Patent Publication Number: US-9844152-B2

Title: Display device

Description:
This application claims the benefit of Korean Patent Application No. 10-2015-0167365 filed on Nov. 27, 2015, and No. 10-2015-0185197 filed on Dec. 23, 2015, the entire contents of which are incorporated herein by reference for all purposes as if fully set forth herein. 
     BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to a display device, and more particularly, to a display device with supports that are positioned between first and third module covers so that the supports are shielded from the outside, and allowing the user to immerse themselves into the display screen. 
     Background 
     With the development of the information society, demand for various displays is increasing. Responding to this demand, various displays such as LCDs (liquid crystal display devices), PDPs (plasma display panels), ELDs (electroluminescent displays), VFDs (vacuum fluorescent displays), etc., are being researched and used. 
     Among these displays, those using organic light-emitting diodes (OLEDs) offer superior luminance and viewing angles compared to LCDs and can be made extremely thin because they work without a backlight. 
     SUMMARY 
     One aspect is to provide a display device including a housing; at least one roller positioned within the housing; and a display portion including a display panel and a module cover, and the module cover is divided into a plurality of sections, wherein the display panel and the module cover can transition from a first state where the display panel and the module cover are wound around the at least one roller to a second state where the display panel and the module cover are unwound from the at least one roller, in contact with each other, and exposed out of the housing. 
     The module cover may include: a first module cover section positioned at a center portion of a back of the display panel in the second state; a third module cover section positioned at both side portions of the back of the display panel in the second state; a second module cover section positioned at a back of the first and third module cover sections in the second state; and a fourth module cover section positioned at top edge portions of the first and second module cover sections, with both side edge portions being connected to the third module cover section. 
     The display device may further include a motor assembly, a top bar attached to a top portion of the display portion, and a plurality of supports to raise or lower the top bar, one end of the supports being connected to either end of the top bar and the other end being connected to the motor assembly, wherein the top bar may be attached to the top edge of the first module cover section and the fourth module cover section. 
     The first and fourth module cover sections may be attached to the top bar through at least one hole, and the second module cover section may be attached to the first and third module cover sections through at least one hole. 
     The first and third module cover sections may be spaced apart from each other by a distance in a horizontal direction. 
     The display device may further include a motor assembly, a top bar attached to a top portion of the display portion, and a plurality of supports to raise or lower the top bar, one end of the supports being connected to either end of the top bar and the other end being connected to the motor assembly, wherein the supports may be positioned in the space between the first and third module covers. 
     The display device may further include a motor assembly, a top bar attached to a top portion of the display portion, and a plurality of supports to raise or lower the top bar, one end of the supports being connected to either end of the top bar and the other end being connected to the motor assembly, wherein the fourth module cover section, and flat regions of the first and third module cover sections, which are positioned in the uppermost part of the first and third module cover sections, may remain flat in the first state. 
     A front surface of the first and third module cover sections may vertically protrude from a front surface of the second module cover section. 
     The display device may further include a motor assembly, a top bar attached to a top portion of the display portion, and a plurality of supports to raise or lower the top bar, one end of the supports being connected to either end of the top bar and the other end being connected to the motor assembly, wherein each support may include: an upper link, one end of which is connected to either end of the top bar; a hinges connected to the other end of the upper link; and a lower link, one end of which is connected to the hinge and the other end is connected to the motor assembly. 
     The hinge may include: a body; and an attachment part protruding towards the first module cover section from the body, wherein the attachment part may include a magnetic material. 
     The second module cover section may include trajectories to correspond to areas where the attachment parts move during a transition from the first state to the second state, where the trajectories may include a magnetic material whose polarity is opposite to that of the attachments parts. 
     The module cover and the display panel may be held together by magnets positioned on the third module cover section. 
     The module cover and the display panel may be held together by magnets positioned on the first and third module cover sections. 
     The display panel and the module cover may be wound or unwound by two rollers. 
     The at least one roller may include a panel roller to wind or unwind the display panel; and an apron roller to wind or unwind the module cover, in conjunction with the winding or unwinding of the display panel. 
     The panel roller and the apron roller may be positioned at a same side of the supports within the housing. 
     The panel roller and the apron roller may be positioned behind the supports within the housing. 
     The panel roller and the apron roller may be positioned at opposite sides of the supports within the housing. 
     The panel roller may be positioned in front of the supports within the housing, and the apron roller may be positioned behind the supports within the housing. 
     The at least one roller may include a guide roller to space the module cover and the panel roller apart from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIGS. 1 to 6  are views showing the configuration of a display device relating to an exemplary embodiment of the present invention; 
         FIGS. 7 to 31  are views showing a display device according to an exemplary embodiment of the present invention; and 
         FIGS. 32 to 43  are views showing a display device according to another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail embodiments of the invention examples of which are illustrated in the accompanying drawings. Since the present invention may be modified in various ways and may have various forms, specific embodiments are illustrated in the drawings and are described in detail in the present specification. However, it should be understood that the present invention are not limited to specific disclosed embodiments, but include all modifications, equivalents and substitutes included within the spirit and technical scope of the present invention. 
     The terms ‘first’, ‘second’, etc., may be used to describe various components, but the components are not limited by such terms. The terms are used for the purpose of distinguishing one component from other components. For example, a first component may be designated as a second component without departing from the scope of the present invention. In the same manner, the second component may be designated as the first component. 
     The term “and/or” encompasses both combinations of the plurality of related items disclosed and any item from among the plurality of related items disclosed. 
     When an arbitrary component is described as “being connected to “or” being linked to” another component, this should be understood to mean that still another component(s) may exist between them, although the arbitrary component may be directly connected to, or linked to, the second component. In contrast, when an arbitrary component is described as “being directly connected to” or “being directly linked to” another component, this should be understood to mean that no component exists between them. 
     The terms used in the present application are used to describe only specific embodiments or examples, and are not intended to limit the present invention. A singular expression can include a plural expression as long as it does not have an apparently different meaning in context. 
     In the present application, the terms “include” and “have” should be understood to be intended to designate that illustrated features, numbers, steps, operations, components, parts or combinations thereof exist and not to preclude the existence of one or more different features, numbers, steps, operations, components, parts or combinations thereof, or the possibility of the addition thereof. 
     Unless otherwise specified, all of the terms which are used herein, including the technical or scientific terms, have the same meanings as those that are generally understood by a person having ordinary knowledge in the art to which the present disclosure pertains. The terms defined in a generally used dictionary must be understood to have meanings identical to those used in the context of a related art, and are not to be construed to have ideal or excessively formal meanings unless they are obviously specified in the present application. 
     The following exemplary embodiments of the present invention are provided to those skilled in the art in order to describe the present disclosure more completely. 
     Hereinafter, a display panel will be described by taking an organic light-emitting display (OLED) as an example. However, display panels applicable to the present invention are not limited to OLEDs, but may include liquid crystal panels (LCPs), plasma display panels (PDPs), or field emission display panels (FED panels). 
       FIGS. 1 to 6  are views showing the configuration of a display device relating to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 1 , in what follows, a display panel  10  may include a first long side LS 1 , a second long side LS 2  facing the first long side LS 1 , a first short side SS 1  adjacent to the first long side LS 1  and the second long side LS 2 , and a second short side SS 2  facing the first short side SS 1 . 
     Here, the first short side SS 1  may be referred to as a first side area, the second short side SS 2  may be referred to as a second side area facing the first side area, the first long side LS 1  may be referred to as a third side area adjacent to the first and second side areas and positioned between the first and second side areas, and the second long side LS 2  may be referred to as a fourth side area adjacent to the first and second side areas, positioned between the first and second side areas, and facing the third side area. 
     For convenience of explanation, the first and second long sides LS 1  and LS 2  are longer in length than the first and second short sides SS 1  and SS 2 ; but, it should be noted that the first and second long sides LS 1  and LS 2  may be approximately the same length as the first and second short sides SS 1  and SS 2 . 
     In what follows, a first direction DR 1  may be parallel to the long sides LS 1  and LS 2  of the display panel, and a second direction DR 2  may be parallel to the short sides SS 1  and SS 2  of the display panel  10 . 
     A third direction DR 3  may be perpendicular (or orthogonal) to the first direction DR 1  and/or the second direction DR 2 . 
     The first direction DR 1  and the second direction DR 2  may be collectively referred to as a horizontal direction or a vertical direction, respectively. 
     The third direction DR 3  may be referred to as orthogonal direction. 
     Referring to  FIG. 2 , the display device  100  according to an embodiment of the present invention may include a display portion  20  and a housing  30 . 
     The display portion  20  may include a display panel  10  and a module cover  15 . The display panel  10  may be provided on the front of the display device  100  and display an image. A controller may display an image at the display panel  10  by breaking an image down into pixels and controlling the color, brightness, and intensity of light emitted by each individual pixel at the display panel  10 . The display panel  10  may be divided into an active region where an image is displayed and an inactive region where no image is displayed. 
     The display panel  10  may be rectangular. However, the display panel  10  is not limited to such a shape and also may be shaped to have a predetermined curvature at the corners. The display panel  10  may be an organic light-emitting diode (OLED) panel. However, the display panel is not limited to such a panel. For example, the display panel may be a liquid crystal display panel. 
     The module cover  15  may be provided behind the display panel  10 . The module cover  15  may be attached directly to the display panel  10 . The module cover  15  may be the same size as or larger than the display panel  10 . 
     The module cover  15  may support the back of the display panel  10 . Accordingly, the module cover  15  may include a material that is lightweight and high in strength. For example, the module cover  15  may include aluminum. 
     The housing  30  may be provided on the back of the display portion  20 . That is, the housing  30  may be provided on the back of the module cover  15 . The housing  30  may shield at least one printed circuit board (PCB). That is, the housing  30  may cover at least one PCB attached at the back of the module cover  15 . A detailed structure of the at least one PCB and a method of attaching the same will be described below. 
     Electronic signals from the at least one PCB may be transmitted to the housing  30 . Accordingly, the housing  30 , though not shown, may be comprised of an inner housing made of conductive material and an outer housing covering the inner housing. However, the housing  30  is not limited to such a structure, and may be a single unit made of conductive material. 
     Referring to  FIG. 3 , in the display device  100  according to an embodiment of the present invention, the housing  30  may be positioned under the display portion  20 . In more detail, the housing  30  may have a shape that covers the bottom of the display portion  20 . The housing  30  may be configured as not to expose drive equipment or drive circuits in it. 
     The widths of the housing  30  along the first and third directions may be larger than the width of the display portion  20 , in order to protect the display portion within the housing  30 . The width of the housing  30  along the second direction may be smaller than the width of the display portion  20 , in order to prevent the housing  30  from obstructing the user&#39;s field of vision. 
     In the display device  100  according to the embodiment of the present invention, the housing  30  may not be positioned in the active region of the display portion  20 . Accordingly, the display portion  20  may be made thinner, allowing the user to immerse themselves in the screen. 
     Referring to  FIG. 4 , in the display device  100  according to the embodiment of the present invention, the active region of the display portion  20  may be in a first state where the active region of the display portion  20  is within the housing  30  or a second state where the active region of the display portion  20  is exposed out of the housing  30 . 
     When the display device  100  is in the first state, the active region of the display portion  20  may be within the housing  30 . That is, the display portion  20  may be shielded in the housing  30 . 
     When the display device  100  is in the second state, the active region of the display portion  20  may be exposed out of the housing  30 . That is, when the display portion  20  is in the second state, part of the display portion  20  may protrude out above the housing  30 . 
     Although not shown in this figure, the display portion  20  may change from the first state to the second state by means of a roller within the housing  30 . In more detail, when the roller unrolls, the display portion  20  may change from the first state in which it is wound around the roller to the second state in which the display portion  20  is unwound from the roller to be exposed to the outside. In contrast, when the roller rolls back, the display portion  20  may change from the second state to the first state. A detailed structure of the roller and the display portion  20  and a method of operating them will be described later. 
     In the display device  100  according to the embodiment of the present invention, the display portion  20  may be either in the first state or in the second state. Accordingly, the user may save space by only exposing the display portion  20  out of the housing  30  when viewing the display device  100 . 
     Referring to  FIG. 5 , in the display device according to the embodiment of the present invention, a panel roller  143  may be connected to one edge of the display panel  10 . The panel roller  143  may wind or unwind the display panel  10  in order to bring the display panel  10  to either the first state or the second state. 
     In the display device according to the embodiment present invention, at least one source PCB  120  may be positioned on at least part of the front surface of the display panel  10 . Each source PCB  120  may be spaced apart from each other. 
     The at least one source PCB  120  may have signal wires for transmitting digital video data and timing control signals from a timing controller board  105  within the panel roller  143 . The source PCB  120  may be connected to the display panel  10  by a source chip on film (COF)  123 . The source COF  123  connected to one side of the source PCB  120  may connect to the display panel  10  as it extends to the active region of the display panel  10 . 
     A seat portion  379  may be positioned on the outer circumference of the panel roller  143 . That is, at least part of the outer circumference of the panel roller  143  is flat. The seat portion  379  may be positioned where the source PCB  120  makes contact with the panel roller  143  as the panel roller  143  is rolled. The seat portion  379  may be shaped in such a way that at least part of the outer circumference of the panel roller  143  is depressed. 
     When the panel roller  143  rolls in the display panel  10 , the source PCB  120  may sit in the seat portion  379  and at least part of it may make contact with the panel roller  143 . Accordingly, the source PCB  120  may not get damaged even if the panel roller  143  rolls in the display panel  10 . 
     The timing controller board  105  may be mounted inside the panel roller  143 . Mounting the timing controller board  105  inside the panel roller  143  may prevent an FFC cable  117  connecting to the source PCB board  120  from getting tangled. 
     The panel roller  143  may include an upper panel roller portion  331  and a lower panel roller portion  337 . As an example, the upper panel roller portion  331  and the lower panel roller portion  337  may be held together with at least one screw. The timing controller board  105  may be mounted in between the upper panel roller portion  331  and the lower panel roller portion  337 . The at least one screw may hold the timing controller board  105  in place while holding the upper panel roller portion  331  and the lower panel roller portion  337  together. The FFC cable  117  may connect the timing controller board  105  with the source PCB  120  via a hole in the upper panel roller portion  331 . 
     The display device according to the embodiment of the present invention allows for connecting the FFC cable  117  without it getting tangled because the timing controller board  105  rotates together with the panel roller  143 , and also can save space because the timing controller board  105  is mounted inside the panel roller  143 . 
     Referring to  FIG. 6 , in the display device according to an embodiment of the present invention, the timing controller board  105  is mounted in the panel roller  143  at one side of the center of the housing  30  where the display panel ascends or descends, and a main board  109  and a power supply  107  may be positioned on the other side of the center of the housing  30 . 
     The timing controller board  105  may be connected to the main board  109  and the power supply  107 . The timing controller board  105  may be connected to the main board  109  and the power supply  107  through wire electrodes  113 . In more detail, the wire electrodes  113  may include a first wire electrode  307  connecting the timing controller board  105  and the power supply  107  and a second wire electrode  309  connecting the timing controller board  105  and the main board  109 . 
     For example, a plurality of first wire electrode  307  may be provided. Also, the first wire electrode  307  may have a round shape. The first wire electrode  307  may connect the timing controller board  105  with the power supply  107  via an opening in the center of the axis of rotation of the panel roller  143 . 
     The second wire electrode  309  may use a flat flexible cable (FFC) cable that connects the timing controller board  105  with the source PCB  120 . The second wire electrode  309  may connect the timing controller board  105  with the main board  109  via an opening in the center of the axis of rotation of the panel roller  143 . 
     The first wire electrode  307  and the second wire electrode  309  may be positioned on opposite sides of the timing controller board  105 . The openings leading to the first wire electrode  307  and the second wire electrode  309  also may be positioned on opposite sides. 
     In the display device according to the embodiment of the present invention, the timing controller board  105  may be mounted in the panel roller  143 , and the power supply  107  and the main board  109  may be positioned on opposite sides of the display panel in the panel roller  143 . This can save a lot of space in the housing  30 . 
       FIGS. 7 to 31  are views showing a display device according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , the display device according to the present invention may include the panel roller  143 , motor assemblies  137 , and supports  73 , within the housing  30 . 
     The panel roller  143  may be positioned in front of where the display portion  20  ascends or descends in the housing  30 . The panel roller  143  may wind or unwind the display panel  10  and the module cover  15  simultaneously. Since the module cover  15  is thick, the diameter of the panel roller  143  may increase a lot during a transition from the first state to the second state. Accordingly, the panel roller  143  may be spaced a certain distance or farther apart from each side of the housing  30 , for instance, in the third direction. 
     The supports  73  may be positioned where the display portion  20  ascends or descends. The supports  73  may function to support the display panel  10  and the module cover  15  as they ascend or descend. In more detail, although not shown in this figure, the supports  73  may raise or lower a top bar attached to the top of the module cover  15  and display panel  10 . A detailed method of operating the supports  73  will be described later. 
     Because only the top portions of the module cover  15  and display panel  10  are connected to the top bar, the rest of them may bend easily. Accordingly, the supports  73  may support the module cover  15  from the back of the module cover  15  to keep the module cover  15  from bending. The supports  73  are not attached to the module cover  15  since they keep moving during a transition from the first state to the second state. However, the supports  73  can still support the module cover  15 . 
     The motor assemblies  137  may be positioned to connect with the supports  73 . The motor assemblies  137  may cause the supports  73  to ascend or descend. The motor assemblies  137  may take electrical signals and convert them into physical force. The motor assemblies  137  may transmit rotational energy to the supports  73 , thereby making a transition from the first state to the second state. Detailed description of the structure and operating principle of the motor assemblies  137  will be given later. 
     In the display device according to the embodiment of the present invention, the display panel  10  and the module cover  15  may be simultaneously wound or unwound by one roller. This may lead to a decrease in the thickness of the housing  30 , thus giving the user a better view of the screen. 
     Referring to  FIG. 8 , the module cover  15  may include a plurality of aprons. The aprons may be rectangular. The aprons may be spaced apart from one another and attached to the back of the display panel  10 . Because the module cover  15  comprises of a plurality of aprons, its shape may deform easily when it is wound around or unwound from the roller. The module cover  15  may include a plastic or aluminum material. Accordingly, the module cover  15  may protect the display panel  10  from external impact. 
     The display panel  10  and the module cover  15  may be held together by an adhesion layer  70 . The adhesion layer  70  may be double-sided tape. Using the adhesion layer  70 , the module cover  15  may be wound or unwound along with the display panel  10 . A segment of the adhesion layer  70  may be positioned on an apron and adhere to the display panel  10 . Each segment of the adhesion layer  70  may be set apart from each other. Accordingly, the shape of the module cover  15  may deform easily when it is wound around or unwound from the roller. The smaller the width of the adhesion layer  70  along the second direction, the less the display panel  10  will deform on external force. In more detail, the smaller the width of the adhesion layer  70  along the second direction, the more flexible it can be, thus transmitting less external force on the display panel  10 . 
     Moreover, the larger the width of the aprons along the second direction, the less likely the display panel  10  will have cracks. In more detail, the larger the width of the aprons along the second direction, the higher the rigidity; thus, no cracks will appear in the display panel  10 . 
     Therefore, if the width of the adhesion layer  70  along the second direction is no more than 30% of the width of the aprons along the second direction, less external force is transmitted to the display panel  10 , and this may lead to less bumps on the display screen. 
     Also, if the width of the adhesion layer  70  along the second direction is no less than 15% of the width of the aprons along the second direction, the rigidity of the display panel  10  is improved, and this may lead to less cracks in the display panel  10 . 
     Moreover, the larger the width of the adhesion layer  70  along the third direction, the less the display panel  10  will deform on external force. In more detail, the larger the width of the adhesion layer  70  along the third direction, the more flexible it can be, thus transmitting less external force on the display panel  10 . 
     In addition, the smaller the width of the aprons along the third direction, the less likely the display panel  10  will have cracks. In more detail, the larger the width of the aprons along the third direction, the higher the rigidity; thus, no cracks will appear in the display panel  10 . 
     Therefore, if the width of the adhesion layer  70  along the third direction is no less than 3% of the width of the aprons along the third direction, less external force is transmitted to the display panel  10 , and this may lead to less bumps on the display screen. 
     Also, if the width of the adhesion layer  70  along the third direction is no more than 6% of the width of the aprons along the third direction, the rigidity of the display panel  10  is improved, and this may lead to less cracks in the display panel  10 . 
     In the display device according to the embodiment of the present invention, the module cover  15  may include a plurality of aprons, and the adhesion layer  70  may sit on the aprons. Accordingly, the shape of the module cover  15  may deform more easily when it is wound around the roller, compared to when the module cover  15  is configured as a single unit. 
     Referring to  FIG. 9 , in a display device according to another exemplary embodiment of the present invention, the aprons may be in the shape of parallelograms. That is, the aprons may be in the shape of rectangles slanted in one direction. The aprons having the shape of parallelograms may prevent the display panel from bending in the opposite direction to the direction in which the display panel is wound. Accordingly, the display panel may remain flat in the second state. 
     When an external force is applied to the aprons in the opposite direction  351  to the direction the display panel is wound, the aprons may not rotate anymore because their surfaces come into contact with one another (see  FIG. 9( a ) ). Accordingly, the display panel may remain flat. 
     In contrast, when an external force is applied to the aprons in the direction  353  the display panel is wound, the aprons may rotate freely because their surfaces do not come into contact with one another (see  FIG. 9( b ) ). Accordingly, the display panel may be wound or unwound with ease. 
     In the display device according to the embodiment of the present invention, the aprons may rotate only in one direction. Accordingly, the screen will not bend even if an external force is applied to the display panel. 
     Referring to  FIG. 10 , in the display device according to an embodiment of the present invention, the module cover  15  and the display panel  10  may be fastened to a top bar  75 . For example, the module cover  15  and the display panel  10  may be fastened to the top bar  75  with at least one screw  115 . 
     The at least one screw  115  allows the module cover  15  and the display panel  10  to ascend or descend together with the top bar  75 , without deviating from each other. The at least one screw  115  may fasten the top bar  75  and the module cover  15  together and fasten the top bar  75  and the display panel  10  together. However, the at least one screw  115  is not limited to such a configuration, but may fasten the module cover  15  and the display panel  10  together. 
     An upper module cover  15   t  of the module cover  15  may differ in shape from the rest of the module cover  15  so as to be attached to the top bar  75 . The upper module cover  15   t  may be the uppermost apron. In more detail, the uppermost apron may have a different shape than the other aprons. At least a part of the upper module cover  15   t  may have a different thickness from the rest along the third direction. The part having a different thickness from the rest may be inserted into a recess of the top bar  75 . 
     The part having a different thickness from the rest of the upper module cover  15   t  may be fastened to the top bar  75 , for example, by at least one screw  115 . Since the upper module cover  15   t  is inserted into the top bar  75 , the module cover  15  may be fastened more firmly to the top bar  75 . 
     As illustrated in  FIG. 10( b ) , the top bar  75 , the module cover  15 , and the display panel  10  may be covered by a top case  167 . The top case  167  may shield the top bar  75 , the module cover  15 , and the display panel  10  on both sides and the top. The at least one screw  115  may fasten the top case  167 , together with the top bar  75 , the module cover  15 , and the display panel  10 . However, the top case  167  is not limited to such a configuration, but may be inserted into recesses in the top bar  75 , module cover  15 , and display panel  10 . 
     In the display device according to the embodiment of the present invention, the top bar  75 , the module cover  15 , and the display panel  10  may be held together. Accordingly, the module cover  15  and the display panel  10  may ascend or descend easily without deviating from each other. 
     Moreover, the top case  167  may cover the top bar  75 , the module cover  15 , and the display panel  10 . Thus, the user may find the look of the display device more neat and tidy. 
     Referring to  FIG. 11 , the display device according to an embodiment of the present invention may be so shaped that both sides of the top bar  75  are supported by the supports  73 . The top bar  75  may ascend or descend by means of the supports  73 . Each support  73  may include an upper link  73   a  and a lower link  73   b.    
     The upper link  73   a  and the lower link  73   b  may be connected by a hinge  152 . One end of the upper link  73   a  may be fastened to the top bar  75  and the other end to the hinge  152 , and one end of the lower link  73   b  may be fastened to the motor assembly and the other end to the hinge  152 . 
     A guide bar  234  may be positioned at the entrance where the supports  73  ascend from or descend into the housing. The guide bar  234  may include first and second guide bars  234   a  and  234   b . The first and second guide bars  234   a  and  234   b  may face each other, with the supports  73  in between. For example, the first guide bar  234   a  may be positioned in front of the supports  73 , and the second guide bar  234   b  may be positioned behind the supports  73 . 
     The panel roller  143  may be positioned at the bottom, in front of the supports  73 . The panel roller  143  may be provided with at least one bracket  221  corresponding to the bottom surface of the housing. For example, at least one bracket  221  may be positioned below the panel roller  143 . The at least one bracket  221  may be spaced apart from one another. For example, the at least one bracket  221  may be fixed to the bottom surface of the housing with screws. 
     The display device according to the embodiment of the present invention may have various operating mechanisms in it. This may reduce the risk of breakdown that may occur when the display panel ascends or descends by means of the roller. 
     Referring to  FIG. 12 , the first guide bar  234   a  may guide the display panel  10  and module cover  15  wound around the panel roller  143  at a part of the housing  30  where they ascend or descend. Accordingly, the display panel  10  and the module cover  15  may ascend or descend from a desired position even if their position does not correspond to where the panel roller  143  ascends or descends the display panel  10  and the module cover  15 . The display panel  10  and the module cover  15 , both in the first and second states, may come into contact with the first guide bar  234   a  at the entrance of the housing  30 . Accordingly, the display panel  10  and the module cover  15  may ascend or descend from the same position regardless of which state they are in. 
     The bracket  221  may be positioned below the panel roller  143 . A side of the bracket  221  facing the panel roller  143  may be concaved. The bracket  221  may guide the display panel  10  and module cover  15  wound around the panel roller  143  in such a way that they are not dragged against the bottom surface of the housing  30 . Accordingly, the diameter BD of the concaved portion of the bracket  221  may be larger than the diameter RD of the panel roller  143 . If the diameter BD of the concaved portion of the bracket  221  is smaller than the diameter RD of the panel roller  143 , the display panel  10  and the module cover  15  may deviate from the bracket  221  and be dragged against the bottom surface of the housing  30 . The bracket  221  may include rubber or plastic in order to prevent damage due to friction with the display panel  10  and the module cover  15 . 
     Referring to  FIG. 13 , in the case that the bracket  221  is not provided as shown in  FIG. 13( a ) , when the display panel  10  and the module cover  15  are unwound from the panel roller  143 , they may be dragged against the bottom surface of the housing  30 . Accordingly, the display panel  10  or the module cover  15  may have cracks. Also, the display panel  10  and the module cover  15  may not be freely wound. 
     In contrast, in the case that the bracket  221  is positioned below the panel roller  143  as shown in  FIG. 13( b ) , when the display panel  10  and module cover  15  are unwound from the panel roller  143 , they may make contact with the bracket  221 . Since the concaved portion of the bracket  221  has a semicircular shape, the display panel  10  and the module cover  15  may keep their rolled shape, rather than hanging down. Also, the bracket  221  may prevent the display panel  10  and the module cover  15  from damage due to friction with the housing  30 . 
     Referring to  FIG. 14 , in the display device according to an embodiment of the present invention, the top bar  75  may ascend during a transition from the first state to the second state. The top bar  75  may ascend or descend as it is pushed by the supports  73  on two opposite edges. 
     As illustrated in  FIG. 14( a ) , in the first state, the angle HRA between the upper link  73   a  and the lower link  73   b  may be very small. Thus, the top bar  75  has not ascended. Also, the display panel and the module cover may be kept wound around the panel roller. 
     As illustrated in  FIG. 14( b ) , as the motor assembly  137  rotates, the angle HRA between the upper link  73   a  and the lower link  73   b  may increase. An increase in the angle HLA between the upper link  73   a  and the lower link  73   b  may allow the top bar  74  to ascend. Accordingly, the display panel and module cover wound around the panel roller may become gradually unwound. 
     As illustrated in  FIG. 14( c ) , in the second state, the upper link  73   a  and the lower link  73   b  may be parallel to each other. That is, the angle HLA between the upper link  73   a  and the lower link  73   b  may be 180 degrees. Accordingly, the top bar  75  may be at the maximum height. Also, the display panel and the module cover may become fully unwound from the panel roller. 
     Referring to  FIG. 15 , in the display device according to the embodiment of the present invention, a stand fixing portion  315  and a stand  317  may be positioned behind the motor assembly. 
     The stand fixing portion  315  may be positioned corresponding to the motor assembly  137  and shield the motor assembly  137 . The stand fixing portion  315  may be fastened to the motor assembly  137  and the housing  30  so that the stand  317  is fixed to the housing  30 . 
     Since the stand fixing portion  315  and the stand  317  correspond to the motor assembly  137 , they may be positioned on either side of the display device. 
     The stand  317  may be connected to the stand fixing portion  315  and be exposed to the outside of the housing  30 . The stand  317  may have the shape of a cylinder extending in one direction. The stands  317  on both sides of the display device may serve as legs of the display device. That is, the stands  317  may serve to support the display device. 
     The stand  317  may rotate with respect to the stand fixing portion  315 . Accordingly, the user may rotate the stand  317  to bring the bottom surface of the housing  30  into contact with the ground. That is, the stand  317  may be rotated in such a way as to not make contact with the ground such that the height of the display panel  10  corresponds to the height of the user&#39;s eyes. In this case, the user may adjust the height of the display panel  10  to the height of their eyes by rotating the stand  317 . 
     Referring to  FIG. 16 , in the display device according to the embodiment of the present invention, the upper link  73   a  may comprise of multiple parts, and likewise the lower link  73   b  may comprise of multiple parts. 
     In more detail, the upper link  73   a  may include a first upper link  73 Ca and a second upper link  73 Fa. Likewise, the lower link  73   b  may include a first lower link  73 Cb and a second lower link  73 Fb. 
     The first upper and lower links  73 Ca and  73 Cb may be positioned further outward than the second upper and lower links  73 Fa and  73 Fb. The first upper and lower links  73 Ca and  73 Cb may be connected to the center of the hinge  152 , and the second upper and lower links  73 Fa and  73 Fb may be connected to both sides of the hinge  152 . 
     The end portions of the first upper and lower links  73 Ca and  73 Cb inside the hinge  152  may be in the shape of gears meshing with each other. The hinge  152  may hold the first upper link  73 Ca and the first lower link  73 Cb in place so that the gears of the first upper and lower links  73 Ca and  73 Cb mesh with each other. 
     The angle HRA 1  from the horizontal line passing between the first upper link  73 Ca and the first lower link  73 Cb (ground) to the first upper link  73 Ca, and the angle HRA 2  from the ground to the first lower link  73 Cb may be equal because the first upper link  73 Ca and the first lower link  73 Cb are in the shape of gears meshing with each other and symmetric with respect to the ground. Also, the angle between the first upper link  73 Ca and the first lower link  73 Cb may be equal for support  73  of both hinges  152 . Accordingly, the top bar  75  operated by the upper link  73   a  and the lower link  73   b  of support  73  of both hinges  152  may ascend or descend to the same height without misalignment. That is, the angle between the first upper link  73 Ca and the first lower link  73 Cb may be equal on both hinges  152 , regardless of which state the display panel is in. 
     The second upper and lower links  73 Fa and  73 Fb may support the first upper and lower links  73 Ca and  73 Cb on the inside of the second upper and lower links  73 Fa and  73 Fb. The angle between the second upper link  73 Fa and the second lower link  73 Fb may change the same way as the angle between the first upper link  73 Ca and the first lower link  73 Cb does. 
     Referring to  FIG. 17 , in a display device according to a previous embodiment of an invention, the upper and lower links  73   a  and  73   b  were configured as a single link, as illustrated in  FIG. 17( a ) . Accordingly, when an external force F was applied to one side of the display panel, the angle HRA between the upper and lower links  73   a  and  73   b  on that side became distorted. Accordingly, the angle HRA between the upper and lower links  73   a  and  73   b  differed between the two hinges. In this case, one side of the display panel became slanted as illustrated in  FIG. 17( b ) . 
     In contrast, in the display device according to the embodiment of the present invention, the second upper and lower links  73 Fa and  73 Fb may support the first upper and lower links  73 Ca and  73 Cb even if an external force F is applied to one side of the display panel, as illustrated in  FIG. 17( c ) . Accordingly, the angle HRA between the upper and lower links  73   a  and  73   b  may not change. In this case, the display panel may be kept from slanting, allowing the user to immerse themselves in the display screen without distraction. Moreover, any damage due to the slant of the display panel may be prevented. 
     Referring to  FIG. 18 , in the display device according to an embodiment of the present invention, one side of the first upper and lower links  73 Ca and  73 Cb may be extended toward the second upper and lower links  73 Fa and  73 Fb. That is, the width of the first upper and lower links  73 Ca and  73 Cb may be increased and larger when viewed from the front (away from the hinge side). Accordingly, the first upper and lower links  73 Ca and  73 Cb may shield the second upper and lower links  73 Fa and  73 Fb in the front. 
     The rotational axis of the first upper and lower links  73 Ca and  73 Cb may be at a different height from that of the second upper and lower links  73 Fa and  73 Fb. In more detail, the rotational axis of the first upper and lower links  73 Ca and  73 Cb may be at a different height from that of the second upper and lower links  73 Fa and  73 Fb, along the third direction (z direction). That is, the vertical height of a portion of the hinge  152  that is connected to the first upper and lower links  73 Ca and  73 Cb may be different from the vertical height of a portion of the hinge  152  that is connected to the second upper and lower links  73 Fa and  73 Fb. Accordingly, even if one side of the first upper and lower links  73 Ca and  73 Cb extends toward the second upper and lower links  73 Fa and  73 Fb, the first upper and lower links  73 Ca and  73 Cb may not come into contact with the second upper and lower links  73 Fa and  73 Fb. 
     Although not shown, one side of the second upper and lower links  73 Fa and  73 Fb may be extended toward the first upper and lower links  73 Ca and  73 Cb. That is, the width of the second upper and lower links  73 Fa and  73 Fb may be increased and larger when viewed from the rear (toward the hinge side). Accordingly, the second upper and lower links  73 Fa and  73 Fb may shield the first upper and lower links  73 Ca and  73 Cb in the front. 
     Referring to  FIG. 19 , in the first state, the first upper and lower links  73 Ca and  73 Cb and the second upper and lower links  73 Fa and  73 Fb may overlap, respectively, at least partially in width, as illustrated in  FIG. 19( a ) . For example, the first upper and lower links  73 Ca and  73 Cb and the second upper and lower links  73 FA and  73 Fb may partially overlap such that there is a certain distance SLD between the first upper link  73 Ca and the second upper link  73 Fa, and a certain distance SLD between the first lower link  73 Cb and the second lower link  73 Fb. Accordingly, the entire width of the upper link  73   a  may be larger than the width HLW of the second upper link  73 Fa or the width CLW of the first upper link  73 Ca. 
     In contrast, as illustrated in  FIG. 19( b ) , in the second state, the first upper and lower links  73 Ca and  73 Cb and the second upper and lower links  73 Fa and  73 Fb may overlap fully in width with each other. For example, the first upper and lower links  73 Ca and  73 Cb and the second upper and lower links  73 FA and  73 Fb may fully overlap such that there is no certain distance SLD between the first upper link  73 Ca and the second upper link  73 Fa, and no certain distance SLD between the first lower link  73 Cb and the second lower link  73 Fb. Accordingly, the entire width HLW of the upper link  73   a  may be equal to the width of the second upper link  73 Fa or the width CLW of the first upper link  73 Ca. 
     Referring to  FIG. 20 , in the case that one side of the first upper link  73 Ca is not extended toward the second upper link  73 Fa, the first upper link  73 Ca and the second upper link  73 Fa may be spaced a certain distance LD apart from each other as the first upper link  73 Ca is moved from the first state to the second state, as illustrated in  FIG. 20( a ) . The distance LD between the first upper link  73 Ca and the second upper link  73 Fa may increase when moving from the first state toward the second state. 
     The problem with this is that the user&#39;s hand may get hurt by getting caught between the first upper link  73 Ca and the second upper link  73 Fa during the transition from the first state to the second state. 
     In contrast, as illustrated in  FIG. 20( b ) , in the case that one side of the first upper link  73 Ca is extended toward, and overlapping with the second upper link  73 Fa, the space between the first upper link  73 Ca and the second upper link  73 Fa may not be exposed even when the first upper link  73 Ca is moved from the first state to the second state. This can avoid the risk of the user&#39;s hand getting caught between the first upper link  73 Ca and the second upper link  73 Fa during the transition from the first state to the second state. 
     Referring to  FIG. 21 , the motor assembly  137  may include a motor  138  and a decelerator  139 . 
     The motor  138  may take electricity and convert them into physical force. The motor may transmit rotational energy to the decelerator  139 . There may be two motors  138  which may be fixed to the bottom of either side of the housing  30 . 
     The decelerator  139  may be shaped to interlock with the motor  138 . The decelerator  139  may be covered in a different casing from the motor  138 . With the decelerator  139  being covered in a different casing from the motor  138 , unnecessary contact between them may be avoided. However, the decelerator  139  is not limited to such a configuration, but may be covered in the same casing as the motor  138 . 
     The decelerator  139  may rotate in the first direction when the motor  138  rotates in the first direction, and rotate in the second direction when the motor  138  rotates in the second direction. The decelerator  139  may transmit a large amount of rotational energy while lowering the rotation speed of the motor  138 . 
     When the decelerator  139  rotates in the first direction, the angle from the ground to the lower link  73   b  connected to the decelerator  139  may increase. When the decelerator  139  rotates in the second direction, the angle from the ground to the lower link  73   b  connected to the decelerator  139  may decrease. 
     Referring to  FIG. 22 , in the display device according to an embodiment of the present invention, the lower link  73   b  may be pushed using a transmission portion  126  connected to an auxiliary link  191 . The auxiliary link  191  may include a fastening portion  151 , a cylindrical portion  153 , and a spring portion  179 . 
     One end of the transmission portion  126  may be connected to a lower part of the first lower link  73 Cb and push the first lower link  73 Cb. The transmission portion  126  may transmit energy from the auxiliary link  191  to the first lower link  73 Cb. The other end of the transmission portion  126  may be connected to the fastening portion  151  of the auxiliary link  191 . 
     A guide wheel  241  may be positioned at the joint of the transmission portion  126  and the auxiliary link  191 . The guide wheel  241  may guide the transmission portion  126  and the auxiliary link  191  during the transition from the first state to the second state in such a way that they do not deviate in the third direction. Since the guide wheel  241  guides the transmission portion  126  and the auxiliary link  191  in this way, the force of the auxiliary link  191  may be correctly transmitted to the first lower link  73 Cb. 
     The fastening portion  151  may be a portion that attaches the auxiliary link  191  and the transmission portion  126  together. The fastening portion  151  may transmit elastic force to the transmission portion  126 . 
     The spring portion  179  may push the fastening portion  151 . The spring portion  179  may be compressed when the lower link  73   b  descends, and stretched when the lower link  73   b  ascends. Thus, the spring portion  179  may exert force using its elasticity when the lower link  73   b  ascends. 
     Without the spring portion  179 , the lower link  73   b  receives force only from the motor  138 . If the angle from the ground to the lower link  73   b  is close to 0°, a considerable amount of torque may be needed. Thus, the motor  138  will require quite a large amount of force. This will require the motor  138  to be large in size, and also will require a large housing size. 
     On the other hand, with the spring portion  179 , much less torque may be required to make the lower link  73   b  ascend. Thus, the force required for the motor  138  may be reduced to a considerable extent. This can reduce the size of the motor and also the size of the housing for accommodating the motor  138 . With such a reduction in the size of the housing, the display device may enable the user to immerse themselves in the display panel without distraction by the size of the housing. 
     The cylindrical portion  153  may shield at least part of the fastening portion  151  and the spring portion  179 . Accordingly, the cylindrical portion  153  may exert force to the fastening portion  151  without deviating when the spring portion  179  is stretched due to its elasticity. 
     In the display device according to the embodiment of the present invention, this elasticity allows the auxiliary link  191  to push the lower link  73   b . Accordingly, the top bar  75  may ascend more easily. 
     Referring to  FIG. 23 , the guide wheel  241  may move on a guide rail  372  during the transition from the first state to the second state. The guide rail  372  may be depressed inward in the center of the guide rail  372 , and the guide wheel  241  may be inserted in the depressed part of the guide rail  372  and be movable. 
     As illustrated in  FIG. 23( a ) , in the first state, most of the fastening portion  151  may be within the cylindrical portion  153 . This means that the spring portion is compressed. Since the fastening portion  151  does not push the transmission portion  126 , the angle from the ground to the transmission portion  126  may be small. The guide wheel  241  may be positioned adjacent to the cylindrical portion  153 , along the guide rail  372 . 
     As illustrated in  FIG. 23( b ) , the fastening portion  151  may be exposed out of the cylindrical portion  153  during the transition from the first state to the second state. That is, the fastening portion  151  may push the transmission portion  126 . In this case, the spring portion may deliver elastic energy as it is uncompressed. Since the fastening portion  151  pushes the transmission portion  126 , the angle from the ground to the transmission portion  126  may increase gradually. The guide wheel  241  may be positioned midway along the guide rail  372 . 
     As illustrated in  FIG. 23( c ) , in the second state, most of the fastening portion  151  may be exposed out of the cylindrical portion  153 . This means that the spring portion is fully uncompressed. Since the fastening portion  151  pushes the transmission portion  126 , the angle from the ground to the transmission portion  126  may be large. The guide wheel  241  may be positioned adjacent to the lower link  73   b , along the guide rail  372 . 
     In the display device according to the embodiment of present invention, the guide wheel  241  may push the lower link  73   b  while moving along the guide rail  372 . Accordingly, the elasticity of the spring portion may be transmitted more easily and correctly. 
     Referring to  FIG. 24 , the spring portion  179  may include first to third springs  179   a  to  179   c . The first spring  179   a  may be more adjacent to the fastening portion  151  than the second and third springs  179   b  and  179   c . Also, the second spring  179   b  may be more adjacent to the fastening portion  151  than the third spring  179   c . That is, the third spring  179   c  may be the farthest spring from the fastening portion  151 . Accordingly, the third spring  179   c  may be the farthest spring from the transmission portion connected to the fastening portion  151 . 
     At least one of the first to third springs  179   a  to  179   c  may have a different spring constant. For example, the third spring  179   c  may have a higher spring constant than the first and second springs  179   a  and  179   b . That is, the third spring  179   c  requires more force to deform than the first and second springs  179   a  and  179   b . The first to third springs may be separated from one another by side supporters  182  and main supporters  184 . 
     The side supporters  182  may include first and second side supporters  182   a  and  182   b . The first side supporter  182   a  may be positioned on one end of the first spring  179   a , and the second side supporter  182   b  may be positioned on the other end of the third spring  179   c . Protrusions of the first and second side supporters  182   a  and  182   b  may be inserted into the first and third springs  179   a  and  179   c.    
     The main supporters  184  may include first and second main supporters  184   a  and  184   b . The first main supporters  184   a  may be positioned between the first spring  179   a  and the second spring  179   b.    
     The first and second main supporters  184   a  and  184   b  may protrude on both sides. Protrusions of the first main supporter  184   a  may be attached to the other end of the first spring  179   a  and one end of the second spring  179   b . Also, protrusions of the second main supporter  184   b  may be inserted into the other end of the second spring  179   b  and one end of the third spring  179   c.    
     The range of displacement of the first to third springs  179   a  to  179   c  may be limited due to the side supporters  182  and the main supporters  184 . That is, the amount of compression of the first to third springs  179   a  to  179   c  may be limited due to the side supporters  182  and the main supporters  184 . 
     In the display device according to the embodiment of the present invention, the spring portion  179  may comprise of a plurality of springs with different spring constants. Accordingly, the force the spring portion  179  exerts may be balanced with the non-linear force needed for the supports to ascend or descend. 
     Referring to  FIGS. 25 and 26 , in the second state, the spring portion  179  may be in an uncompressed state. Accordingly, the spring portion  179  may have a first length SD 1 . The first length SD 1  may be the maximum length when the spring portion  179  is fully uncompressed. The uncompressed spring portion  179  may transmit force to the supports  73  by pushing on the fastening portion  151 . 
     During the transition from the second state to the first state, the angle from the ground to the lower link  73   b  may decrease, pushing the transmission portion  126  toward the center. Accordingly, the force is transmitted to the fastening portion  151 , allowing the fastening portion  151  to compress the spring portion  179 . The spring portion  179  may have a second length SD 2 , which is shorter than the first length SD 1  the spring portion  179  had in the second state. 
     In the second state, the spring portion  179  may not be exposed out of the cylindrical portion  153 . That is, the spring portion  179  may not be exposed out of the cylindrical portion  153  in any circumstances. Since the spring portion  179  is not exposed out of the cylindrical portion  153 , it may push the lower link  73   b  without deviating from the cylindrical portion  153 . Also, since the spring portion  179  is not exposed out of the cylindrical portion  153 , its elasticity is not scattered and the user will find the look of the display device tidy. 
     Referring to  FIG. 27 , if the side supporters  182  and the main supporters  184  are not provided among the first to third springs  179   a  to  179   c , as illustrated in  FIG. 27( a ) , the first and second springs  179   a  and  179   b  with a lower spring constant may be excessively compressed in the first state. In contrast, the amount of compression of the third spring  179   c  with a higher spring constant may be relatively small in the first state, compared to the first and second springs  179   a  and  179   b.    
     In this case, the first and second springs  179   a  and  179   b  may suffer plastic deformation due to the excessive compression. Also, the amount of compression of the third spring  179   c  may be relatively small. Due to the plastic deformation of the first and second springs  179   a  and  179   b , the first and second springs  179   a  and  179   b  may not be restored to their original length during the transition from the first state to the second state. That is, the length of the first and second springs  179   a  and  179   b  may be shorter than that before the plastic deformation by a certain distance SDD. Accordingly, the spring portion  179  does not push on the fastening portion  151  and therefore the lower link  73   b  may not ascend. 
     On the other hand, as illustrated in  FIG. 27( b ) , when the side supporters  182  and the main supporters  184  are provided among the first to third springs  179   a  to  17   c , the amount of compression of the first to third springs  179   a  to  179   c  in the first state may be limited due to the side supporters  182  and the main supporters  184 . That is, the first and second springs  179   a  and  179   b  may be compressed no more than a certain length. Thus, the first and second springs  179   a  and  179   b  may not suffer physical deformation even when they are compressed. Also, the compression force may not be concentrated on the first and second springs  179   a  and  179   b . Accordingly, the length of the spring portion  179  may be longer if the side supporters  182  and the main supporters  184  are provided. 
     The first and second springs  179   a  and  179   b  may not suffer plastic deformation because of the side supporters  182  and the main supporters  184 . Thus, the first and second springs  179   a  and  179   b  may return to their original length after the transition from the first state to the second state. Accordingly, the spring portion  179  may properly push on the fastening portion  151 , allowing the lower link  73   b  to ascend. 
     In the display device according to the embodiment of the present invention, the side supporters  182  and the main supporters  184  may be positioned among the springs. Accordingly, the spring portion  179  may not suffer plastic deformation, which makes it easy to transmit force to the lower link  73   b.    
     Referring to  FIG. 28 , in the display device according to an embodiment of the present invention, a roller hub  278  may be positioned on either side of the housing, corresponding to the panel roller  143 . The roller hub  278  may be attached to the center axis of the panel roller  143 . The roller hub  278  may have a wide circumference so that a transmission belt  314  to be described later may easily wound around it. 
     A constant spring  316  may be spaced apart from the roller hub  278 . The transmission belt  314  may be wound around the constant spring  316  and the roller hub  278 . The transmission belt  314  may tend to remain wound around the constant spring  316 . Accordingly, if the transmission belt  314  is unwound from the constant spring  316 , force may be exerted in a direction in which the transmission belt  314  is to be wound again. 
     The constant spring  316  may be located a first distance CSD below the roller hub  278 , along the second direction. In this case, more force may be transmitted, compared to when the constant spring  316  is at the same height as or above the roller hub  278 . 
     Referring to  FIG. 29 , a first torque T 1  may be applied to the panel roller  143  to wind the display panel around the panel roller  143 , as illustrated in  FIG. 29( a ) . Since the first torque T 1  is small, the amount of rotation of the panel roller  143  may be relatively small, compared to the length of vertical movement of the display panel  10 . In this case, the display panel  10  may hang down from the panel roller  143  and thus may not be correctly wound around the panel roller  143 . 
     As illustrated  FIG. 29( b ) , a second torque T 2  may be applied to the panel roller  143  to wind the display panel  10  around the panel roller  143 . The second torque T 2  may be larger than the first torque T 1 . Accordingly, the amount of rotation of the panel roller  143  may correspond to the length of vertical movement of the display panel  10 . In this case, the display panel  10  may be correctly wound around the panel roller  143  as they interlock with each other. 
     In the display device according to the embodiment of the present invention, a certain amount of torque or more may be required in order that the display panel  10  is correctly around the panel roller  143  by interlocking with it. Accordingly, a device for applying the certain amount of torque or more to the panel roller  143  may be required. 
     Referring to  FIG. 30 , the roller hub  278  may rotate together with the panel roller  143  in a first direction, i.e., counterclockwise direction, during the transition from the first state to the second state, as illustrated in  FIG. 30( a ) . The display panel  10  and the transmission belt  314  may be kept wound in opposite directions. Accordingly, as the display panel  10  and the roller hub  278  rotate in the first direction, the transmission belt  314  may be unwound from the roller hub  278  and the display panel  10  may be wound around the panel roller  143 . 
     Because the constant spring  316  has a certain amount of torque in a clockwise direction, it may help the display panel  10  rotate counterclockwise when it is wound around the roller hub  278 . Since the torque of the constant spring  316  helps when the roller hub  278  rolls, it may help also when the panel roller  143  connected to the roller hub  278  rolls. Accordingly, the display panel  10  may be correctly wound around the panel roller  143  by interlocking with it. 
     In contrast, as illustrated in  FIG. 30( b ) , the roller hub  278  may rotate together with the panel roller  143  in a second direction, which is the opposite direction to the first direction, during the transition from the first state to the second state. The display panel  10  and the transmission belt  314  may be kept wound in opposite directions. Accordingly, as the display panel  10  and the roller hub  278  rotate in the second direction, the transmission belt  314  may be wound around the roller hub  278  and the display panel  10  may be unwound from the panel roller  143 . 
     Because the constant spring  316  has a certain amount of torque in a clockwise direction, it may obstruct the display panel  10  from rotating clockwise when unwound from the roller hub  278 . Accordingly, the force required for the display panel  10  to ascend by means of the supports should be larger than the torque of the constant spring  316 , in order for the constant spring  316  not to obstruct the panel roller  143  and the roller hub  278  from rotating in the second direction. 
     In the display device according to the embodiment of the present invention, when the panel roller  143  and the roller hub  278  rotate in the second direction, the display panel  10  may be wound fast by the torque of the constant spring  316 . This may prevent the display panel  10  from hanging down from the panel roller  143 . 
     Referring to  FIG. 31 , the torque of a conventional torsion spring versus the number of rotations of the roller hub is indicated with a dotted line, and the torque of the constant spring versus the number of rotations of the roller hub is indicated with a solid line. 
     The amount of change in the torque required to wind the display panel around the panel roller may be small depending on the number of rotations. 
     As indicated with the dotted line, the greater the number of rotations, the larger the torque applied to the conventional torsion spring. Accordingly, unnecessary torque may be produced. This may require mechanisms for reducing unnecessary torque, and the addition of these mechanisms may increase noise. 
     On the other hand, as indicated with the solid line, the torque applied to the constant spring may be constant if the number of rotations exceeds a certain value. Accordingly, unnecessary torque may be minimized, and this may lead to less noise and minimum installation space. 
       FIGS. 32 to 43  are views showing a display device according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 32 , in the display device according to an embodiment of the present invention, the panel roller  143  may be positioned in front of the supports  73 , and an apron roller  141  may be positioned behind the supports  73 . That is, the panel roller  143  and the apron roller  141  may face each other on opposite sides of the supports  73 . 
     The panel roller  143  may wind or unwind the display panel  10 , and the apron roller  141  may wind or unwind the module cover  15 . The display panel  10  and the module cover  15  may not be attached with an adhesion layer because they are wound around different rollers. 
     The module cover  15  may be thicker than the display panel  10 , so it may take up a lot of space in the housing  30 . Accordingly, the motor assemblies  137  may be positioned in front of the supports  73  so as to not obstruct the winding or unwinding of the module cover  15 . However, the motor assemblies  137  are not limited to such a configuration, but may be positioned behind the supports  73 . 
     As the display panel  10  and the module cover  15  are separately wound within the housing  30 , the winding force of the panel roller  143  and apron roller  141  may be greater than the attachment force of the display panel  10  and module cover  15 . 
     In the embodiment of the present invention, the display panel  10  and the module cover  15  may be wound by two rollers, respectively. Accordingly, the weight of windings may be shared between the two rollers, and this may prevent the display panel  10  and the module cover  15  from hanging down during winding. 
     Referring to  FIG. 33 , in the display device according to an embodiment of the present invention, the panel roller  143  and the apron roller  141  may be positioned on the same side. For example, the panel roller  143  and the apron roller  141  may be positioned behind the supports  73 . However, the panel roller  143  and the apron roller  141  are not limited to such a configuration, but may be positioned in front of the supports  73 . 
     The apron roller  141  may be positioned below the panel roller  143 . Since the module cover  15  has a large thickness, the diameter of the apron roller  141  may increase quite a lot during the transition from the second state to the first state. Accordingly, the apron roller  141  may be spaced a first distance PGD or longer apart from the panel roller  143  to avoid contact with the panel roller  143 . The distance PGD may be equal to or greater than the distance at which the apron roller  141 , in the first state, does not make contact with the panel roller  143 . 
     A guide roller  145  may be positioned in a line along which the apron roller  141  unrolls. The guide roller  145  may guide the module cover  15  in such a way that the module cover  15  does not make contact with the panel roller  143  when the module cover  15  is in at least one of the first and second states. The guide roller  145  may be positioned below the panel roller  143  so that the module cover  15  does not make contact with the panel roller  143 . 
     In the display device according to the embodiment of the present invention, the panel roller  143  and the apron roller  141  may be positioned one above the other on the same side. This may save more space compared to when the panel roller  143  and the apron roller  141  are on different sides. 
     Referring to  FIG. 34 , in the display device according to the embodiment of the present invention, a pressure roller  147 , instead of the guide roller, may be provided. The pressure roller  147  may press the module cover  1  into contact with the supports  73 . Accordingly, the module cover  15  may remain flat without being bent. The pressure roller  147  may be positioned adjacent to the supports  73  in a third direction so that the module cover  15  makes contact with the supports  73 . The pressure roller  147  may function to guide the module cover  15  so that the module cover  15  and the panel roller  143  make contact with each other. 
     In the display device according to the embodiment of the present invention, the pressure roller  147  may press the module cover  15  into contact with the supports  73 . Accordingly, the display panel  10  may become flat, allowing the user to immerse themselves in the display panel  10 . 
     Referring to  FIG. 35 , in the display device according to an embodiment of the present invention, both the guide roller  145  and the pressure roller  147  may be provided. Thus, the module cover  15  may be kept from making contact with the panel roller  143 , but may come into contact with the supports  73 . This may result in fewer malfunctions in the display device, and the user may enjoy watching on the flat surface of the display panel  10 . 
     Referring to  FIG. 36 , in the display device according to an embodiment of the present invention, the module cover  15  may include a plurality of sections such as a first to fourth module cover sections  15   a  to  15   d.    
     The first module cover section  15   a  may be positioned in the center of the module cover  15 . The first module cover section  15   a  may be attached to the top bar  75 . An exemplary method of attaching the first module cover section  15   a  will be described later. The third module cover section  15   c  may be positioned on either side of the module cover  15 . That is, the third module cover section  15   c  may be positioned on each side of the module cover  15 . 
     The fourth module cover section  15   d  may be positioned on the top side of the module cover  15 . The fourth module cover section  15   d  may be connected to the upper part of the third module cover section  15   c . In the second state, the fourth module cover section  15   d  and the third module cover section  15   c  may be positioned on the rear edge of the display panel. The fourth module cover section  15   d  may be attached to the top bar  75 . For example, the fourth module cover section  15   d  may have a shape that covers the top bar  75  in the rear. An exemplary method of attaching the fourth module cover section  15   d  may be described later. 
     The second module cover section  15   b  may be positioned further back from the first module cover section  15   a  and third module cover section  15   c , and may be attached to the first and third module cover sections  15   a  and  15   c . The center of the second module cover section  15   b  may be attached to the first module cover section  15   a , and both sides of the second module cover section  15   b  may be attached to the third module cover section  15   c.    
     The first module cover section  15   a  and the third module cover section  15   c  may be spaced apart from each other. Also, the front of the first module cover section  15   a  may protrude a certain distance LMD from the front of the second module cover section  15   b . That is, the first module cover section  15   a  and the third module cover section  15   c  may have space in between. The supports  73  may be positioned in the space between the first module cover section  15   a  and the third module cover section  15   c.    
     Although not shown, the display panel  10  may be attached to the front of the module cover  15 . Accordingly, the supports  73  may be shielded by the display panel  10  in the front and by the second module cover section  15   b  in the rear. The user may immerse themselves in the display screen because the operation of the supports  73  is out of their view, and will find the look of the display device tidy. 
     Referring to  FIG. 37 , without the first module cover section  15   a , the display panel  10  is attached only to the third module cover section  15   c  on both sides, as illustrated in  FIG. 37( a ) . Thus, the display panel  10  may be depressed in the center, because of a space between the second module cover section  15   b  and the display panel  10 . 
     Accordingly, the user may not be able to immerse themselves in the display screen because of the non-flatness of the surface of the display panel  10 . Also, the depression may lead to damage to the display panel. 
     In contrast, in the display device according to the embodiment of the present invention, the first module cover section  15   a  may be positioned in the center, as illustrated in  FIG. 37( b ) . The display panel  10  may be attached to the third module cover section  15   c  on both sides, and its center may be attached to the first module cover section  15   a . The first module cover section  15   a  will occupy a space between the display panel  10  and the second module cover section  15   b . As such, the display  10  may remain flat. Accordingly, the user can immerse themselves in the display screen. 
     Referring to  FIG. 38 , in the display device according to an embodiment of the present invention, the third module cover section  15   c  positioned on both sides of the module cover may be attached to the display panel  10 . 
     The third module cover section  15   c  and the display panel  10  may be held together by magnets  64  positioned on at least one apron. The magnets  64  may be attached to the apron with double-sided tape. The magnets  64  may be spaced apart from one another. Thus, their shape may be easily deformed when the module cover  15  is wound by the roller or unwound from it. 
     The display panel  10  may be attached to the magnets  64 . The surface of the display panel  10  that makes contact with the magnets  64  may include a Fe—Ni Invar alloy. Accordingly, the display panel  10  may be firmly attached to the magnets  64 . It should be noted that the surface of the display panel that makes contact with the magnets  64  could be a metallic material that attaches to a magnet. 
     Since the display panel  10  and the module cover are attached by the magnets  64 , which are positioned only on both sides of the module cover  15 , only a small number of magnets  64  are required. This will save manufacturing costs. 
     Referring to  FIG. 39 , in the display device according to an embodiment of the present invention, the magnets  64  may be positioned in recesses  118  of the third module cover section  15   c.    
     The recesses  118  may be positioned on the side of the display panel  10  facing the third module cover section  15   c . The recesses  118  may be positioned in the respective aprons. Since the magnets  64  are positioned in the recesses  118 , the surfaces of the aprons that are in contact with the display panel  10  may be flat. Accordingly, the display device may be made thinner, and therefore have a tidy look. 
     Referring to  FIG. 40 , in the display device according to an embodiment of the present invention, the magnets  64  may be positioned on the first module cover section  15   a  as well as on the third module cover section  15   c . However, the magnets  64  are not limited to such a configuration, but may be positioned in recesses provided in the first module cover section  15   a.    
     In this case, the module cover  15  and the display panel  10  may be held together more firmly, compared to when the magnets  64  are positioned only on the third module cover section  15   c . Accordingly, the display panel  10  and the module cover  15  may be kept from being easily detached from each other even when external force is applied to them. 
     Referring to  FIG. 41 , in the display device according to an embodiment of the present invention, the top bar  75  and the module cover  15  may be attached, for example, with at least one screw. 
     The top bar  75  may be attached to the fourth module cover section  15   d  through first holes  331 . The fourth module cover section  15   d  may cover the back of the top bar  75 . Although not shown, the display panel  10  as well may be attached through the first holes  331 . 
     The top bar  75  may be attached to the first module cover section  15   a  through second holes  333 . As explained with reference to  FIG. 10 , a part which has a different thickness from the other part of the apron in the uppermost part of the first module cover section  15   a , may be inserted into a recess in the top bar  75 . The second holes  333  may be positioned lower than the first holes  331 . The first module cover section  15   a  and the third module cover section  15   c  may be attached to the top bar  75  through different types of holes. Accordingly, the module cover  15  and the top bar  75  may be held together more firmly. 
     The first module cover section  15   a  and the third module cover section  15   c  may be attached to the second module cover section  15   b  in the rear, through third and fourth holes  335  and  337 . The first module cover section  15   a  may be attached to the second module cover section  15   b  through the third holes  335  in the respective aprons, and the third module cover section  15   c  may be attached to the second module cover section  15   b  through the fourth holes  337  in the respective aprons. 
     Since the respective aprons are attached to the second module cover section  15   b  through the third and fourth holes  335  and  337 , the first and third module cover sections  15   a  and  15   c  and the second module cover section  15   b  may be wound easily while being held together. 
     Referring to  FIG. 42 , the top bar  75  may include a first protrusion  75   a  protruding downward in the center and second protrusions  75   b  protruding downward on both sides. The first protrusion  75   a  may be a portion in which the first module cover section  15   a  is inserted, and the second protrusions  75   b  may be portions connecting to the supports  73 . The top bar  75  may not be wound because it does not comprise of multiple parts like the aprons on the module cover  15 . Thus, the first protrusion  75   a  and the second protrusions  75   b  may not be wound either. 
     Accordingly, flat regions FR of the first and third module cover sections  15   a  and  15   c , which correspond to the first and second protrusions  75   a  and  75   b  of the top bar  75 , and the fourth module cover section  15   d , which corresponds to other parts of the top bar  75 , may remain flat in the first state, without being wound around the apron roller  141 . For example, the uppermost apron may be positioned in the flat regions FR of the first and third module cover sections  15   a  and  15   c.    
     Referring to  FIG. 43 , in the display device according to an embodiment of the present invention, each hinge  152  may include a body  152   a  and an attachment part  152   b.    
     As previously described, the body  152   a  may be a part that connects the upper link  73   a  and the lower link  73   b  to allow the upper link  73   ab  and the lower link  73   b  to rotate on the second module cover section  15   b.    
     The attachment part  152   b  may be connected to the body  152   a . The attachment part  152   b  may protrude toward the first module cover section  15   a  from the body  152   a . In the first state, the attachment parts  152   b  may not come into contact with the first module cover section  15   a . Accordingly, the supports  73  may rotate freely without being obstructed by the attachment parts  152   b.    
     During the transition from the first state to the second state, trajectories  367  may be formed on the second module cover section  15   b  in which the attachment parts  152   b  move. The trajectories  367  may be formed on the side of the second module cover section  15   b  facing the display panel. The trajectories  367  may include a magnetic material. One of the trajectories  367  may be shaped like the circumference of a quadrant that extends from the center of the left side of the second module cover section  15   b  along the second direction to the top adjacent to the first module cover section  15   a  along the second direction. The other trajectory  367  may be shaped like the circumference of a quadrant that extends from the center of the right side of the second module cover section  15   b  along the second direction to the top adjacent to the first module cover section  15   a.    
     The attachment parts  152   b  each may include a magnetic material on the side facing the second module cover section  15   b . The attachment parts  152   b  may include a material whose polarity is opposite to that of the trajectories  167 . The attachment parts  152   b  may move along the trajectories  167  during the transition from the second state to the first state. 
     Since the attachment parts  152   b  and the trajectories  167  include magnetic material, the hinges  152  may move while attached to the second module cover section  15   b . Accordingly, the hinges  152  may not protrude forward in any circumstances, thus allowing the display panel to remain flat. Also, the trajectories  367  may guide the movement of the hinges  152 . Accordingly, the protection of the display device during state transitions can be improved. 
     While the aforementioned drawings are illustrated in relation to a structure of a display device in which the display portion is rolled up from inside the housing, the present invention is not limited to this structure but may be applicable to a structure of a display device in which the display portion is rolled down from inside the housing. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.