Patent Publication Number: US-11663933-B2

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. § 119 (a), this application claims the benefit of an earlier filing date and right of priority to International Application No. PCT/KR2019/018801 filed on Dec. 31, 2019, the contents of which are hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a display device. 
     2. Description of the Related Art 
     As the information society has developed, the demand for display device is increasing in various forms, and accordingly, in recent years, various display devices such as a liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), vacuum fluorescent display (VFD), and the like have been studied and used. 
     Thereamong, a display device using an organic light emitting diode (OLED) has excellent luminance and viewing angle characteristics in comparison with a liquid crystal display device and does not require a backlight unit, thereby being implemented in an ultrathin type. 
     In addition, a flexible display panel can be bent or wound around a roller. The flexible display panel may be used to implement a display device that unfolds on a roller or winds around the roller. Many studies have been made on a structure for winding a flexible display panel around a roller or unwinding the flexible display panel from the roller. 
     SUMMARY OF THE INVENTION 
     It is an object of the present disclosure to solve the above and other problems. 
     It is another object of the present disclosure to secure structural rigidity for preventing drooping of a display device. 
     It is another object of the present disclosure to secure structural rigidity for preventing twisting of the display device. 
     It is a further object of the present disclosure to provide a driving mechanism of a rollable display device. 
     In accordance with the present disclosure, the above and other objects can be accomplished by the provision of a display device including a flexible display panel, a panel roller, wherein the flexible display panel is wound around or unwound from the panel roller, a main frame extending in a longitudinal direction of the panel roller, wherein the panel roller is coupled to the main frame, an elongated frame member extending in the longitudinal direction of the panel roller, wherein the elongated frame member is spaced apart from the panel roller and the main frame, and a sub frame coupling the elongated frame member with the main frame, wherein the sub frame is coupled to the main frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1  to  34    are views showing examples of a display device according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 an embodiment is described with reference to a specific figure, if necessary, reference numeral not shown in the specific figure may be referred to, and reference numeral not shown in the specific figure is used when the reference numeral is shown in the other figures. 
     For horizontally symmetrical or vertically symmetrical components shown in the drawings referred to in the following description, the description of a one-side part of each component may be equally applied to the description of an other-side part thereof. 
     Referring to  FIG.  1   , a display device  10  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. 
     The direction parallel to the longitudinal direction of the housing  30  may be referred to as a first direction DR 1 , a leftward direction, or a rightward direction. The direction in which the display unit  20  displays a screen may be referred to as a forward direction or the front. The direction opposite to the direction in which the display unit  20  displays the screen may be referred to as a rearward direction or the rear. The direction parallel to the height direction of the display device  10  may be referred to as a second direction DR 2 , an upward direction, or a downward direction. 
     A 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. A leftward-rightward direction LR may be parallel to the first direction DR 1 , and an upward-downward direction UD may be parallel to the second direction DR 2 . 
     Referring to  FIG.  2   , the display unit  20  may be entirely located inside the housing  30 . At least a portion of the display unit  20  may be located outside the housing  30 . The degree 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  21  and a plate  23 . The display panel  21  may be flexible. For example, the display panel  21  may be an organic light emitting display (OLED). 
     The display panel  21  may have a front surface for displaying an image. The display panel  21  may have a rear surface facing the front surface. The front surface of the display panel  21  may be covered with a light transmissive material. For example, the light transmissive material may be a synthetic resin or film. 
     The plate  23  may be coupled, fastened, or attached to the rear surface of the display panel  21 . The plate  23  may include a metal material. The plate  23  may be referred to as a module cover  23 , a cover  23 , a display panel cover  23 , a panel cover  23 , or an apron  23 . 
     Referring to  FIG.  4   , the plate  23  may include a plurality of segments  23   c . A magnet  24  may be located inside a recess  26  of the segment  15   c . The recess  26  may be located on a surface of the segment  23   c  facing the display panel  21 . The recess  26  may be located in the front surface of each segment  23 . Since the magnet  24  is accommodated inside the recess  26 , the magnet  24  may not protrude from the segment  23   c . The display panel  21  may be flat without being wrinkled even when it is in contact with the segment  23   c.    
     Referring to  FIG.  5   , a bead  27  may be formed in the upper surface of the segment  23   b . The bead  27  may have a shape recessed inwardly of the segment  23   b . For example, the bead  27  may be formed by pressing the segment  23   b . A plurality of beads  27  may be formed on the segment  23   b . The plurality of beads  27  may be spaced apart from each other. The bead  27  may enhance the rigidity of the segment  23   b . The bead  27  can prevent the shape of the segment  23   b  from being deformed due to external impact. The segment  23   b  may be fixed to the rear of the display panel  21  via an adhesive member  22 . For example, the adhesive member  22  may be double-sided tape. 
     Referring to  FIG.  6   , a source PCB  21   b  may be located under the module cover  23 . In the case of roll-down or roll-up, the position of the source PCB  21   b  may be changed with the movement of the module cover  23 . An FFC cable  21   a  may be located in the central part of the module cover  23  in the first direction. The FFC cable  21   a  may be located in both ends of the module cover  23  in the first direction. 
     Referring to  FIG.  7   , a segment  23   d  may include a depression  28  recessed inwardly of the segment  23   d . The depression  28  may form a space between the display panel  21  and the module cover  23 . The FFC cable  21   a  may be accommodated in a space formed by the depression  28 . In addition, the depression  28  may improve the rigidity of the segment  23   d.    
     The bead  27  may be located on the segment  23   d  excluding a portion where the depression  28  is located. The position of the depression  28  may not overlap the position of the bead  27  in order to prevent a reduction in rigidity of the segment  23   d.    
     Referring to  FIG.  8   , a penetrating portion  29  may be located at the central part of a segment  23   e  in the first direction. The penetrating portion  29  may penetrate the central part of the segment  23   e  in the second direction. That is, the penetrating portion  29  may be a hole located in the segment  23   e . The penetrating portion  29  may be a portion where the FFC cable  21   a  is located. Since the penetrating portion  29  is formed in the segment  23   e , the thickness of the segment  23   e  may be reduced in comparison with the case where the FFC cable  21   a  is located in the depression  28  (see  FIG.  7   ). 
     The bead  27  may be located on the segment  23   e  excluding a portion where the penetrating portion  29  is located. The position of the penetrating portion  29  may not overlap the position of the bead  27  in order to prevent a reduction in rigidity of the segment  23   e.    
     Referring to  FIG.  9   , a top case  60  may cover the source PCB  21   b  and a bar  50  as well as the display panel  21  and the module cover  23 . One surface of the bar  50  may be coupled to the rear surface of the module cover  23 , and the other surface thereof may be coupled to the source PCB  21   b . The bar  50  may be fixed to the module cover  23  to support the source PCB  21   b.    
     The distal end of the FFC cable  21   a  may be connected to a timing controller board  41  (see  FIG.  10   ) inside a roller  40  (see  FIG.  10   ). The FFC cable  21   a  may be wound around or unwound from the roller  40  together with the display unit  20 . 
     A portion of the FFC cable  21   a  may be located between the display panel  21  and the module cover  23 . The portion of the FFC cable  21   a  located between the display panel  21  and the module cover  23  may be referred to as a first portion  21   a   1 . The first portion  21   a   1  may be located in the depression  28  formed by the plurality of segments  23   d . Alternatively, the first portion  21   a   1  may be accommodated in the depression  28  formed by the plurality of segments  23   d.    
     A portion of the FFC cable  21   a  may penetrate a segment  23   f . The portion of the FFC cable  21   a  that passes through the segment  23   f  may be referred to as a second portion  21   a   2 . The segment  23   f  may include a first hole  23   fh   1  formed in the front surface and a second hole  23   fh   2  formed in the rear surface. The first hole  23   fh   1  and the second hole  23   fh   2  may be connected to each other to form a single hole  23   fh . The hole  23   fh  may penetrate the segment  23   f  in the third direction. The second portion  21   a   2  may extend through the hole  23   fh . The hole  23   fh  may be referred to as a connection hole  23   fh.    
     The distal end of the FFC cable  21   a  may be electrically connected to the source PCB  21   b . A part of the FFC cable  21   a  may be located in the rear surface of the module cover  23 . The portion of the FFC cable  21   a  located in the rear surface of the module cover  23  may be referred to as a third portion  21   a   3 . The third portion  21   a   3  may be electrically connected to the source PCB  21   b.    
     The third portion  21   a   3  may be covered by the top case  60 . Accordingly, the third portion  21   a   3  may not be exposed to the outside. 
     Referring to  FIG.  10   , the FFC cable  21   a  may be connected to the timing controller board  41  mounted in the roller  40 . A penetrating hole  42  may be formed on the roller  40 , and the FFC cable  21   a  may be connected to the timing controller board  41  through the penetrating hole  42 . 
     The penetrating hole  42  may be located in one side of the roller  40  and may penetrate an outer circumferential portion of the roller  40 . The FFC cable  21   a  may be connected to one side of the timing controller board  41  through the penetrating hole  42 . 
     Even when the FFC cable  21   a  is located in the outer circumference of the roller  40 , it may maintain the connection with the timing controller board  41  due to the penetrating hole  42 . Accordingly, the FFC cable  21   a  may rotate together with the roller  40  to prevent twisting. 
     A portion of the FFC cable  21   a  may be wound around the roller  40 . The portion of the FFC cable  21   a  wound around the roller  40  may be referred to as a fourth portion  23   a   4 . The fourth portion  23   a   4  may be in contact with the outer circumferential surface of the roller  40 . 
     A portion of the FFC cable  21   a  may pass through the penetrating hole  42 . The portion of the FFC cable  21   a  passing through the penetrating hole  42  may be referred to as a fifth portion  23   a   5 . 
     The distal end of the FFC cable  21   a  may be electrically connected to the timing controller board  41 . A portion of the FFC cable  21   a  may be located inside the roller  40 . The portion of the FFC cable  21   a  located inside the roller  40  may be referred to as a sixth portion  23   a   6 . The sixth portion  23   a   6  may be electrically connected to the timing controller board  41 . 
     Referring to  FIG.  11   , the display panel  21  may be connected to the roller  40 . The display panel  21  may be wound around or unwound from the roller  40 . The display panel  21  may be electrically connected to the plurality of source PCBs  21   b . The plurality of source PCBs  21   b  may be spaced apart from each other. 
     A source chip on film (COF)  21   m  may connect the display panel  21  and the source PCB  21   b . The source COF  21 M may be located at a long side of the display panel  21 . The roller  40  may include a first part  43  and a second part  44 . The first part  43  and the second part  44  may be fastened by a screw. The timing controller board  41  may be mounted in the roller  40 . 
     The source PCB  21   b  may be electrically connected to the timing controller board  41 . The timing controller board  41  may send digital video data and a timing control signal to the source PCB  21   b.    
     The cable  21   p  may electrically connect the source PCB  21   b  and the timing controller board  41 . For example, the cable  21   p  may be a flexible flat cable (FFC). The cable  21   p  may penetrate a hole  21   n . The hole  21   n  may be formed in a seating portion  45  or the first part  43 . The cable  21   p  may be located between the display panel  21  and the second part  44 . 
     The seating portion  45  may be formed in an outer circumference of the first part  43 . The seating portion  45  may be formed by stepping a portion of the outer circumference of the first part  43 . The seating portion  45  may form a space B. When the display unit  20  is wound around the roller  40 , the source PCB  21   b  may be accommodated in the seating portion  45 . Since the source PCB  21   b  is accommodated in the seating portion  45 , the source PCB  21   b  may not be twisted or bent, and durability may be improved. 
     Referring to  FIG.  12   , a frame  100  may include a first base  101 , a second base  103 , and a vertical portion  102 . The frame  100  may be referred to as a main frame. The frame  100  may be mounted in the housing  300  (see  FIG.  1   ). The frame  100  may extend long in the leftward-rightward direction LR of the housing  30 , and may be mounted to the housing  300 . 
     The first base  101  may be a long plate. The vertical portion  102  may extend from a long side of the first base  101  in the longitudinal direction of the first base  101 . A first rib  101   a  and a second rib  101   b  may be formed on the first base  101 . The first rib  101   a  may be located adjacent to the vertical portion  102 , and the second rib  101   b  may be opposite the vertical portion  102  with respect to the first rib  101   a.    
     The second base  103  may be formed at the distal end of the vertical portion  102 . The second base  103  may have a third rib  103   a  and a fourth rib  103   b . The third rib  103   a  may be formed at the distal end of one long side of the second base  103 , and the fourth rib  103   b  may be formed at the distal end of the other long side of the second base  103 . Consequently, it is possible to secure rigidity of the frame  100  against drooping or bending. 
     Referring to  FIGS.  12  and  13   , a tower  120 A may be mounted on the frame  100 . The tower  120 A may be referred to as a sub frame  120 A. The tower  120 A may include a first beam  121 , a second beam  122 , and a clamp  124 . The first beam  121  may extend long in the upward-downward direction UD. The second beam  122  may extend long in the upward-downward direction UD while intersecting the first beam  121 . The width of the second beam  122  may gradually decrease in the longitudinal direction. A plurality of second beams  122  may be provided. The clamp  124  may be formed at the distal end of the tower  120 A. Bosses  123   a  and  123   b  may be formed at the side surface of the tower  120 A. A plurality of bosses  123   a  and  123   b  may be provided. The first boss  123   a  may be located adjacent to the middle of the first beam  121 , and the second boss  123   a  may be located at the first beam  121  so as to be adjacent to the clamp  124 . 
     Referring to  FIG.  13   , a link mount  210   a  may be mounted on the frame  100 . For example, the link mount  210   a  may be mounted on the first base  101  (see  FIG.  14   ). The link mount  210   a  may include a first part  211   a  and a second part  212   a . The first part  211   a  may be a plate, and the second part  212   a  may be a plate. The first part  211   a  may be spaced apart from the second part  212   a  by a predetermined distance. 
     Links  220   a  and  230   a  may include an upper arm  230   a  and a lower arm  220   a . The upper arm  230   a  may be referred to as a first arm  230   a , and the lower arm  220   a  may be referred to as a second arm  220   a . One end of the upper arm  230   a  may be connected to one end of the lower arm  220   a  via a joint  240   a . The other end of the lower arm  220   a  may be pivotably coupled to the link mount  210   a . For example, the other end of the lower arm  220   a  may be inserted between the first part  211   a  and the second part  212   a , and may be axially coupled to the first part  211   a  and the second part  212   a  so as to rotate about a shaft  311   a . A first gear box  301   a  may be installed at the link mount  210   a . A second gear box  302   a  and/or a third gear box  303   a  may be mounted on the first base  101  of the frame  100 . 
     Referring to  FIG.  14   , a link gear  310   a  and a worm gear  320  may be mounted in the first gear box  301   a . The link gear  310   a  may be engaged with the worm gear  320 . The worm gear  320   a  may be rotatably installed in the first gear box  301   a . A transmission shaft  321   a  may be rotatably installed in the first gear box  301   a . The transmission shaft  321   a  may be inserted into a first bearing  322   a  and a second bearing  323   a . The worm gear  320   a  may be fixed to the transmission shaft  321   a  between the first bearing  322   a  and the second bearing  323   a . The first bearing  322   a  and the second bearing  323   a  may be fixed to the first gear box  301   a . The second gear box  302   a  may be mounted on the first base  101  of the frame  100  in the state of being adjacent to the first gear box  301   a.    
     The transmission shaft  321   a  may be rotatably installed in the second gear box  302   a . A third bearing  332   a  may be fixed in the second gear box  302   a . The third bearing  332   a  may be located adjacent to the distal end of the transmission shaft  321   a . A first transmission gear  330   a  may be rotated with the transmission shaft  321   a . The first transmission gear  330   a  may be located between the third bearing  332   a  and the second bearing  323   a.    
     The third gear box  303   a  may be mounted on the first base  101  of the frame  100  in the state of being adjacent to the second gear box  302   a . A driving shaft  343   a  may be rotated in the third gear box  303   a . A fourth bearing  342   a  may be fixed in the third gear box  303   a . The driving shaft  343   a  may be inserted into the fourth bearing  342   a  so as to be rotated in the fourth bearing  342   a . The driving shaft  343   a  may be inserted into a second transmission gear  341   a . The second transmission gear  341   a  may be rotated with the driving shaft  343   a . The second transmission gear  341   a  may be engaged with the first transmission gear  330   a . The first transmission gear  330   a  may be referred to as a driving gear  330   a.    
     Referring to  FIG.  15   , a guide rail  213   a  may be located at the inner surface of the first part  211   a  and/or the second part  212   a . The guide rail  213   a  may be fixed to the first part  211   a  and/or the second part  212   a . The lower arm  220   a  may be turned about the shaft  311   a  on the guide rail  213   a  while being engaged with the guide rail  213   a . When the links  220   a  and  230   a  are driven, therefore, the links  220   a  and  230   a  may move along a predetermined track without shaking or twisting. 
     Referring to  FIG.  16   , a motor M may be mounted on the first base  101  of the frame  100 . Motor shafts MS 1  and MS 2  may be installed at opposite sides of the motor M, whereby power may be provided to the opposite sides of the motor M. A left driving shaft  343   a  may be connected to the left motor shaft MS 1  of the motor M, and a right driving shaft  343   b  may be connected to the right motor shaft MS 2  of the motor M. A left coupling  350   a  may connect the left driving shaft  343   a  and the left motor shaft MS 1  to each other. For example, couplings  350   a  and  350   b  may be universal joints. The left driving shaft  343   a  may be rotatably inserted into a left support  104   a  so as to be rotatable. 
     The left support  104   a  may be mounted on the first base  101  of the frame  100 , and may support the left driving shaft  343   a . The right driving shaft  343   b  may be rotatably inserted into a right support  104   b  so as to be rotatable. The right support  104   b  may be mounted on the first base  101  of the frame  100 , and may support the right driving shaft  343   b.    
     The left motor shaft MS 1  may be inserted into a sensor plate  361 . The sensor plate  361  may be rotated with the left motor shaft MS 1 . For example, the sensor plate  361  may have a disc-shaped rotator  361   a  and a plurality of teeth  361   b  protruding from the outer circumferential surface of the rotator  361   a  in the radial direction. A sensor  362  may sense rotation of the sensor plate  361 . For example, the sensor  362  may be a photo sensor. Consequently, the number of rotations of the motor M may be sensed. 
     Referring to  FIGS.  17  and  18   , a pipe  110  may be coupled to the tower  120 . The pipe  100  may extend long, and may be disposed parallel to the frame  100 . The pipe  110  may be inserted into and fixed to the clamp  124  (see  FIG.  12   ) of the tower  120 . A plurality of towers  120  may be provided, and may be mounted on the first base  101  of the frame  100 . The clamp  124  having the pipe inserted thereinto may be tightened by a fastening member. The pipe  110  may be referred to as an elongated frame member  110  or a rod  110 . 
     A first tower  120 A may be located at the left side of the frame  100 . A fourth tower  120 D may be located at the right side of the frame  100 . A second tower  120 B may be located between the first tower  120 A and the fourth tower  120 D, and a third tower  120 C may be located between the second tower  120 B and the fourth tower  120 D. The number of towers  120  may be variously changed. 
     The distance between the first tower  120 A and the second tower  120 B may be substantially equal to the distance between the third tower  120 C and the fourth tower  120 D. The distance between the first tower  120 A and the second tower  120 B may be less than the distance between the second tower  120 B and the third tower  120 C. 
     Referring to  FIG.  18   , a left link mount  210   a  may be located between the first tower  120 A and the second tower  120 B so as to be adjacent to the first tower  120 A. A right link mount  210   b  may be located between the third tower  120 C and the fourth tower  120 D so as to be adjacent to the fourth tower  120 D. The motor M may be located between the second tower  120 B and the third tower  120 C. 
     A first left gear box  301   a  may be fixed on the left link mount  210   a . A second left gear box  302   a  may be located among the left link mount  210   a , the first left gear box  301   a , and the second tower  120 B so as to be adjacent to the first left gear box  301   a . A third left gear box  303   a  may be located between the first left gear box  301   a  and the second tower  120 B so as to be adjacent to the second left gear box  302   a  and the first left link mount  210   a.    
     A first right gear box  301   b  may be fixed on the right link mount  210   b . A second right gear box  302   b  may be located among the right link mount  210   b , the first right gear box  301   b , and the third tower  120 C so as to be adjacent to the first right gear box  301   b . A third right gear box  303   b  may be located between the first right gear box  301   b  and the third tower  120 B so as to be adjacent to the second right gear box  302   b  and the first right link mount  210   b.    
     The left driving shaft  343   a  may transmit power provided by the motor M to the third left gear box  303   a . The right driving shaft  343   b  may transmit power provided by the motor M to the third right gear box  303   b . The left driving shaft  343   a  may receive power from the motor via a left joint  350   a  while being supported by the left support  104   a , and the right driving shaft  343   b  may receive power from the motor via a right joint  350   b  while being supported by the right support  104   b.    
     Left links  220   a ,  230   a , and  240   a  may be pivotably connected to the left link mount  210   a , and may move downwards while being unfolded or upwards while being folded. Right links  220   b ,  230   b , and  240   b  may be pivotably connected to the right link mount  210   b , and may move downwards while being unfolded or upwards while being folded. The left links  220   a ,  230   a , and  240   a  and the right links  220   b ,  230   b , and  240   b  may move downwards to the same height while being unfolded or upwards to the same height while being folded. 
     Consequently, power transmission of the display device may be achieved in the minimum space at high efficiency. 
     Referring to  FIGS.  19  and  20   , a panel roller  40  may be mounted on the frame  100 . The panel roller  40  may be fixed on the first base  101 . The panel roller  40  may be located in front of the towers  120  (see  FIG.  18   ) and the pipe  110 . A guide roller  140  may be coupled to a roller frame  41 . The guide roller  140  may guide motion of the display panel  21  (see  FIG.  10   ) and the module cover  23 . The guide roller  140  may extend long in the leftward-rightward direction of the module cover  23 . 
     The guide roller  140  may have a shaft  142 , a roller  141 , and a fixing plate  143 . The shaft  142  may be supported by the roller frame  41 . The roller frame  41  may have a shaft recess  43  formed by cutting out a portion of the roller frame  41 , and the shaft  142  may be inserted into the shaft recess  43 . The roller  141  may surround the outer circumferential surface of the shaft  142 , and may be rotated in the shaft recess  43 . The fixing plate  143  may be fixed to the roller frame  41  via a fastening member (not shown). 
     Referring to  FIGS.  21  and  22   , the side cover  35  may be coupled to the frame  100  and the pipe  110  while facing the outer surface of the roller frame  41 . The side cover  35  may have a first fastening portion  35   a . The first fastening portion  35   a  may be a plate protruding from the inner surface of the side cover  35 . The first fastening portion  35   a  may be fixed to the inner surface of the first base  101  of the frame  100 . For example, the first fastening portion  35   a  and the first base  101  of the frame  100  may be coupled to each other via a screw. The pipe  110  may be inserted into a coupling port  150  of the side cover  35 , and may be fixed to the side cover  35 . The side cover  35  may be referred to as a first side cover  35  or a left plate  35 . 
     The side cover  35  may have a second fastening portion  35   b . The second fastening portion  35   b  may be a plate protruding from the inner surface of the side cover  35 . The second fastening portion  35   b  may be fixed to the outer surface of the second base  103  of the frame  100 . For example, the second fastening portion  35   b  and the second base  103  of the frame  100  may be coupled to each other via a screw. 
     Consequently, rigidity of the display device against drooping and twisting may be secured. 
     Referring to  FIG.  23   , the side cover  36  may be referred to as a second side cover  36  or a right plate  36 . The description made with reference to  FIGS.  21  and  22    may be equally applied to the construction and structure of the second side cover  36 . At this time, the second side cover  36  may be symmetrical with the first side cover  35 . 
     Consequently, it is possible to secure rigidity of the display device against drooping and to secure rigidity of the display device against twisting. 
     Referring to  FIGS.  24  and  25   , the pipe  110  may have a neck  1102  located adjacent to the distal end thereof, the neck  1102  being formed at the outer circumferential surface of the pipe  110 . The pipe  110  may be coupled to the side covers  35  and  36 . The coupling port  150  may be formed inside each of the side covers  35  and  36 . The pipe  110  may be inserted or forcibly fitted into the coupling ports  150 , whereby the pipe  110  may be fixed to the side covers  35  and  36 . The coupling port  150  may be referred to as an end coupler  150 . 
     Referring to  FIGS.  26  and  27   , the coupling port  150  may have an outer cylinder  151  and an inner insert  152 . The outer cylinder  151  may have a hollow cylindrical shape. The outer cylinder  151  may have an outer surface  151   c , a first inner surface  151   a , and a second inner surface  151   b . The first inner surface  151   a  may be parallel to the outer surface  151   c . The second inner surface  151   b  may extend from the first inner surface  151   a  to the distal end of the outer cylinder  151  in the state of being inclined. The diameter of the second inner surface  151   b  may gradually increase from the diameter of the first inner surface  151   a  to the diameter of the outer surface  151   c . The second inner surface  151   b  may be referred to as a guide surface  151   b , and the first inner surface  151   a  may be referred to as a forcible fitting surface  151   a . A protrusion  153  may be formed inside the outer cylinder  151 . For example, the protrusion  153  may be located at the border of the first inner surface  151   a  and the second inner surface  151   b.    
     The inner insert  152  may be a rib extending from the side covers  35  and  36  (see  FIG.  25   ) toward the distal end of the second inner surface  151   b  of the outer cylinder  151 . The inner insert  152  may have a shape in which at least two ribs intersect. The inner insert  152  may have a first outer surface  152   a  and a second outer surface  152   b . The first outer surface  152   a  may be spaced apart from the first inner surface  151   a  of the outer cylinder  151 , and may be parallel to the first inner surface  151   a  of the outer cylinder  151 . For example, the distance G 1  between the first inner surface  151   a  of the outer cylinder  151  and the first outer surface  152   a  of the inner insert  152  may be substantially equal to or less than the thickness of the pipe  110 . The second outer surface  152   b  of the inner insert  152  may extend from the first outer surface  152   a  to the distal end of the inner insert  152  in the state of being inclined. The second outer surface  152   b  of the inner insert  152  may be gradually distant from the first inner surface  151   a  and/or the second inner surface  151   b  of the outer cylinder  151 . For example, the inner insert  152  may have a wedge shape. The second outer surface  152   b  of the inner insert  152  may face the first inner surface  151   a  and the second inner surface  151   b  of the outer cylinder  151 . 
     The distance G 1  between the first inner surface  151   a  of the outer cylinder  151  and the first outer surface  152   a  of the inner insert  152  may be less than the distance G 2  between the first inner surface  151   a  of the outer cylinder  151  and the second outer surface  152   b  of the inner insert  152 . The distance G 2  between the first inner surface  151   a  of the outer cylinder  151  and the second outer surface  152   b  of the inner insert  152  may be less than the distance G 3  between the second inner surface  151   b  of the outer cylinder  151  and the second outer surface  152   b  of the inner insert  152 . 
     Referring to  FIGS.  28  and  29   , the pipe  110  may have a forcible fitting surface  1103 . The forcible fitting surface  1103  may be formed at the outer surface of the pipe  110  between the neck  1102  of the pipe  110  and the distal end of the pipe  110 . The forcible fitting surface  1103  may be a coarse surface. For example, the forcible fitting surface  1103  may be a knurling portion. 
     The pipe  110  may be inserted or forcibly fitted into the coupling port  150 . The protrusion  153  may be inserted into the neck  1102  of the pipe  110 . Consequently, fastening between the pipe  110  and the coupling port  150  may be more secured. 
     In  FIGS.  30  to  33   , the upward-downward direction UD and the leftward-rightward direction LR are described based on the state shown in  FIGS.  30  to  33   . Referring to  FIG.  30   , a link bracket  951  may be pivotably connected to the first arm  230   a . The link bracket  951  may include a support  951 F and a coupling plate  951 R. 
     The support  951 F may have a horizontal body  9511 , a joint  9512  and  9512   a , and cups  9513   a ,  9513   b , and  9513   c . The horizontal body  9511  may have a bar shape extending long leftwards and rightwards. The joint  9512  and  9512   a  may be formed at the lower side of the horizontal body  9511 . The joint  9512  and  9512   a  may include a fixing plate  9512  and a pivot shaft  9512   a.    
     A bearing  960  may be fastened to the pivot shaft  9512   a . A plurality of bearings  960  may be provided. The plurality of bearings  960  may include a first bearing  960   a  and a second bearing  960   b . The second bearing  960   b  may be stacked on the first bearing  960   a . The first bearing  960   a  and the second bearing  960   b  may be fitted on the pivot shaft  9512   a . Lubricating oil may be applied to the bearings  960 . Assembly of the bearings  960  and application of lubricating oil to the bearings  960  may be performed simultaneously with coupling between the first arm  230   a  and the link bracket  951 , but may be performed independently of fastening of other structures, whereby leakage of the lubricating oil may be prevented. 
     The fixing plate  9512  may be located at the lowers side of the horizontal body  9511  so as to be biased leftwards or rightwards. The fixing plate  9512  may extend long to the lower side of the horizontal body  9511 . The pivot shaft  9512   a  may be formed so as to protrude from one surface of the fixing plate  9512 . 
     The cups  9513   a ,  9513   b , and  9513   c  may be formed as the result of the upper surface of the horizontal body  9511  being recessed. The cups  9513   a ,  9513   b , and  9513   c  may be formed as the result of the upper surface of the horizontal body  9511  being recessed and at the same time the front surface and the rear surface of the horizontal body  9511  being open. For example, each of the cups  9513   a ,  9513   b , and  9513   c  may generally have a U shape. The cups  9513   a ,  9513   b , and  9513   c  may be sequentially disposed in the longitudinal direction of the horizontal body  9511 . Consequently, it is possible to reduce concentration of stress and to eliminate fatigue fracture of the link bracket  951 . 
     The coupling plate  951 R may include a support cover  9515  and a joint cover  9516 . The support cover  9515  may be a plate formed so as to have a length corresponding to the length of the support  951 F. The joint cover  9516  may have the shape of a disc connected to the support cover  9515  at the lower side of the support cover  9515  in the state of being biased leftwards or rightwards. The coupling plate  951 R may have a plurality of holes H and h. 
     The plurality of holes H and h may include first coupling holes h and second coupling holes H. The first coupling holes h may be provided for coupling between the support  951 F, the coupling plate  951 R, and first arms  911 . The second coupling holes H may be provided for coupling between a top case  950  (see  FIG.  31   ) and the link bracket  951 . 
     Referring to  FIG.  31   , the cup  9513   a  may include a support portion  9513   a   1  and a guide portion  9513   a   2 . The support portion  9513   a   1  may form the lower side of the cup  9513   a , and the guide portion  9513   a   2  may form the upper side of the cup  9513   a . For example, the support portion  9513   a   1  may have a semicircular shape or a fan shape, and the guide portion  9513   a   2  may extend from the support portion  9513   a   1  and may have the shape of left and right sides of an inverted trapezoid. 
     The top case  950  may include an inner bar  950 I and a top cover  950 T. The inner bar  950 I may be located at the upper side or the upper end of the module cover  23 , and may be coupled to the module cover  23 . Coupling protrusions  950 P 1 ,  950 P 2 , and  950 P 3  may be mounted on the outer surface of the inner bar  950 I. A plurality of coupling protrusions  950 P 1 ,  950 P 2 , and  950 P 3  may be provided. The number of coupling protrusions  950 P 1 ,  950 P 2 , and  950 P 3  may correspond to the number of cups  9513   a ,  9513   b , and  9513   c . For example, the coupling protrusions  950 P 1  and  950 P 2  may be PEM nuts. The radii of the coupling protrusions  950 P 1 ,  950 P 2 , and  950 P 3  may correspond to the radii of support portions  9513   a   1 ,  9513   b   1 , and  9513   c   1  of the cups  9513   a ,  9513   b , and  9513   c.    
     Referring to  FIGS.  32  and  33   , the link bracket  951  may be assembled with the top case  950  in the state in which the link bracket  951  is coupled to the first arm  230   a . At this time, the link bracket  951  may move to the top case  950  according to motion of the links  220   a  and  230   a  (see  FIG.  34   ) in the upward-downward direction. As the support  951 F of the link bracket  951  approaches the top case  950 , the coupling protrusions  950 P 1 ,  950 P 2 , and  950 P 3  may be inserted into the cups  9513   a ,  9513   b , and  9513   c  (see  FIG.  31   ) of the support  951 F. The coupling protrusions  950 P 1 ,  950 P 2 , and  950 P 3  may be inserted into the cups  9513   a ,  9513   b , and  9513   c  of the support  951 F, and the link bracket  951  and the top case  960  may be fastened to each other via screws S 2  (see  FIG.  30   ). 
     Consequently, the link bracket  951  may be naturally coupled to the top case  960  within a movable range of the links  220  and  230  without straining the joints of the links  220  and  230 . 
     Referring to  FIG.  34   , the driving shaft  343   a  may transmit power provided by the motor M to the third gear box  303   a . The driving shaft  343   b  may transmit power provided by the motor M to the third gear box  303   b . The driving shaft  343   a  may receive power from the motor M via the joint  350   a  while being supported by the support  104   a , and the driving shaft  343   b  may receive power from the motor M via the joint  350   b  while being supported by the support  104   b.    
     The links  220   a ,  230   a , and  240   a  may be pivotably connected to the link mount  210   a  (see  FIG.  18   ), and may move downwards while being unfolded or upwards while being folded. The links  220   b ,  230   b , and  240   b  may be pivotably connected to the link mount  210   b , and may move downwards while being unfolded or upwards while being folded. The links  220   a ,  230   a , and  240   a  and the links  220   b ,  230   b , and  240   b  may move downwards to the same height while being unfolded or upwards to the same height while being folded. 
     Consequently, power transmission of the display device may be achieved in the minimum space at high efficiency. In addition, the display panel  21  (see  FIG.  10   ) and the module cover  23  may be maintained flat in the state in which the display panel  21  and the module cover  23  are unwound from the panel roller  40  and the links  220 ,  230 , and  240  move downwards. 
     In accordance with an aspect of the present disclosure, provided is a display device including a flexible display panel, a panel roller, wherein the flexible display panel is wound around or unwound from the panel roller, a main frame extending in a longitudinal direction of the panel roller, wherein the panel roller is coupled to the main frame, an elongated frame member extending in the longitudinal direction of the panel roller, wherein the elongated frame member is spaced apart from the panel roller and the main frame, and a sub frame coupling the elongated frame member with the main frame, wherein the sub frame is coupled to the main frame. 
     In accordance with another aspect of the present disclosure, the sub frame may include a first beam extending from the main frame to the elongated frame member, and a clamp formed at a distal end of the first beam and configured to clamp the elongated frame member. 
     In accordance with another aspect of the present disclosure, the sub frame may further include a second beam extending from the main frame to the elongated frame member, wherein the second beam is perpendicular to the first beam. 
     In accordance with another aspect of the present disclosure, a width of the second beam may gradually decrease in the longitudinal direction from the main frame to the elongated frame member. 
     In accordance with another aspect of the present disclosure, the main frame may further include a first base, wherein the sub frame is coupled to the first base, a vertical portion extending from a side of the first base in a vertical direction, and a second base formed at a distal end of the vertical portion, wherein the panel roller is coupled to the second base. 
     In accordance with another aspect of the present disclosure, the first base may further include a first rib located at a position between the vertical portion and the sub frame, and a second rib located at a position adjacent to the sub frame. 
     In accordance with another aspect of the present disclosure, the second base may further include a third rib formed at a first end of the second base, and a fourth rib formed at a second end of the second base opposite the first end. 
     In accordance with another aspect of the present disclosure, the sub frame may be one of a plurality of sub frames adjacent to the other side of the first base, and wherein the plurality of sub frames is disposed in a longitudinal direction of the main frame. 
     In accordance with another aspect of the present disclosure, the display device may further include a module cover extending in the longitudinal direction of the panel roller, wherein the module cover comprises a plurality of segments horizontally arranged at a rear surface of the flexible display panel, wherein the flexible display panel and the module cover may be wound around or unwound from the panel roller. 
     In accordance with another aspect of the present disclosure, the flexible display panel may move downwards in response to being unwound from the panel roller, and may move upwards in response to being wound around the panel roller. 
     As is apparent from the above description, a display device according to the present disclosure has the following effects. 
     According to at least one of the embodiments of the present disclosure, it is possible to secure structural rigidity for preventing drooping of a display device. 
     According to at least one of the embodiments of the present disclosure, it is possible to secure structural rigidity for preventing twisting of the display device. 
     According to at least one of the embodiments of the present disclosure, it is possible to provide a driving mechanism of a rollable display device. 
     The additional scope of applicability of the present disclosure will be apparent from the above detailed description. However, those skilled in the art will appreciate that various modifications and alterations are possible, without departing from the idea and scope of the present disclosure, and therefore it should be understood that the detailed description and specific embodiments, such as the preferred embodiments of the present disclosure, are provided only for illustration. 
     Certain embodiments or other embodiments of the disclosure described above are not mutually exclusive or distinct from each other. Any or all elements of the embodiments of the disclosure 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 disclosure and the drawings and a configuration “B” described in another embodiment of the disclosure 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.