KR20050069972A - Foil display with two light guides - Google Patents

Abstract

Selection means for bringing the movable element 17 and the movable element into local contact with a selected one of the two light guides 11, 12, arranged on one of two sides of the movable element Display devices including (15, 16) have been described. This provides an essentially symmetrical display device having one light guide on each side of the movable element. The display can display information in two directions, and the selection means can be controlled in an appropriate way to activate the selected portion of the guide. The present invention can be used to provide a bi-directional display.

Description

Foil display with two light guides {FOIL DISPLAY WITH TWO LIGHT GUIDES}

The present invention relates to a display device comprising a light guide, a movable element and selection means for bringing the movable element into local contact with the light guide.

Such display devices are generally referred to as "foil" displays because the movable element is typically a thin foil sandwiched between the light guide and the passive plate. The foil can be moved by the electrostatic force generated by applying a voltage to the electrodes aligned on the light guide and on the passive plate. Such displays are for example disclosed in WO 99/28890.

In some situations, it is desirable to provide a display device capable of displaying information in two directions, ie on both sides of the screen.

Conventionally, the solution to this problem has been based on using twice the pixels. Even pixels are used to create an image on one side of the screen, while odd pixels are used to create an image on the other side. Such a display can be made using a number of techniques (PolyLED, E-ink) by alternating structures of adjacent pixels.

However, these bidirectional displays have some limitations. Only half of the pixels are active viewing areas. So, the display will not be very bright. Furthermore, two multiples of pixels, column drivers and column electrodes are needed. The fact that at least one front light is required limits the size of the display (smaller than about 5 inches).

1 shows schematically a foil display according to the prior art;

2 schematically shows the alignment with two light guides according to the invention;

3 is a sectional view showing a display according to an embodiment of the present invention;

4A and 4B show the display of FIG. 3 used to display different images in two directions.

5A and 5B show three different pixel layers.

FIG. 6 illustrates how two sets of video data are displayed by the display of FIG. 3.

7A and 7B show the display of FIG. 3 used to display an image with alternating optical properties.

It is an object of the present invention to provide a display capable of displaying information in both directions, wherein all pixels are used to generate an image.

These objects are achieved with a display device of the kind mentioned in the introduction, which further comprises a second light guide, wherein the moving elements are aligned between the light guides and the selection means is one of the moving elements and the light guides. Aligned to bring the selected one into local contact.

According to the invention, there is provided an essentially symmetrical display device with a light guide attached to each side of the moving element. Thus, the display can display information in both directions, and the selection means can be controlled in an appropriate way to activate the selected portion of the guide.

Such bidirectional displays can be further designed to have a larger-sized viewing area with a complete opening, requiring only one set of column drivers, row drivers, and electrodes. No additional absorber is needed and the processing is not more complicated than a normal foil display. Furthermore, unlike the usual light guides used in conventional foil displays, no front light is required.

The display may be independently arranged to display image information on each side of the display. Alternatively, the display can be arranged to display the same information in each direction.

In the first case, the movable element is reflective. As a result, light from one guide is not dispersed into the second guide. The light guides can then be activated alternately and independently of one another. Such a display may be used to play the same or different video content on each side.

In the second case, the movable element is preferably transparent. As a result, light exiting from one light guide will pass through the foil and exit from the other side of the display, so that it will be displayed on both sides of the display of the image. Such a display can be used to alternately display images (on one or both of the displays) with other light guides. (Of course, the image will be reflected on one side.) By arranging the light guides to emit light of different properties, such as different polarizations, such displays can be used as 3D displays with the help of suitable visual aids (eg glasses). Can be.

The means for selecting may comprise row and column electrodes and means for applying a voltage to the row and column electrodes. By locally creating a potential difference between the electrode and the movable element, an electrostatic force is applied to the movable element, attracting against one of the light guides.

In a display according to the invention with two active light guides, only one set of column and row electrodes and drivers, and one movable element are needed to provide one image on each side of the device.

The light guide may be formed by two plates of transparent material, for example glass. The movable element is inserted between these plates to form a compact display with bidirectional display capacity.

The display device may comprise light-emitting means for introducing light into the light guide. This light can then escape from the light guide in the area where the movable element is in contact with the light guide.

The light-emitting means can be arranged to emit UV light into the light guide. The display device then includes an element for emitting visible light when stimulated by UV radiation.

According to a preferred embodiment, the light-emitting means are arranged to alternately introduce light into the first and second light guides. By appropriate control of such a light source, it is possible to prevent undesirable interference of the image produced on both sides of the display.

These and other aspects of the invention will be apparent from the preferred embodiments which will be described in more detail with reference to the accompanying drawings.

The foil display according to the prior art is shown in FIG. 1 and comprises two glass plates 1, 2 and a movable element 3 in the form of a thin foil sandwiched between these plates. The light source 4 is aligned with the edge of one of the plates 1 (active plate) while the other plate 2 is inactive. The active and inactive plates are provided with sets 5, 6 of parallel (and transparent) electrodes, aligned perpendicular to one another. The electrodes are coated with a dielectric layer such as S _i O _2. To generate an electrostatic field that can apply force to the foil 3 (in an area defined by the intersection of the electrodes) to come into contact with one of the two plates 1, 2, an appropriate voltage pulse is applied to the two crossing electrodes. Can be applied to them. When the foil 3 comes into contact with the active plate 1, which acts as a light guide, the light exits from the light guide. This causes the emission of light from the display and enables the representation of the image. In a variant of such display (WO0 / 50949), the light source emits UV radiation and the active plate is coated with fluorescent particles to emit visible light when stimulated by UV radiation.

The alignment according to the invention is shown in FIG. 2. Here, two glass plates 11, 12 are used as active light guides, with independent light sources 13a, 13b, 14a, 14b connected and aligned with each light guide 11, 12. In FIG. 2, two pairs of light sources 13a, 13b, 14a, 14b are located at the edges of the two glass plates 11, 12.

A cross section of two light guide foil displays according to an embodiment of the invention is shown in FIG. 3. Electrodes 15, 16 were provided on plates 11, 12, similar to the conventional display shown in FIG. The foil 17 is fitted by the symmetrical alignment of the spacers 18 between the two glass plates 11, 12. The construction of the foil 17 is also symmetrical with respect to the plates 11, 12. Foil 17 may be made of parylene and light scattering particles such as, for example, T _i O ₂ , which may be incorporated into parylene.

The light moves the foil 17 into contact with the respective light guides 11, 12. By the application of a voltage it can now be extracted from one of the glass plates 11, 12. In order to form an image composed of a pattern of on and off pixels from only one of the light guides 11, it is necessary to turn off the light source on the other light guide 12 during formation of the image.

Because of the inherent short switching time of the foil display, it is feasible to develop the features described above to form a display that alternately emits light from the two light guides in the following manner.

Two pairs of flash light sources, eg LEDs, modulated in a preferred manner, are used to emit light for a period of time (eg 8 ms), alternately into one of the two light guides. In this way, the display can be quickly switched between the two states shown in FIGS. 4A and 4B. The driver electronics are synchronized with the modulated LEDs and video data corresponding to the full screen content is applied to the electrodes of the foil display for each period (eg 8 ms).

Multiline addressing schemes can be advantageously used to address electrodes. Other gray scales may be produced by pulse-period modulation or control of the LED intensity.

The color version of the display according to the invention can be achieved in a sequential manner by using color LEDs. However, for VGA applications with 8-bit gray scale, this addressing method requires fast switching of individual pixels. See FIG. 5A.

Thus, alternatively, it is proposed to use a conventional pixel layout (width 200um x height 600um) and instead define one pixel with three adjacent sub-pixels. Thus, it is possible to adjust the amount of light emitted from the pixel by controlling the three sub-pixels independently. See FIG. 5B. In this way, spatial modulation of three sub-pixels can be used to achieve further gray scaling, while loosening the time constraints on the switching of the foil. For example, with three sub-pixels, eight gray levels can be achieved by simply switching on the correct number of sub-pixels, ie without the need for modulation.

According to the first embodiment of the present invention, shown in FIGS. 4A, 4B, the foil 17 according to this embodiment is reflective. This can be achieved by including a central layer of Al in the parylene, acting as a reflector and as an (unstructured) electrode. TiO ₂ particles can be integrated on both sides of the Al layer.

4A and 4B show how such a display can be used to display different (or identical) images independently on both sides of the display.

When the light sources 13 and 14 are activated, light will be scattered by the foil 17 in the areas in contact with the corresponding light guides 11 and 12 and will exit the light guide in only one direction because of the reflective layer. .

Thus, the reflective characteristic of the foil 17 prevents light from one light guide 11 from passing through the second light guide 12 to create a ghost image in the second viewing direction.

As mentioned above, a full set of video data is provided to the electrodes, and the light guides are alternately switched on and off. With the proper choice of video processing, two sets of video data can be sent to the foil display in such a way that two different independent images are shown at the front and back of the foil display. This is shown in FIG.

During the first time interval T1, the video signal input to the display includes first image information (image A). At the same time and in synchronism with this period, the light source 14 is deactivated (OFF) while the first light source 13 is activated (ON). Thus, the light guide 11 will display the image A. FIG. During the second time interval T2, the video signal contains second image information {image B}, and the light source 13 is deactivated (OFF), while the second light source 14 is activated (ON). , Light guide 12 will display image B. FIG. This process continues, resulting in one image flashing rapidly in each light guide. If the flicker is fast enough (mentioned as 8ms above), the human eye will recognize the flickering image as a single image.

FIG. 6 also shows the foil voltage, switched every frame or every two frames. This is a conventional technique in the field of foil displays to avoid the formation of DC charges in the panel. This means that the column and row addressing voltages generated from the video signal need to be changed between the positive and negative foil voltages.

As shown in FIG. 6, note that the second image information must be processed to produce the correct image on the other side of the display. This is because the foil 17 contacts the opposite light guide. And, without processing, the conventional video signal will produce the reflected image. Of course, this processing can be implemented by the display driver itself or in circuitry in front of the display driver.

There are numerous interesting applications for such bi-directional foil displays. Most notably, using two instead of one active plate places no additional constraints on the scalability of the foil display. Thus, an additional application with a display size of 30 or more can be considered.

In work and research environments (offices, libraries, computing centers, Internet cafes, etc.), two video outputs can be processed and displayed using only one display. Thus, two users can work on the same display, saving money and space.

In information displays in airports, stations and hotel / meeting center entrance areas, two identical displays often work together to give the same or different information, for example Schiphol Airport (time of arrival and departure of planes), It is used to display on two sides. Using the present invention, this can be done at a reduced cost with one display with two viewing areas.

The bi-directional display can be advantageously used in a two-player game where two players are virtually positioned or have different information, such as for example battleships ("Geslag").

Of course, for smaller sized applications, the two-way telephone display can be used with very small or almost no additional cost.

According to the second embodiment, the foil 17 is transparent and the light guides are arranged to emit light of different optical properties (eg polarization, wavelength, etc.).

7A and 7B illustrate how such a device can be operated to display an image that alternates with other optical properties. Elements corresponding to the elements of FIGS. 4A, 4B have been given the same reference numerals.

In this case, when the light sources 13, 14 are activated and the light is scattered by the foil 17, it will exit both sides of the activated light guide.

Again, a full set of video data is provided to the electrodes, and the light guide is alternately switched on and off. With the proper choice of video processing, the image can be reproduced alternately by the first and second light guides, each emitting light of a different nature. The result is the displayed image with alternating optical properties. It should be noted that this image is displayed on both sides of the display, as shown in Figs. 7A and 7B. Of course, if a unidirectional display is desired, one side of the display may be covered.

Referring to the block diagram of FIG. 6, the process for operating the display of FIGS. 7A and 7B is similar to the process mentioned above. However, the display signal does not include two interleaved image signals A and B, but only one image signal that is alternately altered to bring the foil into contact with the alternating light guide (image A). } Is included. Such conversion can be performed in the driver electronic circuit. If a display is used, for example, in a 3D application, the video signal may actually include two slightly different pictures A and A 'to create a 3D effect.

The advantages with regard to display size are the same as the bi-directional display mentioned above.

As described above, the present invention can be applied to a display device comprising a light guide, a movable element and selection means for bringing the movable element into local contact with the light guide.

Claims (8)

A display device comprising a first light guide, a movable element and selection means for locally contacting the movable element with the light guide, The display device comprises a second light guide, wherein the movable element is aligned between the light guides and the selection means is arranged to contact the movable element with a selected one of the light guides. Characterized in that the display device. The display device of claim 1, wherein the movable element is reflective. The display device of claim 1, wherein the movable element is transparent. 2. A display device as claimed in claim 1, wherein the means for selecting comprises row and column electrodes and means for applying a voltage to the row and column electrodes. The display device of claim 1, further comprising light-emitting means for introducing light into the light guide. The display device of claim 5, wherein the light-emitting means is arranged to emit UV light into a light guide, and wherein the display device includes elements for emitting visible light when stimulated by UV radiation. 7. Display device according to claim 5 or 6, wherein the light-emitting means are arranged to alternately introduce light into the first and second light guides. The display device of claim 1, wherein the light guide is formed by a plate of transparent material sandwiching the movable element therebetween.