Patent Publication Number: US-2023161375-A1

Title: Display device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a display device. 
     BACKGROUND ART 
     As the information society develops, the demand for display devices is also increasing in various forms. In response to this, various display devices such as Liquid Crystal Display Device (LCD), Plasma Display Panel (PDP), Electroluminescent Display (ELD), and Vacuum Fluorescent Display (VFD) have been researched and used in recent years. 
     Among them, a display device using an organic light emitting diode (OLED) has superior luminance characteristics and viewing angle characteristics compared to a liquid crystal display device, and can be implemented in an ultra-thin shape as it does not require a backlight unit. 
     In addition, a flexible display panel can be bent or wound on a roller. By using the flexible display panel, it is possible to implement a display device that is roll out from a roller or wound on a roller. A lot of research has been done on a structure for winding or unwinding a flexible display panel on/from a roller. 
     DISCLOSURE 
     Technical Problem 
     An object of the present disclosure is to solve the above and other problems. 
     Another object of the present disclosure may be to improve the sound quality of a speaker provided in a display device. 
     Another object of the present disclosure may be to prevent noise generated by a display device. 
     Technical Solution 
     According to an aspect of the present disclosure for achieving the above object, provided is a display device including: a flexible display panel; a roller which extends long, and around which the display panel is wound, or from which the display panel is unwound; a housing which provides an accommodating space therein, wherein the roller is rotatably mounted in the accommodating space; and a speaker assembly which is located between the roller and the housing, and placed on a bottom of the housing, wherein the housing includes a front cover which is located inside a front surface of the housing, is fixed to the bottom of the housing, and has a coupling hole, wherein the speaker assembly includes a coupling portion which is formed in an upper side of the speaker assembly, and inserted into the coupling hole. 
     Advantageous Effects 
     The effect of the display device according to the present disclosure will be described as follows. 
     According to at least one of the embodiments of the present disclosure, sound quality of a speaker assembly provided in a display device may be improved. 
     According to at least one of the embodiments of the present disclosure, noise that may be generated in a display device may be prevented. 
     Further scope of applicability of the present disclosure will become apparent from the following detailed description. However, it should be understood that the detailed description and specific embodiments such as preferred embodiments of the present disclosure are given by way of example only, since various changes and modifications within the spirit and scope of the present disclosure may be clearly understood by those skilled in the art. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS.  1  to  71    are diagrams illustrating examples of a display device according to embodiments of the present disclosure. 
     
    
    
     MODE FOR INVENTION 
     Description will now be given in detail according to exemplary embodiments disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be denoted by the same reference numbers, and description thereof will not be repeated. 
     In general, suffixes such as “module” and “unit” may be used to refer to elements or components. Use of such suffixes herein is merely intended to facilitate description of the specification, and the suffixes do not have any special meaning or function. 
     In the present disclosure, that which is well known to one of ordinary skill in the relevant art has generally been omitted for the sake of brevity. The accompanying drawings are used to assist in easy understanding of various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. 
     It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. 
     It will be understood that when an element is referred to as being “connected with” another element, there may be intervening elements present. In contrast, it will be understood that when an element is referred to as being “directly connected with” another element, there are no intervening elements present. 
     A singular representation may include a plural representation unless context clearly indicates otherwise. 
     In the following description, even if the embodiment is described with reference to specific drawings, if necessary, reference numerals not appearing in the specific drawings may be referred to, and reference numerals not appearing in the specific drawings are used in a case where the above reference numerals appear in the other figures. 
     Referring to  FIG.  1   , a display device  100  may include a display unit  20  and a housing  30 . The housing  30  may have an internal space. At least a portion of the display unit  20  may be located inside the housing  30 . At least a portion of the display unit  20  may be located outside the housing  30 . The display unit  20  may display a screen. 
     A direction parallel to the length direction of the housing  30  may be referred to as a first direction DR 1 , a +x-axis direction, a -x-axis direction, a left direction, or a right direction. A direction in which the display unit  20  displays a screen may be referred to as a +z axis, a front side direction, or a forward direction. A direction opposite to the direction in which the display unit  20  displays a screen may be referred to as a −z axis, a rear side direction, or a rearward direction. A third direction DR 3  may be parallel to the +z-axis direction or the −z-axis direction. A direction parallel to a height direction of the display device  100  may be referred to as a second direction DR 2 , a +y-axis direction, a −y-axis direction, an upper direction, or a lower direction. 
     The third direction DR 3  may be a direction perpendicular 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. In addition, the third direction DR 3  may be referred to as a vertical direction. The left-right direction LR may be parallel to the first direction DR 1 , and the up-down direction UD may be parallel to the second direction DR 2 . 
     Referring to  FIG.  2   , the entire display unit  20  may be located inside the housing  30 . At least a portion of the display unit  20  may be located outside the housing  30 . The extent to which the display unit  20  is exposed to the outside of the housing  30  may be adjusted as necessary. 
     Referring to  FIG.  3   , the display unit  20  may include a display panel  10  and a plate  15 . The display panel  10  may be flexible. For example, the display panel  10  may be an organic light emitting display (OLED). 
     The display panel  10  may have a front surface for displaying an image. The display panel  10  may have a rear surface opposite to the front surface. The front surface of the display panel  10  may be covered with a light-transmitting material. For example, the light-transmitting material may be a synthetic resin or a film. 
     The plate  15  may be coupled, fastened, or attached to the rear surface of the display panel  10 . The plate  15  may include a metal material. The plate  15  may be referred to as a module cover  15 , a cover  15 , a display panel cover  15 , a panel cover  15 , or an apron  15 . 
     Referring to  FIG.  4   , the plate  15  may include a plurality of segments  15   c.  A magnet  64  may be located inside a recess  118  of the segment  15   c.  The recess  118  may be located on a surface of the segment  15   c  facing the display panel  10 . The recess  118  may be located in the front surface of each segment  15   c.  Since the magnet  64  is received inside the recess  118 , the magnet  64  may not protrude out of the segment  15   c.  The display panel  10  may be flat without being crumpled even when it comes into contact with the segment  15   c.    
     Referring to  FIG.  5   , a plurality of magnets  64  may be located on a link  73 . For example, at least one magnet  64  may be located on a first arm  73   a  and at least one magnet  64  may be located on a second arm  73   b.  The plurality of magnets  64  may be spaced apart from each other. 
     Referring to  FIG.  6   , one magnet  64  may be located on each of the first arm  73   a  and the second arm  73   b.  The magnet  64  may have a shape extending long in the long side direction of the first arm  73   a  and the second arm  73   b.  Since the magnet  64  has a shape extending long in the long side direction of the first arm  73   a  and the second arm  73   b,  an area of a portion where the link  73  is in close contact with the display panel and the module cover may be increased. Accordingly, the adhesion between the link  73  and the display panel and the module cover can be strong. 
     Referring to  FIG.  7   , the magnet  64  may be located in a recessed portion  321  formed on the link  73 . The recessed portion  321  may have a shape recessed into the inside of the link  73 . The magnet  64  may be coupled to the link  73  through at least one screw  187 . 
     A width LHW at which the recessed portion  321  is recessed into the inside of the link  73  may be equal to or larger than a thickness MGW of the magnet  64 . If the thickness MGW of the magnet  64  is larger than the width LHW of the recessed portion  321 , the display panel  10  and the module cover  15  may not be in close contact with the link  73 . In this case, the display panel  10  may be crumpled or not be flat. 
     A panel protection portion  97  may be located on the rear surface of the display panel  10 . The panel protection portion  97  may prevent the display panel  10  from being damaged due to friction with the module cover  15 . The panel protection portion  97  may include a metal material. The panel protection portion  97  may have a very thin thickness. For example, the panel protection portion  97  may have a thickness of about 0.1 mm. 
     Since the panel protection portion  97  includes a metal material, mutual attraction with the magnet  64  may act. Accordingly, the module cover  15  located between the panel protection portion  97  and the link  73  may be in close contact with the magnet  64  even if it does not include a metal material. 
     Referring to  FIG.  8   , the module cover  15  may be in close contact with the link  73  by an upper bar  75  in the upper side and a guide bar  234  in the lower side (refer to  FIG.  15   ). A portion of the link  73  between the upper bar  75  and the guide bar  234  may not be in close contact with the module cover  15 . Alternatively, a central portion of the link  73  may not be in close contact with the module cover  15 . The central portion of the link  73  may be near an arm joint  152 . In this case, a distance (APRD 1 , APLD 2 ) between the module cover  15  and the link  73  may not be uniform. In this case, the display panel  10  may be bent or crooked. 
     Referring to  FIG.  9   , when the magnet  64  is located in the recessed portion  321  of the link  73 , the magnet  64  attracts the panel protection portion  97 , so the module cover  15  may also be in close contact with the magnet 64  at the same time. That is, the central portion of the link  73  may be in close contact with the module cover  15 . 
     Referring to  FIG.  10   , a bead  136  may be formed on the upper surface of the segment  15   b.  The bead  136  may have a shape recessed into the inside of the segment  15   b.  The bead  136  may have a shape recessed in the −y-axis direction. For example, the bead  136  may be formed by pressing the segment  15   b.  A plurality of beads  136  may be formed on the segment  15   b.  The plurality of beads  136  may be spaced apart from each other. The bead  136  may improve the rigidity of the segment  15   b.  The bead  136  may prevent the shape of the segment  15   b  from being deformed from an external impact. 
     Referring to  FIG.  11   , a source PCB  120  may be located in the upper side of the module cover  15 . When the source PCB  120  is rolled up or rolled down, the position may change with the movement of the module cover  15 . A FFC cable  231  may be located in the center portion of the module cover  15  based on a first direction. The FFC cable  231  may be located in opposite ends of the module cover  15  based on the first direction. 
     Referring to  FIG.  12   , the segment  15   d  may include a recessed portion  425  that is recessed in the −z-axis direction. The recessed portion  425  may form a space between the display panel  10  and the module cover  15 . The FFC cable  231  may be received in a space formed by the recessed portion  425 . In addition, the recessed portion  425  may improve the rigidity of the segment  15   d.    
     The bead  136  may be located on the segment  15   d  excluding a portion where the recessed portion  425  is located. The bead  136  may not be located in the portion where the recessed portion  425  is located because the thickness of the segment  15   d  in a third direction becomes thinner. 
     Referring to  FIG.  13   , a penetrating portion  437  may be located in the center portion of the segment  15   e  in the first direction. The penetrating portion  437  may penetrate the central portion of the segment  15   e  in the second direction. That is, the penetrating portion  437  may be a hole located in the segment  15   e.  The penetrating portion  437  may be a portion in which the FFC cable  231  is located. Since the penetrating portion  437  is formed inside the segment  15   e,  the thickness of the segment  15   e  may be reduced compared to a case where the FFC cable  231  located in the recessed portion  425 . 
     The bead  136  may be located on the segment  15   e  excluding the portion where the penetrating portion  437  is located. The bead  136  may not be located in the portion where the penetrating portion  437  is located because the thickness of the segment  15   e  in the third direction becomes thinner. 
     Referring to  FIG.  14   , a top case  167  may cover the source PCB  120  and the upper bar  75  as well as the display panel  10  and the module cover  15 . One surface of the upper bar  75  may be coupled to the rear surface of the module cover  15 , and the other surface may be coupled to the source PCB  120 . The upper bar  75  may be fixed to the module cover  15  to support the source PCB  120 . 
     The lower end of the FFC cable  231  may be connected to a timing controller board  105  (refer to  FIG.  15   ) inside a panel roller  143  (refer to  FIG.  15   ). The FFC cable  231  may be wound on or unwound from the panel roller  143  together with the display unit  20 . 
     A portion of the FFC cable  231  may be located between the display panel  10  and the module cover  15 . A portion of the FFC cable  231  located between the display panel  10  and the module cover  15  may be referred to as a first portion  231   a.  The first portion  231   a  may be located in the recessed portion  425  formed by the plurality of segments  15   d.  Alternatively, the first portion  231   a  may be received in the recessed portion  425  formed by the plurality of segments  15   d.    
     A portion of the FFC cable  231  may penetrate the segment  15   f.  A portion of the FFC cable  231  penetrating the segment  15   f  may be referred to as a second portion  231   b.  The segment  15   f  may include a first hole  521   a  formed on the front surface and a second hole  521   b  formed on the rear surface. The first hole  521   a  and the second hole  521   b  may be interconnected to form one hole  521 . The hole  521  may penetrate the segment  15   f  in the third direction. The second portion  231   b  may penetrate the hole  521 . The hole  521  may be referred to as a connection hole  521 . 
     An upper end of the FFC cable  231  may be electrically connected to the source PCB  120 . A portion of the FFC cable  231  may be located on the rear surface of the module cover  15 . A portion of the FFC cable  231  located on the rear surface of the module cover  15  may be referred to as a third portion  231   c.  The third portion  231   c  may be electrically connected to the source PCB  120 . 
     The third portion  231   c  may be covered by the top case  167 . Accordingly, the third portion  231   c  may not be exposed to the outside. 
     Referring to  FIG.  15   , the FFC cable  231  may be connected to the timing controller board  105  mounted in the panel roller  143 . A through hole  615  may be formed on the panel roller  143 , and the FFC cable  231  may be connected to the timing controller board  105  through the through hole  615 . 
     The through hole  615  may be located in one side of the panel roller  143  and may penetrate the outer circumferential portion of the panel roller  143 . The FFC cable  231  may be connected to one side of the timing controller board  105  through the through hole  615 . 
     Even when the FFC cable  231  is located on the outer circumference of the panel roller  143 , the connection to the timing controller board  105  may be maintained due to the through hole  615 . Accordingly, the FFC cable  231  may not be twisted by rotating together with the panel roller  143 . 
     A portion of the FFC cable  231  may be wound around the panel roller  143 . A portion of the FFC cable  231  wound around the panel roller  143  may be referred to as a fourth portion  231   d.  The fourth portion  231   d  may be in contact with the outer circumferential surface of the panel roller  143 . 
     A portion of the FFC cable  231  may penetrate the through hole  615 . A portion of the FFC cable  231  passing through the through hole  615  may be referred to as a fifth portion  231   e.    
     A lower end of the FFC cable  231  may be electrically connected to the timing controller board  105 . A portion of the FFC cable  231  may be located inside the panel roller  143 . A portion of the FFC cable  231  located inside the panel roller  143  may be referred to as a sixth portion  231 E The sixth portion  231   f  may be electrically connected to the timing controller board  105 . 
     Referring to  FIG.  16   , the lower end of the display panel  10  may be connected to the roller  143 . The display panel  10  may be wound on or unwound from the roller  143 . The front surface of the display panel  10  may be coupled to a plurality of source PCBs  120 . The plurality of source PCBs  120  may be spaced apart from each other. 
     The source chip on film (COF)  123  may connect the display panel  10  and the source PCB  120 . The source COF  123  may be located in the front surface of the display panel  10 . The roller  143  may include a first part  331  and a second part  337 . The first part  331  and the second part  337  may be fastened by a screw. The timing controller board  105  may be mounted inside the roller  143 . 
     The source PCB  120  may be electrically connected to the timing controller board  105 . The timing controller board  105  may transmit digital video data and a timing control signal to the source PCB  120 . 
     The cable  117  may electrically connect the source PCB  120  and the timing controller board  105 . For example, the cable  117  may be a flexible flat cable (FFC). The cable  117  may penetrate the hole  331   a.  The hole  331   a  may be formed in a seating portion  379  or the first part  331 . The cable  117  may be located between the display panel  10  and the second part  337 . 
     The seating portion  379  may be formed in the outer circumference of the first part  331 . The seating portion  379  may be formed by stepping a portion of the outer circumference of the first part  331 . The seating portion  379  may form a space (B). When the display unit  20  is wound around the roller  143 , the source PCB  120  may be received in the seating portion  379 . The source PCB  120  may be received in the seating portion  379 , so that it is not bent or crooked, and durability may be improved. 
     The cable  117  may electrically connect the timing controller board  105  and the source PCB  120 . 
     Referring to  FIG.  17   , the roller  143  around which the display unit  20  is wound may be installed in a first base  31 . The first base  31  may be a bottom surface of the housing  30 . The roller  143  may extend long in the length direction of the housing  30 . The first base  31  may be connected to a side surface  30   a  of the housing  30 . 
     Referring to  FIGS.  18  and  19   , a beam  31   a  may be formed in the first base  31 . The beam  31   a  may improve the bending or torsional rigidity of the first base  31 . Many parts may be installed in the first base  31 , and the first base  31  may receive a large load. Since the first base  31  has improved rigidity, sagging due to a load may be prevented. For example, the beam  31   a  may be formed by a pressing process. 
     A second base  32  may be spaced apart toward the upper side of the first base  31 . A space  51  may be formed in the first base  31  and the second base  32 . The roller  143  around which the display unit  20  is wound may be received in the space  51 . The roller  143  may be located between the first base  31  and the second base  32 . 
     The second base  32  may be connected to the side surface  30   a  of the housing  30 . A bracket  33  may be fastened to the upper surface of the first base  31 . The bracket  33  may be fastened to the side surface  30   a  of the housing  30 . 
     A beam  32   a  may be formed on the second base  32 . The beam  32   a  may improve the bending or torsional rigidity of the second base  32 . For example, the beam  32   a  may be formed by a press process. 
     A third part  32   d  may be connected to a first part  32   b  and a second part  32   c.  A fourth part  32   e  may be connected to the first part  32   b  and the second part  32   c.  A space S 2  may be formed between the third part  32   d  and the fourth part  32   e.  Accordingly, the bending or torsional rigidity of the second base  32  may be improved. The third part  32   d  may be referred to as a reinforcing rib  32   d  or a rib  32   d.  The fourth part  32   e  may be referred to as a reinforcing rib  32   e  or a rib  32   e.    
     Many parts may be installed in the second base  32 , and the second base  32  may receive a large load. Since the second base  32  has improved rigidity, sagging due to a load may be prevented. 
     A first reinforcing plate  34  may be located between the first base  31  and the second base  32 . The first reinforcing plate  34  and the second base  32  may be fastened by a screw. The first reinforcing plate  34  may support the second base  32 . The first reinforcing plate  34  may prevent the second base  32  from sagging. The first reinforcing plate  34  may be located in a central portion of the first base  31  or a central portion of the second base  32 . The first reinforcing plate  34  may include a curved portion  34   a.  The curved portion  34   a  may be formed along the roller  143 . The curved portion  34   a  may not come into contact with the roller  143  or the display unit  20  wound around the roller  143 . The curved portion  34   a  may maintain a certain distance from the roller  143  so as not to interfere with the rotation of the roller  143 . 
     A second reinforcing plate  35  may be fastened to the first base  31  and the first reinforcing plate  34 . The second reinforcing plate  35  may support the first reinforcing plate  34 . The second reinforcing plate  35  may be located in the rearward direction of the first reinforcing plate  34 . The second reinforcing plate  35  may be located in the rearward direction of the first base  31 . The second reinforcing plate  35  may be located perpendicular to the first base  31 . The second reinforcing plate  35  may be fastened to the beam  31   a  of the first base  31 . The second base  32  may face the front or rear surface of the housing  30 . 
     Referring to  FIG.  20   , a second base  32   f  may not form a space. When the load received by the second base  32   f  is not large, the second base  32   f  may have sufficient rigidity by including a beam  32   g.  A first base  31 ′ may include a beam  31   a′.    
     Referring to  FIGS.  21  and  22   , a motor assembly  810  may be installed in the second base  32 . The driving shaft of the motor assembly  810  may be formed in opposite sides. The right driving shaft and the left driving shaft of the motor assembly  810  may rotate in the same direction. Alternatively, the right driving shaft and the left driving shaft of the motor assembly  810  may rotate in opposite directions. 
     The motor assembly  810  may include a plurality of motors. A plurality of motors may be connected in series with each other. The motor assembly  810  may output a high torque by connecting a plurality of motors in series. 
     A lead screw  840  may be located in the left and right sides of the motor assembly  810 , respectively. The motor assembly  810  may be connected to the lead screw  840 . A coupling  811  may connect the lead screw  840  and the driving shaft of the motor assembly  810  to each other. 
     The lead screw  840  may be threaded along the length direction. A direction of a thread formed in the right lead screw  840  and a direction of a thread formed in the left lead screw  840  may be opposite to each other. The direction of the thread formed in the right lead screw  840  may be the same as the direction of the thread formed in the left lead screw  840 . Pitches of the left lead screw  840  and the right lead screw  840  may be the same. 
     A bearing  830   a,    830   b  may be installed in the second base  32 . The bearing  830   a,    830   b  may support opposite sides of the lead screw  840 . The bearing  830   a,    830   b  may include an inner bearing  830   b  located close to the motor assembly  810  and an outer bearing  830   a  located far from the motor assembly  810 . The lead screw  840  may be stably rotated by the bearing  830   a,    830   b.    
     A slide  820  may the lead screw  840 . The slide  820  may move forward and backward in the length direction of the lead screw  840  according to the rotation of the lead screw  840 . The slide  820  may move between the outer bearing  830   a  and the inner bearing  830   b.  The slide  820  may be located in the left lead screw  840  and the right lead screw  840 , respectively. The left slide  820  may be engaged with the left lead screw  840 . The right slide  820  may be engaged with the right lead screw  840 . 
     The left slide  820  and the right slide  820  may be located symmetrically with respect to the motor assembly  810 . Due to the driving of the motor assembly  810 , the left slide  820  and the right slide  820  may move away from or close to each other by the same distance. 
     Referring to  FIG.  23   , the motor assembly  810  may include a plate  813 . The plate  813  may be referred to as a mount plate  813  or a motor mount plate  813 . A coupling portion  32   h  may be formed on the upper surface of the second base  32 . The plate  813  may be fastened to the coupling portion  32   h  through the screw S. The motor assembly  810  may be spaced apart from the upper surface of the second base  32 . A washer  813  may be located between the upper surface of the plate  813  and the screw S. The washer  813  may include a rubber material. The washer  813  may reduce vibration generated in the motor assembly  810 . The washer  813  may improve driving stability of the display device  100 . 
     Referring to  FIG.  24   , a guide rail  860  may be installed in the second base  32 . The guide rail  860  may be located in parallel with the lead screw  840 . The slide  820  may be engaged with the guide rail  860 . A first stopper  861   b  may be located in one side of the guide rail  860 , and a second stopper  861   a  may be located in the other side of the guide rail  860 . A range in which the slide  820  can move may be restricted between the first stopper  861   b  and the second stopper  861   a.    
     A spring  850  may surround the lead screw  840 . The lead screw  840  may penetrate the spring  850 . The spring  850  may be located between the inner bearing  830   b  and the slide  820 . One side of the spring  850  may contact the inner bearing  830   b,  and the other side of the spring  850  may contact the slide  820 . The spring  850  may provide an elastic force to the slide  820 . 
     When the slide  820  is caught by the first stopper  861   b,  the spring  850  may be maximally compressed. When the slide  820  is caught by the first stopper  861   b,  the length of the spring  850  may be a minimum. When the slide  820  is caught by the first stopper  861   b,  a distance between the slide  820  and the inner bearing  830   b  may be a minimum. 
     Referring to  FIG.  25   , when the slide  820  is caught by the second stopper  861   a,  the spring  850  may be maximally tensioned. When the slide  820  is caught by the second stopper  861   b,  the length of the spring  850  may be a maximum. When the slide  820  is caught by the second stopper  861   a,  a distance between the slide  820  and the inner bearing  830   b  may be a maximum. 
     Referring to  FIG.  26   , a first part  820   a  may be engaged with the guide rail  860 . The first part  820   a  may move along the guide rail  860 . Movement of the first part  820   a  in the length direction of the guide rail  860  may be restricted. A second part  820   b  may be located in the upper side of the first part  820   a.  The first part  820   a  and the second part  820   b  may be fastened through a screw. The second part  820   b  may be spaced apart from the guide rail  860 . The lead screw  840  may penetrate the second part  820   b.  For example, the second part  820   b  may include a male thread engaged with a female thread of the lead screw  840 . Accordingly, even when the lead screw  840  rotates, the slide  820  does not rotate and may stably move forward and backward along the guide rail  860 . 
     A third part  820   c  may be coupled to one side of the second part  820   b.  The third part  820   c  may contact the spring  850 . The third part  820   c  may receive elastic force from the spring  850 . 
     Referring to  FIGS.  27  and  28   , a link mount  920  may be installed in the second base  32 . One side of a second arm  912  may be pivotally connected to the link mount  920 . The other side of the second arm  912  may be pivotally connected to a joint  913 . The other side of the second arm  912  may be pivotally connected to a second shaft  913   b.  One side of a rod  870  may be pivotally connected to the slide  820 . The other side of the rod  870  may be pivotally connected to the second arm  912  or a third arm  915 . One side of the third arm  915  may be pivotally connected to the link mount  920 . The other side of the third arm  915  may be pivotably connected to the other side of the rod  870 . The link mount  920  may include a shaft  921 . The second arm  912  or the third arm  911  may be pivotally connected to the shaft  921 . 
     A link bracket  951  may be referred to as a link cap  951 . The link bracket  951  may be coupled to a top case  950 . The top case  950  may be referred to as a case top  950 , an upper bar  950 , a top  950 , or a bar  950 . The top case  950  may be located in an upper end of the display unit  20 . The display unit  20  may be fixed to the top case  950 . 
     One side of a first arm  911  may be pivotally connected to the joint  913 . One side of the first arm  911  may be pivotably connected to a first shaft  913   a.  The other side of the first arm  911  may be pivotably connected to the link bracket  951  or the top case  950 . 
     A gear gl may be formed in one side of the first arm  911 . A gear g 2  may be formed in the other side of the second arm  912 . The gear gl of the first arm  911  and the gear g 2  of the second arm  912  may be engaged with each other. 
     When the slide  820  moves closer to the outer bearing  830   a,  the second arm  912  or the third arm  915  may stand up. this case, a direction in which the second arm  912  or the third arm  915  stands up may be referred to as a standing direction DRS. 
     The second arm  912  may include a protrusion  914  protruding in the standing direction DRS. The protrusion  914  may be referred to as a connecting portion  914 . The third arm  915  may include a protrusion  916  protruding in the standing direction DRS. The protrusion  916  may be referred to as a connecting portion  916 . The protrusion  914  of the second arm  912  and the protrusion  916  of the third arm  915  may face or contact each other. The other side of the rod  870  may be fastened to the protrusion  914  of the second arm  912  or the protrusion  916  of the third arm  915 . 
     The link  910  may include a first arm  911 , a second arm  912 , a third arm  915 , and/or a joint  913 . 
     Referring to  FIGS.  29  and  30   , an angle between the second arm  912  or the third arm  915  and the second base  32  may be referred to as theta S. When the rod  870  is connected to the upper side of the second part  820   b,  an angle between the rod  870  and the second base  32  may be referred to as theta A, and the minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as Fa. When the rod  870  is connected to the middle of the second part  820   b,  an angle between the rod  870  and the second base  32  may be referred to as theta B, and the minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as Fb. When the rod  870  is connected to the lower side of the second part  820   b,  an angle between the rod  870  and the second base  32  may be referred to as theta C, and the minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as Fc. 
     For the same theta S, a relationship of theta A &lt;theta B &lt;theta C can be established for the same theta S. In addition, a relationship of Fc &lt;Fb &lt;Fa may be established for the same theta S. If an angle between the second arm  912  or the third arm  915  and the second base  32  is the same, as the angle between the rod  870  and the second base  32  increases, the force required to stand up the second arm  912  or the third arm  915  may be reduced. The rod  870  may be connected to the lower side of the second part  820   b  to reduce a load applied to the motor assembly  810 . 
     Referring to  FIG.  31   , a rod  870 ′ may not be connected to the protrusion of a second arm  912 ′ or the protrusion of a third arm  915 ′. When an angle between the second arm  912 ′ or the third arm  915 ′ and the second base  32  is theta S, an angle between the rod  870 ′ and the second base  32  may be referred to as theta  1 , and the minimum force for the rod  870 ′ to stand up the second arm  912 ′ or the third arm  915 ′ may be referred to as Fl. 
     Referring to  FIG.  32   , the rod  870  may be connected to the protrusion  914  of the second arm  912  or the protrusion  916  of the third arm  915 . When the angle between the second arm  912  or the third arm  915  and the second base  32  is theta S, an angle between the rod  870  and the second base  32  may be referred to as theta  2 , and the minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as F 2 . 
     Referring to  FIG.  33   , when theta S is the same, theta  2  may be larger than theta  1 . When theta S is the same, F 1  may be larger than F 2 . If the angle between the second arms  912 ,  912 ′ and the second base  32  is the same, as the angle between the rod  870 ,  870 ′ and the second base  32  increases, the force required to stand up the second arm  912 ,  912 ′ may be reduced. Since the rod  870  is connected to the protrusion  914 ,  916 , the second arm  912  may stand up with a small force compared to a case in which the rod  870 ′ is not connected to the protrusion. The rod  870  is connected to the protrusion  914 ,  916 , thereby reducing a load applied to the motor assembly  810 . 
     Referring to  FIG.  34   , the second arm  912  or the third arm  915  may have a central axis CR. When the rod  870  is fastened with the second arm  912  away from the central axis CR by a distance r, the angle between the rod  870  and the second base  32  may be referred to as theta  2 , and a minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as F 3 . When the rod  870  is fastened with the second arm  912  away from the central axis CR by a distance r′, the angle between the rod  870  and the second base  32  may be referred to as theta  2 ′, and a minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as F 4 . When the rod  870  is fastened with the second arm  912  away from the central axis CR by a distance r″, the angle between the rod  870  and the second base  32  may be referred to as theta  2 ″, and a minimum force for the rod  870  to stand up the second arm  912  or the third arm  915  may be referred to as F 5 . 
     Referring to  FIG.  35   , when theta S is the same, theta  2 ″ may be larger than theta  2 ′, and theta  2 ′ may be larger than theta  2 . When theta S is the same, F 3  may be larger than F 4 , and F 4  may be larger than F 5 . As the rod  870  is fastened away from the central axis CR, the force required to stand up the second arm  912  may become smaller. Since the rod  870  is fastened away from the central axis CR, a load applied to the motor assembly  810  may be reduced. 
     Referring to  FIG.  36   , the first arm  911  and the second arm  912  may be located close to or in contact with the rear surface of the display unit  20 . As the first arm  911  and the second arm  912  are located close to or in contact with the rear surface of the display unit  20 , the display unit  20  can be stably wound around or unwound from the roller. The link mount  920  may include a first part  922  and a second part  923 . The first part  922  and the second part  923  may face each other. A space S 4  may be formed between the first part  922  and the second part  923 . The first part  922  may face the display unit  20 . The first part  922  may be located closer to the display unit  20  than the second part  923 . The second arm  912  may be pivotally connected to the front surface of the first part  922 . A portion of the third arm  915  may be received in the space S 4 , and may be pivotally connected to the first part  922  or the second part  923 . 
     Referring to  FIG.  37   , the rod  870  may include a first part  871  and a second part  872 . The first part  871  may include a connection portion  871   a  in one side. The second part  872  of the slide  820  may form a space S 5  therein. The connection portion  871   a  may be inserted into the space S 5 . The connection portion  871   a  may be pivotally connected to the second part  820   b  (refer to  FIG.  36   ) of the slide  820 . The other side of the first part  871  may be connected to one side of the second part  872 . The other side of the second part  872  may be pivotably connected to the second arm  912  or the third arm  915 . The first part  871  may form a space S 3  therein. The first part  871  may include a hole  871   b.  The lead screw  840  may be received in the hole  871   b  or the space S 3 . 
     A distance between the second part  872  and the display unit  20  may be D 1 . The second arm  912  may have a thickness W 1 . A portion of the third arm  915  received in the space S 4  may have a thickness W 3 . The thickness W 3  may be equal to the distance between the first part  922  and the second part  923 . A portion of the third arm  915  that is not received in the space S 4  may have a thickness W 2 . The first part  922  may have a thickness W 4 . The thickness W 2  may be larger than the thickness W 3 . The thickness W 2  may be equal to the sum of the thickness W 3  and the thickness W 4 . D 1  may be the sum of the thickness W 1  and the thickness W 2 . 
     The second arm  912  may be located in contact with or close to the rear surface of the display unit  20 , and the third arm  915  may be located between the second arm  912  and the second part  872 . The second part  872  may stably transmit power for standing up the second arm  912 , due to the third arm  915 . The second part  872  may be connected to the first part  871  by moving forward with respect to the rotation axis of the lead screw  840 , in order to stably stand up the second arm  912  or the third arm  915 . Due to this, a gap between the second arm  912  and the second part  872  may be minimized. 
     Referring to  FIG.  38   , a pusher  930  may be mounted in the link mount  920 . The pusher  930  may be referred to as a lifter  930 . The second part  932  may be fastened to the first part  931 . The second part  932  may be in contact with or separated from the link bracket  951 . The second part  932  may be made of a material having high elasticity. The first part  931  may be made of a material having lower elasticity than the second part  932 . The first part  931  may be made of a material having a higher rigidity than the second part  932 . The first part  931  and the second part  932  may be collectively referred to as a head  936 . The head  936  may be located in the upper side of the link mount  920 . 
     The third part  933  may be connected to the first part  931 . Alternatively, the third part  933  may extend downward from the first part  931 . The third part  933  may be referred to as a tail  933 . The fourth part  934  may protrude from the third part  933 . The link mount  920  may form a space S 6 , and the third part  933  may be received in the space S 6 . The space S 6  may be opened upward. The space S 6  in which the third part  933  is received may be adjacent to the space S 4  (refer to  FIG.  3   ) in which the third arm  915  is received. The second part  932  of the link mount  920  may include a hole  924 . The hole  924  may be a long hole formed long in the vertical direction. The length of the hole  924  may be H 1 . The fourth part  934  may be inserted into the hole  924 . A spring  935  may be received in the space S 6 . The spring  935  may be located in the lower side of the third part  933 . The spring  935  may provide an elastic force to the third part  933  in a vertical direction. 
     The head  936  may be larger than the diameter of the space S 6 . When the head  936  is caught by the upper end of the space S 6 , the height of the head  936  from the second base  32  may be a minimum. The minimum height of the head  936  may be referred to as H 2 . When the height of the head  936  is a minimum, the fourth part  934  may be caught by the lower end of the space S 6 . When the height of the head  936  is a minimum, the spring  935  can be maximally compressed. When the height of the head  936  is a minimum, the elastic force provided by the spring  935  may be a maximum. When the height of the head  936  is a minimum, the height of the top case  950  may be a minimum. 
     The pusher  930  may provide an elastic force to the link bracket  951 , while being in contact with the link bracket  951 . Due to this, the load applied to the motor assembly  810  to stand up the link  910  may be reduced. 
     Referring to  FIG.  39   , when the link  910  sufficiently stands up, the pusher  930  may be separated from the link bracket  951 . When the pusher  930  is separated from the link bracket  951 , the height of the head  936  from the second base  32  may be a maximum. The maximum height of the head  936  may be referred to as H 3 . When the height of the head  936  is maximum, the fourth part  934  may be caught by the upper end of the hole  924  (refer to  FIG.  38   ). When the height of the head  936  is maximum, the spring  935  can be tensioned to the maximum. When the height of the head  936  is the maximum, the elastic force provided by the spring  935  may be the minimum. The maximum height H 3  of the head  936  may be substantially equal to the sum of the minimum height H 2  of the head  936  and the length H 1  of the hole. 
     Referring to  FIG.  40   , the display unit  20  may be maximally wound around the roller  143 . The display device  100  may be symmetrical with respect to the motor assembly  810 . The height of the top case  950  may be a minimum. The slide  820  may be located in a position closest to the inner bearing  830   b.  The slide  820  may be caught by the first stopper  861   b.  The spring  850  may be in a maximally compressed state. The pusher  930  may contact the link bracket  951 . The height of the pusher  930  may be a minimum. 
     Referring to  FIG.  41   , about half of the display unit  20  may be wound around the roller  143 . The display device  100  may be symmetrical with respect to the motor assembly  810 . About half of the display unit  20  may be unwound from the roller  143 . The slide  820  may be located between the first stopper  861   b  and the second stopper  861   a.  The pusher  930  may be separated from the link bracket  951 . The height of the pusher  930  may be a maximum. 
     Referring to  FIG.  42   , the display unit  20  may be in a state of being maximally unwound from the roller  143 . The display device  100  may be symmetrical with respect to the motor assembly  810 . The height of the top case  950  may be a maximum. The slide  820  may be located in a position closest to the outer bearing  830   a.  The slide  820  may be caught by the second stopper  861   a.  The spring  850  may be in a maximum tension state. The pusher  930  may be separated from the link bracket  951 . The height of the pusher  930  may be a maximum. 
     Referring to  FIGS.  43  to  46   , a link mount  920   a,    920   b  may be installed in the base  31 . The link mount  920   a,    920   b  may include a right link mount  920   a  spaced apart to the right from a first right bearing  830   a  and a left link mount  920   b  spaced apart to the left from a second left bearing  830   d.    
     A link  910   a,    910   b  may be connected to link mount  920   a,    920   b.  The link  910   a,    910   b  may include a right link  910   a  connected to the right link mount  920   a  and a left link  910   b  connected to the left link mount  920   b.    
     The right link  910   a  may be referred to as a first link. The left link  910   b  may be referred to as a second link. The right link mount  920   a  may be referred to as a first link mount  920   a.  The left link mount  920   b  may be referred to as a second link mount  920   b.    
     The link  910   a,    910   b  may include a first arm  911   a,    911   b,  a second arm  912   a,    912   b,  and an arm joint  913   a,    913   b.  One side of the second arm  912   a,    912   b  may be rotatably connected to the link mount  920   a,    920   b.  The other side of the second arm  912   a,    912   b  may be rotatably connected to the arm joint  913   a,    913   b.  One side of the first arm  911   a,    911   b  may be rotatably connected to the arm joint  913   a,    913   b.  The other side of the first arm  911   a,    911   b  may be rotatably connected to a link bracket  951   a,    951   b.    
     The link bracket  951   a,    951   b  may include a right link bracket  951   a  connected to the first arm  911   a  of the right link  910   a  and a left link bracket  95  lb connected to the first arm  911   b  of the left link  910   b.  The link bracket  951   a,    951   b  may be connected to the upper bar  950 . 
     The upper bar  950  may connect the right link bracket  951   a  and the left link bracket  951   b.    
     The rod  870   a,    870   b  may connect a slider  860   a,    860   b  and the link  910   a,    910   b.  One side of the rod  870   a,    870   b  may be rotatably connected to the slider  860   a,    860   b.  The other side of the rod  870   a,    870   b  may be rotatably connected to the second arm  912   a,    912   b.  The rod  870   a,    870   b  may include a right rod  870   a  connecting a right slider  860   a  and the second arm  912   a  of the right link  910   a,  and a left rod  870   b  connecting a left slider  860   b  and the second arm  912   b  of the left link  910   b.  The right rod  870   a  may be referred to as a first rod  870   a.  The left rod  870   b  may be referred to as a second rod  870   b.    
     Specifically, a structure formed by a right lead screw  840   a,  the right slider  860   a,  the right rod  870   a,  and the right link  910   a  will be described. The right slider  860   a  may include a body  861   a  and a rod mount  862   a.  The body  861   a  may have a thread SS formed on an inner circumferential surface. The thread formed in the body  861   a  may be engaged with a thread RS of the right lead screw  840   a.  The right lead screw  840   a  may penetrate the body  861   a.    
     The rod mount  862   a  may be formed in the right side of the body  861   a.  The rod mount  862   a  may be rotatably connected to one side of the right rod  870   a.  The rod mount  862   a  may include a first rod mount  862   a   1  and a second rod mount  862   a   2 . The first rod mount  862   a   1  may be disposed in a forward direction of the right lead screw  840   a.  The second rod mount  862   a   2  may be disposed in a rearward direction of the right lead screw  840   a.  The first rod mount  862   a   1  and the second rod mount  862   a   2  may be spaced apart from each other. The second rod mount  862   a   2  may be spaced apart from the first rod mount  862   a   1  in the −z-axis direction. The right lead screw  840   a  may be located between the first rod mount  862   a   1  and the second rod mount  862   a   2 . 
     The rod mount  862   a  may be rotatably connected to one side of the rod  870   a  through a connecting member C 1 . The connecting member C 1  may penetrate the rod mount  862   a  and the right rod  870   a.    
     The right rod  870   a  may be rotatably connected to the second arm  912   a  through a connecting member C 2 . The connecting member C 2  may penetrate the second arm  912   a  and the right rod  870   a.    
     The right rod  870   a  may include a transmission portion  871   a  connected to the second arm  912   a  of the right link  910   a  and a cover  872   a  connected to the rod mount  862   a  of the right slider  860   a.  The transmission portion  871   a  may transmit a force that is generated when the right slider  860   a  moves forward and backward along the right lead screw  840   a  to the right link  910   a.    
     The cover  872   a  may include a first plate  873   a  disposed in a forward direction of the right lead screw  840   a.  The first plate  873   a  may be disposed perpendicular to the base  31 . Alternatively, the first plate  873   a  may face the right lead screw  840   a.    
     The cover  872   a  may include a second plate  874   a  disposed in the rearward direction of the right lead screw  840   a.  The second plate  874   a  may be disposed perpendicular to the base  31 . Alternatively, the second plate  874   a  may face the right lead screw  840   a.  Alternatively, the second plate  874   a  may be spaced apart from the first plate  873   a.  The right lead screw  840   a  may be located between the first plate  873   a  and the second plate  874   a.    
     The cover  872   a  may include a third plate  875   a  connecting the first plate  873   a  and the second plate  874   a.  The third plate  875   a  may be connected to the transmission portion. The third plate  875   a  may be located in the upper side of the right lead screw  840   a.    
     The cover  872   a  may include a fourth plate  876   a  connecting the first plate  873   a  and the second plate  874   a.  The fourth plate  876   a  may be connected to the third plate  875   a.  The fourth plate  876   a  may be located in the upper side of the right lead screw  840   a.    
     One side of the first plate  873   a  may be connected to the first rod mount  862   a   1 . The first plate  873   a  and the first rod mount  862   a   1  may be connected through a connection member Cr. The other side of the first plate  873   a  may be connected to the third plate  875   a.    
     One side of the second plate  874   a  may be connected to the second rod mount  862   a   2 . The second plate  874   a  and the second rod mount  862   a   2  may be connected to each other through a connecting member C 1 . The other side of the second plate  874   a  may be connected to the third plate  875   a.    
     When the right slider  860   a  moves closer to the motor assembly  810 , the right lead screw  840   a  and the right rod  870   a  may come into contact with each other. When the right lead screw  840   a  and the right rod  870   a  come into contact, mutual interference may occur and movement of the right slider  860   a  may be restricted. 
     The cover  872   a  may provide a space S 1  therein. The first plate  873   a,  the second plate  874   a,  the third plate  875   a,  and the fourth plate  876   a  may form a space Si. When the right slider  860   a  moves closer to the motor assembly  810 , the right lead screw  840   a  may be received or escaped into the space Si provided by the cover  872   a.  Due to the space S 1  provided by the cover  872   a,  the right slider  860   a  may move closer to the motor assembly  810  than when the cover  872   a  does not exist. That is, the cover  872   a  provides a space Si therein, thereby increasing the movable range of the right slider  860   a.  In addition, since the right lead screw  840   a  is received in the cover  872   a,  the size of the housing  30  (refer to  FIG.  2   ) can be reduced. 
     In addition, the cover  872   a  may restrict the minimum value of the angle theta S between the second arm  912   a  and the base  31 . When theta S is sufficiently small, the third plate  875   a  of the cover  872   a  may contact the second arm  912   a,  and support the second arm  912   a.  The third plate  875   a  supports the second arm  912   a,  thereby restricting the minimum value of theta S and preventing the second arm  912   a  from sagging. That is, the cover  872   a  may serve as a stopper to prevent the second arm  912   a  from sagging. In addition, the third plate  875   a  restricts the minimum value of theta S, thereby reducing the initial load for standing up the second arm  912   a.    
     The lead screw  840   a,    840   b  may be driven by one motor assembly  810 . The lead screw  840   a,    840   b  may be driven by one motor assembly  810 , so that the second arm  912   a,    912   b  can stand symmetrically. However, when the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the load applied to the motor assembly  810  in order to stand up the second arm  912   a,    912   b  may become excessively large. In this case, the third plate  875   a  restricts the minimum value of theta S, thereby reducing the load applied to the motor assembly  810  in order to stand up the second arm  912   a,    912   b.    
     The structure formed by the left lead screw  840   b,  the left slider  860   b,  the left rod  870   b,  and the left link  910   b  may be symmetrical with the structure formed by the above-described right lead screw  840   a,  right slider  860   a,  right rod  870   a,  and right link  910   a.  In this case, the symmetry axis may be a symmetry axis ys of the motor assembly  810 . 
     Referring to  FIG.  47   , a guide  850   a,    850   b,    850   c,  and  850   d  may be connected to the bearing  830   a,    830   b,    830   c,  and  830   d.  The guide  850   a,    850   b,    850   c,  and  850   d  may include a right guide  850   a,    850   b  disposed in the right side of the motor assembly  810  and a left guide  850   c,    850   d  disposed in the left side of the motor assembly  810 . 
     One side of the right guide  850   a,    850   b  may be connected to the first right bearing  830   a  and the other side may be connected to the second right bearing  830   b.  The right guide  850   a,    850   b  may be located parallel to the right lead screw  840   a.  Alternatively, the right guide  850   a,    850   b  may be spaced apart from the right lead screw  840   a.    
     The right guide  850   a,    850   b  may include a first right guide  850   a  and a second right guide  850   b.  The first right guide  850   a  and the second right guide  850   b  may be spaced apart from each other. The right lead screw  840   a  may be located between the first right guide  850   a  and the second right guide  850   b.    
     The right slider  860   a  may include a protrusion. Alternatively, the display device may include a protrusion formed in the right slider  860   a.  The protrusion may be formed in the body of the slider. The protrusion may include a front protrusion (not shown) protruding from the body  861   a  of the right slider  860   a  in the +z-axis direction and a rear protrusion  865   a  protruding from the body of the slider in the −z-axis direction. 
     The first right guide  850   a  may penetrate the rear protrusion  865   a.  Alternatively, a first hole  863   a  formed in the rear protrusion may be included, and the first right guide  850   a  may penetrate the first hole  863   a.  The first hole  863   a  may be formed in the x-axis direction. The first hole  863   a  may be referred to as a hole  863   a.    
     The second right guide (not shown) may penetrate the front protrusion (not shown). Alternatively, a second hole (not shown) formed in the front protrusion may be included, and the second right guide may penetrate the second hole. The second hole may be formed in the x-axis direction. 
     The right guide  850   a,    850   b  may guide the right slider  860   a  to move more stably, when the right slider  860   a  moves forward and backward along the right lead screw  840   a.  Since the right guide  850   a,    850   b  stably guides the right slider  860   a,  the right slider  860   a  may move forward and backward along the right lead screw  840   a  without rotating with respect to the right lead screw  840   a.    
     The structure formed by the left guide  850   c,    850   d,  the left bearing  830   a,    830   b,    830   c,  and  830   d,  the left slider  860   b,  and the left lead screw  840   b  may be symmetrical with the structure formed by the above-described right guide  850   a,    850   b,  right bearing  830   a,    830   b,    830   c,  and  830   d,  right slider  860   a,  and right lead screw  840   a.  In this case, the symmetry axis may be a symmetry axis ys of the motor assembly  810 . 
     Referring to  FIG.  48   , a first spring  841   a,    841   b  may be inserted into the lead screw  840   a,    840   b.  Alternatively, the lead screw  840   a,    840   b  may penetrate the first spring  841   a,    841   b.  The first spring  841   a,    841   b  may include a first right spring  841   a  disposed in the right side of the motor assembly  810  and a first left side spring  841   b  disposed in the left side of the motor assembly  810 . 
     The first right spring  841   a  may be disposed between the right slider  860   a  and the second right bearing  830   b.  One end of the first right spring  841   a  may be in contact with or separated from the right slider  860   a.  The other end of the first right spring  841   a  may be in contact with or separated from the second right bearing  830   b.    
     When the second arm  912   a  is completely lying with respect to the base  31 , a distance between the right slider  860   a  and the second right bearing  830   b  may be a distance RD 3 . The first right spring  841   a  may have a length larger than the distance RD 3  in a state of not being compressed or tensioned. Accordingly, when the second arm  912   a  is completely lying with respect to the base  31 , the first right spring  841   a  may be compressed between the right slider  860   a  and the second right bearing  830   b.  In addition, the first right spring  841   a  may provide a restoring force to the right slider  860   a  in the +x-axis direction. 
     When the second arm  912   a  changes from a completely lying state to a standing state with respect to the base  31 , the restoring force provided by the first right spring  841   a  may assist the second arm  912   a  to stand up. As the first right spring  841   a  assists the second arm  912   a  to stand up, the load on the motor assembly  810  may be reduced. 
     The lead screw  840   a,    840   b  may be driven by one motor assembly  810 . As the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the second arm  912   a,    912   b  can stand symmetrically. However, when the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the load applied to the motor assembly  810  in order to stand up the second arm  912   a,    912   b  may become excessively large. At this time, as the first right spring  841   a  assists the second arm  912   a  to stand up, the load on the motor assembly  810  may be reduced, and the load on the motor assembly  810  to stand up the second arm  912   a  may be reduced. 
     Alternatively, when the second arm  912   a  is changed from a standing state with respect to the base  31  to a completely lying state, the restoring force provided by the first right spring  841   a  may alleviate an impact generated when the second arm  912   a  lies with respect to the base  31 . That is, the first right spring  841   a  may serve as a damper when the second arm  912   a  lies with respect to the base  31 . As the first right spring  841   a  serves as a damper, a load on the motor assembly  810  may be reduced. 
     The structure formed by the first left spring  841   b,  the left bearing  830   a,    830   b,    830   c,  and  830   d,  the left slider  860   b,  the left lead screw  840   b,  and the second arm  912   a  may be symmetrical with the structure formed by the above-described first right spring  841   a,  right bearing  830   a,    830   b,    830   c,  and  830   d,  right slider  860   a,  right lead screw  840   a,  and second arm  912   a.  In this case, the symmetry axis may be a symmetry axis ys of the motor assembly  810 . 
     Referring to  FIG.  49   , a second spring  851   a,    851   b  may be inserted into the guide  850   a,    850   b,    850   c,  and  850   d.  Alternatively, the guide  850   a,    850   b,    850   c,  and  850   d  may penetrate the second spring  851   a,    851   b.  The second spring  851   a,    851   b  may include a second right spring  851   a  disposed in the right side of the motor assembly  810  and a second left side spring  851   b  disposed in the left side of the motor assembly  810 . 
     The second right spring  851   a  may be formed in plurality. The second right spring  851   a  may include a spring  940   a,    940   b  inserted into the first right guide  850   a  and a spring  940   a,    940   b  inserted into the second right guide  850   b.  Alternatively, the second right spring  851   a  may include a spring  940   a,    940   b  through which the first right guide  850   a  passes and a spring  940   a,    940   b  through which the second right guide  850   b  passes. 
     The guide  850   a,    850   b,    850   c,  and  850   d  may include a locking jaw  852   a,    852   b.  The locking jaw  852   a,    852   b  may include a right locking jaw  852   a  disposed in the right side of the motor assembly  810  and a left locking jaw  852   b  disposed in the left side of the motor assembly  810 . 
     The right locking jaw  852   a  may be disposed between the right slider  860   a  and the second right bearing  830   b.  In addition, the second right spring  851   a  may be disposed between the right slider  860   a  and the second right bearing  830   b.  One end of the second right spring  851   a  may be in contact with or separated from the right slider  860   a.  The other end of the second right spring  851   a  may be in contact with or separated from the right locking jaw  852   a.    
     When the second arm  912   a  is completely lying with respect to the base  31 , the distance between the right slider  860   a  and the right locking jaw  852   a  may be a distance RD 4 . The second right spring  851   a  may have a length larger than distance RD 4  in a state of being not compressed or tensioned. Accordingly, when the second arm  912   a  is completely lying with respect to the base  31 , the second right spring  851   a  may be compressed between the right slider  860   a  and the right locking jaw  852   a.  In addition, the second right spring  851   a  may provide a restoring force to the right slider  860   a  in the +x-axis direction. 
     When the second arm  912   a  changes from a completely lying state to a standing state with respect to the base  31 , the restoring force provided by the second right spring  851   a  may assist the second arm  912   a  to stand up. As the second right spring  851   a  assists the second arm  912   a  to stand up, the load on the motor assembly  810  may be reduced. 
     The lead screw  840   a,    840   b  may be driven by one motor assembly  810 . As the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the second arm  912   a,    912   b  can stand symmetrically. However, when the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the load applied to the motor assembly  810  in order to stand up the second arm  912912   b  can become excessively large. At this time, as the second right spring  851   a  assists the second arm  912   a  to stand up, the load on the motor assembly  810  may be reduced, and the load applied to the motor assembly  810  to stand up the second arm  912   a  may be reduced. 
     Alternatively, when the second arm  912   a  changes from a standing state with respect to the base  31  to a completely lying state, the restoring force provided by the second right spring  851   a  may alleviate an impact generated when the second arm  912   a  lies with respect to the base  31 . That is, the second right spring  851   a  may serve as a damper when the second arm  912   a  lies with respect to the base  31 . As the second right spring  851   a  serves as a damper, the load on the motor assembly  810  may be reduced. 
     The structure formed by the second left spring  851   b,  the left locking jaw  852   b,  the left slider  860   b,  the left guide  850   c,    850   d,  and the second arm  912   a  may be symmetrical with the structure formed by the above-described second right spring  851   a,  right locking jaw  852 right slider  860   a,  right guide  850   a,    850   b,  and second arm  912   a.  In this case, the symmetry axis may be the symmetry axis ys of the motor assembly  810 . 
     Referring to  FIGS.  50  to  52   , the second arm  912   a  may stand by receiving a restoring force from the first right spring  841   a  and the second right spring  851   a.    
     An angle between the second arm  912   a  and the base  31  may be referred to as an angle theta S. An angle between the right rod  870   a  and the base  31  may be referred to as an angle theta T. A force by the motor assembly  810  to move the right slider  860   a  in the +x-axis direction may be referred to as FA. The force applied by the first right spring  841   a  to the right slider  860   a  may be referred to as FB. The force applied by the second right spring  851   a  to the right slider  860   a  may be referred to as FC. The force transmitted by the right rod  870   a  to the second arm  912   a  may be referred to as FT. 
     When the second arm  912   a  is completely lying with respect to the base  31 , the angle theta S and the angle theta T may have a minimum value. When the second arm  912   a  is changed from a completely lying state to a standing state with respect to the second base  31 , the angle theta S and the angle theta T may gradually increase. 
     When the second arm  912   a  is completely lying with respect to the base  31 , the first right spring  841   a  may be compressed. The compressed first right spring  841   a  may provide a restoring force FB to the right slider  860   a.  The restoring force FB can act in the +x direction. When the second arm  912   a  is completely lying with respect to the base  31 , the amount of compression displacement of the first right spring  841   a  may be a maximum, and the magnitude of the restoring force FB may have a maximum value. When the second arm  912   a  is changed from a completely lying state to a standing state with respect to the base  31 , the amount of compression displacement of the first right spring  841   a  may gradually decrease, and the magnitude of the restoring force FB may gradually decrease. 
     When the second arm  912   a  is completely lying with respect to the base  31 , the second right spring  851   a  may be compressed. The compressed second right spring  851   a  may provide a restoring force FC to the right slider  860   a.  The restoring force FC can act in the +x direction. When the second arm  912   a  is completely lying with respect to the base  31 , the amount of compression displacement of the second right spring  851   a  may be a maximum, and the magnitude of the restoring force FC may have a maximum value. When the second arm  912   a  changes from a completely lying state to a standing state with respect to the base  31 , the amount of compression displacement of the second right spring  851   a  may gradually decrease, and the magnitude of the restoring force FC may gradually decrease. 
     The force FT transmitted by the right rod  870   a  to the second arm  912   a  may be a resultant force of the force FA of the motor assembly  810  to move the right slider  860   a  in the +x axis, the restoring force FB of the first right spring  841   a,  and the restoring force FC of the second right spring  851   a.    
     When the second arm  912   a  starts to stand in a state where the second arm  912   a  is completely lying with respect to the base  31 , the load on the motor assembly  810  may be a maximum. At this time, the magnitude of the restoring force FB provided by the first right spring  841   a  may be a maximum. In addition, the magnitude of the restoring force FC provided by the second spring  851   a,    851   b  may be a maximum. 
     When the second arm  912   a  changes from a completely lying state to a standing state with respect to the base  31 , the restoring force provided by the first right spring  841   a  and the second right spring  851   a  may assist the second arm  912   a  to stand up. As the first right spring  841   a  and the second right spring  851   a  assist the second arm  912   a  to stand up, the load on the motor assembly  810  may be reduced. 
     The first right spring  841   a  and the second right spring  851   a  may simultaneously provide a restoring force (a resultant force of the restoring force FB and the restoring force FC) to the right slider  860   a.  The restoring force (a resultant force of the restoring force FB and the restoring force FC) may be provided to the right slider  860   a  until the distance RD 5  between the right slider  860   a  and the right locking jaw  852   a  becomes equal to the length of the second right spring  851   a.    
     When the distance RD 5  between the right slider  860   a  and the right locking jaw  852   a  becomes equal to the length of the second right spring  851   a,  the amount of compression displacement of the second right spring  851   a  may be zero. When the amount of compression displacement of the second right spring  851   a  becomes  0 , the restoring force FC provided by the second right spring  851   a  to the right slider  860   a  may become 0. 
     When the distance RD 5  between the right slider  860   a  and the right locking jaw  852   a  is larger than the length of the second right spring  851   a,  only the first right spring  841   a  can provide the restoring force FB to the right slider  860   a.  The restoring force FB may be provided to the right slider  860   a,  until the distance RD 6  between the right slider  860   a  and the second right bearing  830   b  becomes equal to the length of the first right spring  841   a.    
     When the distance RD 6  between the right slider  860   a  and the second right bearing  830   b  is equal to the length of the first right spring  841   a,  the amount of compression displacement of the first right spring  841   a  may be zero. When the amount of compression displacement of the first right spring  841   a  becomes zero, the restoring force FB provided by the first right spring  841   a  to the right slider  860   a  may be zero. 
     When the distance RD 6  between the right slider  860   a  and the second right bearing  830   b  is larger than the length of the first right spring  841   a,  the motor assembly  810  may stand up the second arm  912   a  without receiving the restoring force from the first right spring  841   a  or the second right spring  851   a.    
     The structure formed by the first left spring  841   b,  the second left spring  851   b,  the left locking jaw  852   b,  the left slider  860   b,  the left guide  850   c,    850   d,  the left lead screw  840   b,  the left rod  870   b,  and the second arm  912   a  may be symmetrical with the structure formed by the above-described first right spring  841   a,  second right spring  851   a,  right locking jaw  852   a,  right slider  860   a,  right guide  850   a,    850   b,  right lead screw  840   a,  right rod  870   a,  and second arm  912   a.  In this case, the symmetry axis may be the symmetry axis ys of the motor assembly  810 . 
     Referring to  FIG.  53   , a pusher  930   a,    930   b  may be connected to the link mount  920   a,    920   b.  The pusher  930   a,    930   b  may include a right pusher  930   a  disposed in the right side of the motor assembly  810  and a left side pusher  930   b  disposed in the left side of the motor assembly  810 . 
     The link mount  920   a,    920   b  may form an accommodating space A. The accommodating space A may accommodate the spring  940   a,    940   b  and the pusher  930   a,    930   b.  The spring  940   a,    940   b  may include a right spring  940   a  disposed in the right side of the motor assembly  810  and a left side spring  940   b  disposed in the left side of the motor assembly  810 . The accommodating space A may be referred to as an internal space A. 
     The link mount  920   a,    920   b  may include a first hole  922   a  connecting the accommodating space A and an external space (the first hole corresponding to  920   b  is not shown). The first hole  922   a  may be formed in the upper surface of the link mount  920   a,    920   b.  The first hole  922   a  may be referred to as a hole  922   a.    
     The pusher  930   a,    930   b  may be located perpendicular to the base  31 . Alternatively, the pusher  930   a,    930   b  may be disposed parallel to the y-axis. The spring  940   a,    940   b  may be located perpendicular to the base  31 . Alternatively, the spring  940   a,    940   b  may be disposed parallel to the y-axis. 
     The pusher  930   a,    930   b  may include a first part  931   a,    931   b  and a second part  932   a,    932   b.  The second part  932   a,    932   b  may be connected to the lower sides of the first part  931   a,    931   b.  The lower end of the second part  932   a,    932   b  may be connected to the spring  940   a,    940   b.  All or part of the second part  932   a,    932   b  may be received in the accommodating space A formed by the link mount  920   a,    920   b.  The second part  932   a,    932   b  may have a diameter equal to or smaller than a diameter of the first hole  922   a.  The second part  932   a,    932   b  may penetrate the first hole  922   a.    
     The first part  931   a,    931   b  may be located outside the link mount  920   a,    920   b.  Alternatively, the first part  931   a,    931   b  may be located outside the accommodating space A of the link mount  920   a,    920   b.  The first part  931   a,    931   b  may have a larger diameter than that of the first hole  922   a.    
     The first part  931   a,    931   b  may be in contact with or spaced apart from the link bracket  951   a,    951   b.  For example, when the second arm  912   a,    912   b  is completely lying with respect to the base  31 , the first part  931   a,    931   b  may contact the link bracket  951   a,    951   b.  Alternatively, when the second arm  912   a,    912   b  completely stand up with respect to the base  31 , the first part  931   a,    931   b  may be spaced apart from the link bracket  951   a,    951   b.    
     When the first part  931   a,    931   b  contacts the link bracket  951   a,    951   b,  the pusher  930   a,    930   b  may receive a force from the link bracket  951   a,    95  lb. The force received by the pusher  930   a,    930   b  may be in a downward direction. Alternatively, the force received by the pusher  930   a,    930   b  may be in the −y-axis direction. Alternatively, the link bracket  951   a,    951   b  may press the pusher  930   a,    930   b.  The direction in which the link bracket  951   a,    951   b  presses the pusher  930   a,    930   b  may be a downward direction. Alternatively, the direction in which the link bracket  951   a,    951   b  presses the pusher  930   a,    930   b  may be the −y-axis direction. 
     When the first part  931   a,    931   b  receives a force, the spring  940   a,    940   b  may be compressed. The compressed spring  940   a,    940   b  may provide a restoring force to the pusher  930   a,    930   b.  The restoring force may be in a direction opposite to the direction of the force applied to the first part  931   a,    931   b.  Alternatively, the restoring force may act in the +y-axis direction. 
     The link mount  920   a,    920   b  may include a second hole  921   a  (the second hole corresponding to  920   b  is not shown). The second hole  921   a  may connect the accommodating space A and an external space. All or part of the spring  940   a,    940   b  may be exposed to the outside through the second hole  921   a.  All or part of the pusher  930   a,    930   b  may be exposed to the outside through the second hole  921   a.  When the display device is maintained or repaired, a service provider may check the operating state of the pusher  930   a,    930   b  through the second hole  921   a.  The second hole  921   a  may provide the convenience of maintenance or repair to the service provider. 
     Referring to  FIGS.  54  to  56   , the right link  910   a  may stand up by receiving a restoring force from the right pusher  930   a.  It will be described with reference to the right link  910   a.    
     An angle between the second arm  912   a  and the base  31  may be referred to as an angle theta S. The force transmitted by the right rod  870   a  to the second arm  912   a  may be referred to as FT. The force transmitted by the right pusher  930   a  to the right link bracket  951   a  may be referred to as FP. 
     Referring to  FIG.  54   , when the second arm  912   a  is completely lying with respect to the base  31 , the angle theta S may have a minimum value. The right spring  940   a  connected to the right pusher  930   a  may be compressed to the maximum, and the magnitude of the restoring force FP may have a maximum value. The compressed right spring  940   a  may provide a restoring force FP to the right pusher  930   a.  The right pusher  930   a  may transmit the restoring force FP to the right link bracket  951   a.  The restoring force FP may act in the +y-axis direction. 
     When the second arm  912   a  is completely lying with respect to the base  31 , the distance HL from the base  31  to the upper end of the right pusher  930   a  may have a minimum value. The first part  931   a  of the right pusher  930   a  may protrude to the outside of the right link mount  920   a,  and the second part  932   a  of the right pusher  930   a  may be entirely received in the accommodating space  923   a  of the right link mount  920   a.    
     Referring to  FIG.  55   , when the second arm  912   a  changes from a completely lying state to a standing state with respect to the base  31 , the angle theta S may gradually increase. The amount of compression displacement of the right spring  940   a  may gradually decrease, and the magnitude of the restoring force FP may gradually decrease. 
     As the angle theta S gradually increases, at least a portion of the second part  932   a  of the right pusher  930   a  may protrude to the outside of the right link mount  920   a.  A length by which the second part  932   a  of the right pusher  930   a  protrudes to the outside of the right link mount  920   a  may be referred to as a length HP. The distance HL from the base  31  to the upper end of the right pusher  930   a  may be increased by HP in comparison with a case where the second arm  912   a  is completely lying with respect to the base  31 . 
     Referring to  FIG.  56   , when the standing of the second arm  912   a  with respect to the base  31  progresses, the right pusher  930   a  and the right link bracket  951   a  may be separated from each other. The amount of compression displacement of the right spring  940   a  may become zero. When the amount of compression displacement of the right spring  940   a  becomes zero, the restoring force FP provided by the right pusher  930   a  to the right link bracket  951   a  may be zero. 
     In addition, a length HP by which the second part  932   a  of the right pusher  930   a  protrudes to the outside of the right link mount  920   a  may have a maximum value. In addition, the distance HL from the base  31  to the upper end of the right pusher  930   a  may have a maximum value. 
     That is, the right pusher  930   a  applies a restoring force to the right link bracket  951   a,  while the right pusher  930   a  and the right link bracket  951   a  are in contact with each other, thereby assisting the second arm  912   a  to stand up, and reducing the load on the motor assembly  810 . 
     The lead screw  840   a,    840   b  may be driven by one motor assembly  810 . As the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the second arm  912   a,    912   b  can stand symmetrically. However, when the lead screw  840   a,    840   b  is driven by one motor assembly  810 , the load applied to the motor assembly  810  in order to stand up the second arm  912   a,    912   b  may be excessively large. At this time, the right pusher  930   a  applies a restoring force to the right link bracket  951   a,  thereby assisting the second arm  912   a  to stand up, and reducing the load on the motor assembly  810 . 
     Alternatively, when the second arm  912   a  changes from a standing state to a completely lying state with respect to the base  31 , the restoring force that the right pusher  930   a  provides to the right link bracket  951   a  can alleviate an impact that is generated when the link  910   a  lies with respect to the base  31 . That is, the restoring force that the right pusher  930   a  provides to the right link bracket  951   a  may serve as a damper, when the link  910   a  lies with respect to the base  31 . As the right pusher  930   a  serves as a damper, a load on the motor assembly  810  may be reduced. 
     The structure formed by the left pusher  930   b,  the left spring  940   b,  the left link bracket  951   b,  the left link mount  920   b,  and the left rod  870   b  may be symmetrical with the structure formed by the above-described right pusher  930   a,  right spring  940   a,  right link bracket  951   a,  right link  910   a  mount, and right rod  870   a.  In this case, the symmetry axis may be the symmetry axis of the motor assembly  810 . 
     Referring to  FIGS.  57  to  59   , the panel roller  143  may be installed in the base  31 . The panel roller  143  may be installed in front of the lead screw  840   a,    840   b.  Alternatively, the panel roller  143  may be disposed parallel to the length direction of the lead screw  840   a,    840   b.  Alternatively, the panel roller  143  may be spaced apart from the lead screw  840   a,    840   b.    
     The display unit  20  may include the display panel  10  and the module cover  15 . A lower side of the display unit  20  may be connected to the panel roller  143 , and an upper side of the display unit  20  may be connected to the upper bar  75 . The display unit  20  may be wound around or unwound from the panel roller  143 . 
     A distance from the symmetry axis ys of the motor assembly  810  to the right slider  860   a  may be referred to as a distance RD. A distance from the symmetry axis ys of the motor assembly  810  to the left slider  860   b  may be referred to as a distance LD. The distance between the right slider  860   a  and the left slider  860   b  may be referred to as a distance SD. The distance SD may be the sum of the distance RD and the distance LD. A distance from the base  31  to the upper end of the display unit  20  may be referred to as a distance HD. 
     Referring to  FIG.  57   , when the second arm  912   a,    912   b  are completely lying with respect to the base  31 , the distance SD between the right slider  860   a  and the left slider  860   b  may have a minimum value. The distance RD from the symmetry axis ys of the motor assembly  810  to the right slider  860   a  and the distance LD from the symmetry axis ys of the motor assembly  810  to the left slider  860   b  may be equal to each other. 
     When the second arm  912   a,    912   b  are completely lying with respect to the base  31 , the distance HD from the base  31  to the upper end of the display unit  20  may have a minimum value. 
     When the second arm  912   a,    912   b  is completely lying with respect to the base  31 , the first spring  841   a,    841   b  may contact the slider  860   a,    860   b.  In addition, the second spring  851   a,    851   b  may contact the slider  860   a,    860   b.  In addition, the pusher  930   a,    930   b  may contact the link bracket  951   a,    951   b.    
     When the second arm  912   a,    912   b  is completely lying with respect to the base  31 , the compression amount of the first spring  841   a,    841   b  may have a maximum value, and the magnitude of the restoring force provided by the first spring  841   a,    841   b  to the slider  860   a,    860   b  may have a maximum value. 
     When the second arm  912   a,    912   b  is completely lying with respect to the base  31 , the compression amount of the second spring  851   a,    851   b  may have a maximum value, and the magnitude of the restoring force provided by the second spring  851   a,    851   b  to the slider  860   a,    860   b  may have a maximum value. 
     When the second arm  912   a,    912   b  is completely lying with respect to the base  31 , the compression amount of the spring  940   a,    940   b  may have a maximum value, and the magnitude of the restoring force provided by the spring  940   a,    940   b  to the pusher  930   a,    930   b  may have a maximum value. 
     When the second arm  912   a,    912   b  start to stand up with respect to the base  31 , the second arm  912   a,    912   b  may stand up by receiving a restoring force from the first spring  841   a,    841   b,  the second spring  851   a,    851   b,  and the spring  940   a,    940   b.  Accordingly, the load applied to the motor assembly  810  may be reduced. 
     Referring to  FIG.  58   , as the standing of the second arm  912   a,    912   b  with respect to the base  31  progresses, the distance SD between the right slider  860   a  and the left slider  860   b  may gradually increase. Even if the distance SD increases, the distance LD and the distance RD may be equal to each other. That is, the right slider  860   a  and the left slider  860   b  may be located symmetrically with respect to the symmetry axis ys of the motor assembly  810 . In addition, a degree to which the second arm  912   a,    912   b  of the right link  910   a  stands up with respect to the base  31  and a degree to which the second arm  912   a,    912   b  of the left link  910   b  stands up with respect to the base  31  may be equal to each other. 
     As the standing of the second arm  912   a,    912   b  with respect to the base  31  progresses, the distance HD from the base  31  to the upper end of the display unit  20  may gradually increase. The display unit  20  may be unwound from the panel roller  143 . Alternatively, the display unit  20  may be deployed from the panel roller  143 . 
     When the second arm  912   a,    912   b  sufficiently stands up with respect to the base  31 , the first spring  841   a,    841   b  may be separated from the slider  860   a,    860   b.  In addition, when the second arm  912   a,    912   b  sufficiently stands up with respect to the base  31 , the second spring  851   a,    851   b  may be separated from the slider  860   a,    860   b.  In addition, when the second arm  912   a,    912   b  sufficiently stands up with respect to the base  31 , the pusher  930   a,    930   b  may be separated from the link bracket  951   a,    951   b.    
     The separation of the first spring  841   a,    841   b  from the slider  860   a,    860   b,  the separation of the second spring  851   a,    851   b  from the slider  860   a,    860   b,  and the separation of the pusher  930   a,    930   b  from the link bracket  951   a,    951   b  may progress independently of each other. That is, the order of the separation of the first spring  841   a,    841   b  from the slider  860   a,    860   b,  the separation of the second spring  851   a,    851   b  from the slider  860   a,    860   b,  and the separation of the pusher  930   a,    930   b  from the link bracket  951   a,    951   b  may be mutually variable. 
     An angle between the axis xsl parallel to the base  31  and the second arm  912   a  may be referred to as theta R. In addition, an angle formed by the axis xsl parallel to the base  31  and the first arm  911   a  may be referred to as theta R′. The axis xs  1  and the x-axis may be parallel to each other. When the second arm  912   a  is completely lying with respect to the base  31 , or while the second arm  912   a  stands up with respect to the base  31 , or when the second arm  912   a  completes standing with respect to the base  31 , theta R and theta R′ may be maintained to be identical with each other. 
     An angle between the axis xs 2  parallel to the base  31  and the second arm  912   b  may be referred to as theta L. In addition, an angle formed by the axis xs 2  parallel to the base  31  and the first arm  911   b  may be referred to as theta L′. The axis xs 2  and the x-axis may be parallel to each other. 
     When the second arm  912   b  is completely lying with respect to the base  31 , or while the second arm  912   b  stands up with respect to the base  31 , or when the second arm  912   b  completes standing with respect to the base  31 , theta L and theta L′ may be maintained to be identical with each other. The axis xsl and the axis xs 2  may be axes identical to each other. 
     Referring to  FIG.  59   , when the second arm  912   a,    912   b  completely stands up with respect to the base  31 , the distance SD between the right slider  860   a  and the left slider  860   b  may have a maximum value. Even when the distance SD is a maximum, the distance LD and the distance RD may be equal to each other. 
     When the second arm  912   a,    912   b  completely stands up with respect to the base  31 , the distance HD from the base  31  to the upper end of the display unit  20  may have a maximum value. 
     Referring to  FIG.  60   , the panel roller  143  may be rotatably installed inside the housing  30 . The module cover  15  and the display panel  10  may be wound around the panel roller  143  inside the housing  30 . The module cover  15  and the display panel  10  wound around the panel roller  143  may be unwound or sag from the panel roller  143  due to vibration or external impact. When the module cover  15  is unwound or sagged, the drooping portion may collide with a structures installed in the lower side of the panel roller  143 . 
     The base  31  may include a first vertical portion  31 V 1 , a first horizontal portion  31 H 1 , a second vertical portion  31 V 2 , and a second horizontal portion  31 H 2 . The first vertical portion  31 V 1 , the first horizontal portion  31 H 1 , the second vertical portion  31 V 2 , and the second horizontal portion  31 H 2  may form a step shape as a whole while forming a step difference. The second horizontal portion  31 H 2  may be located in the vertical lower side of the panel roller  143 . 
     A speaker assembly  900  may be installed in a front lower side of the panel roller  143 . The speaker assembly  900  may be located in the forward direction of the second horizontal portion  31 H 2 . Sound provided by a sound unit  901 ,  902  (refer to  FIG.  61   ) of the speaker assembly  900  may be directed in the forward direction of the housing  30 . 
     Referring to  FIGS.  60  and  61   , the speaker assembly  900  may include a first case  910  and a second case  920 . The first case  910  may form a lower portion of the speaker assembly  900 , and the second case  920  may form an upper portion of the speaker assembly  900 . The first case  910  may be partitioned with the second case  920  while being formed as one body. The first speaker unit  901  may be mounted on the front surface of the first case  910 , and the second speaker unit  902  may be mounted on the front surface of the second case  920 . For example, the first speaker unit  901  may be a woofer, and the second speaker unit  902  may be a tweeter. 
     The second case  920  may have a curved surface  930 . The curved surface  930  of the second case  920  may have a curvature corresponding to the curvature of the panel roller  143  (refer to  FIG.  60   ). The curved surface  930  of the second case  920  may be spaced apart from the panel roller  143  by a certain interval. The curved surface  930  may be located in the rear upper side of the second case  920 . 
     A buffer member  940  may be fixed to the curved surface  930  of the second case  920 . The buffer member  940  may include a plurality of sub buffer members  940 . A first sub buffer member  941  may be located adjacent to a second sub buffer member  942 . For example, the buffer member  940  may be a sponge or a reinforcing sponge. As another example, the buffer member  940  may be rubber. The first sub buffer member  941  may be attached to the upper portion of the curved surface  930 , and the second sub buffer member  942  may be attached to the lower portion of the curved surface  930 . Accordingly, durability in a state in which the buffer members  940  are adhered to the curved surface may be improved due to the curvature of the curved surface  930 . 
     Accordingly, even if the module cover  15  wound around the panel roller  143  is unwound or loosened from the panel roller  143  due to vibration or external impact, the impact applied by the case  920 ,  930  of the speaker  900  to the module cover  15  can be prevented. 
     Referring to  FIG.  62   , the speaker assembly  900  may be placed in the housing  30 . A front cover  1000  may be located in the forward direction of the speaker assembly  900 . The speaker assembly  900  may be coupled to the front cover  1000 . The front cover  1000  may be fixed to the housing  30 . The front cover  1000  may be coupled to a boss  30 P formed by protruding from the bottom surface of the housing  30  by a fastening member  1001 . 
     The front cover  1000  may include a coupling hole  1002 . The coupling hole  1002  may be formed in the front cover  1000  adjacent to the upper end of the second case  920  of the speaker assembly  900 . The coupling hole  1002  may penetrate the front cover  1000 . The front cover  1000  may have a thickness TT. The coupling hole  1002  may have a diameter DD. 
     The second case  920  may include a coupling portion  960 . The coupling portion  960  may be formed in the upper side of the second case  920 . The coupling portion  960  may include a body  961  and an insertion rod  962 . The body  961  may form an upper end of the second case  920 . The body  961  may be formed with the second case  920  as one body. The insertion rod  962  may be formed in the body  961 . The insertion rod  962  may extend from the body  961  in the forward direction of the speaker assembly  900  or toward the front case  1000 . A bushing  970  may be inserted into a coupling hole  1002 . The insertion rod  962  may be inserted into the bushing  970 . For example, the bushing  970  may be rubber. As another example, the bushing  970  may be made of synthetic resin. 
     Referring to  FIGS.  63  and  64   , a support member  980 ,  990  may be located between the speaker assembly  900  (refer to  FIG.  62   ) and the housing  30 . The support member  980 ,  990  may be supported on the bottom surface of the housing  30 . The support member  980 ,  990  may provide an elastic force or a buffering force to the speaker assembly  900 . The support member  980 ,  990  may include a front support member  980  and a rear support member  990 . The support member  980 ,  990  may absorb vibrations generated in the speaker assembly  900 . 
     The front support member  980  may be located between the boss  30 P of the housing  30  and the first case  910 . The front support member  980  may be fixed to the lower surface of the first case  910  and contact the boss  30 P of the housing  30 . The front support member  980  may have two layers. A first layer  981  may be fixed to the lower surface of the first case  910  of the speaker assembly  900 . A second layer  982  may be fixed to the first layer  981  and contact the boss  30 P of the housing  30 . The first layer  981  may be denser than the second layer  982 . The first layer  981  may have a higher hardness than the second layer  982 . For example, the first layer  981  may be rubber. As another example, the second layer  982  may be a soft sponge. 
     The rear support member  990  may be located between the bottom surface of the housing  30  and the first case  910 . The rear support member  990  may be fixed to the lower surface of the first case  910  and contact the bottom surface of the housing  30 . The rear support member  990  may have two layers. The first layer  991  may be fixed to the lower surface of the first case  910  of the speaker assembly  900 . The second layer  992  may be fixed to the first layer  991  and contact the bottom surface of the housing  30 . For example, the first layer  991  may be rubber. As another example, the second layer  992  may be a soft sponge. 
     Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  from being transferred to the housing  30 . 
     Referring to  FIG.  65   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). The body  973  may have a wave surface  974 . The wave surface  974  may be formed on the outer circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  974  may be alternately repeated. As another example, the wave surface  974  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     Referring to  FIG.  66   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). 
     The first head  971  may have a wave surface  975 . The wave surface  975  may be formed on the outer surface of the first head  971  facing the second head  972 . For example, the ridges and valleys of the wave surface  975  may be alternately repeated. As another example, the wave surface  975  may be formed by embossing. 
     The second head  972  may have a wave surface  976 . The wave surface  976  may be formed on an outer surface of the second head  972  facing the first head  971 . For example, the ridges and valleys of the wave surface  976  may be alternately repeated. As another example, the wave surface  976  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     Referring to  FIG.  67   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). 
     The body  973  may have a wave surface  974 . The wave surface  974  may be formed on the outer circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  974  may be alternately repeated. As another example, the wave surface  974  may be formed by embossing. 
     The first head  971  may have a wave surface  975 . The wave surface  975  may be formed on the outer surface of the first head  971  facing the second head  972 . For example, the ridges and valleys of the wave surface  975  may be alternately repeated. As another example, the wave surface  975  may be formed by embossing. 
     The second head  972  may have a wave surface  976 . The wave surface  976  may be formed on the outer surface of the second head  972  facing the first head  971 . For example, the ridges and valleys of the wave surface  976  may be alternately repeated. As another example, the wave surface  976  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     Referring to  FIG.  68   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). 
     The body  973  may have a wave surface  977 . The wave surface  977  may be formed on the inner circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  977  may be alternately repeated. As another example, the wave surface  977  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     Referring to  FIG.  69   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). 
     The body  973  may have a wave surface  974 . The wave surface  974  may be formed on the outer circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  974  may be alternately repeated. As another example, the wave surface  974  may be formed by embossing. 
     The body  973  may have a wave surface  977 . The wave surface  977  may be formed on the inner circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  977  may be alternately repeated. As another example, the wave surface  977  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     Referring to  FIG.  70   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). 
     The body  973  may have a wave surface  977 . The wave surface  977  may be formed on the inner circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  977  may be alternately repeated. As another example, the wave surface  977  may be formed by embossing. 
     The first head  971  may have a wave surface  975 . The wave surface  975  may be formed on the outer surface of the first head  971  facing the second head  972 . For example, the ridges and valleys of the wave surface  975  may be alternately repeated. As another example, the wave surface  975  may be formed by embossing. 
     The second head  972  may have a wave surface  976 . The wave surface  976  may be formed on the outer surface of the second head  972  facing the first head  971 . For example, the ridges and valleys of the wave surface  976  may be alternately repeated. As another example, the wave surface  976  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     Referring to  FIG.  71   , the bushing  970  may include a body  973 , a first head  971 , and a second head  972 . The body  973  may have a cylindrical shape as a whole. The first head  971  may be formed in one end of the body  973 , and the outer diameter H 1  of the first head  971  may be larger than the outer diameter BD of the body  973 . The second head  972  may be formed in the other end of the body  973 , and the outer diameter H 2  of the second head  972  may be larger than the outer diameter BD of the body  973 . 
     The outer diameter H 1  of the first head  971  may be substantially the same as the outer diameter H 2  of the second head  972 . The outer diameter BD of the body  973  may be substantially the same as the diameter DD of the coupling hole  1002  (refer to  FIG.  62   ). The distance HD between the first head  971  and the second head  972  may be larger than the thickness TT of the front cover  1000  (refer to  FIG.  62   ). 
     The body  973  may have a wave surface  974 . The wave surface  974  may be formed on the outer circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  974  may be alternately repeated. As another example, the wave surface  974  may be formed by embossing. 
     The body  973  may have a wave surface  977 . The wave surface  977  may be formed on the inner circumferential surface of the body  973 . For example, the ridges and valleys of the wave surface  977  may be alternately repeated. As another example, the wave surface  977  may be formed by embossing. 
     The first head  971  may have a wave surface  975 . The wave surface  975  may be formed on the outer surface of the first head  971  facing the second head  972 . For example, the ridges and valleys of the wave surface  975  may be alternately repeated. As another example, the wave surface  975  may be formed by embossing. 
     The second head  972  may have a wave surface  976 . The wave surface  976  may be formed on the outer surface of the second head  972  facing the first head  971 . For example, the ridges and valleys of the wave surface  976  may be alternately repeated. As another example, the wave surface  976  may be formed by embossing. 
     The inner diameter B of the body  973  may be substantially the same as the outer diameter of the insertion rod  962  (refer to  FIG.  62   ). Accordingly, it is possible to improve or prevent noise and/or vibration generated in the speaker assembly  900  (refer to  FIG.  62   ) from being transmitted to the front cover  1000 . 
     According to an aspect of the present disclosure, provided is a display device including: a flexible display panel; a roller which extends long, and around which the display panel is wound, or from which the display panel is unwound; a housing which provides an accommodating space therein, wherein the roller is rotatably mounted in the accommodating space; and a speaker assembly which is located between the roller and the housing, and placed on a bottom of the housing, wherein the housing includes a front cover which is located inside a front surface of the housing, is fixed to the bottom of the housing, and has a coupling hole, wherein the speaker assembly includes a coupling portion which is formed in an upper side of the speaker assembly, and inserted into the coupling hole. 
     In addition, according to another aspect of the present disclosure, the display device further includes a bushing which is inserted into the coupling hole of the front cover, and into which the coupling portion of the speaker assembly is inserted. 
     In addition, according to another aspect of the present disclosure, the bushing includes a buffer material. 
     In addition, according to another aspect of the present disclosure, the display device further includes a support member which is disposed on the bottom of the housing, and supports the speaker assembly. 
     In addition, according to another aspect of the present disclosure, the support member includes: a first layer in contact with a lower surface of the speaker assembly; and a second layer in contact with the first layer and the bottom of the housing. 
     In addition, according to another aspect of the present disclosure, the first layer may have a higher hardness than the second layer. 
     In addition, according to another aspect of the present disclosure, the bushing includes: a hollow body; a first head which is hollow, and formed in one end of the body; and a second head which is hollow, is formed in the other end of the body, and faces the first head, wherein an outer diameter of the first head and the second head is larger than an outer diameter of the body, and an inner diameter of the first head and the second head is substantially the same as an inner diameter of the body. 
     In addition, according to another aspect of the present disclosure, the bushing further includes a first wave surface formed on an outer circumferential surface of the body. 
     In addition, according to another aspect of the present disclosure, the bushing further includes a second wave surface formed on an outer surface of the first head facing the second head. 
     In addition, according to another aspect of the present disclosure, the bushing further includes a third wave surface formed on an outer surface of the second head facing the first head. 
     In addition, according to another aspect of the present disclosure, the bushing further includes a fourth wave surface formed on an inner circumferential surface of the body. 
     In addition, according to another aspect of the present disclosure, a distance between the first head and the second head is larger than a thickness of the front cover. 
     In addition, according to another aspect of the present disclosure, the coupling portion of the speaker assembly includes: a body formed on an upper end of the speaker assembly; and an insertion rod which protrudes from the body, and is press-fitted into the coupling hole of the front cover. 
     In addition, according to another aspect of the present disclosure, the display device further includes: a module cover which extends long in a length direction of the housing, and has a plurality of segments sequentially arranged in an up-down direction of the display panel at a rearward direction of the display panel to be wound around or unwound from the roller together with the display panel; and a foldable link which is located in the rearward direction of the display panel, has one end pivotably connected to the housing, and has the other end pivotably connected to an upper side of the module cover to stand up while unwinding the display panel and the module cover from the roller. 
     Certain embodiments or other embodiments of the invention described above are not mutually exclusive or distinct from each other. Any or all elements of the embodiments of the invention described above may be combined or combined with each other in configuration or function. For example, a configuration “A” described in one embodiment of the invention and the drawings and a configuration “B” described in another embodiment of the invention and the drawings may be combined with each other. Namely, although the combination between the configurations is not directly described, the combination is possible except in the case where it is described that the combination is impossible. 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.