EP1647867A1 - Magnifying device for timepieces - Google Patents

Abstract

The magnification device compensates distortion of the marked characters on a dial (10) caused by magnifying lens, by writing the characters with a reverse pin cushion or barrel distortion in direction opposite to distortion caused by lens.

Description

TECHNICAL AREA

The present invention relates to a magnification device for a timepiece which makes it possible to compensate in a simple manner the distortions of the information to be read on part of the dial through a magnifying lens.

BACKGROUND

The information generally appears as alphanumeric characters on an LCD display, or in a window cut in the dial, to give additional information of the current time, such as the date, the month or the day of the week, or even non-hourly information such as the ON / OFF status of a function. In the latter case, this information is carried by discs or rings driven by the watch movement and are constituted by successions of alphanumeric signs or pictograms of small dimensions, with the exception, of course, of so-called "big calendar" devices whose the disadvantage is to use a more bulky mechanism, more complicated and therefore more expensive.

To provide the user with a better reading of the information displayed, the manufacturers have long thought of placing a magnifying glass above the information to be read. By way of example, patent JP 62014083 can be cited in which a convex lens is provided in the dial at an LCD display, said dial also comprising an analogue display by means of hands. In JP 61205889 the magnifying device is constituted by a magnifying ring formed in the outer portion of the ice. The magnifying device may also be provided in the inner face of the glass by adding a lens in a housing provided for this purpose, as described in patent EP 0 814 388, or by machining said lens in the inner face of the lens. ice, as described for example in US Patent 6,406,769.

All these devices magnify and make more readable information carried by the dial, but necessarily induce more or less significant distortions. It is known to correct such distortions, for example in photographic apparatus, by means of a stack of corrective lenses, as described, for example, in patent application US 2003/0189760. In a timepiece, given the small space available between the dial and the ice and the possible occupation of this space by needles, it is not possible to perform this optical correction by means of such a stack of lenses.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the drawbacks of the aforementioned prior art by providing an arrangement between the magnification means and the information to be read which eliminates, or at least greatly reduces, the distortions, by giving back, as it were, to the information read the appearance they should have without a magnifying device.

For this purpose the invention relates to a device for enlarging alphanumeric characters or pictrograms located at the dial of a timepiece by means of a single magnifying lens. The device is characterized in that the character or pictrogram writing is distorted in a direction opposite to the distortion caused by the lens, so that the characters can be read without deformation. From the geometrical and physical characteristics of a lens it is possible to foresee what will be the type of distortion, for example in cushion or barrel for a circular lens, and to modify accordingly the writing of the characters, which would appear then deformed if one did not read them through the lens.

The lens can be positioned at the level of the dial, immediately above the characters, without disturbing the rotation of the needle. It can also be positioned at the inner face or the outer face of the ice.

Regarding the alphanumeric characters to appear under the lens, they can be formed by means of a digital liquid crystal display (LCD), or even more simply, be written on a date disc, driven by the movement of watchmaker next to a counter. The information displayed in these windows may be time-related or time-independent, such as the ON / OFF status of a function built into the timepiece.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1 est une représentation en perspective partiellement arrachée d'un exemple de réalisation d'un dispositif de grossissement selon l'invention ;
• la figure 2 est une coupe diagonale selon les flèches II - II de la figure 1 ;
• la figure 3 est une vue partielle agrandie au niveau de la lentille grossissante ;
• les figures 4A et 4B représentent schématiquement les déformations qu'on peut observe avec une lentille grossissante ;
• la figure 5 correspond au diagramme de distorsion d'une lentille ayant les caractéristiques de celle représentée à la figure 3 ;
• les figures 6A et 6B correspondent à deux écritures d'un nombre, pouvant être lu sans distorsion à travers une lentille, comme représenté à la figure 7, et
• les figures 8A et 8B, et respectivement 9A et 9B, correspondent à deux autres exemples de correction de distorsion pour des lettres.

Other features and advantages of the present invention will appear in the following description given by way of illustration and without limitation, with reference to the appended drawings in which:

• Figure 1 is a partially cutaway perspective representation of an exemplary embodiment of a magnification device according to the invention;
• Figure 2 is a diagonal section along the arrows II - II of Figure 1;
• Figure 3 is an enlarged partial view at the magnifying lens;
• Figures 4A and 4B schematically show the deformations that can be observed with a magnifying lens;
• Figure 5 is the distortion diagram of a lens having the characteristics of that shown in Figure 3;
• FIGS. 6A and 6B correspond to two writes of a number, which can be read without distortion through a lens, as shown in FIG. 7, and
• FIGS. 8A and 8B, and 9A and 9B respectively, correspond to two other examples of distortion correction for letters.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show, by way of example, a wristwatch comprising a magnification device according to the invention at the level of its dial 10. The dial 10 is placed in a circular case comprising a middle part 2 closed at its part upper by an ice 1 maintained between a flange 3 and a bezel 4, and at its bottom by a bottom 5 defining a housing 6. The housing 6 is intended to receive a power source 7 for supplying the control means 8 of the display. In this example, the control means 8 are constituted by a time-keeping circuit designed to control a stepping motor 9 to drive needles 11a, 11b for reading the current time and a date disc 12, located under the dial 10, on which are inscribed characters 14 scrolling next to a window 16 cut in the dial 10. The window 16 is surmounted by a magnifying lens which cooperates with the writing of the characters 14, as explained below by an embodiment of the following figures.

FIG. 3 is an enlarged sectional view at the level of the magnifying device constituted, in this example, by a plano-convex lens made of a material of refractive index n , with a radius of curvature R = 2.5 mm, of maximum thickness d ₂ = 2 mm and located at a distance d ₃ = 2 mm from the characters 14 represented by the number 24. Such a lens induces a pincushion deformation whose frame is shown in FIG. 4A. Figure 6 shows the percentage of distortion along Y corresponding to the radial distance of a point-object from the center of the lens. The scale is 1/10 of the distance from the farthest point-object. To compensate for this distortion, the number 24 is barrel deformed, as shown in FIG. 7A, from the "inverse" distortion percentages deductible from the diagram of FIG. 6, to appear without deformation, as represented in FIG. 7.

With the same lens having different parameters d ₂ , d ₃ , or with another lens giving a distortion of the number 24 in a barrel (FIG. 4B), it suffices to write the number 24 in "pad", as represented in FIG. 6B, so that the observer perceives an undistorted image, as shown in FIG. 7.

Figures 8A and 8B give another example with the letters FEB, to designate the month of February, deformed in barrel (Figure 8A) for a lens causing pincushion deformation. The other example represented in FIGS. 9A and 9B concerns the letters MON to designate a day of the week, as much information as can be delivered by the date wheel.

As seen with the above-mentioned examples, no additional lens is necessary, the optical distortion correction being obtained by the writing of the characters, that is to say very simply and very economically, including for timepieces already in production for which it suffices simply to modify the printing of the characters according to the characteristics (n, R, d ₂ , d ₃ ) of the magnifying lens.

It is quite obvious that the example which has just been given would be entirely transposable to a lens located at the level of the ice, on its internal or external face, or to a digital display with liquid crystals.

Claims (5)

Device for enlarging alphanumeric characters or pictograms (14) to be read on the dial (10) of a timepiece, formed of a housing closed by an ice (1) and a bottom (5) and containing a watch movement, said magnification being obtained by means of a single magnifying lens (20), characterized in that the writing of the characters (14) is deformed in a direction opposite to the distortion caused by the lens (20). Magnification device according to claim 1, characterized in that the lens (20) is positioned at the dial level (10) immediately above the alphanumeric characters or pictograms (14). Magnifying device according to claim 1, characterized in that the lens (20) is positioned at the ice (1) or formed in said ice (1). Magnification device according to Claim 1, characterized in that the alphanumeric characters or the pictograms (14) are inscribed on a date disc (12) driven by the watch movement opposite a window (16). Magnification device according to Claim 1, characterized in that the alphanumeric characters or the pictograms (14) are formed by a digital liquid crystal display (LCD).

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