EP1319998A1 - Luminous hands and display device with such hands, especially for a timepiece - Google Patents

Abstract

The hands consist of a central head (29,35) which rotates about the timepiece axis (15) and the indicating body of the hands (28,34). Light emitted by three diodes (23) located under the dial (10) is directed axially by a cylindrical light guide (18) to the central heads of the hands where reflectors consisting of dihedral cavities (40,41) intensify the lighting to the body of the hands

Description

The present invention relates to a needle comprising a part made of a transparent material capable of being illuminated so that the needle becomes bright and visible even in the dark, especially in a device analog display such as that of a timepiece.

The invention also relates to an analog display device for a room. horology, comprising such hands. The invention further relates to a watch comprising such a display device.

Currently, it is common to use a needle made of transparent material colored that we light up internally so that it appears luminous, in particular to facilitate the night reading of an analog indicator such as the speed in a motor vehicle. We find for example in the publications of WO 96/02810, US 5,546,888 and DE 38 17,874 the description of devices in which a light beam, produced by a stationary source, penetrates axially in a transparent rotating hub of the single needle and reaches a surface of reflection which distributes the light in the elongated body of the needle. So that the body of the needle appears sufficiently and uniformly luminous, it is known to incorporate a fluorescent substance. However, energy consumption electrical devices have limited their applications so far.

The idea of internally lighting the hands of a timepiece in the same goal is already old, but cannot be practiced in the same way so that in the aforementioned devices, mainly because of the layout coaxial of the hour, minute and possibly second hands, and the superposition of the circular heads of the needles. To reach the needle head upper, the axial light beam must pass through the head of each underlying needle, where the light flow must be both divided and directed on the one hand towards the body from the needle and on the other hand towards the overlying needle. Also, like the axis area of rotation is generally occupied by an opaque tree, the light cannot go through this area, unless you are using a transparent tree. This then results in particular difficulties in distributing light.

In Swiss patent no. 160,797 published in 1933, it is planned to carry out each of the two hands of a large clock in the form of a hollow box having a clear or reflective background and a translucent mat cover. A group of three fixed lamps distributed around the coaxial shafts of the needles produces a beam axial light which penetrates from the rear into the head of each needle, where a mirror distributes the light to the entire bottom of the box. The mirror of one of the hands is offset in the radial direction relative to the mirror of the other to avoid shading. Thus, the majority of the light emitted by the lamps is lost because it passes to side of the mirrors. In addition, such a hollow needle construction is obviously too large to be applicable to a watch.

On the other hand, it has been proposed to illuminate the hands of a timepiece with by means of electroluminescent elements fixed to the transparent or translucent body of each needle (see for example US Pat. No. 5,623,456). Such a system has the disadvantage of requiring rotating electrical contacts which take place and are unreliable in the long run.

In the drawings of patent application JP 55-60894, we see a part timepiece with two coaxial luminous hands made of a transparent material and having diffusing surfaces. The superimposed circular heads of these needles are illuminated by an axial beam coming from a stationary source, in front of which the head of the hour hand has an annular groove with a semi-circular transverse profile. Above this groove, the upper face of this head has a annular bead provided with a diffusing surface for transmitting light toward a similar annular groove in the head of the minute hand. However this construction did not meet commercial success, probably because an unsatisfactory distribution of light in the hands.

To allow analog display by means of luminous hands in portable devices where the available electrical energy is very limited, as in watches, so there is a need for a device capable of providing lighting sufficient at least part of each needle from one or more sources low power fixed lights. In particular compared to the prior art, we aims to increase the light output, i.e. the share of light emitted by the source which is actually returned by the needles to an observer. A goal additional consists of arranging a needle of transparent material so as to especially illuminate certain parts of the body of the needle, so that its position be clearly visible to the observer even if the power available to illuminate the needle is weak.

To this end, according to a first aspect, the present invention relates to a needle for an analog display device, especially in a room timepiece, comprising a piece of transparent material which forms a body and a needle head, said head being centered relative to an axis of rotation of the needle and arranged to receive a light flux on its underside and distribute at least part of this flow in the transparent material, characterized in that the head of the needle comprises a plurality of reflectors distributed in said head and arranged to reflect a part of said luminous flux towards the body of the needle.

According to another aspect of the invention, there is provided a display device for luminous hands for a timepiece, comprising: a dial; needles coaxial arranged above the dial and each comprising a piece in transparent material which forms a head and a needle body, the respective heads needles being superimposed and attached to respective shafts to rotate around a common axis of rotation; and a stationary light source arranged to illuminate all of the needle heads from below by means of a luminous flux substantially parallel to the axis of rotation; the device being characterized in that at at least two of the needles are made in accordance with the first aspect of the invention. Preferably, in each needle considered individually, the reflectors are located roughly the same distance from the axis of rotation, but this distance is different from one needle to another to avoid a reflector a lower needle completely masks a reflector of the overlying needle.

Thanks to these arrangements, the reflectors can advantageously be distributed in the head of the needle not only near the body of the needle, but also in parts of the head located at a distance from this body. Intercept a share of the axial luminous flux over different regions around the needle head provides several advantages. The reflectors may have a larger total area and therefore intercept more light than a reflector placed opposite the body of the needle as provided for in document WO 96/02810. When the light source is formed by two or more small elements, spaced from each other around the axis of rotation, an adequate distribution of the reflectors provides a intensity of reflected light which varies less, during the rotation of the needle, than with a single reflector located opposite the body. In addition, some of the reflectors can advantageously have different respective orientations, which allows light to be preferentially directed towards certain regions of the needle, either to illuminate more specifically these regions, or to obtain a fairly uniform light distribution taking into account the shape of the needle.

• la figure 1 est une vue schématique en coupe verticale d'un dispositif d'affichage analogique de l'heure au moyen d'aiguilles lumineuses selon l'invention dans une montre;
• la figure 2 est une vue de dessus des aiguilles des heures et des minutes représentées dans la figure 1;
• la figure 3 est une vue en perspective de l'aiguille des minutes;
• la figure 4 est une vue en perspective de l'aiguille des heures;
• la figure 5 représente plus en détail l'aiguille des heures, vue de dessus;
• la figure 6 est une vue en coupe suivant la ligne VI-VI de la figure 5;
• la figure 7 est une vue en coupe suivant la ligne VII-VII de la figure 5; et
• la figure 8 est une vue analogue à la figure 7 et représente une variante d'exécution.

Other characteristics and advantages of the present invention will emerge from the description of a preferred embodiment, presented below by way of nonlimiting example with reference to the appended drawings, in which:

• Figure 1 is a schematic vertical sectional view of an analog time display device by means of luminous hands according to the invention in a watch;
• Figure 2 is a top view of the hour and minute hands shown in Figure 1;
• Figure 3 is a perspective view of the minute hand;
• Figure 4 is a perspective view of the hour hand;
• Figure 5 shows in more detail the hour hand, seen from above;
• Figure 6 is a sectional view along line VI-VI of Figure 5;
• Figure 7 is a sectional view along line VII-VII of Figure 5; and
• Figure 8 is a view similar to Figure 7 and shows an alternative embodiment.

In Figure 1, there is shown schematically the outer contour of the case of a wristwatch 1 provided with a time display device including in particular a dial 10, an hour hand 11 and a hand minutes 12, these needles being fixed to respective coaxial shafts 13 and 14 driven by a clockwork movement not shown, in order to revolve around their common axis 15. The dial 10 is placed on a dial support 16 and these two elements have a central hole 17 in which is fixed a light guide 18 formed by the wall of a cylindrical tube of transparent material, which extends around shafts 13 and 14. Below the support 16 is a circuit board prints 20 carrying a light source 21 opposite the underside 22 of the light guide 18, to produce an essentially directed light beam axially, i.e. parallel to axis 15, which is led in this direction by the guide 18. In the present example, the light source 21 is formed by a plurality of light emitting diodes (LEDs) 23 which are distributed around the shafts and mounted on the printed circuit board 20 according to the SMD technique. Diodes 23 are preferably in number of three and are distributed uniformly around the axis, in this case at 120 ° from each other. They are all on at the same time time, for example thanks to a control circuit mounted on the card 20 and set action by means of a manual organ such as a push button of the watch.

The watch movement can be of any type. If he is electronic, it can be mounted either on the underside of the circuit board printed 20, or another card located below.

The hands 11 and 12 are intended to be internally illuminated by the light source 21, to facilitate the reading of the time and in particular to make it time possible in the dark. The dial is not illuminated in the example shown here, but it can be expected, as will be explained later.

In Figure 2, the hour hand 11 is shown in broken lines because it is hidden there by the minute hand 12. In Figures 3 to 6, we have omitted the central sleeve of each needle in order to show only the part transparent needle.

The hour hand 11 has a central metal sleeve 26 and a part 27 (Figure 4) of transparent material which forms an elongated body 28 and a head circular 29 of the needle, the head 29 having a central hole 30 in which is fixed the sleeve 26. The part 27 can advantageously be a part molded in material synthetic, for example PMMA, produced by overmolding on the sleeve metallic. The latter is fixed on the corresponding shaft 14 in the manner usual. The body 28 of the needle preferably has a triangular shape or trapezoidal in plan, but other shapes are possible as required.

The minute hand 12, conventionally arranged above the hour hand 11, also includes a central metal sleeve 32 and a part 33 of transparent material (FIG. 3) comprising an elongated body 34 and a circular head 35 provided with a central hole 36 where the socket 32 is fixed. This part transparent 33 can be made in the same way as part 27 on the other needle, with a head of the same size but a longer body. The upper side of the head 35 of the minute hand is covered with an opaque cover 37 which has been omitted in Figures 2 and 3 to clarify the drawings.

Several reflectors 40 are distributed in the head 29 of the hour hand 11, around the central hole 30 of this head. In the present case, these reflectors are eleven in number and are all located approximately the same distance R1 from the axis of rotation 15. Likewise, several reflectors 41 are distributed in the head 35 of the minute hand 12. In the present case, the reflectors 41 are new and are located substantially at the same distance R2 from the axis 15. This distance R2 is smaller than R1, so that each reflector 41 can always receive a part of the axial light flow coming from the light guide 18 through the needle of the 11 hours, without risking being entirely in the shade of one of the reflectors 40 of this needle. Such a risk is also avoided by the fact that the number and distribution reflectors are different from one needle to another. Each of reflectors 40 and 41 is preferably formed by an oblique surface of a hollow 43 (FIG. 6) in the form of dihedral formed in the transparent head of each needle, one of the faces of the dihedral forming the oblique reflector and the other face 44 of the dihedral being substantially vertical, that is to say parallel to the axis of rotation 15, in order to intercept as little as possible of the flow axial light. The other faces 45 of each hollow 43 are also vertical for the same reason.

In the example shown, the transparent part forming the body 28, 34 and the head 29, 35 of each needle is flat, so that the thickness of the head is the same as that of the needle body. The reflectors 40 and 41 can extend to across the entire thickness of this piece and are tilted at about 45 ° from axis 15 and to the light beam, to reflect the light from the latter towards the interior of the body of each needle. In the plan views of Figures 2 and 5, we note that the reflectors 40 and 41 generally have different orientations, on the one hand to distribute the light reflected in the body of the needle and, on the other hand, so that the light reflected by the most distant reflectors from the body passes as much as possible between reflectors located closer to the body. This is why these are more widely spaced than the former. In addition, the reflectors distant from the body are oriented so as to avoid returning the light to the central hole 30, 36 of the head. An opaque coating, preferably reflective, is applied to the surface device 46, 47 of each needle head 29, 35 to prevent light leakage outward at this location.

Note that a needle as described here can also be made of glass cut and polished.

Thanks to the inclination of approximately 45 ° of the reflectors, any light ray arriving from below on a reflector in a direction substantially parallel to the axis 15 undergoes a total internal reflection, provided that the refractive index of the material transparent is greater than √2, which is the case for PMMA, for various types of glass and other transparent materials which can be used to make such needles. The total internal reflection allows more light energy to be directed towards the body the needle that you could not do with metal reflectors. The guide Light 18 can also be made from one of the materials mentioned above.

The three light-emitting diodes 23 are small and therefore almost point. Each of them emits light with a strong predominance in the axial direction, that is to say parallel to the axis 15. A part of the light which is not parallel to this axis can be reflected by total reflection inside the guide 18 by the cylindrical faces of it. A reflective coating can be applied to the lower part of the lateral surfaces of the guide, where the incident rays are too obliques to fulfill the condition of total internal reflection. However, the intensity of the light coming out of the upper surface of the guide towards the needles is not not uniform all around the beam. The distribution of reflectors 40 and 41, as shown in Figures 2 to 5, is chosen so that the share of reflected light in each needle varies relatively little during rotation of the needle. This distribution therefore depends on the number of diodes forming the source bright 21.

As the light guide 18 is fixed relative to the diodes 23, it is possible to give it an optical configuration tending to produce at its output a optimal light beam, either to standardize the light intensity around the perimeter of the beam, so that most light rays have an axial direction at their exit from the guide. For example, the underside of the guide may have opposite of each diode a form producing a lens effect, in particular in the form Fresnel lenses. Similar arrangements can be provided on the face upper part of the guide.

We notice that it is in the upper hand, here the minute hand 12, that the reflectors 41 are closer to the axis 15, while the reflectors 40 of the other needle are further from the axis. There are two reasons for this. On the one hand, the hole 30 of the lower needle 11 is larger and therefore could hardly be bypassed by the reflected light if the reflectors 40 were close to it. Else hand, as the light intensity in the axial beam is a little bit larger near the interior, it is better to use this part of the beam to illuminate the needle higher, taking into account the dispersion and light losses in the head of the lower needle.

With such an arrangement, numerical simulations have shown that it is possible to obtain an excellent uniformity of the lighting intensity of each body needle during rotation, as well as a good light output, this output being defined as the ratio between the light power passing through a section transverse to the base of the body 28, 34 of one of the two needles and the power total light from source 21. It was found by calculating efficiency values of the order of 3.8% to 4.5% with the arrangement shown, while the yields obtained with reflectors located only opposite the body of the needle are neighbors of only 2%.

To clearly see the position of each needle using the light thus reflected towards the inside of the transparent body of the needle, a solution advantageous consists in providing light scattering surfaces in places suitable, especially on the underside of this body. In the prior art, it has been proposed to realize such diffusing surfaces thanks to a frosted structure or grainy from the surface of the transparent material. With low power light available in the device described here, this embodiment of the surfaces diffusing is not optimal, since the illumination of the surfaces remains too low.

A more effective solution is to visualize the body of the needle using one or more light scattering surfaces which are preferably inclined in relation to the general plane of this body, in order to receive light directly from the reflectors, and are covered with white or colored paint, or fluorescent paint. The painted areas also facilitate daytime visibility of the needle. Figures 5 to 7 show an example of the arrangement of such surfaces diffusing 50 which are formed by the inclined sides of a groove 51 formed in the underside 52 of the body 28 of the hour hand. The groove 51 can be formed during the molding of the transparent part. Its layout preferably follows outer contour of the body 28 so that the observer can see substantially the same needle shape day and night. In addition, this arrangement allows placing opaque structural or decorative elements in the middle area of the body the needle. The paint can be applied simply in one coat, as it is represented by a bold line in the drawings, or fill the entire groove. The other needle will be provided with a similar groove, but having a different layout.

In the variant shown in FIG. 8, diffusing surfaces 54 are formed directly by inclined sides of the underside of the body 28 of the needle.

The examples described above can be subject to multiple modifications or variants without departing from the scope of the invention, as defined by the claims attached. In particular, the number of luminous needles is not limited to two. For example, in a watch with a second hand in the center, it can also be bright and made according to the principles set out above, so that the three coaxial hands are lit by the same axial light beam. In another embodiment of the display device illustrated in Figure 1, we could add a non-luminous central second hand, carried by a shaft which crosses the sleeve 32 and the cover 37 of the minute hand 12. Of course, a needle produced according to the principles of the present invention can also be used as single hand of any indicator, for example on the dashboard of a automobile.

The plurality of reflectors distributed in the head of a needle according to the invention may also include reflectors arranged along the peripheral surface of the needle head and having an inclination close to 45 °. In this case, this peripheral surface will preferably have a serrated shape, so that these reflectors direct the reflected light towards the body of the needle.

Instead of being flat, the body of the needle can have a variable thickness, for example thanks to a lower face which rises towards the point of the needle and which reflects upwards the incident rays. This side inclined longitudinally may also have diffusing surfaces.

Since a thin plastic needle body is relatively deformable, in particular by thermal effects, provision can be made for stiffen by means of external or internal metallic elements, for example a radial bar welded to the central bush.

Instead of being formed by the three light-emitting diodes 23 described below, the light source 21 can be in other forms. We can in particular to use elongated or even annular light sources, to ensure better uniformity of light intensity around the axis.

According to a variant not shown, the dial support 16 could be made of transparent material and combined with guide 18 in order to conduct part of the light from the source 21 below the dial to make certain light openings of the dial and / or hour markers arranged thereon.

According to another variant, the annular light guide 18 could be rotatable and secured to the nearest transparent part of the needle, in this case the hour hand 11 in the example of figure 1, in order to avoid a loss of light between these two elements. On the other hand, the manufacture of this part would be more expensive than that of a flat needle.

Claims (16)

Needle (11, 12) for an analog display device, in particular in a timepiece, comprising a piece of transparent material (27, 33) which forms a body (28, 34) and a head (29, 35) of the needle, said head being centered with respect to an axis of rotation (15) of the needle and arranged to receive a light flux on its underside and to distribute at least part of this flux in the transparent material,
characterized in that the head (29, 35) of the needle comprises a plurality of reflectors (40, 41) distributed in said head and arranged to reflect a part of said light flux towards the body (28, 34) of the needle . Needle according to claim 1, characterized in that the reflectors (40, 41) are distributed in the head of the needle not only near the body of the needle, but also in parts of the head located at a distance from this body. Needle according to one of the preceding claims, characterized in that at least some of the reflectors (40, 41) have different respective orientations. Needle according to one of the preceding claims, characterized in that the reflectors (40, 41) are arranged to produce a total internal reflection of the light rays substantially parallel to said axis (15). Needle according to claim 4, characterized in that each reflector (40, 41) is formed by an oblique surface of a hollow (43) formed in the part made of transparent material. Needle according to claim 5, characterized in that said hollow (43) has the shape of a dihedral, one of the faces of which forms the reflector (40, 41) and the other face (44) is substantially parallel to the rotation axis. Needle according to claim 5, characterized in that the part made of transparent material is a molded part made of synthetic material. Needle according to claim 5, characterized in that the piece of transparent material is flat, its upper and lower faces being flat. Needle according to one of the preceding claims, characterized in that said head (29, 35) has a central hole (30, 36) in which is fixed a sleeve (26, 32) of opaque material. Needle according to one of the preceding claims, characterized in that the body (28, 34) of the needle has on its underside one or more light-diffusing surfaces (50, 54), provided with a white coating or colored. Needle according to claim 10, characterized in that at least one diffusion surface (50, 54) is inclined relative to a plane perpendicular to the axis and is located on an inclined flank of the body of the needle or on a groove (51) formed in a lower face of the body of the needle. Display device with luminous hands for a timepiece, the device comprising a dial (10); coaxial needles (11, 12) arranged above the dial and each comprising a piece of transparent material (27, 33) which forms a head (28, 34) and a needle body (28, 34), the heads respective needles being superimposed and fixed to respective shafts (13, 14) to rotate about a common axis of rotation (15); and a stationary light source (21) arranged to light all the heads of the needles from below by means of a light flux substantially parallel to the axis of rotation;
characterized in that at least two of the needles (11, 12) are produced according to one of the preceding claims. Device according to Claim 12, characterized in that , in each of the said needles, the reflectors (40, 41) are situated substantially at the same distance (R1, R2) from the axis of rotation (15) and in that the said distance is different from one needle to another. Device according to claim 12 or 13, characterized in that the light source (21) comprises light-emitting diodes (23) which are distributed around said shafts (13, 14) and mounted on a printed circuit element (20) arranged below the dial (10). Device according to one of claims 12 to 14, characterized in that a light guide (18) formed by the wall of a tube of transparent material is disposed between the light source and the heads of the needles, this tube being fixed in a central opening of the dial. Watch comprising a display device according to one of the claims 12 to 15.

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