FR2572495A1 - LIGHTING AND SIGNALING DEVICE, IN PARTICULAR FOR MOTOR VEHICLES - Google Patents

Abstract

THE INVENTION RELATES TO A LIGHTING AND SIGNALING DEVICE FOR MOTOR VEHICLES CONSISTING OF A REFLECTOR PROVIDED WITH A LIGHTING BULB, INCLUDING A REFLECTING SURFACE AT LEAST PARABOLOIDIC FOR REFLECTING THE FUNCTIONAL LIGHT UNDER THE FORM OF A LIGHTING BULB. PARALLEL, AND WHOSE OPENING IS CLOSED BY A FRONT GLASS WHOSE INTERIOR OPTICAL DISTRIBUTES THE LIGHTING BEAM TO THE EXTERIOR WITH A DETERMINED MAGNITUDE AND A CONVENTIONAL COLOR. ACCORDING TO THE INVENTION, AN INTERMEDIATE SCREEN ARRANGED BETWEEN THE BULB 2 AND THE FRONT GLASS 4 INCLUDES A TRANSPARENT INTERNAL LAYER OF DETERMINED COLOR 5 PROVIDED WITH A PLURALITY OF CONVERGENT LENSES 5 ARRANGED IN QUINCONCE, AN INTERMEDIATE LAYER OF OPAQUE 6 TRUNCONIC 6 COAXIALS WITH SAID LENSES 5, AND A COLORLESS TRANSPARENT EXTERNAL LAYER 7 WITH A PLURALITY OF LENSES CONVERGENT 7 COAXIAL TO THE PREVIOUS 5 AND OF THE SAME DIMENSIONS. APPLICATION TO THE AUTOMOTIVE INDUSTRY.

Description

X-'j. 2572495

  LIGHTING AND SIGNALING DEVICE, IN PARTICULAR

FOR AUTOMOTIVE VEHICLES.

  The invention relates to a signaling device and

  lighting, in particular for motor vehicles.

  The lighting and signaling lamps used on motor vehicles consist of a reflector

  supporting a light bulb, the opening of this reflection

  tor being obtained by a transparent window which is, in general, provided with an optical network determined according to the lighting or signaling to be produced and therefore following

the functions of the device.

  This lighting must also be of a color - for example red, amber or white - determined according to the function of the device (change of direction, rear light, brake or reversing light, etc ...) and it is known to tint generally for this purpose the glass of the

  device depending on the desired lighting color.

  When these lights are juxtaposed at the front or the rear of a vehicle, then, by this coloring

  of the glass, to lighting sets of unsightly appearance

  resulting from the direct juxtaposition of the various colors attributed to the various functions mentioned, these

  conventional colors getting married furthermore very difficult-

  those of the vehicle body.

  According to a known technique, this

  disadvantage by closing the reflector with a trans-

  colorless parentage and giving the functional color of the fire when the light bulb is lit, by a colored transparent balloon which completely encloses the bulb. This balloon interposed between the glass and the light bulb can also be provided with prisms so as to be able to give any structure to the transparent glass to meet all the style requirements concerning the

body profile.

  However, the disadvantage of its lights is that, when they are off, the ambient ambient lighting can make them appear lit, hence a cause of incident or traffic accident. For example, in very sunny weather, a light bulb may appear to be working

while this is not the case.

  Indeed, when an outside light ray strikes the transparent window, this ray passes through the window and, especially as it is grazing, by reflection on the reflector also through the colored transparent balloon to then come out through the window and give the illusion of lighting the device. Many solutions have been proposed to overcome this disadvantage. One of these solutions is to give a neutral color (smoked) to the glass, or to form on the inner surface of the window ribs or opaque or transparent crosslinking, or to weakly metallize this surface under vacuum in order to give it a mirror effect from the outside. But this solution, which significantly reduces the intensity of the incident light from outside, also attenuates the light emitted by the light bulb and it is then necessary to use a stronger bulb or improve the reflection characteristics of the light bulb. reflector to avoid an unpleasant decrease in the functional intensity. This solution also does not always give a very good appearance

outside the fire.

  Another solution of the same kind consists in depositing on the outer face of the colored balloon a thin layer of silver color which absorbs the external light. This solution certainly makes the colorless glass appear from the outside and almost completely eliminates the colored ghost, but still has the disadvantage of a sharp reduction.

  of light by the semi-transparent metallization in degrading

  In addition, the outer homogeneity of the crystal color of the fire pane extinguished by the more earthly vision of the metallization of the balloon reflected in the center of the pane. It then became common practice to employ a deflectable diaphragm mask suitably placed in relation to the transparent window of fire. This deflector comprises a series of transparent parts or diaphragms, each of which is arranged along the optical axis of a converging lens, of a refractive screen placed between the light source and the mask, or of the colored balloon

  forming itself this refractive screen. Each trans part

  parent of the mask has an extent limited to that which is necessary to leave practically all of a ray brush: luminous focused by the converging lens

  corresponding. The remainder of the mask is made of absorbent

  Bant the light, or opaque, and its outer surface facing the transparent window is optionally metallized as it has been stated for the two previous solutions. In this way, the proportion of the light emitted by the bulb of the fire has the maximum value, while the proportion of incident light coming from the outside which passes through the diaphragms of the mask is absorbed at the back in the enclosure relatively obscure -the reflector and can not cross the screen. But, this type of device also has the disadvantage of still having shades of external appearance of the transparent lens of the fire in the off state and can not meet the current requirements on the appearance, crystal of the lens of the fire requested , nor any style requirements regarding the profile of the

bodywork therefore fire.

  Variants of these devices are also obtained

  by combining all these solutions together in embodiments in which the light bulb is wrapped with the colored balloon, inside the reflector, by a coating or an opaque globe of which - only the cylindrical wall is provided with orifices

  or no diaphragms for the passage of light rays-

  colored functional only on the periphery of the balloon, and the front face of the coating or the globe turned vefs outside towards the transparent window occult the entire front of the colored balloon possibly having a reflective surface to match the appearance that the extinguished fire must present from the outside, this

  surface that can still be tinted according to the color of

  like carnations or lighting devices.

  However, this obscured area still can not give the required uniformity of appearance of the transparent window of the fire in the off state and causes, in addition, in addition, a lack of light in the fire lighting range in use due to the occultation of all / or part of the rays emitted from the front by the light bulb, which results in all cases to create a lack of homogeneity in the illuminating range of the fire resulting in particular by a shadow

carried on the optical axis.

  The object of the present invention is therefore to provide a lighting and signaling device which makes it possible to obtain: a fire or a set of fires whose transparent front pane presents externally the homogeneous appearance of a single uniform shade under the light; external ambient lighting, the color of which is preferably chosen in a color other than the conventional colors of the lighting and signaling functions; that is to say that the solar rays that pass through the transparent pane can be reflected only on a metallized or white intermediate surface that does not affect their color before going back

  outwardly said front pane.

  - a fire or a set of lights whose transparent front window can satisfy all the requirements of style

  concerning the profile and the color of the bodywork.

  - a lamp or set of lamps whose functional intensity is not adversely affected to provide illumination in accordance with traffic regulations and whose color and magnitude are clearly different from any

  optical illusion of exterior colored elements.

  - a fire or a set of fires whose front window can be made in an opaque material to follow any development of the style of the other elements of

  bodywork such as bumpers, grilles, protection rods

tion, etc.

  The present invention thus makes it possible to produce lighting and signaling lamps of the type mentioned at the beginning but capable of satisfying the problems and imperatives.

  above-mentioned style with optimum light output.

  To this end, the invention relates to a device for illuminating

  marking and signaling system for motor vehicles consisting of a reflector provided with a light bulb having a reflective surface at least paraboloidal to reflect the functional light in the form of a substantially parallel beam, and whose opening is closed by a front window whose interior optics distributes the lighting beam outside with a specified magnitude and a conventional color; device characterized in that, between the bulb and the front pane, is disposed inside the reflector an intermediate baffle plate constituted respectively by an inner layer of transparent material of determined color, the surface facing the bulb is provided with a plurality of convergent lenses arranged in a staggered manner, by a layer

  median of opaque material with a corresponding arrangement

  of frustoconical orifices positioned in the axis of each of the converging lenses of the inner layer and capable of enveloping the entire convergent volume of each brush of functional light beams polarized by each of said directional lenses, and by an outer layer of transparent material colorless whose outer surface

  oriented towards the front window is also provided with

  correspondingly of a plurality of convergent lenses

  basically the same magnitudes as the convergent lenses

  of the inner layer with which the

  convergent lenses of the outer layer, in the line

  frustoconical orifices of the middle layer, to capture and redistribute in output towards the optics of the front window, in a parallel or substantially parallel direction, all the incident elemental rays of each brush of functional light rays which are substantially concentrated in the end of each of the frustoconical orifices of the middle layer and then diverge inside the

  outer layer of said deflector screen.

  The invention makes it possible to obtain a deflector screen whose opaque median layer visible through the transparency of its colorless outer layer can be of any other color (darker or lighter) than that of the inner layer of screen or, other elements of functional coloring of the light emitted by the light bulb of the lit fire

  which can be positioned upstream of said screen.

  In fact, because of the light bulb extinguished, through the colorless outer layer of the screen, the opaque medial layer does not reveal on its outer surface, and with a perception still very attenuated by the effect of the spherical reliefs of the convergent lenses, a arrangement of barely perceptible points corresponding to the smallest exit ends, (1 mm2 minimum section), frustoconical orifices; and therefore simply to position on the front opening of the fire a clear transparent front glass provided with optical reliefs on its inner wall is sufficient to completely remove the vision of these points on the apparent surface of the opaque layer of the intermediate screen and thus to give perfect homogeneity to the outward appearance of the fire,

  whose front window then, by transparency, feels

  the color of the median opaque layer of the baffle screen (crystal, white, amber, red, etc.) which makes it possible to better integrate the scooping device which is the subject of the invention in the set: juxtaposed equipment that

  dress the vehicle body.

  Also, this arrangement of "upstream" convergent lenses, frustoconical passages and "convergent downstream" lenses, carefully aligned in correspondence in the stated juxtaposition of the materials that make up the deflector intermediate screen of the device, allows, when the light bulb lighting is switched on, collecting, transmitting and directing on the front window (in profile and color meeting all the expected requirements of the style) all of the colored rays of all the elementary luminous brushes composing the emitted light, thus obtaining in fire output, with maximum efficiency, a beam of light well in accordance with the rules of normalization and whose magnitude and the conventional color can not create any confusion in the use nor the range

  illuminating very homogeneous bring discomfort.

  Other characteristics and advantages of the invention will appear on reading the nonlimiting examples described below with reference to the accompanying drawings, in which: FIG. 1 is an axial vertical sectional view of a first embodiment of FIG. realization of the lighting device

according to the invention.

  FIG. 2 is an axial vertical sectional view of a second embodiment of the compliant lighting device;

  to the invention by a variant of the screen design-

intermediate baffle.

  FIG. 3 is a partial sectional view of a

  third embodiment of the deflector screen of the dis-

  positive lighting according to the invention.

  FIG. 4 is a partial sectional view of a

  second embodiment of the front window of the

  tif lighting according to the invention.

  FIG. 5 is a partial sectional view of a

  third embodiment of the front window of the dis-

  positive lighting according to the invention.

  FIGS. 6 and 7 are respectively an axial vertical section and a vertical cross section:

  corresponding to a fourth embodiment of the screen-

  deflector of the lighting device according to the invention.

  The present invention therefore aims at the realization of a lighting and signaling device which is simple and inexpensive, perfectly harmonizes with the color and shapes of other elements adjacent to the vehicle body, and which in the off state ensures the invisibility of a specific and clean tinted part

  to provide the well-defined conventional color lighting

  when the device is turned on.

  According to the embodiment of Figure 1, the device / consists of a reflector 1 provided with a reflective interior surface at least parabololdic and which has at home the filament of the bulb 2 fixed by

a support 3 to this reflector. -

  The opening of the reflector is closed by a transparent window 4 while between the bulb 2 and the ice 4 are arranged against each other from the inside of the reflector outwardly: a transparent flat screen 5 of which the hue is determined to obtain, (cooperating or not with others

  known coloring means arranged upstream such that -

  the vitreous envelope of the light bulb itself, or

  a globe or auxiliary shield enclosing the bulb), the coloring

  conventional convention desired the expected lighting pattern, and whose surface facing the bulb is provided with a plurality of convergent lenses called "upstream" 51

  forming at least spherical reliefs arranged in

  conceive and focus forward the incident light in as many elementary luminous brushes 82. - an interplanar panel 6, opaque color, contributing to give the desired appearance of the external color of the fire in the off state, and comprises an arrangement of frustoconical orifices 61 positioned in the axis of each of: convergent lenses "upstream" 51 of the screen 5 and capable of enveloping the entire convergent volume of each brush of functional rayorlumineux 82 focused in

coincidence by lenses 51.

  a flat, colorless, transparent screen 7 whose outer surface oriented towards the front window 4 is also provided with a plurality of convergent "downstream" lenses 71 of the same magnitudes as the convergent "upstream" lenses 51 of the screen 5 with which the lenses 71 cooperate, in the alignment of the frustoconical orifices 6 of the opaque diaphragm panel 6, for i. capturing and redistributing, by reorienting them in a parallel or substantially parallel direction, on the window pane 4 all the incident 3 rays of each brush of functional light rays diverging at the exit from the small exit ends of the coinciding frustoconical orifices;

  61 of the intermediate diaphragm panel.

  In this example, the diaphragmatic, intermediate or medial panel 6 is constituted by an opaque plastic plate of a specific thickness to position the plane of the smaller exit openings of the frustoconical orifices 61 at or substantially below the point convergence (focus) of the rays 82 refracted forwardly by the lenses of the "upstream" screen 5 closing in coincidence lesgrandes

  inlet openings of said frustoconical orifices 61.

  The layout and the small area (mm min) of the small frustoconical outlet openings 61, the interposition and the arrangement of the transparent "downstream" screen with convergent lenses 71 and the reliefs of the optics

  4, the front transparent window 4 make

  detectable these small orifices when one observes from the outside

  the lighting device in the switched off state and this even in the case where the front window 4 is made in a

  colorless transparent material called "crystal".

  In this case where the front window 4 is made of a colorless transparent material, according to whether the opaque diaphragm panel 6 is given a neutral color such as white, or glossy, such as silver, the transparency of the colorless glass is obtained. 4 and colorless screen

  downstream 7 an external appearance of the front window 4 subsequently

  a very homogeneous white or crystal. Also, for the needs of change of direction or recoil lights associated with other lighting devices, by affecting the diaphragm panel 6 a red metallic or varnished color, it leads to the transparency of the window 4 and the screen 7 to make a front window 4 with a red colored appearance harmonizing very well with the red color

  of the front windows of other lantern sets.

  adjacent lighting such as the associated rear lighting, braking and fog lamps constituting the classic rear lantern assemblies of current vehicles. The operation of this device is as follows: When turned on, the rays 8 from the filament of the bulb 2 are reflected on the inner wall of the reflector 1 to produce rays 81 parallel or substantially parallel to the optical axis x 'x. These rays are then captured and refracted by the convergent lenses 51 of the "upstream" screen tinted in as many luminous brushes 82-colored with the conventional color of lighting and signaling desired and which then completely pass through the frustoconical orifices 61 of the 6. At the outlet of the small end openings of the orifices 61, the focal point of the lenses 51, all of the convergent luminous brushes 82 then diverge symmetrically into as many diverging luminous brushes 83 which then pass through the adjacent screen "downstream 7 to be thus fully captured by the convergent lenses 71 of its front wall, which consequently refract them in as many rays parallel or substantially parallel to the optical axis x'x in the direction of the inner optics 41 of the transparent front window 4 to produce the desired outdoor lighting and signage 85. It can be seen that this screens and panel 5.6. and 7 of the intermediate deflector thus produced does not reduce the optical efficiency of the device since all of the incident rays 81 is reflected by rays emerging tinted 84 of the same direction and always parallel

  or substantially parallel to the optical axis x'x of the device.

  On the other hand, when the fire is extinguished, the arrangement and arrangement of the screens and panel of the 5.6.7 baffle prevent the ambient ambient lighting from

  the illusion that the device is on.

  Indeed, for a large part of the light rays

  external incidents 9 and 10, refracted by the optics

  of the front window 4, then by the convergent lenses

  71 of the "downstream" screen 7, it is not possible to cross the frustoconical orifices 61 of the diaphragmmed median panel 6 and these rays are then absorbed by the opacity of the median panel 6, or reflected towards the outside the device, without having been able to cross the

  staining elements of functional light.

  For the very small part of these incident ambient rays which could pass through the frustoconical orifices of the opaque panel 6, these residual radii already weakened by their passage through the front window 4 and the "downstream" screen 7 are further attenuated by their passage through the screen "upstream" 5 and finally completely absorbed in the relatively dark enclosure of the reflector

  which forms a light trap at the back of the "upstream" screen 5.

  In fact, when the bulb 2 is extinguished, no illusion of illumination can occur by the magnitude and color of the reflection of the ambient light that can be

  obtained in the front chamber of the device.

  The 5.6.7 Baffle Panels and Panel may be a one-piece baffle-composite screen

  (see FIGS. 2 and 3) from an overmoulding or

  three layers of well-defined materials.

  In the non-exhaustive exemplary embodiment of FIG. 2, the transparent "upstream" material layer 12, tinted to the desired conventional color, is respectively molded on its rear wall with the arrangement of convergent lenses 121 arranged in staggered and on its front wall, in correspondence of number and position, a plurality of frustoconical reliefs 122 intended to form the entire transparent volume of functional frustoconical functional passages colliding the diaphragm panel which, for its part is realized in this example by overmoulding, on the front wall 122, an opaque material 13 flush with the top of the reliefs 122. The finish of this baffle composite screen is then obtained by overmoulding, above the opaque material and not covered peaks reliefs 122, colorless transparent material "downstream" 14 whose front wall is the corresponding arrangement of convergent lenses 141 du.disposi Tif object of the invention which occlude the diaphragm portions in order to capture and reorient in a parallel direction 84 all rays 82 focused by the lenses "upstream" convergence 121 in frustoconical passages 122 and then diverging 83

  through the thickness of the transparent material 14.

  According to the non-exhaustive embodiment of FIG. 3, the transparent "upstream" material layer 12, tinted to the desired conventional color and provided respectively on its rear wall with the corresponding arrangement of frustoconical reliefs. of the opaque diaphragm layer of the composite screen, may also be partly covered with a thin coating of opaque material 15 (metallic-or organic) q, not covering the only exit ends of the frustoconical reliefs 122, will constitute the çouche opaque to diaphragms of the intermediate deflector screen; which opaque film 15 will then be covered by overmoulding of the layer of transparent colorless material 14 which will form the convergent "downstream" lenses 141 in coincidence on its outer wall and which will thus terminate the composite structure of said screen-baffle

  intermediate object of the invention.

  Also, to harmonize the lighting and signaling device to the style of other bodywork elements such as bumper, grille, etc ...; the front window 4 of the device which is the subject of the invention can also be obtained (see FIG. 4) from a colorless transparent inner plate 16 whose inner wall is provided with a distribution optic 161, consisting of a plurality of convergent lenses arranged in staggered rows and concentrating all the colored incident functional rays 84 of the device in the corresponding volumes of the frustoconical reliefs 162 formed reciprocally in alignment with its other outer wall; which outer wall then receives, by overmoulding, a layer of opaque material 17 of structure and color closest to that of the neighboring bodywork elements so that on the outer surface of

  this opaque layer, outcrop only the non

  coated and of small surface (lmm min) reliefs 162 diffusing outside the fire realized the lighting and the

  desired color signaling 86.

  In the same way, it is also possible to make the front window of the device so as to also have an outer layer of transparent material of the same color as that of other lantern elements juxtaposed with the device of the invention (see Figure 5); that is to say that in this variant, the layer of transparent colorless material 16, lens distribution, converging 161 on one side and frustoconical reliefs in coincidence 162 on the other side, receives on its reliefs a coating of small thickness of an opaque material (preferably metal) 17 which does not nevertheless close the ends of small dimensions frustoconical reliefs; this coating being then covered by the transparent material layer 18 stained to the desired external shade according to a thickness determined so that its outer surface is flush with the plane of the small-sized outlet ends of the frustoconical reliefs 162 transmitting the differently colored rays of the d 'expected lighting & outside. In this variant, the layer of opaque material 17 is intended to prevent any

  convergent functional color incident ray 85 can

  pour the layer of material of appearance 18 and thus alter the

  desired functional colorimetry of other light rays

  rabies and external signaling 86 having followed a

  correct progression in the volume of frustoconical reliefs 162.

  Of course, the embodiments described above are in no way limiting of the invention; it is-

  that is to say, as an example, that the flat shape of the

  intermediate baffle can not be considered exclusive because it is also possible to bend its structure to the limit, to achieve this screen in the form of a globe completely covering the balloon of the light bulb 2

(see Figures 6 and 7).

  In this extreme embodiment, the lenses

  convergents 191 of the "upstream" inner layer of colora-

  19 form a plurality of protruding generators to

  cylindrical profile whose normal of each is respectively

  aligned with the median plane of as many slits 201 trapezoidal section generating the diaphragm profile of the opaque intermediate layer 20 and filled with the dyed material 19, and aligned with the normal of as many convergent lenses 211 (likewise optical quantity as the lenses 191) formed outside the "downstream" layer of colorless transparent material 21 generating the surface

  the upper volume of said conpcsite globe-deflector. This agency

  The deflector globe captures, colors and concentrates and retransmits in their original direction all the incident light rays 8 and 8 'emitted by the filament of the bulb 2 of the device before their reflection in a direction parallel to the optical axis x'x by the inner reflective surface of the reflector 1. This mode of work substantially different from the globe-deflector, (since it does not intervene after the reflection of the rays incident by the reflector), however retains a functioning and a result sufficiently close to those of the previously described achievements for that. the present globe variant of the device is also within the scope of the present invention. Note however that its appearance in the off state is worse and that its realization is much more complex and expensive than those

  previously described embodiments.

  The intermediate screen may advantageously be manufactured by assembling two identical transparent sheets 5o 7,

  the sheet 5 being colored, on a perforated opaque sheet 6.

  Preferably, the perforated opaque layer 6 is obtained by

  transfer to one or the other of the transparent sheets 5, 7.

  The intermediate screen can be cut from a plate

  prefabricated large.

Claims (7)

  1.- Lighting and signaling device for motor vehicles consisting of a reflector provided   a light bulb with a reflecting surface   at least parabolic to reflect the functional light in the form of a substantially parallel beam, and whose opening is closed by a front window whose interior optics distributes the lighting beam outside with a magnitude and color conventional determined; characterized in that, between the bulb (2) and the front pane (4), is disposed inside the reflector (1) an intermediate deflecting screen constituted respectively by an inner layer of transparent material of color determined (5) whose surface facing the bulb is provided with a plurality of convergent lenses (51) arranged in a staggered pattern, by a medial layer of opaque material (6) having a corresponding arrangement of frustoconical orifices   (61) positioned in the axis of each of the convergent lenses   gentes (51) of the inner layer (5) and capable of wrapping   the whole convergent volume of each luminous ray brush   they functionally (82) polarized by each of said directional lenses (51), and by an outer layer of colorless transparent material (7) whose outer surface oriented towards the front window (4) is also provided in correspondence of a plurality convective lenses (71) of basically the same magnitudes as the convergent lenses (51) of the couch? interior (5) with which the convergent lenses (7p) of the outer layer (7) cooperate in alignment with the frustoconical orifices (61) of the middle layer (6), to capture and redistribute at the output towards the optics of the front window (4), in one direction   parallel or substantially parallel all the elemen-   incidental heads (83) of each brush of functional light rays which are substantially concentrated at the end of each of the frustoconical orifices (61) of the middle layer (6) and then diverge inside the layer   outside said deflector screen.   2.- Device according to claim 1 characterized   by that said intermediate screen (5, 6, 7) is plane.   3.- Device according to claim 1, characterized   by that said intermediate screen (5,6,7) is curved.   4.- Device according to one of claims 1 to 3,   characterized in that the transparent pane (4) consists of a colorless transparent inner plate (16) provided with a plurality of convergent lenses (161) arranged in staggered rows and extended by frustoconical reliefs (162), the face of said plate (16) comprising said frustoconical reliefs (162) being provided with a layer of opaque material (17) flush with the ends said frustoconical reliefs (162).   5.- Device according to claim 4, characterized in that said layer of opaque material (17) is   thin and is covered with a layer of colored matter (18).   6.- Device according to one of claims 1 to 5,   characterized in that said intermediate shield (5, 6, 7) consists of two transparent sheets (5, 7) prefabricated with their convergent lenses (5, 71) which are assembled with the interposition of a perforated opaque material screen 7. Device according to claim 6, characterized by the fact that said opaque screen / kf O formed by transfer onto   one of transparent leaves (5,7).   8.- Device according to one of claims 1 to 7,   characterized by the fact that said intermediate screen (5; 6.7)   is cut from a prefabricated plate of large dimensions.