Computer graphics processing and selective visual display system – Single display system having stacked superimposed display...
Reexamination Certificate
2000-09-12
2003-07-01
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Single display system having stacked superimposed display...
C368S084000
Reexamination Certificate
active
06587083
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a display assembly including two superposed display devices and, more particularly, an assembly of this type including means allowing one of the display devices to appear to an observer selectively, to the exclusion of the other.
The present invention also concerns a timepiece including a display assembly of the aforementioned type and, more particularly, such a display assembly wherein an analogue display device is combined with a digital display device.
A display assembly including two superposed display devices is already known from European Patent No. EP 0 926 574 in the name of the Applicant. This display assembly is shown in
FIG. 1
annexed to the present Patent Application.
FIG. 1
shows a timepiece of the wristwatch type designated as a whole by the general numerical reference
1
. This watch
1
includes, in a conventional manner, a case
2
in the back cover
4
of which are arranged an electronic clockwork movement
6
and a battery
8
which rest on back cover
4
via a contact spring
10
. Movement
6
includes electronic timekeeping circuits associated, via a control circuit, to a drive device (not shown) for a second hand
12
, a minute hand
14
and an hour hand
16
which move above a dial
18
which bears hour symbols (not shown). Case
2
is also closed in a conventional manner by a crystal
20
covering all of dial
18
.
Watch
1
further includes a display assembly including two superposed display devices respectively top device
22
and bottom device
24
.
In the example shown in
FIG. 1
, bottom display device
24
includes analogue time display means formed by hands
12
,
14
and
16
and dial
18
.
According to the invention disclosed in European Patent No. EP 0 926 574, top display device
22
includes a double structure formed of a display cell
26
arranged above an optical valve
28
, this display device
22
extending between bottom display device
24
and crystal
20
.
Top display device
22
is arranged, on the one hand, so that display cell
26
, arranged between crystal
20
and optical valve
28
, like the latter, is transparent in a first switching state of cell
26
and valve
28
, so as to make the data displayed by bottom display device
24
, i.e. hands
12
,
14
and
16
and dial
18
, visible.
On the other hand, top display device
22
is arranged so that display cell
22
displays an item of data, for example of the alphanumerical type, and so that valve
28
masks bottom display device
24
in a second switching state.
As a result of these features, it is possible to use selectively either bottom display device
24
, or top display device
22
. If one chooses to use bottom display device
24
, top display device
22
can be switched into its first state in which it is transparent, so that the data displayed by bottom display device
24
is visible. If, conversely, one chooses to use top display device
22
, optical valve
28
is then switched into the second state in which it is opaque and reflective to completely mask bottom display device
24
, while cell
26
of top display device
22
can display the desired data.
According to the particular embodiment shown in
FIG. 1
, cell
26
is a liquid crystal type display cell. Cell
26
includes a transparent front substrate
30
, a back substrate
32
which is also transparent and a sealing frame
34
forming spacing and closing means which, with substrates
30
and
32
, delimit a closed cavity in which is located a layer of liquid crystals. The opposite faces of substrates
30
and
32
include transparent electrodes respectively
36
and
38
, made, for example, of indium/tin oxide. In the example illustrated, front substrate
30
carries electrodes configured in digits each formed of segments allowing alphanumerical characters to be displayed, while back substrate
32
carries an electrode extending over its entire surface.
When a voltage is applied or removed across electrode
38
and certain of electrodes
36
, the liquid crystals located between these electrodes
36
and
38
are switched alternately from an absorbent state to a transparent state or vice versa, according to the type of liquid crystals in question and/or the presence and arrangement of polarisers associated with the cell. It is thus possible to display data in a light colour on a dark background or in a dark colour on a light background.
In the following description, elements which are identical to those previously described will be designated by the same numerical references.
In the example shown in
FIGS. 2A and 2B
annexed to the present patent Application, display cell
26
is a liquid crystal cell of the twisted nematic type of which the respective outer surfaces of substrates
30
and
32
are provided with absorbent polarisers
40
and
42
of crossed orientation. Thus, cell
26
is completely transparent in the first switching state (FIG.
2
A), when no voltage is applied across the terminals of its electrodes
36
,
38
(non-switched state), and is absorbent or diffusing in the second switching state (FIG.
2
B), when a voltage is applied across the terminals of its electrodes
36
,
38
(switched state). In the example shown, the optical valve includes, starting from the side of dial
18
, a reflective polariser
44
and a liquid crystal cell of the twisted nematic type. Valve
28
is thus transparent in the non-switched state (
FIG. 2A
) and opaque and reflective in the switched state (FIG.
2
B).
In the first switching state shown in
FIG. 2A
the natural non-polarised light, designated by the numerical reference
46
, is vertically polarised by first absorbent polariser
40
. The direction of polarisation of the light, designated by the reference
48
, is then rotated by 90° during its passage through display cell
26
, then it is transmitted unmodified by second absorbent polariser
42
. Polarised light
48
is then again rotated through 90° during its passage through optical valve
28
, then it is transmitted unmodified by reflective polariser
44
to dial
18
. The light follows the same path during its return travel, so that the dial is visible to an observer
50
.
Conversely, when cell
26
and valve
28
are in the switched state, the dial is totally masked. Indeed, as is seen in
FIG. 2B
, the vertically polarised light which passes through cell
26
in the switched zones of the latter is not modified, so that it is absorbed by absorbent polariser
40
. In the same time, the light which passes through cell
26
outside the switched zones of the cell is rotated through 90° as already explained above, then transmitted without being modified by absorbent polariser
42
up to valve
28
. Valve
28
being in the switched state, the polariser light passes through it without being modified is totally reflected by reflective polariser
44
. Dial
18
is thus masked, and the data is displayed in a dark colour on a light background with a mirror-like appearance.
The embodiment described above has several drawbacks.
The mirror-like appearance of the background on which the data displayed by display cell
26
appears is dazzling and thus makes it difficult to read this data, and this is all the more so when the ambient lighting is strong.
Moreover, since the light is reflected on reflective polariser
44
, and thus at a certain distance from display cell
26
, typically of the order of two to three millimetres, the images of the switched segments of cell
26
appear in projection on said reflective polariser
44
, which leads to double vision of the displayed data. This is detrimental not only to the aesthetic appearance of the watch, but also, of course, to the legibility of the displayed data.
Finally, when one looks at the watch from certain angles, bottom display device
24
remains visible although top display device
22
is in the switched state in which it should normally completely mask said bottom device
24
.
SUMMARY OF THE INVENTION
The object of the present invention is to overcome the aforementioned drawbacks of the prior art by pro
Asulab S.A.
Jorgensen Leland R.
Saras Steven
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