Display device having an extendible screen

A display device (1) has an extendible screen (2) and at least one extendible side member (3). The extendible screen (2) is extendible in an extension direction from a relatively compact form to an extended form. The screen (2) in the extended form has opposed edges (17) that are substantially parallel to the extension direction. An extendible side member (3) is provided for at least one of said opposed edges (17). The or each extendible side member (3) is extendible to provide support to and structural rigidity to the screen (2) when the screen (2) is in the extended form. The display device (1) provides an extendible rigid screen (2) suitable for example for creating a rigid collapsible tablet computer, or enabling a compact portable display to support a rigid touch-screen, or for incorporation into a mobile phone or remote control unit.

The present invention relates to a display device having an extendible screen.

There is growing demand for extendible screens for displaying text and/or graphics for use with computers or other electronic and mobile devices. As computing power relative to size increases, it is possible to make electronic devices in ever smaller sizes to meet consumer demand. However, one of the limiting factors encountered with this miniaturisation of technology is in the user interface. Specifically referring to the screen, as the screen is reduced in size the amount of information it can relay is also reduced until a point where it is impractical for the user to use.

In several prior art documents, for example U.S. Pat. No. 6,311,076, US-A-2001/0003450, JP-A-2000/132122 and JP-A-1999/272205, the conflicting demands of providing a small screen for portability and a large screen for useful display of information are addressed by providing flexible screens which can be arranged in more than one form. In each case, a flexible screen can be rolled into a compact form when not being used and unrolled into an extended form for the display of information. The screen is rolled about either one or two axes when in the compact form. The prior art arrangements however have a number of shortcomings, which the present invention addresses.

According to the present invention, there is provided a display device, the display device comprising: an extendible screen that is extendible in an extension direction from a relatively compact form to an extended form, the screen in the extended form having opposed edges that are substantially parallel to the extension direction; and, an extendible side member for at least one of said opposed edges, the or each extendible side member being extendible to provide support to and structural rigidity to the screen when the screen is in the extended form.

The present invention provides an extendible screen with at least one extendible side member in order to provide at least some structural rigidity to the screen when in the extended form. The display device is capable of being arranged in a compact form, for example for storage or transportation purposes. However it is also capable of being deployed with the screen in at least one extended form, with the or each side member also extending to provide support to the screen. The structural rigidity given to the extended screen allows it to be used in a wider range of applications than would otherwise be possible. For example, the screen is capable of being placed on an irregular surface whilst still retaining its flatness. This is in contrast to prior art devices with flexible screens but no support which would need to be held in position by external means or placed on a flat surface of sufficient size. In addition, the support given to the screen can allow the device to be held in one hand, leaving the other hand to provide input to the device for example. The screen is also more suitable to incorporate a touch-sensitive input device. The support and rigidity given to the screen by the or each side member allows the flexible screen to receive touch input without deforming under the pressure of the input. In addition the side member provides a solid edge which protects the potentially delicate edge of the screen. The side member also gives the display device a more solid, robust look and feel. Overall this provides the advantage of a solid tablet display with significantly increased portability and flexibility in terms of screen size and application.

In a preferred embodiment, the display device comprises a respective extendible side member for each of said opposed edges. This gives greater structural rigidity to the display device and more complete protection from damage to the potentially delicate edges of the screen. In one preferred arrangement, the screen can be tautly suspended between the two side members providing further support to the screen.

In a most preferred embodiment, the or at least one of the side members is provided by a bistable material having a first stable state when said side member is extended and a second stable state when said side member is not extended. Bistable materials per se are known and are capable of forming two stable structural forms (see U.S. Pat. No. 6,256,938 and U.S. Pat. No. 6,217,975 for example). In other words a bistable material can transform between a first stable form and a second stable form and are typically capable of bearing significant physical loads when in their stable forms. Hence they can be employed in the present invention to provide side members that have a first stable form in which the side members are in a compact form and a second stable form in which the side members are in an extended form, and are capable of bearing load. Furthermore, the preferred bistable material can exist with one end in one stable form and the other end in a second stable form, the bistable material therefore being capable of forming extendible side members that can be extended to any desired length.

In an embodiment, the screen is extendible to and lockable at an intermediate position between said relatively compact form and said extended form, the or each side member being extendible to provide support to and structural rigidity to the screen when the screen is in the intermediate position. The screen can thus be extended to the desired size according to the application and locked into position. A screen of the desired size can thus be formed, such sizes including for example a large “tablet” computer mode, a “widescreen” for play back of movies, an A4 size screen for displaying documents or web pages, and a smaller A5 size screen for use with a PDA device. The side members also provide a uniform appearance of the device at each size.

In a preferred embodiment, the display device comprises a bar extending between said opposed edges, the bar being fixed to the screen and the or each side member. Such a bar can be used to aid in the extension and/or retraction of the screen. The bar can be fixed to the screen and the or each side member to set their relative position and to ensure that their correct alignment is maintained. In addition, the bar can be used to mark the midpoint, or any other convenient point, of the screen to provide a reference point, and used to fix the or each side member in its load-bearing form at its midpoint. This can be achieved in a simple way in a preferred embodiment by providing the bar with an end profile shaped to lock the side member in its load bearing form. Also, in the embodiment where the screen is rolled about two axes, the bar can be used to define a boundary defining which part of the screen is rolled about which axis. The bar can also be used as part of a mechanism to implement this.

The display device may comprise a locking mechanism for locking the or at least one of the side members in its extended form.

In a preferred embodiment, the display device comprises at least one housing which at least partially accommodates the screen when in said relatively compact form, wherein the or at least one of the side members is at least partially accommodated by the housing when the screen is in said relatively compact form. The housing preferably has a guide aperture through which said side member passes on extension or retraction of the screen in order to guide the movement of said side member between the extended and retracted states of said side member. This is particularly useful in the case of the side member being formed from a bistable material because the guide apertures can be shaped to aid the transition between the two stable states of the side member as it passes through the aperture.

In another preferred embodiment, at least one of said opposed edges of the screen has a groove which receives a tongue of the corresponding side member when the screen is in the extended form. In a further preferred embodiment, the tongue is provided by an edge of the side member. This tongue and groove arrangement between the side member and the screen edge helps to lock the screen to the side member and maintain the side member in an open stable state, and can be arranged to allow force to be transmitted between the side member and the screen. Hence when both sides of the screen are locked to side members in this way, the flexible screen can be tautly suspended between the two rigid side members, thus providing further rigidity to the screen. This locking can exist along the length of the extended screen edges, thus allowing an even distribution of force across side members. Such an arrangement can be dynamically formed, meaning that, in an embodiment where a guide aperture is provided, each part of the tongue and groove engage with each other as and when they are extended through the guide aperture. Accordingly when the screen and side member(s) are not extended, they can be stored separately from each other. This allows the two to be stored in different fashions, allowing flexibility in the storage arrangements (and manufacture) of the screen and side member(s) and therefore permitting the compact form of the device to be small.

In a most preferred embodiment at least one of said opposed edges of the screen has plural projections which are received by respective plural apertures or recesses on the corresponding side member when the screen is in extended form to provide a reversible locking arrangement between said screen edge and said side member. The apertures/recesses and projections provide a further or alternative locking arrangement between the extended portions of the screen edge and the corresponding side member to that of the tongue and groove arrangement of the previously described embodiment. The locking arrangement of the apertures/recesses and projections may provide the same advantages as the tongue and groove arrangement. In addition the locking arrangement of the apertures/recesses and projections restricts relative movement between the side member and corresponding screen edge in a longitudinal direction.

In a most preferred embodiment, the display device comprises at least one guide member for at least one side member, the or each guide member being arranged to guide the side member and screen edge into or out of locking engagement on extension or retraction respectively of said side member and screen. In this instance, upon retraction of the screen and side member, the guide member guides the side member so that the apertures/recesses of the side member disengage from the projections of the screen edge. After disengagement, the guide member may provide the further advantage of guiding the side member and screen edge such that each is guided into a respective storage region inside the housing.

In a most preferred embodiment, the side member has a first cross-sectional shape when in its extended form and a second cross-sectional shape when in its retracted form, the housing has a guide aperture through which said side member passes on extension or retraction of the screen, and said side member has a tongue provided by an edge of said side member and the corresponding edge of said screen has a corresponding groove, wherein said guide aperture is arranged to guide the transition of said side member between its first and second shapes on retraction and extension of the side member respectively and to cause said tongue to engage with said groove on extension of the side member. The guide aperture of this embodiment has the dual function of aiding the transition of the side member between its retracted form and its extended form as the screen is extended and retracted, and aiding the formation of the tongue and groove engagement between the side member and the screen as the side member and screen are extended.

In an embodiment, the screen comprises a screen backing layer formed from a plurality of substantially parallel slats arranged perpendicularly to the extension direction.

In an embodiment, the screen comprises a screen backing layer formed from a bistable material that has increased rigidity when planar. In another embodiment, the screen comprises a screen backing layer formed from a smart material that has increased rigidity when planar and is capable of undergoing a current-assisted solid-state phase transition. These arrangements of the screen backing layer provide the screen with increased rigidity when the screen is in its extended form, and decreased rigidity, which provides the advantage of aiding the screen to assume and maintain a compact form.

In a further preferred embodiment, the screen is arranged to roll from the extended form to the relatively compact form. In one embodiment, the rolling screen rolls about a single axis. However, in a preferred embodiment, the rolling screen rolls partly about a first axis and partly about a second parallel axis.

The display device in a preferred embodiment is capable of providing an extendible rigid screen suitable for creating a rigid collapsible tablet computer, or enabling a compact portable display to support a rigid touch-screen, or for incorporation into a mobile phone or remote control unit.

Referring to the drawings, a display device1comprises a rollable screen2with two opposed side members3. The rollable screen2is rolled at each ends about one of two opposed parallel rollers4. Each roller4is mounted in a housing5and is free to rotate about its axis. An aperture6in the face of the housing5allows the screen2to pass into and out of the housings5. The arrangement of the housings5and rollers4at each end of the screen2is identical in construction and operation and so only one will be described in detail in the following. This symmetric construction is an advantage of the preferred embodiment as it helps to keep down manufacturing costs.

Referring toFIG. 4, a detailed view of part of the housing5is shown. At each end of the roller4there is a pin7which is co-aligned with the axis of the roller4. Each pin7is received by a complementary recess8formed in the housing5which holds the roller4in position whilst allowing it to rotate about its longitudinal axis. A pair of roll bar guides9are positioned adjacent to the housing aperture6, being positioned parallel to the roller4, with one roll bar guide9above the other to form a roll bar aperture between them which is narrower than the housing aperture6. This roll bar aperture acts as a guide for the screen2as it moves back and forth through the housing aperture6. The roll bar guides9are retained at their ends by brackets11formed in the interior of the housing5. The brackets11hold the roll bar guides9in position whilst allowing them to rotate about their axes. Hence, as well as guiding the screen2, the smooth and rotatable nature of the roll bar guides9reduce frictional wear and other stresses on the screen2as it passes through the housing5.

Referring toFIG. 3, a similar view toFIG. 1but with the screen removed for reason of clarity, an X-frame12is shown attached to the two opposed housings5. The X-frame12is positioned immediately under the screen2. In the embodiment shown the X frame12is comprised of two telescopically extendible members13,14, which are pivoted together at their midpoints. Each end15of each X-frame member13,14passes into the housing5through the housing aperture6and is attached to an interior surface of the respective housing5in such a way that allows it to pivot. The X-frame12provides further structural rigidity to the display device1. The X-frame12can also be used to limit the maximum extension of the screen2.

One continuous, extendible side member3is disposed at each side of the screen2. Each end of each side member3is accommodated by a respective housing5which it enters through a guide aperture24. As the screen2extends or retracts from the housing5, the side members3also extend or retract from the housing5to provide a continuous, structurally rigid edge to the screen2. This arrangement provides several advantages.

First, it provides added structural rigidity to the device1as a whole and to the screen2in particular. This gives several beneficial capabilities to the device1when being used in its deployed mode. For example, the device1can be held in one hand, or in both hands, or placed on an uneven surface, whilst maintaining its form. Secondly, it provides support and stiffness to the screen2, allowing it to maintain its flatness. As well as providing the advantages of a flat display surface, this can also prevent damage to the screen2where it is made of a technology susceptible to damage from sharp bending of its surface. Thirdly, the solid edge provides protection for the edge of the screen2from damage from external sources, as well as giving the device1a solid, rigid look, which is substantially uniform regardless of the extended length of the screen2.

Similarly, an extendible backing layer32can also be provided. This can be positioned beneath the screen2, extending between the side members3, and in combination with the side members3would encase the parts of the screen2other than the display surface itself. This would allow circuitry or other components positioned under the screen to be hidden from view and protected from damage. This would also provide a more aesthetically pleasing, solid appearance to the device1, which makes the device1more appealing to consumers, and can increase further the rigidity of the screen2.

The backing layer32may be in the form of plural parallel slats which each extend across the width of the screen2and have increased rigidity by locking into the side member using, for example, a tongue and groove arrangement. (Such slats35are shown in the second example discussed below.)

Alternatively or additionally, the backing layer32can be formed, in whole or in part, from a bistable or smart material (such as a shape memory alloy) that has some increased rigidity in the flat deployed configuration. Such a smart material can utilise a pseudo-elastic effect (which can be enhanced, for example, by passing a current through the layer) to increase flexibility or undergo a solid-state phase change as the screen2rolls about the rollers4.

A cross-bar16is attached to the underside of the screen and runs across its width parallel to the rollers4. The two ends of the bar16are attached to the two side members3respectively. As shown more clearly inFIG. 7, an end profile31, which in the preferred embodiment has a shape corresponding to the cross-sectional shape of the side member3in its open extended form, is formed at each end of the cross-bar16to lock the side members3in their load bearing form. In the preferred embodiment the cross-bar16is positioned at the midpoint of the screen2and the midpoint of the two side members3. The cross-bar16serves a number of purposes. First, it acts as an additional support for the screen2. Secondly, it provides a permanent connection between the screen2and the side members3at their midpoints which has the effect of maintaining their correct relative alignment and holds the midpoints of the side members3in their load-bearing bistable form at all extensions between fully compact and fully extended. Thirdly, it acts as a reference marking the midpoint of the screen2which can be used when retracting the screen or extending it to the desired position. Optionally the cross-bar16and the X-frame12can be attached to each other at their midpoints to further aid this process.

In the preferred embodiment the side members3are formed from a bistable material, such as are known per se. Bistable materials have the property of being able to take on two stable structural forms. Hence a member made using a bistable material is capable of forming two stable structures. Furthermore such a member can have one of its ends in a first stable state, and the other end in a second stable state, without significant instability. Bistable materials are also capable of forming members capable of bearing considerable loads. They are therefore well suited to the side members3, as in a first stable state they can form an extended member capable of bearing load and providing support to the screen, and in a second stable state they can take on a more compact form which is stable.

Referring now toFIGS. 5 and 6, a cross section of a bistable side member3and part of the rest of the device1is shown. In its extended form, each side member3has a cross-sectioned shape that is approximately an inverted tear-drop, though with one edge22slightly more inboard that the other edge23.

In the preferred embodiment the side members3lock to the edges of the screen2as the screen2is extended. A screen edge strip17is attached to each side of the screen2and runs along the extent of its length. Each screen edge strip17has an upper groove18and a lower groove19running along its length. When the screen2is extended, the edges22,23of the side members3locate into the lower groove18and upper groove19respectively of the respective screen edge strips17. The combination of the screen edge strip17with the bistable side members3“locked” into it provides a structurally rigid tubular member capable of bearing considerable load. This provides structural rigidity to the display device1as a whole, as well as supporting the screen2and constraining its edges, providing resistance to deformation of the screen.

In the compact form, each side member3is almost entirely in a relatively flat form. When in this form, the two legs of the lower V-shaped section26close together, whilst the upper curved section27flattens out so the section as a whole is substantially planar. Referring toFIG. 4, the end of the side member3which is accommodated within the housing5takes on this relatively flat form and is accommodated by channels28in the rear wall of the housing5.

In order to aid the transition of each side member3between its two stable forms as it passes between the interior and exterior of the housing5, the channel28stops short of the guide aperture24and the guide aperture24is shaped according to the two forms of the bistable material. Preferably, the guide aperture24has a shape intermediate the cross-sectioned shape of the side member3at its two stable forms. In other words, the guide aperture24is shaped to correspond to the shape of the side member3at its transition between the two stable forms. In a further embodiment, sprung bearings and/or roll-bars (not shown) can be positioned adjacent to the channel28and guide aperture24and arranged to aid the transition. (An example of this arrangement is shown in the second example discussed below.)

Accordingly, as each side member3is extended out of the housing5, it passes through a transition29at which the two legs of the lower V-section26spring apart and its edge23is guided into position to lock into groove19of the screen edge strip17, whilst the upper curved section27curls over to allow its edge22to lock into the upper groove18of the screen edge strip17. This provides a “zip-fastening” effect between each side member3and screen edge strip17, the side members3and edge strip17“locking” together as the side members3extend through their respective guide apertures24.

In an additional embodiment, in place of a bistable material, the side members3can be formed from a material having a single intrinsic stable form, with a second stable form being achieved by the use of a magnetic strip. For example, the V-section26of side member3can have a first stable form where its two legs spring apart, and a second stable form where its two legs are held together by the action of a magnet on one of the legs and exerting a magnetic attraction to a magnetic element on the other leg. The guide apertures24again aid the transition between the two stable forms.

It will be appreciated that the display device1is in principle capable of being deployed in any intermediate configuration between the fully retracted, compact form and its fully extended form if desired.

Referring toFIG. 2, the display device1is shown in its most compact form. The screen2is fully retracted and the housings5have come together to abut each other. The housings5can be locked together in this state with a latch (not shown) to prevent the device1from extending unintentionally. The screen2is rolled about the two rollers4, the cross-bar16is accommodated equally in two recesses in the housings5, the X-frame12has telescopically retracted, and the side members3have largely retracted into the housing5, having assumed their relatively flat form, and are accommodated in the channels28.

There are various options for deploying the device1. For example, the housings5could be manually separated until the screen2achieved the desired width. Alternatively or additionally, one or both rollers4could be motor driven to allow the device to automatically produce a screen2of the desired width/length. The rollers4could be spring loaded to bias the device1to a pre-selected configuration. A brake (not shown), such as a friction pad bearing on one or both side member3can be incorporated into one or both of the housings5to allow the screen2to be locked into position in either a closed or partially or fully deployed configuration. This brake may be manually or electrically operated for example.

It is possible for the display device1to be deployed in more than one configuration, allowing screens2of different sizes and aspect ratios to be formed appropriate to the application for which the device1is being used. It is possible to completely automate the deployment of the screen2. Controls30on the housing5may be used by the user to select an application that the device is to be utilised for (for example PDA or tablet mode). The device1could then automatically extend the screen2to the appropriate size and then lock it in place. The degree of screen extension could be determined for example by measuring the amount of rotation of the rollers4using electronic or optical means, such measuring techniques being known per se.

The screen2itself can be made from an organic LED (OLED) or polymer liquid crystal technology. The screen2can be combined with other technologies such as a flexible circuit control membrane to drive the display, and/or a flexible ion-polymer battery for power supply, and/or electro-luminescent cable to back-light the display. Alternatively circuitry, batteries or other components can be stored inside the rollers4, or elsewhere in the housing5.

In addition, the screen2can be used for input as well as display. A touch-sensitive screen2can be implemented by adding charge grid technology to the screen2. Sufficient support is given to the screen2to provide a substantively solid surface, permitting touch-sensitive operation. The X-frame12, cross-bar16and particularly the side members3all provide support to the screen2, whilst the “zip fastening” interface between the side members3and the screen edge strips17constrain the screen edges to provide a stiffening effect, further adding to its ability to resist deformation of its surface. In addition, ribs or slats (not shown) can be embedded in the screen backing32running parallel to the rollers4. These would provide added stiffness to the screen2in this direction, whilst not affecting the screen's ability to roll about the rollers4. Such ribs may have a cross sectional shape that is square or rectangular or some other shape, such as a sector of a circle.

The display device1can also be used with a simpler screen2, such as a static solid state screen combined with a magnetic print head/refresh bar in the housing5which resets the image each time the device1is opened. This would allow applications such as digital newspapers, key documents or web site display.

The display device1can be combined with other technology to provide other applications. CPU and other processing means could be encased by the housing5. Communication devices can be encased in the housing5to allow the device1to access and display web pages, for example. USB connectivity can be added to allow interfacing to other external devices. Input devices can be associated with the housing5. For example, pointing devices such as a tracker ball or mouse “nubbin” and/or hot keys can be provided in one of the housings5at an ergonomically suitable position.

Referring now toFIGS. 8 to 14, a second example of an embodiment of the present invention is shown. Like reference numerals are used for corresponding features in the first example (shown inFIGS. 1 to 7) and the second example. The second example differs from the first example only in certain features and accordingly not all features of the second example will be discussed in detail here. Generally speaking the second example differs from the first embodiment in that the housings5are more stylised, the channels28are positioned in front of the rollers4rather than in the rear wall of the housings5, and there is a different locking arrangement concerning the side members3and the screen edge strips17, which allow among other things a reduced cross-section profile of the side members3.

FIG. 8shows the display device1in a deployed configuration with the lid33of each housing5removed for clarity. The housings5support the rollers4which are attached to the screen2and side members3which are attached to the screen edge strips17. The screen edge strips17in this example form the top face of the side structure rather than the interior.

FIG. 9ashows the display device1in its collapsed configuration.FIG. 9bshows the profile of the screen2when fully stored and rolled around the rollers4.FIG. 9cshows the device with the lids33attached to the housings. The lids33preferably provide a viewing window34to allow the screen to be partially visible in the collapsed configuration.

FIG. 10shows the display device1with the screen2and housing lids33not shown for clarity. The X-frame12is omitted in this example as the required structural rigidity is provided to the display unit1in particular by the combination of the housings5, the side members3, the screen edge strips17, and the screen backing slats35.

For each housing5, the aperture6is formed as a gap between the housing5and the lid33when in place. The roll bar guide9comprises two upper short roll bars41,42and a lower cogwheel roll bar43(shown only inFIG. 10for one housing5for clarity). The two upper short roll bars41,42are mounted at both sides of the aperture6adjacent to its top. The lower cogwheel roll bar43extends across the width of the aperture6adjacent to its bottom, and comprises of two cogwheels44,45mounted on a roll bar. Each roll-bar41,42,43is mounted in the housing5such that it can rotate about its longitudinal axis. The roll bars41,42,43are arranged so that the screen5passes between the upper roll bars41,42and the lower roll bar43when passing through the aperture6.

The screen5has support slats35formed on its under side32. The slats35have a cross sectional shape in the form of a (partial) sector of a circle. This cross sectional shape allows the slats35to engage with the recesses formed between the teeth of the two cogs44,45of the lower cogwheel roll bar43. As each slat35engages with the cogwheel roll bar43it is constrained in its alignment to be parallel to the cogwheel roll bar43and thereby perpendicular to the direction in which the screen2is being extended or retracted. This arrangement helps maintain the screen in a rectangular/square form.

Referring now toFIGS. 11 to 14, detail sections of the display device1are shown, showing a part of one housing5, side member3, screen edge strip17, etc. Accordingly, in the following discussion in relation toFIGS. 11 to 14, a single instance of these features is generally described. It should be noted, however, that the description applies equally to all instances of the particular feature.

Referring now toFIG. 11(which shows an enlarged detail ofFIG. 10from above), the channels28that store the side members3are positioned in front of the roller4. This position, as opposed to positioning the channels28behind the roller4, has the advantage of reducing the transition curvature29of the side-members3as they pass from their extended open V-shape form through the aperture24to their closed form, which makes extension and retraction easier.

The screen edge strip17has two grooves18,19formed in its underside running along its length. The screen edge strip17comprises an underside surface sheet38(which may conveniently be formed of a metal), which is attached to the underside of the screen edge strip17, running along its length, and being positioned between the two grooves18,19such that its edges are approximately flush with the sides of the grooves18,19. A series of tabs or projections37is formed in the underside surface sheet38on each opposed edge and runs along its length. The projections37overlap the underside grooves18,19. The underside surface sheet38may be biased in order to help retract and wind the screen3about the rollers4.

Referring toFIG. 12, each side member3has an approximately V or Y or “wine glass” cross section shape when in its extended form. The end of each “leg” of the side member3has a series of apertures or recesses or perforations39running along its length which correspond to the series of projections37on the screen edge strip17. When extended, the ends of the two legs of each side member3respectively fit into the two underside grooves18,19such that the projections37are received by the perforations39in a reversible locking arrangement. When extended, the screen edge strip17and the two legs of the side member3form a structurally rigid member with a generally triangular cross section shape which provides structural rigidity and protection to the screen3. When engaged with the screen edge strip17, the two legs of the side member3may have a slight inward bias which helps maintain the engagement of the projections37with the perforations39. The arrangement of the perforations39and projections37has the advantage of providing a strong stable connection between the side member3and the screen edge strip17, and restricts any relative longitudinal movement between them. The side member3locks to the screen edge strip17from below only. This arrangement allows the top of the screen3to be flat across its width with no structures extending above it. This arrangement also allows a side member3with a reduced cross sectional area, which in turn allows a smaller housing5to store it.

A guide member in the form of a prong36is mounted in the housings5between each channel28and guide aperture24. The prong36is positioned such that, as the side member3retracts into the housing5, the legs of the side member3are drawn past either side of the prong36. The free end of the prong36is sized and shaped so as to slightly force apart the legs of the side member3as they pass over the end of the prong36such that the perforations39in the ends of the legs of the side members3disengage with the projections37in the grooves18,19of the screen edge strip17. The screen edge strip17passes above the prong36and is wound on the roller4. Further inwards from its free end, the prong36curves upwards such that, once disengaged from the side member3, the screen edge strip17is lifted as it passes over the prong36such that the screen edge strip17is no longer positioned between the legs of the side member3. The side member3is now unobstructed by the screen edge strip17so that it can make the transition to a substantially planar form so that it can be stored in the channel28.

The prong36performs similarly in reverse to engage the perforations39and projections37when the screen5is being extended.

FIGS. 12,13and14most clearly show (in cross-section) the side member passing through the aperture24. The side member3is preferably arranged with a cross section shape like a wine glass. It is not preferred to form the side member3from a bistable material in this example. It is preferred that the side member3is formed with a stable form that is intermediate between the open profile of its extended form (shown inFIGS. 12,13, and14) and a substantially planar profile. When the side member3is extended, the grooves18,19in the underside of the screen edge strip17hold the side member3in its extended form. When the side member3is retracted, the channel28holds the side member3in its substantially planar form.

The prong36may be provided with wheels or rollers, or a layer or coating of a low friction material, such as ptfe, at its free end. This reduces the friction between the end of the prong36and the legs of the side member3and/or screen edge strip17as they slide over the prong36.

As can be seen most clearly inFIG. 14, the side member3has a flexible edge40at its base to provide a smooth edge. The flexible screen edge strip17has a shaped inward edge to support the screen backing slats35forming the screen back32.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.