GB2143987A - Time display for LCD analog timepiece - Google Patents

Abstract

An LCD Analog watch includes a liquid crystal display with radial segments representing "hands" 3, 4, 5 to show hours, minutes and seconds and having a reflector with time indicating indicia thereon disposed beneath the "hands". The indicia appear in the plane of the reflector and the "hands" provide images spaced above the reflector, giving an illusion of hands of a conventional mechanical watch spaced from a watch dial. <IMAGE>

Description

SPECIFICATION Time display for LCD analog timepiece This invention relates to a time display for a timepiece with a liquid crystal display, such as wristwatch of the type known variously as an LCD analog watch or a liquid crystal analog (LCA) watch, which represents the time simulating conventional mechanical hour and minute hands. More particularly, the invention relates to an improved means to create an illusion of depth or intentional parallax to simulate mechanical hands above a dial.

LCA watches have been proposed and known for some time, an early example being shown in US-3,5409,209 which discloses an electronic watch with radial hour, minute and second hands simulated on a liquid crystal display of the dynamic scattering type with no polarizers, i.e. a display in which the liquid crystal between opposed conductive plates is ordinarily clear when the plates are not activated, but becomes turbid to scatter the light and obscure the plates beneath when the plates are activated. The patent employs conductive radial segments evenly spaced on the back of the crystal or on the face of the dial.

The crystal is spaced from the dial a short distance and the space filled with suitable dynamic scattering liquid crystal material.

Dynamic scattering displays have been found generally unsatisfactory, since the activated segments are silvery and reflective in appearance and are difficult to read. Twisted nematic displays with polarizers have been developed which consume very little power and are particularly suitable for wrist watches.

For the most part, these displays are used to display the time using digits rather than radial "hands". Digits do not need any spatial frame of reference, and the primary emphasis in liquid crystal digital watches has been to provide improved readability and contrast.

Various types of reflectors have been provided, generally with diffusers to provide a uniform background for the digits and to increase the brightness of the display. For example, reflectors of metallic foil have commonly been placed behind the rear polarizer layer of the display. In cases where the display includes a light source for nighttime viewing, a "transflector" has been used. The transflector will reflect incident ambient light during daytime operation, and will also be translucent to light from a light source behind the display. A transflector typically comprises a translucent frosted glass or plastic sheet and/or a thin metallic layer or deposit.

US.-4,196,973 shows a transflector, while US--4, 106,859, US-4,249,801 and Us-3,881 ,809 show LCD reflectors, these only being exemplary of many patents. The foregoing reflectors are generally intended to reflect and diffuse light and have no indicia inscribd on them.

US-3,973,338 shows a digital liquid crystal display in which the glass substrate on the reflector side of the display is reduced in thickness in order to reduce a shadow effect caused by reflection from the upper side of the lower glass substrate. An irregular or lightscattering reflector is used and the stated purpose of the invention is to reduce or eliminate a shadow effect. US-3,910,033 shows a construction for a watch dial, not in a liquid crystal display, which creates an interference pattern by adding a thick layer on a watch dial so that inteferring reflection patterns are created frkom the dial and from the surface of the layer.

LCA watches have heretofore been designed along the same lines as LCD digital watches, which results in a flat or single dimensional apearance of the hands. On the other hand, persons accustomed to conventional watches with hands are also accustomed to the three dimensional effect or parallax due to the spacing between the hands and the top of the watch dial, creating shadows and perception of distance between the hands and the dial.

The illusion of conventional mechanical hands would be enhanced by a construction which caused liquid crystal display hands to appear to be spaced from the dial.

Accordingly, one object of the present invention is to provide an LCA timepiece such as a watch in which the hands appear to be spaced from the conventional watch dial.

Another object of the invention is to provide an LCA timepiece such as a watch giving an illusion of a conventional watch with analog hands.

Briefly stated, the present invention provides a time display for a liquid crystal analog timepiece of the type having a liquid crystal display with radially extending segments adapting to simulate the hands of a timepiece comprising a reflector dial disposed beneath the liquid crystal display, said reflector dial having a reflective surface adapted to reflect incident light to form a perceived visual image of a timepiece hand at a location spaced from the reflector dial, said reflector dial also having light absorbing indicia thereon disposed beneath the segments and adapted to provide perceived images in the reflector dial plane, whereby the hands appear to be spaced above said indicia.

An embodiment of the present invention will now be described by way of example, reference being made to the accompanying drawings, in which: Figure 1 is a plan view of an LCA watch embodying a time display according to the invention.

Figure 2 is an enlarged cross sectional elevation taken along line 2-2 in Fig. 1, Figure 3 is a diagrammatic cross-sectional drawing, not to scale, illustrating the theory of operation, and Figure 4 is a further diagrammatic drawing illustrating operation of the invention.

Referring now to Fig. 1 of the drawings, a timepiece comprises a wrist watch 1 with an exterior case 2 containing an electronic module and power source (not shown). The module includes an integrated circuit adapted to provide multiplexed output drive signals to actuate a twisted nematic, field effect, liquid crystal display of a type also well known in the art. The display provides visible radial segments, which advance clockwise from one position to the next, in the manner of conventional hour, minute and second hands. In the embodiment shown, a short inner radial segment 3 simulates an hour hand, a short outer radial segment 4 simulates a second hand, and two such segments are combined as a long segment to simulate a long minute hand 5. Visible beneath hands 3, 4 and 5 are timekeeping indicia, such as numerals 6, radial minute or "seconds" markers 7.In the embodiment shown, the numerals are imprinted on a partially reflective annular track 8.

Setting of the timepiece is accomplished by means of a side-mounted command bar 9 which actuates internal switches inside the case. Any type of switch actuating mechanism may be employed, but in the preferred embodiment, the actuator is of the type shown in GB 2 100 518A. The hands 3, 4, 5 are obtained in a twisted nematic field effect liquid crystal display by imposing electrical potentials in a preselected sequence on transparent conductive areas on closely spaced upper and lower glass substrates. The space between the substrates contains an aligned, twisted nematic liquid crystal material which, when subjected to an electric field between opposed segments and viewed through crossed polarizers disposed above and below the glass substrates will render the hands visible.The field is created by selectively and periodically applying multiplexed electric potentials to the desired conductive areas or electrodes. A suitable display and driving circuit for a liquid crystal analog timepiece is disclosed in US 4,209,974 there also being other suitable circuits and arrangments known in the art.

Referring to Fig. 2 of the drawings, the electronic module in a plastics pod 10 is enclosed by a case back 11. A transparent front lens 1 2 is sealed within an annular recess 14 in watch case 2 by a gasket 15. An integrated annular ledge 1 6 with a decorativa bevel 1 7 is visible through the lens 1 2 and forms a frame for the display.

A display with reflector dial, indicated generally at 18, is held in place between pod 10 and ledge 16. The display includes a top polarizer 19, a top glass substrate 20, a bottom glass substrate 21, and bottom polarizer 22, and a reflector dial 23. The liquid crystal material is sealed between the upper and lower glass substrates 20, 21 and aligned so that it will rotate incident polarized light in a manner known to those skilled in the art.

In accordance with the present invention, the reflector dial has a light-reflecting surface.

Preferably the reflector dial is a metal sheet, suitably a sheet of brass material which is nickel plated and then silver plated to give a highly reflective surface. This is then mechanically brushed or burnished to give the desired reflective characteristics. The reflector dial has indicia thereon of light-absorbing material, preferably imprinted thereon by transfer printing using ordinary light-absorbing paint in the form of numerals, symbols, radial markers, etc. The annular track 8 may be either imprinted or etched to provide a partially lightabsorbing background which serves to provide a perceived image in the reflector dial plane.

The indicia are also arranged in an annular pattern around the centre of the display so that they are located beneath one or more of the hands 3, 4 and 5. They may be in a circular, elliptical, or racetrack pattern as well.

Referring now to Fig. 3 of the drawings, a diagrammatic representation of a portion of the display shows the polarizer sheets 19, 22, the glass substrates 20, 21, and the reflector dial 23. The liquid crystal material is indicated at 24. Two opposed transparent conductive segments 25, 26 on the upper and lower glass substrates respectively may be activated to provided one of the timepiece hands. A light absorbing indicia 27 on the reflector dial 23 represents a portion of a numeral, hour marker or other indicia providing spatial relationship for indicating time. An incident ray of ambient light 28 is polarized by top polarizer 19, rotated 90 degrees by liquid crystal 24, passes through crossed bottom polarizer 22 and is reflected by the reflective portion of dial 23. The reflected ray is polarized by bottom polarizer 22, and passes through the activated conductive areas 25, 26. Since the rotative power of the liquid crystal is cancelled by the field between conductive areas, the light passes through without rotation and is then extinguished by the crossed polarizer 1 9.

The eye perceives an image in the plane of the top polarizer at 29. On the other hand, the light absorbing indicia 27 is perceived by the eye in the plane of the reflector dial 23.

Under some viewing conditions, depending upon the angle of viewing, an incident ray 30 will create a fainter perceived image at 31, which appears to be a shadow of the darker image 29.

Referring to Fig. 4 of the drawings, where the perceived image 29 of the hand in the plane of the top polarizer is seen together with the indicia 27 on the reflector dial in the plane of the refleCtor, an illusion is created of space between hand image 29 and indicia 27, similar to conventional timepiece hands above a dial. Depending upon whether the images are viewed from a position 32 or from a position 33, image 29 will either be on one side or on the other side of image 27. Therefore, a thee-dimensional effect is obtained due to the eyes of the viewer seeing the images from slightly different angles.

Various other types of reflective surfaces on reflector dial 23 having light absorbing contrasting areas thereon may be used to create the illusion of spacing between the liquid crystal analog hands and the surface of the reflector dial. For example, such surfaces may consist of special radial brushing, i.e. outwardly from the centre of the dial. This serves to reflect the ambient light at different angles and give an effect equivalent to light absorption over preshaped sectors of the dial.

Various other types of liquid crystal displays may be used. A guest/host liquid crystal display, without polarizers, operates to create a perceived image of the hand in the space between the two glass substrates. The effect of parallax is not as great, because the spacing is due only to one thickness of glass rather than two thicknesses. However, the principle of operation is the same.

Claims (8)

1. A time display for a liquid crystal analog timepiece of the type having a liquid crystal display with radially extending segments adapting to simulate the hands of a timepiece comprising a reflector dial disposed beneath the liquid crystal display, said reflector dial having a reflective surface adapted to reflect incident light to form a perceived visual image of a timepiece hand at a location spaced from the reflector dial, said reflector dial also having light absorbing indicia thereon disposed beneath the segments and adapted to provide perceived images in the reflector dial plane, whereby the hands appear to be spaced above said indicia.

2. A time display according to Claim 1, where said liquid crystal display is the guest/ host type providing a perceived hand image between said substrates.

3. A time display according to Claim 1, wherein the liquid crystal display is the twisted nematic field effect type with top and bottom polarizers. wherein the perceived image is formed in the plane of the top polarizer.

4. A time display for a liquid crystal analog timepiece comprising a twisted nematic field effect liquid crystal material between top and bottom transparent substrates, said substrates having transparent conductive areas thereon arranged to provide radially extending segments for simulating the hands of a timepiece, and top and bottom polarizers disposed on either side of said substrates, and a reflector dial disposed beneath the bottom polarizer, said reflector dial having a reflective surface thereon adapted to reflect incident light to form perceived hand images in the plane of the top polarizer, and having light absorbing indicia thereon disposed beneath the segments and adapted to provide perceived images of said indicia in the reflector dial plane, whereby the hands appear to be spaced above said indicia.

5. A time display according to Claim 4, wherein said indicia comprise printed numerals on the reflector dial disposed beneath said perceived hand images.

6. A time display according to Claim 4, wherein said indicia comprises an annular track of partially light-absorbing areas disposed beneath said-perceived hand images.

7. A time display according to Claim 4, wherein said indicia comprise a plurality of radial hour markers arranged around the reflector dial in a closed annular path beneath said perceived hand images.

8. A time display for a liquid crystal analog timepiece, substantially as hereinbefore described with reference to the accompanying drawings.