Patent Publication Number: US-2023152849-A1

Title: Foldable display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. Pat. Application No. 16/817,996, filed on Mar. 13, 2020, which claims priority to and the benefit of Korean Patent Application No. 10-2019-0088463, filed on Jul. 22, 2019 in the Korean Intellectual Property Office, the entire contents of both of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of embodiments of the present disclosure relate to a display device. 
     2. Description of the Related Art 
     Recently, research and development of a foldable display device, a bendable display device, a rollable display device, and the like, using advantages of a flexible display panel that may be bent or folded are in progress. Such display devices may be applied to various fields, such as a television and a monitor, as well as a portable electronic apparatus and a wearable apparatus. 
     The foldable display device may be implemented in an in-folding structure in which display surfaces are folded to face each other, or in an out-folding structure in which the display surfaces are folded outwardly. 
     The foldable display device includes a hinge device for assisting folding and supporting a folded shape and/or an unfolded shape of the foldable display device. Research and development of the hinge device for reducing a manufacturing cost while precisely assisting the folding/unfolding of the foldable display device are in progress. 
     SUMMARY 
     According to an aspect of embodiments of the present disclosure, a foldable display device having a hinge device included therein is provided. According to another aspect of embodiments of the present disclosure, a foldable display device that controls symmetrical folding of a display panel by using interaction of a rotation motion of a rotor and linear motion (or straight line motion) of a follower is provided. 
     However, aspects and objects of the present disclosure are not limited to those described above, and may be variously expanded without departing from the spirit and scope of the disclosure. 
     According to one or more embodiments, a foldable display device includes: a display panel including a first display area, a second display area, and a foldable display area between the first display area and the second display area; a first base plate overlapping a portion of the foldable display area to guide folding and unfolding of the display panel; a second base plate overlapping another portion of the foldable display area to guide the folding and the unfolding of the display panel together with the first base plate; a first rotor coupled to the first base plate to rotate around a first virtual rotation axis; a second rotor coupled to the second base plate to rotate around a second virtual rotation axis in a direction opposite to a rotation direction of the first rotor; a follower in contact with the first and second rotors to reciprocate in a first direction by rotation of at least one of the first and second rotors; and a bracket coupled to the first and second rotors to guide a rotation path of each of the first and second rotors. 
     According to an embodiment, the foldable display device may further include a hinge cover coupled to the bracket to limit movement of the follower in a direction other than the first direction. 
     According to an embodiment, the follower may be arranged between the bracket and the hinge cover. 
     According to an embodiment, the first rotor may include a curved surface having a diameter corresponding to the first rotation axis and a first groove of a spiral shape on the curved surface. 
     According to an embodiment, the second rotor may include a curved surface having a diameter corresponding to the second rotation axis and a second groove of a spiral shape on the curved surface. 
     According to an embodiment, the follower may include a first pin arranged to be inserted into the first groove of the first rotor and moved within the first groove, and a second pin arranged to be inserted into the second groove of the second rotor and moved within the second groove. The first and second pins may convert rotation of the first and second rotors into straight line motion of the follower, and the first direction may be parallel to the first and second rotation axes. 
     According to an embodiment, the first rotor and the second rotor may concurrently rotate at a same angle in directions opposite to each other. 
     According to an embodiment, spiral directions of the first groove and the second groove may be opposite to each other. 
     According to an embodiment, the bracket may include a first side portion arranged to engage with a side surface of the first rotor to guide the rotation path of the first rotor, and a second side portion corresponding to an opposite side of the first side portion, and arranged to engage with a side surface of the second rotor to guide the rotation path of the second rotor. 
     According to an embodiment, a first side surface of the first rotor may be in surface contact with a first side surface of the follower, and a first side surface of the second rotor may be in surface contact with a second side surface of the follower opposite to the first side surface of the follower. 
     According to an embodiment, when the first rotor rotates in a clockwise direction, the follower may be moved in the first direction parallel to the first and second rotation axes, and when the second rotor rotates in a counterclockwise direction, the follower may be moved in a direction opposite to the first direction. 
     According to an embodiment, on a plane, the first side surface of the follower and the second side surface of the follower may be symmetric with each other with respect to a symmetry axis corresponding to a second direction, and the second direction may be a direction perpendicular to the first direction and parallel to an unfolded state of the display panel. 
     According to an embodiment, the bracket may include a first bracket arranged to engage with a second side surface of the first rotor to guide the rotation path of the first rotor, and a second bracket arranged to engage with a second side surface of the second rotor to guide the rotation path of the second rotor. The foldable display device may include a first hinge group including the first rotor, the second rotor, the first bracket, the second bracket, and the follower. 
     According to an embodiment, the foldable display device may further include a second hinge group having a same structure as the first hinge group and arranged to be spaced apart from the first hinge group in the first direction. The second hinge group may be configured in a form of the first hinge group being rotated by 180° on a plane. 
     According to an embodiment, when the display panel is folded or unfolded, the follower included in the first hinge group and a follower included in the second hinge group may be concurrently moved in directions opposite to each other. 
     According to an embodiment, the follower may include a first guide hole in a first side surface that is in contact with the first rotor, and a second guide hole in a second side surface that is in contact with the second rotor. Widths in a horizontal direction of each of the first and second guide holes may be greater than widths in a vertical direction of each of the first and second guide holes. 
     According to an embodiment, the first rotor may include a first protrusion portion arranged on a first side surface of the first rotor to be inserted into the first guide hole, and the second rotor may include a second protrusion portion arranged on a second side surface of the second rotor to be inserted into the second guide hole. 
     According to an embodiment, a portion where the first protrusion portion that is in contact with an inside of the first guide hole may be changed by the rotation of the first rotor, and a portion where the second protrusion portion that is in contact with an inside of the second guide hole may be changed by the rotation of the second rotor. 
     According to an embodiment, the bracket may include a first bracket arranged to engage with a second side surface, which is an opposite side of the first side surface of the first rotor, to guide the rotation path of the first rotor; and a second bracket arranged to engage with a second side surface, which is opposite side of the first side surface of the second rotor, to guide the rotation path of the second rotor. 
     According to an embodiment, the first direction may correspond to the vertical direction. 
     The foldable display device including the hinge device according to embodiments of the present disclosure may implement folding and unfolding by using a simple connection structure of a plurality of rotors and a follower and a two-axes hinge structure based on rotation motion of the rotors and a straight line motion (vertical movement or horizontal movement) of the follower. Therefore, folding/unfolding angles of the first base plate (and a first panel support member) and the second base plate (and a second panel support member) coincide, and symmetrical folding/unfolding of the foldable display device may be implemented. In addition, a manufacturing cost may be reduced by eliminating a configuration including a complicated driving mechanism and a plurality of sophisticated gears, springs, and/or the like, and implementing a two-axes hinge mechanism with a simple structure. 
     However, aspects and effects of the present disclosure are not limited to the above-described aspects and effects, and may be variously expanded without departing from the spirit and scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present disclosure will become more apparent by describing in further detail some example embodiments thereof with reference to the accompanying drawings, in which: 
         FIG.  1    is a perspective view illustrating a foldable display device according to one or more embodiments of the disclosure. 
         FIG.  2 A  is a perspective view illustrating an example of a portion of a hinge device included in the foldable display of  FIG.  1   . 
         FIG.  2 B  is an exploded perspective view illustrating an example of a portion of the hinge device of  FIG.  2 A . 
         FIG.  3    is a perspective view illustrating an example of a method of driving the hinge device of  FIG.  2 A . 
         FIGS.  4 A to  4 C  are diagrams schematically illustrating an example of the method of driving the hinge device of  FIG.  3   . 
         FIG.  5 A  is an exploded perspective view illustrating an example of a portion of a hinge device included in the foldable display of  FIG.  1   . 
         FIG.  5 B  is an exploded perspective view illustrating an example of a portion of the hinge device of  FIG.  5 A . 
         FIG.  6    is a perspective view illustrating an example of a method of driving the hinge device of  FIG.  5 A . 
         FIG.  7    is a plan view illustrating an example of the hinge device of  FIG.  5 A . 
         FIG.  8    is a plan view illustrating an example of a method of driving the hinge device of  FIG.  7   . 
         FIG.  9 A  is an exploded perspective view illustrating an example of a portion of a hinge device included in the foldable display of  FIG.  1   . 
         FIG.  9 B  is an exploded perspective view illustrating an example of a portion of the hinge device of  FIG.  9 A . 
         FIG.  10    is a perspective view illustrating an example of a method of driving the hinge device of  FIG.  9 A . 
         FIGS.  11 A to  11 C  are diagrams schematically illustrating an example of the method of driving the hinge device of  FIG.  10   . 
     
    
    
     DETAILED DESCRIPTION 
     Herein, some example embodiments of the present disclosure will be described in further detail with reference to the accompanying drawings. The present disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. The same reference numerals are used for the same components in the drawings, and repetitive descriptions of the same components may be omitted. 
     It is to be understood that when an element or a layer is referred to as being “on” another element or layer, it may be directly on another element or layer, or one or more intervening elements or layers may also be present. 
     Although the terms “first,” “second,” and the like are used to describe various constituent elements, these constituent elements are not limited by these terms. These terms are used to distinguish one constituent element from another constituent element. Therefore, “first” constituent elements described below may be second constituent elements within the technical spirit of the present invention. When explaining the singular, unless explicitly described to the contrary, it may be interpreted as the plural meaning. 
     Meanwhile, some of the elements not directly related to the features of the present invention in the drawing may be omitted in order to clearly illustrate the present invention. In addition, some of the elements in the drawings may be shown in somewhat exaggerated sizes, ratios, and the like. For the same or similar constituent elements throughout the drawings, the same reference numerals and symbols may be provided even if they are displayed on different drawings, and duplicate descriptions may be omitted. 
     It is to be further understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components. 
     In embodiments set forth herein, when a layer, area, or component is connected to another layer, area, or component, the layers, areas, or components may be directly connected to each other, and the layers, areas, or components may also be indirectly connected to each other with another layer, area, or component therebetween. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments of the inventive concept belong. It is to be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG.  1    is a perspective view illustrating a foldable display device according to one or more embodiments of the disclosure. 
     Referring to  FIG.  1   , the foldable display device may include a display panel DP, a first panel support member DS 1 , a second panel support member DS 2 , and a hinge device  100 . 
     As shown in  FIG.  1   , the foldable display device may display an image on a display surface (for example, shown as FDA, DA 1 , and DA 2 ). The display surface in a fully unfolded (flat) state of the foldable display device is parallel to a surface defined by a first direction axis (herein, a first direction DR 1 ) and a second direction axis (herein, a second direction DR 2 ). A third direction axis (herein, a third direction DR 3 ) indicates a normal direction of the display surface, that is, a thickness direction of the display panel DP. 
     However, the first to third directions DR 1 , DR 2 , and DR 3  shown in the present embodiment are merely examples, and the directions indicated by the first to third directions DR 1 , DR 2 , and DR 3  are relative concepts, and may be converted into different directions. 
     In an embodiment, the foldable display device may be folded in an in-folding manner in which the display surfaces are folded to face each other. However, this is an example, and the foldable display device may include an out-folding area and may include a plurality of folding areas. 
     In an embodiment, the foldable display device of  FIG.  1    may have a folding axis parallel to the first direction DR 1 . For example, the foldable display device may be applied to an electronic apparatus that is folded left and right. 
     The display panel DP may be a flexible display panel. For example, the display panel DP may include a flexible substrate, such as a plastic film, and may display an image by using a pixel circuit (e.g., a plurality of transistors) disposed on the flexible substrate and a light emitting element, such as an organic light emitting diode. The light emitting element and the pixel circuit may be covered with a thin film encapsulation layer. The thin film encapsulation layer may seal the light emitting element from an external air environment including water and oxygen, thereby suppressing characteristic deterioration. Here, the light emitting element is not limited to the organic light emitting diode. For example, the light emitting element may be an inorganic light emitting element including an inorganic light emitting material or a light emitting element (quantum dot display element) that emits light by changing a wavelength of light emitted using a quantum dot. 
     The display panel DP may include a display area formed of pixels. The display area may include a first display area DA 1 , a second display area DA 2 , and a foldable display area FDA between the first display area DA 1  and the second display area DA 2 . The foldable display area FDA may include a portion (for example, a bent portion) that may be substantially changed in shape by the hinge device  100 . 
     In an embodiment, the foldable display device may further include an input sensing sensor disposed on the display surface of the display panel DP or embedded in the display panel DP. In an embodiment, the input sensing sensor may include any of a touch sensor, a fingerprint sensor, a motion sensor, an iris sensor, and the like. 
     A transparent cover window may be provided outside the display surface of the display panel DP. The cover window protects the display panel DP from an external impact, a scratch, and the like, while transmitting the image of the display panel DP as is. In an embodiment, the cover window may include a transparent material having rigidity and flexibility. 
     In an embodiment, the first and second panel support members DS 1  and DS 2  may include a metal or plastic material. The first and second panel support members DS 1  and DS 2  may be attached to surfaces opposite to the display surface of the display panel DP. 
     The first panel support member DS 1  may support a first area of the display panel DP including the first display area DA 1 . The second panel support member DS 2  may support a second area of the display panel DP including the second display area DA 2 . In an embodiment, the first and second panel support members DS 1  and DS 2  may be attached to a surface of the display panel DP by an adhesive. 
     The first and second panel support members DS 1  and DS 2  may support the display panel DP and allow the display panel DP to maintain a constant shape. The first and second panel support members DS 1  and DS 2  cause the display panel DP to maintain a flat shape when the foldable display device is unfolded and cause the display panel DP to maintain a constant folded shape when the foldable display device is folded. In addition, the first and second panel support members DS 1  and DS 2  may protect the display panel DP from an external impact, contamination, and the like. 
     In an embodiment, another surface of the first and second panel support members DS 1  and DS 2  forming an appearance of the foldable display device may include a flat surface or have at least one curved surface. 
     The first panel support member DS 1  may be coupled to a first base plate BP 1 . The second panel support member DS 2  may be coupled to a second base plate BP 2 . The first and second panel support members DS 1  and DS 2  may be moved in conjunction with (dependently to) rotation (rotating movement) of the first and second base plates BP 1  and BP 2 . 
     The hinge device  100  may include the first base plate BP1, the second base plate BP2, and a hinge cover HC. The hinge device  100  may further include a plurality of members disposed in the hinge cover HC to directly rotate the first and second base plates BP 1  and BP 2 . For example, the hinge device  100  may include components such as a rotor, a follower, a bracket, and the like. A configuration and an operation of the hinge device  100  according to one or more embodiments will be described in further detail with reference to  FIG.  2  to  11 C . 
     In an embodiment, the hinge device  100  may be formed in a two-axes hinge structure. The two-axes hinge structure has two rotation axes, and the first and second base plates BP 1  and BP 2  may rotate based on their respective rotation axes. 
     In an embodiment, the first and second base plates BP 1  and BP 2  may include a metal or plastic material. 
     The first base plate BP 1  may overlap a portion of the foldable display area FDA to guide folding and unfolding of the display panel DP. The second base plate BP 2  may overlap another portion of the foldable display area FDA to guide the folding and the unfolding of the display panel DP together with the first base plate BP 1 . In an embodiment, the first base plate BP 1  and the second base plate BP 2  may concurrently (e.g., simultaneously) rotate at a same angle in directions opposite to each other. 
     In an embodiment, the first and second base plates BP 1  and BP 2  may include a plurality of fastening holes  10 ,  20 ,  30 , and  40 . Each of the first and second base plates BP 1  and BP 2  may be connected to or coupled with another member by a fixing pin or a fixing screw passing through the fastening holes  10 ,  20 ,  30 , and  40 . 
     For example, the first base plate BP 1  and a rotor inside the hinge cover HC may be coupled to each other through a first fastening hole  10 . In addition, the second base plate BP 2  and another rotor inside the hinge cover HC may be coupled to each other through a second fastening hole  20 . 
     The first panel support member DS 1  may be coupled to the first base plate BP1. In an embodiment, a portion of the first panel support member DS 1  may be disposed under the first base plate BP 1 . For example, the first base plate BP 1  and the first panel support member DS 1  may be coupled to each other through a third fastening hole  30 . 
     Similarly, the second panel support member DS 2  may be coupled to the second base plate BP 2 . The second base plate BP 2  and the second panel support member DS 2  may be coupled to each other through a fourth fastening hole  40 . 
     In an embodiment, the hinge cover HC may include a metal or plastic material. The hinge cover HC may restrain (support) and protect internal components that substantially perform a hinge operation. 
     The foldable display device according to embodiments of the disclosure may be symmetrically folded and unfolded by disposition and interaction of components included in the hinge device  100 . 
       FIG.  2 A  is a perspective view illustrating an example of a portion of the hinge device included in the foldable display of  FIG.  1   ; and  FIG.  2 B  is an exploded perspective view illustrating an example of a portion of the hinge device of  FIG.  2 A . 
     Referring to  FIGS.  2 A and  2 B , in an embodiment, the hinge device  100  may include a first base plate  110 , a second base plate  120 , a first rotor  130 , a second rotor  140 , a follower  150  (or a slider), a bracket  160 , and a hinge cover  170 . In an embodiment, the hinge device  100  may further include first and second folding auxiliary members  180  and  190 . 
     In an embodiment, the components included in the hinge device  100  may include a metal and/or a plastic material. 
     The first base plate  110  may overlap the portion of the foldable display area FDA to guide the folding and the unfolding of the display panel DP. The first base plate  110  may include the fastening holes  10  of  FIG.  1    for coupling with the first rotor  130  and auxiliary rotors  181  and  191 . In addition, the first base plate  110  may include the fastening holes  30  of  FIG.  1    for coupling with the first panel support member DS 1 . 
     The second base plate  120  may overlap the other portion of the foldable display area FDA to guide the folding and the unfolding of the display panel DP. The second base plate  120  may include the fastening holes  20  of  FIG.  1    for coupling with the second rotor  140  and auxiliary rotors  182  and  192 . In addition, the second base plate  120  may include the fastening holes  40  of  FIG.  1    for coupling with the second panel support member DS 2 . 
     In an embodiment, the first and second base plates  110  and  120  may be disposed symmetrically with each other. 
     The first rotor  130  may be coupled to the first base plate  110  and may be disposed to rotate around a first virtual rotation axis. The first rotor  130  may be disposed on the follower  150 . 
     In an embodiment, the first rotor  130  may have a shape in which a portion of a cylinder is vertically cut. That is, the first rotor  130  may include a curved surface having a diameter corresponding to the first virtual rotation axis. A surface of the curved surface of the first rotor  130  may include a first groove  132  of a spiral shape. 
     A side surface  134  of the first rotor  130  may be coupled to the bracket  160 . For example, the side surface  134  of the first rotor  130  may include a protruded portion of an arc shape. The protruded portion of the first rotor  130  may be engaged with a first side portion  162  of the bracket  160 . For example, the protruded portion of the arc shape of the side surface  134  of the first rotor  130  may be coupled to the first side portion  162  of the bracket  160  so as to be inserted into the first side portion  162  of the bracket  160 . Therefore, the first rotor  130  may be rotated in subordination to (dependent upon) a shape of the first side portion  162  of the bracket  160 . That is, the first side portion  162  of the bracket  160  may guide a rotation path of the first rotor  130 . 
     In an embodiment, the first rotor  130  may include a hole  136  corresponding to the fastening hole  10  of  FIG.  1    of the first base plate  110 . The first rotor  130  and the first base plate  110  may be coupled with each other by coupling a fixing pin or a fixing screw to the fastening hole  10  of  FIG.  1    and the hole  136 . 
     The second rotor  140  may be coupled to the second base plate  120  and may be disposed to rotate around a second virtual rotation axis. The second rotor  140  may be disposed on the follower  150 . 
     The second rotor  140  may have a shape substantially the same as that of the first rotor  130  and may include a second groove  142  of a spiral shape on a surface of a curved shape. However, the second groove  142  of the second rotor  140  may be formed in a direction opposite to the first groove  132  of the first rotor  130 . That is, directions of spirals of the first and second grooves  132  and  142  may be opposite to each other. 
     According to an embodiment, a cross-section of the first and second grooves  132  and  142  may have a rectangular or trapezoidal shape. 
     A side surface  144  of the second rotor  140  may be engaged with a second side portion  164  of the bracket  160 . For example, a protruded portion of an arc shape of the side surface  144  of the second rotor  140  may be coupled to the second side portion  164  of the bracket  160  so as to be inserted into the second side portion  164  of the bracket  160 . Therefore, the second rotor  140  may be rotated in subordination to (dependent upon) the shape of the second side portion  164  of the bracket  160 . That is, the second side portion  164  of the bracket  160  may guide a rotation path of the second rotor  140 . 
     In an embodiment, the second rotor  140  may include a hole  146  corresponding to the fastening hole  20  of  FIG.  1    of the second base plate  120 . The second rotor  140  and the second base plate  120  may be coupled with each other by coupling a fixing pin or a fixing screw to the fastening hole  20  of  FIG.  1    and the hole  146 . 
     In an embodiment, the first rotor  130  and the second rotor  140  may rotate at the same time in directions opposite to each other. 
     The follower  150  may be disposed between the bracket  160  and the hinge cover  170 . The follower  150  may be limited in movement in a direction other than the first direction DR 1  by the bracket  160 . The first direction DR 1  may be a direction parallel to the rotation axes and folding axis. 
     In an embodiment, the follower  150  may be disposed to overlap with the first rotor  130 , the second rotor  140 , and the bracket  160 . The follower  150  may be in contact with the first and second rotors  130  and  140 . The follower  150  may be reciprocated in the first direction DR 1  by rotation of the first and second rotors  130  and  140 . 
     The follower  150  may include first and second pins  152  and  154 . In  FIG.  2 B , the first and second pins  152  and  154  are shown separated from the follower  150 , but this is illustrative, and, in an embodiment, the first and second pins  152  and  154  may be formed integrally with the follower  150 . 
     The first pin  152  may be disposed to be inserted into the first groove  132  and may be moved in the first groove  132  in subordination to (dependent upon) the rotation of the first rotor  130 . The second pin  154  may be disposed to be inserted into the second groove  142  and may be moved in the second groove  142  in subordination to (dependent upon) the rotation of the second rotor  140 . 
     The first and second pins  152  and  154  may convert the rotation (or rotation motion) of the first and second rotors  130  and  140  into a straight line motion of the follower  150 . That is, movements of the first rotor  130 , the second rotor  140 , and the follower  150  may be restrained to each other to act on each other. In an embodiment, a cross-sectional shape of the first pin  152  and the second pin  154  may be a rectangular shape or a trapezoidal shape corresponding to the first and second grooves  132  and  142 , respectively. 
     For example, the first and second rotors  130  and  140  may rotate in opposite directions by the folding or the unfolding of the foldable display device. The rotation of the first and second rotors  130  and  140  causes a force to be applied to the first and second pins  152  and  154 , and, thus, the follower  150  may be pushed in the first direction  DR1  or a direction opposite to the first direction DR 1 . In addition, the first and second rotors  130  and  140  may be concurrently (e.g., simultaneously) rotated by the same rotation amount by restraint force of the follower  150 . That is, the first rotor  130 , the second rotor  140 , and the follower  150  may mutually operate similarly to a cylindrical cam driving principle or a lead screw driving principle. 
     The bracket  160  may be coupled to the first and second rotors  130  and  140 . The bracket  160  may guide the rotation paths of each of the first and second rotors  130  and  140 . In an embodiment, the bracket  160  may be disposed to be inserted into the hinge cover  170 . The bracket  160  may limit the movement of the follower  150  in a direction other than the first direction DR 1 . 
     In an embodiment, the bracket  160  may include the first side portion  162 , the second side portion  164 , and a fixing hole  166 . 
     The first side portion  162  may be disposed to engage with the side surface  134  of the first rotor  130 . The rotation path of the first rotor  130  may be guided based on a shape of the first side portion  162  and a coupling form of the first side portion  162  and the first rotor  130 . 
     The second side portion  164  may correspond to an opposite side of the first side portion  162 . The second side portion  164  may be disposed to engage with the side surface  144  of the second rotor  140 . The rotation path of the second rotor  140   may be guided based on a shape of the second side portion  164  and a coupling form of the second side portion  164  and the second rotor  140 . 
     A fixing member (for example, a fixing pin, a fixing screw, or the like) for coupling and fixing the bracket  160  to the hinge cover  170  may be inserted into the fixing hole  166 . 
     The hinge cover  170  may be coupled to the bracket  160  to limit the movement of the follower  150  in the direction other than the first direction DR 1 . The hinge cover  170  may include at least one protrusion portion into which the follower  150 , the bracket  160 , and the like are inserted, and a groove into which the follower  150 , the bracket  160 , and the like are inserted and coupled. 
     In an embodiment, the hinge device  100  may further include the first and second folding auxiliary members  180  and  190 . The first and second folding auxiliary members  180  and  190  may perform functions of assisting and reinforcing hinge coupling of the first and second rotors  130  and  140  and the first and second base plates  110  and  120 , respectively. For example, the first and second folding auxiliary members  180  and  190  may be disposed on the hinge cover  170  to be spaced apart from the first and second rotors  130  and  140 , and may be coupled to the first and second base plates  110  and  120 . 
     The first folding auxiliary member  180  may include a first auxiliary rotor  181 , a second auxiliary rotor  182 , and a first auxiliary bracket  183  disposed between the first auxiliary rotor  181  and the second auxiliary rotor  182 . 
     The first auxiliary rotor  181  may be coupled to the first base plate  110  and may rotate equally with the first rotor  130 . The second auxiliary rotor  182  may be coupled to the second base plate  120  and may rotate equally with the second rotor  140 . 
     The first auxiliary bracket  183  may guide rotation paths of the first and second auxiliary rotors  181  and  182  and may limit movements other than rotation motion of the first and second auxiliary rotors  181  and  182 . 
     The second folding auxiliary member  190  may include a third auxiliary rotor  191 , a fourth auxiliary rotor  192 , and a second auxiliary bracket  193  disposed between the third auxiliary rotor  191  and the fourth auxiliary rotor  192 . 
     The third auxiliary rotor  191  may be coupled to the first base plate  110  and may rotate equally with the first rotor  130 . The fourth auxiliary rotor  192  may be coupled to the second base plate  120  and may rotate equally with the second rotor  140 . 
     The second auxiliary bracket  193  may guide rotation paths of the third and fourth auxiliary rotors  191  and  192  and may limit movements other than rotation motion of the third and fourth auxiliary rotors  191  and  192 . 
     The first and third auxiliary rotors  181  and  191  may assist the rotation (hinge drive) of the first base plate  110 . The second and fourth auxiliary rotors  182  and  192  may assist the rotation (hinge drive) of the second base plate  120 . 
     Since a rotation method of the first to fourth auxiliary rotors  181 ,  182 ,  191 , and  192  may be substantially the same as that of the first and second rotors  130  and  140  by the bracket  160 , repetitive descriptions is omitted. 
     As described above, the foldable display device including the hinge device  100  according to embodiments of the disclosure may perform folding and unfolding using a two-axes hinge structure through interaction of the rotation motion of the first rotor  130  and the second rotor  140  and the straight line motion of the follower  150 . Therefore, folding/unfolding angles of the first base plate  110  (and the first panel support member DS 1 ) and the second base plate  120  (and the second panel support member DS 2 ) coincide, and symmetrical folding/unfolding of the foldable display device may be implemented. In addition, a manufacturing cost may be reduced by eliminating a configuration including a complicated driving mechanism and a plurality of sophisticated gears, springs, and/or the like, and implementing a two-axes hinge mechanism based on the coupling of the first rotor  130 , the second rotor  140 , and the follower  150 . 
       FIG.  3    is a perspective view illustrating an example of a method of driving the hinge device of  FIG.  2 A ; and  FIGS.  4 A to  4 C  are diagrams schematically illustrating an example of the method of driving the hinge device of  FIG.  3   . 
     For example,  FIGS.  4 A to  4 C  show a schematic planar shape of the hinge device of  FIG.  3    as viewed in the first direction DR 1 . 
     Referring to  FIGS.  1  to  4 C , the first rotor  130  and the second rotor  140  of the hinge device  100  may be concurrently (e.g., simultaneously) rotated in opposite directions, and, thus, the foldable display device may be folded or unfolded. 
     In a state in which the foldable display device is fully unfolded (denoted by FLAT in  FIG.  3   ), as shown in  FIG.  4 A , a horizontal surface of the first and second rotors  130  and  140  may be positioned to be parallel to the foldable display device. The horizontal surface of the first and second rotors  130  and  140  may be a surface opposite each curved surface. 
     When the foldable display device is folded at an angle (e.g., a predetermined angle), the first and second rotors  130  and  140  may rotate in opposite directions. For example, the first rotor  130  may rotate in a clockwise direction about a first virtual rotation axis  RX1 , and the second rotor  140  may rotate in a counterclockwise direction about a second virtual rotation axis RX 2 . In contrast, when the foldable display device is unfolded, the first rotor  130  may rotate in a counterclockwise direction, and the second rotor  140  may rotate in a clockwise direction. 
     A position of the first pin  152  may be changed in the first groove  132  by the rotation of the first rotor  130 , and a position of the second pin  154  may be changed in the second groove  142  by the rotation of the second rotor  140 . Since each of the first and second grooves  132  and  142  has a spiral shape toward the first direction DR 1 , rotation force of the first and second rotors  130  and  140  may be transferred to the follower  150  in the first direction DR 1  through the first and second pins  152  and  154 . Therefore, the follower  150  may move in the first direction DR 1 . 
     For example, as shown in  FIGS.  3  and  4 B , when the foldable display device is folded at about 45°, the follower  150  horizontally moves (or slides) in the first direction DR 1  by a first length L 1 . In addition, the follower  150  may prevent or substantially prevent the first and second rotors  130  and  140  from rotating at different rotation amounts (or rotation angles). 
     In addition, as shown in  FIG.  4 C , when the foldable display device is fully folded (denoted by FOLDED in  FIG.  3   , for example, when the foldable display device is folded at about 90°, the follower  150  may move in the first direction DR 1  by a second length L 2  as compared to when the foldable display device is fully unfolded by the rotation of the first and second rotors  130  and  140 . 
     However, at the time of the folding/unfolding of the foldable display device, the bracket  160  may be fixed about a horizontal axis HX, and only the follower  150  may reciprocate in the first direction DR 1  under the bracket  160 . 
     As described above, the hinge device  100  and the foldable display device including the same according to embodiments of the disclosure may be symmetrically folded/unfolded using a simple connection structure of the first rotor  130 , the second rotor  140 , and the follower  150 . 
       FIG.  5 A  is an exploded perspective view illustrating an example of a portion of a hinge device included in the foldable display of  FIG.  1   ; and  FIG.  5 B  is an exploded perspective view illustrating an example of a portion of the hinge device of  FIG.  5 A . 
     Referring to  FIGS.  1 ,  5 A, and  5 B , a hinge device  200  may include a first base plate  111 , a second base plate  121 , a first hinge group HG 1 , a second hinge group HG 2 , and a hinge cover  270 . 
     In an embodiment, the first hinge group HG 1  may include a first rotor  210 , a second rotor  220 , a follower  230 , a first bracket  240 , and a second bracket  250 . The first hinge group  HG1  may further include a washer  260  for preventing or substantially preventing shaking or twisting of the follower  230  from the hinge cover  270 . 
     A first side surface  212  of the first rotor  210  may be in surface contact with a first side surface  232  of the follower  230 . For example, the first side surface  212  of the first rotor  210  and the first side surface  232  of the follower  230  may correspond to respective cross-sections separated by a member of an arc shape, which is cut in an oblique direction. Therefore, in a state in which the foldable display device is fully unfolded, a surface where the first side surface  212  of the first rotor  210  and the first side surface  232  of the follower  230  are in contact with each other may coincide. 
     A second side surface  214  of the first rotor  210  may be engaged with a side portion  242  of the first bracket  240 . Since a coupling form of the first rotor  210  and the first bracket  240  may be substantially the same as the coupling form and the driving mechanism of the rotor and the bracket described with reference to  FIGS.  2 A to  4 C , repetitive descriptions may be omitted. Similarly, a coupling form and a driving mechanism of the second rotor  220  and the second bracket  250  may also be the same. 
     The first rotor  210  may include a hole  216  corresponding to a fastening hole of the first base plate  111 . As a fixing pin or a fixing screw is coupled to the fastening hole and the hole  216 , the first rotor  210  and the first base plate  111  may be coupled to each other. 
     A first side surface  222  of the second rotor  220  may be in surface contact with a second side surface  234  of the follower  230 . For example, the first side surface  222  of the second rotor  220  and the second side surface  234  of the follower  230  may correspond to respective cross-sections separated by a member of an arc shape, which is cut in an oblique direction. Therefore, in a state in which the foldable display device is fully unfolded, a surface where the first side surface  222  of the second rotor  220  and the second side surface  234  of the follower  230  are in contact with each other may coincide. Accordingly, each of the first side surface  232  and the second side surface  234  of the follower  230  may be formed to have a surface inclined with respect to the second direction DR 2 . 
     A second side surface  224  of the second rotor  220  may be engaged with a side portion  252  of the second bracket  250 . The second rotor  220  may include a hole  226  corresponding to a fastening hole of the second base plate  121 . As a fixing pin or a fixing screw is coupled to the fastening hole and the hole  226 , the second rotor  220  and the second base plate  121  may be coupled to each other. 
     The follower  230  may be disposed between the first and second rotors  210  and  220 . The follower  230  may be reciprocated in the first direction DR 1  by rotation of the first and second rotors  210  and  220 . 
     The follower  230  may be limited to twisting or movement in a direction other than the first direction DR 1  by the washer  260 . In addition, the follower  230  may further include a hole  236  receiving a protrusion portion of the hinge cover  270 . 
     The first bracket  240  may be disposed to engage with the second side surface  214  of the first rotor  210 . The first bracket  240  may guide a rotation path of the first rotor  210 . The first bracket  240  may include a fixing hole  244  for fixing the first bracket  240  to the hinge cover  270 . 
     The second bracket  250  may be disposed to engage with the second side surface  224  of the second rotor  220 . The second bracket  250  may guide a rotation path of the second rotor  220 . The second bracket  250  may include a fixing hole  254  for fixing the second bracket  250  to the hinge cover  270 . 
     The first and second brackets  240  and  250  may prevent or substantially prevent the first and second rotors  210  and  220  and the follower  230  from moving in a direction other than a path (e.g., a predetermined path). Since a shape and a coupling form of the first and second brackets  240  and  250  are described with reference to  FIGS.  2 A to  4 C , repetitive descriptions will be omitted. 
     The second hinge group HG 2  may be disposed to be spaced apart from the first hinge group HG 1 . In an embodiment, the second hinge group HG 2  may include a same configuration as the first hinge group HG 1 . For example, the second hinge group HG 2  may also include a third rotor  210′ , a fourth rotor  220′ , a follower  230′ , a third bracket  240′ , and a fourth bracket  250′ . 
     The second hinge group HG 2  may be disposed on the hinge cover  270  in a shape corresponding to the first hinge group HG 1  being rotated about 180° on a plane. 
       FIG.  6    is a perspective view illustrating an example of a method of driving the hinge device of  FIG.  5 A . 
     Referring to 5A to 6, the first rotor  210  and the second rotor  220  of the hinge device  200  may concurrently (e.g., simultaneously) rotate in directions opposite to each other, and, thus, the foldable display device may be folded or unfolded. 
     In a state in which the foldable display device is completely unfolded, a horizontal surface of the first and second rotors  210  and  220  may be positioned to be parallel to the foldable display device. The horizontal surface of the first and second rotors  210  and  220  may be a surface or face opposite each curved surface. In this case, the follower  230  may be disposed to be spaced apart from a reference point (e.g., a predetermined reference point) on the hinge cover  270  by a first length L 1 . 
     When the foldable display device is folded, the first rotor  210  may rotate in a clockwise direction and the second rotor  220  may rotate in a counterclockwise direction. 
     As a center of the hinge cover  270  with respect to the second direction DR 2 , a length is longer in the first direction DR 1  of the first side surface  212  of the first rotor  210 . On the other hand, the first side surface  232  of the follower  230  that is in contact with the first rotor  210  has an outer side longer than a center side of the hinge cover  270 . Therefore, when the first rotor  210  rotates in the clockwise direction, force pushing the follower  230  in the first direction DR 1  may be generated by the contact between the first side surface  212  of the first rotor  210  and the first side surface  232  of the follower  230 . 
     Therefore, when the foldable display device is folded, the follower  230  may be moved (or slide) in the first direction DR 1  by the rotation of the first rotor  210 . That is, the first rotor  210  (and the second rotor  220 ) and the follower  230  may perform folding/unfolding by a mechanism similar to an end cam driving method using surface contact. 
     For example, as the foldable display device is further folded, a length (or distance) between the follower  230  and the reference point on the hinge cover  270  may increase. That is, as shown in  FIG.  6   , a third length L 3  may be greater than a second length L 2 , and the second length L 2  may be greater than the first length L 1 . 
     In an embodiment, in a folding operation by the first hinge group  HG1 , force acting on the follower  230  by rotation force of the second rotor  220  may be relatively weaker than force acting on the follower  230  by rotation force of the first rotor  210 . In this case, the second base plate  121  may not be fixed to a predetermined folding state. 
     In order to compensate such a problem, the hinge device  200  may further include the second hinge group HG 2  disposed in a direction opposite to the first hinge group HG 1 . A disposition and a method of driving first and second hinge groups HG 1  and HG 2  will be described in further detail with reference to  FIGS.  7  and  8   . 
       FIG.  7    is a plan view illustrating an example of the hinge device of  FIG.  5 A ; and  FIG.  8    is a plan view illustrating an example of a method of driving the hinge device of  FIG.  7   . 
     Referring to  FIG.  5 A to  7   , the hinge device  200  may include the first hinge group HG 1  and the second hinge group HG 2 . 
     The second hinge group HG 2  may have a configuration substantially the same as that of the first hinge group HG 1 . The second hinge group HG 2  may be disposed on the hinge cover  270  in a shape corresponding to the first hinge group HG 1  being rotated about 180° on a plane. 
     For convenience of description, the first hinge group HG 1  may include the first rotor  210 , the second rotor  220 , the follower  230 , the first bracket  240 , the second bracket  250 , and the washer  260 , and the second hinge group HG 2  may include the third rotor  210′ , the fourth rotor  220′ , the follower  230′ , the third bracket  240′ , the fourth bracket  250′ , and a washer  260′ . However, the third rotor  210′  may be coupled to the second base plate  121 , and the fourth rotor  220′  may be coupled to the first base plate  111 . 
       FIG.  7    shows a first extension line SEL 1  corresponding to a surface extending from the first side surface  232  of the follower  230  and a second extension line SEL 2  corresponding to a surface extending from the second side surface  234  of the follower  230 . The first extension line SEL 1  and the second extension line SEL 2  are symmetrical with respect to a first symmetry axis SX 1 . Here, the first symmetry axis SX 1  may be an axis extending in the second direction DR 2  based on a center of the follower  230 . The second direction DR 2  may be substantially perpendicular to the first direction DR 1  and may be parallel to the unfolded state of the display panel DP. 
     Therefore, the first side surface  232  and the second side surface  234  of the follower  230  may be symmetrical with respect to the first symmetry axis SX 1 . 
     Similarly, on a plane, a first side surface and a second side surface of the follower  230′  of the second hinge group HG 2  may be symmetrical with respect to a second symmetry axis SX 2 . A third extension line SEL 3  may be an extension line corresponding to a surface extending from a first side surface of the follower  230′  on the plane, and a fourth extension line SEL 4  may be an extension line corresponding to a surface extending from a second side surface of the follower  230′  on the plane. As shown in  FIG.  7   , the follower  230′  may be disposed in a shape corresponding to the first follower  230  being rotated 180° on a plane. 
     As shown in  FIG.  8   , when the foldable display device is folded, the first and fourth rotors  210  and  220′  may rotate in a clockwise direction, and the second and third rotors  220  and  210′  may rotate in a counterclockwise direction. 
     The follower  230  may be moved in the first direction DR 1  by the rotation of the first rotor  210 . As the rotation amount of the first rotor  210  increases, a movement amount in which the follower  230  is moved (slides) from the reference point in the first direction DR 1  may increase (for example, L 3  &gt; L 2  &gt; L 1 ). 
     At the same time, the follower  230′  may be moved in a direction opposite to the first direction DR 1  by rotation of the third rotor  210′ . As a rotation amount of the third rotor  210′  increases, a movement amount in which the follower  230′  is moved (slides) from the reference point in a direction opposite to the first direction DR 1  may increase (for example, L 3  &gt; L 2  &gt; L 1 ). In an embodiment, the third rotor  210′  may limit the rotation of the second base plate  121 . 
     As described above, the hinge device  200  and the foldable display device including the same according to embodiments of the disclosure may perform folding and unfolding in a two-axes hinge structure through interaction of rotation motion of the first to fourth rotors  210 ,  220 ,  210′ , and  220′  and a straight line motion of the followers  230  and  230′ . Therefore, folding/unfolding angles of the first base plate  111  (and the first panel support member DS 1  of  FIG.  1   ) and the second base plate  121  (and the second panel support member DS 2  of  FIG.  1   ) coincide, and a symmetrical folding/unfolding of the foldable display device may be implemented. 
       FIG.  9 A  is an exploded perspective view illustrating an example of a portion of a hinge device included in the foldable display of  FIG.  1   ; and  FIG.  9 B  is an exploded perspective view illustrating an example of a portion of the hinge device of  FIG.  9 A . 
     Referring to  FIGS.  1 ,  9 A, and  9 B , a hinge device  300  may include a first base plate  112 , a second base plate  122 , a first rotor  310 , a second rotor  320 , a follower  330 , a first bracket  340 , a second bracket  350 , and a hinge cover  370 . In an embodiment, the hinge device  300  may further include first and second folding auxiliary members  180  and  190 . 
     In an embodiment, the follower  330  may be disposed between the first and second rotors  310  and  320 . A first side surface of the first rotor  310  may be coupled to the follower  330 , and a second side surface  314  of the first rotor  310  may be coupled to the first bracket  340 . A first side surface of the second rotor  320  may be coupled to the follower  330 , and a second side surface  324  of the second rotor  320  may be coupled to the second bracket  350 . 
     The first rotor  310  may include a first protrusion portion  312  on the first side surface inserted into a first guide hole  332  of the follower  330 . The first protrusion portion  312  may be moved in the first guide hole  332  by rotation of the first rotor  310  (that is, a portion that is in contact with an inside of the first guide hole  332  may be changed). 
     The first rotor  310  may further include a hole  316  corresponding to a fastening hole of the first base plate  112 . 
     The second rotor  320  may have substantially the same shape as the first rotor. The second rotor  320  may include a second protrusion portion  322  on the first side surface inserted into a second guide hole  334  of the follower  330 . The second protrusion portion  322  may be moved in the second guide hole  334  by rotation of the second rotor  320  (that is, a portion that is in contact with an inside of the second guide hole  334  may be changed). 
     The second rotor  320  may further include a hole  326  corresponding to a fastening hole of the second base plate  122 . 
     The follower  330  may include the first guide hole  332  formed in a first side surface that is in contact with the first rotor  310 , and the second guide hole  334  formed in a second side surface that is in contact with the second rotor  320 . In an embodiment, widths in a horizontal direction of each of the first and second guide holes  332  and  334  may be greater than widths in the vertical direction of each of the first and second guide holes  332  and  334 . 
     The follower  330  may further include a fixing hole  336  for preventing or substantially preventing movement or distortion in a direction other than the vertical direction (for example, the third direction DR 3 ). In an embodiment, a protrusion portion of the hinge cover  370  may be inserted into the fixing hole  336 . 
     The follower  330  may reciprocate in the third direction DR 3  (that is, the vertical direction) by rotation motion of the first and second rotors  310  and  320 . Movement of the first rotor  310 , the second rotor  320 , and the follower  330  may be restrained to each other to act on each other. For example, the first rotor  310 , the second rotor  320 , and the follower  330  may operate similar to a scotch yoke cam driving principle. 
     The first bracket  340  may be disposed to engage with the second side surface  314  of the first rotor  310 . The first bracket  340  may guide a rotation path of the first rotor  310 . The second bracket  350  may be disposed to engage with the second side surface  324  of the second rotor  320 . The second bracket  350  may guide a rotation path of the second rotor  320 . 
     Since the first and second folding auxiliary members  180  and  190  are described with reference to  FIGS.  2 A and  2 B , repetitive descriptions will be omitted. 
     As described above, the foldable display device including the hinge device  300  according to embodiments of the disclosure may perform folding and unfolding in a two-axes hinge structure through interaction of rotation motion of the first and second rotors  310  and  320  and a straight line motion of the follower  330 . Therefore, folding/unfolding angles of the first base plate  112  (and the first panel support member DS 1  of  FIG.  1   ) and the second base plate  122  (and the second panel support member DS 2  of  FIG.  1   ) coincide, and a symmetrical folding/unfolding of the foldable display device may be implemented. 
       FIG.  10    is a perspective view illustrating an example of a method of driving the hinge device of  FIG.  9 A ; and  FIGS.  11 A to  11 C  are diagrams schematically illustrating an example of the method of driving the hinge device of  FIG.  10   . 
     For convenience of description, illustration of the first and second brackets  340  and  350  is omitted in  FIG.  10  to  11 C . In addition,  FIGS.  11 A to  11 C  show schematic planar shapes of the hinge device of  FIG.  10    as viewed from the first direction DR 1 . 
     Referring to  FIGS.  9 A to  11 C , the first rotor  310  and the second rotor  320  of the hinge device  300  may be concurrently (e.g., simultaneously) rotated in directions opposite to each other, and, thus, the foldable display device may be folded or unfolded. 
     As shown in  FIG.  11 A , in a state in which the foldable display device is fully unfolded, a horizontal surface of the first and second rotors  310  and  320  may be positioned to be parallel to the foldable display device. The horizontal surface of the first and second rotors  310  and  320  may be a surface opposite to each curved surface. 
     When the foldable display device is folded, the first rotor  310  may rotate in a clockwise direction and the second rotor  320  may rotate in a counterclockwise direction. Therefore, the first protrusion portion  312  and the second protrusion portion  322  may rotate in the first guide hole  332  and the second guide hole  334 , respectively. The follower  330  may reciprocate in the third direction DR 3  by rotation force of the first and second protrusion portions  312  and  322 . 
     For example, as shown in  FIG.  11 B , when the first and second rotors  310  and  320  rotate at a first angle from the state in which the foldable display device is fully unfolded, the follower  330  may be moved vertically downward. In addition, as shown in  FIG.  11 C , when the first and second rotors  310  and  320  rotate from the first angle to a second angle, the follower  330  may be moved vertically upward. 
     In addition, the first and second base plates  112  and  122  may rotate based on the first and second rotation axes RX 1  and RX 2 , respectively. 
     Therefore, symmetrical folding and unfolding may be performed in a two-axes hinge structure by interaction of rotation motion of the first and second rotors  310  and  320  and a straight line motion of the follower  330 . 
     As described above, the foldable display device including the hinge device according to embodiments of the disclosure may implement folding and unfolding by using a simple connection structure of a plurality of rotors and a follower and the two-axes hinge structure based on rotation motion of the rotors and a straight line motion (vertical movement or horizontal movement) of the follower. Therefore, folding/unfolding angles of the first base plate  110 ,  111 , or  112  (and a first panel support member DS 1 ) and the second base plate  120 ,  121 , or  122  (and a second panel support member DS 2 ) coincide, and symmetrical folding/unfolding of the foldable display device may be implemented. In addition, a manufacturing cost may be reduced by eliminating a configuration including a complicated driving mechanism and a plurality of sophisticated gears, springs, and/or the like, and implementing a two-axes hinge mechanism with a simple structure. 
     Although the present disclosure has been described with reference to some example embodiments, those skilled in the art will understand that the disclosure may be variously changed and modified without departing from the spirit and scope of the disclosure as set forth in the following claims.