units 7, 8 directly at the exit surface. The number and size of the receiver units 7, 8 then determine the resolution. This ensures that a large proportion of the radiation in the protective cover 2 also falls on the detector area of ​​the receiver units 7, 8. In principle, the invention can also be applied to a non-rotating optical system 1 with a curved or flat protective cover 2. For this purpose, the contamination detection system 4 shown here must be equipped with its own rotation, a mechanical rotation, or a linear guide that scans the protective cover 2.

Claims

[1] Optical system (1) comprising a primary optical sensor (3) which is protected from environmental influences by an optically transparent protective cover (2), wherein the optical system (1) comprises a contamination detection system (4), wherein the contamination detection system (4) comprises at least one optical transmitting unit (5, 6) and at least one optical receiving unit (7, 8), wherein a first transmitting unit (5) is configured to couple a first light signal into the protective cover (2) in such a way that the first light signal propagates in a directed manner with at least one total internal reflection within the protective cover (2) on a first propagation path (9), wherein a first receiver unit (7) is configured to couple out and receive the first light signal from the protective cover (2) at one end of the first propagation path (9), wherein the contamination detection system (4) is configured to detect contamination (11) on a surface of the protective cover (2) along the first propagation path (9) by comparing the first light signal received by the first receiver unit (7) with an expected first light signal, wherein the optical system (1) is configured such that by rotating and / or shifting the contamination detection system (4) the first propagation path (9) within the protective cover (2) is shifted and / or rotated so that the contamination detection system (4) detects contamination (11) along the surface of the protective cover (2) swept by the first propagation path (9); characterized by , that the contamination detection system (4) comprises a second optical transmitting unit (6) and a second optical receiving unit (8) which, according to the first propagation path (9), form a second propagation path (10) through the protective cover (2) by means of a second light signal, wherein the second propagation path (10) differs from the first propagation path (9). [2] Optical system (1) according to claim 1, wherein at least two propagation paths (9, 10) run at a relative angle in the protective cover (2), and wherein the contamination detection system (4) is configured to determine a two-dimensional contamination position (13) and / or a two-dimensional extent of the contamination (11) on the surface of the protective cover (2) by comparing two detected one-dimensional positions (12) of a contamination (11) detected by means of the two corresponding light signals. [3] Optical system (1) according to one of the preceding claims, wherein at least one propagation path (9, 10) is configured such that substantially complete strips of an inner surface of the protective cover (2) and an outer surface of the protective cover (2) are scanned along this propagation path (9, 10). [4] Optical system (1) according to one of the preceding claims, wherein at least one propagation path (9, 10) is arranged such that along this propagation path (9, 10) only a part of an inner surface of the protective cover (2) and only a part of an outer surface of the protective cover (2) is scanned. [5] Optical system (1) according to claim 4, wherein at least two propagation paths (9) are substantially parallel and each scan different parts of the inner surface and different parts of the outer surface, and wherein at least one third propagation path (10) is at a relative angle to the two other propagation paths (9), wherein the contamination detection system (4) is configured to additionally determine, by determining in which two of the three propagation paths (9, 10) a detected contamination (11) was detected, whether the contamination (11) is present on the inner surface or the outer surface of the protective cover (2). [6] Optical system (1) according to one of the preceding claims, wherein coupling into and / or coupling out of at least one light signal into the protective cover (2) is carried out via optical components or through at least one light receiving area of ​​the protective cover (2). [7] Optical system (1) according to one of the preceding claims, wherein the contamination detection system (4) is configured to vary at least one signal parameter of a light signal in order to determine the properties of a detected contamination (11). [8] Optical system (1) according to one of the preceding claims, wherein the at least one transmitting unit (5, 6) and the at least one receiving unit (7, 8) are arranged such that they are rotated together with the primary optical sensor (3) about a common axis of rotation during operation of the optical system (1) and the at least one propagation path (9, 10) sweeps over the surfaces of the protective cover (2) for contamination detection. [9] Optical system (1) according to one of the preceding claims, wherein the contamination detection system (4) comprises its own movement mechanism, which is arranged such that at least one propagation path (5, 6) within the protective cover (2) is moved and / or rotated by rotation and / or displacement of at least one transmitting unit (5, 6) and at least one receiver unit (7, 8), so that the contamination detection system (4) detects contamination (11) along the surface of the protective cover (2) swept by this propagation path (9, 10). [10] Optical system (1) according to any of the preceding provisions, wherein the primary optical sensor (3) is configured as a LiDAR sensor, camera or as a combination of a camera and a LiDAR sensor.

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