Abstract:
A detector of stains on a transparent plate surface is arranged on an internal surface of the plate and includes an emitter for emitting a modulated light signal towards the inside of the plate and a receiver for receiving the signal after it has been reflected on an external surface of the plate. An optical unit made with a material having an index substantially higher than the plate, is arranged on the internal surface of the plate. The optical unit is made up of at least three faces returning the light signal and an interface with the internal surface of the plate through an optical coupler. A deflector deflects the signal from the emitter toward the plate and from the optical unit towards the receiver. At least two reflections on the external surface of the plate are produced through the optical coupler without reflection on the internal surface of the plate.

Description:
BACKGROUND 
     The invention concerns a detector of stains on a plate surface transparent to visible rays, in particular, a motor vehicle window. 
     The invention concerns, more specifically, a detector of stains, for example liquid, on the surface of a transparent plate that has two opposite sides notably parallel, and an internal face and an external face defining an interior volume. 
     In this type of detector, an emitter is arranged on the internal face of the plate and emits a modulated light signal in the direction of the interior of the plate such that the signal penetrates the plate. While the signal hits one of the faces of the plate, the signal is reflected towards the interior of the plate if this face is in contact with the air or altered, that is to say, refracted, focalized, absorbed, diffused, etc., in the case where the face is in contact with the stains to detect. Stains are defined here to be all deposits having an aqueous component, such as rain, snow, frost, mud, etc. 
     This type of device also comprises a receptor arranged in a target zone of a face of the plate such that the signal that moves around in the plate, when it hits the target zone, is reflected and is received by the receptor. 
     Such detection devices allow, for example, controlling the activation of motor vehicle wipers when drops of water appear on the windshield. 
     As a function of the material of the windshield and the length of the electromagnetic signal wave, the angle of incidence of the modulated light signal is chosen in such a manner that the ray is reflected in the direction of the internal face of the windshield if the external face is in contact with the air at the level of the impact zone of the signal and in such a manner that the ray is at least partially refracted towards the exterior if the water or stain covers the impact zone of the external face. 
     If the ray is reflected, it will be guided to follow its route to the interior of the windshield, in the thickness of the glass, in order to be reflected several times by the internal and external faces of the windshield. In a place of the internal face that is on the trajectory of the signal, one has places for optical coupling means, the refraction index of which is such that the signal is refracted across the internal face of the windshield in order to be transmitted to an adapted receptor. 
     In this way, if the receptor captures a signal higher than a determined threshold, no stain at the level of the impact zones of the signal against the external face of the windshield is detected. On the other hand, if the receptor no longer receives a signal (for example, due to absorption, diffusion, or refraction), where if it receives a signal at a level notably higher (for example from focalizing), the presence of stains, for example, drops of water, are present on the exterior face of the windshield. 
     One has however noted that in such a unit, the signal received by the receptor was slightly higher. In order to augment the level of detection, in particular the detection of fine, small drops in small numbers, the number of reflections of the signal on the external face of the plate was multiplied by detecting the modulated light after having been reflected several times and alternatively on the external face and on the internal face of the plate. 
     This method&#39;s inconveniences are that it is particularly sensitive to the deposits of condensation on the internal face of the plate, imposing a relatively precise positioning of the emitter and receptor parts, and that it is particularly sensitive to the variations and imperfections of the thickness of the plate. 
     SUMMARY 
     The invention aims to eliminate these inconveniences by proposing a detector that is at the same time compact and likely to supply an adapted number of reflections on the face to survey, by exploiting the principle of total reflection. 
     More precisely, the invention concerns a detector of stains on the surface of a transparent plate that has two notably parallel, opposite sides, an internal face and an external face. Such a detector, arranged on the internal face of the plate, comprises means emitting a modulated light signal in the direction of the interior of the plate, and means receiving this signal after having been reflected on the external face of the plate, and an optical unit made with material having an index substantially higher than one and transparent to the radiance of the modulated light signal. The optical unit is placed on the internal face of the plate and is made up of at least two faces deflecting the light signal, in order to form a trajectory between the emission means and the receiving means, and from the bottom interface with the internal face of the plate across the means of optical coupling. Also planned: deviation means of the signal from the emission means, so that the signal reflects a first time on the external face of the plate according to a direction included in an initial incidence plane, and deviation means of the signal towards the receiving means so that the faces of deflection thus orient the signal successively towards the external face in at least one incidence plane notably not parallel in the initial incidence plane so that the trajectory of the light signal between the emission means and receiving means produce at least two reflections on the external face of the plate across the optical coupling means without reflection on the internal face of this plate. 
     Thus, the trajectory of the signal, between the emission and reflection means, is notably confined in the optical unit and in the volume of the plate situated opposite from the unit. 
     According to the specific modes of production of the invention: 
     the optical unit is, on the whole, outlined according to a parallelepiped rectangle having mainly a front face, an upper face, a rear face, two lateral faces, and a bottom face that interfaces with the plate; 
     the deflection faces are made up of a rear face, the upper face and the front face, or by the front face and the rear face, these two faces being inclined in order to make a deflection signal towards the plate; 
     the light signal penetrates the optical unit after deviation via an input face situated in the front face of the optical unit, and leaves from the front deviation optical unit on the receiving means via an output face situated in the front face while the number of reflection on the external face of the plate is even, and in the rear face when the number of reflections is odd; 
     the input and output faces of the unit form lenses, which can be coupled to an optical deflection in order to make up the deviation means; 
     at least one of the lenses is a convex lens comprising at least a non-spherical or spherical surface, where there is a Fresnel lens, the lenses can make up an integral part of the optical unit; 
     the optical coupling means are formed via a flexible layer of transparent material in the light signal, for example, silicon, the layer being compressed between the bottom face of the optical unit and the internal plate face; 
     an interferential filter is planned between the output face and the receiving means attached on the spectral band of the signal in order to eliminate light interference; 
     the optical unit and the optical coupling means are mass-colored to eliminate light interference; 
     a heating element is placed near or against one of the faces of the optical unit in order to eliminate condensation; thanks to the compactness of the detector the condensation is eliminated in an efficient and rapid manner; 
     the emitting means can be made up of an electro luminescent diode or by a photodiode, and the receiving means by a silicon photo detector cell, the emitting diode and the receiving cell can be placed near each other; 
     the emitting and receiving means are connected to a treatment unit formed on a printed circuit board in order to produce a modulation in amplitude for the signal of the emitting diode and a synchronous detection of the signal received by the photo detector cell; 
     the deflection faces are subjected to a treatment reflecting the light signal, for example, an aluminizing, where they are recovered with a layer of material reflecting the light signal; 
     the faces of the optical unit, other than the deflection faces and the interface, are covered with a material that absorbs the light signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will become clearer in the reading of the description of a method of production that follows, referring to the attached drawings that represent, respectively: 
     FIGS. 1 a  and  1   b  are schematic views in perspective and from the top of an example of a detector conforming to the specifications of the invention; 
     FIGS. 2 a  and  2   b  are schematic views in perspective of another production example of the detector according to the invention; and 
     FIG. 3 is a schematic view in perspective of a variance of the optical unit of the detector according to FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     Illustrated in FIG. 1 a is a plate  1  made of a transparent material that comprises two opposite faces internal  2  and external  3  notably in parallel. In the illustrated example, the plate  1  is notably flat, but the invention could be used in cases of a plate presenting curved shapes, as is the case, for example, for motor vehicle windows, and specifically the windshield. 
     According to the invention, the plate  1  carries a stain detector made up of an optical unit  9 , placed to the side of the internal face  2  of the plate  1 , and which is designed to detect the presence of stains, for example, drops of water, on the external face  3  on the plate. The optical unit according to this non-limiting example possesses a central symmetrical axis X′X. 
     The detector also comprises an emitter  4  and a receiver  5 . The emitter  4  is an electro luminescent diode that emits a light signal S in modulated light, close to infrared in the production example, but which can be in visible light in other examples. The receiver  5  is a silicon cell. 
     The light signal is emitted in the direction of the optical unit  9  that is created in the shape of a body in a plastic transparent material, for example, PMMA (polymethyl methacrylate plastic) with an average index equal to 1.48 in a shape of, on the whole, a parallelepiped rectangle, and with dimensions roughly equal to 25×25×5 mm 3 . The unit can be created in another plastic material (poly carbonate, polyethylene, etc.) or in glass. 
     This unit has faces outlined by dedicated planes, that is to say: 
     a front face  18  and a rear face  15 , in which are outlined, respectively, inclined input  6  and output  17  faces of the light signal S; these input and output faces  6 ,  17  being outlined in order to form, in relation to the normal axis X′X of the plate  1 , an angle equal to 45°; 
     an upper face  14  and a bottom face  16  interfacing with the plate  1  via a silicon layer  7 ; and 
     two lateral faces F 1  and F 2 , that complete the outline of the unit. 
     Between the bottom face  16  of the unit and the internal face  2  of the plate  1 , the silicon layer  7 , outlined according to the perimeter of the bottom face  16 , assures an optical continuity of the route of the light signal by creating a total refraction to the interface  16 - 2  or  2 - 16 —that is to say, respectively: bottom face  16  on internal face  2 , or internal face  2  on bottom face  16 —whatever the direction of the route of the signal S. The silicon layer  7  forms an adequate optical coupling means from the fact that its refraction index is close to that of the unit  9  and of the plate  1 : the possibilities of reflection of the signal are thus considerably reduced while the signal passes through the interface  16 - 2  or  2 - 16 . 
     The reflection of the signal on the deflection faces shows the total reflection in the measure where the angle of incidence on these value of penetration in the unit after deviation, stays higher than the refraction angle limit. 
     Put side by side respectively on the input and output faces,  6  and  17 , the optical deflections R 1  and R 2  are coupled to deviation lenses L 1  and L 2  allowing the orientation of the signal S in the optical unit to leave the emitting diode  4  and towards the receptacle cell  5  upon leaving from the unit. The lenses L 1  or L 2  form non-spherical revolution surfaces. The lenses can be stuck to the input and output faces of the unit or on the optical deflections, or make up an integral part of the optical unit via casting the unit ensemble, deflections and lenses. 
     The signal S follows a optical trajectory oriented in order to create an odd number of reflections on the external face of the plate  1 , three reflections  10 ,  11 ,  12  in the example, with four deflections in the optical unit  9  between the emitting diode  4  and photoreceptor cell  5 , being on the rear  15 , upper  14 , and front  18  faces. 
     After deviation via optical means L 1  and R 1 , the signal S orients itself according to the direction D 1  forming an angle roughly equal to 45° with the normal X′X, this direction being included in an initial incidence plane P 1  perpendicular to the plate  1 . 
     The trace of the plane P 1  is visible on the top view illustrated in FIG. 1 b . In relation to a normal N′N to the input and output faces,  6  and  17 , the plane P 1  forms an angle θ adapted, roughly equal to 13° in order to produce the wanted number of reflections on the external face of the plate and of deflections in the optical unit, respectively three and four in the example between the emitting and receiving means. 
     The signal S thus follows the following optical trajectory: 
     after the crossing of the interface  16 - 2  and a first reflection on the external face  3  of the plate  1 , in an elementary referenced zone  10 , followed by a crossing of the interface  2 - 16 , it is returned by the rear  15  and upper  14  faces, in order to be oriented, towards the external face ( 3 ) in an incidence plane P 2 , forming a angle notably equal to 2θ with the initial incidence plane P 1 ; 
     after the second crossing of the interface  16 - 2  and reflection on the external face  3  in an elementary zone  11 , and recrossing the interface  2 - 16 , it sustains successively two deflections on the upper face  14  and on the front face  18  and is reoriented in an incidence plane P′ 1 , notably parallel to P 1 ; 
     after the third crossing of the interface  16 - 2 , the signal then sustains a reflection on the elementary zone  12  of the external face  3  of the plate  1 , a crossing of the interface  2 - 16 , and leaves the unit  9  via the output face  17  before being deviated via the optical deflection R 2  and the lens L 2  towards the receiving cell  5 . 
     The deviation means allow the orientation of the signal S in such a way as to easily place the emitting and receiving means on a same support with the assistance of known means. 
     There is also a heating element  8  placed on the upper face  14  of the optical unit in order to eliminate condensation that can be formed. From the compactness of the optical unit, the condensation disappeared rapidly and the duration of the heating is greatly reduced. 
     In another example of production illustrated in FIG. 2 a , the input  6 ′ and output  17 ′ faces are placed on the front face  18 ′ of the optical unit  9 ′. The input  6 ′ and output  17 ′ faces are outlined in the front face  18 ′ and are outlined by a pentagon. 
     The other elements correspond to those described in reference to FIG. 1 a : the emitting means  4 , the detection means  5 , the optical coupling  7 , the rear  15 ′, bottom  16 ′, upper  14 ′, and lateral F 1  and F 2  faces, the optical deviation means L 1  and L 2 , and the heating element  8 ′. 
     The signal S follows an optical trajectory initially oriented to produce an even number of reflections on the external face of the plate  1 , four reflections  10 ′,  11 ′,  12 ′, and  13  in the production example, with six deflections in the optical unit  9 ′ between the emitting diode  4  and the photoreceptor cell  5 , on the rear  15 ′, upper  14 ′, and front  18 ′ faces. 
     As is visible on the top view of FIG. 2 b , the initial incidence plane Q 1  of the signal S in the optical unit makes an angle θ around 10° with a normal N′N to the front or rear faces,  18 ′ or  15 ′, in order to obtain the wanted number of reflections on the external face of the plate and of deflections in the optical unit, respectively four and six in the production example, between the emitting diode and the receiving cell. 
     The route of the optical signal S thus follows the round trip twice between the front  18 ′ and rear  15 ′ faces of the unit  9 ′, by creating at each time a reflection on the external face of the plate, and the total reflections on the rear, upper, and front faces, by following the parallel directions to the planes Q 1  and Q 2 , the plane Q 2  being that of the direction of the output. 
     The signal S is finally received by the photoreceptor cell  5  according to a direction of receiving D 2  of the plane Q 2  forming with the plate  1  an angle notably equal to that of the incidence direction. 
     In order to obtain a more compact unit, the distance between the lateral faces F 1  and F 2  can be reduced, as illustrated on FIG. 3, by reducing the front face  18 ″ of the unit  9 ″ to the minimum, with a common edge A of the input  6 ′ and output  17 ′ faces. In these conditions, the path of the signal S sustains two reflections, in  10 ″ and  11 ″, on the plate  1  and two deflections, on the rear face  15 ″ and the upper face  14 ″. The heating element  8 ″ also has a reduced surface. 
     The invention is not limited to the described and represented production examples. For example, the input and output faces can be formed from several spherical or non-spherical surfaces following the incidence and output angle desired, associated to one or several emitters and receptors. In another example, the lenses are Fresnel lenses, able to be associated to the optical deflections. In other examples, a non-spherical lens and a Fresnel lens can serve as the optical input and/or output means. Spherical revolution lenses can also be used. 
     In order to eliminate all light interference, the faces of the optical unit, other than the total reflection and bottom interface, are covered in a material that absorbs the light signal. In addition, in order to perfect the optical output, the total reflection faces can also be covered by a layer of material reflective to the light signal, or can be covered with a metallic layer, for example, via aluminizing. 
     In addition, in order to eliminate the light, light interference coming from other light sources can light the unit, for example, sun light, which can disturb the reception of the signal, an interferential filter attached onto the spectral band of the signal is placed between the output face and the receiving means of the signal. To achieve the same goal, it is also possible to mass-color with an attached colorant on the spectral band emitting means. 
     Moreover, thanks to the optical deviation means, one can place the emitter and receiver, as well as the heat resistant material, on the same support, which notably facilitates their linking to the common electronic treatment circuits necessary for their functioning. These electronic circuits can thus be easily produced on one treatment unit formed on a printed circuit board of reduced dimensions. Such a unit produces a modulation of amplitude for the signal of the emitting diode and a synchronous detection of the signal received by the photo detection cell. Moreover, it is possible to exchange the emitter and the receiver due to the reversible character of the light&#39;s route. 
     In addition, the front and rear deflection faces can be inclined to create a direct deflection of the signal towards the plate without reflection on the upper face.