AU755600B2

AU755600B2 - Optical sensor

Info

Publication number: AU755600B2
Application number: AU12598/00A
Authority: AU
Inventors: Winfried Bernhard; Andre Mueller; Lutz Mueller; Roland Mueller-Fiedler; Helmut Sautter; Rainer Schink
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1998-09-15
Filing date: 1999-09-15
Publication date: 2002-12-19
Anticipated expiration: 2019-09-15
Also published as: WO2000015478A1; EP1045779A1; AU1259800A; JP2002524756A; BR9906951A; EP1045779B1

Description

OPTICAL SENSOR The invention relates to an optical sensor for the detection of humidity on a surface.

Prior Art Optical sensors of the above type are known. These serve, for example, to control a light and/or windscreen wiper system of motor vehicles. Here, an acquisition of data takes place essentially according to an optoelectronic principle. In it, light is coupled in from the visible zone or the infrared zone from the inner side of the windscreen into them. The light is reflected on the non-moistened outer surface and reaches a receiver. In order to increase the degree of effectiveness, the irradiation takes place so that total reflection occurs on the outer side. The total reflection is disturbed by means of moistening the outer surface with water. All known solutions have this in common, that the coupling S. in and coupling out of the electromagnetic rays takes place on points spatially clearly S* 15 removed from one another and that the sensor element and the evaluating technology are S* located in the same housing.

An error-free detection of signals can take place if the optical sensor is housed in the area of the windscreen, which is cleaned by the windscreen wiper system. For this reason, the sensor must, in vehicles of many types, be positioned at distances of up to cm from the upper edge of the windscreen. The disadvantage here is that the sensor .housing is in the driver's range of vision and, because of its lack of transparency has a ":disturbing effect. Miniaturising is not possible as, for the detection of moisture at the right time, for example through rain, which is setting in, a detection zone of approximately 4 to 2 cm 2 is necessary.

SUMMARY OF THE INVENTION According to the present invention there is provided an optical sensor for detecting moisture on a surface, in particular a vehicle windscreen, including at least one transmitter and at least one receiver for electromagnetic waves, said surface being arranged in a detection zone between said at least one transmitter and said at least one receiver, wherein moistening of said surface in said detection zone effects a signal change, wherein said optical sensor includes a mono-mode or multi-mode light-guiding element in which said electromagnetic waves are guided bidirectionally into and out of said detecting zone, a Sretroreflector being positioned in said detection zone in such a way that it guides said I HIAC,l 1293 jpoc. I electromagnetic waves reflected from said surface, back to the surface, and from there to said light-guiding element.

Advantages of the Invention The optical sensor according to the invention has the particular advantage that the detection zone need not be arranged in the direct vicinity of the evaluating electronics.

Because the light between the at least one transmitter and the at least one receiver is led bidirectionally over a light-guiding element to the detection zone, a retroreflector being arranged in the detection zone, the detection zone can be situated at a distance from the io transmitter or receiver. The reflection of the sensor signal takes place on retroreflector, which is made preferably of transparent material. The sensor components, which cannot be constructed from a transparent material, in particular the transmitter and the receiver can, in a preferred application, only be arranged outside of the driver's field of vision. By this means, the optical embodiment of the sensor, in particular in its application as rain sensor S* 15 in motor vehicles, can be constructed so as to be less conspicuous. Furthermore, a common coupling in and coupling out of light results.

Advantageous embodiments for the light-guiding element are mono- or multimode optical wave guides of glass or plastic, in single or bundled form. In addition, plates or appropriately-formed bodies of glass or plastic which are so formed that they can o* 20 guide light. For the optimising of the light guidance, it is advantageous to apply a coating onto the light-guiding element which possesses a refractive index of at least some percent less than the light guiding element. By this means, the total reflection necessary for the light guidance does not take place on the surface of the light-guiding element, but on the bounding surface between the coating and the core material of the light-guiding element.

Further, the bidirectional guidance of light over common or separated optical fibre waveguides which are arranged one alongside another or one above another, takes place.

For the coupling in of the light beam from the light-guiding element into the windscreen and vice versa, a coupling element is planned which can preferably be designed in one piece with the light-guiding element. As a result, the ray of light will be deflected in such a way that it meets the bounding surface of the surface with the critical angle of the total reflection. Advantageous embodiments can be elbows, prisms or a roughened underside of the light-guiding element.

The reflection of the ray of light takes place, advantageously, by means of prismatic reflectors. These can preferably be arranged as microstructures with dimensions 08/10/02.all 1293.spec,2 -3of between 2 pm and 100 upm in circular segments or in strips. Instead of a prismatic reflector, a reflecting colouring substance or glass balls embedded in plastic can also be used. If a transparency is not necessary the prisms can be preferably replaced by mirror surfaces, in particular through concave mirror segments which focus the ray of light onto the coupling out point.

Additionally, the reflection can be realised by means of a hologram placed on the screen or, for example, adhered in the windscreen in the form of film. By this means, a mechanical protection of the hologram results and the inner surface of the windscreen need not be adhered to. Other than this, the hologram film on the surface of the windscreen can o0 cause no light reflection, resulting in it being less visible for the driver and consequently less disturbing.

A further possibility exists in the constructing of the adhesive film in the windscreen in an appropriate position as a hologram itself It is further of advantage that Sthis principle can be used in easily modifiable form for the detection of various substances, 15 as liquid, aerosol, in solution or in gaseous form. By this means a substance is brought into the detection zone which reacts in the presence of the measurement substance with the changing of the refractive index or the colour. The resulting refraction, absorption or reflection of the ray of light in the detection zone leads to a signal change which can be S. registered in the receiver. In this embodiment, retroreflectors and the bearers of the 20 sensitive substance can be preferably constructed as a component.

It is further advantageous that, by means of the spatial separation of electronics and retroreflector, a damaging influence of the measurement substance on the electronic components can be avoided, as contact with the measurement substance takes place only over the detection zone. The material of the bearer can preferably be of glass or plastic.

Essential here is that this body have a surface on which total reflection results.

The construction of the invention makes it possible that in the range of the primary data acquisition, markedly fewer components need be present. For this reason, a greater variation range of the sensor forms and dimensions is also given.

3o Drawings The invention will be described in more detail in terms of embodiments with the aid of drawings belonging to them. Shown are: Vigure 1 a schematic total view of the arrangement of an optical sensor on the windscreen of a motor vehicle; 08/1/.all 1293.spec,3 -4- Figure 2 an enlargement of a detail according to Figure 1; Figure 3 a further application of the optical sensor; Figures 4a to 4c various embodiments of a coupling element; Figures 5a and 5b various embodiments of a prism-retroreflector; Figure 6a and 6d various embodiments of the retroreflector and Figure 7a and 7b various embodiments of the light guide.

Figure 8a and 8b section and plan view of a windscreen in the detection zone.

Description of the Embodiments io Figure 1 shows in a schematic total view the arrangement of an optical sensor on a windscreen 12 of a vehicle. Here a retroreflector 10 and a light-guiding element 18 are mounted on the inner side of the windscreen 12 by means, for example, of adhesion. The surface of the outer side of the windscreen 12 on which light is reflected in a way to be described defines a detection zone. A housing 14 for electronics which comprise at least 15 one transmitter 13 and at least one receiver 15 is situated spatially separated from the retroreflector 10 and is consequently drawn into the visual range of the driver. The electronics are integrated, for example, in the foot of an interior rear vision mirror.

Figure 2 shows, in a schematic partial section, the optical sensor as rain sensor on the windscreen 12 of a vehicle. The elements of the sensor, the light-guiding element 18 20 and the retroreflector 10 are positioned on the inner side of the windscreen 12. The lightguiding element 18 guides the light generated from at least the one sensor, over the coupling element 20, the light then being diverted in such a way that at least the critical angle of the total reflection is reached on the outer glass bounding surface. The light is then returned over the prismatic retroreflector 10 and over the outer surlace I i o the screen I 1 and enters again, via the coupling element 20, the light-guiding element 18 and is directed from it to at least one receiver 15. If the detection zone 16 is moistened by a fluid an increase of the refractive index results, leading to a decrease in the intensiveness of the reflected light ray on the receiver 15, as the total reflection is absent. The present embodiment enables the carrying out of the signal processing spatially separated from the detection zone 16.

Figure 3 shows, in a partial sectional view, a slightly modified embodiment which can be used for the detection of various kinds of substances. The guiding of the light waves takes place in the same way as in the embodiment described for Figure 2. The detection zone 16 is coated here with a sensor active substance 24. The presence of a measurement substance, which preferably exists as a fluid, aerosol, in solution or in a gaseous form can lead to a change of the refractive index or the colour in the detection zone 16. This effect can be achieved, for example, via a chemical reaction or a complexing. From this, a change in intensity of the reflected ray of light on the receiver results. The retroreflector 10 and a bearer 22 of the sensor material can here being combined into one unit.

Figures 4a to 4c show in a schematic sectional view three different embodiments of the coupling element 20. The light guided parallel to the surface of the bearer 22 or to the windscreen 12 via the light-guiding element 18 is therefore reflected in such a way that at least the critical angle is achieved on the outer bounding surface.

Alternative embodiments are an elbow 26 (Figure 4a), a prism 28 (Figure 4b) or a structuring 30 of the light guide 18 (Figure 4c), through roughening or an embossing of grid-like structures. This structuring can be brought onto the lower or upper side of the light guide end, and in such a way that it is turned toward the bearer 22 or the windscreen 15 12, whereby losses in light intensity will have to be taken into account.

SFigures 5a and 5b show, in perspective views of the retroreflector 10, two alternative embodiments. In Figure 5a the prisms 40 are arranged in circular segments necessary for reflection. Figure 5b shows a strip arrangement of the prisms 42. The dimension of these microstructures (prisms) can be between 2 rtm and 100 pnm.

*ee* 20 In Figures 6a to 6d further alternative embodiments of the retroreflector are represented in schematic sectional views. The Figures 6a and 6b show mirror segments 32 °and concave mirror segments 34 which focus light on the coupling out point. The mirror surfaces must here be at least partially metallised and therefore this embodiment is limited in that no transparency is required. For the reflection of the ray of light, glass balls 36 embedded in a plastic or a reflective colouring material can be used, as is shown schematically in Figure 6c. In Figure 6d, the reflection takes place via a schematically represented hologram 38 which is applied as a plate, film or flat pane ol'glass.

In Figures 7a and 7b two alternative embodiments of the light guide 18 are depicted. The bidirectional conduction of the light guide, which is reflected, for example, on the schematically represented circular segment shaped retroreflector, can take place in two ways. Either there are separate light guides 18 which are arranged next to or above one another (Figure 7a) or the ray of light is directed via a common light guide to the coupling element 20, a beam splitter 50 being arranged in front of the transmitter 13 or the receiver ii.1 Io12.,ill l 29. In Figure 8a a windscreen 12 is schematically depicted in sectional view and in Figure 8b a windscreen 12 is schematically represented in plan view.

If an infrared light (IR) is to be used for detection, then the IR-opaque adhesive film adhered in the windscreen 12 must be recessed in the detection zone 16 in order to guarantee that the detection light passes through.

In the windscreen 12, in particular in one part of this recess 42 the hologram 38 is situated. The remaining part remains empty or is filled with IR-opaque adhesive film.

The IR light enters the windscreen 12, is let in the IR transmissive area of the recess 42, totally reflected on the surface of the windscreen 12, reflected on the hologram 38 in the i) entry direction and, following another total reflection on the surface of the windscreen 12, is led through the 1R transmissive area of the recess 42 into the receiver 1 08/10/02.all 1293.spec.i

Claims

1. An optical sensor for detecting moisture on a surface, in particular a vehicle windscreen, including at least one transmitter and at least one receiver for electromagnetic waves, said surface being arranged in a detection zone between said at least one transmitter and said at least one receiver, wherein moistening of said surface in said detection zone effects a signal change, wherein said optical sensor includes a mono- mode or multi-mode light-guiding element in which said electromagnetic waves are guided bidirectionally into and out of said detecting zone, a retroreflector being positioned in said detection zone in such a way that it guides said electromagnetic waves reflected from said to surface, back to the surface, and from there to said light-guiding element.

2. The optical sensor according to Claim I, wherein said lig ht-guidiMn element is a light wave guide which consists especially ol'glass or plastic. 99*

3. The optical sensor according to Claim 2, wherein said light-guiding element has a single light wave guide or a bundle of light wave guides. .I 15

4. The optical sensor as claimed in any one of the preceding claims, wherein said light-guiding element is a plate or another appropriately formed body, which can guide light.

The optical sensor as claimed in any one of the preceding claims, wherein said light-guiding element has separated wave guides for bidirectional conduction 9•o.9 20 of said electromagnetic waves. o

6. The optical sensor according to Claim 1, wherein said retroreflector is *i constructed of prisms.

7. The optical sensor according to Claim 1, wherein said retroreflector is constructed of mirror segments, or concave mirror segments.

8. The optical sensor according to Claim 1, wherein said retroreflector is constructed of a hologram consisting of a plate or a film.

9. The optical sensor according to Claim 1, wherein said retroreflector is constructed of glass balls embedded in plastic or of a reflective colouring material.

The optical sensor according to any one of Claims 6 to 9, wherein the arrangement of the reflecting signals of said retroreflector is circular or strip-shaped.

1 1. The optical sensor according to any one of Claims 6 to 10, wherein said retroreflector is formed of optically transparent material.

12. The optical sensor according to any one of Claims I to 5, wherein said light-guiding element features a coupling element by means of which a diversion of the 08/110/0 2 .all 1293 chn.' -8- electromagnetic waves onto the sensor range takes place.

13. The optical sensor according to Claim 12, wherein said coupling element consists of an elbow, prisms or is constructed by means of a structuring of the surface of said light-guiding element.

14. The optical sensor according to Claim 1, wherein a sensor active substance is brought into the detection zone which changes, in the presence of a measuring substance, its refractive index or colour.

The optical sensor according to Claim 1, wherein said coupling element and the said light-conducting element form a component.

16. The optical sensor according to Claim 14, wherein said retroretlector and a bearer of said substance form a component.

17. Use of an optical sensor according to any one of Claims I to 13, as a rain sensor on vehicles.

18. Use of an optical sensor according to any one of Claims 14 to 16 as a 1 15 sensor for various kinds of substances existing as fluid, aerosol, in solution or in a gaseous form.

19. The optical sensor according to Claim 1, wherein said retroreflector is arranged inside said windscreen.

20. The optical sensor according to Claim 8, wherein said hologram is 20 arranged inside said windscreen. OS

21. The optical sensor according to Claim 20, wherein said film is an "i adhesive film arranged inside said windscreen and is at least partially itself constructed as a hologram. DATED this day of October, 2002 ROBERT BOSCH GMBH By their Patent Attorneys: CALLINAN LAWR1E I s!-4 I( 'C 12 1,95 c I