Patent Publication Number: US-2022225514-A1

Title: Flexible Display Devices

Description:
This application is a continuation of U.S. patent application Ser. No. 16/905,817, filed Jun. 18, 2020, which is a continuation of U.S. patent application Ser. No. 16/159,253, filed Oct. 12, 2018, now U.S. Pat. No. 10,694,624, which is a continuation of U.S. patent application Ser. No. 15/270,936, filed Sep. 20, 2016, now U.S. Pat. No. 10,104,787, which is a continuation of U.S. patent application Ser. No. 14/335,783, filed Jul. 18, 2014, now U.S. Pat. No. 9,504,170, which is a divisional of U.S. patent application Ser. No. 13/177,165, filed Jul. 6, 2011, now U.S. Pat. No. 8,787,016, all of which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to electronic devices with flexible displays. 
     Electronic devices such as cellular telephones, media players, and computers are often provided with displays. For example, electronic devices may be provided with liquid crystal displays. Liquid crystal displays are often mounted under a rigid layer of cover glass. The cover glass protects the liquid crystal display from damage, but the rigid nature of the cover glass and other display layers render the display inflexible. 
     Flexible display technologies are available that allow displays to be bent. For example, flexible displays may be formed using flexible organic light-emitting diode (OLED) display technology. 
     It would be desirable to be able to use flexible display technology to provide improved electronic devices. 
     SUMMARY 
     Electronic devices may be provided that contain multiple housing portions. The housing portions may include, for example, first and second rectangular housing portions. 
     The housing portions may be coupled together using hinges. The hinges may include hinges based on a three-bar linkage, hinges based on a four-bar linkage, hinges with slotted members, hinges formed from flexible support structures, and hinges based on flexible housing structures. 
     Flexible displays may be mounted to the housing portions overlapping the hinges. When the housing portions in a device are rotated relative to each other, the flexible display may bend. Hinges may be configured to allow the flexible display to be placed in a front-to-front configuration in which the active side of the display faces itself or a back-to-back configuration in which the active portions of the display face away from each other. To avoid stretching the display, the display may be tensioned with tensioning structures and dispensed from a roller or an opening in a housing structure. 
     Engagement structures may be used to help the housing grip external objects and to hold the housing portions in desired positions. The hinges may also be provided with rotational detents to help hold the flexible display in desired positions. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device with a flexible display in accordance with an embodiment of the present invention. 
         FIG. 2  is a side view of an illustrative electronic device with a flexible display and a hinge formed using a three-bar linkage arrangement in which the flexible display has been placed in a planar configuration in accordance with an embodiment of the present invention. 
         FIG. 3  is a side view of an illustrative electronic device with a flexible display and a hinge formed using a three-bar linkage arrangement in which the flexible display has been placed in a face-to-face configuration in accordance with an embodiment of the present invention. 
         FIG. 4  is a side view of an illustrative electronic device with a flexible display and a hinge formed using a three-bar linkage arrangement in which the flexible display has been placed in a back-to-back configuration in accordance with an embodiment of the present invention. 
         FIG. 5  is a side view of an illustrative electronic device having a tensioning structure and a roller for controlling the dispensing and retracting of a flexible display in accordance with an embodiment of the present invention. 
         FIG. 6  is a side view of an illustrative electronic device having a tensioning structure and a housing structure protrusion with an opening to accommodate deployment and retraction of a tensioned flexible display in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of an illustrative electronic device in which a housing has been provided with overhanging portions along its edges that serve to hold a flexible display in place on the planar surface of the housing while the flexible display slides along the surface of the display during deployment and retraction operations in accordance with an embodiment of the present invention. 
         FIG. 8  is a top view of an electronic device having a housing with overlapping edge portions that guide and hold a flexible display as the flexible display slides relative to the housing in accordance with an embodiment of the present invention. 
         FIG. 9  is a side view of an illustrative electronic device with a flexible display that has first and second housing portions that have been rotated relative to each other to place the electronic device housing into a triangular configuration in accordance with an embodiment of the present invention. 
         FIG. 10  is a side view of an illustrative electronic device with a flexible display having a hinge that is based on a four-bar linkage in accordance with an embodiment of the present invention. 
         FIG. 11  is a side view of an illustrative electronic device of the type shown in  FIG. 10  that has a flexible display and a hinge that is based on a four-bar linkage in which the device housing has been manipulated to place the display in a back-to-back configuration in accordance with an embodiment of the present invention. 
         FIG. 12  is a side view of an illustrative electronic device having a flexible display mounted on two housing portions that are coupled using a hinge with first and second slots that receive sliding shafts attached to the housing portions in accordance with an embodiment of the present invention. 
         FIG. 13  is a side view of a portion of an illustrative electronic device with a hinge that may be provided with rotational detents in accordance with an embodiment of the present invention. 
         FIG. 14  is a top view of an illustrative shaft with a recess that receives a ball in a ball detent mechanism in accordance with an embodiment of the present invention. 
         FIG. 15  is a side view of the illustrative shaft of  FIG. 14  showing how the shaft may be provided with a circular recess to receive the ball of the ball detent mechanism in accordance with an embodiment of the present invention. 
         FIG. 16  is a side view of an illustrative electronic device with a flexible display that has a housing that is based on a rigid housing structure and an associated flexible support structure such as a sheet of flexible metal in accordance with an embodiment of the present invention. 
         FIG. 17  is a side view of an illustrative electronic device of the type shown in  FIG. 16  in which the flexible support structure and the flexible display have been bent backward to tilt a portion of the flexible display away from its planar position in accordance with an embodiment of the present invention. 
         FIG. 18  is a side view of an electronic device of the type shown in  FIG. 16  in which the flexible display has been bent backwards sufficiently to create a viewable display portion while a portion of the display rests on a flat surface in accordance with an embodiment of the present invention. 
         FIG. 19  is a cross-sectional side view of an illustrative electronic device having a flexible display mounted to a flexible support structure showing how the device may be provided with engagement features such as a hook and mating notch to help hold the flexible display in a back-to-back configuration in accordance with the present invention. 
         FIG. 20  is a side view of an illustrative electronic device with a flexible display in which the electronic device housing has been formed from a flexible material that forms a hinge and in which rigid structures form enclosures for internal device components in accordance with an embodiment of the present invention. 
         FIG. 21  is a side view of an illustrative electronic device with a flexible display that has a hinge formed from a flexible housing material in which the flexible display has been placed in a face-to-face configuration in accordance with an embodiment of the present invention. 
         FIG. 22  is a side view of an illustrative electronic device with a flexible display that has a hinge formed from a flexible housing material in which the flexible display has been placed in a back-to-back configuration in accordance with an embodiment of the present invention. 
         FIG. 23  is a side view of an illustrative electronic device with at least three separate housing portions connected by at least two hinges and covered with a flexible display in accordance with an embodiment of the present invention. 
         FIG. 24  is a side view of an illustrative electronic device with at least three separate housing portions connected by at least two hinges and covered with a flexible display in which the portions of the device housing have been positioned to place the device in a folded configuration in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device with a flexible display is shown in  FIG. 1 . Electronic device  10  may be a portable electronic device or other suitable electronic device. For example, electronic device  10  may be a laptop computer, a tablet computer, a somewhat smaller device such as a wrist-watch device, pendant device, headphone device, earpiece device, or other wearable or miniature device, a cellular telephone, a media player, larger devices such as desktop computers, computers integrated into computer monitors, televisions, set-top boxes or other electronic devices. 
     Electronic device  10  may have a flexible display such as flexible display  14 . Flexible displays such as flexible display  14  may be based on electronic ink displays, organic light-emitting diode displays, or other suitable flexible displays. Arrangements in which the flexible displays in the electronic devices are formed from organic light-emitting diode displays are sometimes described herein as an example. This is, however, merely illustrative. Flexible display  14  may be provided using other display technologies if desired. 
     Device  10  may include a housing such as housing  12 . Housing  12 , which may sometimes be referred to as a case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of these materials. Housing  12  may be provided with features such as buttons  16 , speaker ports, microphone ports, connector ports such as illustrative connector port  24 , ports or other structures for accommodating sensors and antennas, or other device features. 
     Device  10  may include one or more displays. The displays may include one or more flexible displays such as display  14  and may include optional rigid displays (e.g., displays mounted under rigid cover glass layers and/or displays with rigid layers of display components). 
     Displays such as flexible display  14  of device  10  in  FIG. 1  may be bent by moving portions of housing  12  with respect to each other. Housing  12  may, in general, have two or more parts that may be moved with respect to each other while bending a portion of flexible display  14 . In the example of  FIG. 1 , housing  12  has upper portion  12 A and lower portion  12 B. Housing portions  12 A and  12 B may be coupled to each other using hinge  26 , so that the relative positions of portions  12 A and  12 B may be adjusted by rotation of portions  12 A and  12 B with respect to each other. If desired, three or more pieces of housing  12  may be coupled together using hinges. Coupling mechanisms other than hinges that allow portions  12 A and  12 B and optional additional housing portions to move with respect to each other may also be used. The  FIG. 1  arrangement in which device  10  has two housing portions that are connected using hinge structures is merely illustrative. 
     Hinge  26  may allow housing portion  12 A to rotate relative to housing portion  12 B about axis  18 . Hinge  26  may, for example, allow portion  12 A to rotate in direction  20  or direction  22 . When rotated in direction  20 , housing portion  12 A may close on top of portion  12 B to enclose and protect display  14 . Display  14  may bend along axis  18 , so axis  18  may sometimes be referred to as a bend axis, flex axis, hinge axis, or rotational axis. 
     Hinge  26  may allow housing portions  12 A and  12 B to be flattened into a planar device configuration of the type shown in  FIG. 2 . As shown in the side view of  FIG. 2 , device  10  may be placed into a configuration in which display  14  is substantially planar. In this type of arrangement, display  14  is not bent in the vicinity of hinge  26 , but rather is maintained in a flat configuration in which display  14  and its outermost surface are planar. This type of position may be desirable when a user of device  10  is viewing a video, text, or graphics over all of display  14  (i.e., over all of a display surface that spans housing portions  12 A and  12 B). 
     Device  10  may include internal components  36 . Components  36  may include electrical components such as display driver circuitry, one or more batteries, sensors, microphones, speakers, integrated circuits, microprocessors, power management units, radio-frequency transceiver circuitry, baseband processor circuitry, discrete components such as capacitors, resistors, and inductors, switches, vibrators, connectors, printed circuit boards, wires, transmission lines, and other electrical devices. 
     Components  36  may be mounted on one or more substrates such as substrates  34 . Substrates  34  may include rigid printed circuit boards (e.g., boards formed from fiberglass-filled epoxy such as FR4 printed circuit boards on which patterned metal traces have been formed), flexible printed circuit boards (e.g., “flex circuits” formed form sheets of polymer such as polyimide on which patterned conductive traces have been formed), rigid flex (e.g., boards with both rigid portions and flex circuit tails), plastic carriers, or other substrates. Interconnect paths such as paths  38  may be used to interconnect components  36  with each other and with components such as display  14 . Interconnect paths  38  may include flex circuits (e.g., traces on flex circuits that form signal paths), wires, cables, traces on rigid printed circuit boards and other substrates, or other suitable conductive paths. Using interconnect paths  38 , signals may be routed between respective components  36  and signals may be routed from between components  36  and display  14 . For example, signals from a display driver integrated circuit may be routed to display pixels and traces in display  14 . 
     Hinge  26  may be based on a flexible material (e.g., a sheet of flexible polymer or metal), may be based on a single-shaft mechanism, may be based on a two-shaft mechanism, may be based on a three-shaft mechanism, or may use four or more shafts (i.e., pins or other structures that support rotational motion about a rotational axis) for allowing housing members  12 A and  12 B to move relative to one another. In the example of  FIG. 2 , hinge  26  has a central member  28  that has two associated shafts. Shaft  30  is attached between hinge member  28  and housing portion  12 A. Hinge member  28  is attached to housing portion  12 B by shaft  32 . The structures for forming shafts such as shafts  30  and  32  may be formed from pins, cylindrical rods, or other suitable rotational axis mechanisms for supporting rotational motion about a rotational axis. Hinge  26  may be made up of structures on side of device  10 , structures on both sides of device  10  (e.g., on the opposing ends of hinge axis  18 ), or in more than two locations along axis  18 . 
     Because there are three movable parts in this type of hinge mechanism (i.e., housing  12 A, member  28 , and housing  12 B), hinge arrangements of the type shown in  FIG. 2  are sometimes referred to as three-bar linkages. Hinge  26  may, in general, be implemented using a two-bar linkage, a three-bar linkage, a four-bar linkage, or a linkage involving more than four bars. Combinations of these linkages may also be used in forming flexible connecting structures between separate housing portions such as housing portions  12 A and  12 B (and, if desired, one or more additional housing portions). 
     As shown in  FIG. 2 , portions  12 A and  12 B of housing  12  may be separated by a gap such as gap W. Gap W and the mechanism used for hinge  28  (e.g., a three-bar linkage) may provide sufficient flexibility to allow portions  12 A and  12 B to be folded together by moving portions  12 A and  12 B in directions  40  and may provide sufficient flexibility to allow portions  12 A and  12 B to be placed in a back-to-back arrangement by moving portions  12 A and  12 B in directions  42 . 
     When portions  12 A and  12 B are folded together, the outer surface of the portion of display  14  that is supported by housing portion  12 A faces the outer surface of the portion of display  14  that is supported by housing portion  12 B. The outer surface of display  14  is therefore protected from undesired contact, as shown in the folded arrangement of  FIG. 3 . When folded into the configuration of  FIG. 3 , bent portion  44  of display  14  may be exhibit a bend radius of about 1 mm (e.g., 4 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, or 0.5 mm or less, as examples). Configurations of the type shown in  FIG. 3  are sometimes referred to as face-to-face configurations, because active surface portions of display  14  are face to face with each other. 
     When portions  12 A and  12 B are rotated in directions  42  of  FIG. 2 , housing portions  12 A and  12 B may be placed in a back-to-back configuration of the type shown in  FIG. 4 . In this type of configuration, part of display  14  may be exposed on the outer surface of housing structure  12 A and part of display  14  may be exposed on the outer surface of housing structures  12 B (i.e., the display surface on housing portion  12 A is oriented back to back with respect to the display surface on housing portion  12 B). 
     Engagement features such as engagement features  48  may be provided on some or all of rear surfaces  49  of housing structures  12 A and  12 B to allow device  10  to grip external objects such as external object  46 . External object  46  may be, for example, an item of the user&#39;s clothing. Engagement features  48  may be roughened surface structures such as teeth. The teeth may be formed as an integral portion of the housing or may be attached to the exterior of the housing. The teeth may be formed from plastic, metal, or other suitable materials. Features  48  may have a sawtooth profile, a smooth undulating corrugated profile, may be implemented using one or more spikes or hooks, or may be formed using other suitable structures that protrude from the surface of housing  12 . 
     When housing portions  12 A and  12 B are rotated from a position of the type shown in  FIG. 3  into a position of the type shown in  FIG. 4 , ends  51  of flexible display  14  may be pulled in directions  50 . The length of the display (i.e., the distance along the longer lateral dimension of the display between opposing ends  51 ) does not change substantially as the display is flexed. In the housing configuration shown in  FIG. 3 , display  14  runs along the opposing inner surfaces of the housing. In the vicinity of bend  44 , display  14  covers minimal distance along dimension Z. As a result, the amount of housing surface over which the display extends is minimized. If, however, device  10  is placed into the position shown in  FIG. 4 , bent portion  44  of display will cover a height H along dimension Z. During the process of moving device  10  from the configuration of  FIG. 3  into the configuration of  FIG. 4 , one or both ends  51  of display  41  may be permitted to slide along dimension X in direction  50  to accommodate the extra height H. 
     Any suitable mechanism may be used to allow display  14  to slide along the surface of housing  12  to accommodate changes in the configuration of housing  12 . For example, one end of display  14  may be tensioned using a tensioning member, while the opposing end of display  14  is attached to housing  12  using a rigid attachment mechanism (as an example). As the device is placed into different configurations, the tensioning member may stretch and thereby allow at least a portion of the flexible display to slide relative to the surface of the device. 
     In this type of arrangement, one end of display  14  may be tensioned with a tensioning member or both ends of display  14  may be tensioned with respective tensioning members. The tensioning members may be formed from metal or polymer springs, springs formed from planar elastomeric members that stretch, or other materials that can be placed under tension to tension display  14 . An arrangement in which device  10  has been tensioned with a tensioning structure is shown in  FIG. 5 . As shown in  FIG. 5 , one end of flexible display  14  (i.e., end  61  and the structures adjacent to end  61  may be attached to the device  12  in a non-sliding (fixed) arrangement). Screws, adhesive, or other fastening mechanisms may be used in attaching display  14  to housing  12 . 
     In the example of  FIG. 5 , end  61  of display  14  has been attached to the planar exposed surface of display  12 A using adhesive  54 . Adhesive  54  may be, for example, epoxy, pressure sensitive adhesive, or other suitable adhesive. Tensioning member  58  has been attached between end  60  of display  14  and support structure  56 . Support structures  56  may be formed from part of housing  12  (e.g., an integral portion of housing portion  12 B), an internal frame structure or other housing structure, or other suitable portion of device  10 . When tensioned between member  56  and end  60  of display  14 , tensioning member  58  may pull end  60  of flexible display  14  in direction  68 . Roller  62  may be mounted on rotational axis member  64 . Roller  62  may rotate about rotational axis  64  to allow display  14  to slide relative to housing  12  with minimal friction. A non-rotating member may be used in place of roller  62 , if desired. 
     Flexible display  14  may slide within housing  12 B in directions  66  and  68  when needed to accommodate motion of housings  12 A and  12 B, as described in connection with  FIGS. 3 and 4 . For example, when housing  12  is folded so that display  14  is enclosed within housing portions  12 A and  12 B as shown in  FIG. 3 , slack may tend to develop in display  14 . Accordingly, tensioning member  58  may pull end  60  of display  14  in  FIG. 5  in direction  68 . If, on the other hand, housing  12  is placed into a configuration of the type shown in  FIG. 4 , tensioning member  58  may stretch to allow end  60  of display  14  move in direction  66 . 
     In the illustrative configuration shown in  FIG. 5 , roller  62  was used to facilitate the deployment and retraction of end  60  of flexible display  14 . If desired, additional rollers and/or other structures for facilitating the dispensing and retraction of flexible display  14  may be used. For example, a fixed member that has been coated with a low-friction coating may be used to dispense and retract flexible display  14 , multiple rollers may be used to dispense and retract flexible display  14 , etc. 
       FIG. 6  is a side view of an illustrative configuration that may be used for device  10  in which end  60  of display  14  is housed within protruding portion  83  of housing  12 B and is dispensed without using roller  62 . Protruding housing portion  83  may have an opening such as opening  81  that allows display  14  to enter and exit housing portion  83 . When housing portions  12 A and  12 B are folded together to place device  10  in a configuration of the type shown in  FIG. 3  (in which the display-covered surfaces of device  10  face each other to protect display  14 ), tensioning member  58  may retract end  60  of display  14  into device housing  83  in direction  82  to avoid creating slack in display  14 . When housing portions  12 A and  12 B are rotated away from each other to place device  10  into a configuration of the type shown in  FIG. 4  (in which the display-covered surfaces of device  10  are facing away from each other), spring  58  may stretch and allow an appropriate portion of display  14  in the vicinity of end  60  to exit opening  81  in protrusion  83  in direction  80 , thereby accommodating the need for additional display length. 
     The edge of display  14  may be covered with housing features such as ledges or other overlapping display retention structures to help hold display  14  on the surface of device  10 . As shown in  FIG. 7 , housing  12  may, for example, have portions  76  that overlap the edges of display  14  to help hold display  14  flat against the planar surface of housing  12 . Portions  76  may overlap the edges of display  14  in overlap regions  74 . The width of overlap regions  74  may be, for example, more than 4 mm, 4 mm or less, 3 mm or less, 2 mm or less, 1 mm or less, or 0.5 mm or less. 
     To accommodate sliding motion of display  14  (e.g., into and out of the page in the orientation of  FIG. 7 ), a layer of low-friction material  70  may be placed between display  14  and the outermost surface of housing  12 . For example, housing  12  may have a planar surface such as planar surface  71  that may be formed form a layer of plastic or metal. To reduce the friction that display  14  might otherwise exhibit, low-friction material  70  may be interposed between surface  71  and display  14 . Material  70  may be formed from one or more coating layers on housing  12 , a layer of low-friction polymer such as a sheet of polytetrafluoroethylene, etc. 
       FIG. 8  is a top view of a portion of device  10  showing how display  14  may slide on the surface of housing  12  while side edge portions of display  14  are retained using retention features  76  in regions  74 . To facilitate even tensioning of leading edge  60  of display  14  by tensioning structures  58 , a display edge stiffening member such as edge stiffening member  85  of  FIG. 8  may be attached to edge  60  of display  14 . Edge stiffening member  85  may be formed from plastic, metal, or other suitable materials. Openings  87  may be formed in edge stiffening member  85  to receive hooked features  89  on tensioning structures  58 . If desired, engagement features on edge stiffening member  85  and/or tensioning structures  85  may be formed using other configurations. The arrangement of  FIG. 8  in which edge stiffening member  85  has holes and tensioning structures  85  (e.g., springs) have mating hook-shaped features is merely illustrative. 
     In the example of  FIG. 8 , edge stiffening member  85  is being tensioned using three tensioning structures  58  (e.g., three springs). Other numbers of tensioning structures  58  may be used if desired. For example, one spring or other tensioning structure may be used to tension edge stiffening member  85 , two or more springs or other tensioning structures may be used to tension edge stiffening member  85 , three or more springs or other tensioning structures may be used to tension edge stiffening member  85 , etc. 
     Housing portions  12 A and  12 B may be used to place device  10  in an arrangement of the type shown in  FIG. 9  in which display  14  has a non-planar shape other than the back-to-back configuration of  FIG. 4 . In an arrangement of the type shown in  FIG. 9 , one portion of display  14  (i.e., display portion  14 A mounted on the surface of housing portion  12 A) may be viewed by a user on one side of device  10  (i.e., from position VPL), whereas another portion of display  14  (i.e., display portion  14 B mounted on the surface of housing  12 B) may be viewed by a user on the other side of device (i.e., from position VPR). The triangular shape of device  10  in this type of configuration may allow device  10  to rest on top of a table or other flat surface, as illustrated by horizontal line  91 . This configuration may be used, for example, to allow multiple users to use device  10  simultaneously (e.g., to play a two-person game, to use two separate applications, one of which is displayed on portion  14 A and another of which is displayed on portion  14 B, etc.). 
     In arrangements such as the arrangement of  FIG. 9 , hinge  26  of device  10  has been illustrated as being implemented using a three-bar linkage. This is merely illustrative. Hinge  26  may use any suitable type of flexible joint.  FIG. 10  is a side view of an illustrative device showing how hinge  26  may be formed using a four-bar linkage having first shaft (rotational axis)  88 , second shaft (rotational axis  90 ), and third shaft (rotational axis)  92 . Hinge  26  may include first hinge member  28 A and second hinge member  28 B. There may be identical hinge structures at both ends of the hinge axis of display  14 . Only one set of hinge structures (e.g., the right-hand set) is visible in the example of  FIG. 10 . 
     Hinge member  28 A may be coupled to housing  12 A at shaft  88 . Hinge member  28 B may be coupled to housing  12 B at shaft  92 . Shaft  90  may be used to link hinge member  28 A and hinge member  28 B. 
     When rotating housings  12 A and  12 B with respect to each other, the use of the four-bar linkage design for hinge  26  may provide desirable degrees of freedom. The four-bar linkage design may, as an example, be able to accommodate a range of relative positions for housing members  12 A and  12 B without requiring the same amount of sliding motion for display  14  relative to housing  12  that might otherwise be involved in bending display  14  (e.g., when bending display  14  using a hinge based on a three-bar linkage). In particular, sliding motions  94  along the surface of housing portion  12 B of  FIG. 11  may be minimized by the use of the four-bar linkage for hinge  26 . If desired, portion  14 B may be attached to housing  12 B using a fixed (non-sliding) arrangement such as an arrangement based on adhesive (e.g., adhesive such as adhesive  54 ). 
     The side view of device  10  of  FIG. 12  shows how hinge  26  may be implemented using a slotted member such as hinge member  94 . As shown in  FIG. 12 , hinge member  94  may have slots such as slot  96  and slot  98 . Pin (shaft structure  100 ) may be received within slot  96  (or other opening in member  94 ). Pin (shaft structure  102 ) may be received within slot  98  (or other opening in member  94 ). 
     The use of openings in member  94  such as slots  96  and  98  may provide additional degrees of freedom when positioning housing structures  12 A and  12 B relative to each other. For example, slots  96  and  98  may allow housings  12 A and  12 B to be placed in either the face-to-face configuration of  FIG. 3  or the back-to-back configuration of  FIG. 4 . In a face-to-face configuration of the type shown in  FIG. 3 , shaft  100  may be located in position  106  of slot  96  and shaft  102  may slide to position  106  of slot  98 . In a back-to-back configuration of the type shown in  FIG. 4 , shaft  100  may be located in position  104  of slot  98  and shaft  102  may be located in position  104  of slot  98 . There may be identical hinges on both sides of device  10 . A single set of hinge structures for a single hinge  26  is shown in the example of  FIG. 12 . In configurations with suitable hinge structures such as hinges with slotted hinge members such as hinge member  94  of  FIG. 12 , flexible display  14  may be fixedly attached to the surfaces of housing members  12 A and  12 B. This is because the hinge structures are sufficiently flexible to accommodate the fixed length of display  14 . The use of flexible display arrangements where the flexible display slides relative to the surface of housing  12  may therefore not be needed. 
     In devices  10  in which display structures such as two or more housing portions such as housings  12 A and  12 B can be placed in a variety of different positions relative to each other, it may be desirable to provide hinges  26  with detents. Detent structures may, for example, be formed using spring-loaded structure.  FIG. 13  is a side view of an illustrative hinge  26  of the type that may be provided with a rotational detent. As shown in  FIG. 13 , device  10  may have a housing such as housing  12 . Hinge member  110  may be used in forming hinge  26 . In the  FIG. 13  example, hinge member  110  rotates around shaft (rotational axis)  108  so that hinge member  110  (and any structures attached to member  110 ) may be placed at a variety of rotational angles A with respect to housing  12 . 
     To provide rotational detents for hinge  26 , shaft  108  may be provided with indentations such as indentations  118  and  122  of  FIG. 14 . A mating detent biasing structure such as biasing structure  121  may be used to engage indentations  118  and  122 . Biasing structure  121  may have a body portion  120 . A cylindrical bore such as bore  116  may be provided in the interior of body structure  120 . Ball  112  may be received within bore  116 . Spring  114  may be used to bias ball  112  in direction  123  towards shaft  108  to engage shaft  108  and retard rotational motion of shaft  108 . In the example of  FIG. 14 , biasing structure  121  is using ball  112  to engage indentation  118 . If member  110  were to be rotated 180°, biasing structure  121  would engage indentation  122  on the opposing side of shaft (pin)  108 .  FIG. 15  is a side view of shaft  108  showing how indent  118  (and indent  122 ) may have circular outlines for receiving ball  112  (as an example). 
     Shaft  108  may be attached to housing  12  and biasing structure  121  may be attached to member  110  or vice versa. During operation, the detent mechanism may hold housing portions  12 A and  12 B in two positions (one associated with indentation  118  and one associated with indent  122 ). In general, shafts such as shaft  108  and hinge  26  may have any suitable number of indentations (e.g., one, two, more than two, three, four or more, and/or five or more). Each indentation may be used in providing a rotational detent at a different respectively angular position A. 
     There may be one rotational detent in hinge  26  (e.g., holding the housings in device  10  at an angle A 1  with respect to each other), two rotational detents (e.g., at angles A 1  and A 2 ), or more rotational detents. The detents in hinge  26  may be used, for example, to hold device housings  12 A and  12 B in a position such as the face-to-face position of  FIG. 3 , a back-to-back position such as the back-to-back position of  FIG. 4 , a planar position (e.g., a position in which display  14  is held flat in a planar configuration as shown in  FIG. 2 ), an angled (triangular) position of the type shown in  FIG. 9  in which display surfaces  14 A and  14 B are oriented away from each other, a tilted display position of the type shown in  FIG. 1 , other suitable positions, and/or subsets of these positions. Ball detents or any other suitable detent mechanisms may be used in forming rotational detents for hinge  26 . The use of ball detents is merely illustrative. 
     As shown in the side view of  FIG. 16 , device  10  may include a flexible support structure such as support structure  124 . Flexible display  14  may be mounted on support structure  124  (e.g., using adhesive, fasteners, or other suitable attachment mechanisms). Support structure  124  may, for example, be formed from a planar layer of material, a skeletal structure (e.g., a frame structure), side support members, or other suitable shapes. Support structure  124  may be formed from a flexible metal, a flexible polymer, a flexible composite structure, other materials, or a combination of these materials. As an example, support structure  124  may be formed form a flexible sheet metal structure such as a layer of nitinol (nickel titanium). 
     Structure  124  may have a thickness of about 1 mm or less, 0.5 mm or less, 0.2 mm or less, etc. Openings may be provided in structure  124  to reduce weight and/or to increase flexibility. The openings may be, for example, an array of holes. If desired, electrical current may be applied to structure  124  to ohmically heat structure  124 . In configurations where structure  124  is formed from a shape memory alloy such as NiTi (nitinol), CuZnAl, or CuAlNi, the application of heat to structure  124  may be helpful in restoring a desired shape to structure  124  (e.g., a planar shape). Electrical current for restoring support structure  124  to a desired shape after flexing may be applied to structure  124  using internal device components such as a battery and control circuit (as an example). 
     Flexible support structure  124  may be attached to main housing  12  by molding parts of a plastic housing structure for housing  12  over support structures  124 , by welding support structures  124  to housing structures, by mounting support structure  124  to housing  12  using screws or other fasteners, or by using other mounting techniques. 
     As shown in  FIG. 17 , a user of device  10  may bend flexible support structure  124  to place flexible display  14  in a desired bent configuration. The illustrative bent configuration of  FIG. 17  involves a backwards tilt of display  14  at an angle B away from planar (flat) display position  125 . Angle B may be, for example, 0° to 180°. If desired, a user may tilt display  14  to a position such as position  127 . In position  127 , display  14  is tilted forward from planar display position  125  by an angle C. Angle C may be, for example, an angle in the range of 0° to 180°. 
     As shown in the example of  FIG. 18 , flexible display  14  and flexible support structure  124  may be bent in direction  126  to move display  14  and structure  124  from position PA to position PB. When flexible display and support structure  124  are in a position such as position PB of  FIG. 18 , device  10  may be placed on a surface such as surface  91 , so that portion  14 C of display  14  may be viewed by a user. If desired, the portion of display  14  that rests against surface  91  may be protected by a layer of cover glass and/or by providing housing  12  with raised peripheral ridge portions that prevent scratching of display  14 . 
     As shown in  FIG. 19 , device  10  may be provided with engagement features such as hook  128  and notch  132 . Hook  128  may be attached to support structure  124  or other portion of the housing structures that support display  14 . Notch  132  may be configured to receive hook  128  when display  14  is bent downwards in direction  130 . As shown by dashed line  136 , hook  128  may mate with notch  132  when display  14  has been placed in position  134 . This type of configuration or other suitable engagement feature arrangement may be used in holding display  14  into a back-to-back position (i.e., a configuration in which the folded portion of display  14  is in position  134  of  FIG. 19  and is facing upwards while the unfolded portion of display  14  is facing downwards). The use of engagement features based on a hook-and-notch arrangement is merely illustrative. Other types of engagement features (e.g., engagement features  129  and  131  in the example of  FIG. 19 ) may be used if desired (e.g., magnetic structures, snaps, hook-and-loop fastener material, other interlocking shapes, etc.). 
     As shown in  FIG. 20 , device  10  may have a hinge that is formed from a flexible portion of housing  12 . In the configuration of device  10  that is shown in  FIG. 12 , housing  12  has first portion  12 A and second portion  12 B that are interconnected using hinge  26 . Components  144  may be mounted in housing  12 . For example, components  144  may be mounted in the interior of housing portion  12 A and/or in the interior of housing portion  12 B. Components  144  may be mounted on substrates such as rigid printed circuits boards, flexible printed circuit boards, plastic carriers, or other substrates (shown as substrates  142  in  FIG. 20 ). Interconnection paths formed from flex circuit cables, wires, interconnect traces on printed circuit boards and other substrates, and other interconnect paths may be used in interconnecting components  144  and flexible display  14 . For example, flexible communications path  140  may be coupled between substrate  142  in housing portion  12 A and substrate  142  in housing portion  12 B. Path  140  may be connected to traces on the substrate in housing portion  12 A at connection point  146  and may be connected to traces on the substrate in housing portion  12 B at connection point  148 . The traces on the substrates may be used to interconnect components  144  with each other and to path  140 . Components  144  may include components such as connectors, integrated circuits (e.g., display driver circuitry for controlling display  14 ), discrete components such as inductors, resistors, and capacitors, sensors, status indicator lights, cameras, microphones, speakers, antennas, batteries, etc. 
     To facilitate bending of display  14  and housing  12  in the vicinity of hinge  26 , housing  12  may, as an example, be formed from a flexible material. Examples of flexible materials that may be used in forming housing  12  include flexible polymers, composite structures (e.g., fiber-based composites, fiber-impregnated polymers, etc.), fabrics, and flexible metals. When housing portions  12 A and  12 B are rotated relative to each other around hinge axis  18 , housing  12  may flex. 
     Inflexible structures such as structures  138  may be used to locally strengthen the walls of housing  12  in regions of housing  12  away from hinge  26 . For example, housing  12  may be provided with rigid support structures such as support structures  138 . Structures  138  may be formed from glass, ceramic, metal, fiber-composites, other suitable materials, combinations of these materials, or other suitable materials. Structures  138  may be configured to form rigid box-shaped shells or shells of other shapes that partly or completely surround and protect internal components  144  in housing portions  12 A and  12 B from damage when the flexible material of housing  12  is being used as a hinge and is being flexed (with flexible display  14 ) about axis  18 . When device  10  is flexed around axis  18 , the flexible portions of housing  12  that form hinge  26  may flex. Recessed region  150  may be provided in housing  12  to facilitate flexing of housing  12 . As device  10  is flexed, flexible communications path  140  may flex, while maintaining an electrical pathway for signals passing between housing portions  12 A and  12 B. 
       FIG. 21  shows how a device having a hinge formed from a flexible portion of housing  12  such as device  10  of  FIG. 20  may appear when housing portions  12 A and  12 B have been manipulated to flex hinge  26  and place flexible display  14  in a face-to-face configuration.  FIG. 22  shows how device  10  of  FIG. 20  may appear when housing portions  12 A and  12 B have been manipulated to place flexible display  14  in a back-to-back configuration. In configurations of the type shown in  FIGS. 21 and 22 , engagement features  129  and  131  (e.g., magnetic structures, hook-and-loop fasteners, hook and notch structures, other mating structures, or other suitable engagement features) may be used in holding housing portions  12 A and  12 B in desired positions. 
       FIG. 23  is a side view of an illustrative electronic device with three separate housing portions  12 A,  12 B, and  12 C. As shown in  FIG. 23 , housing portions  12 A and  12 B in device  10  may be coupled using hinge  26 A and housing portions  12 B and  12 C may be coupled using hinge  26 B. Additional housing portions may be provided in device  10  if desired, as indicated by dots  200 . Hinges  26  may be formed form flexible housing portions, from three-bar or four-bar linkages, from members containing slots (as shown in  FIG. 23 ), from flexible metal layers or other sheets of flexible support structure material, from other hinge structures, or from combinations of such structures. 
     When it is desired to place a device such as device  10  into a folded configuration, housing portion  12 A may be rotated relative to housing portion  12 B in direction  202  and housing portion  12 C may be rotated in direction  204  relative to housing portion  12 B (as an example). Following folding in this way, electronic device  10  may have a configuration of the type shown in  FIG. 24 . In this type of configuration, the portions of flexible display  14  that are associated with housing portions  12 A and  12 B may have a face-to-face configuration, whereas the portions of flexible display  14  that are associated with housing portions  12 B and  12 C may have a back-to-back configuration. If desired, hinges  26 A and  26 B may be configured so that housing portions  12 A and  12 C can both fold inwardly onto housing portion  12 B. The arrangement shown in  FIG. 24  is merely illustrative. 
     Device  10  may, in general, have any suitable hinge structure (a three-bar linkage, a four-bar linkage, a flexible housing hinge, hinge structures with rotational detents, hinges based on slotted members, etc.), any suitable housing structure (e.g., metal, plastic, rigid, flexible, composite, etc.), any suitable number of housing portions (two, three, four, two or more, three or more, four or more), any suitable type of flexible display attachment mechanism (fixed, sliding, fixed at one end, sliding at another), any suitable number of detents, any suitable type of tensioning structures (e.g., springs, etc.), any suitable type of flexible display dispensing and retracting structures (roller-based, housing-protrusion-based, etc.), any suitable type of housing structure engagement features (magnetic structures, hook-and-loop fastening material, hooks and recesses, etc.), any suitable type of external object engagement features (e.g., raised housing ridges for gripping cloth), other suitable features, combinations of any or all of these features, etc. 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention.