WO2012078040A1

WO2012078040A1 - Illuminator for flexible displays

Info

Publication number: WO2012078040A1
Application number: PCT/NL2011/050835
Authority: WO
Inventors: Petrus Van Lieshout; Cornelis De Zeeuw; Michiel Van Rijnbach
Original assignee: Polymer Vision BV
Current assignee: Polymer Vision BV
Priority date: 2010-12-06
Filing date: 2011-12-05
Publication date: 2012-06-14
Anticipated expiration: 2013-06-06
Also published as: CN103348398A; EP2649608A1

Abstract

The invention provides a flexible display device, comprising a device body (2); an at least partially flexible display screen (3), cooperating with the device body; and an illuminator (4), for illuminating at least part of the display screen, wherein the illuminator (4) is provided along a flexible edge portion (5) of the screen (3), such that the illuminator (4) follows the movement of the screen.

Description

Titled Illuminator for flexible displays

The invention relates to flexible display devices and more particularly to an illuminator for flexible display devices.

Reflective displays have a great readability in sunlight. In low ambient light conditions however, a front lighting system is needed to enhance the readability of the display.

The quality of a front lighting system is determined - among others - by the degree of lighting uniformity of the system: a higher degree of uniformity improves the readability of the display.

In front lighting systems known from the prior art, hght sources are positioned along the border of a rigid (liquid crystal) display screen. Placing the light sources on all sides of the screen decreases the area a single light source has to act on, and increases the lighting uniformity. Lighting

uniformity is explained in more detail in the description of the embodiments. An example of a system with good lighting uniformity is a backlight display with a planar hght guide behind the display, supphed with light from a hght guide at the edge.

This solution is not easily applied for devices with a flexible display because of mechanical constraints at the edges of the display. A known compromise is to only position the light sources on the side where the flexible display is connected to the housing. This results however in an inferior lighting uniformity.

In one aspect, the invention provides a lighting system that provides increased lighting uniformity for flexible displays. In another aspect, the invention provides a lighting system that retains the flexibility of the display. Disclosure of the invention

According to one aspect, the invention provides a flexible display device, comprising a device body; an at least partially flexible display screen, cooperating with the device body; and an illuminator, for illuminating at least part of the display screen, wherein the illuminator is provided along a flexible edge portion of the screen, such that the illuminator follows the movement of the screen.

The present invention will become more readily apparent from the following detailed description of embodiments of the present invention taken in conjunction with the accompanying drawings.

Brief description of the drawings

Figure 1^: Schematic representation of the flexible display device according to the present invention

Figure 2 - Examples of flexible display devices: a wrappable and rollable display device.

Figure 3^: Schematic explanation of lighting uniformity.

Figure 4- Flexible display device according to the present invention with light sources around the display.

Figure 5- Cross section of the flexible display device as shown in

Figure 4.

Figure 6^: Flexible display device according to the present invention comprising a strip of light emitting material. Figure T- Flexible display device according to the present invention comprising a light guide with outcoupling structures for illuminating the screen.

Figure 8^: Detailed outcoupling structures as shown in Figure 7. Figure 9^: Cross section of the flexible display device as shown in

Figure 7.

Figure 10 ^: Schematic representation of a segmented light guide in a bent and straight position comprising a collimator -collector pair.

Figure 11^: Detailed collimator -collector pairs as shown in Figure 10.

Detailed description of the embodiments

FIG. 1 schematically shows the flexible display device according to the present invention 1. The device 1 comprises a device body 2, an at least partially flexible display screen 3, cooperating with the device body 2, and an illuminator 4 for illuminating at least part of the display screen 3. The illuminator 4 is provided along a flexible edge portion 5 of the screen 3, such that the illuminator 4 follows the movement of the screen 3. Flexible display screens 3 concern among others, extendable, bendable, wrappable or rollable display screens.

FIGS. 2 A and 2B respectively show examples of flexible display devices 21 and 22, wherein the flexible display screen 3 is wrappable and rollable. FIG. 3 schematically explains lighting uniformity. A light source 6 is positioned at a height 7 above a display, thus illuminating a display area with length 8. The lighting uniformity is proportional to the aspect ratio height divided by length of the lighting situation and may thus benefit from

increasing height 7 or decreasing length 8. For flexible displays, increasing the height 7 is - in general - not an option, since the lighting structure will protrude more from the surface of the display device. This decreases the flexibility (rollability or wrappability) of the display screen 3.

As a result, for improving lighting uniformity, length 8 may be decreased, which may be achieved by positioning light sources 6 around the display screen 3. Thus, providing an illuminator along a flexible portion of the display screen may increase the lighting uniformity of the lighting system up to a factor four when all four display edges are used.

To provide the illuminator 4 along a flexible edge portion 5 of the screen 3, light or current to generate light has to be transported to locations that are not fixed with respect to the main device body 2. FIG. 4 shows an embodiment of a flexible display device 41, wherein the illuminator 4 is integrated in the flexible edge portion or bezel 5 of the display screen 3. In this embodiment, the integrated illuminator 4 may comprise a number of electrically interconnected light sources 6. The light sources may be electrically connected with a bendable electrical interconnect 9 for routing the electrical connections to the light sources 6 around the display. Further, the light sources 6 may be equipped with optics to diffract or reflect light optimally towards the display. The integrated light sources 6 may be light emitting diodes (LED's).

A bendable electrical interconnect 9 may be implemented as wires that may be bendable without being damaged. Alternatively, it may be implemented as hinged, rigid or conducting segments, in which the hinges are able to convey an electrical current. FIG. 5 shows a cross section of embodiment 41 of the flexible display device according to the present invention. The roll direction of the display screen is orthogonal to the drawing plane. A light source 6 is positioned at a height 7 above the neutral plane 16 of the display screen 3, illuminating a display area with length 8. The electric interconnect comprises wires 17 and 17' that may run through the neutral plane 16 of the flexible (rollable or wrappable) display screen with taps to each light source 6, so as to reduce tensile and compressive strain in the electrical interconnect wires when the display screen is rolled or bent.

FIG. 6 shows another embodiment of a flexible display device 61 according to the present invention, wherein the illuminator 4 is integrated in the flexible edge portion or bezel 5 of the flexible display screen 3. In this embodiment, the integrated illuminator 4, supplied by hght from a hght source 6, may comprise a strip of light emitting material, integrated in the flexible edge portion 5 of the flexible screen 3. The light emitting material may be organic LED (OLED) or electroluminescent (EL) material. To retain the flexibility of the display screen 3, the strip of material may be bendable.

Diffractive or reflective optics may be added to improve the lighting efficiency of the strip of material.

Alternatively, instead of using an electrically driven strip of emitting material, the illuminator may comprise a strip of phosphorescent material integrated in the flexible edge portion (5) of the screen (3). Such material may be charged using hght and may emit light for a certain amount of time after being charged. An advantage of this embodiment may be that the strip of phosphorescent material may emit light without being energized via a battery or alternative energy source. FIG. 7 shows another embodiment of the flexible display device 71 according to the present invention. In this embodiment, the illuminator 4 comprises a light guide 10 for illuminating the screen 3. Light from a light source 6, e.g. a LED, is coupled into the light guide 10 and is kept in the light guide 10 by total internal reflection (TIR). At certain points, the light guide 10 may comprise outcoupling structures 11 for uniformly illuminating the screen 3. An outcoupling structure 11 couples light out of the light guide, e.g. by means of frustrated total internal reflection (FTIR). FIG. 8 shows the outcoupling structures 11 of embodiment 71 in more detail. FIG. 8A schematically shows the light guide 10 with outcoupling structures 11. FIGS. 8B, 8C and 8D show variants of the outcoupling

structures within framed part 18, wherein the outcoupling structure 11 respectively has a grooved or jagged edge, a painted edge or a matte edge.

The outcoupling structures 11 may be further equipped with optics to diffract or reflect light towards the display 3. At the end of the light guide 10, light may be recycled by reflecting it back into the guide 10. Reflection may be optimized by providing a reflector or a reflecting surface 12 at the end of the guide 10.

The light guide 10 may be integrally made of flexible material, e.g. of glass fibre. Such a fibre may be bent to a radius comparable to the radius of a display in the rolled or wrapped situation (e.g. 1 - 10 millimeters). TIR is not guaranteed under all bending conditions, but the light guide 10 only needs to function correctly when the flexible screen 3 is straightened. Care has to be taken not to damage the fibre irreversibly while bending it. A fibre light guide 10 may be positioned with respect a roll-up display such that the guide 10 serves as a side protection for the display. FIG. 9 shows a cross section of embodiment 71 of the flexible display device according to the present invention. The roll direction of the display screen is orthogonal to the drawing plane. An outcoupling structure 11 forming a hght source 6 is positioned at a height 7 above the neutral plane 16 of the display screen 3, illuminating a display area with length 8. The fibre may run through the neutral plane 16 of the flexible (rollable or wrappable) display screen, so as to reduce tensile and compressive strain in the fibre when the display screen is rolled or bent. FIG. 10 shows a wrappable embodiment of a flexible display device according to the present invention 101, wherein the light guide 10 comprises a number of optically coupled light guiding segments 13. The individual segments 13 may be rigid or somewhat flexible, but may have a lower flexibility than the fibre used in the hght guide 10 that is integrally made of flexible material, as described in the embodiment shown in FIG. 7. The individual segments 13, 13' and 13" are optically coupled through air.

The wrappable device 101 as shown in FIG. 10 comprises two substantially straight, rigid or somewhat flexible display cover parts 15a, 15b, connected via hinges 15d with a display hinge part 15c . The hght guide 10 comprises three hght guiding segments 13, 13' and 13 " corresponding to the display parts, 15a, 15c, 15b respectively.

FIG. 10A shows wrappable display device 101 in a closed position, wherein the segments 13, 13' and 13" of the hght guide 10 form a U-shape. In closed position, the front hghting system will be switched off and therefore the light guiding capacity of the fibre in a U-shape is not relevant. FIG. 10B shows wrappable display device 101 in an open position, wherein the individual segments 13, 13' and 13" of the light guide 10 are separated by an air gap 14. The gap 14 is so small that hght emitted from the end of a segment of the light guide 10 will be coupled into the next, adjacent segment with sufficient efficiency, even when there is a translational or rotational alignment imperfection between segments 13, 13' and 13". To create an efficient optical coupling, the neighbouring ends of adjacent light guiding segments 13 may be shaped as a collimator-collector pair 19 (within frame 18). FIG. 11 shows the collimator-collector pair 19 of embodiment 101 in more detail. FIG. HA schematically shows the light guide 10 comprising a collimator-collector pair 19 within frame 18. FIG. 11B shows the collimator- collector variant wherein no special arrangements are made. This results in diverging light beams and a loss of light intensity. In FIG. 11C, the

neighbouring sides 20 of the collimator-collector pair are curved to parallelize the light and to enable a smooth transition from the collimator to the collector. FIG. 11D shows two lenses 21 being positioned in gap 14 arranged to

parallelize the light and to enable a smooth transition from the collimator to the collector. FIG. HE schematically shows another way of optically coupling the segments, i.e. by a flexible coupling section, in this embodiment fluidic (e.g. using silicon oil) within a deformable frame 18. The fluid 22 has substantially the same diffractive index as the light guide material.

When using a light guide 10, a light source may be present for coupling light into the light guide 10. It seems practical to place one or more LED's in the main device body 2 for this purpose, as shown among others in FIGS. 6 and 7. However, besides LED's other light sources are possible, like halogen lamps and besides placing the light sources 6 in the body 2, placing the light source outside the body 2 is contemplated, e.g. by using an external light source.

In the embodiments described and shown so far, the illuminator extends completely along all the edges of a flexible display screen. In another embodiment, the illuminator extends along a substantial part of an edge of a flexible display screen only. In yet another embodiment the illuminator extends along a substantial part of all the edges of a flexible display screen.

The detailed drawings, specific examples and particular formulations given serve the purpose of illustration only. In the embodiments described, the illuminator is adapted for front lighting reflective displays. Alternatively, the illuminator may be adapted for back lighting transmissive displays. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design, operating conditions, and arrangement of the exemplary embodiments without departing from the scope of the invention as expressed in the appended claims.

Claims

1. A flexible display device (l), comprising

- a device body (2);

- an at least partially flexible display screen (3), cooperating with the

device body (2); and

- an illuminator (4), for illuminating at least part of the display screen (3), wherein

- the illuminator (4) is provided along a flexible edge portion (5) of the screen (3), such that the illuminator (4) follows the movement of the screen (3).

2. The flexible display device according to claim 1, wherein the illuminator (4) is integrated in the flexible edge portion (5) of the display screen (3).

3. The flexible display device according to claim 1, wherein the illuminator (4) comprises a light guide (10) for illuminating the screen (3).

4. The flexible display device according to claim 3, wherein the light guide (10) comprises outcoupling structures (ll) for uniformly illuminating the screen (3).

5. The flexible display device according to claim 3, wherein the light guide (10) is integrally made of flexible material.

6. The flexible display device according to claim 3 wherein the light guide (10) comprises a number of optically coupled light guiding segments (13).

7. The flexible display device according to claim 6, wherein the neighbouring ends of adjacent light guiding segments (13) are shaped as a collimator- collector pair, so as to create an efficient optical coupling.

8. The flexible display device according to claim 6, wherein the neighbouring ends of adjacent light guiding segments (13) are coupled by a flexible coupling.

9. The flexible display device according to claim 8, wherein the flexible coupling uses a fluid (22) having substantially the same diffractive index as the material of the hght guide (10).

10. The flexible display device according to any of claims 1-9, further

comprising a light source (6), for coupling light into the light guide (10).

11. The flexible display device according to claim 10, wherein the illuminator (4) comprises a number of electrically interconnected light sources (6), integrated in the flexible edge portion (5) of the screen (3).

12. The flexible display device according to claim 11, wherein the hght sources (6) are light emitting diodes (LED's).

13. The flexible display device according to claim 2, wherein the illuminator (4) comprises a strip of light emitting material, integrated in the flexible edge portion (5) of the screen (3).

14. The flexible display device according to claim 13, wherein the strip of light emitting material comprises phosphorescent material.

15. The flexible display device according to any one of the previous claims, wherein the illuminator (4) extends along a substantial part of an edge of a flexible display screen (3).

16. The flexible display device according to any one of the previous claims, wherein the illuminator (4) extends along a substantial part of all the edges of a flexible display screen (3).

17. The flexible display device according to any one of the previous claims, wherein the illuminator (4) is adapted for front lighting reflective displays.

18. The flexible display device according to any one of the previous claims, wherein the illuminator (4) is adapted for back lighting transmissive displays.