The present invention relates to display panels for motor-vehicle dashboards, of the type having a substantially opaque front surface, of a uniform dark colour, for example black or dark grey, on which symbols, icons, or the like can be displayed, as well as wordings, numbers, or graphic images generated, for example, by a liquid-crystal display.
The purpose of the present invention is to provide a panel of the type specified above, in which the presence of the symbols, icons and/or of LCDs is absolutely not perceivable except when said elements are backlighted, said panel having a uniformly black surface.
With a view to achieving the above purpose, the subject of the present invention is a display panel for a motor-vehicle dashboard, having a front surface of a uniform dark colour, on which symbols or icons or images can be displayed, said display panel comprising:
said display panel being characterized in that it comprises also a film set in front of the aforesaid opaque mask and comprising:
In a first embodiment, the aforesaid film is of the type in which the array of focusing optical elements is constituted by microspheres of transparent material, a hemisphere of each microsphere being immersed in a layer of absorbent material having a maximum thickness substantially equal to the radius of the microspheres. The thickness of absorbent material varies from point to point within the layer, reaching a maximum value in the peripheral area of each microsphere and a minimum value in a position corresponding to the centre of the microsphere itself. The aforesaid film is positioned in such a way that the “free” hemisphere, i.e., the one not immersed in the absorbent material, faces said opaque mask.
In the case of said first embodiment, the light emitted by the source, by passing through said mask bearing the symbols, icons, or LCDs and impinging upon the microspheres is focused in an axial direction in the area in which the absorbent layer has a minimum thickness and substantially passes through said absorbent layer, with consequent high transmittance. Instead, the light impinging on the side opposite to the one facing said mask is substantially absorbed by the absorbent substrate. The minimal part of light that is not absorbed and is hence transmitted is not in any case substantially reflected back. Said film is consequently substantially transmissive to the light that impinges on the film from the side facing the mask and is uniformly opaque to the light that impinges on the film from the side opposite to the one facing the mask.
In a second embodiment, the array of focusing optical elements is constituted by spherical or aspherical caps made on the face of a substrate of transparent plastic material facing said mask bearing the symbols, icons or LCDs, there being made on the opposite face, for example by means of serigraphy or lithography, a substantially opaque mask, present on which is an array of transmissive pin-holes set substantially in a position corresponding to the axes of said focusing optical elements.
Also in said second embodiment, as in the case of the first embodiment, the light emitted by the source, which passes through said mask bearing the symbols, icons or LCDs and impinges from the side of the caps is focused and traverses said transmissive pin-holes made within said substantially opaque mask, whilst the light which impinges upon the side opposite to said mask is absorbed by said substantially opaque mask, or else passes through said transmissive pin-holes made within said substantially opaque mask to be reflected back only in part. As in the case of the first embodiment, also in the second embodiment the result is that of obtaining a film that is substantially transmissive to the light that impinges on the film from the side facing said mask bearing the symbols, icons or LCDs and substantially opaque to the light that impinges on the film from the side opposite to said mask.
Preferably, set between the light source and the mask bearing the symbols, icons or LCDs is an optical collimator for reducing the divergence of the beam of light coming from the source. In this way, the transmittance of the film is increased. Even in the absence of the collimator, however, the characteristics of the panel according to the invention enable in any case satisfactory results to be obtained as long as the angle formed between the light coming from the source and the direction normal to the aforesaid film does not exceed values of around 30°.
Further characteristics and advantages will emerge from the ensuing description with reference to the annexed plate of drawings, which is provided purely by way of non-limiting example and in which:
With reference to
The panel according to the invention is characterized in that the symbols or icons 4 and the liquid-crystal display 5 are absolutely not visible when they are not illuminated by a light source set behind the panel, said panel having a uniformly black surface.
The structured film 10 comprises, in the first embodiment illustrated in
With reference to
With the solution illustrated in
In general, the light that impinges on the film from the side of the mask 9 is focused in a focal region the dimension of which depends upon the divergence of the beam incident on said microspheres 11 or on said array of focusing elements 15. In fact, also in the case where said focusing elements constituting said array 15 are aspherical caps and said focusing elements are hence corrected from spherical aberration, only the rays that impinge on the structured film 10 in a direction perpendicular to the plane of the structured film 10 itself are focused in a point on the optical axis 19, where the rays that impinge on the structured film 10 with a different angle are focused in points that do not lie on the optical axis 10. Said rays will be transmitted by the structured film 10 only if the diameter of the transmissive pin-holes 18 is sufficiently large. On the other hand, larger dimensions of the transmissive pin-holes 19 imply a higher transparency of the structured film 10 also to the light incident from the side opposite to that of the mask 9, the latter being an effect that jeopardizes in part the performance thereof.
In order to maximize the transmittance of the structured film 10 to the light incident on said structured film 10 from the side of the mask 9, albeit maintaining a low transparency to the light incident on said structured film 10 from the side opposite to that of said mask 9, it is therefore advantageous for the divergence of the incident beam to be as small as possible, a fact that renders desirable the use of a collimation system 7. It is also desirable for said mask 9, in a position corresponding to the high-transmittance regions, to be completely transparent instead of translucid, i.e., to transmit the incident light without diffusing it.
In general, the maximum angle that the light coming from the source can form with respect to the direction normal to the panel 1, in order to have satisfactory results, is around 30°. It should likewise be noted how the divergence of the light leaving the structured film 10 is decidedly greater than the divergence of the beam incident on said structured film 10 from the side of the mask 9. This is due to the principle known in optics as “conservation of, the étendue”, whereby the product of the solid angle in which the beam propagates and the cross section of the beam itself is maintained constant in an optical system following upon successive refractions. To a first approximation it may hence be stated that, if A is the surface of the cross section of a single microsphere 11 or of a single focusing element 15 and A′ is the area of the focal region, Ω is the solid angle for the beam incident on the single microsphere 11 or on a single focusing element 15, and Ω′ is the solid angle for the beam leaving the structured film 10, according to the present invention, the following law applies: Ω′=Ω*A/A′. Since A is much greater than A′, in general the divergence of the beam leaving the structured film 10 will be much greater than the divergence of the beam incident upon said structured film 10. The area A′ of the focal region depends in turn upon the solid angle of the incident beam and upon the focal length d of said microsphere 11 or of said single focusing element 15.
In the case where at least a portion of said mask 9 is constituted by a backlighted LCD 5, it is expedient for the angle of vision of said LCD 5, determined by the divergence of the beam leaving the backlighting device and by the optical behaviour of the different layers constituting said LCD 5, to be limited so as to maximize the transmittance of the structured film 10. The final angle of vision perceived by the user will be enlarged, thanks to the effect of said microspheres 11 or of the array of focusing elements 15 described in the previous paragraph. In the case of coupling of the structured film 10 with an LCD 5 it is hence expedient not to use standard LCDs 5, in which typically a field of vision as wide as possible is persued, but rather personalized solutions with a narrow and predefined field of vision.
Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein purely by way of example, without thereby departing from the scope of the present invention.
Number | Date | Country | Kind |
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06425657.1 | Sep 2006 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2007/002293 | 8/3/2007 | WO | 00 | 6/2/2008 |