DE19951831A1 - Sensor for the detection of drops of moisture and / or dirt particles on a pane and method for operating such a sensor - Google Patents

Abstract

The invention relates to a sensor (1) for detecting humidity drops (7) and/or dirt particles (8) on a glass surface (2), especially a rear window of a motor vehicle. The sensor (1) is provided with at least one emitter (3) for emitting optical beams (4) onto the glass surface. The sensor is also provided with at least one detector (10) for receiving at least a portion of the beams (9) that are reflected by the humidity drops (7) and/or the dirt particles (8) and for generating a receiving signal (11) which depends upon the received beams (9). The sensor (1) is further provided with evaluation means for evaluating the receiving signal (11). The invention also relates to a method for operating such a sensor (1). The aim of the invention is to reduce fabrication costs for such a sensor (1) and to enable digitalisation of the receiving signal (11) of the sensor (1) with a sufficiently high resolution and dynamic. The or each emitter (3) emits optical beams (4) in a temporally successive manner, whereby said beams have different luminous intensities. The evaluation means allocate the luminous intensities of the emitted optical beams to the receiving signal (11). The luminous intensities are considered during evaluation of the receiving signal (11).

Description

The present invention relates to a sensor for Detection of moisture drops and / or dirt particles on a window, especially on a rear window Motor vehicle. The sensor has at least one emitter for emitting optical rays onto the pane and at least one detector for receiving at least one Part of that from moisture drops and / or from Dirt particles reflected rays. The detector generates a receive signal that is dependent on the received rays. The sensor also points Evaluation means for evaluating the received signal.

Such a sensor works according to an optical one Measuring principle. When using the sensor for the detection of Drops of moisture and / or dirt particles on the Rear window of a motor vehicle, is the sensor preferably on the inside of the rear window in the Wiping area of a wiper arranged. He can Rain, snow, dust and a. Detect on the rear window.  

With the sensor, this is from the or each emitter light emitted from the inside through the pane onto the Headed outside. The or each detector observes the Light exit surface on the pane. If on the Outside of the disc dirt particles or If drops of moisture precipitate, they scatter it emitted light and at least partially reflect it on the or each detector. The or each detector generates a receive signal that is dependent on the Illuminance of the received light.

The or each emitter is, for example, as a luminescent diode (LED) and the or each detector as a photodiode trained depending on the received optical rays a photo stream as a received signal generated. By evaluating the time course and the Amplitude of the received signal can depend on the type of Rain on the disc. The Analysis of the received signal is based u. a. on Empirical values. For example, it means continuous slow decrease in the amplitude of the received signal from an amplitude maximum over a longer period of time (several minutes) for dirt on the rear window there. Likewise indicates a continuous slow rise of the amplitude value of the received signal to moisture the disc. Depending on the type of Precipitation on the disc can then take appropriate actions triggered to remove the precipitation. For Removal of moisture drops can be a Wipers are activated to eliminate Dirt particles can also Windscreen washer can be activated.

The received signal is preferably with a Microprocessor evaluated. That presupposes that  Received signal is in digital form. That's it for known in the art, an A / D converter to use. Inexpensive A / D converters, however, have one relatively low resolution and dynamic range required for the Use in sensors of the type mentioned at the beginning is too low is. A / D converter with higher resolution and dynamics, those for use in the sensors of the aforementioned Kind would be sufficient, but are quite expensive and would be too a considerable increase in the price of sensors for the detection of Drops of moisture and / or dirt particles.

In the sensors of the type mentioned at the outset, A / D Transducers with a relatively high resolution and dynamics needed so that even minor changes in the Received signal can be detected. As a disruptive factor affects the received signal especially that Ambient light that is next to that of the Drops of moisture and / or dirt particles reflected Light is received by the or each detector and too leads to a relatively large offset of the received signal. The Changes in the received signal due to precipitation are on the disc in relation to the offset of the Received signal very low. This applies in particular to Drops of moisture as they become even less Changes in the received signal result as dirt particles. For this reason, the received signal must be in the sensor with high dynamics and resolution.

Hence the object of the present invention: digitization of the received signal from a sensor Detection of moisture drops and / or dirt particles of the type mentioned with a sufficiently high Resolution and dynamics allow for reliable Detection and differentiation of moisture drops and Allow dirt particles on a disc without  however, thereby increasing the manufacturing costs. To achieve this object, the invention suggests from the sensor for the detection of moisture drops and / or dirt particles of the type mentioned at the beginning, that the or each emitter is consecutive optical rays with different light intensities sends out, the evaluation means the received signal Assign light intensities to the emitted optical beams and take into account when evaluating the received signal.

To the optical rays with different light intensities the or each emitter will be able to send out different services operated. A higher one Luminous intensity of the emitted optical rays leads to a higher luminous flux and thus a higher one Illuminance of the rays received by the Detector can then be evaluated (cf. Kuchling, Horst, Taschenbuch der Physik, 11th edition, published by Harm Deutsch, 1988, pp. 385 to 394). With optical rays with one high light intensity can make minor changes to the Received signal due to drops of moisture on the Disc can be detected particularly well. With optical In contrast, beams with low light intensity can be slow Changes in the received signal due to Dirt particles on the glass are particularly well detected become. The sensor according to the invention thus enables particularly reliable detection and differentiation from Drops of moisture and dirt particles on the pane.

In the sensor according to the invention, the Digitization of the received signal necessary resolution and Dynamics significantly reduced because the useful shares in the Received signal, d. H. the changes in the received signal due to moisture drops and / or from Dirt particles on the disc, in relation to that  Offset of the received signal are significantly stronger.

According to an advantageous development of the present Invention it is proposed that the or each emitter alternating optical beams with a high and a emits low light intensity. This can cause a sufficiently reliable detection and differentiation from Drops of moisture and / or dirt particles on the Disk can be achieved and the additional circuitry for the sensor according to the invention is limited.

The optical rays with a high light intensity and the need optical rays with a low light intensity not be broadcast for the same length of time. Rather can at the time for which optical rays with a high or with a low light intensity, the Fact taken into account that Drops of moisture on a pane relatively quickly knock down and only for a relatively short period of time are detectable, whereas dirt particles in the Usually slow over a long period of time Knock down disk. Therefore, according to a preferred Embodiment of the present invention proposed that the or each emitter is at least 90% of the total Broadcasting time optical rays with a high light intensity sends out. During the remaining 10% of the airtime then optical rays with a low Luminous intensity emitted. Practical tests have shown that that particularly good detection and Get distinction results when optical Beams with a high light intensity for about 950 ms (95% the broadcasting time) and then optical rays with a low light intensity can be emitted for 50 ms.

According to another advantageous development of the  The present invention proposes that the sensor has two emitters, the one emitter such is arranged that a drop of moisture and / or part of the rays reflected by dirt particles predominantly scattering forward on the or each detector hits, and the other emitter is arranged such that one of moisture drops and / or dirt particles reflected part of the rays predominantly backscattering hits the or each detector. Rapidly occurring and disappearing changes the received signal (e.g. due to drops of moisture on the disc) can be particularly well with the Observe and assess forward scatter. Slow Changes in the received signal (e.g. due to Dirt particles on the pane) can be particularly bad well with a combination of the reverse and the Forward scatter can be observed and assessed.

The sensor advantageously has a detector. If if the sensor has more than one emitter, it receives it Detector the emitted by all emitters and to the Drops of moisture and / or the dirt particles reflected optical rays. To do this, it is necessary that the rays emitted by the individual emitters are identifiable. It is conceivable that the individual Emitter optical rays are staggered in time send out. Alternatively or additionally, the Properties of those emitted by the individual emitters optical rays can be modulated differently.

According to a preferred embodiment of the present Invention, it is proposed that the emitter by one Normal of the disc rotated by 180 ° relative to each other are arranged and the detector around the normal of the disc by <45 ° relative to the predominantly backward scattering  receiving emitter is arranged twisted, the Emitter and the detector on the same measuring range are aligned. The emitters and the detector must do this be arranged that optical emitted by the emitters Radiate neither from the outside nor from the inside the disc properly, d. H. not on drops of moisture and / or dirt particles, reflected on the detector become. In addition, none should be properly reflected Rays fall on surfaces within the measuring range of the sensor and are observed by the detector.

The detector is advantageously around the normal of Disc at 40 ° relative to the predominantly backward scattering receiving emitter twisted. Let it through particularly good detection and Achieve differentiation properties of the sensor.

According to another advantageous development of the The present invention proposes that the emitter and the detector at an angle of <45 ° relative to that Normals of the disc are arranged inclined. The emitters and the detector are advantageously in an angle of 70 ° relative to the normal to the disc arranged. Leave with such a trained sensor particularly good detection and Get differentiation results.

According to another advantageous development of the The present invention proposes that the emitter emit optical rays of different wavelengths, the evaluation means the wavelengths of the received signal assign the emitted optical beams and at Consider evaluating the received signal. With optical Rays in what is visible to the human eye  Wavelength range, the optical differ Rays with different wavelengths through their different color from each other. When using a Detector for receiving the emitted by all emitters and on moisture drops and / or dirt particles reflected optical rays, can be received Rays as part of the evaluation of the received signal assigned to individual emitters.

According to a further preferred embodiment of the The present invention proposes that the or each emitter first optical components to influence the beam path of the emitted optical beams and the or each detector has second optical components Influencing the beam path of the reflected rays assigned. This embodiment of the invention Sensor allows the emitters and detectors to be freely located in the Arrange sensor. With the help of the optical components can match the optical beams from the emitters to appropriate ones Places for decoupling the rays or the reflected optical rays from suitable locations for coupling the Beams are directed to the detectors.

Advantageously, the first optical parallelize Components the emitted optical rays. The one from the Emitters emitted divergent rays are at Entry into the first optical component in parallel directed. Advantageously, the second optical bundle Components the received rays on the or each Detector. That of the second optical component received optical rays are exited from the second optical component on the detector, in particular bundled on its light-sensitive surface.

The optical components are preferably light guides  educated. The coupling surface of the first light guide and is the decoupling surface of the second light guide preferably aspherical.

According to yet another advantageous development of the The present invention proposes that the sensor with a contact surface on the inside of the pane rests, the bearing surface having a protruding edge has an elastically resilient material and the Sensor is pressed against the window. Advantageously is the sensor by means of a spring element against the Disk pressed. The sensor is, for example, in one Rear wiper motor module or in a third Integrated brake light. The spring element can on the Motor module or the housing of the third brake light support and so the sensor against the inside of the disc to press. With the help of the elastic edge on the Contact surface of the sensor can be uneven on the inside the disc balanced and a full-surface edition of the Sensor on the disc can be guaranteed. The measuring room of the sensor that is inside the elastic edge between the sensor and the inside of the disc can be so protected from dust and moisture.

The sensor advantageously has an angled opening on which the from the contact surface of the sensor, from the Inside of the disc and from the elastic edge limited measuring room with the surroundings of the sensor. The measuring room can be ventilated via this opening without that moisture or dust can enter.

Finally, according to a preferred embodiment, the Present invention proposed that the or everyone Emitter is designed as a luminescent diode (LED). Of It is further proposed that the or each detector  is designed as a photodiode. When using a The photodiode is the received signal as a photocurrent educated.

A preferred embodiment of the present In the following, the invention is explained in more detail with reference to the drawings explained. Show it:

FIG. 1 is a sensor for detecting drops of moisture and / or dirt particles according to a preferred embodiment, in section; and

Fig. 2 shows the sensor of Fig. 1 in a view from below.

In FIG. 1, a sensor for the detection of moisture drops and / or dirt particles on a pane is designated in its entirety by reference number 1 . The window is designed as a rear window 2 of a motor vehicle. The sensor 1 lies with a contact surface on the inside of the window 2 in the wiping area of a window wiper (not shown). The bearing surface has a projecting edge 6 made of an elastically flexible material. The sensor 1 is pressed against the pane with the aid of a spring element (not shown). The sensor 1 is integrated, for example, in a third brake light or in a rear window wiper motor module. The spring element can be supported on the housing of the brake light or on the motor module.

The sensor 1 has two emitter 3 a, 3 b for emitting optical beams 4 to the rear window. 2 The emitter 3 a, 3 are formed as light emitting diodes (LEDs) b. The optical beams 4 are coupled into a first optical component 15 . A coupling surface 16 of the first component 15 is designed aspherically. As a result, the diverging beams 4 are directed parallel when they enter the first optical component 15 . The rays 4 emerging from the first optical component 15 first pass through an air gap 5 , hit the inside of the rear window 2 and pass through it. If there are no drops of moisture and / or dirt particles on the window 2 , the rays 4 emerge on the outside of the rear window 2 again.

In the present exemplary embodiment, however, there are moisture drops 7 and / or dirt particles 8 on the outside of the rear window 2 . At least a part 9 of the of the emitters 3 a, 3 b 4 emitted optical beam is reflected at the moisture drops 7 and / or dirt particles or scattered 8. The reflected rays 9 are first coupled into a second optical component 17 and then coupled out of this onto a detector 10 of the sensor 1 . The detector 10 is designed as a photodiode. A coupling-out surface 18 of the second component 17 is aspherical. As a result, the rays 9 are focused on a photosensitive surface of the detector 10 when they exit the second optical component 17 . The optical components 15 , 17 are preferably designed as light guides.

Of the emitters 3 a, 3 b 4 emitted beams are coupled out at an angle of 70 ° to the normal 19 of the disc 2 from the first optical device 15 °. Likewise, the rays 9 reflected by the moisture drops 7 and / or dirt particles 8 are coupled into the second optical component 17 at an angle of 70 ° to the normal 19 of the pane 2 . The two emitters 3 a, 3 b are arranged opposite one another (cf. FIG. 2). The emitter 3 a is arranged such that the moisture from the droplets 7 and / or the dirt particles 8 9 reflected beams meet predominantly forward-scattering to the detector 10th The other emitter 3 b is arranged in such a way that the rays 9 reflected by the moisture drops 7 and / or the dirt particles 8 predominantly strike the detector 10 in a backwards scattering manner. The detector 10 is rotated by the normal 19 of the disk 2 by 40 ° to the predominantly backward scattering emitter 3 b.

The detector 10 generates a received signal that is dependent on the quantity and the light intensity of the received beams 9 . The received signal is designed as a photo stream. The time course and the amplitude of the received signal are evaluated in evaluation means (not shown) of the sensor 1 . The sensor 1 can detect rain, snow, dust, insects and others on the rear window 2 and differentiate them from one another.

Depending on the type of precipitation 7 , 8 detected on the rear window 2 , suitable measures for removing the precipitation 7 , 8 are initiated. A windshield wiper can be activated to remove moisture drops 7 , and the windshield washer system can also be activated to remove dirt particles 8 .

In order to enable digitization of the received signal from sensor 1 with a sufficiently high resolution and dynamic range, without thereby increasing the manufacturing costs for sensor 1 , emitters 3 a, 3 b transmit successively different powers in time, so that they emit optical beams 4 emit with different light intensities. The evaluation means assign the light intensity of the emitted optical beams 4 to the received signal. When evaluating the received signal, the changing light intensities of the optical beams 4 are taken into account. The emitters 3 a, 3 b alternately emit optical rays 4 with a high light intensity for a period of approximately 950 ms and then emit optical rays 4 with a low light intensity for a duration of approximately 50 ms. This takes into account the fact that drops of moisture 7 deposit relatively quickly on a pane 2 , whereas dirt particles 8 generally settle slowly on the pane 2 over a longer period of time.

With the help of optical rays 4 with a high light intensity, small but rapid changes in the received signal due to drops of moisture 7 on the pane 2 can be detected particularly well. With optical beams 4 with a low light intensity, however, slow changes in the received signal due to dirt particles 8 on the pane 2 can be detected particularly well.

It is also contemplated that the emitters 3 a, 3 b 4 optical beams emit different wavelengths. The evaluation means allocate the wavelengths of the emitted optical beams 4 to the received signal of the detector 10 and take the wavelengths into account when evaluating the received signal. Because of the different wavelengths of the beams 4 , the received beams 9 can be used by the individual emitters 3 a; 3 b can be assigned.

In the case of the sensor 1 , the resolution and dynamics necessary for digitizing the received signal are decisively reduced, since the useful components in the received signal, ie the changes in the received signal due to precipitation 7 , 8 on the disk 2 , are significantly increased in relation to the offset of the received signal are. This enables the use of conventional A / D converters with a relatively low resolution and dynamic range for digitizing the received signal in the evaluation means of sensor 1 without sacrificing the detection and differentiation properties of sensor 1 .

Claims (20)

1. Sensor ( 1 ) for detecting drops of moisture ( 7 ) and / or dirt particles ( 8 ) on a window ( 2 ), in particular on a rear window of a motor vehicle, with at least one emitter ( 3 a, 3 b) for emitting optical rays ( 4 ) on the pane ( 2 ), at least one detector ( 10 ) for receiving at least some of the rays ( 9 ) reflected by moisture drops ( 7 ) and / or dirt particles ( 8 ) and for generating a reception signal ( 11 ) as a function of the received beams ( 9 ) and with evaluation means for evaluating the received signal ( 11 ), characterized in that the or each emitter ( 3 a, 3 b) successively emits optical beams ( 4 ) with different light intensities in succession, the evaluation means giving the received signal ( 11 ) assign the light intensities of the emitted optical beams ( 4 ) and take them into account when evaluating the received signal ( 11 ). 2. Sensor ( 1 ) according to claim 1, characterized in that the or each emitter ( 3 a, 3 b) alternately emits optical beams ( 4 ) with a high and a low light intensity. 3. Sensor ( 1 ) according to claim 2, characterized in that the or each emitter ( 3 a, 3 b) emits at least 90% of the total transmission time optical rays ( 4 ) with a high light intensity. 4. Sensor ( 1 ) according to one of claims 1 to 3, characterized in that the sensor ( 1 ) has two emitters ( 3 a, 3 b), the one emitter ( 3 a) being arranged such that one of drops of moisture ( 7 ) and / or part ( 9 ) of the rays reflected from dirt particles ( 8 ) predominantly forward scattering strikes the or each detector ( 10 ), and the other emitter ( 3 b) is arranged such that one of moisture drops ( 7 ) and / or part of the rays ( 9 ) reflected by dirt particles ( 8 ) predominantly backscattering strikes the or each detector ( 10 ). 5. Sensor ( 1 ) according to one of claims 1 to 4, characterized in that the sensor ( 1 ) has a detector ( 10 ). 6. Sensor ( 1 ) according to claim 4 and 5, characterized in that the emitters ( 3 a, 3 b) are arranged rotated by 180 ° relative to one another about a normal of the disk ( 2 ) and the detector ( 10 ) about the normal the disc (2) to <45 ° relative to the most backward scattering receiving emitter (3 b) is arranged rotated, wherein the emitter (3, 3 b a) and the detector (10) are aligned to the same measurement range. 7. Sensor ( 1 ) according to claim 6, characterized in that the detector ( 10 ) is rotated about the normal of the disc ( 2 ) by 40 ° relative to the predominantly backward scattering emitter ( 3 b) 8. Sensor ( 1 ) according to claim 7, characterized in that the emitters ( 3 a, 3 b) and the detector ( 10 ) are arranged inclined at an angle of <45 ° relative to the normal of the disc ( 2 ). 9. Sensor ( 1 ) according to claim 8, characterized in that the emitters ( 3 a, 3 b) and the detector ( 10 ) are arranged inclined at an angle of 70 ° relative to the normal of the disc ( 2 ). 10. Sensor ( 1 ) according to one of claims 4 to 9, characterized in that the emitters ( 3 a, 3 b) emit optical rays of different wavelengths, the evaluation means of the received signal ( 11 ) the wavelengths of the emitted optical rays ( 4 ) assign and take into account when evaluating the received signal ( 11 ). 11. Sensor ( 1 ) according to any one of claims 1 to 10, characterized in that the or each emitter ( 3 a, 3 b) first optical components ( 15 ) for influencing the beam path of the emitted optical beams ( 4 ) and the or each Detector ( 10 ) are assigned to second optical components ( 17 ) for influencing the beam path of the reflected beams ( 9 ). 12. Sensor ( 1 ) according to claim 11, characterized in that the first optical components ( 15 ) parallelize the emitted optical beams ( 4 ). 13. Sensor ( 1 ) according to claim 11 or 12, characterized in that the second optical components ( 17 ) focus the received beams ( 9 ) on the or each detector ( 10 ). 14. Sensor ( 1 ) according to one of claims 11 to 13, characterized in that the optical components ( 15 , 17 ) are designed as light guides. 15. Sensor ( 1 ) according to claim 14, characterized in that the coupling surface ( 16 ) of the first light guide ( 15 ) and the coupling surface ( 18 ) of the second light guide ( 17 ) is aspherical. 16. Sensor ( 1 ) according to any one of claims 1 to 15, characterized in that the sensor ( 1 ) rests with a support surface on the inside of the disc ( 2 ), the support surface having a projecting edge ( 6 ) made of an elastically flexible material has and the sensor ( 1 ) is pressed against the disc ( 2 ). 17. Sensor ( 1 ) according to claim 16, characterized in that the sensor ( 1 ) is pressed by means of a spring element against the disc ( 2 ). 18. Sensor ( 1 ) according to claim 16 or 17, characterized in that the sensor ( 1 ) has an angled opening, which from the contact surface of the sensor ( 1 ), from the inside of the disc ( 2 ) and from the elastic edge ( 6 ) connects the limited measuring room with the surroundings of the sensor ( 1 ). 19. Sensor ( 1 ) according to one of claims 1 to 18, characterized in that the or each emitter ( 3 ) is designed as a luminescent diode (LED). 20. Sensor ( 1 ) according to one of claims 1 to 19, characterized in that the or each detector ( 10 ) is designed as a photodiode.