GB1579088A - Electro-optical display installed in a housing and use of the display - Google Patents

Abstract

For the purpose of producing liquid-crystal wristwatches whose entire display surface can be read even when they are in a tilted state, provision is made of a front fibre-optic cell plate (14) with light-conducting fibres (14a) running perpendicular to the display surface. The display device has, in addition, a cholesteric guest/host liquid-crystal cell. The front fibre-optic cell plate (14) has an optical resolution of 5 to 100 lines per millimetre and a numerical aperture (NA) of 0.5 to 1.05. The measures described furthermore permit the realisation of flat digital watches which are aesthetically pleasing, i.e. provided with dished/cambered front cell plates. <IMAGE>

Description

(54) ELECTROOPTICAL DISPLAY INSTALLED IN A HOUSING, AND USE OF THE DISPLAY (71) We, BBC BROWN, BOVERI & COMPANY LIMITED, a Company organised under the laws of Switzerland, of CH-5401, Baden, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The present invention relates to an electrooptical display of the type installed in the front of a housing, preferably intended for a wristlet watch, with mutually opposite cell plates provided internally with electrode patterns which conjointly with spacing elements at the edges enclose an electrooptical medium, at least the front cell plate and the front electrode pattern being transparent, and a fibre optics cell plate with optical fibres extending at right angles to the display surface being provided in front.

Such a display, intended preferably for a balance, is known from DT-OS 24 61 239.

Because the electrooptical effect in this known device is caused solely by the dynamic control, such devices can be operated exclusively on the transmission principle with collimated illumination. The reflection behaviour of the device described is unsuitable for applications in practice, because the information displayed is much too dark. This is because the electrooptical effect in this device can be observed only by virtue of the extremely low return scatter of the dynamically scattered incident light.

It is therefore the aim of the invention to produce a display of the aforesaid type which exhibits good readability and high contrast even when operated on the reflection principle, and which furthermore is readable on its entire display surface even in the tilted state.

According to the present invention, we provide an electrooptical display of the aforesaid type, wherein as the electrooptical medium a cholesteric liquid crystal substance utilizing the guest-host effect is provided, the front fibre optics cell plate exhibiting an optical resolution of 5 to 100 lines per millimetre and a numerical aperture (NA) of 0.5 to 1.05, and a reflector being arranged on the side of the display remote from the observer.

The invention will be explained more fully with reference to the accompanying drawings showing exemplary embodiments in comparison to the prior art.

In the drawings: Fig. 1 shows the fundamental cell structure of electrooptical displays according to the prior art, Fig. 2 shows a display of fig. 1 installed in a wristlet watch according to the prior art, Fig. 3a shows the wristlet watch of fig. 2, viewing the display surface at right angles, Fig. 3b shows the wristlet watch of fig. 2 viewed at an oblique angle to the display surface, Fig. 4 shows a first electrooptical display with front fibre optics cell plate, installed in a wristlet watch, Fig. 5a shows the wristlet watch of fig. 4, viewed at right angles to the display surface, Fig. 5b shows the wristlet watch of fig. 4, viewed at an oblique angle to the display surface, and Fig. 6 shows a wristlet watch with a second display according to the invention with domed front fibre optics cell plate, installed in a wristlet watch with housing domed in the same radius.

Parts with identical functions are designated by the same reference numerals in all the drawings.

The fundamental construction of such displays may be seen in fig. 1, where a front cell plate lis provided with a transparent electrode 2 exhibiting e.g., an alphanumeric and/or ríumeri- cal pattern. A rear cell plate 4 exhibits a likewise rear electrode 3. The two cell plates 1 and 4 eonstitute, by a spacing element 5 - e.g., an encircling glass solder strip - at the edges a cell which encloses an electrooptical medium 6, e.g., nematic and/or cholesteric liquid crystals.

By the application, e.g., of a voltage source, to mutually opposite segments of the electrodes 2 and 3, the electrooptical medium 6 can be changed over from a first optical state into a second optical state. An observer B consequently sees the light incident upon the cell in the direction of the arrow, which is reflected by a reflector 7 integrated in the cell or present outside the cell, as optical information.

The disadvantage of the prior art can be demonstrated by the example of an electrooptical display incorporated in a wristlet watch, figs. 2, 3a and 3b.

When observing the watch, or its front glass 10, at right angles, fig. 3a, the time indicated can be read without difficulty. However if the watch is tilted - the state during normal wear on the wrist - illustrated in fig. 3b, a part of the numerals displaying the time disappears from view.

Considering the assembly of the display in the watch housing 11, in the sectional view fig. 2, it will be seen that the above illustrated disadvantage comes about because the electrooptical cell, characterised by the cell plates 1 and 4, is set too deeply in the watch housing.

This construction, fig. 2, comprising a relatively thick front glass 10 inserted in the watch housing 11 and a mask 12 having a configuration suited to the display surface of the cell, is virtually compulsory from aesthetic and mechanical considerations in the prior art.

For the sake of completeness, the contacting of electrode leads by a contact-rubber strip 13 is likewise illustrated in fig. 2.

A first electrooptic'al display according to the invention, fig. 4, is incorporated in a flat watch housing 11. This display is a cholesteric guest-host liquid crystal display (e.g., as DT-OS 24 10 557) with a reflector integrated'in the cell, cf. fig. 1.

14 designates in fig.4'a fibre optics cell plate which exhibits optical fibres 14a extending at right angles to the display surface.

For this purpose, fibre optics cell plates 14 with an optical resolution of 5 to 100 lines per millimetre, preferably with 80 lines per millimetre, and with a numerical aperture NA of 0.5 to 1.05, have been found satisfactory. The numerical aperture NA corresponds to the aperture of the optical fibres and is a function of the materials for the core and envelope glasses used in fibre optics, and their refractive indices.

It has been found advantageous to use fibre optics cell plates with a numerical aperture of 1.05, because with values differing greatly from NA 1.0 a reduction of the observàtion angle prescribed by the optical characteristics of the electrically switchable medium (liquid crystal layer) would occur.

As may be seen from fig. 4, the fundamental construction of the display has not been modified by the use of a fibre optics cell plate 14.

Fibre optics plates are commercially well known; their physical characteristics also demand no modification to the production technique of displays hitherto equipped with conventional glasses equipped with conductive electrode coatings.

In addition to the application of gluing techniques at relatively low process temperatures, the well-tried glass soldering technique is also suitable for cell production; suitable glass solder powders are available (Fibre Optics Information Leaflet No. 7022e, Jenaer Glaswerk Schott & Gen., Mainz BRD).

The front transparent electrode 2 required to activate the electrically switchable medium, cf. fig. 1, can likewise be deposited in known manner on the inside of the fibre optics cell plate 14 (cf. e.g., J. Fan and F. Bachner, Journal of Electrochem. Soc. 122, 1719 (1975)).

Such a display can be incorporated or glued into the front of a housing.

The assembly and operating principle of the display can be demonstrated by the example of a wristlet watch, figs. 4 - Sb.

The fibre optics cell plate 14, fig. 4, is ground so as to be shouldered at its edges, and is glued form-lockingly and fluid-tightly into the watch housing 11, its display surface being flush with the front of the housing.

When observing the display surface at right angles, fig. Sa, the time indication (12.03) appears parallax-free on the front surface of the fibre optics cell plate 14 and is readable irrespectively of its thickness chosen according to the desired mechanical characteristics, without restricting the original. The rectangular window in the watch housing 11 acts here as an ideal mask without shading the display surface. Even under night illumination - by a miniature lamp on the rear cell plate - the reading is clearly visible.

It will be seen from fig. Sb that even when observing the display surface at an oblique angle, the time indication is completely readable without distortion notwithstanding its optical transformation at the surface (cf. by comparison fig; 3b).

The second exemplary embodiment of the invention, fig. 6, shows a fibre optics cell plate 14 domed correspondingly to the radius of the watch housing 11. Thus the invention finally makes possible the desired realisation of aesthetically appealing digital watches, which hitherto appeared impossible due to the necessity of flat cell plates.

The application of the invention is restricted to a of cholesteric guest-host liquid crystal display as e.g. described in J..,A pl. Phys., 45, No. 11, Nov. 1974, pp. 4718 - 4723.

The novel display is provided for installation in fronts of housings of stationary appliances (as in switch rooms etc.) and mobile appliances. However, due to the excellent optical characteristics, such a display is particularly advantageous when used to indicate information in wristlet watches.

WHAT WE CLAIM IS: 1. An electrooptical display installed in the front of a housing, with mutually opposite cell plates provided internally with electrode patterns which conjointly with spacing elements at the edges enclose an electrooptical medium, at least the front cell plate and the front electrode pattern being transparent, and a fibre optics cell plate with optical fibres extending at right angles to the display surface being provided in front, wherein as the electrooptical medium a cholesteric liquid crystal substance utilizing the guest-host effect is provided, the front fibre optics cell plate exhibiting an optical resolution of 5 to 100 lines per millimetre and a numerical aperture (NA) of 0.5 to 1.05, and a reflector being arranged on the side of the display remote from the observer.

2. An electrooptical display according to claim 1, wherein the front fibre optics cell plate extends with its display surface flush with the front of the housing.

3. An electrooptical display according to claim 2, wherein the front fibre optics cell plate is shouldered at its edges.

4. An electrooptical display according to claim 2 or 3, wherein the front fibre optics cell plate is domed.

5. An electrooptical display substantially as hereinbefore described with reference to and as shown in Figs. 4, Sa and Sb, or in Fig. 6, of the accompanying drawings.

6. A wristlet watch in which is installed a display according to any of claims 1 to 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. It will be seen from fig. Sb that even when observing the display surface at an oblique angle, the time indication is completely readable without distortion notwithstanding its optical transformation at the surface (cf. by comparison fig; 3b). The second exemplary embodiment of the invention, fig. 6, shows a fibre optics cell plate 14 domed correspondingly to the radius of the watch housing 11. Thus the invention finally makes possible the desired realisation of aesthetically appealing digital watches, which hitherto appeared impossible due to the necessity of flat cell plates. The application of the invention is restricted to a of cholesteric guest-host liquid crystal display as e.g. described in J..,A pl. Phys., 45, No. 11, Nov. 1974, pp. 4718 - 4723. The novel display is provided for installation in fronts of housings of stationary appliances (as in switch rooms etc.) and mobile appliances. However, due to the excellent optical characteristics, such a display is particularly advantageous when used to indicate information in wristlet watches. WHAT WE CLAIM IS:

1. An electrooptical display installed in the front of a housing, with mutually opposite cell plates provided internally with electrode patterns which conjointly with spacing elements at the edges enclose an electrooptical medium, at least the front cell plate and the front electrode pattern being transparent, and a fibre optics cell plate with optical fibres extending at right angles to the display surface being provided in front, wherein as the electrooptical medium a cholesteric liquid crystal substance utilizing the guest-host effect is provided, the front fibre optics cell plate exhibiting an optical resolution of 5 to 100 lines per millimetre and a numerical aperture (NA) of 0.5 to 1.05, and a reflector being arranged on the side of the display remote from the observer.

2. An electrooptical display according to claim 1, wherein the front fibre optics cell plate extends with its display surface flush with the front of the housing.

3. An electrooptical display according to claim 2, wherein the front fibre optics cell plate is shouldered at its edges.

4. An electrooptical display according to claim 2 or 3, wherein the front fibre optics cell plate is domed.

5. An electrooptical display substantially as hereinbefore described with reference to and as shown in Figs. 4, Sa and Sb, or in Fig. 6, of the accompanying drawings.

6. A wristlet watch in which is installed a display according to any of claims 1 to 5.