EP0860755A1 - Device for uniformly illuminating the dial of a display apparatus - Google Patents

Abstract

The system for illuminating the dial (4) of a watch fits within the casing (1) which includes a cover glass (8) lying over the dial and held in place by a cover ring (9). At least one light source (13) is mounted at the periphery of the dial with a light guide (20) extending around the circumference of the dial. The light guide has an internal surface which is polished, and an external surface held within the space defined by the dial (4), the cover glass (8) and the internal wall of the cover ring (9). The outside surface of the light guide has a progressively increasing degree of surface roughness, causing an increasing degree of scattering as the distance from the light source(s) increases.

Description

The present invention relates to a device uniform illumination of the dial of a device display thanks to the particular configuration of a guide of the light emitted by at least one source light, the guide and the light source being located the periphery of the dial in the substantially understood space between it and a shutter glass.

We already know the display devices in which a dial and in particular the dial of a coin of watches, is illuminated by means of at least one source luminous, formed by a miniature electric bulb or a diode, associated with a light guide in matter translucent in the form of a loop, placed between the glass and the dial. Such a device corresponds for example to that described in the Swiss patent CH 549 237. In use however, it turned out that the dial area located at proximity to the light source was naturally more lit as the diametrically opposite area. To fix to this drawback document US 4,908,739 proposes to distribute at least two light sources at equal distance inside an annular guide. Such a device locally increases the illumination of the dial, but does not not help make it more uniform. By increasing the number of light sources, it would be possible to get more uniform lighting, but at the cost of increased energy consumption, which would be a critical factor for the lifespan of batteries in the case of a one-room application of watchmaking.

Various other arrangements have been proposed for direct light more effectively towards the dial emerging from the guide. As an example we can cite the device of document CH 677 306, in which a ring forming a diffuser has a cross section which has a polished side inclined towards the dial, the other faces being uniformly coated with a matt paint. In the document CH 336 763 a greater concentration of light rays towards the dial is obtained by increasing the reflection of light rays on the ice, including the face facing the dial is coated with a thin reflective metallic layer.

Thanks to these devices of the prior art, it results in more intense illumination of the dial but still does not get uniform lighting, which is not neither satisfactory from an aesthetic point of view, nor as regards concerns the good readability of the information entered on the dial, such as hour markers in the case a timepiece with analog display.

The object of the present invention is to overcome the disadvantages of this prior art by providing a special arrangement of the light guide, allowing obtain a high uniformity of illumination of the dial a display device.

To this end, the invention relates to a device of illumination of the dial of a formed display device by a case closed by a glass arranged above the dial and maintained by a casing circle, said device comprising at least one light source arranged in at least one accommodation fitted out in a guide luminous positioned at the periphery of the dial, said guide having a polished internal surface oriented towards the dial and an external surface maintained in a space delimited by the dial, the crystal and the inner wall of the circle casing, characterized in that all or part of said outer surface of the guide is arranged to allow a gradual increase along the guide of the amount of light scattered by said outer wall at as we move away from one of the sources bright.

In what has just been said "encagrage circle" must be understood broadly as being everything device maintaining the relative position of the glass by relation to the dial, regardless of the respective contour of these two elements. In the case of a timepiece, the "casing circle" will for example be the middle or a glasses.

It is known that light energy in a guide decreases as one moves away from a source bright not only due to total reflections on the inner wall through which the rays should emerge, but also due to the phenomena of refraction or absorption by the external surface of the guide.

The new design of the guide according to the invention essentially allows to optimize the illumination of a dial by straightening a light ray incident on the external surface by diffusion according to a lobe oriented towards the internal surface, decreasing there, even the losses by total refraction on said surface, this diffusion being planned to be all the stronger away from a light source, compensating by somehow, the decrease in light energy along of the guide.

In the case of a device not comprising for example only one light source, the diffusion will therefore maximum in the portion of the guide diametrically opposite to the light source.

Different treatments of the external surface are possible to vary the useful diffusion surface, on which the light quantity gradient depends broadcast. It will first be recalled that the optimum diffusion is obtained with a Lambertian reflector, whose model type is the surface of a block of magnesium oxide, with which all the incident light is diffused according to a spherical lobe.

A first embodiment therefore consists in apply a smooth outer surface of the guide coating in a Lambertian type diffusing material, in growing the covered area as you go away from a light source. In the case of a rectangular section guide, this coating will be applied as a priority on the small side opposite the surface internal polished. It can also be applied in the same way way on the other two surfaces held between the glass and the dial, still on three sides forming the outer surface.

According to a second embodiment, one performs structuring of the external surface by increasing the structuring density as we go moves away from a light source. According to a first variant, this structure consists of grooves in the outer surface, oriented on the guide parallel to the line of curvature of said guide and of which the number increases as we move away of a light source. According to one embodiment preferred, the grooves are V-shaped.

According to a second variant, this structuring consists of small indentations in the surface of the guide and whose number per unit area increases as one moves away from a source bright. According to a preferred embodiment these hollows have a conical shape. Structuring in grooves or hollow is carried out for example by laser machining or simply by molding.

According to a third embodiment, the variation the amount of light scattered along the guide by the external surface is obtained by performing both a structuring of the external surface in grooves or in hollow, as indicated in the second embodiment, and by depositing in the hollow parts the material diffusing used in the first embodiment.

Whatever the embodiment allowing obtain a variation in the amount of light scattered along the guide, it is also possible to have a mirror surface behind the entire outer surface of the guide so as to reflect the rays which would not undergo a total reflection in the untreated guide portions. According to the preferred embodiment the mirror surface is not pressed on the guide itself, but separated from this by an air space.

The material constituting the guide is chosen for have a high reflection index, while being good market and easily machinable. A suitable material is for example polymethyl methacrylate (PMMA) or polycarbonate (P.C).

The shape of the straight section of the guide is not decisive for obtaining uniform illumination. However, according to a preferred embodiment, corresponding in particular to industrial implementation easiest and most economical, the straight section of the guide is rectangular, a short side perpendicular to the surface of the dial corresponding to the internal surface polished, while the other three sides correspond to the outer surface.

The shape of the light guide is of course adapted to the shape of the dial around which it follows. It is likewise the number and location of sources bright. When only one light source is used, the light guide will preferably have no angular point and will then appear as a circular or oval loop. When the guide presents angular points, for example when it has a shape rectangular, it is desirable to have at each angular point, either a light source or a mirror to straighten the light rays.

Although the uniform illumination device of a be applicable to any type of display, the description which follows will be made, for convenience, in reference to a timepiece and more specifically to a wristwatch. Likewise, this device is applicable to any display mode, but the detailed description will be made essentially by reference a display analog, i.e. a display in which at least a needle moves opposite marks carried by a dial.

This in no way excludes that the device illumination according to the invention can be adapted to a dial comprising, in whole or in part, a device digital for displaying time information or not hours. Similarly, the illumination device according to the invention can be incorporated into other arrangements changing the visual appearance of the dial. In rectangular dial configuration an illumination uniform can also be obtained simply by means a guide formed by two separate bars each provided a light source at one end and a mirror at the other end, being arranged near two edges the dial.

• la figure 1 est une vue en perspective d'une montre-bracelet montrant partiellement un premier mode de réalisation d'un dispositif d'illumination selon l'invention;
• la figure 2 est une vue partielle en coupe agrandie selon la ligne II-II de la figure 1;
• la figure 3 est une vue de dessus agrandie du guide lumineux de la montre-bracelet représentée à la figure 1;
• la figure 4 est la vue développée du petit côté externe du guide de la figure 3 entre la source lumineuse et le point diamétralement opposé;
• la figure 5A est une vue en coupe du guide lumineux selon la ligne V-V de la figure 3;
• la figure 5B est une autre représentation de la coupe selon la ligne V-V de la figure 3;
• la figure 6 est une vue en perspective du guide lumineux d'un deuxième mode de réalisation d'un dispositif d'illumination selon l'invention;
• la figure 7 est une vue en perspective du guide lumineux d'un troisième mode de réalisation plus particulièrement adapté à l'illumination d'un cadran rectangulaire, et
• la figure 8 est une vue de dessus d'un quatrième mode de réalisation également adapté à l'illumination d'un cadran rectangulaire.

Other characteristics and advantages of the present invention will appear in the following description of various embodiments, with reference to the appended drawings in which:

• Figure 1 is a perspective view of a wristwatch partially showing a first embodiment of an illumination device according to the invention;
• Figure 2 is a partial enlarged sectional view along line II-II of Figure 1;
• Figure 3 is an enlarged top view of the light guide of the wristwatch shown in Figure 1;
• Figure 4 is the developed view of the small outer side of the guide of Figure 3 between the light source and the diametrically opposite point;
• Figure 5A is a sectional view of the light guide along the line VV of Figure 3;
• Figure 5B is another representation of the section along the line VV of Figure 3;
• Figure 6 is a perspective view of the light guide of a second embodiment of an illumination device according to the invention;
• FIG. 7 is a perspective view of the light guide of a third embodiment more particularly adapted to the illumination of a rectangular dial, and
• Figure 8 is a top view of a fourth embodiment also suitable for the illumination of a rectangular dial.

With particular reference to Figures 1 and 2, it can be seen that the wristwatch shown is of the type running with a box 1 of round shape, containing a watch movement, and a bracelet 2, each strand of which is fixed to the box between horns 3. The time display takes place on a dial 4 by means of hands 5 moving next to time markers 7. The display is closed by a glass 8 held in place by a telescope 9 made integral with the box 1 and whose periphery overflows on the dial, as it appears more clearly in the section of figure 2. The part in which the ice and bezel have been partially ripped off done appear the light guide 20. The light guide 20, annular shape with rectangular section, is housed in the space delimited by the internal wall 10 of the telescope 9 and the facing faces of the dial 4 and of the crystal 8. As this appears more clearly in Figure 2, the guide 20 is kept in its housing by spacers 11 arranged from place to place so as to have a small air space between the outer surface of the guide and the facing walls, against which are arranged mirror surfaces 12 for reflecting the rays which would escape from the guide. These mirror surfaces are by example made using PET sheets with a silver coating.

At the 12 o'clock position, the guide presents a interruption forming a housing in which is arranged a light source 13. In the embodiment shown, this light source consists of two LEDs 13a, 13b arranged back to back and glued to the straight sections of the guide, and allowing to inject the light in the guide in opposite directions. We for example use Al-Ga-As diodes emitting at 639 nm with a supply voltage of 1.65 V. The power source can be the same as that of the watch movement and power-up can be performed on demand by pressing a push button 6.

Referring now more particularly to Figures 3, 4, 5A and 5B, it can be seen that the annular guide 20 of rectangular section, includes an internal surface 21 polished formed by a small side perpendicular to the dial 4 and oriented towards the center of it, and a surface external 22 formed by the three other sides 22a, 22b, 22c. In the example shown, the three sides forming the outer surface of the guide are arranged to obtain a increased active surface to diffuse light as we move away from the light source 13, that is to say to have a maximum diffusion in a zone 23 of the guide diametrically opposite the source 13.

This arrangement consists of a structuring progressive of the entire external surface by grooves 24a, 24b, 25c oriented along the line of curvature of the guide, on the faces 22a, 22b, 22c forming the surface external 22.

Figure 3 shows the structure of the face upper 22a of the guide opposite the glass 8. On observe that the number of grooves 24a, counted transversely to the guide, increases on the one hand when moves away from the light source 13, on the other hand when we move away from the center of dial 4, and their density is therefore maximum in zone 23 from which they have a symmetrical arrangement on guide. Structuring performed on face 22c oriented towards the dial has grooves 24c having the same configuration as those of the face 22a.

In Figure 4 there is shown a developed half-view of the face 22b, that is to say of the portion going from the light source 13 at zone 23. As can be seen, the number of grooves 24b, counted transversely to guide, increases with distance from the source luminous, the grooves being in this case distributed symmetrically on either side of the midline of the face 22b.

The enlarged section of FIG. 5A, carried out at a point of the guide at some distance from the zone 23 of greatest density, gives an example of embodiment of these V-shaped grooves of angle α, separated by flats 25. According to the refractive index of the material forming the light guide 20 and the radius of curvature of the surface at a given point, this angle may vary between 30 and 45 °. As an example, for a PMMA circular guide with a refractive index n = 1.49 the angle α will preferably have the value 40 °. Similarly, the maximum number of grooves and their densification along the curvature of the guide may vary depending on the dimensions of the guide. By way of illustration only, the faces 22a and 22c of a guide having a width of 2 mm have 7 grooves in the zone 23, the outermost groove having a length substantially equal to 2/3 of the circumference of the guide. These grooves can be formed in the guide by any suitable means such as a laser machining with CO ₂ , or a molding during the manufacture of the guide itself.

FIG. 5B represents the same guide as that of the Figure 5A, in which the grooves 24a, 24b, 24c have been filled with a diffusing material 26. For the face 22a, an embodiment has been shown in which the diffusing material is flush with the surface and for the face 22c another embodiment in which the material diffusing form of the beads 27 above the grooves. These beads 27 may be sufficient to maintain a small air space between the outer surface 22 of the guide and the facing surfaces of the crystal, the dial and the build, and thereby make the use of spacers 11.

The diffusing material 26 which has been found to be the most suitable consists of titanium oxide paint containing an equal part of barium sulfate and a small amount of powdered PTFE, for example in proportions 42/42/16.

In FIG. 6 another mode of realization of a guide 30 which differs from that which comes to be described essentially in that its general form is oval and in that it has two light sources 33, 35 and a structuring of the external surface formed by recesses 34. The light sources 33, 35 are diametrically opposed along the major axis and each is housed in a notch formed by the straight sections of the guide and a connecting base 36, 37. These notches, or equivalent light sources, therefore delimit in guide 30 two symmetrical sectors whose zones 31, 32 having the greatest density of valleys, and therefore the stronger diffusion power, are significantly located on the minor axis.

These recesses 34 will be made for example in the form conical with an angle which can vary, as already indicated for the grooves. For the distribution of these hollows on each of the faces forming the external surface, we will also refer to the description made for grooves.

Referring now to Figure 7, we have shown a top view of a light guide 40 configured to follow the entire perimeter of a dial rectangular. This guide includes only one source light 43 located in the middle of a small side. Each angle of the external surface oriented towards the circle casing is treated to have a mirror portion 42 to straighten the light rays. In this example the variation of the surface diffusion power external is obtained by applying a coating diffusing 46 having the composition previously indicated, and with maximum overlap in zone 41, at middle of the short side opposite to that provided with the source bright. Alternatively, the single light source can be replaced by two light sources arranged in adjacent or opposite angles, the other two corners being provided with mirrors, and the covering diffusing being adapted to the arrangement of sources bright.

In Figure 8, there is shown in top view, a another embodiment of a dial wristwatch rectangular in which the illumination device according to the invention 50 consists of two bars 50a, 50b shaped in the same way and arranged head to tail. Each straight bar includes at one end a source light 53 and at the other end a mirror 52. The structuring to vary the distribution on along each guide, here represented by grooves is arranged so that the fronts of equal illumination substantially overlap. As we also see the dial includes both an analog display 54 and a digital display 55. It is also perfectly possible, and compatible with the illumination device according to the invention, to modify the background of the part of the dial reserved for analog display by any process known to those skilled in the art, for example by having this place a cell that can be modified by electrophoresis.

According to a variant not shown, it can be advantageous, especially in the case of a substantially dial square, to arrange the two bars parallel to the axis 3h - 6h by arranging the light sources of the bars no longer head to tail but on the same side.

The examples which have just been described are susceptible to numerous variations and adaptations to the scope of the skilled person without departing from the scope of the invention.

Claims (22)

Illumination device for the dial (4) of a display device formed by a housing (1) closed by a crystal (8) disposed above the dial (4) and held by a casing circle (9), said device comprising at least one light source (13, 33, 35, 43, 53) arranged in at least one accommodation in a light guide (20, 30, 40, 50) positioned at the periphery of the dial (4), said guide having an internal surface (21) polished oriented towards the dial (4) and an external surface (22) held in a space delimited by the dial (4), the glass (8) and the inner wall (10) of the circle casing (9), characterized in that all or part of said outer surface (22) of the guide is arranged to allow a gradual increase along the guide (20, 30, 40, 50) of the amount of light scattered by said outer wall as one moves away from one of the light sources (13, 33, 35, 43, 53). Illumination device according to claim 1, characterized in that the external surface has a coating of a diffusing material (26) of the type Lambertian which gradually covers said surface external (22) as one moves away from a light source (13, 33, 35, 43, 53). Illumination device according to claim 2, characterized in that the coating of material diffusing (26) is a titanium oxide paint incorporating barium sulfate and polytetrafluoroethylene in powder. Illumination device according to claim 1, characterized in that the external surface (22) has a structure whose density increases as and distance from a light source (13, 33, 35, 43, 53). Illumination device according to claim 4, characterized in that the structuring is formed by grooves (24a, 24b, 24c) oriented on the guide (20, 30) parallel to the line of curvature of said guide (13) and whose number increases as we moves away from a light source. Illumination device according to claim 5, characterized in that the grooves (24a, 24b, 24c) are V-shaped Illumination device according to claim 4, characterized in that the structure is formed by hollows (34) whose number per unit area increases as one moves away from a source luminous (13, 33, 35, 43, 53). Illumination device according to claims 2 and 4, characterized in that the surface external involves both structuring and diffusing material deposited in the grooved parts or hollow. Illumination device according to claim 1, characterized in that the arrangement of the surface external (22) is such that the diffusion power increases further as one moves away from the surface internal. Illumination device according to claim 1, characterized in that the light guide (20, 30) has a rectangular cross section, one short side perpendicular to the surface of the dial forms the surface internal polished (21), the other three sides of which form the outer surface (22). Illumination device according to claim 10, characterized in that the arrangement making it possible to have a variation in the spread along the guide is performed only on part of the external surface (22b) opposite to the polished internal surface (21). Illumination device according to claim 10, characterized in that the arrangement making it possible to have a variation in the spread along the guide is performed over the entire outer surface (22a, 22b, 22c). Illumination device according to claim 1, characterized in that it further comprises a surface mirror (12) arranged opposite the external surface (22), but not tacked on it. Illumination device according to claim 1, characterized in that the light guide (20, 30) is adapted to the shape of a circular or oval dial. Illumination device according to claim 1, characterized in that the light guide (40, 50) is adapted to the shape of a square or rectangular dial. Illumination device according to claim 15, characterized in that the light guide (40) follows everything the perimeter of the dial and further comprises at least two mirrors (42) applied to the external surface part in look of the casing circle and arranged in the corners. Illumination device according to claim 15, characterized in that the light guide (50) is consists of two separate bars (50a, 50b) provided each of a light source (53) at one end, of a mirror (52) at the other end and arranged near two parallel edges of the dial. Illumination device according to claim 1, characterized in that the housing of a source light is formed between two straight sections of the guide. Illumination device according to claim 1, characterized in that the housing of a source light is formed between two straight sections of the guide interconnected by a strip (36, 37) of material forming the guide. Illumination device according to claim 1, characterized in that each light source is consists of two diodes arranged back to back. Timepiece comprising a device illumination according to any one of the claims previous. Timepiece according to claim 20, characterized in that the illumination device is incorporated in other arrangements modifying the visual appearance of the dial.

Images