Patent Description:
Flexible and especially rollable displays are manufactured on an organic substrate and are very thin. This makes it possible to repeatedly bend them with a small radius, a requirement for a rollable display. The advantages of a rollable display are the small volume needed for storing in the closed position and the lack of glass making the display unbreakable and of light weight.

A number of product concepts have been developed for flexible displays. The present invention focuses on the 'book' and the 'wrap' concept. A 'wrap' concept is shown in <CIT>.

The 'book' concept is the simplest implementation of a rollable display comprising two hingeably connected support halves with a continuous display. In the middle near the hinge mechanism is a hollow space to accommodate the curved segment of the display in the situation where the 'book' is in the closed position. The display size is at most twice the size of the closed display system. In practice, it will be around <NUM>. 8x the size due to the bezel of the support halves needed around the display.

The 'wrap' concept comprises a display, wrapped with its front side to a device body. Thus the display is protected when the 'wrap' is in the closed position. The display is supported with flat covers and hinge covers. The display currently makes by hinging of the covers one complete turn around the device body when wrapped. Therefore, the size of the display will be about twice the size of the device. For larger displays compared to the device body more turns are required, which adds mechanical complexity.

There are a lot of possibilities to realize the movement of the display with respect to the display system, but most of them result in unsupported parts of the display. In the conventional 'book' and 'wrap' concepts there are hinge areas where a segment of the display is unsupported. In <FIG> for both concepts is shown the theoretical shape (<FIG>) and the actual shape (<FIG>) which a display <NUM> tends to take in the closed position. The theoretically ideal shape of display segments 1a, 1b would have a perfect circular radius Rt, perhaps only varying in direction (+Rt or -Rt) but not in magnitude. However in practice in the known art the display <NUM> tends to take on with its segments 1a, 1b an ellipse like shape. The display <NUM> in a closed position as shown in <FIG> will encounter forces that will 'push' the segment 1a into a more elliptical shape. See the location in a circle in <FIG> for the difference with <FIG> respectively. These actual shapes will have a varying radius in the unsupported segments 1a, 1b which at some point(s) will be smaller than the theoretical radius and with a minimal radius at a certain point (Rmin < Rt).

One reason that the display segment 1a, 1b will not take on the theoretical circular shape when in closed (rolled or wrapped) position is that the flexible display <NUM> is a stack consisting of a number of layers with varying mechanical properties. Another reason is that even in a mono-layer display (which is by definition impossible) internal tensions caused by the thickness and opposing forces of the material will cause a non-uniform radius in the display.

As mentioned before this deviance from the ideal circular shape results locally in smaller radii than specified for a flexible display. Test with flexible displays in a conventional 'book' concept showed that after some time opening and closing and also after lifetime accelerating tests, buckles appeared in the display. This buckle in the flexible display causes a failure of the display. <FIG> shows the cross section of a flexible display <NUM> that has been curved to a circle. The layers of the display that are on the inside of the curve will be under compressive strain (arrows e and f) whereas the layers on the outside of the display will be under tensile strain (arrows c and d). Due to the compressive strain, the layers at the inside of the curve might form a buckle (see 1c) leading to display failure. On the other hand, the tensile strain in the layers on the outside of the curve can lead to cracks in these layers leading to display failure or a sharply reduced lifetime (in case a water barrier cracks). To avoid the above mentioned damage mechanisms, the radius with which the display can be curved must exceed a certain critical value Rcrit (which is the smallest radius at which no damage occurs). In practice the specified value will be in a range between <NUM> and <NUM>.

In practice the unsupported part of a flexible display will not generally take a circular shape. However, locally, at each point a radius can be defined (the radius of the osculating circle), which is a measure for the curvature of the flexible display at that point. The radius at each point along the display contour must exceed the critical value Rcrit to avoid damage.

It is an object of the invention to prevent a too small radius in the unsupported area of the display when the display is in the storage position. It is also an object to improve the lifetime of the display system.

<CIT> discloses a clearance groove for receiving a bend in a flexible liquid crystal display panel that is formed by folding a liquid crystal display panel mounting member.

<CIT> discloses a display system having a continuous flexible display an a support frame comprising two main display supports being hingeable with respect to each other and an additional display support being located between the two main display supports.

According to one aspect the invention there is provided a display system according to claim <NUM>.

The invention focuses in the different embodiments on the support of the display segment in parts of the construction where the display segment cannot be connected to a rigid support. This can be the case near hinges, guiding mechanisms and other mechanical elements that facilitate the movement of the display and supporting frame between a closed storage and an open position. The invention provides technical solutions to constrain the display segment in order to prevent a radius which is too small and which can lead to damage during lifetime of the display system.

The advantages of the different embodiments are that the predefined curvature of the display segment in the closed position is advantageous for the lifetime of the display.

A display system <NUM> schematically shown in <FIG> and in perspective view (but without display) in <FIG> is a 'book' embodiment as described in applicant's non pre-published application number <CIT> (herewith incorporated by reference). It comprises a flexible display <NUM> and a display support frame comprising two main display supports <NUM>, <NUM>. These supports are connected via hinges <NUM>, <NUM> located in a hinge part and are each structurally configured to support a respective portion of the flexible display <NUM>. The hinge part is also working as an additional display support <NUM>. The two main display supports <NUM>, <NUM> are rotatable in the direction of arrows a, b between a configuration shown in <FIG> for fixing the flexible display in a planar configuration to a closed storage position shown in <FIG>. In the open position the gap created by the hinges <NUM>, <NUM> between the main supports <NUM>, <NUM> is closed for a major part by the display support <NUM> and substantially the whole surface of the display <NUM>, including a display segment 3a in the area between the main supports <NUM>, <NUM>, is supported.

In the storage position of the flexible display <NUM> between the main display supports <NUM>, <NUM> there is sufficient free space for enabling a partial curvature of the display segment 3a without conflicting with the respective main display supports. In this position the additional display support <NUM> constrains with its support surface 8a the display segment 3a in order to prevent a radius of the curvature which is too small. This is achieved by placing the additional display support <NUM> with its support surface 8a as a "bridge" behind the display. In closed position the bridge pushes against the display, facilitates the curvature of the display segment 3a with a predefined curvature, ensures during the lifetime of the display that the radius R over the whole area of the curvature is larger than the specified minimum radius Rcrit and thus improves the lifetime of the display system. Preferably, the additional display support <NUM> facilitates a curvature of the unsupported display segment 3a with a radius along the display contour which is above, but close to the critical value Rcrit. Since the radius is everywhere close to but above the critical value Rcrit, the unsupported display segment 3a takes up close to the least possible amount of space.

The additional display support <NUM> can have its support surface 8a over either the partial, the full width or with interruptions (seen in a lateral direction to <FIG>) of the display <NUM>. Over a part of the width may be useful if electrical connections have to be guided between the both 'book' parts. The additional display support <NUM> has a radius R over the support surface 8a, see <FIG> Thus the support offers sufficient place for creating holes for the hinges <NUM>, <NUM>. In <FIG> is shown an embodiment with a display support <NUM> comprising two mutually spaced parts having support surfaces 8b, 8c, respectively and both with a radius R, which parts are connected on a way not shown by hinges of the display system (for more details see the embodiment of <FIG>).

In an experiment flexible displays were tested including an additional display support <NUM> for the prevention of having an ellipse shape in their display segment 3a. In these tests the displays did not have a buckle and therefore no damage to the display was caused either after some time (static storage) or after simulated dynamic lifetime experiments.

<FIG> shows a 'wrap' concept of a display system <NUM>. Two hinges <NUM>, <NUM> are used for each hinge part <NUM>, <NUM>, connecting flat display supports <NUM>, <NUM>, <NUM> and acting as an additional display support. By means of the hinge parts display segments 13a, 13b of a display <NUM> the display segments will be constrained and will be prevented from having a very small Rmin as shown in <FIG>. The hinge parts ensure during the lifetime of the display that the radius R over the whole area of the curvature is larger than the specified minimum radius Rcrit. Therefore damage to the display caused by buckling (see <FIG>) will be prevented. It is noted that the described solution for preventing damage to the display can also be implemented for hinge parts with one or with more than two hinge shafts.

<FIG> shows schematically different ways of applying another type of additional display support in a 'book' or 'wrap' concept. In this solution an extra layer or component is, locally, adhered to the back of a display segment 17a of a display <NUM>. As shown in <FIG> there are three solutions : solid flexible material <NUM> (<FIG>), 'self-locking' material <NUM> ("watch band", type <FIG>) and segmented component <NUM> (<FIG>). The 'self-locking' material and segmented component solution stimulates by its configuration that in the closed position the local curvature the radius R over the whole area of the curvature is larger than the specified minimum radius Rcrit. This extra layer or component is adhered to a central area of the display segment 17a most at risk of taking on an ellipse-like shape when wrapping or folding. However the application area can also be extended to all parts of the display segment 17a that will undergo bending (either positive or negative).

In <FIG> a component or material <NUM> can be applied on the front of the display segment 17a; either on the "inactive" areas of the display (borders) or on the front of the display if the material itself is transparent.

It is observed that a combination of an additional display support <NUM> of <FIG> or <NUM>, <NUM> of <FIG> and the use of a display with an extra layer <NUM>, <NUM>, <NUM> or <NUM> of <FIG> is also part of the invention.

Both the 'wrap' and 'book' concepts work with the additional display support on the principle of locally preventing the display of having a too small radius <Rcrit at a particular location, shown in <FIG>. This location is a point in the curved shape of the display segment (see <FIG>), or line in the width of the display (see <FIG>).

However it is also possible to fully constrain the display with the ideal closed shape of the display at the hinge area, see <FIG> for 'book' concepts with such an ideal closed shape. The concept of <FIG> is a symmetrical version of such a 'book' type display system <NUM> with equally shaped housings of display support panels and in the storage position a display <NUM> with its display segment 23a symmetrically curved with respect to a plane s between display supports <NUM>, <NUM> and their housings. These two display supports with their integral local curvature at the location of an additional display support 24a, 25a fully constrain the display segment 23a with the ideal closed shape of the display adjacent to the location of a hinge <NUM>.

In <FIG> the display support housings have different dimensions measured perpendicular to the plane s between both display support housings. In the closed position the display segment 23a is curved only into the housing of the display support <NUM>. Thus the support <NUM> with its integral local curvature at the location of an additional display support 25a fully constrains the display segment 23a with the ideal closed shape of the display adjacent to the location of a hinge <NUM>. This solution can be applied in asymmetrical 'book' systems, in which the display segment 23a is asymmetrically curved with respect to the plane s between both display supports <NUM>, <NUM> and their housings.

The concepts of <FIG> allow the display <NUM> at the location of the display segment 23a to approach the theoretical radius Rt (see <FIG>) by providing the additional display supports 24a, 25a with an inner radius which approaches or equals the preferred theoretical radius.

The embodiment shown in <FIG> is a 'book' or 'wrap' display system <NUM> with a flexible display <NUM>, a display segment 29a and main display supports <NUM>, <NUM>. These main supports are hingeable connected via hinges <NUM>, <NUM> like the supports <NUM>, <NUM> in the embodiment of <FIG>. In this embodiment the additional display support comprises a support strip <NUM> which is connected to a central part of the display segment 29a and which working is comparable with the additional display support <NUM> of <FIG>. The main display supports <NUM>, <NUM> are provided with hooks 30a, 31a and push with the hooks during their movement from the storage position of <FIG> to the open position of <FIG> the support strip <NUM> with the display segment 29a to the flat position. In the open position the gap created by the hinge mechanism of hinges <NUM>, <NUM> between the main supports <NUM>, <NUM> is closed by the display support strip <NUM> and substantially the whole surface of the display is supported. In the closed position the support strip <NUM> facilitates by positioning its support surface 32a against the display segment 29a a predefined curvature of the display segment <NUM> in a way as described before for the embodiment of <FIG>. ensuring that the radius R over the whole area of the curvature is larger than the specified minimum radius Rcrit. Like the additional display support <NUM> the support strip <NUM> can have its support surface 32a over either the partial or the full width (lateral direction to <FIG>) of the display <NUM>. The support strip <NUM> has a radius R over the support surface 32a, like in <FIG>.

In the embodiment shown in <FIG> a display system <NUM> with a display <NUM> has main display supports <NUM>, <NUM> with housing parts 38b, 39b and extended parts 38a, 39a. Two panels <NUM>, <NUM>, rotatably connected around an axis <NUM>, in <FIG> in the closed state shown inside the housing parts 38b, 39b, are configured as an additional display support. The flexible display <NUM> has free space between the housing parts 38b, 39b to form with its display segment 37a a predefined curvature, facilitated by support portions 41a, 42a of the panels <NUM>, <NUM>. These portions 41a, 42a are symmetrically arranged with respect to the curvature of the segment 37a and to a plane between the supports <NUM>, <NUM> comprising the axis <NUM>. By pivots 41b, 42b the panels <NUM>, <NUM> are connected with panel parts 41c, 42c. For ensuring stable end positions this connection may be spring loaded. Upon opening the two main displays supports <NUM>, <NUM> with the extended parts 38a, 39a push and support the supporting flat panels <NUM>, <NUM> via the position as shown in <FIG>. towards the open position as shown in <FIG>. Between the two flat panels <NUM>, <NUM> the angle of rotation can be limited so that in open state the panels <NUM>, <NUM> and their parts 41c, 42c are parallel, therefore support the flexible display segment 37a in the region of the hinge mechanism and ensure that the radius R over the whole area of the curvature is larger than the specified minimum radius Rcrit. Reference is made to <FIG>, especially the supports <NUM> in <FIG>, the support portions 41a, 42a have curved surfaces like the surfaces 8b, 8c.

An alternative solution in a display system <NUM> for an additional display support <NUM> for the preceding 'book' or 'wrap' concepts shown in <FIG> in an open flat position (<FIG>) and in a storage position (<FIG>), respectively. This solution uses a number of specially designed, by hinges 46a interlinked segments <NUM>. An end segment <NUM> is coupled by a pivot 31c with the display support <NUM> and an abutment 31b limits the pivotal movement of this end segment. These segments are substantially parallelogram-shaped with one rounded corner 46b and are mutually configured such that when a segment <NUM> is locally bent to a radius, its interlinkage will make sure that other segments follow (see arrow g in <FIG>). The segments <NUM> ensure that the local radius R of the curvature of the display segment 29a along the display contour is larger than the specified minimum radius Rcrit. The configuration and interlinkage of the segments prevent that a segment <NUM> is bent in the direction of the arrow h in <FIG>. During the movement from the position shown in <FIG> to the to the flat position shown in <FIG> all segments <NUM> are pushed flat by their configuration and interlinkage. A stable positioning towards the flat position of the segments is supported due to the length of the gap 30d between the display and the support <NUM>. In addition, in the position shown in <FIG> at the left side of the gap 30d an end segment <NUM> may be stable positioned in an optional hook shaped recess 30b in the support <NUM>. Further in addition, in the area of the gap 30d an optional recess 30c in the support may be applied for extra stabilizing the flat position of the segments <NUM>. Due to this stable positioning the flat position of the whole additional support <NUM> is ensured. In the flat position the combined segments <NUM> support substantially the whole surface of the display segment 2a in an effective way.

It is noted that in addition a spring (not shown) may be applied between the left side segment <NUM> and the support <NUM>, urging the end segment <NUM> into the gap 30d towards its end position.

The minimum achievable radius of the curvature will be determined by the positioning of the individual hinges 46a, the design of end stops near the corners of the segments and the distance between hinge points. This enables in the storage position a facilitation of the curvature of the display segment 29a with a predefined curvature, in this embodiment shown as a combination of circular arches.

A special advantage of the invention is the dual function of the additional display support, in the open position of the display system as a display touch support and in the closed position as a display curvature facilitator.

Claim 1:
A display system (<NUM>) comprising:
a continuous flexible display ( <NUM>) ;
a support frame comprising two main display supports (<NUM>, <NUM>) being hingeable with respect to each other and supporting a first portion of the flexible display and a second portion of the flexible display, and
at least one additional display support (<NUM>) supporting a third portion of the flexible display being located between the first portion and the second portion in an open configuration and a closed configuration;
wherein the two main display supports being hingeable between the closed configuration for bending the flexible display and the open configuration for unbending the flexible display,
characterized in that
the at least one additional display support (<NUM>) has a curved support surface so that when the two main display supports (<NUM>, <NUM>) are positioned in the closed configuration, the additional display support (<NUM>) facilitates to bend the third portion of the flexible display (<NUM>) with a predefined radius which is larger than the critical radius for the flexible display (<NUM>).