EP2176098A1

EP2176098A1 - Device for determining the reflective properties of a boundary

Info

Publication number: EP2176098A1
Application number: EP08774765A
Authority: EP
Inventors: Andreas Pack; Markus Wolff
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2007-08-01
Filing date: 2008-07-04
Publication date: 2010-04-21
Also published as: WO2009015988A1; DE102007039349A1

Abstract

The invention relates to a device for determining the reflective properties of a boundary (10) between a first and a second medium, comprising an electromagnetic radiation source (6) and an optical arrangement (13), provided for coupling the radiation (4) emitted from the radiation source (6) into the first medium. If using the arrangement according to the invention as a rain sensor for motor vehicles, the first medium can be part of a vehicle window pane (1), particularly a windscreen; the second medium in this case is air or in the case of a windscreen (1) covered with rain it is water. In order to decouple the radiation (5) reflected on the boundary (10) from the first medium, the above-mentioned optical arrangement (13) is used, which deflects the reflected radiation (5) decoupled from the first medium to a receiver (7). The optical arrangement (13) comprises the regions (14) reflecting the radiation (4, 5) and parts of a Fresnel lens.

Description

Device for determining the reflection properties of an interface

State of the art

The invention relates to a device for determining the reflection properties of an interface, as for example in an optical system for an optical sensor such. B. can find a rain sensor use.

Rain sensors are known from the prior art which generally operate according to the principle illustrated in FIG. 1:

An electromagnetic radiation source 6 such as an infrared LED emits electromagnetic radiation 4 at a certain angle from the inside of a pane 1, ie usually from the passenger compartment of a motor vehicle, in the direction of the pane 1. The radiation 4 passes through the interface between the interior and disc 1 and is deflected against the interface 10 formed by disc 1 and the vehicle exterior, which is referred to as the sensitive area in this area. The angle of incidence of the electromagnetic radiation 4 with respect to the interface 10 is selected such that the electromagnetic radiation 4 in the case of a disk 1 not wetted by raindrops at the interface 10 according to the laws of optics in the direction of the inside of the disk 1 as reflected radiation 5 is totally reflected and is detected by a arranged near the disc inside, for example, designed as an infrared LRD receiver 7 is detected. When wetting the disk 1, this total reflection is disturbed or canceled due to the changed refractive index ratios at the interface 10, so that a portion of the electromagnetic radiation 4 is coupled to the outside and arrives at the LRD 7 less radiation than in the case of total reflection. From the collapse of Lichtein- case includes one of the LED 6 and LRD 7 associated, for example, arranged on a circuit board Evaluation unit 8 to the present degree of wetting and controls according wiping operations of the windscreen wiper. To realize this basic principle, LED 6, LRD 7 and the evaluation unit 8 are housed together with a control unit, not shown, in a housing 9 which, for the purpose of effective light beam guidance, is associated with a coupling optics 13a associated with the LED 6 and one of the LRDs 7 Auskoppeloptik 13b is equipped and for the purpose of undisturbed light conduction and coupling the radiation 4 or 5 in and out of the disc 1 with an optical coupling medium as an intermediate layer 2, for example made of silicone, bubble-free to the disc 1 is coupled. The aforementioned Einkoppelbzw. Coupling optics 13a, 13b usually consist of lenses, one side of which is convex and the other side is planar.

Rain sensors of the previously described embodiment are described, for example, in German Patent Application DE 102 61 244 A1, in European Patent Application EP 0 997 360 A2 and in International Patent Application Publication No. PCT / US98 / 20881. However, the design of optics requires that the electromagnetic radiation source and the receiver be laterally (i.e., parallel to the disk) at a greater distance than the coupling-in or coupling-out optics themselves.

From the German patent application DE 198 30 120Al the optical arrangement 13 shown in FIG. 2 is known, which in each case has segmented lenses 13a and 13b, so-called Fresnel elements.

Lenses, used for beam guidance for an LED 6 and a LRD 7, wherein both lenses are designed ient. The Fresnel lenses 13a, described in said application,

13b are arranged in such a way that the optical axis of the lenses is oriented at an angle of approximately 45 ° to the disk surface and only refraction is used for deflecting the electromagnetic radiation 4 or 5. As a consequence, LED

6 and LRD 7 arranged laterally outside the boundary of the Fresnel lens area.

Furthermore, German Patent Application DE 10 2004 015 699 A1 discloses a rain sensor. beard, which has an optical arrangement with reflective areas.

Advantages of the invention

The device according to the invention for determining the reflection properties of an interface between a first and a second medium shows an electromagnetic radiation source and an optical arrangement which serves to couple the radiation emitted by the radiation source into the first medium. In the case of using the arrangement according to the invention in a rain sensor for motor vehicles, the first medium may be a part of a vehicle window, in particular a front window; the second medium is air in this case, or water in the case of a rain wetted disk. For decoupling the radiation reflected at the interface from the first medium, the already mentioned optical arrangement is likewise used, which directs the reflected radiation coupled out of the first medium onto a receiver. The optical arrangement has areas where the radiation reflects, in particular totally reflected, as well as at least parts of a Fresnel lens. This embodiment of the optical arrangement has the advantage that the radiation source and the receiver do not have to be arranged at a greater distance than that which corresponds to the lateral extent of the optical arrangement. This is due to the fact that the reflective areas, in particular in combination with the parts of the Fresnel lens, offer an advantageous possibility of particularly efficiently redirecting the electromagnetic radiation used, so that the radiation can be deflected by almost any angle, in particular also by approximately 180 ° , Thus, this measure allows a very compact design of the optical arrangement and thus also equipped with the optical arrangement according to the invention rain sensor.

An advantageous embodiment of the invention consists in the realization of the optical arrangement in the form of two partial optics, in particular a coupling-in optical system and a coupling-out optical system, each of which is designed as a Fresnel lens or as part of a Fresnel lens. The mischief In this case, the nel lens can be designed in such a way that refraction and total reflection take place exclusively in first partial regions of the lens and in second partial regions of the lens. The receiver and the radiation source are each assigned a partial optics, both of which need not be made identical, but rather can be chosen so that they are optimally matched to the directional characteristic of the radiation source or the receiver and in particular an arrangement of the radiation source and the Allow receiver within the lateral extent of the optics assembly.

In a further advantageous variant of the invention, the optical arrangement, in particular the coupling optics, is chosen such that the radiation emanating from the radiation source runs as a parallel beam in the first medium and, after being totally reflected at the interface, the coupling-out optics also as a parallel beam is reached and focused by this on the receiver. In this embodiment, the ratio of sensitive area to the dimensions of the optical arrangement is particularly advantageous. Another advantage of the device according to the invention is good utilization of the radiation emitted by the radiation source, since the radiation source can be arranged directly opposite the coupling optics and thus has the main lobe of its directional characteristic in the direction of the coupling optics.

Brief description of the drawing

Show it:

Figure 1 is an illustration of the principle of action of a rain sensor according to the prior

Technology; Figure 2 shows an embodiment of a rain sensor according to the prior art, in which two identically designed Fresnel lenses are used; FIG. 3 shows a first embodiment of a rain sensor according to the invention; Figure 4 is a plan view of the optical arrangement of a rain sensor according to the invention; and FIG. 5 and FIG. 6 show further variants of a rain sensor according to the invention.

Description of exemplary embodiments

FIG. 3 shows a device according to the invention in a cross-sectional representation. The optical assembly 13 is connected to the disk 1 via the intermediate layer 2, which simultaneously serves to improve the coupling and decoupling of the electromagnetic radiation 4 or 5 used by index matching. In this case, the radiation 4 emitted by the radiation source 6 designed as an LED, for example, is coupled into the pane 1 via the partial optics 13a of the optical arrangement 13 and the intermediate layer 2 and is totally reflected on the opposite side. The reflected partial beam 5 of the electromagnetic radiation subsequently passes through the intermediate layer 2 and is focused via the partial optics 13b of the optical arrangement onto the receiver 7 embodied as an LRD, for example.

The two partial optics 13a, 13b respectively show partial areas 15 in which only refraction and partial areas 14 in which refraction and total reflection occurs. The partial optics 13a associated with the radiation source 6 is selected such that the electromagnetic radiation 4 emitted by the radiation source 6 is parallelized and impinges on the boundary surface 10 between the pane 1 and the exterior space at an angle at which total reflection occurs. If the pane 1 is unwetted on its side facing the outer space, the electromagnetic radiation is totally reflected as partial beam 5 and falls onto the receiver 7 after passing through the focusing partial optics 13b. In this case, the partial optics 13a and 13b need not be geometrically identical; Rather, they can be individually adapted to the directional characteristic of the radiation source 6 and of the receiver 7. In addition, in this case, the individually designed geometry opens up the possibility of compensating for a height difference 18 of the optically active regions of radiation source 6 and receiver 7. The arranged in a partial optics 13a and 13b total reflection surfaces need not all run perpendicular to the disc 1 and may in particular have different heights. Likewise, the areas of the partial optics 13a or 13b which provide the targeted refraction of the electromagnetic radiation can all be configured differently from one another geometrically.

FIG. 4 shows a further advantageous embodiment of the coupling-in and coupling-out optical system 13a or 13b, viewed from the vehicle-internal side. In this embodiment, the coupling-in and coupling-out optics 13a and 13b respectively consist of at least one arcuate circular segment (20). In a further embodiment, the individual, for example, arcuate segments (20) themselves may also be composed of a plurality of straight sections (20a-d). If one refers to the plane lying parallel to the disc not shown as xy-plane, so for example a subdivision .der segments (20) in the y-direction is possible or possible in the direction of the respective arc. The shape of each further subdivided segments is no limit set. The effect of the described design of the coupling-in or coupling-out optics 13a and 13b consists essentially in a homogenization of the light field and in an increase in the efficiency of the arrangement. The coupling-in and coupling-out optics 13a, 13b are preferably made of plastic, but may also consist of other materials which are translucent and have a different refractive index than the environment. The coupling-in and coupling-out optics 13 a, 13 b may be made in one piece or as separate parts. Furthermore, there is the possibility that the coupling-in and coupling-out optics 13a, 13b consist of different materials. A further degree of freedom results, even if the different segments of the coupling-in and coupling-out optics 13a, 13b at least partially consist of different materials. In addition, coupling-in and coupling-out optics 13a, 13b can be composed of several parts.

A device according to the invention used for a rain sensor is shown in a cross-sectional representation in FIG. It comprises at least one invention The optical device 13 is coupled via an acting as a coupling medium intermediate layer 2 free of air bubbles on the inside of the disc 1 and in a preferably opaque example plastic optical carrier 19 is arranged. Furthermore, FIG. 5 shows an evaluation electronic unit 8 associated with the optical device 13, which is arranged in a housing 9 made of preferably opaque material (eg an opaque plastic). The communication with subordinate actuators or control devices (not shown) as well as the power supply takes place by means of an electrical interface (also not shown in FIG. 5). The LED 6 and the LRD 7 work preferably in the infrared wavelength range; In this way, irritation of the vehicle driver or other road users is effectively prevented by escaping electromagnetic radiation in the visible spectral range.

In a further embodiment shown in FIG. 6, the optics carrier 19 is dispensed with; rather, the optics arrangement 13 itself forms the cover of the housing 9. To protect against extraneous light penetrating from the outside, a layer of opaque material 16 is arranged directly on the optics assembly 13. The layer 16 may for example consist of silicone or plastic and be connected for example by gluing, adhesion or mechanical fastening, in particular by clips with the optical assembly 13.

The possible use of the device according to the invention is of course not limited to use in a rain sensor; Rather, the invention can be used wherever electromagnetic radiation must be efficiently coupled and disconnected under the stress of as little space as possible in a medium.

Claims

claims

1. Device for determining the reflection properties of an interface (10) between a first and a second medium, with an electromagnetic radiation source (6) and an optical arrangement (13) for coupling the radiation emitted by the radiation source (4) into the first medium and for decoupling the radiation (5) reflected at the interface (10) from the first medium and a receiver (7) for the reflected radiation coupled out of the first medium, the optical arrangement having regions (14) at which the radiation (4 , 5) is reflected, characterized in that the optical arrangement (13) shows at least parts of a Fresnel lens.

2. Device according to claim 1, characterized in that the optical arrangement (13) as partial optics has a coupling-out optical system (13b) and a coupling-in optical system (13a), which in each case comprise at least parts of a Fresnel lens.

3. A device according to claim 2, characterized in that the coupling optics (13a) and the coupling-out optics (13b) are respectively adapted to the directional characteristic of the radiation source (6) or of the receiver (7).

4. Apparatus according to claim 2, characterized in that the coupling optics (13a) and the coupling-out optics (13b) are identical.

5. Device according to one of the preceding claims, characterized in that it is the first medium is a part of a vehicle window (1), in particular a windscreen.

6. Device according to one of the preceding claims, characterized in that the optical arrangement (13) is designed in such a way that the radiation (4) coupled into the first medium runs therein as a parallel bundle of rays.

7. Device according to one of the preceding claims, characterized in that between the optical arrangement (13) and the first medium, an intermediate layer (2) is arranged.

8. The device according to claim 1, characterized in that the Fresnel lens shows at least one arcuate segment (20).

9. Apparatus according to claim 8, characterized in that the at least one arcuate segment of a plurality of straight sections (20a-d) is composed.

10. rain sensor for a motor vehicle with a device according to any one of claims 1-